Transcription factor that specifically binds to the upstream regulatory region of type I interferon (IFN) and IFN-inducible MHC class I genes (the interferon consensus sequence (ICS)) (PubMed:2111015, PubMed:12393690). Can both act as a transcriptional activator or repressor (PubMed:2111015). Plays a negative regulatory role in cells of the immune system (PubMed:2111015). 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 IRF8 and activation of genes (PubMed:12393690, PubMed:22992524). Required for the development of plasmacytoid dendritic cells (pDCs), which produce most of the type I IFN in response to viral infection (PubMed:12461077, PubMed:12393690, PubMed:12538667, PubMed:23382217). Positively regulates macroautophagy in dendritic cells (By similarity). Interacts with COPS2 (By similarity). Interacts (via C-terminus) with TRIM21 (via C-terminus). Interacts with the BATF-JUNB heterodimer. Interacts with BATF (via bZIP domain); the interaction is direct. In resting macrophages, localizes in the cytoplasm. Translocated in the nucleus upon IFN-gamma induction. Mainly expressed in lymphoid tissues (PubMed:2111015). Predominantly expressed in CD8(+)-expressing dendritic cells (PubMed:12393690). By interferon gamma. Ubiquitinated (PubMed:17579016). Ubiquitination by TRIM21 in macrophages, a process that is strongly increased upon interferon gamma stimulation, leds to the enhanced transcriptional activity of target cytokine genes (PubMed:17579016). Ubiquitination leads to its degradation by the proteasome (By similarity). Sumoylated with SUMO3. Desumoylated by SENP1. Mice display an absence of interferon (IFN)-producing cells and show impaired IFN production in response to viral infection (PubMed:12461077). Complete absence of plasmacytoid dendritic cells (pDCs) and conventional CD8(+)-expressing dendritic cells (cDCs) (PubMed:12393690, PubMed:12538667, PubMed:23382217). Mice display reduced autoimmunity (PubMed:23382217). Belongs to the IRF family.