TY - JOUR T1 - The Aryl Hydrocarbon Receptor in Barrier Organ Physiology, Immunology, and Toxicology JF - Pharmacological Reviews JO - Pharmacol Rev SP - 259 LP - 279 DO - 10.1124/pr.114.009001 VL - 67 IS - 2 AU - Charlotte Esser AU - Agneta Rannug A2 - Ma, Qiang Y1 - 2015/04/01 UR - http://pharmrev.aspetjournals.org/content/67/2/259.abstract N2 - The aryl hydrocarbon receptor (AhR) is an evolutionarily old transcription factor belonging to the Per-ARNT-Sim–basic helix-loop-helix protein family. AhR translocates into the nucleus upon binding of various small molecules into the pocket of its single-ligand binding domain. AhR binding to both xenobiotic and endogenous ligands results in highly cell-specific transcriptome changes and in changes in cellular functions. We discuss here the role of AhR for immune cells of the barrier organs: skin, gut, and lung. Both adaptive and innate immune cells require AhR signaling at critical checkpoints. We also discuss the current two prevailing views—namely, 1) AhR as a promiscuous sensor for small chemicals and 2) a role for AhR as a balancing factor for cell differentiation and function, which is controlled by levels of endogenous high-affinity ligands. AhR signaling is considered a promising drug and preventive target, particularly for cancer, inflammatory, and autoimmune diseases. Therefore, understanding its biology is of great importance. ER -