Fas-costimulated T cells respond more vigorously to antigen rechallenge and are partially resistant to death induction via Fas engagement.

After purification of viable cells, OT-II T cells were rechallenged with ovalbumin-pulsed DCs 6 days after the start of initial activation. (A) Proliferation of OT-II T cells initially activated in the presence of control mAb (“Control Ab”) or anti-Fas mAb (“a-Fas Ab”) cross-linked FasL (“FasL”) or the cross-linker (“a-FLAG Ab”) alone, during the first 24 hours of reactivation. (B) Viability of the same cells was assessed by trypan blue staining in triplicates from cultures made in parallel with panel A at day 2. (C) IFN-γ production was measured after 24 hours by ELISA as explained in Figure 2B. Results in all panels are pooled from 3 separate experiments (mean ± SEM). Cells were rechallenged in the presence of control antibody (■) or anti-Fas antibody (▪) or in the presence of cross-linker (▥) or cross-linked FasL (▤).P values were calculated by the Student t test and are given for differences between cells preactivated under different conditions and rechallenged under Fas ligation.