Aryl hydrocarbon receptor and colitis.

The aryl hydrocarbon receptor (AhR), a transcription factor activated by a large variety of natural and synthetic ligands, has recently become the object of great interest among researchers since it represents an important link between environment and immune-mediated pathologies. In this context, evidence has been accumulated to show that AhR is necessary for the maintenance/expansion of intraepithelial lymphocytes and interleukin-22-producing innate lymphoid cells in the gut and that defects in AhR-delivered signals may contribute to amplify gut tissue destructive immune-inflammatory reactions. We here review the available data supporting the role of AhR in the control of immune homeostasis in the gut and discuss whether and how AhR activators can help dampen inflammatory processes.