IDO1 encodes indoleamine 2,3-dioxygenase (IDO) - a heme enzyme that catalyzes the first and rate-limiting step in tryptophan catabolism to N-formyl-kynurenine. This enzyme acts on multiple tryptophan substrates including D-tryptophan, L-tryptophan, 5-hydroxy-tryptophan, tryptamine, and serotonin. This enzyme is thought to play a role in a variety of pathophysiological processes such as antimicrobial and antitumor defense, neuropathology, immunoregulation, and antioxidant activity. Through its expression in dendritic cells, monocytes, and macrophages this enzyme modulates T-cell behavior by its peri-cellular catabolization of the essential amino acid tryptophan.IDO1 (Indoleamine 2,3-Dioxygenase 1) is a Protein Coding gene. Diseases associated with IDO1 include Listeriosis and Trypanosomiasis. Among its related pathways are superpathway of tryptophan utilization and Viral mRNA Translation. GO annotations related to this gene include heme binding and tryptophan 2,3-dioxygenase activity. An important paralog of this gene is IDO2.