Studies on properties of guinea pig peritoneal macrophage Fc receptor.

Properties of guinea pig peritoneal macrophage Fc receptor for IgG are described. It was found that the receptor was binding both monomeric and aggregated rabbit IgG. The values of apparent affinity constants were 2.6 +/- 0.6 x 10(8) M-1 and 3.84 +/- x 10(8) m-1 for IgG monomers and aggregates, respectively. The number of monomeric IgG molecules bound was calculated to be 3.3 +/- 0.2 x 10(5) per cell and of aggregated IgG 3.95 +/- 0.12 x 10(5) per cell. When the homologous system: guinea pig IgG2 and guinea pig macrophages was investigated, the affinity constant found was 1.66 +/- 0.45 x 10(8) M-1 and 2.6 +/- 0.24 x 10(5) molecules of IgG were bound per cell. Both, rabbit IgG and, guinea pig IgG2, interacted wih the same receptor binding sites on macrophages. Treatment of macrophages with 2-mercaptoethanol, formaldehyde, and iodoacetamide was without any effect on the IgG binding properties of cells. Periodate, trypsin, pronase, phospholipase C considerably diminished the number of IgG molecules bound to macrophages. Treatment of macrophages with neuraminidase increased the number of IgG molecules bound per cell. The results obtained suggests that both sugar and protein components are important for the IgG binding activity of guinea pig peritoneal macrophages. Studies on the effect of pH, ionic strength, and temperature on the interaction of macrophages with IgG showed that electrostatic interactions are important for binding of IgG to the macrophage Fc receptor.