Abstract
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.