KMO and brain disorder: When the immune system is activated, KMO is stimulated by cytokines in the periphery and brain, which activates inflammation‐mediated dysregulation of the KP, producing neurogenic excitatory damage, which is responsible for many major brain diseases (Garrison et al., 2018), and the lower KMO expression and the higher KYNA production may contribute to dysfunctional effector CD4+ T‐cell response (Rad Pour et al., 2019).