Distinct roles of IRF4 and c-Rel in the expression of IL-17, IL-9, and IL-6. A and C, effects of siRNAs against IRF4 (A) or c-Rel (C) on the protein expression of IRF4 and c-Rel by Western blot. B and D, effects of IRF4 (B) and c-Rel (D) siRNAs on the expression of IL-17A, IL-9, and IL-6 were examined by real-time PCR.