Indoleamine 2,3-Dioxygenase (IDO)

Indoleamine 2, 3-dioxygenase (IDO) is an intracellular enzyme that catalyzes the transformation of L-tryptophan to N-formylkynurenine, which is the first and rate-controlling step in the kynurenine pathway. IDO is a rate-limiting enzyme that catalyzes the degradation of tryptophan into kynurenine and is recognized to exert a tolerizing effect on T cells that require tryptophan to proliferate5. IDO also plays an important role in the activation and regulation of functionally quiescent regulatory T cells. IDO is a heme-containing enzyme that catalyzes the oxidative cleavage of 2,3 double bond of indole ring. IDO has the ability to inhibit T-cell activation by tryptophan starvation, whereas T-cell survival and proliferation are regulated by O2 free radicals and kynurenine derivatives. IDO plays a crucial role in autoimmunity,infections and malignancies. Indoleamine-2,3-dioxygenase (IDO) one of the most important immunoregulator enzyme responsible for metabolism of tryptophan as part of Kynurenin pathway. Tryptophan is catabolized in the tumor tissue by the rate-limiting enzyme IDO expressed in tumor cells or antigen presenting cells.