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n. Abbr. IgM
1. The class of antibodies that are the first to appear after initial exposure to an antigen and that function to activate the complement system, promote phagocytosis of pathogens, and neutralize toxins. IgM antibodies are composed of five identical subunits and are found chiefly in the blood.
2. An antibody of this class.
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|Noun||1.||immunoglobulin M - one of the five major classes of immunoglobulins; involved in fighting blood infections and in triggering production of immunoglobulin G|