Although these immunoregulatory and thus, stress-protective effects of IDO activation at first glance are in contrast to the above described effects of IDO activation on brain tryptophan and/or 5-HT depletion and induction of sickness behavior (see “How do inflammatory signals contribute to the development of mental disorders?”) , we hypothesize that the latter, at least in the acute context, also represents a positive adaptation increasing an individual’s regenerative capacities during stress/inflammation. The gene discussed is IDO1; the disease is mental disorder.