DD stimulates survival of resting T_reg. (A) Resting PBMC were treated with different doses of DD as indicated for 3 days and then were analyzed by FACS. Note that the proportion of CD4⁺CD25⁺ and CD4⁺CD25⁺Foxp3⁺ T cells increased at all DD concentrations; however, the CD4⁺CD25^highFoxp3⁺ cells increased only at 25 to 75 ng/mL DD. Error bars were calculated on the basis of triplicates of 3 independent experiments. (B) (upper panels) CD4⁺ CD25⁻ T_eff and CD4⁺ CD25⁺ T_reg, isolated from healthy donors were stimulated with anti-CD3/anti-CD28 or were left untreated and were incubated with DD for 48 hours before apoptosis was assessed by FACS (annexin-V staining). (B) (lower panels) Aliquots of the same cells were treated with equivalent doses of IL-2 (44 ng/mL of IL-2 are equivalent to 10 ng/mL of DD). The data represent mean values ± SD from 2 (upper panels) or 3 (lower panels) independent experiments. (C) Purified T_eff or T_reg were treated for 15 minutes with DD or IL-2 as indicated before intracellular pStat5 was assessed by FACS. The data represent mean values ± SD from 3 independent experiments.