Background and purpose: Our previous study found adoptively transferred regulatory T cell (Treg) protected against ischemic stroke via attenuating blood brain barrier (BBB) disruption. Here, we examined the role of CCR5, a chemokine receptor in the Tregs’ recruitment and protection to the ischemic BBB after stroke.
Methods: Transient focal cerebral ischemia was induced in widetype C57/BL6 or CCR5(-/-) mice by unilateral middle cerebral artery occlusion (MCAO) for 60 minutes. Tregs (2x106/mouse) in 200 μl PBS or PBS control were injected intravenously at 2 hours after MCAO. Chemo-attractant migration of Tregs to the ischemic BBB was examined by two photon in vivo imaging and cell migration test in vitro. RT-PCR, Immunofluorescence staining and confocal microscopy were used to assess the chemokine expression, endothelial ICAM-1 expression and peripheral immune cell infiltration following cerebral ischemic injury. In vivo endogenous IgG leakage and in vitro BBB integrity were examined to determine the important role of CCR5 in Tregs’ protection on the ischemic BBB.
Results: We found that cerebral ischemia reduced Treg number in the peripheral but the expression of CCR5 on Tregs in the blood was increased. In the ischemic brain, the expression of CCR5 ligands were significantly upregulated, and the expression of CCL5 co-localized with ischemic brain endothelial cells. Genetic depletion of CCR5 on the donor Tregs significantly impaired the transferred Tregs’ ability to migrate to the ischemic BBB and attenuated Tregs’ protection against BBB disruption and peripheral immune cell infiltration as determined by two photon in vivo imaging, immunofluorescence staining and MMP-9 ELISA. In vitro migration test further revealed that depletion of CCR5 hindered Tregs to migrate across endothelial cell layer.
Conclusions: In conclusion, CCR5 plays an indispensible role in Tregs’ recruitment and protection against ischemic BBB disruption. Therapeutic strategies targeting CCR5 warrants further investigation to improve Treg based cell therapy in stroke treatment.