RELEASE OF PREFORMED FAS LIGAND IN SOLUBLE FORM IS THE MAJOR FACTOR FOR ACTIVATION-INDUCED DEATH OF JURKAT T-CELLS

Interaction of Fas/APO-1 (CD95) and its ligand (Fast) plays an importa nt role in the activation-induced cell death (AICD) of T lymphocytes. In the present work, the contribution of soluble Fast to AICD of the h uman T-cell line Jurkat has been studied. Jurkat cells prestimulated w ith phytohaemagglutinin (PHA) induced the death of non-activated Jurka t cells, and also of L1210Fas, but not that of Fas-negative L1210 cell s. Culture supernatants from prestimulated Jurkat cells were highly to xic to their non-activated counterparts. Time-course analysis revealed that PHA-stimulated Jurkat cells quickly release (less than 15 min) t o the medium a toxic molecule following a biphasic pattern, with maxim al cytotoxic activities at 1 hr and 7 hr after stimulation. The cytoto xic effect of those supernatants was prevented by the addition of a bl ocking anti-Fas monoclonal antibody, suggesting that PHA-stimulated Ju rkat cells exert Fas-based cytotoxicity mainly through the release of soluble Fast. The constitutive intracellular expression of Fast in non -activated Jurkat cells and its release as a consequence of PHA activa tion were detected by immunostaining and immunoblotting using an anti- Fast antibody. These data indicate that, at least in Jurkat cells, AIC D is mainly mediated by the rapid release of preformed Fast in soluble form upon stimulation.