Given that the protective effect of IL-21R was more evident in permanent middle cerebral artery occlusion (pMCAO) than in tMCAO, and T lymphocytes infiltration, which was the source of IL-21, was obvious in tMCAO while poor in pMCAO, the reason for the difference above may be the source of IL-21 and IL-21R, resident or infiltration, and maybe also related to a collateral-independent effect on cerebral injury (78). Here, IL21R is linked to cerebral artery occlusion.