Cloning and expression of an antigenic domain of glycoprotein gE of pseudorabies virus in Escherichia coli and its use as antigen in diagnostic assays

SUMMARY Use of a combination of an effective gE gene-deleted pseudorabies virus ( prv ) vaccine with a companion diagnostic kit for prv glycoprotein gE has proven successful in several pseudorabies-eradication programs. To produce a large quantity of functional gE protein for development of a prv -gE diagnostic kit, an Escherichia coli expression system containing the distal region of the prv -gE gene of a prv strain CF was constructed. The expressed protein contained 134 amino adds of gE protein (amino acids 77-210) fused to a 19-amino acids tag containing 6 histidine residues. After induction, a truncated prv -gE polypeptide of 18-kd was expressed to about 20% of the total E coli proteins. Results of immunoblot analysis indicated that this E coli -produced prv -gE protein reacted specifically with serum from prv -hyperimmunized pigs and from field prv -infected pigs, but not with serum samples from specific-pathogen-free pigs or pigs inoculated with gE-deleted prv vaccine. These data indicate that, although the recombinant gE protein is produced in E coli, it still retains the antigenicity of the viral gE glycoprotein. Comparison between the recombinant gE protein, using immunoblot analysis with a commercial gE ELISA containing natural prv -gE protein, revealed comparable test performance. This finding indicated that recombinant gE protein produced by E coli can be used for development of a companion serologic assay for a prv -gE gene-deleted vaccine.