Antibodies against Fc receptors to aggregated IgG of mouse spleen cells: selective blocking of the receptors of splenocytes and peritoneal macrophages, and abolition of the phagocytosis enhancement produced by the opsonizing IgG antibodies.

The Fc receptors to aggregated IgG of mouse spleen cells were solubilized with Nonidet P-40, absorbed by immune precipitate, and the complex obtained was used to raise anti-Fc receptor antibodies in a rabbit. The antibody and its F(ab')2 fragment inhibit binding of heat-aggregated IgG with mouse spleen cells and peritoneal macrophages. When F(ab')2 from the anti-Fc receptor antibody was absorbed exhaustively with mouse peritoneal macrophages, it still partially inhibited the reaction between aggregated IgG and mouse spleen cells devoid of the adherent cells. These data indicate that the Fc receptors to aggregated IgG which are located on the surface of splenocytes and peritoneal macrophages carry both common and private antigenic determinants. It was also demonstrated that the pretreatment of the macrophages with Fab' from anti-Fc receptor antibody abolished completely the phagocytosis enhancement produced by the IgG opsonins.