Fine tuning of the immune response by the Aryl Hydrocarbon Receptor

Abstract

This issue of Seminars in Immunopathology focuses on the role of the ligand-activated transcription factor aryl hydrocarbon receptor (AhR) in controlling the immune response. AhR has been studied for many years by toxicologists as the receptor mediating the toxic effects of the environmental pollutant 2,3,7,8tetrachlorodibenzo-p-dioxin. However, AhR ligands are provided by the diet and are also generated in the gastrointestinal as a result of complex interactions between the host and the commensal flora. Moreover, endogenous ligands such the 2-(1′H-indole-3′carbonyl)-thiazole-4-carboxylic acid methyl ester or the tryptophan-derivative kynurenine are produced by the metabolism. Thus, the high degree of conservation of AhR throughout evolution and the existence of natural, nontoxic ligands suggests that AhR plays a physiological role in health and disease. The past decade has witnessed significant advances in our understanding of the importance of AhR as a regulator of innate and adaptive immunity. This issue covers several aspects of the role of AhR in the control of the immune response and its relevance for the pathogenesis of immune related diseases. Lawrence and Vorderstrasse outline how AhR influences host response to viruses, bacteria, and parasites, noting how the effects of AhR signaling differ during the response to each pathogen and, therefore, suggesting the existence of pathogen-specific cues that modulate AhR activity. Quintana discusses indetailthe roleofAhR signaling inthecontrol ofT cell and dendritic cell differentiation, and its relevance for the