Synthetic peptides induce antibody against a host-protective antigen of Echinococcus granulosus

The immunogenicity of four synthetic peptides was investigated in sheep. Th e sequences of the peptides (6, 12/13, 21/22 and 24) were derived from line ar, antibody-binding epitopes of the EG95 recombinant protein, a host-prote ctive antigen of the parasite Echinococcus granulosus. Sheep were immunised with either free peptide or peptide conjugated to diphtheria toroid. All s heep responded to both conjugated and unconjugated forms of the peptides. F or two of the four peptides (6 and 21/22), the amount of antibody elicited was significantly greater for the conjugated form of the peptides than for the corresponding unconjugated forms. For the other two peptides (12/13 and 24), peak antibody levels to both forms of the peptide were equivalent. Ma ximal antibody titres against peptides 6, 12/13 and 21/22 were established after only one immunisation and were not boosted by a second dose. Antisera to all four peptides reacted with the recombinant antigen, and three of th e four peptides generated antibodies, which bound to the native parasite on cosphere antigen. Antisera raised against the peptides were unable to kill the parasite in in vitro culture, although each of the peptides could be us ed to affinity purify lethal antibody from antisera raised against the reco mbinant protein. These results indicate that peptides 6, 12/13, 21/22 and 2 4 of the EG95 recombinant vaccine are immunogenic and suggest that they are associated with host-protective epitopes. (C) 1999 Elsevier Science Ltd. A ll rights reserved.