e-course Materilas for all Courses
FS 207-Fish Immunology 2(1+1)
(ICAR e-Course Material)
____________________________________________
Unit 1- Fish Immunology
1. 1.
General concepts in
immunology
Immunology is the study of the immune system and its responses to invading pathogens. The immune system includes the molecules, cells, tissues, and organs that are associated with immunity in the host defense mechanisms. The coordinated reaction of these cells and molecules to invading pathogen is called immune response. The organs of the immune system are positioned throughout the body. They are called lymphoid organs. The generation of an immune response of either the innate or acquired variety requires the interaction of specific molecules, cells, and tissues.
The immune system of fish is almost similar to that of higher vertebrates. Immunity is referred as the state of acquired or innate resistance or protection from a pathogenic microorganism or its products or from the effect of toxic substances. The cells of the immune system consist of lymphocytes, specialized cells that capture and display microbial antigens, and efffector cells that eliminate pathogens.
Microorganisms in the environment are blocked by physical barriers like skin, mucus etc from being enter into the host. If the pathogens overcome this barrier and invade the host the innate immune mechanism is activated and destroys the pathogen. If the pathogen survives the innate immunity the adaptive immunity is activated and combats the pathogen, added to it adaptive immunity also keeps the memory of the pathogen which helps the immune system during the secondary invasion of the same pathogen.
Host defense mechanisms consist of innate immunity and adaptive immunity. Nonspecific immunity is a fundamental defence mechanism in fish. Non specific immunity also plays a key role in activating acquired immune response.
Immunology is the study of the immune system and its responses to invading pathogens. The immune system includes the molecules, cells, tissues, and organs that are associated with immunity in the host defense mechanisms. The coordinated reaction of these cells and molecules to invading pathogen is called immune response. The organs of the immune system are positioned throughout the body. They are called lymphoid organs. The generation of an immune response of either the innate or acquired variety requires the interaction of specific molecules, cells, and tissues.
The immune system of fish is almost similar to that of higher vertebrates. Immunity is referred as the state of acquired or innate resistance or protection from a pathogenic microorganism or its products or from the effect of toxic substances. The cells of the immune system consist of lymphocytes, specialized cells that capture and display microbial antigens, and efffector cells that eliminate pathogens.
Microorganisms in the environment are blocked by physical barriers like skin, mucus etc from being enter into the host. If the pathogens overcome this barrier and invade the host the innate immune mechanism is activated and destroys the pathogen. If the pathogen survives the innate immunity the adaptive immunity is activated and combats the pathogen, added to it adaptive immunity also keeps the memory of the pathogen which helps the immune system during the secondary invasion of the same pathogen.
Host defense mechanisms consist of innate immunity and adaptive immunity. Nonspecific immunity is a fundamental defence mechanism in fish. Non specific immunity also plays a key role in activating acquired immune response.
1.2.
Innate immunity
Innate immunity also called natural or native immunity, takes part in the initial protection against Pathogens. Innate immunity in healthy host is prepared to block the entry of microbes and to rapidly destroy pathogens that enter into host tissues.
Innate immunity acts non specifically where the nature or quality of the reaction to a foreign substance does not change when the organism encounters repeatedly.
Innate immunity does not discriminate between the pathogens. The mechanisms of innate immunity provide the initial defense against infections. Majority of the microbes are blocked by physical barrier. If the pathogens succeed in entering the host then these pathogens are eliminated by phagocytes, NK cells, complement system etc.
There are two types of innate immunity
Innate immunity also called natural or native immunity, takes part in the initial protection against Pathogens. Innate immunity in healthy host is prepared to block the entry of microbes and to rapidly destroy pathogens that enter into host tissues.
Innate immunity acts non specifically where the nature or quality of the reaction to a foreign substance does not change when the organism encounters repeatedly.
Innate immunity does not discriminate between the pathogens. The mechanisms of innate immunity provide the initial defense against infections. Majority of the microbes are blocked by physical barrier. If the pathogens succeed in entering the host then these pathogens are eliminated by phagocytes, NK cells, complement system etc.
There are two types of innate immunity
·
Humoral immunity and
·
Cell-mediated immunity
Humoral
immunity
Humoral immunity is mediated by the antimicrobial peptides, cytokines etc where the cellular substance are involved.
Cell-mediated immunity
Cell-mediated immunity is mediated by the non specific immune cells like macrophages, NK cells, granular cells etc.
Humoral immunity is mediated by the antimicrobial peptides, cytokines etc where the cellular substance are involved.
Cell-mediated immunity
Cell-mediated immunity is mediated by the non specific immune cells like macrophages, NK cells, granular cells etc.
1.3.
Adaptive immunity
Adaptive immunity also called specific or acquired immunity develops more slowly and take part after innate immunity, adaptive immunity is even more effective against pathogens. Adaptive immunity is stimulated by the presence of pathogens.
If the pathogen survives the innate immunity, adaptive immunity develops later and mediated by lymphocytes and their products. Where antibodies block infections and eliminate pathogens, T lymphocytes also helps in eradicating intracellular microbes.
There are two types of adaptive immunity
Adaptive immunity also called specific or acquired immunity develops more slowly and take part after innate immunity, adaptive immunity is even more effective against pathogens. Adaptive immunity is stimulated by the presence of pathogens.
If the pathogen survives the innate immunity, adaptive immunity develops later and mediated by lymphocytes and their products. Where antibodies block infections and eliminate pathogens, T lymphocytes also helps in eradicating intracellular microbes.
There are two types of adaptive immunity
·
Humoral immunity and
·
Cell-mediated immunity
Humoral
immunity
Humoral immunity is mediated by the antibodies which are immunoglobulins and these immunoglobulins are produced by plasma cells differentiated from B cells.
Antibodies are formed against antigens, secreted into the blood and mucosal fluids so these antibodies can neutralize and eliminate pathogens and microbial toxins that are harmful to host.
Cell-mediated immunity
Cell-mediated immunity is mediated by different immune cells that are formed to provide protection against pathogen.
Antibodies cannot reach the pathogen that divide inside infected cells. Defense against such intracellular pathogens is mediated by cell mediated immunity. Cell mediated immunity is mainly through T lymphocytes. Here a type of T lymphocyte, stimulates the phagocytes to quickly recognize the pathogen and destroy them. Other T lymphocytes kill any type of host cells that are harboring infectious microbes in their cytoplasm.
Adaptive immunity may be sub-divided into two major types depending on how the immunity was introduced.
Naturally acquired immunity occurs through contact with a pathogen in environment, whereas artificially acquired immunity develops with vaccination.
Both naturally and artificially acquired immunity can be further subdivided depending on whether immunity is induced in the host or passively transferred from an immune host. Passive immunity is acquired through transfer of antibodies or activated T-cells from an actively immunized host, passive immunity may last only a few months, whereas active immunity is induced in the host by vaccination, and lasts longer duration may be life-long.
An individual exposed to an antigen of a microbe develops an active immune response to eradicate the infection and develops resistance to later infection by that microbe. Such and individual is said to be immune to that microbe.
The most important properties of adaptive immunity is the fine specificity for antigens and memory to the prior exposed antigen.
The tissue of the immune system consist of primary lymphoid organs, in which T and B lymphocytes mature and become competent to respond to antigens, and the peripheral or secondary lymphoid organs, in which adaptive immune response to microbes are initiated.
Humoral immunity is mediated by the antibodies which are immunoglobulins and these immunoglobulins are produced by plasma cells differentiated from B cells.
Antibodies are formed against antigens, secreted into the blood and mucosal fluids so these antibodies can neutralize and eliminate pathogens and microbial toxins that are harmful to host.
Cell-mediated immunity
Cell-mediated immunity is mediated by different immune cells that are formed to provide protection against pathogen.
Antibodies cannot reach the pathogen that divide inside infected cells. Defense against such intracellular pathogens is mediated by cell mediated immunity. Cell mediated immunity is mainly through T lymphocytes. Here a type of T lymphocyte, stimulates the phagocytes to quickly recognize the pathogen and destroy them. Other T lymphocytes kill any type of host cells that are harboring infectious microbes in their cytoplasm.
Adaptive immunity may be sub-divided into two major types depending on how the immunity was introduced.
Naturally acquired immunity occurs through contact with a pathogen in environment, whereas artificially acquired immunity develops with vaccination.
Both naturally and artificially acquired immunity can be further subdivided depending on whether immunity is induced in the host or passively transferred from an immune host. Passive immunity is acquired through transfer of antibodies or activated T-cells from an actively immunized host, passive immunity may last only a few months, whereas active immunity is induced in the host by vaccination, and lasts longer duration may be life-long.
An individual exposed to an antigen of a microbe develops an active immune response to eradicate the infection and develops resistance to later infection by that microbe. Such and individual is said to be immune to that microbe.
The most important properties of adaptive immunity is the fine specificity for antigens and memory to the prior exposed antigen.
The tissue of the immune system consist of primary lymphoid organs, in which T and B lymphocytes mature and become competent to respond to antigens, and the peripheral or secondary lymphoid organs, in which adaptive immune response to microbes are initiated.
..............................................................................................................
Unit 2 - Evolution of immune system
2.1.
Evolution of immune system
Innate immune mechanisms can be found in species at almost every level of the evolutionary tree of life.
When life evolved the primitive organisms like of bacteria, archaea and eukaryotes brought change in environment, also increased the concentration of atmospheric oxygen, this facilitated the evolution of multicellular organisms (metazoans) around 600 million years ago. Evolution in multicellular organisms provided new host opportunities for microbial pathogens so these multicellular organisms developed new mechanisms of defence to protect themselves form pathogens, thus the origin of defence mechanisms begin and evolved along with the life.
The most primitive metazoans like sponges and coelenterates possess an epithelial layer of cells within an intermediate mesogleal layer which performs the role of digestive cells and defensive cells that engulf foreign organisms. These phagocytic cells lead the way for the development of vertebrate macrophage. This innate immunity uses germline encoded pattern recognition receptors for pathogens to distinguish between self and foreign.
Second layer of complex immune defences called adaptive immunity evolved in vertebrates around 500 million years ago. The adaptive immunity have not evolved overnight but it took several years. The unique feature of an adaptive immune system is the development of lymphocytes, where each lymphocyte possess an antigen recognition receptor that can be used to trigger specific defence mechanism. This lymphocytes are the key cells in evolution of specific immune system. Lymphoid cells found first in pre‑vertebrate named Deuterostomes. Later these lymphocytes evolved along with the life and the development of the diverse lymphocyte receptor allows vertebrates to recognize almost any potential pathogen or toxin and can generate antigen-specific responses to it. Antigen-activated lymphocytes differentiate into mature lymphocytes with cytotoxic and pro-inflammatory functions or into plasma cells that secrete antibodies and also provide protective memory of the antigen to fight the pathogen in future invasion.
Two types of adaptive immune system have evolved in vertebrates:
Innate immune mechanisms can be found in species at almost every level of the evolutionary tree of life.
When life evolved the primitive organisms like of bacteria, archaea and eukaryotes brought change in environment, also increased the concentration of atmospheric oxygen, this facilitated the evolution of multicellular organisms (metazoans) around 600 million years ago. Evolution in multicellular organisms provided new host opportunities for microbial pathogens so these multicellular organisms developed new mechanisms of defence to protect themselves form pathogens, thus the origin of defence mechanisms begin and evolved along with the life.
The most primitive metazoans like sponges and coelenterates possess an epithelial layer of cells within an intermediate mesogleal layer which performs the role of digestive cells and defensive cells that engulf foreign organisms. These phagocytic cells lead the way for the development of vertebrate macrophage. This innate immunity uses germline encoded pattern recognition receptors for pathogens to distinguish between self and foreign.
Second layer of complex immune defences called adaptive immunity evolved in vertebrates around 500 million years ago. The adaptive immunity have not evolved overnight but it took several years. The unique feature of an adaptive immune system is the development of lymphocytes, where each lymphocyte possess an antigen recognition receptor that can be used to trigger specific defence mechanism. This lymphocytes are the key cells in evolution of specific immune system. Lymphoid cells found first in pre‑vertebrate named Deuterostomes. Later these lymphocytes evolved along with the life and the development of the diverse lymphocyte receptor allows vertebrates to recognize almost any potential pathogen or toxin and can generate antigen-specific responses to it. Antigen-activated lymphocytes differentiate into mature lymphocytes with cytotoxic and pro-inflammatory functions or into plasma cells that secrete antibodies and also provide protective memory of the antigen to fight the pathogen in future invasion.
Two types of adaptive immune system have evolved in vertebrates:
·
Adaptive immune system in jawless vertebrates
(hagfish and lamprey)
·
Adaptive immune system of jawed vertebrates
Adaptive
immune system in jawless vertebrates (hagfish and lamprey)
Lymphocytes present in jawless fish are indistinguishable from mammalian cells. But these Fish lymphocytes lack MHC (major histocompatibility complex) molecules, T-cell receptors and B-cell receptors. So jawless fishes use different types of antigen recognition receptor but use similar lymphocyte differentiation process to elicit specific immune response.
Lymphocytes present in jawless fish are indistinguishable from mammalian cells. But these Fish lymphocytes lack MHC (major histocompatibility complex) molecules, T-cell receptors and B-cell receptors. So jawless fishes use different types of antigen recognition receptor but use similar lymphocyte differentiation process to elicit specific immune response.
Adaptive immune system of jawed vertebrates
MHC (major histocompatibility complex) molecules, T-cell receptors and B-cell receptors based adaptive immune system is detected in cartilaginous fish but absent in lower chordates. For the evolution of adaptive immune system in jawed vertebrates it is believed that two macroevolutionary events that had provided the plat form for evolution of specific immune system are:-
·
The invasion of recombination-activating
gene transposon (RAG transposon)
·
Whole-genome duplication (WGDs)
2.2. The invasion of recombination-activating
gene transposon (RAG transposon)
The gene encoding an immunoglobulin superfamily (IgSF) exon was invaded by the recombination-activating gene transposon (RAG transposon) and invasion of this transposon helped in triggering B cell receptor and T cell receptor based immunity. RAG genes are present in all gnathostomes but not in jawless fish, and this suggest the reason for the absence of B cell receptor and T cell receptor in jawless fishes. RAG transposon activity is the major incident in the evolution of adaptive immunity, because the jawed vertebrates have an advance mechanisms and molecules that are involved in adaptive immunity when compared with jawless fish.
The gene encoding an immunoglobulin superfamily (IgSF) exon was invaded by the recombination-activating gene transposon (RAG transposon) and invasion of this transposon helped in triggering B cell receptor and T cell receptor based immunity. RAG genes are present in all gnathostomes but not in jawless fish, and this suggest the reason for the absence of B cell receptor and T cell receptor in jawless fishes. RAG transposon activity is the major incident in the evolution of adaptive immunity, because the jawed vertebrates have an advance mechanisms and molecules that are involved in adaptive immunity when compared with jawless fish.
2.3. Whole-genome duplication (WGDs)
The vertebrate genome has under gone two rounds of Whole-genome duplication (WGD) after the emergence of urochordates and before the radiation of jawed vertebrates. The first round of WGD occurred in a common ancestor of jawed and jawless vertebrates, and the second round in a common ancestor of jawed vertebrates. These WGDs played a crucial role in the emergence of adaptive immune system in jawed vertebrates, in the form like many ohnologues, that formed during WGDs, are now acting as an essential components of the adaptive immune system in jawed vertebrate.
The vertebrate genome has under gone two rounds of Whole-genome duplication (WGD) after the emergence of urochordates and before the radiation of jawed vertebrates. The first round of WGD occurred in a common ancestor of jawed and jawless vertebrates, and the second round in a common ancestor of jawed vertebrates. These WGDs played a crucial role in the emergence of adaptive immune system in jawed vertebrates, in the form like many ohnologues, that formed during WGDs, are now acting as an essential components of the adaptive immune system in jawed vertebrate.
2.4. Immunoglobulins
The development of adaptive immune system lead to the production of immunoglobulins where, among living animals immunoglobulins are first found in cartilaginous fish like sharks, skates and rays. These are generated by a somatic recombination mechanism. Among immunoglobulins, IgM is the most ancient antibody class and conserved the same function in all gnathostomes. In cartilaginous fish, IgM is abundantly secreted as monomer, but in bony fish it is secreted as tetramer. In addition to IgM and IgD other immunoglobulins are also found in higher vertebrates. IgG, which is involved in memory responses, Ig E, involved in inflammatory (and allergic) responses at epithelial surfaces. IgA involved in mucosal antibody. IgG and IgE are evolved from IgY, this IgY was found in amphibians and perform the function similar to IgG.
The development of adaptive immune system lead to the production of immunoglobulins where, among living animals immunoglobulins are first found in cartilaginous fish like sharks, skates and rays. These are generated by a somatic recombination mechanism. Among immunoglobulins, IgM is the most ancient antibody class and conserved the same function in all gnathostomes. In cartilaginous fish, IgM is abundantly secreted as monomer, but in bony fish it is secreted as tetramer. In addition to IgM and IgD other immunoglobulins are also found in higher vertebrates. IgG, which is involved in memory responses, Ig E, involved in inflammatory (and allergic) responses at epithelial surfaces. IgA involved in mucosal antibody. IgG and IgE are evolved from IgY, this IgY was found in amphibians and perform the function similar to IgG.
Unit 3- Nonspecific immunity
3.1.
Nonspecific immunity
The innate immune system is believed to be the first line of host defense against invading pathogenic organisms and other foreign material. These components of the innate response are evolutionarily conserved in organisms lacking the typical adaptive immunity of vertebrates.
In fish, the innate immune response has been considered as an essential and primary component in combating pathogens due to limitations of the specific immune response and also their poikilothermic nature. The innate immune system is commonly divided into three compartments: the Physical (epithelial/mucosal) barrier, the humoral parameters and the cellular components.
The epithelial and mucosal barrier of the skin, gills and alimentary tract is an extremely important disease barrier in fish, being constantly immersed in media contain¬ing potentially harmful agents. This type of response requires a series of mecha¬nisms that involve humoral factors, cell and tissue, antimicrobial peptides and complement factors. Humoral factors may be cellular receptors or mol¬ecules that are soluble in plasma and other body fluids.
The innate immune system is believed to be the first line of host defense against invading pathogenic organisms and other foreign material. These components of the innate response are evolutionarily conserved in organisms lacking the typical adaptive immunity of vertebrates.
In fish, the innate immune response has been considered as an essential and primary component in combating pathogens due to limitations of the specific immune response and also their poikilothermic nature. The innate immune system is commonly divided into three compartments: the Physical (epithelial/mucosal) barrier, the humoral parameters and the cellular components.
The epithelial and mucosal barrier of the skin, gills and alimentary tract is an extremely important disease barrier in fish, being constantly immersed in media contain¬ing potentially harmful agents. This type of response requires a series of mecha¬nisms that involve humoral factors, cell and tissue, antimicrobial peptides and complement factors. Humoral factors may be cellular receptors or mol¬ecules that are soluble in plasma and other body fluids.
3.2. Physical barriers
The epithelial and mucosal barrier of the skin, scales, gills and alimentary tract act as the first barrier to infection. This physical barrier is much important in fish because the fish being aquatic in nature and constantly immersed in water that contain potentially harmful agents. The mucus of fish contains lectins, pentraxins, lysozymes, complement proteins, antibacterial peptides and immunoglobulin M (IgM), which have an important role in inhibiting the entry of pathogens. In addition, the epidermis is able to react by thickening and cellular hyperplasia to different attacks and its integrity is essential for osmotic balance and to prevent the entry of foreign agents. On the other hand, defending cells such as lymphocytes, macrophages and eosinophilic granular cells are also present.
The epithelial and mucosal barrier of the skin, scales, gills and alimentary tract act as the first barrier to infection. This physical barrier is much important in fish because the fish being aquatic in nature and constantly immersed in water that contain potentially harmful agents. The mucus of fish contains lectins, pentraxins, lysozymes, complement proteins, antibacterial peptides and immunoglobulin M (IgM), which have an important role in inhibiting the entry of pathogens. In addition, the epidermis is able to react by thickening and cellular hyperplasia to different attacks and its integrity is essential for osmotic balance and to prevent the entry of foreign agents. On the other hand, defending cells such as lymphocytes, macrophages and eosinophilic granular cells are also present.
3.3. Nonspecific Humoral defence
Teleost fish have been shown to possess non-specific humoral defense substances which are physicochemical and functionally similar to mammals, but still different features.
Antimicrobial polypeptides
Antimicrobial polypeptides are small molecular peptides which are active against microorganisms and have been identified as a component of the innate immune response and been found in the tissues of teleost fishes, These peptides have been found in the mucus, liver and gill tissue of teleost fish. These low molecular weight polypeptides have the ability to break down cell wall of both Gram-positive and Gram-negative bacteria and also some of the evolutionarily conserved cationic, bactericidal polypeptides have been found.
Complement
Fish complement, in general, exhibits highest activity between 15 ⁰C and 25 ⁰C and can remain active at temperatures as low as 0 ¬- 4 ⁰C which is in contrast to mammalian complement with an optimal temperature of 37 ⁰C.
The complement system in teleosts, as well as that in higher vertebrates, can be activated in three ways:
The classical pathway which is triggered by antibody binding to the cell surface, but can also be activated by proteins such as ligand-bound C-reactive protein or directly by viruses, bacteria and virus-infected cells
The alternative pathway, which is independent of antibodies and is activated di¬rectly by foreign microorganisms, and
The lectin pathway, which is activated by the binding of a protein complex consisting of mannose/mannan-binding lectin in bacterial cells.
Cytokines
A cascade of pro-inflammatory cytokines is released as part of the non-specific innate immune response. The major drawback in identifying fish cytokines is the low sequence identity compared to their mammalian counterparts. The low sequence identities also limit the detection of proteins of fish cytokines by using the antibodies of human cytokines. In general, however, fish appear to possess a repertoire of cytokines similar to that of mammals.
Several cytokine homologues that are observed in fish species are
tumour necrosis factor-a (TNFa) and TNFb,
interleukin-1b (IL-1b), IL-2, IL-4, IL-6, IL-10, IL-11, IL-12, IL-15, IL-18, IL-21, IL-22, IL-26, IFN-g and
chemokines IL-8 or CXCL8, gIP-10, CK-1 and CK-2.
Tumor necrosis factor (TNF)
TNF-α and -β are impor¬tant activators of macrophages leading to increased respiratory activity, phagocytosis and nitric oxide production.
Interleukins (IL)
IL present in tel¬eost fish species are involved in the regulation of immunity through the stimulation of T cells. The expression of the IL-1 receptor in fish appears to be in the ante¬rior kidney, spleen, liver and gills after stimula¬tion with LPS and TNF-α, suggesting a role for the IL-1 receptor in regulating IL-1β during the inflammatory response. The expression of the IL-1 receptor in fish appears to be found in all tissues and is regulated in the ante¬rior kidney, spleen, liver and gills after stimula¬tion with LPS and TNF-α, suggesting a role for the IL-1 receptor in regulating IL-1β during the inflammatory response.
Teleost fish have been shown to possess non-specific humoral defense substances which are physicochemical and functionally similar to mammals, but still different features.
Antimicrobial polypeptides
Antimicrobial polypeptides are small molecular peptides which are active against microorganisms and have been identified as a component of the innate immune response and been found in the tissues of teleost fishes, These peptides have been found in the mucus, liver and gill tissue of teleost fish. These low molecular weight polypeptides have the ability to break down cell wall of both Gram-positive and Gram-negative bacteria and also some of the evolutionarily conserved cationic, bactericidal polypeptides have been found.
Complement
Fish complement, in general, exhibits highest activity between 15 ⁰C and 25 ⁰C and can remain active at temperatures as low as 0 ¬- 4 ⁰C which is in contrast to mammalian complement with an optimal temperature of 37 ⁰C.
The complement system in teleosts, as well as that in higher vertebrates, can be activated in three ways:
The classical pathway which is triggered by antibody binding to the cell surface, but can also be activated by proteins such as ligand-bound C-reactive protein or directly by viruses, bacteria and virus-infected cells
The alternative pathway, which is independent of antibodies and is activated di¬rectly by foreign microorganisms, and
The lectin pathway, which is activated by the binding of a protein complex consisting of mannose/mannan-binding lectin in bacterial cells.
Cytokines
A cascade of pro-inflammatory cytokines is released as part of the non-specific innate immune response. The major drawback in identifying fish cytokines is the low sequence identity compared to their mammalian counterparts. The low sequence identities also limit the detection of proteins of fish cytokines by using the antibodies of human cytokines. In general, however, fish appear to possess a repertoire of cytokines similar to that of mammals.
Several cytokine homologues that are observed in fish species are
tumour necrosis factor-a (TNFa) and TNFb,
interleukin-1b (IL-1b), IL-2, IL-4, IL-6, IL-10, IL-11, IL-12, IL-15, IL-18, IL-21, IL-22, IL-26, IFN-g and
chemokines IL-8 or CXCL8, gIP-10, CK-1 and CK-2.
Tumor necrosis factor (TNF)
TNF-α and -β are impor¬tant activators of macrophages leading to increased respiratory activity, phagocytosis and nitric oxide production.
Interleukins (IL)
IL present in tel¬eost fish species are involved in the regulation of immunity through the stimulation of T cells. The expression of the IL-1 receptor in fish appears to be in the ante¬rior kidney, spleen, liver and gills after stimula¬tion with LPS and TNF-α, suggesting a role for the IL-1 receptor in regulating IL-1β during the inflammatory response. The expression of the IL-1 receptor in fish appears to be found in all tissues and is regulated in the ante¬rior kidney, spleen, liver and gills after stimula¬tion with LPS and TNF-α, suggesting a role for the IL-1 receptor in regulating IL-1β during the inflammatory response.
Chemokines
Chemokines are a superfamily of cytokines, produced by different cell types that have, among other functions, chemoattractant properties stimulating the recruitment, activation, and adhesion of cells to sites of infection or injury.
Chemokines play a key role in the movement of immune effector cells to sites of infection and it is becoming increasingly clear that their function is also necessary to translate an innate immune response into an acquired adaptive response.
Innate immune stimuli activate toll receptors and set in motion the expression of chemokines from resident tissue macrophages and dendritic cells and, modulate the expression of chemokine receptors on dendritic cells. These changes in chemokine/chemokine-receptor expression direct the movement of antigen-loaded dendritic cells from the tissue into lymphoid tissue to activate native T and B cells and initiate the adaptive response.
Interferon (INF)
INFα and β are cytokines with a nonspecific anti¬viral function that is based on the inhibition of nu¬cleic acid replication within infected cells. INF plays an important role in the defence against viral infec¬tion in vertebrate host cells, which secrete INFα/β upon recognition of viral nucleic acid. These INFs protect other cells from viral infection by binding to different receptors, which results in the induction of several hundred genes that are stimulated by INF (ISGs).
Protease inhibitors
Several protease inhibitors are present in the serum and other body fluids of fish. The main function of protease inhibi¬tors is to maintain body fluid homeostasis. These molecules are involved in acute phase reactions and defence against pathogens that secrete pro¬teolytic enzymes. The most widely studied of the protease inhibitors is the α-2 macroglobulin, which has a high specificity for inhibiting the physical encapsulation of protease.
Lysozyme
Lysozyme is a bacteriolytic enzyme that is widely distributed throughout the body and is part of the nonspecific defence mechanisms in most animals. lysozyme has been detected in se¬rum, secretions, mucous membranes and tissues rich in leucocytes, mainly the kidney and intestine. Apparently, the main sources of lysozyme are monocytes/macrophages and neutrophils. The bactericidal ac¬tion of this enzyme involves the hydrolyzation of the peptidoglycan of bacterial cell walls resulting in cell lysis. Furthermore, this enzyme is known to trigger an opsonin of the complement system and phagocytic cells.
Natural antibodies
Natural antibodies are produced in fish at a level that is regulated in the absence of antigenic stimu¬lation of cells that are equivalent to B1 cells. These natural antibodies are found in high levels in the serum of fish, where they provide im¬mediate and broad protection against bacterial and viral pathogens, making these factors key compo¬nents of nonspecific immunity. Natural antibodies are also linked to adaptive immunity. Teleost fish are capable of generating specific IgM-type natural antibodies against various antigens. The intensity of this response, however, has been shown to vary between different species and environmental con¬ditions.
Pentraxins
C-reactive protein (CRP) and serum amyloid protein (SAA) are present in the body fluids of vertebrates and invertebrates and are commonly associated with the acute phase response of inflammation. Different stimuli, such as tissue damage, trauma or infection, generate various patterns of CRP production in teleost fish, in which either the level of CRP is decreased in serum (negative acute phase protein) or the level of CRP is increased in serum (positive acute phase protein). Although the pentraxinas of teleosts have a recognized role in defence mechanisms.
Transferrin
Iron is an essential element in the establishment of infection by many pathogens, but the availability of iron in the tissue fluids of vertebrates is extremely low due to its high affinity for the blood protein transferrin. Transferrin is a globular glycopro¬tein with a high iron chelator activity. This protein is the major iron ion transport protein in animals and plants. Only bacteria with high affinity systems for iron absorption are able to maintain sufficient iron levels to grow in the host.
Chemokines are a superfamily of cytokines, produced by different cell types that have, among other functions, chemoattractant properties stimulating the recruitment, activation, and adhesion of cells to sites of infection or injury.
Chemokines play a key role in the movement of immune effector cells to sites of infection and it is becoming increasingly clear that their function is also necessary to translate an innate immune response into an acquired adaptive response.
Innate immune stimuli activate toll receptors and set in motion the expression of chemokines from resident tissue macrophages and dendritic cells and, modulate the expression of chemokine receptors on dendritic cells. These changes in chemokine/chemokine-receptor expression direct the movement of antigen-loaded dendritic cells from the tissue into lymphoid tissue to activate native T and B cells and initiate the adaptive response.
Interferon (INF)
INFα and β are cytokines with a nonspecific anti¬viral function that is based on the inhibition of nu¬cleic acid replication within infected cells. INF plays an important role in the defence against viral infec¬tion in vertebrate host cells, which secrete INFα/β upon recognition of viral nucleic acid. These INFs protect other cells from viral infection by binding to different receptors, which results in the induction of several hundred genes that are stimulated by INF (ISGs).
Protease inhibitors
Several protease inhibitors are present in the serum and other body fluids of fish. The main function of protease inhibi¬tors is to maintain body fluid homeostasis. These molecules are involved in acute phase reactions and defence against pathogens that secrete pro¬teolytic enzymes. The most widely studied of the protease inhibitors is the α-2 macroglobulin, which has a high specificity for inhibiting the physical encapsulation of protease.
Lysozyme
Lysozyme is a bacteriolytic enzyme that is widely distributed throughout the body and is part of the nonspecific defence mechanisms in most animals. lysozyme has been detected in se¬rum, secretions, mucous membranes and tissues rich in leucocytes, mainly the kidney and intestine. Apparently, the main sources of lysozyme are monocytes/macrophages and neutrophils. The bactericidal ac¬tion of this enzyme involves the hydrolyzation of the peptidoglycan of bacterial cell walls resulting in cell lysis. Furthermore, this enzyme is known to trigger an opsonin of the complement system and phagocytic cells.
Natural antibodies
Natural antibodies are produced in fish at a level that is regulated in the absence of antigenic stimu¬lation of cells that are equivalent to B1 cells. These natural antibodies are found in high levels in the serum of fish, where they provide im¬mediate and broad protection against bacterial and viral pathogens, making these factors key compo¬nents of nonspecific immunity. Natural antibodies are also linked to adaptive immunity. Teleost fish are capable of generating specific IgM-type natural antibodies against various antigens. The intensity of this response, however, has been shown to vary between different species and environmental con¬ditions.
Pentraxins
C-reactive protein (CRP) and serum amyloid protein (SAA) are present in the body fluids of vertebrates and invertebrates and are commonly associated with the acute phase response of inflammation. Different stimuli, such as tissue damage, trauma or infection, generate various patterns of CRP production in teleost fish, in which either the level of CRP is decreased in serum (negative acute phase protein) or the level of CRP is increased in serum (positive acute phase protein). Although the pentraxinas of teleosts have a recognized role in defence mechanisms.
Transferrin
Iron is an essential element in the establishment of infection by many pathogens, but the availability of iron in the tissue fluids of vertebrates is extremely low due to its high affinity for the blood protein transferrin. Transferrin is a globular glycopro¬tein with a high iron chelator activity. This protein is the major iron ion transport protein in animals and plants. Only bacteria with high affinity systems for iron absorption are able to maintain sufficient iron levels to grow in the host.
3.4.
Nonspecific Cellular Defence
Cell types that are involved in the non-specific cellular defense responses of teleost fish are the phagocytic cells, monocytes/macrophages, the non-specific cytotoxic cells (NCC) and granulocytes (neutrophils). Some teleosts have both acidophilic and basophilic granulocytes in peripheral blood in addition to the neutrophils, but in others only the neutrophils has been found.
Phagocytes
Fish phagocytic cells are formed mainly in the head-kidney from stem cells, as they mature, they spread throughout the body. They are most frequent in tissues underlying epithelial barriers, their principal locations being the head kidney, blood, spleen, gut-associated lymphoid tissue, liver, atrium of heart and gills.
Phagocytes are divided into two main types,
Cell types that are involved in the non-specific cellular defense responses of teleost fish are the phagocytic cells, monocytes/macrophages, the non-specific cytotoxic cells (NCC) and granulocytes (neutrophils). Some teleosts have both acidophilic and basophilic granulocytes in peripheral blood in addition to the neutrophils, but in others only the neutrophils has been found.
Phagocytes
Fish phagocytic cells are formed mainly in the head-kidney from stem cells, as they mature, they spread throughout the body. They are most frequent in tissues underlying epithelial barriers, their principal locations being the head kidney, blood, spleen, gut-associated lymphoid tissue, liver, atrium of heart and gills.
Phagocytes are divided into two main types,
·
neutrophils and
·
macrophages
These
phagocytes are involved in ingestion of microbes.
Neutrophils
These cells also called polymorphonuclear leukocytes (PMNs) play a key role in the development of acute inflammation. In addition to the phagocytic nature, neutrophils also contain granules that contain acidic and alkaline phosphatases, defensins and peroxidase which necessary for successful elimination of the pathogens.
Macrophages
Macrophages termed as monocytes when present in the blood stream, these are large cells. The function of macrophages include phagocytosis and antigen presentation to T cells. Macrophages are long-lived cells. Macrophages can produce chemicals that can act as antibacte¬rial agents, peroxynitrites and hydroxyl groups
Phagocytosis
Phagocytosis is one of the most important processes in poikilothermic animals because it is the process that is least influenced by tempera¬ture. Phagocytosis is the process by which cells engulf microorganisms and particles. During phagocytosis the phagocytes are attracted towards the microbe by the chemical signals. Phagocyte attaches to the microbe with the help of either microbial sugar residues present on its surface or with the help of complement/antibody which is bound to the pathogen. Once attached the phagocytic cell engulf the microbe and form phagosome. This phagosome fuses with lysosomes to form a phagolysosome. Which leads to the destruction of the pathogen.
Natural killer (NK) cells
NK cells are large granular lymphocytes that are mainly found in the blood. These NK cells of fish are morphologically distinct from the large granular lymphocytes of mammals but they are functionally similar. They contain two unique cell surface receptors known as killer activation receptor and killer inhibition receptor.
The activation of NK cells, killer activation receptor initiates the release of cytokine molecules, while the activation of killer inhibition receptor inhibits the release of cytokine molecules. NK cells attack virally-infected cells and certain tumour cells and destroy these cells by releasing perforins and granyzymes from its granules. NK cells also secrete interferon-γ (IFN-γ), where this interferon molecule to prevent healthy host cells from becoming infected by a virus and it also increase the T cell response to other virally infected cells.
Neutrophils
These cells also called polymorphonuclear leukocytes (PMNs) play a key role in the development of acute inflammation. In addition to the phagocytic nature, neutrophils also contain granules that contain acidic and alkaline phosphatases, defensins and peroxidase which necessary for successful elimination of the pathogens.
Macrophages
Macrophages termed as monocytes when present in the blood stream, these are large cells. The function of macrophages include phagocytosis and antigen presentation to T cells. Macrophages are long-lived cells. Macrophages can produce chemicals that can act as antibacte¬rial agents, peroxynitrites and hydroxyl groups
Phagocytosis
Phagocytosis is one of the most important processes in poikilothermic animals because it is the process that is least influenced by tempera¬ture. Phagocytosis is the process by which cells engulf microorganisms and particles. During phagocytosis the phagocytes are attracted towards the microbe by the chemical signals. Phagocyte attaches to the microbe with the help of either microbial sugar residues present on its surface or with the help of complement/antibody which is bound to the pathogen. Once attached the phagocytic cell engulf the microbe and form phagosome. This phagosome fuses with lysosomes to form a phagolysosome. Which leads to the destruction of the pathogen.
Natural killer (NK) cells
NK cells are large granular lymphocytes that are mainly found in the blood. These NK cells of fish are morphologically distinct from the large granular lymphocytes of mammals but they are functionally similar. They contain two unique cell surface receptors known as killer activation receptor and killer inhibition receptor.
The activation of NK cells, killer activation receptor initiates the release of cytokine molecules, while the activation of killer inhibition receptor inhibits the release of cytokine molecules. NK cells attack virally-infected cells and certain tumour cells and destroy these cells by releasing perforins and granyzymes from its granules. NK cells also secrete interferon-γ (IFN-γ), where this interferon molecule to prevent healthy host cells from becoming infected by a virus and it also increase the T cell response to other virally infected cells.
...............................................................................................................
Unit 4- Fish Leucocytes
4.1.
Fish Leucocytes
Lymphocytes, macrophages/monocytes, granulocytes (neutrophilic, eosinophilic, and basophilic), and nonspecific cytotoxic cells (NCCs) can be seen in teleost, but there is a difference in occurrence, morphology and function in leukocytes of fish depending on the species of fish and this differences make difficult in generalizations about fish leukocytes.
The cell involved in non-specific cellular response are macrophages/monocytes, granulocytes (neutrophilic, eosinophilic, and basophilic), and nonspecific cytotoxic cells (NCCs). These cells play a major role in combating the pathogen once it enters into the fish.
Lymphocytes, macrophages/monocytes, granulocytes (neutrophilic, eosinophilic, and basophilic), and nonspecific cytotoxic cells (NCCs) can be seen in teleost, but there is a difference in occurrence, morphology and function in leukocytes of fish depending on the species of fish and this differences make difficult in generalizations about fish leukocytes.
The cell involved in non-specific cellular response are macrophages/monocytes, granulocytes (neutrophilic, eosinophilic, and basophilic), and nonspecific cytotoxic cells (NCCs). These cells play a major role in combating the pathogen once it enters into the fish.
4.2. Monocytes/Macrophages
Macrophages differentiated from mononuclear cells derived from circulating blood monocytes. In fish macrophages are mainly involved in phagocytosis which is one of the most ancient immune mechanism, and macrophages were observed in almost all lymphoid tissues. Several subpopulations of macrophages are also present in fish. Distribution of macrophages in the fish is species dependent but these macrophages are commonly observed in both lymphoid organ (spleen, kidney, and thymus) and non lymphoid organ (liver, gonads, and heart) tissue. The environmental change influence on the size, pigmentation, and number of macrophages.
Macrophages differentiated from mononuclear cells derived from circulating blood monocytes. In fish macrophages are mainly involved in phagocytosis which is one of the most ancient immune mechanism, and macrophages were observed in almost all lymphoid tissues. Several subpopulations of macrophages are also present in fish. Distribution of macrophages in the fish is species dependent but these macrophages are commonly observed in both lymphoid organ (spleen, kidney, and thymus) and non lymphoid organ (liver, gonads, and heart) tissue. The environmental change influence on the size, pigmentation, and number of macrophages.
4.3. Granulocytes
Fish granulocytes are involved in non-specific defence mechanisms and activate in the presence of foreign material in the body but do not stimulated by specific antigens. These cell are involved in phagocytosis, respiratory burst activity, and chemotaxis. Granulocytes are generated in the haemopoietic tissues of the kidney, have wide morphological variations in granulocyte subpopulations and immature (blast) cells are circulated throughout the fish.
In fish, we can find three types of granulocytes they are neutrophils and eosinophils are the most common while basophils are much rare in fish.
Neutrophil: This is the most abundant among leucocyte. Neutrophils has no affinity for acidic or basic dyes, but stainable with neutral dye. They can migrate into the tissues from blood to engulf bacteria.
Eosinophil: This is a polymorphonuclear leucocyte that can be stained with eosin which is an acidic dye. Eosinophils can neutralize internal parasites and also can modulate allergic inflammatory reactions.
Basophil: These basophils are present only in few fish species, even though they are present their numbers are normally very low in blood. Basophils shows an affinity for basic dyes. Basophils also participate in neutralizing microorganisms.
Fish granulocytes are involved in non-specific defence mechanisms and activate in the presence of foreign material in the body but do not stimulated by specific antigens. These cell are involved in phagocytosis, respiratory burst activity, and chemotaxis. Granulocytes are generated in the haemopoietic tissues of the kidney, have wide morphological variations in granulocyte subpopulations and immature (blast) cells are circulated throughout the fish.
In fish, we can find three types of granulocytes they are neutrophils and eosinophils are the most common while basophils are much rare in fish.
Neutrophil: This is the most abundant among leucocyte. Neutrophils has no affinity for acidic or basic dyes, but stainable with neutral dye. They can migrate into the tissues from blood to engulf bacteria.
Eosinophil: This is a polymorphonuclear leucocyte that can be stained with eosin which is an acidic dye. Eosinophils can neutralize internal parasites and also can modulate allergic inflammatory reactions.
Basophil: These basophils are present only in few fish species, even though they are present their numbers are normally very low in blood. Basophils shows an affinity for basic dyes. Basophils also participate in neutralizing microorganisms.
4.4. Nonspecific Cytotoxic Cells
These cells are involve in nonspecific cytotoxic activity against the invading foreign materials. These nonspecific cytotoxic cells can be seen in head kidney, spleen, and blood. Circulating nonspecific cytotoxic cells are morphologically and functionally different from the nonspecific cytotoxic cells present in the spleen.
These cells are involve in nonspecific cytotoxic activity against the invading foreign materials. These nonspecific cytotoxic cells can be seen in head kidney, spleen, and blood. Circulating nonspecific cytotoxic cells are morphologically and functionally different from the nonspecific cytotoxic cells present in the spleen.
4.5. Lymphocytes
Lymphocytes are produced in both thymus and kidney and are of 2 types namely B lymphocytes and T lymphocytes. These lymphocytes function in developing specific immune mechanisms in fish. Lymphocytes contain prominent nucleus and basophilic cytoplasm with few mitochondria and ribosomes present in it. The size and number of lymphocytes vary among species and also with season. Specific antigen responses of lymphocytes differ between cells produced by each organ. There is also a belief that fish lymphocytes may involve in phagocytic activity.
Lymphocytes are produced in both thymus and kidney and are of 2 types namely B lymphocytes and T lymphocytes. These lymphocytes function in developing specific immune mechanisms in fish. Lymphocytes contain prominent nucleus and basophilic cytoplasm with few mitochondria and ribosomes present in it. The size and number of lymphocytes vary among species and also with season. Specific antigen responses of lymphocytes differ between cells produced by each organ. There is also a belief that fish lymphocytes may involve in phagocytic activity.
...............................................................................................................
Unit 5- Specific defence mechanism in Fish
5.1.1.
Specific defence mechanism in Fish
Specific immune system can be seen in vertebrates which is also referred as advance defence system in organisms.
Specific immune system are made up of two cellular systems:
Specific immune system can be seen in vertebrates which is also referred as advance defence system in organisms.
Specific immune system are made up of two cellular systems:
·
Humoral antibody system (B cells)
·
cell-mediated immunity (T cells)
5.1.2.
Humoral Antibody System (B cells)
Humoral antibody uses B cells where the B cells differentiate into antibody producing Plasma cells and Memory cells. Series that involved in stimulating B cells to produce antibody are:-
Antigen presentation
The antigen-presenting macrophages recognize the pathogen (e.g., virus) engulf the pathogen, digests it and displays antigen on their surface. The processing involves proteolysis, which presumably occurs within acidic subcellular compartments. These macrophages display residual foreign antigen on the cell membrane and this is l0 times more effective than unbound antigen in promoting immune response.
Humoral antibody uses B cells where the B cells differentiate into antibody producing Plasma cells and Memory cells. Series that involved in stimulating B cells to produce antibody are:-
Antigen presentation
The antigen-presenting macrophages recognize the pathogen (e.g., virus) engulf the pathogen, digests it and displays antigen on their surface. The processing involves proteolysis, which presumably occurs within acidic subcellular compartments. These macrophages display residual foreign antigen on the cell membrane and this is l0 times more effective than unbound antigen in promoting immune response.
On
the other hand, other viral particles infect nearby host cells.
The macrophages also secrete a protein called interleukin- 1 (IL- 1) which activates the helper-T cells. Besides macrophage, the B cell also acts as antigen presenting cell due to its antigen-binding receptor.
The macrophages also secrete a protein called interleukin- 1 (IL- 1) which activates the helper-T cells. Besides macrophage, the B cell also acts as antigen presenting cell due to its antigen-binding receptor.
5.1.3. Helper T cells
These T cells are activated when macrophages-bound antigen linked to class II Major Histocompatibility Complex (MHC) in the presence of interleukin-l and they secrete two factors like B cell growth factor (IL-4) and B cell differentiating factor (IL-5). The IL- l, IL-4 and IL-5 act together to provoke B cell to respond quickly.
These T cells are activated when macrophages-bound antigen linked to class II Major Histocompatibility Complex (MHC) in the presence of interleukin-l and they secrete two factors like B cell growth factor (IL-4) and B cell differentiating factor (IL-5). The IL- l, IL-4 and IL-5 act together to provoke B cell to respond quickly.
5.1.4. B cell activation
If B cell immunoglobulin receptor molecules are crosslinked by foreign antigen and its IL-1 and IL-4 receptors are stimulated, the B cells are activated and express new class II MHC antigen. The membrane receptors for antigen are concentrated at a particular position on the surface of the B cells. The B cells divide repeatedly to form antibody-secreting plasma cells and memory cells. These plasma cells are widely distributed throughout the body but concentrated in the head kidney and spleen of fish. The plasma cells usually die after 3-6 days of secretion and the immunoglobulin levels in the serum decline gradually. The second populations of cells derived from antigen- sensitive B cells and morphologically indistinguishable from parent cells are known as memory cells.
If B cell immunoglobulin receptor molecules are crosslinked by foreign antigen and its IL-1 and IL-4 receptors are stimulated, the B cells are activated and express new class II MHC antigen. The membrane receptors for antigen are concentrated at a particular position on the surface of the B cells. The B cells divide repeatedly to form antibody-secreting plasma cells and memory cells. These plasma cells are widely distributed throughout the body but concentrated in the head kidney and spleen of fish. The plasma cells usually die after 3-6 days of secretion and the immunoglobulin levels in the serum decline gradually. The second populations of cells derived from antigen- sensitive B cells and morphologically indistinguishable from parent cells are known as memory cells.
5.1.5. Cell-Mediated Immunity (T cells)
Antigenic fragments present on the macrophage alert a specific type of T lymphocyte (“helper” T) about the attack of intruder. These helper T cells recognizes antigen particles and binds to the macrophage via an antigen receptor. Helper T cells are unique to a specific antigen.
Antigenic fragments present on the macrophage alert a specific type of T lymphocyte (“helper” T) about the attack of intruder. These helper T cells recognizes antigen particles and binds to the macrophage via an antigen receptor. Helper T cells are unique to a specific antigen.
This binding stimulates production of chemical
substances such as interleukin-1 (IL-1), tumor necrosis factor (TNF) by
macrophage
Helper T cells generates interleukin-2 and gamma interferon (IFN-y)
All substances facilitate intercellular communication
Helper T cells generates interleukin-2 and gamma interferon (IFN-y)
All substances facilitate intercellular communication
TNF steps up production of IL-1, it also causes
fever in homeotherms
TNF and IL-1 are cytokines (cellular)
Apart from causing fever IL-1 forms immune cell clusters and stimulates the helper T cell to release IL-2
IL-2 causes T cells to release gamma interferon which, in-turn, activates macrophages
IL-2 also instructs other helper T cells and “killer” T cells to multiply
Proliferating helper T cells release substances that cause B cells (another type of lymphocyte) to multiply and produce antibodies
TNF and IL-1 are cytokines (cellular)
Apart from causing fever IL-1 forms immune cell clusters and stimulates the helper T cell to release IL-2
IL-2 causes T cells to release gamma interferon which, in-turn, activates macrophages
IL-2 also instructs other helper T cells and “killer” T cells to multiply
Proliferating helper T cells release substances that cause B cells (another type of lymphocyte) to multiply and produce antibodies
Meanwhile, many invader cells have been
consumed by macrophages, but other “daughter” viral particles have escaped and
are infecting other cells
Killer T cells will kill the host cells that are infected with virus by making pores to the infected cell.
Killer T cells will kill the host cells that are infected with virus by making pores to the infected cell.
Finally, as the infection is brought under
control, yet another type of T cell called the suppressor T cell will signal B
cells, helper T’s and killer T’s to stop the work.
After the work has stopped most immune cells die, but a few remain in the body these are called memory cells. This memory cells will keep the memory of the antigen so that they will be able to respond more quickly the next time the body is invaded by the same foreign substance
After the work has stopped most immune cells die, but a few remain in the body these are called memory cells. This memory cells will keep the memory of the antigen so that they will be able to respond more quickly the next time the body is invaded by the same foreign substance
5.2.1. Lymphoid organs in fish
There are two types of lymphoid organs can be seen in fish. Primary lymphoid organs include thymus and head kidney that produce and mature stem cells' The secondary lymphoid organs include kidney, spleen, and Mucosa lymphoid tissue. Besides, liver, skin, intestine and heart are also important organs that take part in the defence. The endothelial cells and macrophages present in these organs are highly endocytic towards 'self' or 'non-self' substances. The development lymphoid organs does not necessarily correspond to the maturation of immune functions' Even though the organs develop simultaneously in trout and salmon, the surface IgM positive cells appear 8 days pre-hatching in frout and 45 days post-hatch in salmon.
There are two types of lymphoid organs can be seen in fish. Primary lymphoid organs include thymus and head kidney that produce and mature stem cells' The secondary lymphoid organs include kidney, spleen, and Mucosa lymphoid tissue. Besides, liver, skin, intestine and heart are also important organs that take part in the defence. The endothelial cells and macrophages present in these organs are highly endocytic towards 'self' or 'non-self' substances. The development lymphoid organs does not necessarily correspond to the maturation of immune functions' Even though the organs develop simultaneously in trout and salmon, the surface IgM positive cells appear 8 days pre-hatching in frout and 45 days post-hatch in salmon.
5.2.2. Primary lymphoid organs
Primary lymphoid organs mainly contains thymus and anterior kidney.
Thymus
It is situated in the dorsolateral region of the gill chamber close to the opercular cavity. Thymus is as the primary lymphoid organ and mostly contains T cells and few populations of B cells. The thymus starts developing from 24 hours after fertilization and it is the first lymphoid tissue to become populated by lymphocytes during development. Once developed the thymocytes migrate from thymus to spleen and kidney. Along with sIg– and sIg+ lymphocytes thymus also possess epithelial cells monocytes, macrophages, neuroendocrine cells etc.
Anterior kidney
The anatomy of the kidney varies from species to species. The kidney of teleost fish not only function as the excretory organ, it also contains the medullary and cortical adrenal homologs and hematopoietic tissue. Kidney is situated along the dorsal wall of the body cavity. Based on location and function kidney of teleost fish has been classified into two types they are:- 1) anterior or head kidney, and 2) posterior or trunk kidney.
Anterior kidney losses its excretory role after the fish matures and Mature anterior kidney is the primary hematopoietic organ in adult teleosts. It is the first lymphoid organ to possess sIg+ cells. Based on the species the anterior kidney may be bifurcated or single extension. B cells will generate and mature in head kidney. Anterior kidney can even act as secondary lymphoid organ.
Primary lymphoid organs mainly contains thymus and anterior kidney.
Thymus
It is situated in the dorsolateral region of the gill chamber close to the opercular cavity. Thymus is as the primary lymphoid organ and mostly contains T cells and few populations of B cells. The thymus starts developing from 24 hours after fertilization and it is the first lymphoid tissue to become populated by lymphocytes during development. Once developed the thymocytes migrate from thymus to spleen and kidney. Along with sIg– and sIg+ lymphocytes thymus also possess epithelial cells monocytes, macrophages, neuroendocrine cells etc.
Anterior kidney
The anatomy of the kidney varies from species to species. The kidney of teleost fish not only function as the excretory organ, it also contains the medullary and cortical adrenal homologs and hematopoietic tissue. Kidney is situated along the dorsal wall of the body cavity. Based on location and function kidney of teleost fish has been classified into two types they are:- 1) anterior or head kidney, and 2) posterior or trunk kidney.
Anterior kidney losses its excretory role after the fish matures and Mature anterior kidney is the primary hematopoietic organ in adult teleosts. It is the first lymphoid organ to possess sIg+ cells. Based on the species the anterior kidney may be bifurcated or single extension. B cells will generate and mature in head kidney. Anterior kidney can even act as secondary lymphoid organ.
5.2.3. Secondary lymphoid organs
Secondary lymphoid organs contains kidney, spleen, mucosa.
Kidney
The head kidney which also works as secondary lymphoid organ is important in mounting immune response. The head kidney is a major organ where antibody producing cells are formed. The presence of monocytes, macrophages and neutrophils and the lack of lymphocytes in the early life of many fish species indicate the importance of innate immune system during early stage of life. The mature kidney in Indian major carp contains mostly lymphocytes besides other blood cells.
Spleen
Spleen is the secondary lymphoid organ and it is the last organ to form during the development of the lymphoid organs in teleosts. In most teleosts, the spleen is present as an encapsulated organ with abundant red pulp and poorly developed white pulp but in majority of the teleosts these pulp are not clearly distinct. The red pulp occupies most of the space in spleen and contains lymphocytes and macrophages. The white pulp occupies less space and contains poorly developed ellipsoids and numerous melano-macrophage aggregations. Ellipsoids purifying the blood by trapping immunocomplexes and later digested by the macrophages.
Mucosa
Mucosa is highly diffused and unorganized lymphoid tissue that consists of granulocytes, macrophages in the gut, gills and skin. These lymphoid tissue occur mainly under the epithelial cells of the gut and in lamina propria. Macrophages and sIg+ lymphocytes also present in the mucosal lymphoid tissues
Secondary lymphoid organs contains kidney, spleen, mucosa.
Kidney
The head kidney which also works as secondary lymphoid organ is important in mounting immune response. The head kidney is a major organ where antibody producing cells are formed. The presence of monocytes, macrophages and neutrophils and the lack of lymphocytes in the early life of many fish species indicate the importance of innate immune system during early stage of life. The mature kidney in Indian major carp contains mostly lymphocytes besides other blood cells.
Spleen
Spleen is the secondary lymphoid organ and it is the last organ to form during the development of the lymphoid organs in teleosts. In most teleosts, the spleen is present as an encapsulated organ with abundant red pulp and poorly developed white pulp but in majority of the teleosts these pulp are not clearly distinct. The red pulp occupies most of the space in spleen and contains lymphocytes and macrophages. The white pulp occupies less space and contains poorly developed ellipsoids and numerous melano-macrophage aggregations. Ellipsoids purifying the blood by trapping immunocomplexes and later digested by the macrophages.
Mucosa
Mucosa is highly diffused and unorganized lymphoid tissue that consists of granulocytes, macrophages in the gut, gills and skin. These lymphoid tissue occur mainly under the epithelial cells of the gut and in lamina propria. Macrophages and sIg+ lymphocytes also present in the mucosal lymphoid tissues
...............................................................................................................
Unit 6- Ontogeny of Fish Immune System
6.1.Ontogeny
of Fish Immune System
In fish, as in all vertebrates, the thymus is the first lymphoid organ to develop and to become lymphoid. Later kidney and spleen develops as lymphoid organ and remaining throughout life. In the early life of the carp, the thymus contribute majorly to lymphoid cell pool (70% or about 3 X l05 cells at day 28). Later as the organism grows say at 2 months of age, the total lymphocyte cell pool (5 x l06 cells) was distributed among the lymphoid organs with 38% in the mesonephros, 32% in the thymus, 15% in the pronephros, 12% in the peripheral blood, and 3% in the spleen.
The development of the lymphoid system in fish is explained by two hypotheses.
In fish, as in all vertebrates, the thymus is the first lymphoid organ to develop and to become lymphoid. Later kidney and spleen develops as lymphoid organ and remaining throughout life. In the early life of the carp, the thymus contribute majorly to lymphoid cell pool (70% or about 3 X l05 cells at day 28). Later as the organism grows say at 2 months of age, the total lymphocyte cell pool (5 x l06 cells) was distributed among the lymphoid organs with 38% in the mesonephros, 32% in the thymus, 15% in the pronephros, 12% in the peripheral blood, and 3% in the spleen.
The development of the lymphoid system in fish is explained by two hypotheses.
·
Natural selection will favor individuals in which development of
the immune system coincides with their first exposure to potential pathogens
either from their environment or in their food (i.e., hatching in oviparous
species, parturition is viviparous species, or at the time of first feeding).
·
Development of the lymphoid organs occurs at a preset time during
embryogenesis. Once a certain "physiological age" has been reached
lymphoid organs develop and is independent of first exposure to antigenic
challenge.
The
state of immunological maturity of the fish may be correlated with the age,
weight, and water temperature. The weight of fish is approximately 0.24 g when
the first antibody is detected.
6.2. Evidence for Ig in the Eggs and Passive
Transfer of Immunity from Mother to Young
Nonspecific humoral factors, such as C-reactive protein and lectin-like agglutinins are found in fish egg, in addition to that Immunoglobulin has aslo been detected in both fertilized and unfertilized eggs of carp. The levels in the whole fish increased slowly to reach a peak, in terms of milligrams per gram of tissue, at the time of hatching, and slowly decline. IgM-like protein was maternally derived and that it was depleted by the time of first feeding, after which the larvae start to produce their own.
Nonspecific humoral factors, such as C-reactive protein and lectin-like agglutinins are found in fish egg, in addition to that Immunoglobulin has aslo been detected in both fertilized and unfertilized eggs of carp. The levels in the whole fish increased slowly to reach a peak, in terms of milligrams per gram of tissue, at the time of hatching, and slowly decline. IgM-like protein was maternally derived and that it was depleted by the time of first feeding, after which the larvae start to produce their own.
6.3. Ontogeny of T and B Cells in Lymphoid
Organ Development
The sIg+ cells (cells bearing Ig on their surface) could be detected in the thymus and pronephros from day 14 after fertilization, and in the mesonephros and spleen from day 28. Cytoplasmic Ig+ cells (cells bearing Ig in their cytoplasm) were first seen in the pronephros at day 21. The percentage of sIg' cells increased gradually to the age of 16 months, with 15.8-48.1% for blood, pronephros 9.7-21.6%, mesonephros 7.2-16.8% , spleen 15.9-21.6% , and thymus 1.5-3.7%. but in the case of cIg+ cells, the percentage was very low or even absent in spleen, thymus, and blood. Plasma cells were not found in the kidney of the fishes of the age below 1 month old and 0.17% can be seen in the fishes of 1 month old followed by increase in plasma cells, and increased to 1% at the age of 8 months.
The sIg+ cells (cells bearing Ig on their surface) could be detected in the thymus and pronephros from day 14 after fertilization, and in the mesonephros and spleen from day 28. Cytoplasmic Ig+ cells (cells bearing Ig in their cytoplasm) were first seen in the pronephros at day 21. The percentage of sIg' cells increased gradually to the age of 16 months, with 15.8-48.1% for blood, pronephros 9.7-21.6%, mesonephros 7.2-16.8% , spleen 15.9-21.6% , and thymus 1.5-3.7%. but in the case of cIg+ cells, the percentage was very low or even absent in spleen, thymus, and blood. Plasma cells were not found in the kidney of the fishes of the age below 1 month old and 0.17% can be seen in the fishes of 1 month old followed by increase in plasma cells, and increased to 1% at the age of 8 months.
6.4. Ontogeny of nonspecific immunity
Along with maternally derived immune protection in newly hatched fry a variety of nonspecific defence mechanisms develops prior to specific immunity. Nonspecific immunity is the major defence mechanism in earlier life before the specific mechanism is fully developed. Where the nonspecific lectins and hemagglutinins found in fish eggs and fry, in addition to this presence phagocytic cells can be seen in newly hatched fry. This nonspecific immunity helps in defending the fish throughout the life. Non specific defence system also plays a significant role when the specific immune response is suppressed.
Along with maternally derived immune protection in newly hatched fry a variety of nonspecific defence mechanisms develops prior to specific immunity. Nonspecific immunity is the major defence mechanism in earlier life before the specific mechanism is fully developed. Where the nonspecific lectins and hemagglutinins found in fish eggs and fry, in addition to this presence phagocytic cells can be seen in newly hatched fry. This nonspecific immunity helps in defending the fish throughout the life. Non specific defence system also plays a significant role when the specific immune response is suppressed.
6.5. Ontogeny of specific immunity
Matured T lymphocytes that can function in defence system can be seen soon after their morphological appearance in about 14-18 days after hatching. The presence circulating antibodies in the blood indicates activation of specific immunity in tern the presence of matured plasma cell can be seen in carp at the age of 4 month. Also the development of these immune system depends on temperature.
Matured T lymphocytes that can function in defence system can be seen soon after their morphological appearance in about 14-18 days after hatching. The presence circulating antibodies in the blood indicates activation of specific immunity in tern the presence of matured plasma cell can be seen in carp at the age of 4 month. Also the development of these immune system depends on temperature.
................................................................................................................
Unit 7- Lymphocytes
7.1.
Introduction
A lymphocyte is a type of white blood cell that present in the vertebrate immune system. There are two main types of lymphocytes are present in fish they are B-cells and T-cells. In teleost fish, the head kidney is an important source of B cells, B cells can also be found in spleen of the adult fish. The T cells can be found in thymus which is a primary lymphoid organ in fish. The primary function of fish lymphocytes is to executive the specific immune response against the antigen, lymphocytes may even act as phagocytic cells.
A lymphocyte is a type of white blood cell that present in the vertebrate immune system. There are two main types of lymphocytes are present in fish they are B-cells and T-cells. In teleost fish, the head kidney is an important source of B cells, B cells can also be found in spleen of the adult fish. The T cells can be found in thymus which is a primary lymphoid organ in fish. The primary function of fish lymphocytes is to executive the specific immune response against the antigen, lymphocytes may even act as phagocytic cells.
7.2. B-cells
B cells are primarily responsible for specific humoral immunity (relating to antibodies).These B cell in the presence of antigen are activated and differentiated into plasma cells in spleen, after differentiation Plasma cells migrate to the head kidney. These B cells are characterized by the expression of B cell receptor, a surface immunoglobulin receptor (sIG). B cells of teleost fish are highly phagocytic and display microbicidal properties. In case of intestine there is an increase in number of IgM+ cells from the anterior and middle to the posterior part of the intestine because the higher absorption of antigens is present in posterior part of gut. In skin of fish, B cells are present only in the epithelium layer and the numbers of IgM-secreting cell present in the skin can increase up to 20-fold if the fish is immunized with antigen. B cells are also present in the stratified epithelium of the gill arch and filaments.
B cells are primarily responsible for specific humoral immunity (relating to antibodies).These B cell in the presence of antigen are activated and differentiated into plasma cells in spleen, after differentiation Plasma cells migrate to the head kidney. These B cells are characterized by the expression of B cell receptor, a surface immunoglobulin receptor (sIG). B cells of teleost fish are highly phagocytic and display microbicidal properties. In case of intestine there is an increase in number of IgM+ cells from the anterior and middle to the posterior part of the intestine because the higher absorption of antigens is present in posterior part of gut. In skin of fish, B cells are present only in the epithelium layer and the numbers of IgM-secreting cell present in the skin can increase up to 20-fold if the fish is immunized with antigen. B cells are also present in the stratified epithelium of the gill arch and filaments.
7.3. T-cells
T-cells take part in cell mediated immune response. T cells are part of white blood cells known as lymphocytes, and take part in cell mediated immune response. They are different from other lymphocytes, such as B cells and natural killer cells (NK cells), by the presence of a T cell receptor (TCR) on the cell surface. They are called T cells because they mature in the thymus.
T-cells take part in cell mediated immune response. T cells are part of white blood cells known as lymphocytes, and take part in cell mediated immune response. They are different from other lymphocytes, such as B cells and natural killer cells (NK cells), by the presence of a T cell receptor (TCR) on the cell surface. They are called T cells because they mature in the thymus.
7.4. The life history of T lymphocytes
There
are several subsets of T cells, each with a distinct function they are :-
·
Cytotoxic T cells (CD8)
·
T helper cells (CD4).
·
Regulatory T Cells (Treg cells)
T
helper cells (CD4):
T helper cells are also known as CD4+ T cells because they express the CD4 protein on their surface. Helper T cells are activated by the antigen presenting cells (APCs). Activated T cell secretes small proteins called cytokines that assist in the active immune response include maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells and macrophages.
Cytotoxic T cells:
Cytotoxic T cells are called "killer cells" because they produce chemical substances known as lymphokines. These cells are also known as CD8+ T cells because they express the CD8 on their surface. These cells destroy virally infected cells and also tumor cells. These cells recognize their targets by binding to antigen associated with MHC class I, which is present on the surface of nearly every cell of the body.
Regulatory T Cells (Treg cells):
Treg cells formerly known as suppressor T cells can regulate the mechanisms to prevent sustained inflammatory responses that may attacks on healthy tissue. Regulatory T cells are involved in preventing autoimmunity, moderating inflammation, and minimizing tissue damage. The function of regulatory T cells is to suppress the function of antigen-presenting cells and effector T cells (Teff cells). If Treg cell activity is reduced it may cause autoimmune diseases.
Treg cells are divided into 3 subsets.
T helper cells are also known as CD4+ T cells because they express the CD4 protein on their surface. Helper T cells are activated by the antigen presenting cells (APCs). Activated T cell secretes small proteins called cytokines that assist in the active immune response include maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells and macrophages.
Cytotoxic T cells:
Cytotoxic T cells are called "killer cells" because they produce chemical substances known as lymphokines. These cells are also known as CD8+ T cells because they express the CD8 on their surface. These cells destroy virally infected cells and also tumor cells. These cells recognize their targets by binding to antigen associated with MHC class I, which is present on the surface of nearly every cell of the body.
Regulatory T Cells (Treg cells):
Treg cells formerly known as suppressor T cells can regulate the mechanisms to prevent sustained inflammatory responses that may attacks on healthy tissue. Regulatory T cells are involved in preventing autoimmunity, moderating inflammation, and minimizing tissue damage. The function of regulatory T cells is to suppress the function of antigen-presenting cells and effector T cells (Teff cells). If Treg cell activity is reduced it may cause autoimmune diseases.
Treg cells are divided into 3 subsets.
·
Naturally occurring CD4+CD25+
·
Tr1 cells and
·
Th3 cells
Naturally
occurring CD4+CD25+
Naturally occurring CD4+CD25+ Treg cells develops in the thymus and performs the function like Induction of cytolysis, Disruption of metabolic activities, Inhibition of dendritic cell maturation and Secretion of IL-10, IL-35, TGF-b1, Galectin-1. This cells plays a major role in immune control.
Tr1 cells
Develop in the periphery during a normal immune response. Perform the function like cell-cell contact, secretion of IL-10, TGF-b1 and IFN-g
Th3 cells
Develop in the periphery during a normal immune response and secret TGF-b1.
Naturally occurring CD4+CD25+ Treg cells develops in the thymus and performs the function like Induction of cytolysis, Disruption of metabolic activities, Inhibition of dendritic cell maturation and Secretion of IL-10, IL-35, TGF-b1, Galectin-1. This cells plays a major role in immune control.
Tr1 cells
Develop in the periphery during a normal immune response. Perform the function like cell-cell contact, secretion of IL-10, TGF-b1 and IFN-g
Th3 cells
Develop in the periphery during a normal immune response and secret TGF-b1.
................................................................................................................
Unit 8- Antibody (Immunoglobulin)
8.1.
Introduction
All antibodies are proteins known as immunoglobulins. An antibody is defined as “an immunoglobulin capable of specific combination with the antigen that caused its production in a susceptible animal.” Antibodies are produced by plasma cells which are differentiated by B cells, in response to the foreign proteins, called antigens. The part of the antigen to which an antibody binds is called the epitope. The epitope is a short amino acid sequence that the antibody is able to recognize. Antibodies contain four polypeptide chains and are arranged in Y-shape.
All antibodies are proteins known as immunoglobulins. An antibody is defined as “an immunoglobulin capable of specific combination with the antigen that caused its production in a susceptible animal.” Antibodies are produced by plasma cells which are differentiated by B cells, in response to the foreign proteins, called antigens. The part of the antigen to which an antibody binds is called the epitope. The epitope is a short amino acid sequence that the antibody is able to recognize. Antibodies contain four polypeptide chains and are arranged in Y-shape.
8.2.
Basic Structure and Isotypes
Antibody molecule contain 4 polypeptide chains, among them two are identical heavy chains and two identical light chains. These chains are held together by disulphide bonds, some are inter-chain and some are intra-chain. Each part of the molecule has different functions:
Antibody molecule contain 4 polypeptide chains, among them two are identical heavy chains and two identical light chains. These chains are held together by disulphide bonds, some are inter-chain and some are intra-chain. Each part of the molecule has different functions:
·
The fab fragment: Fab is for "fragment antigen binding"
this Fab part of the antibody that binds to antigens. Variable amino acid
sequences can be seen in this fragment.
·
The Fc fragment: Fc is for "fragment crystallizable".
The Fc fragment is where complement binds and also the anti-antibodies
(anti-IgG) will bind. The amino acid sequences present here are constant.
There
are five different isotypes of antibody depending on their difference in heavy
chain. These includes:
IgG, IgM, IgA, IgD and IgE.
Heavy chains of IgG, IgM, IgA, IgD, and IgE, are known as gamma, mu, alpha, delta, and epsilon, respectively.
IgG
This is the principle antibody found in blood and body fluids. Nearly 75% of the antibody circulating in the blood is IgG. IgG is a monomeric immunoglobulin, built of two heavy chains and two light chains. Each molecule has two antigen binding sites. This is the only isotype that can pass through the placenta, thereby providing protection to the fetus in its first weeks of life before its own immune system has developed.
IgA
IgA represents about 15% to 20% of immunoglobulins in the blood. IgA is involved in mucosal immunity and prevent the colonization of bacteria in the digestive and respiratory tracts. It does not activate complement.
IgM
The IgM isotype is expressed on the surface of B cells and it is also secreted by plasma cells. IgM present in the form of polymers where multiple immunoglobulins are covalently linked together with disulfide bonds, normally as a pentamer or occasionally as a hexamer. Each monomer has two antigen binding sites, so an pentameric IgM has 10 antigen binding sites, however it cannot bind 10 antigens at the same time because they hinder each other. It is also a "natural antibody" where it is found in the serum without any prior contact with antigen. Due to its polymeric nature, a single IgM-antigen complex can trigger the complement cascade, whereas multiple IgG-antigen complexes are required.
IgD
The function of IgD is not well known but it makes up about 1% of proteins in the plasma membranes of immature B-lymphocytes. It is also in serum in very small level. It is monomeric in nature. IgD's function is currently unknown but it may function as a regulatory antigen receptor.
IgE
IgE is a monomeric immunoglobulin which is heat labile and plays an important role in defending against parasitic worms. IgE is mainly responsible for allergies and this is through their ability to trigger the release of chemicals from the granulocytes when the antibody reacts with specific antigen. The IgE antibodies do not activate complement.
IgG, IgM, IgA, IgD and IgE.
Heavy chains of IgG, IgM, IgA, IgD, and IgE, are known as gamma, mu, alpha, delta, and epsilon, respectively.
IgG
This is the principle antibody found in blood and body fluids. Nearly 75% of the antibody circulating in the blood is IgG. IgG is a monomeric immunoglobulin, built of two heavy chains and two light chains. Each molecule has two antigen binding sites. This is the only isotype that can pass through the placenta, thereby providing protection to the fetus in its first weeks of life before its own immune system has developed.
IgA
IgA represents about 15% to 20% of immunoglobulins in the blood. IgA is involved in mucosal immunity and prevent the colonization of bacteria in the digestive and respiratory tracts. It does not activate complement.
IgM
The IgM isotype is expressed on the surface of B cells and it is also secreted by plasma cells. IgM present in the form of polymers where multiple immunoglobulins are covalently linked together with disulfide bonds, normally as a pentamer or occasionally as a hexamer. Each monomer has two antigen binding sites, so an pentameric IgM has 10 antigen binding sites, however it cannot bind 10 antigens at the same time because they hinder each other. It is also a "natural antibody" where it is found in the serum without any prior contact with antigen. Due to its polymeric nature, a single IgM-antigen complex can trigger the complement cascade, whereas multiple IgG-antigen complexes are required.
IgD
The function of IgD is not well known but it makes up about 1% of proteins in the plasma membranes of immature B-lymphocytes. It is also in serum in very small level. It is monomeric in nature. IgD's function is currently unknown but it may function as a regulatory antigen receptor.
IgE
IgE is a monomeric immunoglobulin which is heat labile and plays an important role in defending against parasitic worms. IgE is mainly responsible for allergies and this is through their ability to trigger the release of chemicals from the granulocytes when the antibody reacts with specific antigen. The IgE antibodies do not activate complement.
8.3.
Antibody functions
The antibodies have two primary functions:
The antibodies have two primary functions:
·
they bind to antigens
·
they combine with different immunoglobulin receptors specific for
them and exert effector functions.
Antigen
binding
Immunoglobulins bind specifically to the antigens. Antigen binding by antibodies is the primary function of antibodies and result in protection of the host. If an antibody binds to an antigen on the virus surface then the antibody hinders the virus from binding to the receptor so that the infection cannot be established. Thus, the antibodies neutralize the virus infectivity. Similarly in the case with microbial toxins where antibodies to toxins bind and prevent the induction of biological effects of toxins.
Effector functions
In addition to binding to specific antigen, the antibodies participate in a number of other biological activities known as effector functions. These functions are initiated once the antibody binds to an antigen. The effector functions are mediated by the heavy chain constant regions (Fc regions) of the antibody. Different antibody classes possess different heavy chain constant regions and hence are specialized to perform different effector functions. The various effector functions carried out by antibodies are described below.
Complement activation
Complement refers to a group of serum proteins where the product of one reaction catalyze a second reaction, the product form the second reaction catalyze a third reaction and so on. The complement activation pathway is triggered by antigen-antibody reactions. The Fc region of antibody is involved in the activation of the first component of complement. Then a series of reactions takes place and form a 'membrane attack complex' (MAC). This MAC is able to attack the membrane of the pathogen and cause the lysis of pathogen by forming a hole on membrane that releases the cell components.
Opsonization
Opsonization is a process where macrophages and neutrophiis are involved. These phagocytes carry Fc receptors on their surfaces and once the pathogen is coated with antibody molecules, it encances the opsonizing activity because of the Fc region of antibody, the phagocytes bind the antibodies through Fc receptors, which help them to phagocytose the target organism. Once the phathgen is engulfed it is killed inside the macrophage.
Antibody-dependent cell-mediated cytotoxicity (ADCC)
Natural Killer (NK) cells present in fish also possess Fc receptors. Antibodies after binding to the target cell (e.g., virus infected cell) activate the NK cells to kill the target cell by extracellular mechanism. This process is known as antibody-dependent cell-mediated cytotoxicity.
Transcytosis
Transcytosis is a process by which some antibodies can cross the epithelial layer to reach the mucosal surfaces of the respiratory, gastro–intestinal tract and can bind antigens. The process of transcytosis depends on the properties of constant region of antibody molecules. IgA is the major antibody that can undergo transcytosis.
IgE-mediated function
Mast cells and Basophils (which are rarely seen in fish) contain Fc receptors for IgE antibodies. When IgE binds with antigen the Fc region induces these cells to degranulate. These granular contents initiates an inflammatory response by attracting various molecular and cellular immune effectors which intern destroy the pathogen. This type of defence is effective particularly against parasitic infection.
Immunoglobulins bind specifically to the antigens. Antigen binding by antibodies is the primary function of antibodies and result in protection of the host. If an antibody binds to an antigen on the virus surface then the antibody hinders the virus from binding to the receptor so that the infection cannot be established. Thus, the antibodies neutralize the virus infectivity. Similarly in the case with microbial toxins where antibodies to toxins bind and prevent the induction of biological effects of toxins.
Effector functions
In addition to binding to specific antigen, the antibodies participate in a number of other biological activities known as effector functions. These functions are initiated once the antibody binds to an antigen. The effector functions are mediated by the heavy chain constant regions (Fc regions) of the antibody. Different antibody classes possess different heavy chain constant regions and hence are specialized to perform different effector functions. The various effector functions carried out by antibodies are described below.
Complement activation
Complement refers to a group of serum proteins where the product of one reaction catalyze a second reaction, the product form the second reaction catalyze a third reaction and so on. The complement activation pathway is triggered by antigen-antibody reactions. The Fc region of antibody is involved in the activation of the first component of complement. Then a series of reactions takes place and form a 'membrane attack complex' (MAC). This MAC is able to attack the membrane of the pathogen and cause the lysis of pathogen by forming a hole on membrane that releases the cell components.
Opsonization
Opsonization is a process where macrophages and neutrophiis are involved. These phagocytes carry Fc receptors on their surfaces and once the pathogen is coated with antibody molecules, it encances the opsonizing activity because of the Fc region of antibody, the phagocytes bind the antibodies through Fc receptors, which help them to phagocytose the target organism. Once the phathgen is engulfed it is killed inside the macrophage.
Antibody-dependent cell-mediated cytotoxicity (ADCC)
Natural Killer (NK) cells present in fish also possess Fc receptors. Antibodies after binding to the target cell (e.g., virus infected cell) activate the NK cells to kill the target cell by extracellular mechanism. This process is known as antibody-dependent cell-mediated cytotoxicity.
Transcytosis
Transcytosis is a process by which some antibodies can cross the epithelial layer to reach the mucosal surfaces of the respiratory, gastro–intestinal tract and can bind antigens. The process of transcytosis depends on the properties of constant region of antibody molecules. IgA is the major antibody that can undergo transcytosis.
IgE-mediated function
Mast cells and Basophils (which are rarely seen in fish) contain Fc receptors for IgE antibodies. When IgE binds with antigen the Fc region induces these cells to degranulate. These granular contents initiates an inflammatory response by attracting various molecular and cellular immune effectors which intern destroy the pathogen. This type of defence is effective particularly against parasitic infection.
8.4.Monoclonal
anitbody
Each B lymphocyte in an organism synthesizes only one kind of antibody and a huge population of different types of B cells can be seen in an organism capable of producing specific antibodies to the various antigens that the organism had been exposed to. Specific population of B cells would produce a specific type of antibody so that we can get a single kind of antibody. Monoclonal antibodies are single B lymphocyte generating antibodies to one specific epitope.
In 1975 Kohler and Milstein developed a technology to fuse immortal Myleoma cells with B cells, using poly ethylglycol (PEG). The resulting cell type is called a hybridoma. This hybridoma takes on the characteristics of both the B cell (that produce antibody) and Myeloma cell (which is immortal), creating an immortal cell with the ability to produce antibody. This hybridoma cells are selectively grown using HAT media. As the hybridoma cells grow they produce a specific antibody which is called a Monoclonal antibody.
Advantages
Each B lymphocyte in an organism synthesizes only one kind of antibody and a huge population of different types of B cells can be seen in an organism capable of producing specific antibodies to the various antigens that the organism had been exposed to. Specific population of B cells would produce a specific type of antibody so that we can get a single kind of antibody. Monoclonal antibodies are single B lymphocyte generating antibodies to one specific epitope.
In 1975 Kohler and Milstein developed a technology to fuse immortal Myleoma cells with B cells, using poly ethylglycol (PEG). The resulting cell type is called a hybridoma. This hybridoma takes on the characteristics of both the B cell (that produce antibody) and Myeloma cell (which is immortal), creating an immortal cell with the ability to produce antibody. This hybridoma cells are selectively grown using HAT media. As the hybridoma cells grow they produce a specific antibody which is called a Monoclonal antibody.
Advantages
·
Once hybridomas are made it is a constant and renewable source and
all batches will be identical
·
They are less likely to cross-react with other proteins
Disadvantage
·
High technology required.
·
Training is required for the technology used.
·
Time scale is long for hybridomas.
8.5.
Polyclonal antibody
Bacterial cell possess different epitopes, upon injection each epitope will stimulate the proliferation and differentiation of B-cell to produce antibody, each particular antibody derived from a B cell that recognizes a particular epitope. Hence large numbers of antibodies are produced with different specificities and epitope affinities, The resulting antibodies in the serum are heterogeneous in nature, each specific for one epitope.
Thus polyclonal antibodies are antibodies that are obtained from different B cell resources and are combination of immunoglobulin molecules secreted against a specific antigen, each identifying a different epitope.
So these antibodies are purified from the serum of immunised animals were the antigen of interest stimulates the B-lymphocytes to produce a diverse range of immunoglobulin's specific to that antigen.
Advantages
Bacterial cell possess different epitopes, upon injection each epitope will stimulate the proliferation and differentiation of B-cell to produce antibody, each particular antibody derived from a B cell that recognizes a particular epitope. Hence large numbers of antibodies are produced with different specificities and epitope affinities, The resulting antibodies in the serum are heterogeneous in nature, each specific for one epitope.
Thus polyclonal antibodies are antibodies that are obtained from different B cell resources and are combination of immunoglobulin molecules secreted against a specific antigen, each identifying a different epitope.
So these antibodies are purified from the serum of immunised animals were the antigen of interest stimulates the B-lymphocytes to produce a diverse range of immunoglobulin's specific to that antigen.
Advantages
·
Inexpensive to produce
·
Technology and skills required for production low
·
Production time scale is short
Disadvantages:
·
Prone to batch to batch variability.
·
Multiple epitopes may cross-reactivity and give false result.
................................................................................................................
Unit 9- Immune response
9.1.
Introduction
The reaction of an organism to a foreign substance is called immune response.
The reaction of an organism to a foreign substance is called immune response.
9.2. Primary immune response
When a new pathogen enters in to the body, specific immune system is activated and mounts an immune response against that pathogen, this immune response to the new antigens is known as primary response. Primary immune response results in a proliferation of B-cells that were stimulated by pathogens. If the antigen is given as vaccine then the the first injection of the antigen producing primary immune response is called priming dose.
The period between the invasion of pathogen and expression of immune response is known as "latent period" which can vary from several hours to days. This latent period depends on the factors like type of antigen, amount of antigen entered, rout of entry, health status of the individual etc. In this latent period the immune system prepares to activate and proliferate the lymphocytes which produce plasma cells and memory cells.
Plasma cells secrete antibodies and memory cells store memory of the pathogen. During primary response IgM type of antibodies are produced with a half life of 5 days. Secreted antibodies are different at different stages of latent period.
The amount of antibodies produced by the immune response to antigen is called antibody titre. The antibody titre plotted against time gives a sigmoid curve called immune response curve. The curve obtained for primary immune response is
called primary immune response curve.
In the initial phase of infection non specific immune response activates followed by specific immune response and that’s the reason in initial stage antibodies against the antigens are almost absent, and this period is known as “Lag phase”. Later the concentration of antibodies rises and this raising period is referred as “Log phase”. Once the antibody level attains maximum it remains constant for some period called as “plateau phase”. If the level of antibody remains constant for several days indicates that the antibodies are produced and replaced the antibodies that were lost. After plateau phase the level of antibodies starts to decrease called decline phase.
The antigen is necessary to stimulate immune response which intern produce antibodies from plasma cells. After the removal of antigens by the antibodies, B-cells are not stimulated which intern stops producing plasma cells. Some of the B-cells are stored as memory cells.
When a new pathogen enters in to the body, specific immune system is activated and mounts an immune response against that pathogen, this immune response to the new antigens is known as primary response. Primary immune response results in a proliferation of B-cells that were stimulated by pathogens. If the antigen is given as vaccine then the the first injection of the antigen producing primary immune response is called priming dose.
The period between the invasion of pathogen and expression of immune response is known as "latent period" which can vary from several hours to days. This latent period depends on the factors like type of antigen, amount of antigen entered, rout of entry, health status of the individual etc. In this latent period the immune system prepares to activate and proliferate the lymphocytes which produce plasma cells and memory cells.
Plasma cells secrete antibodies and memory cells store memory of the pathogen. During primary response IgM type of antibodies are produced with a half life of 5 days. Secreted antibodies are different at different stages of latent period.
The amount of antibodies produced by the immune response to antigen is called antibody titre. The antibody titre plotted against time gives a sigmoid curve called immune response curve. The curve obtained for primary immune response is
called primary immune response curve.
In the initial phase of infection non specific immune response activates followed by specific immune response and that’s the reason in initial stage antibodies against the antigens are almost absent, and this period is known as “Lag phase”. Later the concentration of antibodies rises and this raising period is referred as “Log phase”. Once the antibody level attains maximum it remains constant for some period called as “plateau phase”. If the level of antibody remains constant for several days indicates that the antibodies are produced and replaced the antibodies that were lost. After plateau phase the level of antibodies starts to decrease called decline phase.
The antigen is necessary to stimulate immune response which intern produce antibodies from plasma cells. After the removal of antigens by the antibodies, B-cells are not stimulated which intern stops producing plasma cells. Some of the B-cells are stored as memory cells.
9.3. Secondary immune response
During vaccine, the injection of the same antigen for the second time is called secondary dose or booster dose.
When the animal is invaded by the same pathogen that caused primary response, the immune system responds very quickly because of the presence of memory cells. Secondary immune response differ both qualitatively and quantitatively from primary response. In the case of secondary response the log phase is very short because of the presence of memory B cells specific for antigen induce the production of antibody with the level of antibody peaking up in a short time. The rise of antibody is around 100 to 1000 times higher than the primary response.
The antibodies formed in response to the secondary antibody is IgG type. IgG type of antibodies have a life span of around 3 weeks so the duration of plateau phase is much extended in the secondary response, and the antibodies decline very steadily even if the plasma cells does not produce antibody.
During vaccine, the injection of the same antigen for the second time is called secondary dose or booster dose.
When the animal is invaded by the same pathogen that caused primary response, the immune system responds very quickly because of the presence of memory cells. Secondary immune response differ both qualitatively and quantitatively from primary response. In the case of secondary response the log phase is very short because of the presence of memory B cells specific for antigen induce the production of antibody with the level of antibody peaking up in a short time. The rise of antibody is around 100 to 1000 times higher than the primary response.
The antibodies formed in response to the secondary antibody is IgG type. IgG type of antibodies have a life span of around 3 weeks so the duration of plateau phase is much extended in the secondary response, and the antibodies decline very steadily even if the plasma cells does not produce antibody.
................................................................................................................
Unit 10 - Immunological
Memory
10.1.
Introduction
The immune system to work successfully it must recognize a large number of microorganisms and molecules that it has never seen before, and it must decide how to respond to them. It should also differentiate between self and non self antigens such as viruses, bacteria, parasites and toxins. The body to defend itself against non self specific invading pathogen it has developed a resistance referred as immunity. Immunity have a memory for most invading pathogens invaded before, and for this invading pathogen they form memory cells that can last for decades. During the second invasion the immune system remembers pathogen it has seen before leading the rapid proliferation of memory cells and stimulates the release of antibodies. These antibodies are capable of eliminating the pathogens before disease occurs reffered as immunological memory. It is also proved that in vertebrates exposed to antigens in early life has resistance for the same antigen causing illness later. The concept of vaccination is based on immunological memory.
The immune system to work successfully it must recognize a large number of microorganisms and molecules that it has never seen before, and it must decide how to respond to them. It should also differentiate between self and non self antigens such as viruses, bacteria, parasites and toxins. The body to defend itself against non self specific invading pathogen it has developed a resistance referred as immunity. Immunity have a memory for most invading pathogens invaded before, and for this invading pathogen they form memory cells that can last for decades. During the second invasion the immune system remembers pathogen it has seen before leading the rapid proliferation of memory cells and stimulates the release of antibodies. These antibodies are capable of eliminating the pathogens before disease occurs reffered as immunological memory. It is also proved that in vertebrates exposed to antigens in early life has resistance for the same antigen causing illness later. The concept of vaccination is based on immunological memory.
10.2.
Recognition
The immune system uses a large number of highly specific B and T cells to
recognize antigen. The number of possible distinct antigens is to be in the range 1012 to 1016. B and T cell receptors are stimulated by antigen. Typically around105 B cells of an individual are stimulated by antigens. B-cells that are activated but not differentiate into plasma cells are transformed into memory B-cells. These memory cells can provide memory for longer period.
This was explained by theories like:-
The immune system uses a large number of highly specific B and T cells to
recognize antigen. The number of possible distinct antigens is to be in the range 1012 to 1016. B and T cell receptors are stimulated by antigen. Typically around105 B cells of an individual are stimulated by antigens. B-cells that are activated but not differentiate into plasma cells are transformed into memory B-cells. These memory cells can provide memory for longer period.
This was explained by theories like:-
·
Memory cells live for a long time
·
Memory cells are restimulated at some low level
·
Small amounts of the antigen are retained in lymph nodes
·
Related environmental antigens provide cross-stimulation
10.3. Response
B and T cells that are stimulated by antigen divide, during division B cell receptor sometimes mutates leading to increase in the affinity of its daughter cells for the antigen. This B cells change into plasma cells and secrete antibodies which eliminate the antigen. Once the antigen is cleared the B cells with increased affinity for the antigen are selected for keeping memory for an antigen.
B and T cells that are stimulated by antigen divide, during division B cell receptor sometimes mutates leading to increase in the affinity of its daughter cells for the antigen. This B cells change into plasma cells and secrete antibodies which eliminate the antigen. Once the antigen is cleared the B cells with increased affinity for the antigen are selected for keeping memory for an antigen.
................................................................................................................
Unit 11 - Immunologic tolerance
11.1.
Introduction
Our own bodies produce some 100,000 different proteins and these proteins are capable of eliciting an immune response, but our bodies can be tolerable to these proteins and this is Self-tolerance.
Definition: immunological tolerance occurs when an immunocompetent host fails to respond to an immunogenic challenge with a specific antigen.
Our own bodies produce some 100,000 different proteins and these proteins are capable of eliciting an immune response, but our bodies can be tolerable to these proteins and this is Self-tolerance.
Definition: immunological tolerance occurs when an immunocompetent host fails to respond to an immunogenic challenge with a specific antigen.
11.2. General features of Immunologic
tolerance
Tolerance is antigenic specific and results from the recognition of antigens by specific lymphocytes.
Normal individuals are tolerant of their own antigens (self antigen) -----Self-tolerance.
Foreign antigens may be administered in ways that can preferentially inhibit immune response by inducing tolerance in specific lymphocytes and it is called antigen induction.
Tolerance can be referred as specific immunological non-reactivity to an antigen resulting from a previous exposure to the same antigen. While the most important form of tolerance is non-reactivity to self antigens, it is possible to induce tolerance to non-self antigens. When an antigen induces tolerance, it is termed tolerogen.
Tolerance is antigenic specific and results from the recognition of antigens by specific lymphocytes.
Normal individuals are tolerant of their own antigens (self antigen) -----Self-tolerance.
Foreign antigens may be administered in ways that can preferentially inhibit immune response by inducing tolerance in specific lymphocytes and it is called antigen induction.
Tolerance can be referred as specific immunological non-reactivity to an antigen resulting from a previous exposure to the same antigen. While the most important form of tolerance is non-reactivity to self antigens, it is possible to induce tolerance to non-self antigens. When an antigen induces tolerance, it is termed tolerogen.
11.3. Tolerance to self antigens
Organisms do not mount a strong immune response against its own (self) antigens, a phenomenon called self-tolerance. When the immune system recognizes a self antigen and mounts a strong response against it, autoimmune disease develops. Nonetheless, the immune system has to recognize self-MHC to mount a response against a foreign antigen. Thus, the immune system is under pressure to discriminate between self and non-self antigen to mediate the right response.
Tolerance to tissue and cell antigens can be induced by injection of hemopoietic (stem) cells in new born or severely immunocompromised animals. Also, grafting of thymus from different animal in early induce tolerance in the animal to the cells and tissue of donor animal. Such animals are known as chimeras.
Organisms do not mount a strong immune response against its own (self) antigens, a phenomenon called self-tolerance. When the immune system recognizes a self antigen and mounts a strong response against it, autoimmune disease develops. Nonetheless, the immune system has to recognize self-MHC to mount a response against a foreign antigen. Thus, the immune system is under pressure to discriminate between self and non-self antigen to mediate the right response.
Tolerance to tissue and cell antigens can be induced by injection of hemopoietic (stem) cells in new born or severely immunocompromised animals. Also, grafting of thymus from different animal in early induce tolerance in the animal to the cells and tissue of donor animal. Such animals are known as chimeras.
11.4. Mechanism of tolerance induction
The exact mechanism of induction and maintenance of tolerance is not fully understood, but there are several mechanism to induce tolerance. They are:-
Clonal deletion
T and B lymphocytes during development come across self antigens and such cells undergo clonal deletion through a process known as apoptosis or programmed cell death. But sometimes these cells can escape and can trigger autoimmune disease.
Peripheral tolerance
The clonal deletion is not a fool proof system and often T and B cells fail to undergo deletion but enter the periphery, here the regulatory T cells recognize these cells and prevent these cells form exerting autoimmunity.
Activation-induced cell death
T cells upon activation not only produce cytokines or carryout their effector functions but also die through programmed cell death or apoptosis. In this process, the death receptor (Fas) and its ligand (FasL) play a crucial role. Thus, normal T cells express Fas but not FasL. Upon activation, T cells express FasL which binds to Fas and triggers apoptosis.
Clonal anergy
Auto-reactive T cells when exposed to antigenic peptides on antigen presenting cells (APC) that do not possess the co-stimulatory molecules become anergic (nonresponsive) to the antigen. B cells when exposed to large amounts of soluble antigen down-regulate their surface IgM and become anergic. These cells also up-regulate the Fas molecules on their surface. An interaction of these B cells with Fas-ligand bearing T cells results in their death via apoptosis.
Clonal ignorance
Sometimes T cells reactive to self-antigen mature and migrate to the periphery, but they may not come across the appropriate antigen because it may embedded in the tissue and inaccessible to T cells. These cells may die later. Likewise, the B cells capable of autoimmunity that escape deletion, may not find the antigen or the specific T-cell help and thus not be activated and die out.
Anti-idiotype antibody
These are antibodies that are produced against the specific idiotypes of other antibodies. Anti-idiotypic antibodies are produced during the process of tolerization and have been demonstrated in tolerant animals. These antibodies may prevent the B cell receptor from interacting with the antigen.
Regulatory T cells (Formerly called suppressor cells)
These regulatory T cells suppress the function of other T cells which are engaged in combating the pathogen. But the exact mechanism through which regulatory T cells suppress other T cell function is unclear.
The exact mechanism of induction and maintenance of tolerance is not fully understood, but there are several mechanism to induce tolerance. They are:-
Clonal deletion
T and B lymphocytes during development come across self antigens and such cells undergo clonal deletion through a process known as apoptosis or programmed cell death. But sometimes these cells can escape and can trigger autoimmune disease.
Peripheral tolerance
The clonal deletion is not a fool proof system and often T and B cells fail to undergo deletion but enter the periphery, here the regulatory T cells recognize these cells and prevent these cells form exerting autoimmunity.
Activation-induced cell death
T cells upon activation not only produce cytokines or carryout their effector functions but also die through programmed cell death or apoptosis. In this process, the death receptor (Fas) and its ligand (FasL) play a crucial role. Thus, normal T cells express Fas but not FasL. Upon activation, T cells express FasL which binds to Fas and triggers apoptosis.
Clonal anergy
Auto-reactive T cells when exposed to antigenic peptides on antigen presenting cells (APC) that do not possess the co-stimulatory molecules become anergic (nonresponsive) to the antigen. B cells when exposed to large amounts of soluble antigen down-regulate their surface IgM and become anergic. These cells also up-regulate the Fas molecules on their surface. An interaction of these B cells with Fas-ligand bearing T cells results in their death via apoptosis.
Clonal ignorance
Sometimes T cells reactive to self-antigen mature and migrate to the periphery, but they may not come across the appropriate antigen because it may embedded in the tissue and inaccessible to T cells. These cells may die later. Likewise, the B cells capable of autoimmunity that escape deletion, may not find the antigen or the specific T-cell help and thus not be activated and die out.
Anti-idiotype antibody
These are antibodies that are produced against the specific idiotypes of other antibodies. Anti-idiotypic antibodies are produced during the process of tolerization and have been demonstrated in tolerant animals. These antibodies may prevent the B cell receptor from interacting with the antigen.
Regulatory T cells (Formerly called suppressor cells)
These regulatory T cells suppress the function of other T cells which are engaged in combating the pathogen. But the exact mechanism through which regulatory T cells suppress other T cell function is unclear.
11.5.
Termination of tolerance
Termination of tolerance can be induced by
Termination of tolerance can be induced by
·
Prolonged absence of exposure to the tolerogen,
·
Severly damaging the immune system (x-irradiation)
·
Immunization with cross reactive antigens.
...............................................................................................................
Unit 12 - Stress and immune response
12.1.
Introduction
Stress is defined as physical or chemical factors that cause bodily reactions that may contribute to disease and death. Stress is a condition in which an animal is unable to maintain a normal physiologic state because of various factors adversely affecting its well-being. Stress is caused by placing a fish in a situation which is beyond its normal level of tolerance.
Stress is defined as physical or chemical factors that cause bodily reactions that may contribute to disease and death. Stress is a condition in which an animal is unable to maintain a normal physiologic state because of various factors adversely affecting its well-being. Stress is caused by placing a fish in a situation which is beyond its normal level of tolerance.
12.2.
Types of stressors
The different types of stressors are
Chemical stressors:
The different types of stressors are
Chemical stressors:
·
Poor Water Quality
·
Pollution
·
Nitrogenous and other metabolic wastes
·
Acidification
Biological
stressors:
·
Over crowding
·
Stress by other species of fish
·
Pathogenic Microorganisms
·
Parasites
Physical
stressors:
·
Temperature
·
Light
·
Sounds
·
Dissolved oxygen
·
Ammonia
Procedural
stressors:
·
Handling
·
Shipping
·
Disease Treatments
12.3.
Stress and immune system
Stress affects the immune system of fish as it affects in higher animals, the cause of stress is referred as stressor. The stress response in fish is controlled by HPI axis. This stands for Hypothalamus-Pituitary- inter-renal axis. That means that the brain, pituitary, and inter-renal tissue.
Stress stimulates a part of the brain called the hypothalamus. The hypothalamus releases a hormone called corticotrophin releasing factor, or CRF and this hormone stimulate the pituitary gland to release Adrenocorticotropic hormone, or ACTH. ACTH intern stimulates the inter-renal tissue to release Two important hormones.
Stress affects the immune system of fish as it affects in higher animals, the cause of stress is referred as stressor. The stress response in fish is controlled by HPI axis. This stands for Hypothalamus-Pituitary- inter-renal axis. That means that the brain, pituitary, and inter-renal tissue.
Stress stimulates a part of the brain called the hypothalamus. The hypothalamus releases a hormone called corticotrophin releasing factor, or CRF and this hormone stimulate the pituitary gland to release Adrenocorticotropic hormone, or ACTH. ACTH intern stimulates the inter-renal tissue to release Two important hormones.
·
Epinephrine
·
Cortisol
Epinephrine
Epinephrine, is responsible for what is called the "fight or flight" reaction. This hormone produces a number of physiological changes that prepare the animal to stand and face the problem or fly away from the area.
When Epinephrine is release numerous reactions occur, such as
Epinephrine, is responsible for what is called the "fight or flight" reaction. This hormone produces a number of physiological changes that prepare the animal to stand and face the problem or fly away from the area.
When Epinephrine is release numerous reactions occur, such as
·
Increase in heart rate, that result in increased blood pressure
and respiration.
·
Increase of glucose content in blood to provide a quick energy
source.
·
Increase of blood flow to the brain
Cortisol
Cortisol is the other hormone released by the inter-renal tissue in response to stress. This hormone prepare the animal to overcome stress. The level of cortisol increase rapidly when fish are crowded together or handled badly. Cortisol can directly interfere with the normal functioning of the immune system, specifically it interfere with the phagocytosis. If cortisol stays for a long time in body it can exhaust the body and cortisol itself become stressors and this exhaustion in the animal leads to the diseases associated with stress,
Physiological changes produced by the cortisol are
Cortisol is the other hormone released by the inter-renal tissue in response to stress. This hormone prepare the animal to overcome stress. The level of cortisol increase rapidly when fish are crowded together or handled badly. Cortisol can directly interfere with the normal functioning of the immune system, specifically it interfere with the phagocytosis. If cortisol stays for a long time in body it can exhaust the body and cortisol itself become stressors and this exhaustion in the animal leads to the diseases associated with stress,
Physiological changes produced by the cortisol are
·
Protein breakdown
·
Elevated thyroid hormones
·
Biochemical exhaustion
In
fish, physiological stress and physical injury are the major factors that cause
disease and mortality. In aquaculture fish are confined to the production unit
and are weakened by stressors like:
·
Increased fish density
·
Poor water quality
·
Injury during handling
·
Inadequate nutrition
·
Accumulation of metabolic waste.
These conditions can result in the spread of disease and parasite infestation
Stress and injury initially trigger an alarm reaction (fight or flight response), which results in a series of changes within the fish. A blood sugar increase occurs in response to hormone secretion from the adrenal gland as liver glycogen is metabolized. This produces a burst of energy which prepares the animal for an emergency situation.
In addition, the inflammatory response, a defense used by fish against invading disease organisms, is suppressed by hormones released from the adrenal gland. Water balance in the fish (osmoregulation) is disrupted due to changes in the metabolism of minerals. Under these circumstances, freshwater fish absorb excessive amounts of water from the
environment (over-hydrate); saltwater fish lose water to the environment (dehydrate), This disruption increases energy requirements for osmoregulation. Respiration increases, blood pressure increases, and reserve red blood cells are released into the blood stream.
Fish are able to adapt to stress for a period of time; they may look and act normal. However, energy reserves are eventually depleted and hormone imbalance occurs, suppressing their immune system and increasing their susceptibility to infectious diseases.
12.4. Effect of stress on protective barriers
Mucus
Stress in fish causes chemical changes in mucus leads to decrease in its effectiveness against invading pathogens. It also upsets the normal electrolyte balance in fish so in freshwater fish the water is absorbed into the body where as in marine fish the water is dehydrated. In addition Handling stress and chemicals used in disease treatment in fish disrupts the physical barrier which makes easy for the pathogens to invade the fish and cause the disease. Stress also cost the fish its energy and also compromise in osmoregulatory function.
Scales and Skin
Handling stress is the most common stress that causes most damage in the scales and skin of the fish. Cut in skin or remove of scale creates an opening for invasion by pathogenic organisms. The infestations with parasites cause damage to gills, skin, fins, and loss of scales which favors bacteria to enter into fish and cause disease in fish.
Immunity
Stress also play its role in immune system among physical stress temperature in particular has a major impact on the immunity. Cold temperature can severely decrease the activity of killer cells which intern affect the immune system. quick decrease in temperature leads to decrease in antibody release in the fish.
Prevention of Stress
To prevent the stress in aquaculture system main emphasis should be given to the water quality, followed by good nutrition and sanitation.
Mucus
Stress in fish causes chemical changes in mucus leads to decrease in its effectiveness against invading pathogens. It also upsets the normal electrolyte balance in fish so in freshwater fish the water is absorbed into the body where as in marine fish the water is dehydrated. In addition Handling stress and chemicals used in disease treatment in fish disrupts the physical barrier which makes easy for the pathogens to invade the fish and cause the disease. Stress also cost the fish its energy and also compromise in osmoregulatory function.
Scales and Skin
Handling stress is the most common stress that causes most damage in the scales and skin of the fish. Cut in skin or remove of scale creates an opening for invasion by pathogenic organisms. The infestations with parasites cause damage to gills, skin, fins, and loss of scales which favors bacteria to enter into fish and cause disease in fish.
Immunity
Stress also play its role in immune system among physical stress temperature in particular has a major impact on the immunity. Cold temperature can severely decrease the activity of killer cells which intern affect the immune system. quick decrease in temperature leads to decrease in antibody release in the fish.
Prevention of Stress
To prevent the stress in aquaculture system main emphasis should be given to the water quality, followed by good nutrition and sanitation.
...............................................................................................................
Unit 13 - Defence mechanisms in crustaceans
13.1.
Defence mechanisms in crustaceans
Aquatic animals are surrounded by microorganisms in aquatic environment that are capable of initiating infection in these animals. Unlike fish that possess both innate and adaptive immunity, the lower aquatic animals such as shrimps that are invertebrates lack true adaptive immune system and they depend upon their innate immune system for the defense mechanism against the invading pathogen. In normal conditions, crustaceans maintain a healthy state by mounting a defense reaction against potential pathogens. Among them, the external cuticle is a first line of defense to provide an effective physical and chemical barrier against the attachment and penetration of pathogens. The digestive tract, which is a main route of invasion of the pathogen, is partly lined with chitin layers and its hostile environment of acids and enzymes is able to inactivate and digest many bacteria and viruses.
Crustacean hemocytes (blood cells) play a central role in their immune reactions and are capable of phagocytosis, encapsulation, nodule formation and mediation of cytotoxicity. When the host defence encounters a pathogen, a series of pathways get activated to protect crustacean against infection by a variety of microorganism. The entry of a pathogen into the hemocoel of the host triggers a complex system of innate defense mechanisms involving cellular and humoral immune components.
Cellular immune components are :-
Aquatic animals are surrounded by microorganisms in aquatic environment that are capable of initiating infection in these animals. Unlike fish that possess both innate and adaptive immunity, the lower aquatic animals such as shrimps that are invertebrates lack true adaptive immune system and they depend upon their innate immune system for the defense mechanism against the invading pathogen. In normal conditions, crustaceans maintain a healthy state by mounting a defense reaction against potential pathogens. Among them, the external cuticle is a first line of defense to provide an effective physical and chemical barrier against the attachment and penetration of pathogens. The digestive tract, which is a main route of invasion of the pathogen, is partly lined with chitin layers and its hostile environment of acids and enzymes is able to inactivate and digest many bacteria and viruses.
Crustacean hemocytes (blood cells) play a central role in their immune reactions and are capable of phagocytosis, encapsulation, nodule formation and mediation of cytotoxicity. When the host defence encounters a pathogen, a series of pathways get activated to protect crustacean against infection by a variety of microorganism. The entry of a pathogen into the hemocoel of the host triggers a complex system of innate defense mechanisms involving cellular and humoral immune components.
Cellular immune components are :-
·
Hemocytes
·
Phagocytosis
·
Encapsulation
·
Clotting reaction
·
Prophenoloxidase (proPO) system
Humoral
immune components include:-
·
Lysozymes,
·
Anti-microbial peptides and
·
Lectins
13.2.
Cellular immune components
Hemocytes
Hemocytes present in the circulating hemolymph play a crucial role in invertebrate immunity providing protection against invading microorganisms. Three types of circulating hemocytes can be found in the crustaceans, they are hyaline (H) cells, semigranular (SG) cells and granular (G) cells.
Hyaline (H) cells
Hyaline cells are small, spherical and are least in numbers among all hemocytes. The number of hyaline cell population varies between different crustacean species. Hyaline cells are capable of phagocytosis and destruction of invading pathogens.
Semigranular cells
These semigranular cells have variable number of small eosinophilic granules that are mainly responsible for encapsulation and also contain the prophenoloxidase activating systems (proPO).
When pathogens or any foreign particles invade into the body these semigranular cells activate and degranulate. After degranulation these cells attach and spread on the foreign particles.
Granular cells
These cells are filled with large number of granules in their cytoplasm. These cell do not participate in phagocytosis but involved in cytotoxicity activity, nodule formation, proPO system and sometimes involved in encapsulation process.
Phagocytosis
The process trapping, ingestion, destruction and elimination of pathogen or foreign body from host tissue by the phagocytic cells are called "Phagocytosis". The mechanism of intracellular destruction of microorganisms through phagocytosis in shellfish is similar to other animals.
Phagocytes are of two types
Hemocytes
Hemocytes present in the circulating hemolymph play a crucial role in invertebrate immunity providing protection against invading microorganisms. Three types of circulating hemocytes can be found in the crustaceans, they are hyaline (H) cells, semigranular (SG) cells and granular (G) cells.
Hyaline (H) cells
Hyaline cells are small, spherical and are least in numbers among all hemocytes. The number of hyaline cell population varies between different crustacean species. Hyaline cells are capable of phagocytosis and destruction of invading pathogens.
Semigranular cells
These semigranular cells have variable number of small eosinophilic granules that are mainly responsible for encapsulation and also contain the prophenoloxidase activating systems (proPO).
When pathogens or any foreign particles invade into the body these semigranular cells activate and degranulate. After degranulation these cells attach and spread on the foreign particles.
Granular cells
These cells are filled with large number of granules in their cytoplasm. These cell do not participate in phagocytosis but involved in cytotoxicity activity, nodule formation, proPO system and sometimes involved in encapsulation process.
Phagocytosis
The process trapping, ingestion, destruction and elimination of pathogen or foreign body from host tissue by the phagocytic cells are called "Phagocytosis". The mechanism of intracellular destruction of microorganisms through phagocytosis in shellfish is similar to other animals.
Phagocytes are of two types
·
Fixed phagocytes
·
Mobile or circulating phagocytes
Fixed
phagocytes
These fixed phagocytes are fixed in certain places in the tissue of the organs. These fixed phagocytes can be observed in the lacunae of gills, pericardial sinuses and base of appendages.
Mobile or circulating phagocytes
These phagocytes can be seen in haemolymph with continuous circulation. These phagocytes localize in the site of infection and destroy the pathogen by the process of phagocytosis.
These fixed phagocytes are fixed in certain places in the tissue of the organs. These fixed phagocytes can be observed in the lacunae of gills, pericardial sinuses and base of appendages.
Mobile or circulating phagocytes
These phagocytes can be seen in haemolymph with continuous circulation. These phagocytes localize in the site of infection and destroy the pathogen by the process of phagocytosis.
13.3.
Cellular immune components
Encapsulation
When the pathogen like parasites which are too big to engulf by phagocytes invade the crustaceans, the haemocytes present in haemolymph collaborate and deposit on the surface of the parasite and block off the parasite from circulation. Normally the cells involved in the encapsulation is semigranular cells.
Cytotoxicity
Haemocytes are capable of destroying tumor and non-tumor cells present in the host by secreting cytotoxic molecules. Cells that are mainly responsible for cytotoxicity is Granular and semigranular cells which are similar to mammalian natural killer cells (NK cells). Once these cytotoxic cells recognize the foreign particle or tissue, they attach to the foreign particle or tissue and release the cytotoxic chemicals, that kills the target.
Clotting reaction
Clotting reaction is the mechanism of formation of extracellular and intravascular clots for rapid sealing of wounds. Clotting prevents the loss of haemolymph and invading pathogens. Intravascular clots produce stasis by adhering to the walls of blood vessels and extracellular clots
Inhibit movement of pathogens and make them vulnerable to phagocytosis.
Two different coagulation mechanisms
Encapsulation
When the pathogen like parasites which are too big to engulf by phagocytes invade the crustaceans, the haemocytes present in haemolymph collaborate and deposit on the surface of the parasite and block off the parasite from circulation. Normally the cells involved in the encapsulation is semigranular cells.
Cytotoxicity
Haemocytes are capable of destroying tumor and non-tumor cells present in the host by secreting cytotoxic molecules. Cells that are mainly responsible for cytotoxicity is Granular and semigranular cells which are similar to mammalian natural killer cells (NK cells). Once these cytotoxic cells recognize the foreign particle or tissue, they attach to the foreign particle or tissue and release the cytotoxic chemicals, that kills the target.
Clotting reaction
Clotting reaction is the mechanism of formation of extracellular and intravascular clots for rapid sealing of wounds. Clotting prevents the loss of haemolymph and invading pathogens. Intravascular clots produce stasis by adhering to the walls of blood vessels and extracellular clots
Inhibit movement of pathogens and make them vulnerable to phagocytosis.
Two different coagulation mechanisms
·
Haemocyte derived clotting cascade
·
Transglutaminase dependant clotting reaction
Haemocyte
derived clotting cascade
Haemocyte derived clotting cascade can be seen in horseshoe crab. This mechanism is activated by lipopolysaccharide (LPS) of bacteria leading to the cascade of reaction where the activated clotting enzyme catalyzes the change of a soluble protein (coagulogen) into an insoluble clot (coagulin). That seals the wound and entraps parasites or pathogens that are trying to invade the host.
Transglutaminase dependant clotting reaction
Transglutaminase dependant clotting reaction can be seen in crustaceans like shrimp, lobster, crab, cray fish etc. Here clottable protein (CP) play a major role. TGase is an enzyme released from the haemocyte during the invasion of pathogen or injury. TGase after release activates by calcium ions (Ca2+) then catalyze the linking of CP into large insoluble aggregates. These insoluble aggregates are responsible for clotting process.
Prophenoloxidase (proPO) system
The prophenoloxidase (proPO) system is an efficient innate immune response against foreign materials in the haemolymph of invertebrates. This system is involved in proPO mediated melanization process, in response to infection, invasion or wound healing.
It is initiated by the recognition of lipopolysaccharides and peptidoglycans from bacterial cell wall and β-1, 3 glucans from fungal cell wall, even when they are in minute amounts. This suggests that the system will be activated in the presence of pathogens. proPO system contains pattern-recognition proteins (PRPs), several zymogenic proteinases and prophenoloxidase (proPO) enzyme.
proPO is synthesized in the hemocytes and are localized in the granules of the hemocytes. When β-1, 3 binding protein (β-1, 3 BP) binds to β-1, 3 glucans, it becomes activated and binds specifically to a cell surface associated protein, a superoxide dismutase (SOD). The recognition of non-self materials triggers degranulation of semigranular and granular cells. Prophenoloxidase activating enzymes (proppA) is released during the process which is further activated to ppA by the pathogen associated molecular patterns (PAMPs). Active ppA converts the proPO to phenoloxidase. PO is a bifunctional copper containing enzyme, which is known as a tyrosinase and catalyzes the early steps in the pathway to melanin formation. Melanin is a pigment which is black in color and helps the host to neutralize the pathogen.
Haemocyte derived clotting cascade can be seen in horseshoe crab. This mechanism is activated by lipopolysaccharide (LPS) of bacteria leading to the cascade of reaction where the activated clotting enzyme catalyzes the change of a soluble protein (coagulogen) into an insoluble clot (coagulin). That seals the wound and entraps parasites or pathogens that are trying to invade the host.
Transglutaminase dependant clotting reaction
Transglutaminase dependant clotting reaction can be seen in crustaceans like shrimp, lobster, crab, cray fish etc. Here clottable protein (CP) play a major role. TGase is an enzyme released from the haemocyte during the invasion of pathogen or injury. TGase after release activates by calcium ions (Ca2+) then catalyze the linking of CP into large insoluble aggregates. These insoluble aggregates are responsible for clotting process.
Prophenoloxidase (proPO) system
The prophenoloxidase (proPO) system is an efficient innate immune response against foreign materials in the haemolymph of invertebrates. This system is involved in proPO mediated melanization process, in response to infection, invasion or wound healing.
It is initiated by the recognition of lipopolysaccharides and peptidoglycans from bacterial cell wall and β-1, 3 glucans from fungal cell wall, even when they are in minute amounts. This suggests that the system will be activated in the presence of pathogens. proPO system contains pattern-recognition proteins (PRPs), several zymogenic proteinases and prophenoloxidase (proPO) enzyme.
proPO is synthesized in the hemocytes and are localized in the granules of the hemocytes. When β-1, 3 binding protein (β-1, 3 BP) binds to β-1, 3 glucans, it becomes activated and binds specifically to a cell surface associated protein, a superoxide dismutase (SOD). The recognition of non-self materials triggers degranulation of semigranular and granular cells. Prophenoloxidase activating enzymes (proppA) is released during the process which is further activated to ppA by the pathogen associated molecular patterns (PAMPs). Active ppA converts the proPO to phenoloxidase. PO is a bifunctional copper containing enzyme, which is known as a tyrosinase and catalyzes the early steps in the pathway to melanin formation. Melanin is a pigment which is black in color and helps the host to neutralize the pathogen.
13.4. Humoral defence mechanism
The humoral defence mechanism is a defence mechanism in which the direct cellular involvement is absent. Instead the cellular products like Lysozymes, Anti-microbial peptides and Lectins can be seen involved.
Lectins
Lectins protect the animals against infection. Lectin, or agglutinin, is a carbohydrate binding protein that can bind to the carbohydrate on the cell wall of pathogens or foreign bodies, causing the reaction known as agglutination. Lectins are produced in hemocytes and some of them are transported on the membrane surface and here they participate in recognition of foreign molecules or participate in carbohydrate transportation. Lectins can induce agglutination that can lead to phagocytosis and lectins can also act as opsonins. Lectins are present in almost all crustaceans.
Antimicrobial peptides (AMPs)
The antimicrobial compound is a part of humoral defense system in crustaceans that plays an important role in innate immunity. Antimicrobial peptides (AMPs) which are 150-200 amino acids long are produced by different types of cells. A family of AMPs called penaeidins displaying both antifungal and antibacterial activities is present in hemolymph of the shrimp. Anti-lipopolysaccharide factors (ALFs) have been recently identified from hemocytes of P. monodon, and this ALF has a broad spectrum of antifungal properties and antibacterial activities against both Gram-positive and Gram-negative bacteria. Another antimicrobial peptide named crustin a peptide present in Carcinus maenas of 11.5 kDa size has an antibacterial activity against Gram-positive bacteria.
Lysozymes
The haemocytes and haemolymph contain lysozymes that can act against the pathogen. Once the antigen or pathogen enters the body cavity, it will stimulate the haemocytes to synthesis the higher quantities of lysozyme followed by release of these enzymes into the haemolymph where these enzyme will act on pathogen or susceptible material and destroy them.
The humoral defence mechanism is a defence mechanism in which the direct cellular involvement is absent. Instead the cellular products like Lysozymes, Anti-microbial peptides and Lectins can be seen involved.
Lectins
Lectins protect the animals against infection. Lectin, or agglutinin, is a carbohydrate binding protein that can bind to the carbohydrate on the cell wall of pathogens or foreign bodies, causing the reaction known as agglutination. Lectins are produced in hemocytes and some of them are transported on the membrane surface and here they participate in recognition of foreign molecules or participate in carbohydrate transportation. Lectins can induce agglutination that can lead to phagocytosis and lectins can also act as opsonins. Lectins are present in almost all crustaceans.
Antimicrobial peptides (AMPs)
The antimicrobial compound is a part of humoral defense system in crustaceans that plays an important role in innate immunity. Antimicrobial peptides (AMPs) which are 150-200 amino acids long are produced by different types of cells. A family of AMPs called penaeidins displaying both antifungal and antibacterial activities is present in hemolymph of the shrimp. Anti-lipopolysaccharide factors (ALFs) have been recently identified from hemocytes of P. monodon, and this ALF has a broad spectrum of antifungal properties and antibacterial activities against both Gram-positive and Gram-negative bacteria. Another antimicrobial peptide named crustin a peptide present in Carcinus maenas of 11.5 kDa size has an antibacterial activity against Gram-positive bacteria.
Lysozymes
The haemocytes and haemolymph contain lysozymes that can act against the pathogen. Once the antigen or pathogen enters the body cavity, it will stimulate the haemocytes to synthesis the higher quantities of lysozyme followed by release of these enzymes into the haemolymph where these enzyme will act on pathogen or susceptible material and destroy them.
................................................................................................................
Unit 14 - Vaccine
14.1.
Introduction
Prevention of disease through vaccination is an important approach to maintain fish health. Exposure of a fish to a pathogen stimulates the immune response and the fish will develop the memory to these pathogens so that it can combat the pathogen very quickly during future encounter. This adaptive immunity is specific against the pathogen and persists for a relatively long period. This persistence is because of an adaptive change in the population of lymphocyte which results from the exposure of the fish to the pathogen that consist the antigen.
Vaccines exploit the two key elements of adaptive immunity and those are specificity and memory. This is because after vaccination the adaptive immune system responds specifically to the invading pathogen and the response become stronger and stronger on the second and subsequent exposure to the pathogen.
Vaccines are preparations of antigens derived from pathogenic organisms, rendered non-pathogenic by various means, which will stimulate the immune system in such a way as to increase the resistance to disease from subsequent infection by a pathogen.
Inducing a protective immune response to a pathogenic organism before the individual becomes naturally exposed to it seems at first sight an highly sensible way of preventing an infectious disease. Unfortunately, achieving this goal not an easy task. vaccines must be safe (no side effects) and potent (induce a high level of protection) and although occasionally it has been possible to achieve these characteristics using simple procedures (usually heat or chemical inactivation of cultures of pathogenic microorganisms) in most cases some degree of antigen purification or enrichment is necessary and the problem lies in identifying the relevant antigens, out of many hundreds present, which are important in stimulating a protective immune response.
Vaccines are generally of two types: Dead vaccines, which are composed of inactivated pathogens or extracts, and Live vaccines, which are attenuated pathogens with no or low virulence."
Prevention of disease through vaccination is an important approach to maintain fish health. Exposure of a fish to a pathogen stimulates the immune response and the fish will develop the memory to these pathogens so that it can combat the pathogen very quickly during future encounter. This adaptive immunity is specific against the pathogen and persists for a relatively long period. This persistence is because of an adaptive change in the population of lymphocyte which results from the exposure of the fish to the pathogen that consist the antigen.
Vaccines exploit the two key elements of adaptive immunity and those are specificity and memory. This is because after vaccination the adaptive immune system responds specifically to the invading pathogen and the response become stronger and stronger on the second and subsequent exposure to the pathogen.
Vaccines are preparations of antigens derived from pathogenic organisms, rendered non-pathogenic by various means, which will stimulate the immune system in such a way as to increase the resistance to disease from subsequent infection by a pathogen.
Inducing a protective immune response to a pathogenic organism before the individual becomes naturally exposed to it seems at first sight an highly sensible way of preventing an infectious disease. Unfortunately, achieving this goal not an easy task. vaccines must be safe (no side effects) and potent (induce a high level of protection) and although occasionally it has been possible to achieve these characteristics using simple procedures (usually heat or chemical inactivation of cultures of pathogenic microorganisms) in most cases some degree of antigen purification or enrichment is necessary and the problem lies in identifying the relevant antigens, out of many hundreds present, which are important in stimulating a protective immune response.
Vaccines are generally of two types: Dead vaccines, which are composed of inactivated pathogens or extracts, and Live vaccines, which are attenuated pathogens with no or low virulence."
Dead vaccines
·
Inactivated virus or bacterial antigens
·
Sub-unit vaccines
·
Recombinant vaccines
Live
vaccines
·
Attenuated live vaccine
·
Gene deleted live vaccine
The
Ideal Fish Vaccine should have
·
Sustained immunity and protection
·
Early mass application
·
Efficacious for a broad number of species
·
Safe to use
·
Cheaply available
·
Easily produced
·
Should have stable antigen
·
Can be stored for long time.
·
Will not interfere with diagnosis
·
Easily licensed
Types
of vaccine
14.2. Killed whole cell vaccines
Killed whole cell vaccine is a suspension of heat or chemical-killed pathogens that are able to induce specific protective immune response against those pathogens when administered into the host. Killed whole cell vaccine are administrated when it is unsafe to use live microorganisms. These vaccines are prepared from normal wild type bacteria that are made nonpathogenic usually by treating with heat, formaldehyde or gamma irradiation.
Killed whole cell vaccine can be used in controlling some of the important fish bacterial pathogens like V. anguiliarum, V. salmonicida, V. ordalli, Y. ruckeri, E. tarda and A. sarmonicida.
Among carp virus killed vaccine of spring viremia of carp virus (SVCV) was commercially available for some years.
14.2. Killed whole cell vaccines
Killed whole cell vaccine is a suspension of heat or chemical-killed pathogens that are able to induce specific protective immune response against those pathogens when administered into the host. Killed whole cell vaccine are administrated when it is unsafe to use live microorganisms. These vaccines are prepared from normal wild type bacteria that are made nonpathogenic usually by treating with heat, formaldehyde or gamma irradiation.
Killed whole cell vaccine can be used in controlling some of the important fish bacterial pathogens like V. anguiliarum, V. salmonicida, V. ordalli, Y. ruckeri, E. tarda and A. sarmonicida.
Among carp virus killed vaccine of spring viremia of carp virus (SVCV) was commercially available for some years.
Advantages:
·
Safe to use
·
Cheaper than live attenuated vaccine
·
Storage is easier than live vaccine
Disadvantages:
·
Large number of microorganisms is required to stimulate immunity.
·
High cost of their production in cell culture,
·
Difficulty in the purification and delivery.
·
In general killed vaccines alone trigger only the humoral immune
response
·
Needs to be given booster doses
·
Presence of some un-inactivated microbes can lead to
vaccine-associated disease.
·
Inactivation, by formaldehyde may alter antigenicity.
14.3.
Live-attenuated vaccines
Live-attenuated vaccine is a suspension of attenuated live pathogens that are able to replicate inside the host and induce protective immune response but unable to cause disease. To make an attenuated vaccine, the pathogen is grown in foreign host such as animals, embryonated eggs or in tissue culture under controled conditions and altered to a non-pathogenic form to make it less virulent. They mimic the actual infection by pathogens and hence a small dose of vaccine is enough to induce long lasting protective immune response. Live attenuated vaccines can induce both humoral and cell-mediated immune responses.
Live-attenuated vaccine is a suspension of attenuated live pathogens that are able to replicate inside the host and induce protective immune response but unable to cause disease. To make an attenuated vaccine, the pathogen is grown in foreign host such as animals, embryonated eggs or in tissue culture under controled conditions and altered to a non-pathogenic form to make it less virulent. They mimic the actual infection by pathogens and hence a small dose of vaccine is enough to induce long lasting protective immune response. Live attenuated vaccines can induce both humoral and cell-mediated immune responses.
Advantages
·
Live-attenuated vaccine can stimulate cellular immune responses,
memory cells as well as humoral immune responses.
·
Administrating lesser quantities is sufficient to induce
protection.
·
Single administrating of vaccine is sufficient to produce high
efficacy and long lived immunity.
·
Administration of live attenuated vaccine has a possibility to
stimulate immune response to all protective antigens.
Disadvantages
·
Live-attenuated vaccine may rarely revert to its virulence form
and cause disease.
·
Live-attenuated vaccine cannot be given to immunosuppressed
individuals.
·
Since they are live they require proper storage.
14.4.Subunit Vaccines
Subunit vaccines are the purified antigens of
the whole organisms. These antigens are capable of stimulating antibody response.
Subunit vaccines may contain toxoids, subcellular fragments, or surface
antigens. The effect of subunit vaccine can be increased by administrating
these subunits with adjuvants.
Advantages
·
They can be safely administrated to the immunosuppressed animal.
·
The side effects caused by sub unit vaccines are very rare.
Disadvantages
·
Since the vaccines are purified the purification process may
affect antigen in retaining its native form, so the organism may not recognize
the antigen on pathogen.
·
These proteins may not stimulate the immune response.
14.5.
DNA vaccine
This vaccine is still in experimental form. Here the gene of the pathogen is clone into vector and the vector is inserted into the animal by using gene gun. Once the vector is introduced the protein that act as antigen is produced inside the host and stimulate the immune response. DNA vaccine can induce both humoral and cellular immunity.
Advantages
This vaccine is still in experimental form. Here the gene of the pathogen is clone into vector and the vector is inserted into the animal by using gene gun. Once the vector is introduced the protein that act as antigen is produced inside the host and stimulate the immune response. DNA vaccine can induce both humoral and cellular immunity.
Advantages
·
DNA is stable, hence can be easily stored and transported.
·
DNA sequence can be changed easily in the laboratory.
·
DNA does not replicate and encodes only the proteins of interest
Disadvantages:
·
Insertional mutation may be possible
·
Anti DNA antibodies may be produced against the inserted vector
·
Since the antigen is expressed in the host immunologic tolerance
may develop.
·
Ethical issues.
14.6.Vaccination
Methods
Vaccines may be delivered to fish by
Vaccines may be delivered to fish by
·
Intraperitoneal or intramuscular injection method
·
Oral vaccine method
·
Direct immersion method
Vaccination
is done to the healthy fish because it is a preventive measure and not a cure.
14.7.
Oral Vaccination
During the oral vaccination, the vaccine is given orally and it may be either through feed, where it is either mixed along with feed or coated on top of the feed or bio-encapsulated. During oral vaccination proper care must be taken to ensure that the antigen is successfully absorbed into the body. It is because the antigens incorporated in feed may be the heat sensitivity or the digestive system may digest the antigen. So when the vaccine is coated on the feed usually a coating agent is applied to prevent leaching of vaccine or to prevent the digestion of an antigen in the acidic environment of the fish stomach. Bio encapsulations are used usually when the fish fry are to be vaccinated, Bio encapsulation include the live feed such as Artemia nauplii, copepods or rotifers which are fed after incubation in a vaccine suspension. During incubation they accumulate the antigen in their digestive tract and as such, transform themselves into living microcapsules.
Advantages
During the oral vaccination, the vaccine is given orally and it may be either through feed, where it is either mixed along with feed or coated on top of the feed or bio-encapsulated. During oral vaccination proper care must be taken to ensure that the antigen is successfully absorbed into the body. It is because the antigens incorporated in feed may be the heat sensitivity or the digestive system may digest the antigen. So when the vaccine is coated on the feed usually a coating agent is applied to prevent leaching of vaccine or to prevent the digestion of an antigen in the acidic environment of the fish stomach. Bio encapsulations are used usually when the fish fry are to be vaccinated, Bio encapsulation include the live feed such as Artemia nauplii, copepods or rotifers which are fed after incubation in a vaccine suspension. During incubation they accumulate the antigen in their digestive tract and as such, transform themselves into living microcapsules.
Advantages
·
Vaccine mixed with feed
·
Easiest method for mass vaccination of all sizes of fish
·
Saves labour
·
Avoids stress to fish
Disadvantages
·
Large quantities of vaccines are required
·
Some fish may not consume the feed.
·
Protection generally weak and of short duration
14.8.
Immersion vaccination
Fish being aquatic in nature it is constantly surrounded by the microorganisms of which some may be pathogenic ones. These fish have a mechanism to recognize these pathogens and elicit an immune response. So when the fish comes in contact with vaccine during immersion these vaccine is absorbed by the skin and gills, the specialized cells such as antibody-secreting cells are activated and will protect the fish during the later stage of exposure to the pathogen.
Immersion vaccine can be applied in two ways:-
Fish being aquatic in nature it is constantly surrounded by the microorganisms of which some may be pathogenic ones. These fish have a mechanism to recognize these pathogens and elicit an immune response. So when the fish comes in contact with vaccine during immersion these vaccine is absorbed by the skin and gills, the specialized cells such as antibody-secreting cells are activated and will protect the fish during the later stage of exposure to the pathogen.
Immersion vaccine can be applied in two ways:-
·
Dip method
·
Bath method
Dip
method
In dip vaccination method fish are immersed in a highly concentrated vaccine solution for very short time say usually few minutes.
Bath method
In bath vaccination method fish are immersed in a lower concentration of vaccine solution for a longer period, usually one to several hours.
Advantages
• Suitable for mass vaccination of all sizes of fish
• Reduced stress for fish
• Lower labour costs
• Less risk to vaccination team
Disadvantages
• Major disadvantages are the large amount of vaccine required
• Lower level of protection and
• Low duration of immunity
In dip vaccination method fish are immersed in a highly concentrated vaccine solution for very short time say usually few minutes.
Bath method
In bath vaccination method fish are immersed in a lower concentration of vaccine solution for a longer period, usually one to several hours.
Advantages
• Suitable for mass vaccination of all sizes of fish
• Reduced stress for fish
• Lower labour costs
• Less risk to vaccination team
Disadvantages
• Major disadvantages are the large amount of vaccine required
• Lower level of protection and
• Low duration of immunity
14.9.
Injection vaccination
Vaccination by injection works well with fish that are 5–10 g or larger and the injection vaccination is very popular in salmon industry. Light anaesthesia is given to the fish before injection to prevent mechanical injuries and also to overcome handling stress. Vaccine can be administrated through intramuscular or intraperitonial with intraperitonial vaccination is beeing very common. The immune response development depends on the needle and method of injection. Short needles might deliver the vaccine in the muscle and cause inflammation and a bad immune response, while long needles may damage the internal organ. The right thickness of needle is also important because the viscous vaccine has to pass through the needle and if the needle is too large the vaccine may fall back and may lead to infection. Once vaccination is administrated it will take weeks to develop immune response, so it is important maintain the fish in ambient temperature and not to stress fish because temperature variation and stress may suppress the immune system.
Advantages
Vaccination by injection works well with fish that are 5–10 g or larger and the injection vaccination is very popular in salmon industry. Light anaesthesia is given to the fish before injection to prevent mechanical injuries and also to overcome handling stress. Vaccine can be administrated through intramuscular or intraperitonial with intraperitonial vaccination is beeing very common. The immune response development depends on the needle and method of injection. Short needles might deliver the vaccine in the muscle and cause inflammation and a bad immune response, while long needles may damage the internal organ. The right thickness of needle is also important because the viscous vaccine has to pass through the needle and if the needle is too large the vaccine may fall back and may lead to infection. Once vaccination is administrated it will take weeks to develop immune response, so it is important maintain the fish in ambient temperature and not to stress fish because temperature variation and stress may suppress the immune system.
Advantages
·
Provide protection for long duration
·
multiple antigens can be administrated in single injection
·
every fish in farm can be vaccinated
·
every fish in farm receives the correct dose
·
Highly efficient in generating both humoral (antibody) and
cellular cytotoxic response
Disadvantages
·
Needs sophisticated machinery or large skilled workforce
·
Significant handling stress and risk of post vaccination fungal
infections
·
Local reactions
·
Unsuitable for small fish
...............................................................................................................
Unit 15 - Adjuvants
15.1. Introduction
The
term adjuvant has been derived from a Latin word adjuvare, which means to help,
thus any material that enhances the immunity is referred as adjuvant. An
adjuvant by definition is a substance, Adjuvants are diverse range of
substances those modulate/enhance the immune response when used in combination
with antigen. Addition of adjuvants helps in lowering the dosage of vaccine
given, efficient absorption and slower processing of antigen, application of
vaccine at low temperature and reduction of side-effects of antigenic
preparations. The use of adjuvant is quite common in human and veterinary
medicine and goes together with the concept of immunization/ vaccination and
has gradually been shifted to aquaculture.
Adjuvants can act as immunostimulators, immunomodulators and immunopotentiators. They can either be administered in combination with or before or after the immunization while some of them can also be given alone. Those are given along with the antigen are FCA, FIA, MDP, polynucleotides, aluminium salts, endotoxins etc. Some of them are immunostimulants and given after the antigen administration, they include glucan and others, however, if given before, they cause immune tolerance. Some are given as immunopotentiators to restore the depressed immunity and others are either given alone or prior to antigenic stimulation. These include levamisole, BCG, dextran sulphate, etc.
Adjuvants can act as immunostimulators, immunomodulators and immunopotentiators. They can either be administered in combination with or before or after the immunization while some of them can also be given alone. Those are given along with the antigen are FCA, FIA, MDP, polynucleotides, aluminium salts, endotoxins etc. Some of them are immunostimulants and given after the antigen administration, they include glucan and others, however, if given before, they cause immune tolerance. Some are given as immunopotentiators to restore the depressed immunity and others are either given alone or prior to antigenic stimulation. These include levamisole, BCG, dextran sulphate, etc.
15.2. Classification of adjuvants
Microbial/biological substances
These include Mycobacterium sp., M. tuberculosis incorporated in Freund's complete adjuvant (FCA), BCG, M. marinum, mixed bacterial toxins, cholera toxin beta unit, saponin including quil-A and immunostimulating complexes (ISCOMs), hemin and haemoglobin, crustaceans, insects and cell wall of certain fungi) etc .
Chemically defined yeast/bacterial/fungal products
Most important of these include lipopolysaccharides (LPS) such as β (1, 3)-D- glucan (laminaran), lentinan, muramyl dipeptide (MDP) and cord factor (trehalose dimycolate (TDM) of Mycobacteria, polar glycopeptidolipids (PGPL) of M. chelonae and peptidoglycan.
Biological products of immune system
They include lymphokines, cytokines, lactoferrin, growth hormones and prolactin.
Synthetic biological analogues
Double stranded complementary RNA homopolymers, synthetic MDP,synthetic TDM, lauroyl tetrapeptide, stearyl tyrosine hydrochloride, dimerized lysozyme, inosine pranobe, formyl peptide (FMLP), short chain peptide, and FK-565 (a peptide related to lactoyl tetrapeptide isolated from cultures of Streptomyces olivaceogriseus) are common adjuvants of synthetic biological analogues.
Chemical preparations
These include aluminium compounds like aluminium hydroxide, aluminium sulphate and aluminium phosphate, calcium phosphate, dextran sulphate, oil emulsions including mineral and vegetable oils in Freund's complete (FCA) and incomplete (FIA) adjuvants, wax D, levamisole, liposomes, polyacrylic adjuvants, serum albumen beads. CP-20, CP-960, synthetic polymers, squalene, rnicrosilica, quaternary ammonium compounds hydrocarbon adjuvants like aliphatic amines of chain length around C 16- like dimethyldioctade cyclamine and N,N-dioctadecyl-N-N-bis (2 hydroxyethyl) propanediamine.
The most commonly used adjuvant is Freund's complete adiuvant (FCA) because it serves as a storehouse for immunogen over a prolonged period thus helps in prolonged release of antigens. It is a combination of paraffin oil, lanonin-like substances and killed Mycobacterium sp. Its bacterial component stimulates T-cell response. Freund's incomplete adjuvant is used after FCA to enhance vaccine effect, this adjuvant doesn't contain bacterial component as in FCA. Other commonly used adjuvants are light oils and lipopolysaccharides.
Microbial/biological substances
These include Mycobacterium sp., M. tuberculosis incorporated in Freund's complete adjuvant (FCA), BCG, M. marinum, mixed bacterial toxins, cholera toxin beta unit, saponin including quil-A and immunostimulating complexes (ISCOMs), hemin and haemoglobin, crustaceans, insects and cell wall of certain fungi) etc .
Chemically defined yeast/bacterial/fungal products
Most important of these include lipopolysaccharides (LPS) such as β (1, 3)-D- glucan (laminaran), lentinan, muramyl dipeptide (MDP) and cord factor (trehalose dimycolate (TDM) of Mycobacteria, polar glycopeptidolipids (PGPL) of M. chelonae and peptidoglycan.
Biological products of immune system
They include lymphokines, cytokines, lactoferrin, growth hormones and prolactin.
Synthetic biological analogues
Double stranded complementary RNA homopolymers, synthetic MDP,synthetic TDM, lauroyl tetrapeptide, stearyl tyrosine hydrochloride, dimerized lysozyme, inosine pranobe, formyl peptide (FMLP), short chain peptide, and FK-565 (a peptide related to lactoyl tetrapeptide isolated from cultures of Streptomyces olivaceogriseus) are common adjuvants of synthetic biological analogues.
Chemical preparations
These include aluminium compounds like aluminium hydroxide, aluminium sulphate and aluminium phosphate, calcium phosphate, dextran sulphate, oil emulsions including mineral and vegetable oils in Freund's complete (FCA) and incomplete (FIA) adjuvants, wax D, levamisole, liposomes, polyacrylic adjuvants, serum albumen beads. CP-20, CP-960, synthetic polymers, squalene, rnicrosilica, quaternary ammonium compounds hydrocarbon adjuvants like aliphatic amines of chain length around C 16- like dimethyldioctade cyclamine and N,N-dioctadecyl-N-N-bis (2 hydroxyethyl) propanediamine.
The most commonly used adjuvant is Freund's complete adiuvant (FCA) because it serves as a storehouse for immunogen over a prolonged period thus helps in prolonged release of antigens. It is a combination of paraffin oil, lanonin-like substances and killed Mycobacterium sp. Its bacterial component stimulates T-cell response. Freund's incomplete adjuvant is used after FCA to enhance vaccine effect, this adjuvant doesn't contain bacterial component as in FCA. Other commonly used adjuvants are light oils and lipopolysaccharides.
15.3. Application in aquaculture
The success of aquaculture industry directly depends on the health aquatic animals. Since these animals are in surrounded by potential pathogens in aquatic media, these animals often get clinical syndromes caused by many infectious organisms, where some of them may leads to serious disease and vaccination can be given to fish against that pathogen in order to protect the fish form disease. This vaccine is given along with adjuvant. In fish vaccination alum and oil are used as adjuvant. Some new adjuvants like hemin and haemoglobin, ECP of Mycobacterium, microsilica, and polar glycopeptidolipids of Mycobacterium chelonae are introduced newly in fish vaccine. Also the immunostimulants like B-D-glucan, levamisole, vitamine E, vitamin C etc. have been used to enhance the immunity in immunocompromised aquatic animals. Light oil adjuvants are successfully used with injectable vaccine of A. salmonicida, a multivalent vaccine containing A. salmonicida, Yersinia sp. and/or Vibrio sp. Some of these adjuvants can be used alone as well.
The success of aquaculture industry directly depends on the health aquatic animals. Since these animals are in surrounded by potential pathogens in aquatic media, these animals often get clinical syndromes caused by many infectious organisms, where some of them may leads to serious disease and vaccination can be given to fish against that pathogen in order to protect the fish form disease. This vaccine is given along with adjuvant. In fish vaccination alum and oil are used as adjuvant. Some new adjuvants like hemin and haemoglobin, ECP of Mycobacterium, microsilica, and polar glycopeptidolipids of Mycobacterium chelonae are introduced newly in fish vaccine. Also the immunostimulants like B-D-glucan, levamisole, vitamine E, vitamin C etc. have been used to enhance the immunity in immunocompromised aquatic animals. Light oil adjuvants are successfully used with injectable vaccine of A. salmonicida, a multivalent vaccine containing A. salmonicida, Yersinia sp. and/or Vibrio sp. Some of these adjuvants can be used alone as well.
Unit 16 - Immuno-stimulants
16.1.
Introduction
During evolution the immune system has developed the mechanisms to detect foreign molecules that are part of the pathogen, so that once the pathogen enters the body of an organism these foreign molecules that are part of the pathogen are detected and activate the defense system against the pathogen. Simple presence of such foreign molecules is sufficient to trigger the immune system and can act as if pathogenic organism might have entered the body. So the administration of these foreign molecules which will act as immunostimulant can activate the defense system and keeps the defense system in alert to combat any invading pathogen.
Immunostimulant can be defines as a chemical, drug, stressor, or action that enhances the innate or non-specific immune response by interacting directly with cells of the system activating them.
Most immune-stimulants are chemical compounds which exist as structural elements of bacteria,
mycelial fungi and yeasts. However, there are also a couple of purely synthetic compounds that possess immune-stimulating properties.
The chemical nature of a number of different immune-stimulants are:
During evolution the immune system has developed the mechanisms to detect foreign molecules that are part of the pathogen, so that once the pathogen enters the body of an organism these foreign molecules that are part of the pathogen are detected and activate the defense system against the pathogen. Simple presence of such foreign molecules is sufficient to trigger the immune system and can act as if pathogenic organism might have entered the body. So the administration of these foreign molecules which will act as immunostimulant can activate the defense system and keeps the defense system in alert to combat any invading pathogen.
Immunostimulant can be defines as a chemical, drug, stressor, or action that enhances the innate or non-specific immune response by interacting directly with cells of the system activating them.
Most immune-stimulants are chemical compounds which exist as structural elements of bacteria,
mycelial fungi and yeasts. However, there are also a couple of purely synthetic compounds that possess immune-stimulating properties.
The chemical nature of a number of different immune-stimulants are:
·
Structural elements of bacteria (lipopolysaccarides (LPS),
lipopeptides, capsular glycoproteins and muramylpeptides)
·
Various ß-1,3-glucan products from bacteria (Curdlan) and mycelial
fungi (Krestin, Lentinan, Schizophyllan, Scleroglucan, SSG, VitaStim)
·
ß-1,3/1,6-glucans from the cell wall of baker’s yeast (MacroGard,
Betafectin)
·
Complex carbohydrate structures (glycans) from various biological
sources including seaweed
·
Peptides present in extracts of certain animals or made by
enzymatic hydrolysis of fish protein
·
Nucleotides, and
·
Synthetic products (Bestatin, muramylpeptides, FK-156, FK-565,
Levamisole).
Among
all the immune-stimulants ß-1,3/1,6-glucans more effective and widely used in
veterinary medicine , human medicine, and also in traditional animal farming.
Because this immune-stimulants acts at a very basic level of the immune system.
ie., the ß-1,3/1,6-glucan molecule is recognized by the specific receptor
present on white blood cells in all animal groups, from the simple
invertebrates to humans, and switches trigger the most basic defence
mechanisms.
16.2.
Mode of action of ß-1,3/1,6-glucans
ß-1,3/1,6-Glucans bind specifically to a “receptor molecule” on the surface of the immune cells that has been retained during evolution and is found in all animal groups from simple invertebrates to man. This is why ß-1,3/1,6-glucans have the same basic biological effect within the whole animal kingdom. When the immune cells are stimulated by ß-1,3/1,6-glucan, the cells become more active in engulfing, killing and digesting bacteria and at the same time they secrete signal molecules (cytokines) which stimulate the formation of new white blood cells. In vertebrates which have the specific immune system, the activated phagocytes produce cytokines which also activate antibody-producing lymphocytes. So ß-1,3/1,6-glucan if used as vaccine it enhances the efficacy. ß-1,3/1,6-glucans intern also contribute in growth, wound healing, repair of cells etc. Purified form of ß-1,3/1,6-glucan do not induce any antibody production which is an added advantage because the immune system will not be stimulated to waste antibody against immune-stimulant itself.
Immune-stimulants are being used in the aqua-culture sector and in traditional animal husbandry to reduce mortality due to infections and to improve general performance of animals.
Immune-stimulants when used may provide the benefits like:
ß-1,3/1,6-Glucans bind specifically to a “receptor molecule” on the surface of the immune cells that has been retained during evolution and is found in all animal groups from simple invertebrates to man. This is why ß-1,3/1,6-glucans have the same basic biological effect within the whole animal kingdom. When the immune cells are stimulated by ß-1,3/1,6-glucan, the cells become more active in engulfing, killing and digesting bacteria and at the same time they secrete signal molecules (cytokines) which stimulate the formation of new white blood cells. In vertebrates which have the specific immune system, the activated phagocytes produce cytokines which also activate antibody-producing lymphocytes. So ß-1,3/1,6-glucan if used as vaccine it enhances the efficacy. ß-1,3/1,6-glucans intern also contribute in growth, wound healing, repair of cells etc. Purified form of ß-1,3/1,6-glucan do not induce any antibody production which is an added advantage because the immune system will not be stimulated to waste antibody against immune-stimulant itself.
Immune-stimulants are being used in the aqua-culture sector and in traditional animal husbandry to reduce mortality due to infections and to improve general performance of animals.
Immune-stimulants when used may provide the benefits like:
·
Reduce mortality due to opportunistic pathogens.
·
Prevent virus disease
·
Enhance disease resistance of farmed shrimp
·
Reduce mortality of juvenile fish
·
Enhance the efficacy of anti-microbial substances
·
Enhance the resistance to parasites
·
Enhance the efficacy of vaccines
16.3. Action in fish
The most common immunostimulants used are non-virulent microorganisms or their by-products and in fish once the immunostimulant is injected, the first defense system are substance found in mucus secreted by endothelial cells, followed by macrophage activation that acts against pathogens. Then lytic factors, agglutinating factors, proteins and enzymes act directly on the molecules or on the microbe’s surface to suppress bacterial growth or to assist in phagocytosis.
The most common immunostimulants used are non-virulent microorganisms or their by-products and in fish once the immunostimulant is injected, the first defense system are substance found in mucus secreted by endothelial cells, followed by macrophage activation that acts against pathogens. Then lytic factors, agglutinating factors, proteins and enzymes act directly on the molecules or on the microbe’s surface to suppress bacterial growth or to assist in phagocytosis.
********************************************************
Comments
Post a Comment