NKG2C⁺ NK cells are predominantly KIR⁺ and education through self-KIR are required for robust IFNγ production. (A) NKG2C⁺ (black bars) and NKG2C⁻ (white bars) NK cells were gated as being KIR⁺ based on staining with a cocktail of Abs against CD158a/h, CD158b/j, and CD158e. Bars represent the means ± SEM. NKG2C⁺ cells were compared with NKG2C⁻ samples using the paired t test. *P ≤ .05, **P < .01, and ***P < .001. (B) NKG2C⁺ NK cells were gated as being either KIR⁺ or KIR⁻ and IFNγ production was measured after incubation in either medium alone (not shown) or with K562 cells for 5 hours. Bars represent the means ± SEM. KIR⁺ cells were compared with KIR⁻ samples using the paired t test. *P ≤ .05, **P < .01, and ***P < .001. (C) Single KIR⁺ NKG2C⁺ NK cells were grouped as expressing either self-KIR (black bars) or nonself KIR (white bars) based on the recipient KIR ligand status (left panel). IFNγ production was measured after incubation in either medium alone (not shown) or with K562 cells for 5 hours. Bars represent the means ± SEM. Self-KIR⁺ cells were compared with non-self-KIR⁺ samples using the Student t test. Bars represent the means ± SEM. **P < .01.