IRF4 regulates IL-10 gene expression in CD4⁺ T cells through differential nuclear translocation

CD4⁺ T cells play critical roles in the generation of protective immunity against a variety of pathogens. The main two types of effector CD4⁺ T cells, Th1 and Th2 are characterized by their ability to produce signature cytokines. Among them, IL-10 is a multi-functional cytokine that plays a crucial role in maintaining the balance between immunity and tolerance. Although IL-10 is produced by both differentiated primary Th1 and Th2 cells, Th2 cells produce much higher levels of IL-10 upon stimulation. However, little information is available on the molecular mechanisms of IL-10 gene regulation at the transcriptional level. Interferon regulatory factor IRF4 is a member of the IRF family of transcription factors and plays critical roles in the development of CD4⁺ T cells into Th2 cells. In this present study, we elucidate the underlying mechanism of IRF4 mediated IL-10 gene transcription in primary CD4⁺ T cells. Th2 specific binding of IRF4 to the IRF4 responsive elements in IL-10 locus potentiated IL-10 expression in Th2 cells. Knockdown of IRF4 by siRNA decreased IL-10 expression level in Th2 cells. Nuclear translocation of IRF4 was much higher in Th2 cells upon stimulation, which contribute to maintain IL-10^high phenotype of Th2 cells. Collectively, our results suggest that stimulation driven quantitative differences of IRF4 in the nucleus and its binding to IL-10 regulatory elements are crucial mechanisms to induce IL-10^high gene expression in Th2 cells.