Antigenic Variants of Arboviruses

Summary A method for monitoring variations in antigenic constitution of arbovirus strains has been developed. The technique is based upon the magnitude of cross neutralization of virus strains by antisera prepared against virus fractions obtained from gradient sedimentation of a single strain. At a specific point in time, antigenically distinct Western encephalitis viral populations were found to coexist within various tissues of an infected mouse. The antigenic nature of such populations was found to be unstable and in a continuous state of flux. Eastern encephalitis virus strains had distinct antigenic properties when stocks were examined directly. The antigenic properties also varied when strains were carried from one passage to another in mice or in tissue culture, or when passaged in parallel in mice and tissue culture. The phenomenon of antigenic variation of strains was explained in part by the differential selection and ultimate accumulation of certain antigen subpopulations over others during virus replication in various tissue or cell types.