Abstract
Three group A arboviruses, Sindbis (SIN), western (WEE) and eastern equine encephalitis (EEE), were selectively degraded with a nonionic detergent to yield a core particle and a soluble envelope component. Antigenic analysis by using radioimmune precipitation techniques revealed marked antigenic similarity among the core particles of the three viruses. The soluble envelope component exhibited antigenic specificity similar to that of intact virions. A close relationship between SIN and WEE envelopes was shown, whereas EEE envelope antigen appeared antigenically specific. These data indicate that nucleocapsids of group A arboviruses contain an antigenic determinant common to the group; the envelope contains virus-specific antigens as well as antigens which relate members of a subgroup.