IRF5 is a genetic risk factor for many autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis, and inflammatory bowel disease (Dideberg et al., 2007; Dieguez-Gonzalez et al., 2008; Graham et al., 2006; Kristjansdottir et al., 2008). Here, IRF5 is linked to rheumatoid arthritis.