K cell activity of murine-cultured lymphocytic leukemic cell line independent of other fc receptor functions

A murine-cultured lymphocytic leukemic cell line, SC-1, showed remarkable cytotoxicity against ⁵¹Cr-labeled rabbit erythrocytes as target cells in the presence of anti-target antibodies in vitro. This cytotoxicity was complement independent, inhibited by the addition of aggregated human γ-globulin, and reduced by pepsin digestion of antitarget IgG. Moreover, SC-1 cells also induced cytotoxicity to trinitrophenyl-modified rabbit erythrocytes in the presence of antitrinitrophenyl antibodies but not to unmodified rabbit erythrocytes used as bystander cells. SC-1 cells which showed such K cell activity, however, escaped from Fc receptor detection by erythrocyte antibody rosettes and FITC-conjugated aggregated human γ-globulin binding. In morphological studies using the scanning electron microscope, SC-1 cells seemed to induce cytotoxicity through a light attachment to target cells via ‘point contact’ of the microvilli. From these findings the characteristics of Fc receptors on effector cells in the mechanism of antibody-dependent cellular cytotoxicity was discussed.