immunoglobulin M

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immunoglobulin M

n. Abbr. IgM
The class of antibodies found in circulating body fluids and the first antibodies to appear in response to an initial exposure to an antigen.

immunoglobulin M (IgM)

one of the five classes of antibodies produced by the body and the largest in molecular structure. It is found in circulating fluids and is the first immunoglobulin produced when the body is challenged by antigens. IgM triggers the increased production of immunoglobulin G and the complement fixation required for effective immune response. It is the dominant antibody in ABO blood group incompatibilities. The normal concentration of IgM in serum is 40 to 120 mg/dL. Compare immunoglobulin A, immunoglobulin D, immunoglobulin E, immunoglobulin G.

immunoglobulin M

Abbreviation: IgM
An immunoglobulin formed in almost every immune response during the early period of the reaction. IgM controls the A, B, O blood group antibody responses and is the most efficient antibody in stimulating complement activity. Its size prevents it from moving across the placenta to the fetus.
See also: immunoglobulin
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