B Cell Epitope Mapping On VP3 Protein Of Infectious Bursal Disease Virus

Infectious bursal disease virus (IBDV), a member of the Birnaviridae family, is a pathogen of infectious bursal disease and causes a highly contagious and severe immunosuppression by destroying B-lymphoid cells presented in the bursa of Fabricius, leading to an increased susceptibility to other pathogens and considerable economic losses in poultry industries worldwide. The genome of IBDV consists of two segments of double-stranded RNA (A and B), And the VP3 protein is encoded by segment A.B cell epitopes or antigenic determinants are defined as an antigenic sites for antibody binding. In protein antigen, an epitope that constituts part of a linear amino acid sequence on a polypeptide chain is known as a continuous or linear epitope, while the conformational epitope is formed from residues separated in the primary sequence which are distant from one another, but brought together in the folded molecule's secondary or tertiary structure. Identification of the B cell epitopes of IBDV is very useful in understanding the nature of IBDV humoral immunity.In this study, the VP3 genes were cloned into the pET28a vector to construct expression vector of pETVP3. Subsequently, the recombinant VP3 (rVP3) were expressed in E. coli BL21(DE3) by inducing with IPTG. The expressed VP3 proteins were recognised specifically with anti-IBDV antisera in western blot assays.Based on bioinformatic analysis of peptide VP3 of IBDV, a series of overlapping peptides were synthesized respectively by solid phase peptide synthesis. These peptides include 28 VP3 20-mer peptides, 30 VP3 12-mer peptides, To identify the reactivity of synthesized peptides with anti-IBDV polyclonal antibodies (pAbs), these peptides were conjugated to the carrier protein BSA and were detected using peptide-ELISA and Dot-ELISA. Results showed that the B cell epitopes recognized by pAbs in the VP3 protein of IBDV are as follows, there are six antigenic sites : EP6: 728PRDWDRLPYLNL739,ES7:818LANAPQAGSKSQRA831,ES8:851QREKDTRI SKKMETMGIYFATP872,ES9:876ALNGHRGPSPGQLKYWQNTREI897,ES10: 961QMKDLLLTAMEMK973, EP7:982PKPKPKPNAPTQ993.In summary, the B cell epitope map on the IBDV polyprotein VP3 was identified. It is suggested that these epitopes on IBDV be valuable in development of peptide-based vaccines for IBDV.