Adaptive humoral immunity

adaptive immune system of fish :humoral

1. Adaptive immune system in fish: humoral immunity Harapriya behera DPHFM

2. Immune system:

3. Introduction: Adaptive immunity relies on the generation of random and highly diverse repertoires of T and B-lymphocyte receptors encoded by recombinant activation genes (RAGs) and contributes to a more specific and efficient response against infections ( McGuinness et al., 2003; Medzhitov, 2007 ) Adaptive immune recognition is mediated by antigen (Ag) receptors, with random but narrow specificities . Adaptive or combinatorial system, characterized by the presence of Ig, T cell receptors (TCR) and products of the MHC that allow clonal selection of B and T cells.

4. combinatorial immune response All jawed vertebrates possess the genetic elements essential for the function of the adaptive/combinatorial immune response ( Marchalonis et al., 2006). The combinatorial immune system ( CIS) consists of Ag-recognizing lymphocytes, immunoglobulins (Abs and Ig-family TCR), MHC products, and recombination activating (RAG) 1 and 2 genes. The overall shape of the molecules and the recombination mechanisms that create junctional diversity in TCRs and Igs are similar in fish and mammals (Du Pasquier , 2001). Naturally occurring Abs whether in serum or on lymphocytes as receptors for Ag are also essential to the selective basis of combinatorial/adaptive vertebrate immunity

5. Specific immunity Specificity • Memory • Ability to distinguish b/w self vs non-self • T and B cell

6. Adaptive humoral immunity Results in production of proteins called “immunoglobulin's ” or “antibodies ”. • Body exposed to “foreign ” material termed “antigen” which may be harmful to body: virus , bacteria, etc. • Antigen has bypassed other protective mechanisms , ie , first and second line of defense . Antibodies are specific proteins produced by plasma cells Belong to immunoglobulin superfamily Located in blood and extravascular tissues , secretions and excretions Bind pathogenic microorganism and their toxins in extracellular compartments

7. Antibodies are Proteins that Recognize Specific Antigens

8. The innate immune system activates Acquired immunity • Cells of the innate immune system activate the specific immune response . • A group of cells called Antigen presenting cells (APC ) activate the acquired immune system. Ex-Macrophages , Dendritic cells and B-cells. • APCs turn on the acquired immune system by activating T-Helper cells (TH-cells ). • TH-cells in turn activate either the cell mediated or the humoral immune system.

9. Specific defence mechanism Lymphocyte, is the immunocompetent cell. Which is responsible for initiating and mediating the : Humoral immunity- production of soluble antibody [immunoglobulin] Cell-mediated immunity (CMI) responses which are mediated by a variety of cells including lymphocytes and macrophages. Immunological memory constitutes an adaptive change in the lymphoid cell populations.

10. Induction of b cells Ags an be classified into TI or TD. For induction of Ab response for TI A gs the auxillary assistance of macrophage or monocyte are required. And for induction of Ab response for TD Ags , The Ag must be processed by an accessory cells (macrophage) and be presented on the cell surface to T cell, which in turn helps in B cell differentiation. B cell differentiate into plasma or effector cell which produces Abs and memory cells which carries Ag for recognition property. Myelopoiesis generally occurs in the head kidney (HK) and/or spleen, whereas thymus, kidney and spleen are the major lymphoid organs HK exhibits morphological similarities with the bone marrow of higher vertebrates and also serves as a second lymphoid organ (a lymph node analogue), and in the clearance of soluble and particulate Ags from the circulation. Furthermore, it is also the major site of Ab production

11. Only one type of antibody and one type of B cell responds to the antigenic determinant That cell type then produces large number of clones

12. Immunological Memory Antibody Titer : The amount of antibody in the serum. Pattern of Antibody Levels During Infection Primary Response: – After initial exposure to antigen, no antibodies are found in serum for several days. – A gradual increase in titer , first of IgM and then of IgG is observed. – Most B cells become plasma cells, but some B cells become long living memory cells . – Gradual decline of antibodies follows.

13. Secondary Response: – Subsequent exposure to the same antigen displays a faster and more intense antibody response. – Increased antibody response is due to the existence of memory cells , which rapidly produce plasma cells upon antigen stimulation.

14. Immunoglobulins (I g ) 3 immunoglobulin classes IgM , IgD , and IgT in bony fishes. IgM constitutes the main systemic immunoglobulin, IgT plays the prevalent role in mucosal surfaces . IgD in fish immunity is also present. Both IgM and IgD are co-expressed in B cells found both in systemic and mucosal lymphoid areas, where as IgT is uniquely expressed by a B-cell subset. Serum IgM concentrations have been found between 800 and 9000 µg/mL in teleosts

15. ( I g )s present in different types of fishes Bony fish are the only animals that produce IgT /Z. R ainbow trout ( IgT ) a nd zebra fish ( IgZ ). IgT , a monomer in trout serum but a tetramer in mucous, is able to pass through the mucosal epithelium using a fish polymeric immunoglobulin receptor ( pIgR ). IgT and IgM are also found in Thunnus orientalis  (Pacific blue fin tuna)  B cells extensively populate teleost SALT (skin associated lymphoid tissue) and are responsible for secreting polymeric IgT into the skin mucus to protect the skin from infectious microbes.

16. Mucosal immunity First line of humoral defence, where pathogens get blocked and neutralized is the mucosal surface. Enterocytes of secondary gut segment appears to have evolved the specialized function of antigen uptake and processing of antigen. Carp mucosal intraepithelial lymphoid cells are composed of sIg - cells NK cells, sIg + (B cells) and Ig binding APCs. Specific antibody secreting cells were detected in both head kidney and intestinal mucosa after intraperitoneal injection or oral intubation of antigens

17. Structure of antibody Antibody (Ab) also know as Immunoglobulin (Ig) is the large Y shaped protein produced by the body’s immune system when it detects harmful substances, called antigens. The tetramer structure of fish Ig is composed of four monomeric units , two identical heavy (H) chains (70 kD ) and two light (L ) chains (25 kD ). Disulphide bonds and non-covalent combinations of units may coordinate the assembly of the subunits.

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19. Antibody (Ab) also know as Immunoglobulin (Ig) is the large Y shaped protein produced by the body’s immune system when it detects harmful substances, called antigens.  The B cells producing these Igs appear to be mutually exclusive, at least for IgM and IgT production. Ig also exists in mucus secretions of the skin and gut, and in the bile in the form of IgT . The number of VH families varies tremendously between different teleost species

20. The functional B-cell receptor is a multi-protein complex consisting of an antigen binding subunit and a signaling subunit.The BCR is composed of membrane immunoglobulin ( mIg ) molecules and associated Ig α/Igβ (CD79a/CD79b) heterodimers (α/β). The mIg subunits bind antigen, resulting in receptor aggregation, while the α/β subunits transduce signals to the cell interior. BCR aggregation rapidly activates the Src family kinases Lyn, Blk , and Fyn as well as the Syk and Btk tyrosine kinases. This initiates the formation of a ' signalosome ' composed of the BCR, the tyrosine kinases, adaptor proteins such as CD19 and BLNK, and signaling enzymes such as PLCγ2, PI3K, and Vav . Signals emanating from the signalosome activate multiple signaling cascades that involve kinases, GTPases , and transcription factors. This results in changes in cell metabolism, gene expression, and cytoskeletal organization. The outcome of the response is determined by the maturation state of the cell, the nature of the antigen, the magnitude and duration of BCR signaling , and signals from other receptors such as CD40, the IL-21 receptor, and BAFF-R. Many other transmembrane proteins, some of which are receptors, modulate specific elements of BCR signaling . A few of these, including CD45, CD19, CD22, PIR-B, and FcγRIIB1 (CD32), are indicated here in yellow. The magnitude and duration of BCR signaling are limited by negative feedback loops including those involving the Lyn/CD22/SHP-1 pathway, the Cbp / Csk pathway, SHIP, Cbl , Dok-1, Dok-3, FcγRIIB1, PIR-B, and internalization of the BCR. In vivo, B cells are often activated by antigen-presenting cells that capture antigens and display them on their cell surface. Activation of B cells by such membrane-associated antigens requires BCR-induced cytoskeletal reorganization. Please refer to the diagrams for the PI3K/ Akt signaling pathway, the NF- κB signaling pathway, and the regulation of actin dynamics for more details about these pathways.

21. Antigen trapping: The (MMCs) of the haemo-lymphopoietic organs of teleost fish trap and retain antigens and are closely associated with immunoglobulin-secreting cells . B memory cells are specific for the antigen trapped. These structures are considered to be involved in the execution and/or establishment of immune memory. antigen and immunoglobulin become trapped within the reticulin fibres of the splenic ellipsoids and then subsequently also on the surface of the cells within the MMC . . The antigen is probably trapped as an immune complex. Ag coexist with Ig. The Ag-Ab complexes are thus held, mainly extracellularly. In the kidney, antigen is mainly taken up by the reticuloendothelial cells , intracellularly .

22. Lymphoid organs of bony fish: Lymphoid organ Organised tissues in which lymphocytes interact with non lymphoid cells sites of maturation & initiation of adaptive immune responses Central lymphoid organs- T cell maturation head kidney Thymus Peripheral lymphoid organs – B cell maturation Spleen GALT MALT SALT T and B cell activation antigen trapping.

23. The thymus, a primary lymphoid organ and a major site of T-cell development in teleosts . Basically , thymus can be considered as an encapsulated aggregation of MFs that processes the proliferation of T cells . T he gut-associated lymphoid tissue (GALT) of teleosts consists principally of different sized lymphocytes, plasma cells and MFs , as well as several types of granulocytes, PAS positive cells and eosinophil granular cells (Zapata and Amemiya , 2000 ). In teleosts , gut intraepithelial lymphocytes are largely considered as T cells, whereas lymphoid cells in the lamina propria are mainly as B lymphocytes IgM can be present in serum and secretions of fish, including cutaneous and gut mucus. The Ab response and serum concentration of IgM may vary between teleost species. * The SALMONIDS are high responders that produce a relatively large amount of specific Abs to a variety of Ags ,where as GADUS MORHUA is that no, or only a low, increase in Ab levels are seen after immunisation with hapten -carriers or bacteria.

24. Antibody effector mechanism Neutralisation Precipitation /agglutination Opsonization Complement activation Hypersensitivity responses

25. Neutralisation- blocks the entry of antigen into the cell. 2. Precipitation- when soluble Ag binds to Ab 3. agglutination – when particulate Ag get bind with Ab

26. 3 . Opsonization -  is the process by which a pathogen is marked for ingestion and eliminated by a phagocyte.  4. Hypersensitive reaction-skin in perciform fish do EGC contain histamine. Skin sensitivity responses in the plaice have been associated with C-reactive protein mediating degranulation of mast cells and, as fish possess the C3a and C5a components of complement, these may mediate hypersensitivity responses

27. Complement activation Complement is amongst the main mechanisms involved in the initiation of the innate response and further mounting of an adaptive response. .

28. Factors affecting immune response Temperature Antigen dose Nature of antigen Route of administration Adjuvants and immunostimulant Seasonal effect Environmental effects

29. References Fish Immunoglobulins Sara Mashoof 1  and  Michael F. Criscitiello 1,2 ,* Brian Dixon, Academic Editor Fish Pathology FOURTH EDITION Edited by Ronald J. Roberts Basic immunology by Gregory Heath BSc (Hons), MCOptom , Dip. Clin . Optom The fish immune system by George Iwama Fish immune system. A crossroads between innate and adaptive responses L . Tort, J.C. Balasch, S. Mackenzie The innate immune response of finfish e A review of current knowledge Shona K. Whyte* Centre for Aquatic Health Sciences, Department of Health Management,

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