C3AR1 and Alzheimer disease: To gain further understanding of the relationship between microglial C3aR and Aβ, we costained postmortem human AD brain tissues with anti-C3aR and anti–Iba-1 antibodies and found that Iba-1–positive microglia proximal to methoxy-X04–positive plaques displayed much higher C3aR expression compared with microglia distal from the plaques (Figure 1A).