C‐C Chemokine Receptor Type 5 (CCR5)‐Mediated Docking of Transferred Tregs Protects Against Early Blood‐Brain Barrier Disruption After Stroke

Abstract

Background Despite recent evidence demonstrating a potent protective effect of adoptively transferred regulatory T cells (Tregs) in ischemic stroke, the mechanism for Treg mobilization and activation in the ischemic brain is, remarkably, unknown. This study determines the role of C‐C chemokine receptor type 5 ( CCR 5) in mediating the docking and activation of transferred Tregs in their protection of early blood‐brain barrier disruption after stroke. Methods and Results Adoptive transfer of CCR 5 −/− Tregs failed to reduce brain infarct or neurological deficits, indicating an indispensable role of CCR 5 in Treg‐afforded protection against cerebral ischemia. Two‐photon live imaging demonstrated that CCR 5 was critical for Treg docking at the injured vessel wall, where they interact with blood‐borne neutrophils/macrophages after cerebral ischemic injury. CCR 5 deficiency on donor Tregs deprived of their early protection against blood‐brain barrier damage. Using flow cytometry, real‐time polymerase chain reaction, and immunostaining, we confirmed that the expression of CCL 5, a CCR 5 ligand, was significantly elevated on the injured endothelium after cerebral ischemia, accompanied by CCR 5 upregulation on circulating Tregs. In a Treg‐endothelial cell coculture, CCR 5 expression was induced on Tregs on their exposure to ischemia‐injured endothelial cells. Furthermore, CCR 5 induction on Tregs enhanced expression of the inhibitory molecule programmed death ligand 1, which in turn inhibited neutrophil‐derived matrix metallopeptidase 9. Conclusions These results suggest that CCR 5 is a critical molecule for Treg‐mediated blood‐brain barrier protection and a potential target to optimize Treg therapy for stroke.