Immunologic Characterization of Western Equine Encephalomyelitis Virus Strains

Abstract

Ten WEE strains and plaques derived from each were compared by the plaque reduction neutralization test with antisera prepared in guinea pigs. The analysis indicated that most of the strains were comprised of subpopulations of virus having antigenically distinct properties and that the quantitative distribution of common but distinct antigens determined in part the immunologic properties of each strain. Hyperimmune guinea pig sera prepared from plaque purified viruses were more specific in their cross-neutralizing properties than similar antisera prepared from unpurified strains. The antigenic variations of 100 WEE strains were studied using goat antiserum prepared from antigenically distinct plaque viruses derived from the McMillan strain of WEE. Three antigenic groups (phases) of the virus could be differentiated, and these were designated aphasic, phase I and phase II variants. There appeared to be a general pattern in the geographic distribution of these variants. The antigenic properties of phasic strains could be altered by serial intracerabral passage in infant mice or passage in primary rhesus monkey kidney cultures. No changes in antigenic properties were recognized when phasic strains were passaged in primary chick embryo cultures. Aphasic virus strains were antigenically stable when passaged in different host systems.