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Lecture 6

IMIN200 Lecture 6: IMIN 200 Lecture 6: Antibody Structure and Function

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University of Alberta
Immunology and Infection
Kevin Kane

6. Antibody Structure and Function Tyler Nguyen Lecture 6 – Antibody Structure and Function - Friday, January 20 th Lecture Summary I. B-Cell Origin and Development • bone marrow • naïve B-cells • mature B-cells o B-cell receptors (BCR) o extracellular antigens o antibody production: BCR activation, second signalling II. Antibodies (also called immunoglobulin) III. Antibody Structure • light chains, heavy chains • disulphide bonds • variable (V) region: antigen recognition (specificity) • constant (C) region: structural integrity, effector functions • identical constant regions induce an identical immune response IV. Binding of Antigen by Antibody • epitope • affinity • avidity V. Immunoglobulin Isotypes • IgA: neonatal passive immunity to newborns; J-chain • IgD: function unknown • IgE: mast cell degranulation, allergic reactions o FCε receptor on mast cells • IgG: neutralizes toxins; o FCγ receptor § opsonization; macrophages; MHC II presentation § antibody-dependent cellular cytotoxicity (ADCC); natural killer (NK) cells • IgM: 10 antigen binding sites; complement activation I. B-cell Origin and Development - bone marrow: possess multipotent (or pluripotent? See lecture 7) stem cells that can differentiate into B-lymphocytes or T-lymphocytes • both B-cells and T-cells begin development in the bone marrow o B-cells finish maturing in the bone marrow o T-cells finish maturing in the thymus - naïve B-cells: B-lymphocytes (aka B-cells) that have not encountered an antigen, hence “naïve” (innocent, unexposed, or not knowing) • travel via circulatory pathways into bodily structures (e.g. lymph nodes, spleen, etc.) o if they do not encounter antigens, they continuously recirculate back into the blood until they do, or until they die o when exposed to antigen, they become a mature B-cell - mature B-cells: • possess B-cell receptors (BCR): receptors found on B-cells that detect antigens o each B-cell has a unique BCR → unique antigen specificity • identify presence of only extracellular antigens (not intracellular) • antibody production: o produces antibodies that have identical antigen specificities as the parent naïve cell that produced them o occurs through: § BCR activation: antigen receptor binds to appropriate antigen on found microbe, pathogen, etc. § second signalling: contingent upon receptor-ligand interactions, cytokines, etc. This two-step process initiates the production of soluble antibodies and helps prevent accidental production, aiding in the reliable generation of immune responses. II. Antibodies - antibody: glycoproteins produced by B-cells that are a secreted version of a BCR; also called immunoglobulin • possess a high degree of specificity and affinity to antigens • share identical antigen specificities with the parental naïve cell → target exact same antigen that initially stimulated the BCR • unique from T-cells (e.g., CD8, CDT cells, etc.): o B-cells able to recognize amino acids, lipids, carbohydrates o T-cells only able to recognize protein peptide derivatives III. Antibody Structure - antibodies are made of a number* of polypeptides, consisting of light and heavy chains • *the numbers vary between different types of immunoglobulin • each light chain will be identical to the other light chain on the same antibody; likewise with the heavy chain • the heavy chain is the “backbone” and larger than the light chains - each antibody has: • variable (V) region o unique for each antibody o specificity is solely determined by this region o function: antigen recognition (specificity) • constant (C) region o conserved shared region, common to all clones and all antibodies o
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