Fas ligation at the time of activation promotes early apoptosis in naive CD4 T cells (OT-II T cells).

(A) Proliferation of T cells in the presence of control (■) or anti-FasL (▨) or anti-Fas (▪) mAb at day 3 during coculture with dendritic cells pulsed with a low or high concentration of antigen: 0.02 mg/mL (left) or 2.0 mg/mL (right) ovalbumin. Without antigen, proliferation was always less than 200 cpm (not shown). (B) Proliferation of T cells in the presence of anti-FLAG alone (▥) or cross-linked FasL (ie, FasL plus anti-FLAG) (▤). (C) Viability of T cells responding in the presence of the indicated antibodies or FasL at day 3. Viability was calculated after trypan blue staining by counting living and dead cells in triplicate cultures in each experiment. DCs were pulsed with 2 mg/mL ovalbumin. (D) Viability of responding T cells activated in the presence of the indicated antibodies or FasL-plotted against cell division. Viability was determined by 7-AAD staining of CFSE-labeled T cells at day 3 and day 6. A representative staining from 1 of 3 experiments is shown. In panels A-C, results are the mean ± SEM of 3 individual experiments. P values were calculated using the Studentt test.