In a systemic LPS-induced shock model, AHR-deficient mice are more susceptible while AHRR-deficient mice showed increased survival.31,42,43 This contrasts with experimental dextran sulfate sodium–induced colitis, in which both AHR- and AHRR-deficient mice exhibit increased disease severity, indicating that the local tissue environment affects the role of AHRR in limiting or promoting inflammatory reactions. This evidence concerns the gene AHR and colitis.