Resistance to chemically-induced mammary tumors in Copenhagen X nude-derived F2 athymic rats: evidence that T-cell immunity is not involved in Copenhagen resistance.

Resistance to chemically-induced mammary tumors in the Copenhagen rat is well defined, but the mechanism of resistance has yet to be determined. We have tested whether or not Copenhagen rat resistance is dependent on T-cells, since several lines of evidence supported an involvement of the immune system. We crossed Copenhagen rats with an athymic nude rat to produce F1s, that were interbred to produce F2 animals, some of which were athymic with partial Copenhagen rat background. A comparison of the mammary tumor incidences between the nude athymic F2 animals and their non-nude littermates allowed us to determine what role, if any, T-cells played in resistance. Following treatment with N-methyl-N-nitrosourea, we observed no difference in the tumor incidences between the two groups. Furthermore, the mammary tumor incidences in the F2 nude and non-nude animals was almost zero. These results indicate that T-cells are not involved in Cop resistance, and that nude rats are resistant to N-methyl-N-nitrosourea-induced mammary tumorigenesis.