Altogether, these findings suggest that IDO has prominent importance during bacterial meningitis due to the following: its capacity to maintain PARP-1 activity through NAD synthesis, protecting against cell death [6,16]; the generation of reactive oxygen species (ROS), helping the defense mechanisms in addition to maintaining IDO activity [8-10,26]; its capacity to produce some antioxidant metabolites [27]; and regulating the immune response via the known vessel-relaxing ability which KYN possess during inflammation and other immunosuppressive mechanisms [18,19,42]. This evidence concerns the gene IDO1 and bacterial meningitis.