Interferon Regulatory Factor 5 (IRF5) is a member of the IRF family. It contains one IRF tryptophan pentad repeat DNA-binding domain. IRF5 shuttles between the nucleus and the cytoplasm. IRF5 can form homodimer when it is phosphorylated. IRF5 functions as a transcription factor involved in the induction of interferons IFNA and INFB and inflammatory cytokines upon virus infection. Genetic variations in IRF5 are associated with susceptibility to systemic lupus erythematosus type 10. In addition, the genetic variations wil result in susceptibility to rheumatoid arthritis.