A new monoclonal antibody reactive with several Ly49 NK cell receptors mediates redirected Lysis of target cells

We produced a novel hamster monoclonal antibody (MAb), 14B11, that recogniz es the majority of mouse natural-killer (NK) cells. Transfection studies de monstrated that 14B11 MAb binds a subset of Ly49 receptors, including three putative inhibitory receptors, Ly49F, I, and C, No binding to Ly49A, B, D, or G was detected, In addition, 14B11 was shown to bind the putative activ ating receptor Ly49H, which required co-transfection of the signaling molec ule DAP12 for detectable cell surface expression. Thus, 14B11 is the first reported MAb to bind Ly49H and F, At the functional level, 14B11. MAb enhan ced the lysis by IL-2 activated NK cells of an FcR(+) target cell line (Dau di), but not an FcR(-) target cell (EL-4), Because F(ab')(2) fragments of 1 4B11 failed to enhance lytic activity, the enhancement of lysis by intact a ntibody is apparently due to "redirected lysis," in which stimulatory recep tors on the NK cell are bridged by antibody to Fc receptors on the target c ell. Cell separation experiments demonstrated that the 14B11-dependent redi rected lysis was markedly increased using NK cell populations that had been depleted of Ly49F,(+) I,(+) or C+ NK cells, Because such depletions are ex pected to enrich for Ly49H(+) NK cells, these results suggest that the enha ncement of lysis mediated by 14B11 MAX, may be due to stimulation of the ac tivating Ly49H receptor. In conjunction with other anti-Ly49 MAbs, the 14B1 1 MAb will be useful in further studies of Ly49 receptor function and speci ficity.