Key role for PLC-γ2 in NK cell cytotoxicity. (A) Fresh splenocytes from WT (▪) but not Plcg2^-/- (○) mice were spontaneously cytotoxic toward YAC-1 cells at the indicated NK/target ratios. Data are the mean ± SD of triplicates from one representative of 4 independent experiments. (B) IL-2-activated splenocytes from WT (▪, 2 individual mice) but not Plcg2^-/- mice (○, 2 individual mice) were cytotoxic toward YAC-1, RMA, RMA-S, and RMA-Rae1γ cells at the indicated NK/target ratios. Data are the mean ± SD of triplicates of one representative of 5 independent experiments. (C) IL-2-activated CD3^-NK1.1⁺ purified NK cells were coated with anti-NK1.1 and tested in redirected ADCC against P815 targets. WT (▪) but not Plcg2^-/- (○) NK cells were cytotoxic toward P815 at the indicated NK/target ratios. Data are the mean ± SD of 2 to 4 experiments. (D) Cells were prepared as described and coated with the indicated antibodies prior to redirected ADCC toward P815 targets. Data are from one representative of 2 independent experiments that gave similar results. In all experiments, NK/target ratios were calculated based on actual CD3^-NK1.1⁺ NK cell numbers, as measured by cell counts and flow cytometry prior to the assays.