THE LY-49D RECEPTOR ACTIVATES MURINE NATURAL-KILLER-CELLS

Proteins encoded by members of the Ly-49 gene family are predominantly expressed on murine natural killer (NK) cells. Several members of thi s gene family have been demonstrated to inhibit NK cell lysis upon rec ognizing their class I ligands on target cells. In this report, we pre sent data supporting that not all Ly-49 proteins inhibit NK cell funct ion. Our laboratory has generated and characterized a monoclonal antib ody (mAb) (12A8) that can be used to recognize the Ly-49D subset of mu rine NK cells. Transfection of Cos-7 cells with known members of the L y-49 gene family revealed that 12A8 recognizes Ly-49D, but also cross- reacts with the Ly-49A protein on B6 NK cells. In addition, 12A8 demon strates reactivity by both immunoprecipitation and two-color now cytom etry analysis with an NK cell subset that is distinct from those expre ssing Ly-49A, C, or G2. An Ly-49D(+) subset of NK cells that did not e xpress Ly-49A, C, and G2 was isolated and examined for their functiona l capabilities. Tumor targets and concanovalin A (ConA) lymphoblasts f rom a variety of H2 haplotypes were examined for their susceptibility to lysis by Ly-49D(+) NK cells. None of the major histocompatibility c omplex class I-bearing targets inhibited lysis of Ly-49D(+) NK cells. More importantly, we demonstrate that the addition of mAb 12A8 to Ly-4 9D(+) NK cells can augment lysis of Fc gamma R(+) target cells in a re verse antibody-dependent cellular cytotoxicity-type assay and induces apoptosis in Ly-49D(+) NK cells. Furthermore, the cytoplasmic domain o f Ly-49D does not contain the V/Ix-YxxL immunoreceptor tyrosine-based inhibitory motif found in Ly-49A, C, or G2 that has been characterized in the human p58 killer inhibitory receptors. Therefore, Ly-49D is th e first member of the Ly-49 family characterized as transmitting posit ive signals to NK cells, rather than inhibiting NK cell function.