Abstract
Cloned tumor‐cell lines were derived from two antigenically distinct ascites variants of diethylnitrosamine‐induced guinea‐pig hepatomas (designated line 1 and line 10). Cell‐surface antigens on the ascites and in vitro‐grown tumor cells were analyzed with immunofluorescence, C1 fixation and transfer, and antibody‐complement‐mediated cytotoxicity tests. Tumor‐specific and Forssman antigens continued to be expressed during 3–6 months of in vitro cultivation. Differences between ascites and cultured cells were noted in the degree of antigen expression and sensitivity to antibody‐complement‐mediated cytotoxicity. Cells grown in vitro exhibited a greater number of Forssman and tumor‐specific antigen sites than in vivo grown cells as determined by the quantitative C1 fixation and transfer test. Immunofluorescent staining indicated that some cloned lines were considerably more homogeneous in terms of antigen expression than were the cultured, non‐cloned parent cells or ascites‐grown cells. Cloned lines were frequently more sensitive to the cytotoxic action of antibody and complement than were the in vivo grown and cultured non‐cloned parent tumor cells. Sensitivity to cytotoxicity did not necessarily correlate, however, with the degree of antigen expression. These results suggest that; (1) the expression of Forssman and tumor‐specific antigens does not diminish on cells cultivated in vitro and (2) ascites hepatoma cells in vivo are a heterogeneous population of cells differing in their degree of antigen expression and sensitivity to antibody‐complement‐mediated cytotoxicity.