CX3CR1 and Cerebral ischemia: In the wild type parabiotic partner, CX3CR1GFP/+ infiltrating cells started to populate the brain 5 days after ischemia onset, were less numerous than activated microglia and did not proliferate, suggesting that microglia and monocyte-derived CX3CR1 macrophages are two distinct populations with presumably different roles in cerebral ischemia.