Qualitative and Quantitative Differences in the Cellular Responses Mediated Through Fas Antigen and Tumor Necrosis Factor Receptor

Like tumor necrosis factor (TNF), antibodies against the Fas antigen (anti-Fas) are cytotoxic to some and induce proliferation of other Fas-expressing cells. In this study, we compared cellular responses mediated through TNF with anti-Fas using a T cell line (Jurkat) and a macrophage cell line (U-937). These two cell types differed in that the Jurkat cells expressed higher levels of Fas antigen than U-937 cells, whereas the latter expressed higher levels of the p80 form of the TNF receptor than Jurkat cells. Treatment for 72 h with anti-Fas inhibited the growth of both Jurkat and U-937 cells, the 50% inhibitory concentrations (IC₅₀) being 10 and 100 ng/ml, respectively. Under similar conditions, the IC₅₀ for TNF was >100 and 0.8 ng/ml for Jurkat and U-937 cells, respectively. Like TNF, the cytotoxic effects of anti-Fas were potentiated by cycloheximide, showing they did not require protein synthesis. Interestingly, in the presence of cycloheximide, the kinetics of cell killing was more rapid for TNF than anti-Fas (50% inhibition occurred at 3 versus 6 h). Treatment of both cell types with anti-Fas led to time-dependent DNA fragmentation, but TNF-induced DNA fragmentation occurred only in the presence of cycloheximide. Pretreatment of cells with TNF led to resistance to TNF but not to anti-Fas, suggesting that the receptors for the two are not cross-modulated. Furthermore, TNF activated the nuclear transcriptional factor NF-κB in both cell types, whereas anti-Fas had no effect. Overall, our results demonstrate that anti-Fas and TNF transduce overlapping and nonoverlapping signals in macrophage-like and T cell lines through distinct pathways.