Apoptosis Study in Thymic Involution in Tumour-Bearing Mice

By using a colorectal carcinoma induced by s.c. injection of 1,2-dimethylhydrazine and a transplantable fibrosarcoma developed in inbred BALB/c mice 6–8 weeks old we found that tumour development was accompanied by a remarkable thymic involution.

Mice bearing small fibrosarcoma or carcinoma (0,05 cm³) had thymuses and spleens with the same weight as those of normal mice. Thymic atrophy and splenomegalia developed in mice bearing large fibrosarcoma (5,00 cm³) and large carcinoma (0,20 cm³). Thymic involution was not the result of an increase in spontaneous cellular apoptosis. However, an increased susceptibility to apoptosis induced by etoposide was observed in thymocytes from mice bearing large carcinomas or large fibrosarcomas, as compared to the same cells derived from normal or small tumour-bearing mice. Dexamethasone induced comparable levels of apoptosis in thymocytes from all groups (normal mice, mice bearing small and large carcinoma and mice bearing small and large fibrosarcoma); doxorrubicin had no significant effect in any group.