Attenuation of Japanese encephalitis virus by selection of its mouse brain membrane receptor preparation escape variants

Six variants of Japanese encephalitis (JE) virus strain P3 were selected for resistance to binding to mouse brain membrane receptor preparations (MRP). All but one of these MRP escape (MRP(R)) variants were significantly attenuated in mice for both neuroinvasiveness (>200-fold) and neurovirulence (>500-fold) compared to their parent virus. Attenuated mouse brain MRP(R) variants could be detected in the sera of mice following either intracerebral (i.c.) or intraperitoneal inoculation, whereas virus was detected only in brains of mice following ic inoculation. Immunization of mice with MRP(R)S induced neutralizing antibodies and protected mice against challenge with wild-type JE virus. A common amino acid mutation was found in the envelope (E) protein gene of all attenuated mouse brain MRP(R) variants at residue E- 306 compared to P3 virus grown in mosquito C6-36 cells or plaque purified and amplified in monkey kidney Vero cells. This amino acid is putatively responsible for attenuation due to alteration in binding of JE virus to its cell receptor in mouse brain. The methodology developed in this study has general applicability to the attenuation of virulence of viruses and to the identification of agents that will block amino acids in a viral attachment protein(s) that interacts with cell receptors.