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. This evidence concerns the gene STAT3 and autoimmune hepatitis.