| Abstract: | Human T cell clones were analyzed for their susceptibility to activation-induced cell death (AICD) in response to CD3/T cell receptor ligation. AICD was observed only in Th1 clones and was Fas-mediated, whereas Th2 clones resisted AICD. Analysis of a panel of Th0 clones, characterized by their ability to secrete both Th1 and Th2 cytokines, revealed that this subset included both AICD-sensitive (type A) and -resistant (type B) clones. Resistance to AICD by Th2 and Th0-type B clones was not due to lack of expression of either Fas receptor or its ligand. Paradoxically, the AICD-resistant clones were susceptible to apoptosis when Fas receptor was directly ligated by anti-Fas antibodies. However, prior activation of the resistant clones by monoclonal antibodies to CD3/TCR complex induced resistance against Fas-mediated apoptosis. Thus, the Fas–FasL pathway is critical for the induction of AICD in T cells, and moreover this pathway can be negatively regulated in the AICD-resistant clones by signals that are generated from ligation of the CD3/TCR complex. |
