Inhibition through Bw4-expressing HLA-A alleles can be reversed by addition of anti-KIR3DL1. Clone C3 from donor 4 expressing the low allele KIR3DL1*005 was tested in a 4-hour 51Cr release cytotoxicity assay against the class I–negative cell line (721.221), a Bw6 control (HLA-B*0801; Table 2), a Bw4 control (HLA-B*2705; Table 2), and targets expressing one of the 4 Bw4-expressing HLA-A alleles: A23, A24, A25, and A32 (Table 2). KIR3DL1 was blocked with either anti-KIR3DL1 antibody (DX9; □) or isotype control (IgG1; ■). Clone C3 lysed both 721.221 and the Bw6 control, and inhibition was not enhanced by anti-KIR3DL1 antibody. Clone C3 was inhibited by the Bw4 control and the A24 A23, and A32 targets, and this inhibition was reversed by addition of anti-KIR3DL1 antibody. Clone C3 lysed the A25 target and the anti-KIR3DL1 antibody only weakly enhanced specific lysis. Error bars represent SEM.
