Antibodies (Eng) PDF Presentation

In the name of God Antibodies Dr. Saeid Taghiloo Assistant Professor of Medical Immunology Department of Immunology, School of Medicine, Mazandaran University of Medical Sciences, Sari,Iran Email: [email protected] ...

In the name of God Antibodies Dr. Saeid Taghiloo Assistant Professor of Medical Immunology Department of Immunology, School of Medicine, Mazandaran University of Medical Sciences, Sari,Iran Email: [email protected]  Definitions Antibody: Glycoproteins found in vertebrates that are produced in response to foreign structures known as antigens. Antigen: Substances that trigger the production of antibodies and are recognized by them.  Detection of Antibodies in Human Serum Serum Protein Electrophoresis (SPE) is a laboratory technique used to separate proteins in serum based on their size and charge. It helps in diagnosing various conditions by analyzing the protein patterns. Antibodies are typically found in the gamma globulin fraction of the serum, which is one of the key components separated during electrophoresis.  Production of Antibody ✓After stimulation, B cells differentiate into plasma cells, & secrete antibodies,(immunoglobulins), mediators of humoral immunity.  Antibody Gamma globulin proteins that react specifically with antigen that stimulated their production. 20% of plasma protein. Five classes of antibodies: o IgG, IgM, IgA, IgD, and IgE (based on differences in heavy chains)  Structure of Antibody Antibodies, have a Y-shaped structure consisting of four polypeptide chains: o two heavy chains and two light chains. o These chains are linked by disulfide bonds, providing stability. 1. Variable Region: The tips of the Y are the variable regions, which bind to specific antigens. 2. Constant Region: The stem of the Y is the constant region, which determines the antibody's class and its role in the immune response. Structure of Antibody  Definitions of Fc and Fab Regions One part of the antibody, the antigen binding fragment (Fab), recognizes the antigen, the other part of the antibody, known as the crystallizable fragment (Fc), interacts with other elements of the immune system  Antibody-Binding Site Within the variable domains are three regions of extreme variability. These are referred to as the hypervariable regions. These regions of the variable domains actually contact the antigen. They therefore make up the antigen- binding site. These regions are also called the complementarity-determining regions, or CDRs.  Variable Regions of Antibodies Complementarity Determining Regions (CDRs) CDRs in the Light Chain CDRs in the Heavy Chain Binding of an antigen by an antibody Flexibility of antibody molecules via Hinge region Enzymatic Digestion of Antibodies 13  Membrane-bound and Secreted Antibodies Membrane-bound antibodies are essential for the activation of B cells upon binding to specific antigens. This interaction triggers B cell proliferation and differentiation. Types of Heavy and Light Chains in Antibodies Heavy Chains Light Chains Gamma (γ)  Kappa (κ) Alpha (α)  Lambda (λ) Mu (μ) Epsilon (ε) Delta (δ) Classes and Subclasses of Immunoglobulins Classes Heavy chain Subclasses γ1 (IgG1) γ2 (IgG2) IgG γ γ3 (IgG3) γ4 (IgG4) IgM µ none 1 (IgA1) IgA  2 (IgA2) IgD δ none IgE  none  Immunoglobulin G ( IgG) Most abundant antibody in serum Most important antibody in secondary immune response Provides long-term immunity.  IgG 75% of total immunoglobulins. 4 subclasses: IgG1, IgG2, IgG3 & IgG4 Major Antibody of secondary response, found in serum & body fluids. Only maternal Ig to be transported across placenta natural passive immunity in newborn. Participates in complement fixation, precipitation & neutralization of viruses & toxins. 18  IgG Subclasses IgG1 IgG2 IgG3 IgG4 Half-life (day) 21-23 21-23 7 21-23 Percentage / Total IgG 60-70% 14-20% 4-8% 2-6% MW (×103) 146 146 170 146 Binding to Staphiloccocal Protein A + + - + Placental Transfer + +/- + + FcR Binding ++ +/- ++ + Complement Fixation (classic) ++ + +++ -  Immunoglobulin M (IgM) First secreted antibody in immune response Most important cell-surface antibody  IgM 5-8 % of serum immunoglobulins. Pentameric structure. Predominant in primary immune response. Earliest antibody synthesized by fetus. Not transported across placenta. Presence of IgM in newborn indicates intra uterine infection.  Immunoglobulin A (IgA) More produced than other classes Found in mucosal areas and secretions (e.g., saliva, tears, breast milk). Provides mucosal immunity.  IgA 2nd most abundant antibody: 10-13 % Major antibody in colostrum, saliva, tears & other body fluids. Two forms : IgA1 & IgA2. Secretory IgA in dimeric form ¡V composed of 2 basic chain units, a J chain & the secretory component. Secretion of IgA Molecules into the Gut  Immunoglobulin E (IgE) Involved in allergic reactions Defense against parasitic infections  IgE Low levels in serum. On surface of mast cells & basophils which have specific receptors for Fc portion of IgE. Produced in linings of respiratory & intestinal tracts. Causes anaphylactic type of hypersensitivity. Defense against parasitic infections.  Immunoglobulin D ( IgD) Functions mainly as a B cell receptor. Have a Transmembrane region  Functions of antibodies I. Neutralize toxins and viruses. II. Opsonize microbes to be easily phagocytosed. III. Antibody dependent cell-mediated cytotoxicity (ADCC). IV. Activate Complement, and prevent attachment of microbes to mucosal surfaces. V. Complement dependent cytotoxicity (CDC). Functions of antibodies  Fc receptors  These are protein receptors expressed on the surface of various cells that recognize the Fc region of antibodies. The binding of antibodies to these receptors induces various functions. Thanks