The enhanced levels of subset response conferred by receptor coexpression are dampened to various degrees by the combinations of HLA allotypes on target cells. (A) The capacity of 221 transfectant expressing C1 (top subpanel) and Bw4 (bottom subpanel) to inhibit NK cells bearing their cognate KIR2DL2/3 and 3DL1*1502 receptors did not differ between NK cells from donors who have or lack the cognate ligand. The C1 inhibitor was Cw*1202, and the Bw4 inhibitor was B*5801. The results are the means obtained from the following donors: KIR2DL2/3⁺ Cw*07⁺, n = 13; Cw*07⁻, n = 19; C1⁻, n = 6; 3DL1*1502⁺ Bw4⁺, n = 15; Bw4⁻, n = 5. (B) Coexpression of inhibitory MHC class I receptors increases the enhanced IFN-γ response to missing-self, but the effect is attenuated in cells with multiple receptors. The response of NK cells expressing different combinations of receptors (2DL3, 3DL1, and NKG2A) was compared among donors who have the identical A1A1 KIR genotype and both the Bw4 and C1 ligands. Donors having Cw*07 (♦, n = 3) are distinguished from donors lacking Cw*07 (♢, n = 4). (C) NK cells expressing inhibitory receptors for 2 different HLA class I ligands are not fully inhibited by either of the ligands alone. NK cells expressing KIR2DL3 and 3DL1 from Bw4⁻ donors are fully inhibited by C1, whereas 2DL3⁺ 3DL1⁺ cells from Bw4⁺ donors are incompletely inhibited by C1 (top subpanel). Similarly, NK cells expressing KIR2DL3 and 3DL1 from Bw4⁻ donors are fully inhibited by Bw4, whereas 2DL3⁺3DL1⁺ cells from Bw4⁺ donors are incompletely inhibited by Bw4 (bottom subpanel). The C1 inhibitor was Cw*1202, the Bw4 inhibitor was Bw*5801, and the 3DL1 allele was 1502. 5 Bw4⁺ donors and 2 Bw4⁻ donors with the A1A1 KIR genotype were studied. Plots show mean values with the range of variation indicated by the SEM. *P < .05, **P < .005. (D) NK subset responses against allogeneic PHA blasts and 721.221. KIR ligands of 3 group A homozygote donors are shown on the left, and HLA genotypes of PHA blasts are shown at the top of the each panel. Receptor combinations of KIR2DL1, 2DL3, 3DL1, or NKG2A on each NK subset are indicated by the presence of a dotted line in the center of each box; gray shading in the left half of each box indicates presence of a ligand conferring enhancement of missing-self response to a subset; gray shading in the right half of each box indicates presence of the ligand on the target cell that induces inhibition. Length of bar indicates missing-self response as assessed by IFN-γ production. Subset frequencies for each donor are indicated in the far left column. Donor HLA allotypes are: donor 1, HLA-B*07/57, Cw*06/07; donor 2, HLA-B*52/58, Cw*03/12; donor 3, HLA-B*39/40, Cw*07/07.