ICOS and IL-17 expression are up-regulated by IL-23 and suppressed by IL-10. cIELs from IL-10−/− mice were cultured in the absence of CD3 stimulation for 24 h in the presence of media, media plus rIL-23, or media plus rIL-10. (A) rIL-23 increased the percent of IL-17-producing cells and the (C) MFI of ICOS expression. IL-10 supplementation resulted in (A and B) a decrease in ICOS expression and (C) a decrease in the MFI of ICOS expression. (D) rIL-23 supplementation resulted in an overall increase in the percent of ICOS+, IL-17+ cells, whereas IL-10 supplementation resulted in a decrease in the percent of ICOS+, IL-17+ cells. (E) Levels of ICOS and IL-17 gene expression were lower in cIELs from IL-10−/− mice following culture with rIL-10. Data are derived from three to five independent experiments.