FIGURE 4. TGF- concentration influences Il23r expression and levels of IL-17 in response to T_H17-inducing cytokines.

a, Foxp3-mediated inhibition of IL-6/IL-21-induced Il23r expression. This was measured in arbitrary units relative to expression of transcripts encoding actin. Naive CD4⁺ T cells were transduced with MIG, full length Foxp3 or Foxp3Ex2 viruses, and were treated with the indicated cytokines. RNA was isolated from GFP⁺ cells at day 2. Il23r expression was measured by real-time RT–PCR and was normalized to the actin level. Error bars represent standard deviations obtained using the standard curve method. b, Induction of Il23r mRNA in response to cytokines. Naive CD4⁺ T cells were stimulated with anti-CD3 and anti-CD28 throughout the culture period in the presence of the indicated combinations of cytokines. TGF- was titrated into the cultures at the concentrations of 5 ng ml^-1, 2.5 ng ml^-1, 1 ng ml^-1, 200 pg ml^-1, 40 pg ml^-1 or 8 pg ml^-1. Il23r mRNA expression was measured after 48 h by real-time RT–PCR and was normalized to the actin expression level. c, d, IL-23 enhancement of IL-17 expression at low concentrations of TGF-. The percentage of IL-17⁺ cells at 96 h of stimulation with the indicated cytokines is shown. Results in histogram format are shown in Supplementary Fig. 7. e, Induction of Foxp3 at different concentrations of TGF-. Representative data from at least three experiments are shown for each set of panels.