Identification of neutralizing epitopes on the VP2 protein of infectious bursal disease virus by phage-displayed heptapeptide library screening and synthetic peptide mapping

Infectious bursal disease virus (IBDV) is the causative agent of infectious bursal disease, which is one of the most important and widespread infectious diseases in commercial chickens. Conformational epitopes have been reported in the highly variable region of the VP2 protein of IBDV. In the present study, a random heptapeptide library was screened by using monoclonal antibodies (mAbs), YNW17 and YNW29, directed to the VP2 of IBDV and two peptide motifs, D-X-P-R and A-R-G, were identified. The motifs are present on the N and C terminal sequences of the highly variable region of VP2. Synthetic overlapping peptides covering the motifs on VP2 were analyzed by Dot-ELISA with the mAbs and two epitopes 197CDSSDRPRVYTIT209 and 329ARGSLAVTI337 identified. The above epitopes were also recognized by chicken anti-IBDV sera and shown to inhibit the binding of their mAbs to recombinant VP2. Both mAbs and sera from mice immunized with the conjugated epitope-peptides were able to neutralize serotype I IBDV. These results indicated that the epitopes are two neutralizing linear B-cell epitopes and would be useful for the development of peptide-based IBD vaccines.