IDO1 and HIV infectious disease: Bacteria belonging to the Proteobacteria phylum enhanced indoleamine 2,3-dioxygenase (IDO) activity and increased metabolism of tryptophan into kynurenine derivatives, corresponding with an imbalance of Th17/Treg during chronic HIV infection and in HIV-infected subjects under ART (Jenabian et al., 2013; Vujkovic-Cvijin et al., 2013).