Analysis of immune responses in the sheep to synthetic peptides of foot-and-mouth disease virus using ovine polyclonal and monoclonal antibodies.

A 40-residue peptide incorporating residues 200-213 and 141-158 of foot-and-mouth disease virus VP1 capsid protein strain O1 Kaufbeuren was injected uncoupled into sheep, and the immune responses analysed. Direct-binding and inhibition experiments showed that the polyclonal antibody response was directed mainly against epitopes unique to the 40-residue peptide but absent from the constituent peptides containing residues 200-213 or 141-158, respectively. Further confirmation of the presence of unique epitopes on the 40-residue peptide was obtained from similar experiments performed with sheep monoclonal antibodies generated through the use of an aminopterin-sensitive sheep/mouse heterohybridoma cell line as a fusion partner. The sheep polyclonal antisera to the 40-residue peptide had high neutralization titres and were fully active in a mouse protection assay, whereas none of the sheep monoclonal antibodies conferred protection. The results suggest that the conformation of the 40-residue peptide is important for its ability to induce neutralizing antibodies.