<qa>  What is a relapsing disease of unknown cause?Ulcerative colitis is a relapsing disease of unknown cause characterized by bloody diarrhea. Therapy usually involves 5-aminosalicylates, corticosteroids and immunosuppressants. However, steroid resistance and dependency can become problematic. Immunosuppressive drugs, such as azathioprine, are beneficial but may have serious side effects. Therefore, new therapeutic approach is needed. 