NK cells participate in cerebral ischemia. (A,B): NK cells stained brown in ischemic tissues (magnification, 400×). Differences between the ischemic (A) and non-ischemic (B) hemispheres were significant for the 2 to 5 day group, and were fewer in the non-ischemic hemispheres; (C): Infiltration of NK cells into human ischemic tissue. The highest number of NK cells were detected in the 2 to 5 day group; (D,E): NK cells in mouse ischemic tissue penumbra. NK positive cells (FITC) were found in ischemic tissues (D) (bar = 30 μm); (F): Infiltration of NK cells detected in mouse ischemic tissue by FACS; (G): Of the infiltrating lymphocytes detected, the percentage of NK cells is reported; (H): After NK cells depletion in vivo, infiltration of NK cells detected in mouse ischemic tissue by FACS; (I): Representative TTC-stained sections of NK cells depletion mouse at 12 hours following pMCAO. (*P < 0.05, **P < 0.01, ***P < 0.001, compared with the corresponding values for the contralateral hemispheres). pMCAO, permanent middle cerebral artery occlusion.