Failure of viral protein 3 of infectious bursal disease virus produced in prokaryotic and eukaryotic expression systems to protect chickens against the disease

In recent years, infectious bursal disease virus (IBDV) has become a seriou s economic problem as a result of the emergence of new and very virulent st rains. Most of the antibodies produced against IBDV art: for the structural proteins viral protein (VP) 2 (VP2) and VP3. The purpose of this study was to test the potential of recombinant VP3 to induce protective antibodies. The gene for VP3 was isolated from a virulent strain of the virus and clone d into prokaryotic (Escherichia coli) and eukaryotic (baculovirus) expressi on systems. The protein expressed by both syst ems was of the expected size (32 kD) and was detected by anti-IBDV antibodies. Following partial purifi cation, the polypeptides were injected into intact birds and induced the pr oduction of high levels of anti-IBDV antibodies, as detected by immunoblot and enzyme-linked immunosorbent assay tests. These antibodies did not preve nt changes in the bursa and mortality when birds were challenged with a vir ulent IBDV strain after vaccination with the recombinant VP3. The results s how that VP3 polypeptide cannot be used as a subunit vaccine against IBDV a nd raise questions concerning the nature of the neutralizing epitope on thi s structural protein.