Antigenic parvovirus B19 coat proteins VP1 and VP2 produced in large quantities in a baculovirus expression system

Two baculovirus expression vectors derived from Autographica californica nuclear polyhedrosis virus (AcNPV) were prepared containing the complete 2.5 kb coding region for parvovirus B19 coat protein VP1 (AcB19VP1L) and the 1.8 kb coding region for VP2 (AcB19VP2L), placed under the control of the polyhedrin promoter. The recombinant viruses were used to infect Spodoptera frugiperda cells and the proteins expressed were analysed using appropriate antibodies. AcB19VP1L-infected cells produced B19 VP1 as shown by its reaction with 13 human sera containing B19-specific antibodies in Western blot analysis and indirect immunofluorescence. The signal seen with VP1 in immunofluorescence makes it suitable for the development of a diagnostic assay based on this technique. VP1 also reacted with two monoclonal antibodies (mAbs) specific for the B19 protein part of a 196 kDa beta-galactosidase B19 fusion protein expressed in E. coli. Cells infected with AcB19VP2L produced B19 VP2 which reacted with the same human sera in indirect immunofluorescence and with five of the 13 sera in Western blots. VP2 did not react with the fusion protein-specific mAbs. The large amounts of viral antigen produced in this system means the development of widely available diagnostic tests for B19 infection and the further characterization of the B19 structural proteins are within reach.