The susceptibility of inbred mice to the production of malignant thymoma by N-methyl-N-nitrosourea.

The susceptibility of inbred mice to the induction of malignant thymoma by N-methyl-N-nitrosourea (MNU) has been quantified and compared. Strain differences emerged and this was also apparent in congenic lines of C57BL/10 mice, differing at the H-2 locus. However, different strains of inbred mice, with identical H-2 haplotypes, also showed varying susceptibility to MNU, indicating that the role of the MHC was not a simple one, but apparently depended on other, undefined genes. Proficiency of repair of O6-methylguanine by thymic tissue was not responsible for these strain differences and the increased resistance to induction of thymoma by MNU in older mice was due to age-dependent changes within the thymus gland. Interestingly, the thymus of older mice, grafted with neonatal thymic tissue, still provided a suitable environment for the development of thymic tumours.