Constitutive IFNγ production by RMA-H60-exposed NK cells. RMA- (□) and RMA-H60-exposed NK cells (▦) were restimulated with the indicated cell lines or plastic-bound mAbs. The bar graph depicts the mean percentage (± SD) of intracellular IFNγ⁺ NK cells obtained in 4 to 8 independent experiments. Statistical significance of differences between the indicated groups were determined using the 2-tailed Student t test. ^**P < .02; ^***P < .01; NS, not significant; §P < .02 as compared with the corresponding values in the control RMA-exposed group.