Recombinant interleukin 27 inhibits human type 17 T helper cell differentiation via upregulation of IRF8. (A) The expression of interferon regulatory factor 8 (IRF8) in naïve CD4+ T cells (n = 5) cultured under type 17 T helper cell (Th17) polarizing conditions in the presence or absence of interleukin 27 (IL-27) was detected by RT-PCR. (B) Real-time PCR analysis was carried out to determine IRF8 expression in naïve CD4+ T cells from healthy controls (n = 5) nucleoporated with IRF8-specific small interfering RNA (siRNA; siIRF-8) or control siRNA (siCtrl) and then cultured under Th17 polarizing conditions. Naïve CD4+ T cells from healthy controls (n = 8) were nucleoporated with control siRNA or IRF8-specific siRNA and cultured with or without recombinant IL-27 (rIL-27) under Th17 polarizing conditions for another 48 hours. (C) IRF8 expression in these cells was detected by RT-PCR. (D) IL-17 production in the cell culture supernatants was measured by enzyme-linked immunosorbent assay. (E) Representative flow cytometry dot plots of intracellular IL-17 expression are shown. Paired-samples t-tests for related samples and analysis of variance for three different groups were used for statistical analysis. All of the data are representative of three independent experiments and are expressed as average ± standard deviation.