IDO1 is also known as Indolamine 2,3-dioxygenase, Indole 2,3-dioxygenase, and Indoleamine-pyrrole 2,3-dioxygenase. IDO is a ubiquitously expressed cytoplasmic protein with a predicted molecular weight of approximately 45 kD. Indoleamine 2,3-dioxygenase (IDO) is one the best known IFN-gamma inducible genes. The product of IDO gene catalyzes the degradation of the essential amino acid L-tryptophan to N-formylkynurenine. IDO has been implicated to protect against intracellular and extracellular pathogens. It also has been shown to maintain the special immune suppressive status of immune-privileged sites such as the brain, eyes, kidney, and placenta.