Alphavirus neurovirulence: monoclonal antibodies discriminating wild-type from neuroadapted Sindbis virus.

Wild-type Sindbis virus strain AR339 (SV) and a neurovirulent mutant (NSV), derived by neonatal and weanling mouse brain passage, both cause acute fatal encephalitis in neonatal mice, but NSV alone kills adult mice. NSV cannot be distinguished from SV by immune sera or simple biochemical tests. To localize the molecular changes associated with neuroadaptation, we used a new array of 30 anti-SV monoclonal antibodies to probe for differences between SV and NSV in four tests: immunoprecipitation, enzyme-linked immunosorbent assay binding, neutralization, and hemagglutination inhibition. Seventeen monoclonal antibodies detected differences. Both E1 and E2 glycoprotein gene products were altered during neuroadaptation, but the preponderance of changes was clustered on E2. The capsid protein C was not measurably altered. Mapping of both viruses with these monoclonal antibodies showed that during neuroadaptation SV topography substantially shifted, masking and unmasking biologically important neutralization and hemagglutination inhibition sites. These conformational rearrangements, predominantly on E2, coincided with the acquisition of increased neurovirulence and new lethality for adult mice.