Enhanced IFNγ production by licensed but not unlicensed ItpkB^−/− NK cells. (A) WT or ItpkB^−/− splenic NK cells were stimulated with plate-bound anti-NK1.1 Abs (5 μg/mL) in the presence of 2μM monensin for 5 hours. IFNγ production was analyzed by intracellular FACS. (B) Splenic NK cells were stimulated with the indicated plate-bound anti-NK1.1 Ab concentrations. IFNγ secretion was normalized to the maximum observed (100%) and is shown as mean ± SEM; n = 5 different experiments. Asterisks denote statistical significance for the indicated comparisons as determined by Student t test: ***P < .001; **P < .01; and *P < .05. (C) IFNγ production by CD11b⁺CD27⁺ versus CD11b⁺CD27⁻ splenic NK cell mature subpopulations stimulated as in panel A. Horizontal bars denote mean ± SEM (n = 5). P values for genotype comparisons were obtained via paired Student t test. (D) Splenic NK cells from WT and ItpkB^−/− mice crossed to a TAP-deficient (MHCI^−/−) background, which lacks licensing self-ligands, were stimulated as in panel A and evaluated for IFNγ production.