We have used a serotype-specific monoclonal antibody to locate a neutralization epitope on the outer capsid protein, VP2, of the bluetongue virus 13. This surface-accessible region of the virion was recognized by a monoclonal antibody, D24.15, which exhibited serotype-specific neutralizing activity as determined by plaque reduction assay. In Western blots, this monoclonal antibody reacted only with the VP2 of bluetongue virus 13, but not with any of the other US BTV serotypes. Competition with sequence-specific synthetic peptides identified only one linear synthetic peptide (EMDD-DETEYE), corresponding to amine acids 642-651 of VP2 of bluetongue virus 13 that could block both the neutralizing activity of MAb D24.15 and its specific binding to VP2 of BTV-13. However, oligoclonal antibody against this synthetic peptide did not exhibit any neutralizing activity. These data suggest that the serotype-specific neutralization determinant of the outer capsid protein VP2 is located on the surface of the BTV-13 virion and represents the major component of a conformational epitope.
