Symptoms like depression and impaired quality of life have also been proposed to be exacerbated by IFN-γ induced indoleamine 2,3-dioxygenase 1 (IDO1): as the subsequent degradation of Trp along the kynurenine pathway reduces the formation of serotonin, which can go along with heightened anxiety, cognitive deficits, and sleep disturbances22–26. Here, IDO1 is linked to major depressive disorder.