The site of action of peripheral cytokines in the CNS is the hypothalamus, where a significant increase in the expression of TNFα, interleukin-12 (IL-12), induced nitric oxide synthase (iNOS) and indolamine 2,3-dioxygenase (IDO) was observed from day 21 post-infection when the peak of maximal immune protection in the lungs was observed in this murine model [10]. Here, IDO1 is linked to infection.