The polyclonal antibody recognizes rat indoleamine 2,3-dioxygenase 1 (IDO1 or INDO). IDO1 is an intracellular heme-containing enzyme of 45 kD that catalyzes the oxidative cleavage of the indole ring of several important regulatory molecules, like tryptophan, serotonin and melatonin. By doing this, IDO1 initiates the production of biologically active metabolites, commonly referred to as kynurenines. IDO1 is widely expressed in a variety of human tissues as well as in macrophages and dendritic cells (DCs). In inflammation, interferons (IFNs) act on specific receptors to trigger IDO1 induction. The production of IFN-gamma and induction of IDO1 represent important antimicrobial mechanisms. Degradation and depletion of tryptophan by IDO1 inhibits the growth of viruses, bacteria and parasites. Furthermore, IDO1 plays a complex and crucial role in immunoregulation during infection, pregnancy, autoimmunity, transplantation, and neoplasia. By local depletion of tryptophan and increasing proapoptotic kynurenines, IDO1 greatly affects T-cell proliferation and survival, both in vitro and in vivo, and also affects B-cell and NK-cell function and survival. There is a central role for IDO1 expression in tolerance involving regulatory cells and DCs. IDO1 acts as an intermediate pathway in LPS-induced production of reactive oxygen species and NF-kappaB activation, two processes that lead to DC maturation.In addition to classic IDO (IDO1) indoleamine 2,3-dioxygenase-2, indoleamine 2,3-dioxygenase-like protein or proto-indoleamine 2,3 dioxygenase (IDO2, IDO-2, INDOL1 or proto-IDO) has been described.