A review also described the promotion of MDD by the pro-inflammatory factor IFN-γ, which induces IDO1, activates hypothalamic-pituitary-adrenal (HPA) axis as well as microglia, and drives Th1 cell infiltration into the CNS, thus participating in the pathogenesis of MDD (Inserra et al., 2019). The gene discussed is IDO1; the disease is major depressive disorder.