INSECT CELL-DERIVED VP2 OF INFECTIOUS BURSAL DISEASE VIRUS CONFERS PROTECTION AGAINST THE DISEASE IN CHICKENS

Infectious bursal disease virus (IBDV) has become a major problem in r ecent years. Conventional vaccines make use of attenuated or inactivat ed viral strains, but these are gradually losing their effectiveness. We investigated the possibility of using purified VP2, a subunit of IB DV structural protein expressed in insect cells, as a vaccine. The VP2 gene was cloned into pAcYM1. The cloned gene was expressed in a bacul ovirus system, giving rise to a high quantity of recombinant VP2 (rVP2 ) protein. The length of the VP2 is 453 amino acids, and it contains t wo additional amino acids of the baculovirus at the carboxyl terminus. The molecular mass of the protein is about 48 kD. The rVP2 protein re acted with antibodies raised against viral VP2 and had a similar molec ular weight. This protein was tested in a controlled vaccination exper iment and compared with an inactivated commercial vaccine. High levels of antibodies were raised by the vaccinated birds. The vaccinated bir ds were challenged with a pathogenic viral strain. rVP2-vaccinated chi ckens exhibited high resistance to the virus. No mortality or weight c hanges in the bursa of Fabricius were observed in the vaccinated birds , whereas in the negative control birds, vaccinated with phosphate buf fer, up to 50% mortality was found. Higher levels of antibodies were f ound by enzyme-linked immunosorbent assay in birds vaccinated with rVP 2 compared with those vaccinated with the commercial vaccine. This stu dy suggests the potential use of the isolated rVP2 as a subunit vaccin e.