Figure 3: Possible model for NO-mediated regulation of IDO in IFN-γ-primed mononuclear phagocytes. NOS, nitric-oxide synthase; IDO, indoleamine 2,3-dioxygensae, L-Arg, L-arginine; L-Trp, L-tryptophan; IFN-γ, interferon-; NO, nitric oxide; Kyn, kynurenine; 3-HAA, 3-hydroxyanthranilic acid; QA, quinolinic acid; SNP, sodium nitroprusside; GTN, glyceryl trinitrate; SNAP, S-nitroso-N-acetylpenicillamine; DEANO, diethylaminodinitric oxide. SNP, DEANO, and SNAP release NO extracellularly, while GTN is thought to release NO intracellularly [201].