B Cell Epitope Mapping On VP2 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). Segment B encodes the VP1 protein, the putative viral RNA-dependent RNA polymerase and segment A contains two partially overlapping open reading frames (ORF). The smaller ORF encodes VP5, a nonstructural protein of 17 kDa. The larger ORF encodes a polyprotein precursor with a molecular weight of 110kDa, which is proteolytically cleaved to produce the structural virus protein of VP2, VP3 and VP4. These proteins form the viral capsid and represent the B cell epitopes inducing the neutralization antibodies.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 VP2 genes were cloned into the pET28a vector to construct expression vector of pETVP2 a. Subsequently, the recombinant VP2 (rVP2) were expressed in E. coli BL21(DE3) by inducing with IPTG. The expressed VP2 proteins were recognised specifically with anti-IBDV antisera in western blot assays. Eleven monoclonal antibodies (mAbs) against VP2 were characterized with rVP2.Based on bioinformatic analysis of peptide VP2 of IBDV, a series of overlapping peptides were synthesized respectively by solid phase peptide synthesis. These peptides include 51 VP2 16-mer peptides, 64 VP2 12-mer peptides, To identify the reactivity of synthesized peptides with anti-IBDV mAbs and 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 mAbs and pAbs in the VP2-4-3 polyprotein of IBDV are as follows. In VP2, there are five neutralizing B cell epitopes (EP1: 37TLRSETSTYNLTV49, EP2:...