Virological and immunological characteristics of tumors induced in adult rats by Rous sarcoma.

Forty primary tumors of Wistar rats and first seven passages of tumors of August rats were investigated by different virological and immunological methods. The tumors were induced in adult rats by Schmidt--Ruppin strain of Rous sarcoma. Based on the virus-cell interaction, the tumors were divided into four groups. The first group of tumors of Wistar rats (2 out of 40) contained mature RSV and viral antigens could be detected by means of the FA test, while the rats had virus neutralizing antibodies in their sera. The second group of Wistar rat tumors (19 out of 40) and August rats tumors contained virus connected with the cells. The third group was composed of "virus-free" tumors of Wistar rats (8 out of 40). Application of the method of cells association increased rescue RSV in tumors of the 2nd group by 2--4 fold and caused activation of the virus in tumors of the 3rd group. Irradiation of rat tumor cells with a dose of 5000-10 000 R did not enhance the rescue or activation of oncogenic virus in any case. In tumors of the second and third group viral antigen was detected by the FA test in 47% and gs antigen by the CF test in 17%. gs antibodies were found in 29% of the sera from rats with these tumors. The 4th group of Wistar rats tumors were "virus-free" (11 out of 40) showing a negative effect of RSV activation. These tumors with one exception contained no virus antigen, and there were no antibodies against them in sera of the rats.