NK cell function reflects CD57 expression, irrespective of age. Bright (CD56^brightCD57⁻), CD57⁻ (CD56^dimCD57⁻),CD57int (CD56^dimCD57^int) and CD57⁺ (CD56^dimCD57⁺) 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⁻, CD57^int, and CD57⁺subsets (P < .001 for all comparisons, Wilcoxon-signed rank).