A new Fc receptor on mouse macrophages binding IgG3

Abstract

Monoclonal antibodies to sheep erythrocytes (SRBC) have proved useful in identifying two Fc receptors on mouse macrophages, one for IgG2(a), and one for IgG1 and IgG2(b). We have used monoclonal IgG3 anti-SRBC to identify a third Fc receptor on mouse macrophages which binds IgG3 uniquely. This receptor is present on primary resident and thioglycolate-induced peritoneal macrophages and on some macrophage cell lines. The binding of IgG3-coated SRBC is inhibited by aggregated but not monomeric IgG3, and not by IgG1, IgG2(a), and IgG2(b) aggregates. It is unaffected by treating the macrophages with trypsin or cytochalasin B and occurs at both 4° and 37°C. IgG3, like all other IgG subclasses, mediates phagocytosis. We have also generated a variant macrophage line which bears the receptors for IgG1 and IgG2(b) and for IgG2(a), but not for IgG3.