ABSTRACT
Two bluetongue virus (BTV) serotype 10-specific single-chain Fv chicken antibody fragments (scFvs) were evaluated in a competitive ELISA. The binding of one (F3) to purified BTV was only inhibited by antibodies against the homologous serotype. The binding of the other (F10) was blocked by antisera to each of the 24 BTV serotypes. F10 recognised VP7, a major structural protein of the BTV core, but not if the protein was directly adsorbed to a plastic surface. It did, however, bind to recombinant VP7 that had been captured from suspension by rabbit IgG. This made it possible to develop an scFv based inhibition ELISA for BTV antibodies using recombinant VP7 without prior purification. The resulting immunoassay detected antibodies to 24 BTV serotypes, but not those directed against three serotypes of the related epizootic haemorrhagic disease virus. A phage library displaying fusion peptides expressed by fragments of the BTV genome segment 7 cDNA was constructed and screened using F10. Comparing selected peptides with the amino acid sequence of VP7 showed that recognition by the scFv required at least 131 residues representing the protein's upper domain. By providing well-characterised immunological reagents, recombinant antibody technology can contribute to the development of improved immunoassays for BTV diagnosis.
Subject(s)
Antibodies, Viral/analysis , Antigens, Viral/analysis , Bluetongue virus/classification , Enzyme-Linked Immunosorbent Assay/methods , Animals , Antigens, Viral/chemistry , Antigens, Viral/genetics , Antigens, Viral/immunology , Bluetongue virus/genetics , Chickens , Serotyping , Viral Core Proteins/immunologyABSTRACT
Two complementary techniques have been used to delineate an epitope on VP7 of bluetongue virus. Two MAbs (F10 and D11), both of which bound within a region spanning amino acids 255 to 274 in the 349 amino acid protein, were used to probe overlapping synthetic peptides covering this region. A pentapeptide, QYPAL, and a hexapeptide, QY-PALT (amino acids 259-264), preferentially bound both MAbs. MAb F10 also reacted with a heptapeptide (TAEIFNV) immediately adjacent to QYPALT. The MAbs were also used to affinity-purify fusion phages from a random hexapeptide library. All phage peptides selected were similar to QYPALT. Comparison of the peptides suggested that residues Q and P at positions 1 and 3 were critical for recognition. Some affinity-purified phages displayed the hexapeptide QYPSLL, which is similar to a sequence in VP7 of another orbivirus, epizootic hemorrhagic disease virus. This finding allowed a potentially cross-reactive site to be identified.
