Insect Cell-Derived VP2 of Infectious Bursal Disease Virus Confers Protection against the Disease in Chickens

Abstract

Infectious bursal disease virus (IBDV) has become a major problem in recent years. Conventional vaccines make use of attenuated or inactivated viral strains, but these are gradually losing their effectiveness. We investigated the possibility of using purified VP2, a subunit of IBDV structural protein expressed in insect cells, as a vaccine. The VP2 gene was cloned into pAcYM1. The cloned gene was expressed in a baculovirus system, giving rise to a high quantity of recombinant VP2 (rVP2) protein. The length of the VP2 is 453 amino acids, and it contains two additional amino acids of the baculovirus at the carboxyl terminus. The molecular mass of the protein is about 48 kD. The rVP2 protein reacted with antibodies raised against viral VP2 and had a similar molecular weight. This protein was tested in a controlled vaccination experiment and compared with an inactivated commercial vaccine. High levels of antibodies were raised by the vaccinated birds. The vaccinated birds were challenged with a pathogenic viral strain. rVP2-vaccinated chickens exhibited high resistance to the virus. No mortality or weight changes in the bursa of Fabricius were observed in the vaccinated birds, whereas in the negative control birds, vaccinated with phosphate buffer, up to 50% mortality was found. Higher levels of antibodies were found by enzyme-linked immunosorbent assay in birds vaccinated with rVP2 compared with those vaccinated with the commercial vaccine. This study suggests the potential use of the isolated rVP2 as a subunit vaccine.

Expression of ORF A1 of infectious bursal disease virus results in the formation of virus-like particles.

“…This might explain why both subunit vaccines based on purified VP2 and recombinant live vaccines, generated by insertion of the VP2 coding region within the genome of heterologous viruses, fail to match the protection levels induced after immunization with inactivated virus (Mu$ ller et al, 1992 ;Heine & Boyle, 1993 ;Vakharia et al, 1993, Darteil et al, 1995Pitcovski et al, 1996). The structure of the VLP described in this report appears to be identical to that of complete IBDV particles.…”

Self-assembly of the infectious bursal disease virus capsid protein, rVP2, expressed in insect cells and purification of immunogenic chimeric rVP2H particles by immobilized metal-ion affinity chromatography

“…We demonstrate that the immunoreactive expressed rVP2 protein can form a particulate structure. This observation may explain the high protective efficacy obtained for chickens vaccinated with the rVP2 protein generated from the baculovirus expression system (Pitcovski et al, 1996). As widely believed, the particulation of the antigen can enhance its immunogenic performance in vaccinated animals.…”

“…The baculovirus expression system has also been applied to the expression of IBDV structural proteins (Pitcovski et al, 1996;Varharia et al, 1993;Wang et al, 1994). Varharia et al (1993) constructed a recombinant baculovirus to express the first coding region of IBDV structural proteins (VP2, VP4, and VP3) in Sf9 cells.…”

Genetic detoxification and adjuvant-activity retention ofEscherichia colienterotoxin LT

“…end of each primer to allow cloning of the resultant polymerase chain reaction (PCR) fragment into pQE30 plasmid (Qiagen, Valencia, California, USA). The gene coding for the wild-type LT protein (wtLT) was amplified by PCR, as described previously (Pitcovski et al ., 1996). Briefly, the PCR solution contained 1 u Taq polymerase (Promega, Madison, Wisconsin, USA), 5 ml Taq buffer (20 mM Tris Á/HCl, pH 8.3, 50 mM KCl, 2 mM MgCl 2 ) and 20 pmol each primer, in a final volume of 50 ml.…”