Treatment with indigo naturalis for inflammatory bowel disease and other immune diseases.

Indigo naturalis (IN) is a herbal medicine extracted from leaves and stems of plants and is a component of crude drugs used in China. Recently, IN was reported to be effective for treating (UC) and psoriasis. The mechanisms of IN for UC is not clear, but aryl hydrocarbon receptor ligand, the active components of IN, can promote mucosal healing by inducing the production of interleukin-22 from type-3 innate lymphocytes cells. Although IN is effective even for refractory cases, critical adverse effects including IN-induced colitis and pulmonary arterial hypertension should be concerned. Due to adverse effects of IN, topical treatment of IN is useful for distal UC as well as psoriasis to secure patients' safeties. Many refractory patients may be helped by IN if it becomes available in appropriate forms for clinical practice. In the near future, the mechanism that underlies the adverse effects of IN needs to be determined, and extraction of active ingredients with fewer side effects, investigated.