Relation Between the Tumor-Specific Antigen and Cytological Characteristics in Mouse Mammary Tumors 1,2

SUMMARY-The modal chromosome number of FM3A/B, a cultured cell line of mouse mammary tumor, is hyperdiploid. Its karyotype changed spontaneously into hypotetraploidy (FM3A/BR) during serial culture. FM3A/B and FM3A/BR were converted into ascites form (FM3A and FM3A/R, respectively). Transplantation of FM3A and FM3A/R was suc-cessful in all syngeneic C3H/He mice, with a mean survival of 26 and 23 days, respectively. Judged from cell numbers in the peritoneal cavity, growth rate of FM3A/R was more rapid than that of FM3A. Cytotoxic sensitivity of these cells was tested with syngeneic antiserum against the tumor-specific antigen of the mouse mammary tumor and with complement. FM3A/R was far more sensitive to the antibody than FM3A. The concen-tration of the antigens on the cell surface of FM3A/R was demonstrated by absorption tests to be 35 times higher than that of FM3A. Cytotoxic sensi-tivity of other mouse mammary tumors, MM102, MM2, and MM12, was also higher than that of FM3A. The chromosomal population of FM3