Abstract
Skin tumor induction in thymectomized CFW mice was compared to that in sham-operated and unoperated control animals. In the first experiment, in which mice were treated with daily paintings of croton oil after urethan initiation, skin papillomas occurred fewer in number and later in appearance in neonatally thymectomized animals than in unoperated controls, although the first tumor appeared accelerated in the experimental animals. In the second experiment, with repeated paintings with 3-methylcholanthrene, skin papillomas appeared earlier in some of the thymectomized mice than in controls. The accelerated or suppressed induction of papillomas in these two experiments was also seen in sham-operated animals, so this is due probably to the neonatal surgical invasion to the host and not to the anticipated impairment of immunological development.
In contrast, skin carcinomas occurring in mice in the second experiment appeared earlier in the neonatally thymectomized than in the sham-operated animals. Six weeks, the time difference of the tumor appearance between these two groups, is so significant as immune-suppressing factors might be removed by the operation.
The data from these experiments suggest that immune mechanism, if any, may affect the induction of carcinomas but not of papillomas.
