Protective and immunogenic effects of Escherichia coli-expressed infectious pancreatic necrosis virus (IPNV) VP2-VP3 fusion protein in rainbow trout

• IPNV VP2-VP3 fusion gene was cloned into a pET-26b expression vector and recombinant protein was produced in E. coli host.
• E. coli-expressed IPNV VP2-VP3 fusion protein (vaccine) was intraperitoneally administered to rainbow trout.
• The recombinant IPNV vaccine induced strong immune responses and protected vaccinated fish against IPNV challenge.
• The relative percent survival rate (RPS) of survivors was 83% for the vaccinated group.
• E. coli-expressed IPNV vaccine significantly reduced virus load in tissues of the vaccinated fish.

Infectious Pancreatic Necrosis Virus (IPNV) is a member of the family Birnaviridae which causes significant losses in the aquaculture industry. To develop a recombinant vaccine for IPNV, a cDNA construct of IPNV VP2-VP3 fusion gene was prepared and cloned into an Escherichia coli (E. coli) expression vector (pET-26b) to obtain recombinant protein products. A study was conducted to determine the antibody responses and protective capacity of this recombinant vaccine expressing VP2-VP3 fusion protein. Subsequently, juvenile rainbow trout were inoculated by injecting purified recombinant IPNV VP2-VP3 proteins, followed by challenge with virulent IPNV in rainbow trout. Our results demonstrate that recombinant E. coli derived VP2-VP3 fusion protein induced a strong and significantly (P < 0.05) higher IgM antibody response in serum samples compared to control groups. Following intraperitoneal challenge, the relative percent survival (RPS) rate of survivors was 83% for the vaccinated group. Statistical analysis of IgM levels indicated that immunogenicity of recombinant VP2-VP3 protein, combined with adjuvant, was much higher than any other groups of rainbow trout challenged with virulent IPNV. This result was confirmed by measuring the viral loads of IPNV in immunized rainbow trout which was drastically reduced, as analyzed by real-time RT-PCR. In summary, we demonstrate that E. coli-expressed IPNV VP2-VP3 injectable vaccine is highly immunogenic and protective against IPNV infection.