METHYLCHOLANTHRENE-INDUCED SARCOMAS IN NUDE-MICE HAVE SHORT INDUCTIONTIMES AND RELATIVELY LOW-LEVELS OF SURFACE MHC CLASS-I EXPRESSION

In order to study the role of the T-cell-mediated immune defense in tu mor development, a total of 93 sarcomas were induced using different d oses (8 mu g (0.1%), 40 mu g (0.5%) and 400 mu g (5%)) of 3-methylchol anthrene in athymic nude Balb/c mice and phenotypically normal immunoc ompetent Balb/c mice. A shorter tumor induction time and a higher tumo r incidence after treatment with low doses of methylcholanthrene were seen in nude mice than in immunocompetent mice, indicating that they h ave a lower resistance to the carcinogen. Contrary to expectations we found that the MHC class I expression of tumors from nude mice was low er than that of tumors from normal mice. Higher surface expression of MHC class I was demonstrated on high dose tumors from normal mice than on low dose tumors from normal mice. The cellular composition of the individual tumors raised in nude mice was more heterogeneous with resp ect to MHC class I expression. Since the mice differ genetically only with respect to the nu gene, these results indicate that a lack of T-c ell-mediated defense mechanisms may confer upon the bearer a lower res istance to 3-methylcholanthrene and a different MHC profile of the ens uing tumor.