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immunoglobulin(Ig)
(im″u-no-glob´u-lin)
a protein of animal origin with known antibody activity; immunoglobulins are major participants in humoral immunity are synthesized by lymphocytes and plasma cells, and are found in the serum and other body fluids and tissues, including the urine, spinal fluid, lymph nodes, and spleen.
(See also immunity.) Each immunoglobulin molecule consists of four polypeptide chains: two heavy chains (H chains) and two light chains (L chains). Differences in the H chains are the basis for the classification of immunoglobulins; the five major classes are IgA, IgD,
IgE, IgG, and IgM.
Schematic representation, using an IgG molecule, of the basic structure of immunoglobulins.
secretory immunoglobulin A
IgA immunoglobulin in which two IgA molecules are linked by a polypeptide (secretory piece) and by a J chain; it is the predominant immunoglobulin.
Copyright 2007. An Elsevier publication. All rights reserved.
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