Differential regulation of Th17 and T regulatory cell differentiation by aryl hydrocarbon receptor dependent xenobiotic response element dependent and independent pathways.

The aryl hydrocarbon receptor (AHR) is regarded as an environmental sensor and has been shown to link environmental stresses with chronic inflammatory and autoimmune diseases. The AHR can be activated to regulate both the X/DRE (xenobiotic or dioxin response elements) as well as a non-X/DRE mediated pathway. Selective AHR modulators (SAhRMs) are recently identified compounds that activate non-X/DRE mediated pathway without activating the X/DRE-driven responses. Here, we have used 3 classes of AHR ligands; agonist, antagonist, and a SAhRM, to delineate the role of these AHR-driven pathways in T helper 17 (Th17)/T regulatory (Treg) regulation. We show that Th17 differentiation is primarily dependent on X/DRE-driven responses, whereas Treg differentiation can be suppressed by inhibiting non-X/DRE pathway. Using a model of Citrobacter rodentium infection, we further show that AHR agonist enhances Th17 production and promoted resolution of infection, whereas a SAhRM inhibited Th17 mediated responses with reduced resolution of infection. These data indicate that Th17/Treg function may be differentially regulated by SAhRMs that differentially activate the X/DRE and non-X/DRE mediated pathways, and point to a therapeutic strategy to leverage AHR function in the treatment of chronic inflammatory and autoimmune disease.