NK cell function reflects CD57 expression, irrespective of age. Bright (CD56brightCD57−), CD57− (CD56dimCD57−),CD57int (CD56dimCD57int) and CD57+ (CD56dimCD57+) NK cell subsets were analyzed for CD107a (A,D,G), CD25 (B,E,H), or IFN-γ (C,F,I) after in vitro culture in medium alone (A-C), with K562 target cells (D-F) or with IL-12 + IL-18 (HCC; G-I). Horizontal bars represent median values, boxes extend from the 25th to the 75th percentile, and whiskers represent the 95th percentiles. There were no significant age-related trends in response within any of the subsets. Asterisks denote statistically significant differences between CD57−, CD57int, and CD57+subsets (P < .001 for all comparisons, Wilcoxon-signed rank).