Borna Disease Virus p24 and p38/40 Synthesized in a Baculovirus Expression System: Virus Protein Interactions in Insect and Mammalian Cells

To facilitate studies of the individual vital proteins, two Borna disease virus proteins, p24 and p38/40, were synthesized in vitro by means of a baculovirus expression system and examined for antigenic identity to vital proteins from BDV-infected cells. Recombinant proteins p24 and p38/40 were nearly identical in size to the vital proteins from SDV-infected cells. Immunoblot and immunocytochemistry analysis of BDV proteins from infected tissue culture cells and rat brain showed binding of antisera directed against the recombinant proteins. Specific recognition of the recombinant proteins by Borna disease virus-specific convalescent antisera and monoclonal antibodies further demonstrated that the antigenic characters of the p24 and p38/40 had been conserved. Polyclonal antibody directed against either of the recombinant proteins recognized only the protein used as immunogen, without cross reactivity with the other recombinant protein, indicating no common epitopes. Moreover, these data confirmed the proposed gene coding assignments of ORF I and II of SDV p38/40 and p24, respectively. Both of the recombinant proteins were secreted Into the media of insect cells in tissue culture, but secretion of recombinant p24 was evident only as a dimeric form and not with the monomeric form. Immunoprecipitation studies performed with monoclonal antibodies and BDV proteins from infected rat brain suggested that a heterodimer forms via binding of p40 to the p24.