Complement C5a receptor knockout has diminished light-induced microglia/macrophage retinal migration

PURPOSE: The complement system is involved in the pathogenesis of age-related macular degeneration (AMD). Because activated microglia are also associated with AMD, we studied the relationship between complement anaphylatoxin receptors and microglial recruitment. METHODS: We assessed the effect of anaphylatoxin C3a receptor (C3aR) and C5a receptor (C5aR) knockout (KO) on light damage–induced migration of microglia/macrophages into the mouse outer retina via immunofluorescence and real-time quantitative PCR. RESULTS: We found that the mRNA levels of C3, C5, C3aR, C5aR, and two activators of the complement alternative pathway, Cfb and Cfd, were all upregulated after light exposure. Retinal Iba1-positive microglia/macrophages express receptors for C3a and C5a. Light damage increased the number of retinal Iba1-positive cells and the mRNA levels of Iba1. Compared with the wild-type (WT) mice, these increases were attenuated in the C5aR KO mice but not in the C3aR KO mice. CONCLUSIONS: C5aR but not C3aR promoted the recruitment of microglia/macrophages. These divergent properties of complement anaphylatoxins in the light damage model provide a rationale for testing the differential effects of these receptors in additional retinal and neurodegeneration models.