Analysis of Fc Receptors for IgG on Guinea Pig Peritoneal Macrophages by the Use of a Monoclonal Antibody to One of the Fc Receptors1

Abstract

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, VJA2 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 IgGi 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 ovalbumin-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 (FcR₁,₂) binds monomeric IgG1 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 FcR₁,₂. When FcR₁,₃ was isolated by affinity chromatography on F(ab′)₂ of VJA2 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 FcR₁,₂ per macrophage cell was estimated to be 2×l0⁵ by measuring the binding of ¹²⁵I-Fab′ of VIA2 IgG1.