The Q9-343 monoclonal antibody specifically recognizes human and mouse Interferon Regulatory Factor 4 (IRF4 or IRF-4) which is also known as Lymphocyte specific interferon regulatory factor (LSIRF), Multiple myeloma oncogene 1 (MUM1), or PU.1 interaction partner (PIP). IRF4 belongs to the Interferon Regulatory Factor (IRF) family of transcription factors that includes nine members, IRF1-9. IRF4 has a conserved N-terminal DNA binding domain with a unique tryptophan pentad repeat. Its C-terminal regulatory domain regulates IRF4 activity and mediates interactions with other IRF proteins, transcription factors and co-factors. IRF4 plays essential roles in the regulation of innate and adaptive immune responses. IRF4 is widely expressed in leucocytes and is essential for the development, activation, differentiation, and/or apoptosis of T helper (Th) cell subsets including Th2, Th9, Th17, T follicular helper (Tfh) cells, or T (Treg) cells. IRF4 is involved in the development or differentiation of CD8+ effector and memory cells, B cells and plasma cells, as well as different dendritic cell (DC) subsets and M2 macrophages. IRF4 is also expressed by adipocytes and melanocytes. Cellular IRF4 expression is primarily upregulated by antigen-receptor engagement, or by stimulation with lipopolysaccharide (LPS), CD40, or IL-4, rather than by interferons. TLR4 has been implicated in suppressing or promoting oncogenisis and autoimmunity.