IDO expression is low or absent in the normal CNS,59 but can be induced in macrophages, microglia, neurons, astrocytes,60,61 and vascular endothelial cells.62,63 Increased enzyme expression can be provoked in neuro-inflammatory disorders, such as cerebral malaria.12,59 The increased IDO expression is believed to be mainly caused by the presence of T-lymphocytes and/or IFN-γ59 and other cytokines such as TNF.64 The predominant physiological inducer of IDO expression is IFN-γ. This evidence concerns the gene TNF and cerebral malaria.