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

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 (CCR5) 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 CCR5-/- Tregs failed to reduce brain infarct or neurological deficits, indicating an indispensable role of CCR5 in Treg-afforded protection against cerebral ischemia. Two-photon live imaging demonstrated that CCR5 was critical for Treg docking at the injured vessel wall, where they interact with blood-borne neutrophils/macrophages after cerebral ischemic injury. CCR5 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 CCL5, a CCR5 ligand, was significantly elevated on the injured endothelium after cerebral ischemia, accompanied by CCR5 upregulation on circulating Tregs. In a Treg-endothelial cell coculture, CCR5 expression was induced on Tregs on their exposure to ischemia-injured endothelial cells. Furthermore, CCR5 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 CCR5 is a critical molecule for Treg-mediated blood-brain barrier protection and a potential target to optimize Treg therapy for stroke.