MCQ MAHE 2000 Microbiology Answer 06
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IgG is the only antibody that crosses the placenta. Thus, newborns are born with an adult level of IgG, which gradually disappears over the next few months. They start making their own antibody at 2-3 months of age. IgG is the major antibody of the secondary immune response (i.e., the response that occurs upon re-exposure to a specific antigen), also called the anamestic or memory response.
THE FIVE IMMUNOGLOBULIN CLASSES
- IgG — Most abundant. Involved in secondary immune responses. Fixes complement and crosses the placenta. Important in binding of macrophages and PMNs for phagocytosis. Contains 4 subclasses: IgG 1, IgG 2, IgG 3, and IgG 4.
- IgM — Involved in primary immune response. Consists of 5 subunits linked by disulfide bonds and the J chain. Fixes complement like IgG but does not cross the placenta. Efficiently lyses antigen.
- IgA — Present in mucosal surfaces and exocrine secretions, can exist structurally as either a monomer, dimer, or trimer. Contains the secretory piece that allows secretion across mucous membranes. Deficiency of IgA constitutes the most common primary immunodeficiency.
- IgD - Found in only small quantities in serum. Acts mainly as a surface receptor. Functional role is not completely elucidated.
- IgE — Present in elevated quantities in allergic diseases. Bridging of IgE molecules releases inflammatory mediators characteristic of the immediate hypersensitivity response; i.e. histamine.
Tags: MCQ, Immunology, Immunoglobulins
Category: MAHE 2000 MCQs
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