Antibody-induced augmentation of murine natural killer cell activity

Antibodies reactive with effector cells were shown to augment the cytotoxicity of spleen cells from athymic nude and euthymic mice. The addition of alloantibody to the assay or pretreatment of the effector cells with alloantibody resulted in increased cytotoxicity against the human cell K562, a relatively poor target for spontaneous mouse NK activity. When monoclonal antibodies were tested, cytotoxicity was markedly increased by some antibodies, such as anti-H-2, anti-la, and anti-Thy 1.2, while others had no effect. The degree of augmentation of cytotoxicity was dependent on the concentration of antibody added. Nylon-wool-nonadherent nu/nu splenic effector cells mediated the antibody-induced cytotoxicity and anti-asialo GMI plus complement abolished activity, indicating that the cells mediating the cytotoxicity were NK cells and not mature T cells, B cells or macrophages. When spleen cells from mice having different levels of NK activity were evaluated in this system, the magnitude of augmentation by antibody correlated with the level of spontaneous NK activity and no increased cytotoxicity was found with cell populations that had low spontaneous NK activity. Testing a panel of target cells, showed that certain human and mouse cell lines, with low to moderate susceptibility to spontaneous NK activity, were sensitive to antibody-induced NK-cell-mediated cytotoxicity whereas others were completely resistant. Both Fc-IgG receptor-positive and -negative cell lines were susceptible target cells. These results indicate that antibodies reactive with murine NK cells can increase their cytolytic activity.