The 20/IRF-1 monoclonal antibody specifically binds to Interferon regulatory factor 1 (IRF1). IRF1 belongs to the human IRF family of transcription factors that contains nine members, IRF1-9. IRF1 is broadly expressed and its levels are upregulated in response to certain cytokines, interferons, bacterial or viral infections. IRF1 binds to specific DNA motifs such as IFN-stimulated response elements (ISRE) and regulates the activity of IFN-responsive genes. IRF1 plays roles in inflammation as well as innate and adaptive immune responses. It is involved in the regulation of cellular proliferation, Major Histocompatibility Complex (MHC) antigen expression, and the differentiation and effector functions of macrophages, dendritic cells, natural killer (NK) cells, and various T cell subsets. In addition, IRF1 may function as a tumor suppressor, since deletions in the IRF1 locus is associated with myelodysplasia and leukemias.