Protection against hydatid disease induced with the EG95 vaccine is associated with conformational epitopes

This paper describes attempts to map the location of host-protective epitop es of a recombinant vaccine antigen by assessing the ability of truncated r egions of the antigen to elicit protective immune responses in sheep. Sheep were immunised with three truncated regions (EG95-1, EG95-2 and EG95-3) of the hydatid vaccine antigen, EG95. These regions overlapped each other and corresponded to amino acids 1-70 (EG95-1), 51-106 (EG95-2) and 89-153 (EG9 5-3) of the full length recombinant protein. Each region elicited antibody which reacted with the parent antigen, although these reactivities were a s mall proportion of the level of reactivity generated by immunisation with t he full length antigen. Antisera raised against each of the truncated prote ins reacted with the native parasite antigen. In vaccination and parasite c hallenge trials in sheep, none of the truncated regions elicited significan t protection against challenge infection or antibody which was lethal to th e parasite in vitro. Antibodies from sheep immunised with the combination o f all three overlapping truncations elicited a comparatively low but signif icant level of lysis of the parasite in vitro. These antigens did not inhib it anti-EG95 antibody reactivity with EG95 nor did they inhibit in vitro on cosphere killing induced by anti-EG95 antibodies. These results indicate th at the major part of the immune response induced by EG95 vaccination is dir ected against conformational epitopes and that the host-protective epitope( s) is/are conformational. (C) 2000 Elsevier Science Ltd. All rights reserve d.