Identification of an antigenic peptide specific for bluetongue virus using phage display expression of NS1 sequences

Background: NS1 is a non-structural protein associated with the replication of bluetongue virus (BTV), an orbivirus (Reoviridae) that infects sheep and cattle. NS1 is potentially useful as a diagnostic antigen since the presence of specific antibodies is an indication that the virus has replicated in the host. It is, however, not antigenically unique and crossreacts serologically with the analogous protein of the related epizootic haemorrhagic disease virus (EHDV). Objectives. To investigate phage display of peptides derived from the gene encoding NS1 as a way of identifying unique antigenic regions that can be mimicked by synthetic peptides. Study Design: A cDNA clone of a large portion of the gene encoding NS1 of bluetongue virus was fragmented by partial DNase digestion. The fragments were ligated into the filamentous phage display vector, fUSE 2. Peptides expressed on the surface of the phages as part of the gene III proteins were selected from the library using antibodies affinity-purified from an antiserum to NS1. The peptides were identified by sequencing the phage DNA and alignment with the sequence of the target gene. Results. Two antigenic regions were identified, one of which could be effectively mimicked by a 28 residue synthetic peptide. This peptide did not cross-react with an antiserum directed against NS1 of EHDV, Conclusion: The strategy of screening gene-derived phage display libraries with antibodies from an immune serum is expected to be useful in the development of highly specific peptide-based diagnostic assays.