Antibody-dependent cellular cytotoxicity (ADCC) was demonstrated against strain-2 guinea pig line-10 hepatocarcinoma cells by using syngeneic mineral oil-induced peritoneal exudate cells and rabbit antibodies to line-10 cells (anti-10). Cytotoxicity was dependent on the amount of anti-10 sera or IgG used. F(ab′)2 of rabbit anti-10 IgG was not active and cytotoxicity could be inhibited by addition to the assay of aggregated human IgG or of heat-killed Staphylococcus aureus containing protein A. Rabbit antibodies that were eluted from an immunoadsorbent to which antigens derived from line-10 cells were coupled mediated ADCC, whereas antibodies isolated similarly from an immunoadsorbent to which antigens drived from another syngeneic tumor, line-1, were coupled had little activity.
When 51 syngeneic sera from line-10 tumor-resistant guinea pigs were tested, a broad range of activity was observed and a large proportion of sera mediated ADCC. Immune sera were obtained from animals rendered tumor resistant by several different protocols, and it appeared that the method used to immunize animals influenced the level of ADCC observed. Sera from 44 normal guinea pigs had considerably less activity. Line-10-resistant guinea pig serum antibodies eluted from a line-10 immunoadsorbent mediated ADCC, whereas eluates of the same serum eluted from a line-1 immunoadsorbent had no activity. These data suggested that syngeneic line-10-specific antibodies in sera of tumor-resistant guinea pigs as well as rabbit anti-10 were capable of mediating ADCC in vitro.