Expression of the Major Core Protein vp7 of Bluetongue Virus in E coli and Use as a Diagnostic Antigen in c-ELISA

The RNA S7 encoding serogroup-specific antigen VP7 of bluetongue virus (BTV) was cloned and inserted into pBAD/Thio TOPO vector. The recombinant plasmid was identified by restriction analysis, PCR and sequence. The results of SDS-PAGE and Western immunoblotting revealed that the VP7 was expressed in E coli LGM194 in a high level and the recombinant fusion protein with a molecular mass of approximately 54.5 kDa. Competition enzyme-linked immunosorbent assay (c-ELISA) indicated that the expressed BTV VP7 was similar in antigenicity to that of the native virus as revealed by its reactivity with monoclonal antibody (MAb) specific to BTV. The availability of a reliable BTV recombinant VP7 could enhance our existing assay for detection of BTV-specific antibodies. The performance of the c-ELISA and agar gel immunodiffusion (AGID) were compared using 3657 animal field sera from herds in China and animal imported. The purified recombinant VP7 antigen is highly immunogenic and has been shown in a c-ELISA to be reactive with antisera of 24 BTV serotypes (1 to 24). No cross-reactivities were detected between BTV and EHDV in c-ELISA tests. The data indicated that VP7 is a highly conserved protein amongst BTV serotypes. The c-ELISA tests indicate that the recombinant VP7 is useful as a diagnostic reagent for serological tests of BTV.