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Related to immunoglobulin M: immunoglobulin D, immunoglobulin G, immunoglobulin A
immunoglobulin M[‚im·yə·nō‚gläb·yə·lən ′em]
The first immunoglobulin class to appear during the primary immune response; it is mainly contained in the bloodstream, where it can readily neutralize agents attempting to gain entrance through the blood. Abbreviated IgM.