Low DNAM-1 expression defines a unique subset of CD56^dimNK cells displaying reduced expression of CD57, inhibitory KIRs, and LFA-1. (A) Representative fluorescence-activated cell sorter staining of healthy donor peripheral blood lymphocytes displaying the gating strategy used to identify NK cells (left) and CD56^brightDNAM-1^pos, CD56^dimDNAM-1^pos, and CD56^dimDNAM-1^neg NK cell subsets (right). Numbers show percentages of the gated populations. (B) Proportions of NK cell subsets defined as in panel A are shown as mean percentage ± standard deviation from 13 healthy donors. (C) Histograms showing DNAM-1 and CD16 expression on the 3 NK cell subsets defined as in panel A; CD56^brightDNAM-1^pos (red histogram), CD56^dimDNAM-1^pos (blue histogram), and CD56^dimDNAM-1^neg (green histogram). (D) Marker expression by NK cell subsets pre- and postovernight stimulation with IL-12 (10 ng/mL), IL-15 (100 ng/mL), and IL-18 (50 ng/mL) is shown as percentages of positive cells or mean fluorescence intensity (MFI). Single data points represent the mean value of duplicate wells. Data are shown as mean ± standard error of the mean (SEM) from 4 to 9 healthy donor samples and were analyzed by using a 2-way ANOVA followed by a Tukey multiple comparisons post hoc test. *P < .05; **P < .01; ***P < .001; ****P < .0001.