Level of Bw4 expression does not correlate with percentage of CD107a expression induced on KIR3DL1⁺ NK cells. Each Bw4⁺ target cell was stained with an anti-Bw4 mAb to detect Bw4 expression. The mean channel fluorescence (MCF) for each target was plotted against the percentage of CD107a⁺ NK cells induced by the target on NK cells with a high-expression KIR3DL1 receptor, averaged across the 4 NK-cell donors. Target A25 did not stain with the Bw4 mAb and does not inhibit NK-cell cytotoxicity. Target B51, which weakly inhibited NK-cell cytotoxicity, has lower expression of Bw4 than the other Bw4-expressing alleles. However, the B13 target, which also weakly inhibited NK-cell cytotoxicity, expressed levels of Bw4 comparable with most Bw4⁺ targets. After excluding the A25 and B51 targets, there was no significant correlation between percentage of KIR3DL1⁺ cells expressing CD107a and Bw4 expression on the target cell (r = −0.13; P = .68).