Antigenic relationship and further characterization of two major Borna disease virus-specific proteins.

After immunization of mice with isolated Borna disease virus (BDV)-specific proteins having Mrs of 38/39K and 24K, monoclonal antibodies (MAbs) were obtained which were specific for one of the antigens in Western blot analysis. However, in immunoprecipitation assays it was found that some MAbs of each specificity reacted exclusively with their respective antigen from BDV-infected cells, whereas other MAbs coprecipitated the heterologous protein. The relationship between the 38/39K and 24K proteins was demonstrated by two-dimensional peptide mapping, which revealed four identical peptides. Additionally, it was found that neither the 38/39K nor the 24K protein is glycosylated, but that the 24K protein is phosphorylated at serine residues. Experiments employing various cell separation protocols revealed that the 38/39K and the 24K proteins are evenly distributed within infected cells; this was confirmed by immunofluorescence techniques using 38/39K- or 24K-specific MAbs. Iodination experiments clearly demonstrated that only the 38/39K protein is expressed on the surface of virus-infected cells.