Antibody recognition of cathepsin L1-derived peptides in Fasciola hepatica-infected and/or vaccinated cattle and identification of protective linear B-cell epitopes.

Fasciola hepatica infection causes important economic losses in livestock and food industries around the world. In the Republic of Ireland F. hepatica infection has an 76% prevalence in cattle. Due to the increase of anti-helminthic resistance, a vaccine-based approach to control of Fasciolosis is urgently needed. A recombinant version of the cysteine protease cathepsin L1 (rmFhCL1) from F. hepatica has been a vaccine candidate for many years. We have found that vaccination of cattle with this immunodominant antigen has provided protection against infection in some experimental trials, but not in others. Differential epitope recognition between animals could be a source of variable levels of vaccine protection. Therefore, we have characterised for first time linear B-cell epitopes recognised within the FhCL1 protein using sera from F. hepatica-infected and/or vaccinated cattle from two independent trials. Results showed that all F. hepatica infected animals recognised the region 19-31 of FhCL1, which is situated in the N-terminal part of the pro-peptide. Vaccinated animals that showed fluke burden reduction elicited antibodies that bound to the regions 120-137, 145-155, 161-171 of FhCL1, which were not recognised by non-protected animals. This data, together with the high production of specific IgG2 in animals showing vaccine efficacy, suggest important targets for vaccine development.