Purification and characterization of the major group-specific core antigen VP7 of bluetongue virus synthesized by a recombinant baculovirus.

The major core protein, VP7, of bluetongue virus serotype 10 (BTV-10) has been purified from insect cells infected with a genetically manipulated recombinant baculovirus. The high level expression of VP7 (in excess of 100 mg per litre of culture) and its presence in the soluble fraction of infected cells following lysis by detergent has allowed the purification of the protein virtually to homogeneity (95%) by a simple two-step procedure of ammonium sulphate fractionation and ion-exchange chromatography. The purified antigen is highly immunogenic and has been shown in an ELISA to be reactive with antisera of 24 BTV serotypes (1 to 24) as well as with an antiserum raised to African horsesickness virus type 4 (AHSV-4), a representative of another serogroup of orbiviruses. In confirmation of these data a monospecific antiserum raised with the expressed product has been shown by Western blot analyses to react with other BTV serotypes as well as with two serotypes of epizootic haemorrhagic disease virus (EHDV-1 and EHDV-2), a closely related orbivirus. The data indicated that VP7 is a highly conserved protein amongst BTV serotypes and at least partly conserved amongst three serogroups of orbiviruses.