Assessment of protective immune responses against hydatid disease in sheepby immunization with synthetic peptide antigens

Four synthetic peptides which comprise the immunodominant linear epitopes o f the EG95 recombinant protein, were investigated fur their ability tu indu ce host-protective immunity against Echinococcus granulosus in sheep. Sheep were immunized with either free peptide or peptide conjugated to diphtheri a toxoid and challenge infected with E. granulosus eggs. All of the peptide s elicited specific antibody, but these did not kill the parasite in in vit ro culture assays, nor did the peptides induce protection against challenge infection. In contrast, anti-EG95 antibodies affinity purified against eac h of the 4 peptides were lethal to the parasite in in vitro culture. These affinity-purified antibodies were shown to contain specific antibody to bot h peptide and EG95. In in vitro inhibition assays, the peptides did not dim inish anti-EG95 antibody binding to EG95 or parasite lysis in oncosphere ki lling assays. These results suggest that the fine specificities of antibodi es raised against the recombinant protein are different to those raised aga inst the peptide immunogens and that the majority of the antibody induced b y vaccination with EG95 is raised against conformational determinants.