Evidence of CCR2-independent transmigration of Ly6Chi monocytes into the brain after permanent cerebral ischemia in mice

• Effect of CCR2 inhibition in a mouse model of permanent middle cerebral artery occlusion.
• No inhibition by INCB3344 on Ly6Chi monocyte infiltration after permanent ischemia, unlike in transient ischemia.
• Possible CCR2-independent transmigration of Ly6Chi monocytes after permanent cerebral ischemia.

Previously we showed that INCB3344, a CCR2 antagonist, inhibits transmigration of Ly6Chi monocytes into the brain after ischemia-reperfusion. Here we tested the effect of CCR2 inhibition during permanent cerebral ischemia. Mice were administered either vehicle (dimethyl sulfoxide/carboxymethylcellulose) or INCB3344 (30 or 100 mg/kg IP) 1 h before middle cerebral artery occlusion and at 2 and 6 h after the initiation of ischemia. After 24 h, we assessed functional outcome, infarct volume and quantified immune cells in blood and brain. The increase in circulating bone marrow-derived Ly6Chi monocytes, but not the infiltration of those cells into the brain, was blocked by the CCR2 antagonist. INCB3344 had no effect on either neurological deficit or infarct volume. Our data confirm that cerebral ischemia triggers a CCR2-dependent increase in circulating Ly6Chi monocytes, but suggest that in the absence of reperfusion these cells may transmigrate into the ischemic brain in a CCR2-independent manner.