Tumor-associated Cytotoxicity of Autoantibodies in Sera from Rats with Chemically Induced Hepatomas1

Complement-dependent cytotoxicity in tumor bearer sera (TBS) from Wistar rats carrying any of five transplantable aminoazo dye-induced hepatomas (D23, D33, D23/Not, D30, or D202) were investigated by a short-term 51Cr release assay. Extensive tests of various TBS against the hepatomas revealed that the tumors could be divided into two groups. Group 1 hepatomas (D23, D33, and D23/Not) all shared antigens which could induce serum antibodies in syngeneic hosts as shown by complement-dependent cytotoxicity. The Group 2 tumors (D30 and D202) elicited such an immune response occasionally and less efficiently. This immune response was demonstrable only with Group 1 tumors as targets. It was shown that this reactivity was directed against antigens also present in several homogenates made from normal tissues. Furthermore, absorption experiments with viable tumor cells confirmed that the target antigens for the cytotoxic effect of Group 1 TBS were poorly expressed on the Group 2 tumors. In allogeneic sera raised in Dark Agouti rats against the tumors, a similar immune response was detected when the sera were tested against the tumors and Wistar spleen cells. The alloantisera against the Group 1 tumors reacted strongly with tumorassociated antigens as well as with Wistar alloantigens, but no reactivity against the Group 2 tumors was found. In some of the alloantisera against the Group 2 tumors, reactivities against Group 1 tumor antigens as well as against Wistar alloantigens were detected, thus confirming the results obtained with the syngeneic TBS. From these results, it was concluded that the predominant humoral immune response against the tumors detected herein was directed to autoantigens present in all tumors as well as in normal tissues.