It has been reported that IDO2 can convert tryptophan into kynurenine upon the stimulation by proinflammatory cytokines, resulting in increased depressive symptoms.[26] Another study indicated IDO2-v1 and IDO2-v3 were most susceptible to induction by inflammation in the mouse hippocampus OHSCs to meet the increased energy demand related to inflammation.[27] Combined with our study result, IDO2 was an inflammation-induced gene associated with the development of depression. Here, IDO2 is linked to major depressive disorder.