Indoleamine 2,3-Dioxygenase (IDO) (吲哚胺 2,3 双加氧酶)

Indoleamine 2, 3-dioxygenase (IDO) is an inflammatory cytokine-inducible rate-limiting enzyme of the tryptophan (Trp) catabolism, which is involved in the inhibition of intracellular pathogen replication as well as in immunomodulation. To date, three types of tryptophan-metabolizing enzymes have been identified: IDO1, IDO2 and tryptophan 2,3-dioxygenase 2.

IDO is an intracellular enzyme that is constitutively expressed in several human and mouse cells. Being present in innate immune cells, such as Mos and dendritic cells (DCs), IDO catalyzes the initial rate-limiting step of tryptophan (Trp) catabolism, thus leading to the production of immunoregulatory catabolites (collectively known as kynurenines).

The IDO gene promoter contains multiple sequence elements that confer responsiveness to proinflammatory mediators, thereby demonstrating the strong correlation between inflammation and induced IDO expression.