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Medical Definition of Macrophage-activating factor
1. An agent that stimulates macrophages to attack and ingest cancer cells. They are secreted by stimulated lymphocytes that prime macrophages to become non-specifically cytotoxic to tumours. They also modulate the expression of macrophage cell surface ia antigens. One maf is interferon-gamma (interferon type II). Other factors antigenically distinct from ifn-gamma have also been identified. (12 Dec 1998)