Biological activities of Junin virus proteins. II. Complement-fixing polypeptides associated with the soluble antigen...

In the Junin virus-infected cell, there is a soluble antigen (SAg), which we have detected by complement fixation. PAGE of purified SAg revealed two polypeptides with molecular weights of 20,000 and 25,000. An antigenically identical component, which was demonstrated by complement fixation and immunodiffusion tests and which had the same electrophoretic profile as SAg, was found after proteolytic breakdown of purified virions. SAg is an internal component of the virion, since it is unable to stimulate neutralizing antibodies and it can be obtained from viral particles whose envelopes have been removed by Triton X-100 treatment. The antigenic determinant apparently resides in the major nonglycosylated polypeptide (nucleoprotein P64), since the proteolytic degradation product is obtained in quantity and it is nonglycosylated.