Advance of the role of Aromatic hydrocarbon receptor in immunoregulation related to tryptophan metabolism

Aromatic hydrocarbon receptor(AhR), an intracellular receptor, contains multiple ligand binding sites. Various ligands of AhR are divided into exogenous and endogenous ligands according to the origination. Different ligands bind and activate AhR, regulating the transcription of downstream target genes, especially CYP1 from Cypcytochrome P450 gene family, which plays an essential role in different pathological problems, as well as in the normal development and function of organism. Kynurenine(Kyn), a key metabolic product of tryptophan(Trp), metabolic products of which are major types of endogenous ligands of AhR, has an impact on adaptive immune by manipulating the polarization and activity of immunocytes. Kyn has been focus for its supressive effect in anti-tumor immunity and raised concern recently for its intriguing role in allograft immunoregulation. Research advances in the role of AhR in immunoregulation related to tryptophan metabolism will be illustrated in this review in detail. Key words: Receptors, aryl hydrocarbon; Tryptophan; Kynurenine; Tumor escape; Transplantation tolerance