Since monocyte-derived macrophages do not persist in the peri-infarct region beyond P8 (34), the effects of genetic manipulation of the C3a/C3aR axis on the peri-infarct density of Iba-1–positive cells 3 weeks after stroke were likely mediated predominantly by microglia migration and/or proliferation in the acute phase. The gene discussed is C3AR1; the disease is stroke disorder.