Transcriptional activator. Binds to the interferon-stimulated response element (ISRE) of the MHC class I promoter. Binds the immunoglobulin lambda light chain enhancer, together with PU.1. Probably plays a role in ISRE-targeted signal transduction mechanisms specific to lymphoid cells. Involved in CD8(+) dendritic cell differentiation by forming a complex with the BATF-JUNB heterodimer in immune cells, leading to recognition of AICE sequence (5'-TGAnTCA/GAAA-3'), an immune-specific regulatory element, followed by cooperative binding of BATF and IRF4 and activation of genes (By similarity). Interacts with the BATF-JUNB heterodimer. Interacts with BATF (via bZIP domain); the interaction is direct (By similarity). Interacts with SPIB and DEF6. Directly interacts with NLRP3 in the nucleus of Th2 cells; this interaction enhances IRF4 ability to bind to the IL4 promoter and is required for optimal IRF4-dependent IL4 transcription (By similarity). Lymphoid cells. Not induced by interferons. Phosphorylation by ROCK2 regulates IL-17 and IL-21 production. Genetic variants in IRF4 define the skin/hair/eye pigmentation variation locus 8 (SHEP8) [MIM:611724]. Hair, eye and skin pigmentation are among the most visible examples of human phenotypic variation, with a broad normal range that is subject to substantial geographic stratification. In the case of skin, individuals tend to have lighter pigmentation with increasing distance from the equator. By contrast, the majority of variation in human eye and hair color is found among individuals of European ancestry, with most other human populations fixed for brown eyes and black hair. The gene represented in this entry may be involved in disease pathogenesis. A chromosomal aberration involving IRF4 has been found in multiple myeloma. Translocation t(6;14)(p25;q32) with the IgH locus. Belongs to the IRF family.