Rate of Interaction of IgG1 and IgG3 Sensitized Red Cells with Monocytes in the Phagocytosis Assay

Another aspect of the preferential binding to monocytes of IgG3-coated erythrocytes over IgG1-coated erythrocytes has been demonstrated by measuring the rate of interaction in the phagocytosis assay. Erythrocytes sensitized with comparable numbers of IgG1 and IgG3 monoclonal and polyclonal anti-D antibodies were incubated with a monocyte preparation for up to 2 h. Interaction with the erythrocytes sensitized with monoclonal or polyclonal IgG3 was much more rapid than with erythrocytes sensitized with IgG1. With IgG3-sensitized erythrocytes maximum interaction was found after 30 min, whereas with IgG1-sensitized erythrocytes 2 h were required for maximum interaction. These results are consistent with the longer hinge region of IgG3 allowing bridges to be formed more easily between the negatively charged erythrocytes and monocytes.