Consequently, the expression of mucins produced by cuprocytes and activation of Signal Transducer and Activator of Transcription 3 (STAT3)-dependent signaling induces the expression of mucin-associated genes in mucosal epithelial cells, etc. Therefore, the key role played by tryptophan metabolite in the development of AIH should not be overlooked. The gene discussed is MUC5AC; the disease is autoimmune hepatitis.