Cytotoxicity of KIR3DL1⁺ NK clones against target cells with or without expression of Bw4. (A) KIR3DL1⁺ NK clones of both donor 1 expressing Bw4 on HLA-A only and donor 2 expressing Bw4 on HLA-B only are tolerant to autologous target cells. Lysis can be reconstituted in both cases by antibody-blocking of either KIR3DL1 on NK cells or MHC class I on target cells. (B) KIR3DL1⁺ NK clones lyse target cells lacking Bw4 or expressing A*2501, whereas target cells expressing A*2301, A*2402, or A*3201 are protected from lysis, similar to target cells expressing an HLA-B antigen containing the Bw4 epitope (B*5703). Lysis of target cells expressing A*2301/A*2402/A*3201 or B*5703 is reconstituted by antibodies directed against KIR3DL1 or MHC class I but not by control antibody (KIR2DL1). Results of experiments with different target cells expressing the same allele were pooled.