Expression patterns of NKG2A, CD57, and KIRs on CD56^dim NK cells. (A) Identification of NK cells and representative stainings for expression of the 4 major inhibitory KIRs. (B) Representative staining for expression of CD57 and NKG2A on NK-cell subsets defined by expression of 0, 1, 2, 3, or 4 KIRs. (C) Relative distribution of CD57- and NKG2A-expressing cells within NK-cell subsets defined by expression of 0, 1, 2, 3, or 4 KIRs on CD56^dim NK cells from 38 individuals homozygous for the group A KIR haplotype (n = 38; mean ± SEM). (D) Frequencies of NK cells from adult individuals (n = 29) and cord blood (n = 11) expressing 0-4 KIRs (***P < .001; mean). (E) Representative staining of CD57 on NK cells from one cord blood specimen. (F) Correlation between frequency of KIR-negative NK cells and expression of CD57 (n = 66). (G) NK cells were FACS sorted based on expression of CD57 and KIRs into the indicated subsets, stimulated for 5 days with IL-2, and then assessed for the expression of CD57 (n = 6; one representative example is shown).