HLA-C ligands differentially affect frequencies but not expression levels of cognate KIR in donors with group A and group B haplotypes. (A) The cohort was divided into 4 genetic subgroups: donors with group A (A/A) haplotypes (n = 68), donors with group B (A/B and B/B) haplotypes (n = 82), donors with genotype 2 (KIR2DL2⁺; n = 23), and donors with group B haplotypes lacking KIR2DL2 (n = 13). In panels A through D, the frequency of NK cells expressing KIR2DL1 or KIR2DL2/3 is separately shown for the 3 subgroups of HLA-C ligands. Results are shown as stapled bars with overall frequency of NK cells expressing a given KIR () and frequency of single-positive NK cells, that is NK cells expressing a given KIR without coexpression of any other detectable KIR or NKG2A (). Results represent mean and an error bar represents SD. Statistical significance was determined by ANOVA at *P < .05, **P < .01, ***P < .001) and is shown for single-positive KIR frequencies.