Impact of γ-irradiation on NK cell function. Bulk NK cells expanded from the PBMCs of healthy donor KR0350 were γ-irradiated (50 Gy) and tested for cytotoxicity against K562 cells (A) 0, 24, 48, 60, and 96 hours after irradiation. (B) Although irradiation induced NK apoptosis (annexin V–positive) and necrosis (PI-positive), persistent NK cell cytotoxicity was observed up to 48 hours after γ-irradiation. (C) C-G1 homozygous NK cell lines 8-5 from donor KR0350 maintained a high level of cytotoxicity against KIR-incompatible R-EBV-LCL cells 24 hours after 50 Gy γ-irradiation. Mean values +SD of 3 samples are shown.