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. {ECO:0000269|PubMed:29537367, ECO:0000269|PubMed:36662884, ECO:0000269|PubMed:36917008}. This is the function of Ensembl gene identifier ENSG00000137265 (IRF4, interferon regulatory factor 4).