Purified NK cells were pre-activated with LD15 (control), IL-12+IL-18, or IL-15+IL-18, washed extensively, and re-plated in cytokine-free media for 2 days to allow recovery to a resting state. IL-2 was added at the indicated concentrations for 15 minutes and levels of phospho-STAT5 were analyzed by intracellular flow cytometry. Shown is one representative donor (A), or summary data of the mean ± SEM percentage pSTAT5 positive CD56dim NK cells from n=3 donors and experiments (B). Pre-activated NK cells respond to 10 and 100 pM IL-2 with enhanced STAT5 phosphorylation over control. Significance was calculated by ANOVA.