Antibody-dependent cell-mediated cytotoxic activity in syngeneic moouse ascites tumors

Eight different syngeneic murine ascites tumor preparations were tested for their ability to lyse antibody-coated chicken erythrocytes in an assay for antibody-dependent cell-mediated cytotoxicity (ADCC). All of the tumor preparations demonstrated significant ADCC effector activity, even at effector-cell:target-cell ratios of less than 1:1. In contrast, none of eight in vitro murine tumor-cell lines showed any consistent ability to function as ADCC effector cells. Several cell fractionation experiments were performed to ascertain the nature of the effector cells in the ascites tumors. Adherent cells were removed from tumor preparations by passage of cells over columns of Degalan plastic beads and 19S Fc-receptor-bearing cells were removed by sedimentation of EA rosette-forming cells. Although each of these procedures depleted only a minority of the total cells, all the ADCC activity was simultaneously removed in each case. Depletion of phagocytic cells by treatment of tumor preparations with carbonyl iron and magnetism only slightly diminished the ADCC activity. These results indicate that the ADCC activity associated with ascites tumors is due to effector cells most probably of host origin, but possibly representing an atypical sub-population of tumor cells. The characteristics of the effector cell closely parallel those defined for the major non-phagocytic ADCC effector cell in normal mouse spleen and peritoneal exudate.