Extensive cell death in thymocytes in colon 26-induced cachectic mice

Extensive atrophy has been reported to occur in the thymus in a cancer-burd en state but the mechanisms of this atrophy have not been fully elucidated. We investigated changes in the thymus in tumour-bearing mice inoculated wi th two subclones of the murine colon 26 adenocarcinoma cell line: clone 5 ( non-cachectic) and clone 20 (cachectic). In clone 20 mice, body weights and thymocyte numbers decreased significantly compared with controls. Flow cyt ometric analysis of the thymocytes demonstrated that the frequency of singl e positive cells (CD4(+) CD8(-) and CD4(-) CD8(+)) was significantly increa sed and that of double positive cells (CD4(+) CD8(+)) was significantly dec reased in clone 20 mice and, to a lesser extent, in clone 5 mice compared w ith controls. Serum levels of interleukin 6 and granulocyte-macrophage colo ny-stimulating factor (GM-CSF) were significantly elevated, These results s uggested that thymocyte apoptosis was accelerated in the cancer-cachectic s tate, and increased GM-CSF might be partly responsible for thymic atrophy.