Definition of neutralizing sites on African horse sickness virus serotype 4 VP2 at the level of peptides

The antigenic structure of African horse sickness virus (AHSV) serotype 4 c apsid protein VP2 has been determined at the peptide level by PEPSCAN analy sis in combination with a large collection of polyclonal antisera and monoc lonal antibodies. VP2, the determinant for the virus serotype and an import ant target in virus neutralization, was found to contain 15 antigenic sites . A major antigenic region containing 12 of the 15 sites was identified in the region between residues 223 and 400. A second domain between residues 5 68 and 681 contained the three remaining sites. These sites were used for t he synthesis of peptides, which were later tested in rabbits. Of the 15 syn thetic peptides, three were able to induce neutralizing antibodies for AHSV -4, defining two neutralizing epitopes, 'a' and 'b', between residues 321 a nd 339, and 377 and 400, respectively. A combination of peptides representi ng both sites induced a more effective neutralizing response. Still, the re latively low neutralization titres make the possibility of producing a synt hetic vaccine for AHSV unlikely. The complex protein-protein interaction of the outer shell of the viral capsid would probably require the presence of either synthetic peptides in the correct conformation or peptide segments from the different proteins VP2, VP5 and VP7.