IDO1 and psychiatric disorder: This, then, suggests the possibility of a link between COVID-19 infections and neuroinflammation, peripheral immune cell invasion into the CNS, hypothalamic-pituitary (HPA) axis dysfunction, BBB disruption, neurotransmission alteration, microglia activation, oxidative stress, and indoleamine 2,3-dioxygenase 1 (IDO) activation, all of which represent the pathways linking the psychopathological mechanism and the immune system, possibly underpinning the etiology of psychiatric disorders [135,141,143,144,145].