In the context of HIV infection, HIV infection upregulates IDO expression by HIV tat, nef, and proinflammatory mediators (Smith et al., 2001; Schroecksnadel et al., 2007), which promote Trp degradation to KP to generate various Kyn intermediate metabolites (Huengsberg et al., 1998; Murray, 2003b). The gene discussed is IDO1; the disease is HIV infectious disease.