Sequence Analysis Of The VP2Gene Hypervariable Region Of Infectious Bursal Disease Virus And The Complete Genomic Of IBDV BC6/85with Preliminary Study Of IBDV Subunit Vaccine

Infectious bursal disease (IBD), caused by infectious bursal disease virus (IBDV), is an acute and highly contagious infectious disease of chicken and turkey.The disease mainly damages young chickens in3-6weeks. In addition to causing chickens'death and production decrease, the disease could lead to serious immunosuppression. The VP2hypervariable region of different IBDV strains and the genome sequence of BC6/85were analysed. The IBDV VP2gene of BC6/85was also expressed in E.Coli. The main results in this study are as follows:(1) The VP2genes of10IBDV strains have been sequenced. Sequence analysis showed that VP2hypervariable region changed regularly between different strains. Phylogenetic tree based on the nucleotide sequences of VP2hypervariable region (435bp) revealed that all IBDV strains of serum type I were evolved from the same ancestor, and most of the strains can be divided into three major evolutionary groups:the first evolutionary group includes attenuated and variant IBDV, classical IBDV belongs to the second evolutionary group and the third evolutionary group is vvIBDV.(2) The full-length of double segments of the IBDV BC6/85was sequenced. A segment of BC6/85strain was3260bp, and B segment was2827bp. Homologous analysis indicated that both segments are homologous with attIBDV, cIBDV and varIBDV; VP1, VP3, VP4and VP5of BC6/85are more conservative than VP2. The comparison of protein VP2showed that BC6/85was clearly distinguished from other classical, attenuated, variant and vvIBDVs, as most alternation of amino acid residues located in VP2hypervariable regions.(3) The VP2gene was amplified from IBDV BC6/85by PCR. The target gene cloned into expression vector pET-28a, and the recombinant plasmids pET-VP2was obtained. The expressed protein in form of inclusion body has specific immunoreactivity with chicken polyclonal antiserum to IBDV in western blot assays.21-day old chickens were conducted for vaccination trials. Blood samples were collected from the wing vein of each chicken14days of postvaccination and serum antibody titres to the expressed IBDV protein were determined. All vaccinated chickens and controls are challenged with cIBDV and vvIBDV21days of postvaccination.Serum antibody titres of chickens inoculated with different dosage groups were significantly higher than control group. Chickens that received both inclusion body and the protein processed by denature and renaturation were well protected. The results revealed that the subunit vaccine provides a new thinking of IBD vaccines.