IL22 and colorectal carcinoma: Activation of innate lymphocytes and aromatic hydrocarbons in gut‐resident T cells increases IL‐22 production, which helps to prevent colonic inflammation (colitis) and inflammatory bowel disease, which can lead to precancerous lesions.[141] In addition, in vivo, tryptophan metabolites not only suppress inflammation, but also fix abdominal wall structures and in association with beneficial bacteria in the gut, may slow the progression of CRC.[142] Tryptophan metabolism plays an important role in inhibiting the growth of CRC, although the underlying mechanism remains nebulous.