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 effective ly neutralize avirulent isolates (2). The MAbs immunoprecipitated VP2, an outer capsid protein, of both virulent and avirulent BLU-17 isolat es despite their failure to neutralize the virulent isolates. The mole cular mass (M(r)) of VP2 was calculated from the mobility in sodium do decyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The M(r) of VP2 was estimated as 100,000 Da for the virulent isolates and 97,50 0 Da for the avirulent isolates. The seven MAbs were tested in a compe titive enzyme-linked immunosorbent assay (ELISA) and found to bind at least three overlapping epitopes. In addition, neutralization-resistan t variants were selected for five different MAbs. The Variants were te sted in virus neutralization assays against the panel of seven MAbs, a nd three major neutralization patterns were observed, again suggesting at least three distinct epitopes. Minor differences within each neutr alization 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 e pitopes.