TUMOR-NECROSIS-FACTOR-ALPHA ENHANCES CAMP-INDUCED PROGRAMMED CELL-DEATH IN MOUSE THYMOCYTES

During T-lymphocyte differentiation in the thymus, the majority of thymocytes die by apoptosis in situ. This process is characterized by internucleosomal DNA fragmentation and is induced by a number of stimuli including glucocorticoids, calcium ionophore, cAMP and 12-o-tetradecanoylphorbol 13-acetate (TPA). In this study, the effect of cytokines tumour necrosis factor-α (TNF-α) and interferon γ (IFN-γ) on the programmed cell death of thymocytes was examined by measuring DNA fragmentation and LDH release. TNF-α and IFN-γ had no effect on DNa fragmentation in control and TPA, or A23187-treated thymocytes. Both human and murine rTNF-α enhanced cAMP-induced programmed cel death dose-dependently, but IFN-γ had no effect on the process. TNF-α did not stimulate cAMP accumulation in control or 2-chloroadenosine-treated thymocytes. TPA markedly stimulated cAMP-induced DNA fragmentation as a result of 6 h incubation, whereas TNF-α did not. Thus TNF-α did not appear to activate protein kinase C directly. The effect of TNF-α did not. observed in the cell preparations from which adherent cells had been removed, suggesting that cytokines secreted by adherent cells ini response to TNF-α are not involved in the process. The enhancement of cAMP-induced DNA fragmentation was observed in CD4+CD8+-double positive cells, but not in CD4+CD8—-single positive cells. The results of the present study indicate that a physiological cytokine, TNF-α, may modulate programmed cell death in immature thymocytes in concert with cAMP. © 1993 Academie Press Limited.