IL22 and inflammatory bowel disease: Clinical studies have confirmed that AHR-agonistic indole levels in the feces of patients with IBD are significantly positively correlated with serum IL-22 concentrations(p < 0.01), and that their deficiency is directly associated with increased intestinal permeability(elevated plasma lactoferrin levels) and worsening disease activity index(CDAI) (Wang et al., 2023).