TNFRSF9 and Japanese encephalitis: Because virus load at the periphery of 4-1BB KO mice was lower than that of wild-type BL/6 mice in the present study, we assessed whether 4-1BB signaling would affect JEV replication and IFN-I innate response in myeloid-derived cells as primary target cells, in order to further define the role of 4-1BB signaling in controlling JE progression.