Aryl Hydrocarbon Receptor Activation Invovled In Ameliorating Colitis And The Regulation Of CD8αα~+TCRαβ~+ IELs

Background:Inflammatory bowel disease(IBD)is a chronic,recurrent inflammatory diseases caused by a variety of reasons,which primarily involved in colon.Evidence suggests that the gut immunity plays an important role in the pathogenesis of IBD.Increasing data have demonstrated that the intestinal mucous immune system is involved in the development of intestinal inflammation.More recently,innate immune system defects have been found to contribute to gut destructive immune-inflammatory reactions,which if corrected might improve the efficacy of curing IBD.Intestinal intraepithelial lymphocytes(IELs),settling in the intestinal epithelium,can be classified based on their phenotypes and origins into conventional and unconventional subsets.The unconventional subset includes CD8αα~+TCRαβ~+ and TCRγδ~+ IELs.TCRγδ~+ IELs are widely recognized to play a protective role in mucosa homeostasis.There is a resemblance between the function of CD8αα~+TCRαβ~+ IELs and TCRγδ~+ IELs.CD8αα~+TCRαβ~+ IELs were found to have an immunoregulatory role in the intestine.Studies have proven that CD8αα~+TCRαβ~+ IELs can relieve intestinal inflammation,and primarily play a protective role in intestinal homeostasis.Aryl hydrocarbon receptor(AhR),a ligand-dependent transcription factor,controls development and function of several types of immune cells including IELs and macrophages.6-Formylindolo(3,2-b)carbazole(FICZ)is the endogenous ligand of AhR.Recent advances have shown that FICZ can inhibit chronic inflammation by AhR signaling in vivo and down-regulated the expression of Th1-related molecules in vitro.Interestingly,the expression of AhR in intestinal tissue of patients with Crohn’s disease is decreased.More recent evidence demonstrated that AhR plays a critical role in the development of TCRγδ~+ IELs and CD8αα~+TCRαβ~+ IELs,indicating that FICZ potentially affects acute inflammation andmodulates the unconventional IELs in acute colitis by activating AhR signaling.Methods:1.For the induction of the model of acute colitis,3% DSS was dissolved in the drinking water and administered to mice for 7 days.Mice were weighed and assessed,and colon tissues were measured.2.Flow cytometry was used to detecting the changes of unconventional IEL subsets,and the corresponding secretion of cytokines were deteced by RT-PCR and flow cytometry.3.FICZ was given intraperitoneally on a daily basis beginning 2 days after starting DSS administration.Body weight,DAI score,RT-PCR and HE staining were used to detected the inflammatory responses changes,and flow cytometry used to observe the changes of colonic unconventional IEL and the cytokines in IELs.Results:1.Compared with the control group,mice in the DSS group experienced weight loss from day four after DSS administration,the colon length in the DSS group was shorter than that of the control group,DAI score of the DSS group was increased after day three.Histological examination demonstrated that the DSS group showed severe mucosal ulceration and depletion of crypts,but all these changes were ameliorated by FICZ administration.2.The percentage of CD8αα~+TCRαβ~+IELs was lower in the DSS group than in the control group,furthermore in numbers CD8αα~+TCRαβ~+ IELs were statistically significant.Administration of FICZ obviously reversed the change.The expression of CYP1A1 in IELs increased significantly after treatment with FICZ compared with the DSS group.3.Compared with the control group,the apoptotic ratio of CD8αα~+TCRαβ~+ IELs was increased in the DSS group,although the administration of FICZ could decrease the apoptotic rate of CD8αα~+TCRαβ~+ IELs.The expression of AhR,IL-15Rα,CD122,and CD132 in CD8αα~+TCRαβ~+ IELs were significantly reduced in the DSS group compared with the control group.However,injection with FICZ increased the expression of AhR and IL-15Rα,CD122,CD132 subunits in CD8αα~+TCRαβ~+ IELs.4.In the DSS group,the expression of IFN-γ,TNF-α,IL-1β,and IL-6 were increased,but TGF-β1 was unchanged,and IL-10 was decreased compared with the control group;Treatment with FICZ,IFN-γ,TNF-α,IL-1β,and IL-6 were decreased,but IL-10 was increased.In the DSS group,the percentage of IL-10-producing CD8αα~+TCRαβ~+ IELs waslower than that of the control group,but IFN-γ was much higher.Administration of FICZ,IL-10 was increased and IFN-γ was decreased in CD8αα~+TCRαβ~+ IELs.Conclusion:1.FICZ ameliorated the severity of DSS-induced acute colitis.2.FICZ restored the number and proportion of CD8αα~+TCRαβ~+ IELs by activating AhR in DSS-induced colitis.3.FICZ upregulated the IL-15 receptor and AhR in DSS-induced colitis.4.FICZ regulated the expression of cytokines from CD8αα~+TCRαβ~+IELs by activating AhR in DSS-induced colitis.