IRF5 and systemic lupus erythematosus: Systemic lupus erythematosus (SLE) [1-4], Sjögren's syndrome [5-7], systemic sclerosis [8-11] and primary biliary cirrhosis [12,13] are complex autoimmune diseases with a genetic component that includes among their strongest susceptibility loci the interferon regulatory factor 5 gene (IRF5).