Comparison of C1q-receptors on rat microglia and peritoneal macrophages

A comparison of the expression and ligand specificity of the C1q (first com plement component) receptor on rat microglia and peritoneal macrophages was made. This revealed that radiolabelled C1q was competed from the peritonea l macrophages with intact C1q, and additively displaced by calf-skin collag en and purified C1q globular heads, suggesting the presence of at least two receptors. This was in contrast to microglia, where radiolabelled C1q was displaced with intact C1q and to a modest degree with collagen, but not wit h globular heads. Taken together, this implies that under these conditions, peritoneal macrophages and microglia both express a C1q receptor which bin ds to the collagen-like region, and that peritoneal macrophages additionall y express a molecule which binds to the globular head of C1q. Analysis of t he ligand bound by these cells reflected the differences observed in the co mpetitive binding experiments, with the novel identification of naturally-o ccurring peptides from the globular head of C1q bound to the peritoneal mac rophages, but not the microglia. (C) 1999 Elsevier Science B.V. All rights reserved.