THE BW4 PUBLIC EPITOPE OF HLA-B MOLECULES CONFERS REACTIVITY WITH NATURAL-KILLER-CELL CLONES THAT EXPRESS NKB1, A PUTATIVE HLA RECEPTOR

Although inhibition of natural killer (NK) cell-mediated lysis by the class I HLA molecules of target cells is an established phenomenon, knowledge of the features of class I molecules which induce this effect remains rudimentary. Using class I alleles HLA-B(*)1502 and B(*)1513 which differ only at residues 77-83 which define the Bw4 and Bw6 serological epitopes, we tested the hypothesis that the presence of the Bw4 epitope on class I molecules determines recognition by NKB1(+) NK cells. HLA-B(*)1513 possesses the Bw4 epitope, whereas B(*)1502 has the Bw6 epitope. Lysis by NKB1(+) NK cell clones of transfected target cells expressing B(*)1513 as the only HLA-A, -B, or -C molecule was inhibited, whereas killing of transfectants expressing B(*)1502 was not. Addition of an an anti-NKB1 monoclonal antibody reconstituted lysis of the targets expressing B(*)1513, but did not affect killing of targets bearing B(*)1502. The inhibitory effect of B(*)1513 could be similarly prevented by the addition of an anti-class I monoclonal antibody. These results show that the presence of the Bw4 epitope influences recognition of HLA-B molecules by NK cells that express NKB1, and suggest that the NKB1 molecule may act as a receptor for Bw4(+) HLA-B alleles. Sequences outside of the Bw4 region must also affect recognition by NKB1(+) NK cells, because lysis of transfectants expressing HLA-A(*)2403 or A(*)2501, which possess the Bw4 epitope but are in other ways substantially different from HLA-B molecules, was not increased by addition of the anti-NKB1 antibody. Asparagine 86, the single site of N-linked glycosylation on class I molecules, is in close proximity to the Bw4/Bw6 region. The glycosylation site of the Bw4-positive molecule B(*)5801 was mutated, and the mutant molecules tested for inhibition of NKB1(+) NK cells. Inhibition that could be reversed by addition of the anti-NKB1 monoclonal antibody was observed, showing the presence of the carbohydrate moiety is not essential for class I recognition by NKB1(+) NK cell clones.