Regulation by FasL of T-cell blast growth in the presence of increasing doses of IL-2. (A) Day-6 T-cell blasts were cultured for an additional period of 48 hours in the presence of increasing doses of IL-2, as indicated, in the presence (□) or absence (▪) of 1 μg/mL of the anti-FasL–blocking mAb NOK-1, and cell growth was estimated by counting trypan blue–negative cells. Results are expressed as the ratio between the number of viable cells at a given time (N(t)) and the number of viable cells at time 0 (N(o)). (B) In the same experiments, cell death was analyzed by counting trypan blue–positive cells, and results were expressed as the percentage of dead cells. Results are the mean ± SD of experiments performed using T-cell blasts from 3 different donors. *P < .05. (C) Using T-cell blasts from one of the donors used in panels A and B, the surface and whole-cell (WC) expression of FasL was evaluated by flow cytometry in CD4⁺ and CD8⁺ T-cell blasts. (D) Using T-cell blasts from the same donor, supernatants (Ssn) were collected after 48 hours of culture in the absence or presence of the indicated IL-2 concentrations and tested on Jurkat cells for 16 hours in the absence (Ssn control) or presence (Ssn+NOK-1) of 1 μg/mL of NOK-1. Results are expressed as the percentage of DiOC₆³-low Jurkat cells.