Structure of tumor antigen on hybrid cells between mouse mammary ascites tumor and mouse fibroblast L cells

Somatic cell hybrids between mouse fibroblast L cells and MM2 mouse mammary ascites tumor grown in BALB/c mice were isolated and the structures of tumor‐associated surface antigen of the hybrid cells, and parental MM2 and mouse L cells were investigated by the methods of radioiodination of membrane proteins, immunoprecipitation with a specific antiserum against tumor‐associated surface antigens of MM2 tumor (anti‐MM2 serum), and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Two molecules of 105,000 and 76,000 daltons were detected on the MM2 cell surface, but no MM2 tumor antigen was detected on the mouse L cells. On the hybrids between these two kinds of cells, in addition to the two MM2 tumor antigens, molecules of 48,000–51,000 and 12,000 daltons were observed. On Sendai‐virus‐infected mouse L cells only a molecule of 68,000 daltons was detected by the anti‐MM2 serum, and furthermore this molecule was also detected by normal mouse serum, indicating that antibodies against Sendai virus were contaminating in both the anti‐MM2 and normal mouse sera used, and thus the molecules detected on the hybrid cells were distinguishable from possible viral components of Sendai virus on the hybrid cells. The results indicate that somatic cell hybrids between mouse L cells and MM2 tumor grown in BALB/c mice expressed on their cell surface the molecules that were not exposed on either parent cell. The experiments comparing newly detected molecules with the H‐2 antigen suggested that they were similar to H‐2 in their electrophoretic pattern.