Analysis of Fc Receptors for IgG on Guinea Pig Peritoneal Macrophages by the Use of a Monoclonal Antibody to One of the Fc Receptors

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The variety and properties of Fc receptors (FcR's) for homologous IgG on guinea pig peritoneal macrophages were investigated with the use of a mouse monoclonal antibody, VIA2 IgG1, prepared by fusion of splenic cells of a mouse immunized with guinea pig macrophages with a mouse myeloma cell line. VIA2 IgG1 completely inhibited the formation of macrophage rosettes with IgG1 antibody-sensitized erythrocytes, but not that with IgG2 antibody-sensitized erythrocytes. The Fab' of VIA2 IgG1 also completely inhibited the bindings of both monomeric and ovalbu-min-bound IgG1 antibodies to macrophages. On the other hand, the Fab' did not affect the binding of monomeric IgG2 antibody to macrophages, although it partially inhibited that of ovalbumin-bound IgG2 antibody. These results show that at least two distinct types of FcR are present on guinea pig macrophages; one (FcR_{1, 2}) binds monomeric IgGI antibody and also antigen-bound IgG1 and IgG2 antibodies, and the other (FcR₂) binds monomeric and antigen-bound IgG2 antibodies alone, and also that VIA2 IgG1 binds specifically to FcR_{1, 2}.
When FcR_{1, 2} was isolated by affinity chromatography on F(ab')₂ of VIA2 IgG1 coupled to Sepharose, it gave a main band with a molecular weight of 55, 000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which was indistinguishable from the main band isolated with the IgG1 immune complex. The number of FcR_{1, 2} per macrophage cell was estimated to be 2×10⁵ by measuring the binding of ¹²⁵I-Fab' of VIA2 IgG1.