Macrophage colony-stimulating factor enhances the expression of Fc receptors on murine peritoneal macrophages

Experiments were performed to test the postulate that macrophage colony-stimulating factor (M-CSF) modulates the expression of specific membrane structures on mature murine macrophages. Resident peritoneal macrophages were incubated with M-CSF for 48-72 hr and analysed for Fc receptor and Ia antigen expression. M-CSF treatment of macrophages increased the expression of Fc receptors two- to three-fold over that of unstimulated macrophages. The effect was detected at 1 U/ml of M-CSF, with maximal expression between 100 and 500 U/ml. The specificity of the enhancement was indicated by two sets of experiments. Purified rabbit anti-M-CSF IgG, but not normal rabbit IgG, inhibited the M-CSF-mediated Fc receptor enhancement. Also, a highly purified M-CSF preparation, which was essentially free of endotoxin and interferon, was active in these assays. M-CSF augmented both major types of IgG Fc receptors, FcR I (recognizing IgG 2a) and FcR II (recognizing IgG 2b/IgG1). A second membrane marker, the Ia antigen, was induced by recombinant IFN-γ (rIFN-γ) but not by M-CSF. These results indicate that M-CSF is an inducer of two classes of IgG Fc receptors on mature tissue macrophages.