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 thymom a by N-methyl-N-nitrosourea (MNU) has been quantified and compared. St rain differences emerged and this was also apparent in congenic lines of C57BL/10 mice, differing at the H-2 locus. However, different strai ns of inbred mice, with identical H-2 haplotypes, also showed varying susceptibility to MNU, indicating that the role of the MHC was not a s imple one, but apparently depended on other, undefined genes. Proficie ncy of repair of O-6-methylguanine by thymic tissue was not responsibl e for these strain differences and the increased resistance to inducti on of thymoma by MNU in older mice was due to age-dependent changes wi thin the thymus gland. Interestingly, the thymus of older mice, grafte d with neonatal thymic tissue, still provided a suitable environment f or the development of thymic tumours.