Studies of Aphthovirus Subunits and Synthetic Peptides Relevant to Their Use as Vaccines Against Foot and Mouth Disease.

Laboratory animals and cattle were vaccinated with the aphthovirus capsid protein VPl or with aphthovirus-specific synthetic peptides. The peptides used copied either the sequence of amino-acids 141-160 from the VPl of aphthovirus strains OlBFS 1860 and 01 Kaufbeuren (the 0 peptide) or the equivalent sequence from aphthovirus strain A24 Cruzeiro (the A peptide). VPl was isolated by chromatofocusing from aphthovirus strains OlBFS 1860, A24 Cruzeiro and Asia 1 Iran 1/73. The 0 peptide and the VPls were poorly immunogenic, even when coupled to keyhole limpet haemocyanin (KLH), and conferred little or no protection against challenge with infectious virus. In contrast KLH-A peptide had good immunogenicity and vaccinated guinea-pigs were protected from challenge. All animals vaccinated with KLH-peptide demonstrated considerable diversity in their responses, both between strains and between individuals of the same strain. These results may reflect differences between 0 and A serotype viruses and variations in the immune response genes of the animals studied. The immune responses were long-lasting. Guinea-pigs and rabbits possessed significant levels of antibody a year after vaccination, though the specificity of the antibody varied with species and peptide. In some species KLH-peptide stimulated an anamnestic immune response. However, in vitro experiments with mouse splenocytes showed that peptides were less effective than virus in this respect. KLH-peptide was less immunogenic, in terms of conferring protection and generating neutralizing antibodies, than virus. Sera from KLH-peptide-vaccinated guinea-pigs were relatively inefficient at forming immune complexes with virus and at neutralizing virus. Peptide-induced neutralizing antibodies appeared to correspond to a weakly-neutralizing sub-population of virus-induced neutralizing antibodies