NKG2A and KIR expression distinguishes populations of CD56^dim NK cells. PBMCs were enriched for NK cells using a negative immunomagnetic bead depletion strategy. A representative example of a 4-color analysis shows gating of (A) CD56^bright and CD56^dim cells and analysis of the expression of NKG2A and KIR (using a cocktail of EB6, GL183, and DX9 mAbs) on (B) CD56^bright and (C) CD56^dim cells. Each of the 4 subpopulations shown in panel C was sorted and then analyzed by Q-RT-PCR for the expression of (D) KIR exhibiting variegated expression (vr) (n = 33 reactions), (E) KIR2DL4 (n = 6), (F) NKG2A (n = 7), (G) NKG2D (n = 7), and (H) NKG2E (n = 7). The numbers of NKG2 and KIR2DL4 transcripts in each subpopulation are compared with the positive control of IL-2 activated NK cells to give a relative expression. For comparison of vrKIR expression in the 4 subpopulations, the data for each KIR were normalized to those of the NKG2A⁺KIR⁺ (designated by a †). These values were used to calculate a mean relative expression for the activating (KIR2DS1–3, 2DS5, 3DS1) and inhibitory (KIR2DL1–3, 2DL5, 3DL1, 3DL2). When a KIR was not expressed in the NKG2A⁺KIR⁺ population, indicating absence of the gene, it was excluded from the calculation of mean relative expression. Error bars indicate SEM.