Indoleamine 2,3-dioxygenase

Indoleamine-pyrrole 2,3-dioxygenase (IDO or INDO EC 1.13.11.42) is an immunomodulatory enzyme secreted by some alternatively activated macrophages and other immunoregulatory cells (also used as an immune subversion strategy by many tumors).

IDO is the first and rate limiting enzyme of Tryptophan catabolism through Kynurenine pathway, thus causing depletion of tryptophan which can cause halted growth of microbes as well as T cells.

It catalyzes conversion of L-tryptophan to N-formylkynurenine.