3. Antigens or immunogens and Antibodies.pptx

the presentation illustrates immunogengs or Antigens and the various types. it also depicts the types of Antibodies

1. Immunogens Or Antigens

2. Immunogens or Antigen s Immunogen or antigen: * A foreign substance, when introduced into human body, stimulate formation of specific antibodies or sensitized lymphocytes * Antigens have the ability to combine specifically with antibodies produced or sensitized T-lymphocytes induced

3. Immunogens or Antigen s Haptens : - Low molecular weight substances - These substances not immunogenic by itself - If couple to a larger carrier molecule (albumin, globulins), they become immunogenic - Examples : simple chemicals and drugs: penicillin, sulphonamid , aspirin, cosmetic, t ranquillizers, neomycin skin ointment

4. Immunogens or Antigen s Epitopes or Antigenic determinants: * Sites on or within antigen with which antibodies react * Antibodies are specific for epitopes

5. Types of Antigens Exogenous Antigens 1- Bacterial antigens: a- Antigens related to bacterial cells - Somatic antigen (O): part of cell wall gm – ve bacter . - Capsular antigen: usually polysaccharide - Flagellar Ag (H) : a protein made of flagellin - Fimbrial Ag: surface antigens in fimbriated bacilli b- Antigen secreted by bacteria: - Exotoxins - Enzymes 2- Viral antigens: a- protein coat viral antigens b- Soluble antigens (soluble nucleoproteins as in influenza)

6. Types Of Antigens Endogenous antigens Human tissue antigens: a- Blood group antigens: A, B and Rh antigens b- Histocompatibility antigens: Glycoprotein molecules on all nucleotide cells: - Major histocompatibility complex antigens (MHC) - Human leucocyte antigen (HLA)

7. Major Histocompatibility Complex Antigens (MHC) * MHC has an important function in presentation of antigens to T-cells * Helper T-cells recognize foreign antigens on surface of APCs, only when these antigens are presented in the groove of MHC II molecule * Cytotoxic T-cells will only recognize antigens, on the surfaces of virus infected cells or tumor cells only when these antigens are presented in the groove of Class I molecule (MHC restriction)

8. Superantigens (SAgs) * They activate multiple clones of T-lymphocytes * Bacterial toxins: Staph. aureus toxic shock syndrome toxin (TSST) and enterotoxins Strpt . pyogenes pyrogenic toxin A * They have the ability to bind both class II MHC molecules and TCR β chain * They act as a clamp between the two, providing a signa l for T-cel l activation

9. Superantigens (SAgs) * They are active at very low concentration causing release of large amounts of cytokines * The massive T-cell activation and release of large amounts of cytokines cause systemic toxicity * This method of stimulation is not specific for the pathogen * It does not lead to acquired immunity i.e no memory

10. Antigen Binding And Recognition Molecules Antigens are recognized by and bind to: 1) B-cell receptors (BCR) : - These are membrane-bound immunoglobulins (IgM and IgD ) on B-cells - BCRs can be secreted in plasma as antibodies 2) T-cell receptors (TCR) - α and β chains anchored to T-cells - There is a groove which binds small peptides presented by MHC on surface of APCs 3) MHC molecules They are essential for presentation of peptides so that they can be recognized and bind to TCRs

11. Factors influencing Immunogenicty 1-Foreigness : Foreign substances are immunogenic 2- Molecular size: High molecular weight increase immunogenicty 3- Chemical structure complexity: High complexity increase immunogenicty 4- Route of administration : Parenteral routes are more immunogenic to oral route

12. Factors influencing Immunogenicty 5- Method of administration : a- Antigen dose: A ppropriate dose optimum antigenicty Low dose low- zone tolerance High dose high-zone tolerance b- Adjuvant: Substance when injected with an antigen enhance immunogenicty

13. ANTIBODIES

14. A. Antibodies: Formed by B-cells They are immunoglobulins which react specifically with the antigen that stimulated their production Make up to about 20% of plasma proteins

15. A. Antibodies: Structure and function Light (L) and Heavy (H) polypeptide chains based on their molecular weights: two types: λ (Lambda) or к (Kappa) based on amino acid differences in the constant region The amino part of each L-chain contains part of the antigen binding site H-chains are distinct for each of the five), immunoglobuli classes designated as µ (mu), ԑ (epsilon ᵞ (gamma) ᵟ Delta) The amino terminal portion of the H-chain participates in the antigen-binding site; The carboxyl group forms the Fc fragment with various biologic activity

16. A. Antibodies: Structure and function The L – and H- Chains are subdivided into Variable regions and Constant regions. The regions are sub-divided into 3 dimensionally folded repeating segments called domains. L-Chain: Consists of – 1 variable domain & 1 constant domain H-Chain: Consists of – 1 variable domain & 3 or more constant domains

17. A. Antibodies: Structure and function Variable regions: Responsible for antigen binding Have hyper-variable amino acid sequences that form the antigen binding sites Antigen binding involves vaan-dar-waals forces, electrostatic forces, and other weak forces Constant region : responsible for biologic functions such as hypersensitivity reactions, complement activation

18. A. Antibodies: Immunoglobulin classes IgG : Each IgG molecule consists of two L chains and 2 H- chains linked by disulphide bonds Divalent There are 4 classes based on amino acid sequence differences in the Constant region Predominant Ab in secondary immune responses Important against bacterial and viral infections Can cross the placenta The most abundant in new borns

19. A. Antibodies: Immunoglobulin classes IgM : main Immunoglobulin produced in primary immune responses Present on the surface of all uncommitted B-cells Has five H-L chain units ie has ten Fab units Most efficient Ig in agglutination, complement fixation and other Ab -Ag reactions Important in bacterial and viral infections Can be produced by a fetus undergoing infection Cannot cross the Placenta

20. A. Antibodies: Immunoglobulin classes IgA: Main Ig in seretions ie saliva, tears, milk, etc Protects mucous membranes from attacks Bivalent Exists in serum

21. A. Antibodies: Immunoglobulin classes IgE : Fc region binds to receptors on Mast cells, Basophils, and Eosinophils Important in allergic reactions May appear in external secretions Also important in helminth infection

22. A. Antibodies: Immunoglobulin classes IgD : Acts as antigen receptor when present on the surface of certain B-lymphocytes Present only in trace amounts in serum