Receptors for IgG complexes activate synthesis of monocyte chemoattractant peptide 1 and colony-stimulating factor 1

The chemotactic factors responsible for complement-independent macrophage accumulation in immune-complex diseases such as glomerulonephritis remain unknown. Fc receptors for IgG complexes are found on mesangial cells of the kidney, which produce the macrophage growth factor colony-stimulating factor 1 (CSF-1). We therefore investigated the possible stimulation of mesangial- cell expression of CSF-1 and the recently identified monocyte-specific chemoattractant protein 1 (MCP-1) by IgG complexes. IgG complexes, but not monomeric IgG or F(ab')₂ fragments of IgG, rapidly (2-8 h) increased mRNA for both CSF-1 (10-fold) and MCP-1 (20-fold) in cultured mouse mesangial cells. The increase of mRNA for CSF-1 and MCP-1 was not reduced by either cytochalasin B or D, indicating that Fc receptor occupancy is sufficient for signaling and that phagocytosis is not required to elicit this response. IgG complexes also caused a 10-fold increase in the secretion of CSF-1 and a 3- to 5-fold increase in secretion of MCP-1 into the cell culture medium. The synthesis and release of CSF-1 and MCP-1 by mesangial cells as a consequence of Fc receptor occupancy may be responsible for macrophage recruitment and activation at sites of immune-complex deposition.