In our mechanistic studies on the role of IDO in regulating JE progression, IDO-ablated mice showed early and increased CNS infiltration by myeloid cells (Ly-6Chi monocytes and Ly-6Ghi granulocytes) and lymphoid cells (CD3−NK1.1+DX5+ NK, CD4+, and CD8+ T-cells), which were associated with a reduced viral burden in the CNS. This evidence concerns the gene IDO1 and Japanese encephalitis.