The aryl hydrocarbon receptor (AhR) is a pivotal chemical sensor that transduces external and internal stimuli into biological responses. AhR was originally thought to be involved in not only xenobiotic metabolism but also carcinogenic and toxicological responses against environmental pollutants, such as polycyclic aromatic hydrocarbons and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, recent studies demonstrate that the AhR plays multiple intrinsic roles in host defense and homeostasis.

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... This includes immunity, stem cell maintenance, and cell differentiation upon binding with an increasing number of newly defined dietary, cellular, and microbe-derived ligands. In addition, AhR is a convergence point for several signaling cascades, which may be involved in the diverse diseases caused by binding of the persistent ligand TCDD with extremely high affinity to AhR. A comprehensive understanding of physiological and pathological processes initiated by endogenous AhR agonists and antagonists may allow for the therapeutic regulation of AhR activity. Thus, the AhR can be a valuable diagnostic marker and therapeutic target for human diseases.