Cytotoxic effect of cytokines on murine colon carcinoma cells involves TNF-mediated apoptosis

We have studied the cytotoxic effect of TNF-alpha on C-26 murine colon carcinoma cells in vitro. Treatment with TNF-alpha alone did not result in any demonstrable cytotoxicity. However, when combined with IFN-gamma, the cytotoxic effect of TNF-alpha was enhanced in a dose-dependent manner. An agonistic TNF-R1 specific antibody and recombinant human TNF-alpha both exerted a cytotoxic effect when combined with IFN-gamma, suggesting that the cytotoxicity was mediated through the TNF-R1. The cytotoxicity was associated with production of nitric oxide without any direct involvement in the cytotoxic effect. At the ultrastructural level, treated cells displayed a typical apoptotic morphology which was not accompanied by internucleosomal cleavage of DNA as shown by conventional electrophoresis.