Immunogens, Antigens, and Antibodies PDF

Immunogens, Antigens and Antibodies Nov 18, 2024 Ken Hirasawa Immunogens and Antigens Immunogens and Antigens Immunogens are capable of inducing an immune response Antigens bind specifically t...

Immunogens, Antigens and Antibodies Nov 18, 2024 Ken Hirasawa Immunogens and Antigens Immunogens and Antigens Immunogens are capable of inducing an immune response Antigens bind specifically to antibodies or T cells Antigens Immunogens All immunogens are antigens, but not all antigens are immunogens Immunogens and Antigens Requirements for Immunogenicity 1) Foreignness - Do not respond to self (except: autoimmune diseases). - More foreign --> more immunogenic 2) Sizes (molecular weight) - > 6kD are generally immunogenic - < 1kD are not (ie. penicillin, aspirin) 3) Chemical Complexity - Homopolymers of amino acid are not immunogenic. Immunogens and Antigens Requirements for Immunogenicity 4) Degradability Antigen Processing - Susceptibility to enzymatic degradation - Stability for antigen presentation 5) Dosages - Insufficient doses may cause tolerance - Repeated administration may be required for a sufficient immune response Immunogens and Antigens Hapten 1) Low molecular weight (antigen but not immunogen) 2) Non-immunogenic by itself 3) Conjugation with an immunogenic compound (carrier) Immunogens and Antigens Epitopes Recognized by lymphocytes Surface antigens Peptides Immunogens and Antigens Major Classes of Antigens Carbohydrates (polysaccharides) - immunogenic as part of glycoproteins Lipid - rarely immunogenic Nucleic Acid - not immunogenic - systemic lupus erythematosus (SLE) Proteins, Glycoproteins - very immunogenic Immunogens and Antigens Major Classes of Antigens Immunogens and Antigens Cross-reactivity - ability of an antibody, specific for one antigen, to react with a second antigen. - most antibodies cross-react with closely related antigens Shared epitopes Tetanus Toxoid Immunogens and Antigens Adjuvant - an adjuvant is a substance that when mixed with an immunogen enhances its immunogenicity - how do adjuvants work? 1) Physically prolonging the persistence and/or slowing the release of antigens 2) Causing local Inflammation and proliferation of immune cells 3) Improving the uptake and processing of compounds by immune cells Human Aluminum hydroxide (or phosphate) - the only adjuvant with FDA approval for human use Animals Freund’s complete adjuvant - oil in water with killed mycobacteria Function & Structure of Antibodies Antibodies -are g-globulins -are produced by plasma cells (B lymphocytes) -exist in secreted and membrane-bound forms -form the B cell receptor on the surface of B cells Function & Structure of Antibodies Why do we need antibodies? - neutralization of toxin/virus - immobilization of bacteria/parasite - activation of complement - initiation of opsonization - antibody-dependent cell mediated cytotoxicity (ADCC) Function & Structure of Antibodies Antibody Structure Antigen binding, Hypervariable regions Fc Function & Structure of Antibodies Hypervariable Regions - highly variable in amino acid sequence - 3 hypervariable regions in both light and heavy chain Function & Structure of Antibodies Five major classes of antibody Function & Structure of Antibodies Five major classes of antibody Function & Structure of Antibodies Distribution of various Ig isotypes in body fluids serum secretions IgM IgG IgA IgE Function & Structure of Antibodies IgG - four subclasses (IgG1, IgG2, IgG3 and IgG4) - placental passage - opsonization Function & Structure of Antibodies IgG - Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC) - activation of complement - toxin/viral neutralization - bacterial immobilization Function & Structure of Antibodies IgG Antibody levels early in life Function & Structure of Antibodies IgM - first immunoglobulin produced following infection/immunization - most efficient immunoglobulin for complement fixation Function & Structure of Antibodies IgA - mainly in secretions (tears, saliva, sweat and mucus) - abundant on respiratory and mucosal surfaces (first line defense) - antibacterial and antiviral activity Function & Structure of Antibodies IgE - mediates Type I hypersensitivity reactions - high levels during parasitic infection