A complex neutralization domain of bluetongue virus serotype 17 defines a virulence-associated marker

A panel of seven monoclonal antibodies (MAb) was used to characterize a virulence-associated marker on bluetongue virus serotype 17 (BLU-17). These MAbs poorly neutralize virulent BLU-17 isolates, but effectively neutralize avirulent isolates (2). The MAbs immunoprecipitated VP2, an outer capsid protein, of both virulent and avirulent BLU-17 isolates despite their failure to neutralize the virulent isolates. The molecular mass (M(r)) of VP2 was calculated from the mobility in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The M(r) of VP2 was estimated as 100,000 Da for the virulent isolates and 97,500 Da for the avirulent isolates. The seven MAbs were tested in a competitive enzyme-linked immunosorbent assay (ELISA) and found to bind at least three overlapping epitopes. In addition, neutralization-resistant variants were selected for five different MAbs. The Variants were tested in virus neutralization assays against the panel of seven MAbs, and three major neutralization patterns were observed, again suggesting at least three distinct epitopes. Minor differences within each neutralization pattern were also observed. The results from the binding and neutralization studies suggested that the seven MAbs define a complex neutralization domain on VP2, comprising at least three overlapping epitopes.