MICROANATOMY

Detailed explanation-1: -IgM is specialized to activate complement efficiently upon binding antigen. IgG antibodies are usually of higher affinity and are found in blood and in extracellular fluid, where they can neutralize toxins, viruses, and bacteria, opsonize them for phagocytosis, and activate the complement system.

Detailed explanation-2: -About 2000 IgG antibody molecules were required to form a Cl-fixing site on the guinea pig erythrocyte surface. 60 IgM complement-fixing sites per erythrocyte were required for the immune clearance of IgM-sensitized erythrocytes. This number of sites could be detected by a direct agglutination test.