These data strongly suggest that FhLAP is recognized during infection of sheep by F. hepatica but that this protease provokes a lesser antigenic stimulus than L-cathepsins, probably due to two facts: i) unlike FhLAP (cytoplasmatic), Fasciola L-cathepsins are the most abundant secreted proteins, thus being permanently in contact with host immune cells, and ii) during its biological cycle, Fasciola produces different L-cathepsins [35] that have high sequence identity and thus may reciprocally boost the production of antibodies. This evidence concerns the gene CTSL and infection.