Antigens description binding part 2 .ppt
- 1. Universities Press © Universities Press (India) Private Limited Universities Press 3-6-747/1/A & 3-6-754/1, Himayatnagar Hyderabad 500 029 (A.P.), India Part II Immunology Email: info@universitiespress.com marketing@universitiespress.com Phone: 040-2766 5446/5447
- 2. Universities Press © Universities Press (India) Private Limited ANTIGEN • Substance - introduced parenterally • Production of antibody • Reacts specifically and in an observable manner • Some antigens do not induce antibody • Sensitise specific lymphocytes
- 3. Universities Press © Universities Press (India) Private Limited ANTIGEN • Antigen – Interact specifically with antibodies, B cell receptor and/or T cell receptor • Immunogen – Induces detectable immune response (humoral/cellular). Results in either production of antibodies or activation of T cells.
- 4. Universities Press © Universities Press (India) Private Limited ANTIGEN Parenteral - outside GIT Specifically - particular immunocytes antigenicity: • Induction of immune response (Immunogenecity) • Specific reaction with antibodies (Immunological reactivity)
- 5. Universities Press © Universities Press (India) Private Limited ANTIGENS • Complete antigen: Induce antibody-specific and observable reaction • Hapten - Incapable of inducting antibody • Hapten – Greek for to fasten • Hapten - Immunogenic on combining with larger molecule carrier
- 6. Universities Press © Universities Press (India) Private Limited HAPTEN • Complex - precipitate with special antibody multivalent • Simple - non-precipitating monovalent
- 7. Universities Press © Universities Press (India) Private Limited EPITOPE • Smallest unit of antigenicity • Antigenic determinant/epitope • Epitope - 4 or 5 amino acids or monosaccharides • Specific chemical structure electrical charge • Steric configuration sensitising immunocyte • Reacts with complimentary antibody
- 8. Universities Press © Universities Press (India) Private Limited EPITOPE • Linear or sequential epitope - single linear segment of primary sequence. Epitopes: linearised
- 9. Universities Press © Universities Press (India) Private Limited EPITOPE • Conformational epitope – epitopes formed by being brought together on surface residues from different sites on peptide chain Epitopes: conformational
- 10. Universities Press © Universities Press (India) Private Limited EPITOPE • T cells recognise sequential epitopes • B cells recognise conformational epitopes • Paratope – combining area on antibody corresponding to epitope • Antigenic mosaic - antigens such as bacteria or virus carry different types of epitopes, presenting an antigenic mosaic
- 11. Universities Press © Universities Press (India) Private Limited DETERMINANTS OF ANTIGENICITY Size: Related to molecular size, large molecules - highly antigenic Low molecular weight - weakly antigen Chemical nature: • Naturally occurring antigens • Proteins/polysaccharides • Lipids/Nucleic acid-less antigenic
- 12. Universities Press © Universities Press (India) Private Limited DETERMINANTS OF ANTIGENICITY Susceptibility to tissue enzymes: • Antigens – degraded fragments • Phagocytosis and intracellular enzymes – antigens, immunogenic fragments synthetic polypeptides, D-amino acids-not antigenic • Amino acids - antigenic
- 13. Universities Press © Universities Press (India) Private Limited DETERMINANTS OF ANTIGENICITY Foreignness - Induce immune response Ehrlich - ‘Horror autotoxicus’ Tolerance to self antigen, during development Breakdown of mechanism - autoimmunity
- 14. Universities Press © Universities Press (India) Private Limited ANTIGEN SPECIFICITY Determined - single chemical grouping Species specificity: All individual in a species Forensic application - blood stains, etc. Isospecificity: lso antigens found in some but not all members Example: Human erythrocyte antigen - blood groups
- 15. Universities Press © Universities Press (India) Private Limited ANTIGEN SPECIFICITY Auto specificity: Self-antigens, sequestrated antigens – not recognised as self-antigens Organ specificity: Some organs – brain kidney, lens protein of different species share same antigen
- 16. Universities Press © Universities Press (India) Private Limited HETEROPHILE SPECIFICITY Closely related antigens - different biological species, classes, kingdom Heterogenetic/heterophile antigens: • Frossman antigen • Weil–Felix reaction - typhus fever • Paul–Bunnel - infectious mononucleosis • Cold agglutinin - primary atypical pneumonia
- 17. Universities Press © Universities Press (India) Private Limited BIOLOGICAL CLASSES OF ANTIGEN T cell dependent (TD) antigens T cell independent (TI) antigens
- 18. Universities Press © Universities Press (India) Private Limited BIOLOGICAL CLASSES OF ANTIGEN T cell dependent (TD) antigens • Most natural proteins are T cell dependent • Require preliminary processing • Induce a full gamut of immunoglobulin types IgM, IgG, IgA and IgE • Show immunological memory • Rapidly metabolised in the body
- 19. Universities Press © Universities Press (India) Private Limited BIOLOGICAL CLASSES OF ANTIGEN T cell independent antigen • Structurally simple - composed of limited number of repeating epitopes as seen with pneumococcal capsular polysaccharide, bacterial lipopolysaccharide • Does not require preliminary processing • Antibody response limited to IgM and IgG3 • Do not show immunological memory
- 20. Universities Press © Universities Press (India) Private Limited SUPERANTIGENS • Superantigens are certain protein molecules such as staphylococcal enterotoxins, that activate a large number of T cells, irrespective of their antigen specificity
- 21. Universities Press © Universities Press (India) Private Limited SUPERANTIGENS • Superantigens bind outside the antibody binding groove directly to the lateral aspect of the TCR β chain • Conventional antigen fragments bind to the άβ heterodimer groove of the MHC molecule through the V region of the TCR ά and β chains
- 22. Universities Press © Universities Press (India) Private Limited SUPERANTIGENS Schematic diagram of a superantigen
- 23. Universities Press © Universities Press (India) Private Limited DETERMINANTS RECOGNISED BY INNATE IMMUNE SYSTEM • Innate immune system recognise unique molecular patterns - pattern recognition • Pathogen associated molecular patterns (PAMPs) - broad molecular patterns • Pattern recognition receptors (PRRs) – receptors for PAMPs
- 24. Universities Press © Universities Press (India) Private Limited PATTERN RECOGNITION RECEPTORS TYPES • Toll-like receptors (TLRs) – transmembrane receptors present on macrophages and dendritic cells • Scavenger receptors – include CD 36, CD 68 and SRB-1 • Mannose receptors - receptors on the surface of phagocytes bind mannose-rich glycans found in microbial glycoproteins.