TDO is primarily found in the liver and neuronal tissue and is regulated by glucocorticoids, where it helps to maintain homeostasis of dietary Trp levels and mediate immune-related diseases and central nervous system disorders (41) The function of IDO1 was initially described as an innate mechanism of defense against microbial invasion because IDO1 could induce depletion of Trp (41). This evidence concerns the gene IDO1 and central nervous system disorder.