FTI-mediated suppression of cytokine production is reversible and not caused by diminished viability of T cells. (A) Th1 (3 × 10⁶) and Th2 (2 × 10⁶) cells were incubated with varying concentrations of FTI. Survival of T cells after 24-hour culture was determined by trypan blue exclusion. Data are representative of 3 independent experiments. (B) Th1 cells were preincubated with 10 μM FTI or medium for 24 hours and stimulated with anti-CD3 + anti-CD28 antibodies. IFN-γ production was determined by ELISA of stimulated FTI- or medium-treated cells. After the first 24 hours of incubation, Th1 cells initially cultured with medium alone were kept in medium for an additional 24 hours. Initially FTI-treated Th1 cells were washed and kept in medium alone for an additional 24 hours. Both populations were stimulated with anti-CD3 plus anti-CD28 antibodies after total culture of 48 hours, and IFN-γ production was determined by ELISA.