Localization of the IgG effector site for monocyte receptors.

A peptide consisting of 10 amino acids derived from the CH3 region of human IgG was shown to bind to monocytes and to inhibit rosette formation of antibody-coated erythrocytes with human monocytes. Two myeloma proteins of the IgG1 and IgG3 subclass, both with known deletions in the CH2 region of the gamma chain, showed unimpaired ability to bind to monocytes. These experiments suggest that the isolated peptide represents the primary site of attachment of IgG to monocytes.