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Definitions

Definitions. Immune -Exempt from the pathogen. Immunology is used to mean the study of defense mechanisms against infectious disease. √ Specific √ Non-specific innate or natural immunity : attributed to inherited ability to produce antibodies without stimulation by antigens

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Definitions

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  1. Definitions • Immune-Exempt from the pathogen. • Immunology is used to mean the study of defense mechanisms against infectious disease. • √ Specific • √ Non-specific • innate or natural immunity: attributed to inherited ability to produce antibodies without stimulation by antigens • acquired immunity: host is stimulated by contact with antigens

  2. Table 1 Non-specific Immunity Specific Immunity Response is antigen-independent Response is antigen-dependent There is immediate maximal response There is a lag time between exposure and maximal response Not antigen-specific Antigen-specific Exposure results in no immunologic memory Exposure results in immunologic memory

  3. Introduction • Fish is a heterogenous group of organisms that include agnathans(lampreys and myxines),condryctians(sharks and rays),Teleosteans(bony fish). • Fish and mammals shows some similarities and some diffrences regarding immune function.

  4. Immune Response in Fish • Fish are the most primitive vertebrates, but had to develop an immune system for protection • the only exception was cold water species: due to low bacterial generation time at lower temperatures • those living under schooling conditions and in warm environments needed a highly developed response • all fish pathogens contain antigens: viral particles, bacteria, fungi, toxins and animal parasites

  5. Response of Fish Following an Encounter with a Pathogen Fish Contacts Pathogen Innate Immunity Failure (Disease and Death) Success (No Disease or Infection) Initiation and Instruction of the Specific Immune Response Humoral Response (Extracellular Pathogens and Toxins) Acquired Immunity, Immunologic Memory, and Protection (Survival) Cell-Mediated Immune Response (Intracellular Pathogens and Viruses)

  6. Non-specific defence mechanisms • External barriers • Mucus • Skin • Lysozyme

  7. Mucus • Mucus which by entrapping micro organisms and continuously inhibits colonization of the integument. • The rate of mucus production in fish can be increased in the response to infection. • Mucus of the fish is toxic to certain micro organisms.

  8. Skin • Active immune responses occurring in the skin. • The epidermal integrity is vital to fish in maintaining osmotic balance & excluding micro organisms. • Ig is present in low concentration in skin mucus. • lymphocytes, plasma cells & macrophages present in the epidermis of fish.

  9. Lysozymes • Lysozyme is one of the most studied innate responses in fish. • It can act on the peptidoglycan layer of the bacterial cell walls and resulting in the lysis of the bacteria. • Lysozyme response in fish is very rapid not only related to bacteria,but also to other alarm situation such as after stress

  10. Phagocytic activation • Macrophages and neutrophils can be enhanced in two differents ways • Opsonins • Lymphokines • Opsonins: • An opsonin is any molecule that acts as a binding enhancer for the process of phagocytosis. • Lymphokines: • Lymphokines are a subset of cytokines that are produced by a type of immune cell known as a lymphocyte.

  11. Opsonins • The alternative complement pathway can be activated in normal serum by pathogen(bacteria). • Then more attach to phagocytic cell resulting in enhancing phagocytosis.

  12. Cont… • Fish antibody seems to have weak opsoniting activity but in the presence of complemet, opsonization is strong because activation of the classical complement path way. • CRP&MBP have also been reported to have opsonizing effect in fish.

  13. Lymphokines • Macrophages are able to kill pathogen or multiply within normal macrophages respectively. • The lymphokine responsible for this activation is known as macrophages activating factor. • It’s produced by fish T lymphocytes following exposure to specific antigen.

  14. Immune Response Sequence: 1 Begins when macrophage encounters this non-self entity (e.g., virus): macrophage literally “eats” the substance, digests it and displays pieces of the invader on its surface. These pieces are antigens. Meanwhile, other viral particles are at work, infecting nearby host cells.

  15. Immune Response Sequence: 2 Antigenic fragments alert a specific type of T lymphocyte (“helper” T) to begin choreographed attack of intruder Helper recognizes antigen particles and binds to the macrophage via an antigen receptor Helper T cells are unique to a specific antigen

  16. Immune Response Sequence: 3 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

  17. Immune Response Sequence: 4 As mentioned IL-2 instructs helper T’s and “killer T’s” to multiply Proliferating helper T’s 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

  18. Immune Response Sequence: 5 Killer T cells start shooting “holes” in the surface of infected host cells Antibodies released by B cells bind in a lock-and-key fashion to antigens on the surface of invaders that have escaped macrophages (Ag-Abcomplex). Makes it easier for macrophages and special killer lymphocytes to destroy unwelcomed entities. Binding of antibodies with antigens signals release of a blood component, complement, to puncture virus membrane (death)

  19. Natural Cytotoxic Cells(NCC) • NCC cells similar properties to NK cells. • The fish NCC cells morphologically resemble agranular lymphocytes or monocytes. Role in defense mechanisms. • They may be important protection against viral parasitic & neoplastic disease.

  20. Eosinophiles, Basophils & Mast cells • Some fish species posses blood granulocytes with eosinophilic or basophilic granules and basophils. • Many species posses eosinophil granular cells in connective tissues in the skin and gills or intestinal wall. • Mast cells release of vasoactive amines. • Fish do not posses IgE

  21. Eosinophil, Basophil & Mast cell

  22. Specific defence mehanisms • Specific defense mechanisms are two types.They are • 1. Humoral immunity. • 2. Cell mediated immunity.

  23. Humoral Immunity in Fish Defined: the antibody response to foreign antigens Fish posses B-cells (surface immunoglobulin-positive cells), similar to mammals in structure Surface IgM of B-cells serves as receptor for antigen recognition and is of same specificity as the antibody molecule that will be produced (Janeway and Travers, 1994) Unlike crustaceans, fish possess immunologic memory (Arkoosh and Kaattari, 1991) Their primary and memory response both use the same IgM molecule, with eight antigen binding sites, a potent activator of complement

  24. Cell-Mediated Immunity in Fish Used to eliminate intracellular pathogens (e.g., bacteria, virus, parasites) Relies on contact of the foreign invader with the subsequent presentation of an antigen having the same major histocompatability complex (MHC I or II) to T-helper cells (REM?) Once T-helper cells are stimulated, the produce cytokines that result in stimulation of effectorcells (cytotoxic lymphocytes) or macrophages Cytokines stimulate aforementioned cells and also recruit new cells to the area, activate them Work quite well against bacteria, important against Edwardsiella ictaluri (Shoemaker, et al., 1999)

  25. Lymphoid organs

  26. Immune Tissues and Organs Most important immunocompetent organs: thymus, kidney (head, trunk), spleen and liver Immune tissues in these organs not well defined (Manning, 1994) Thymus: develops T-lymphocytes (helpers, killers; similar to other vert’s), indirect evidence Kidney: important in both immunity and hematopoiesis, site of blood cell differentiation Early immune response handled by entire kidney With maturity, anterior used for immune response; posterior for blood filtration, urinary activities

  27. Immune Tissues and Organs Kidney (cont.): blood flows slowly through kidney and antigens are “trapped” or exposed to reticular cells, macrophages, lymphocytes Anterior is where “memory” occurs (Secombs et al., 1982) Spleen: secondary to kidney, involved in immune reactivity and blood cell formation, contains lymphocytes and macrophages Liver: could be involved in production of components of the complement cascade, important in resistance; not real clear

  28. Thanks

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