Fasciola hepatica M17
leucine aminopeptidase (FhLAP) is thought to play a role in catabolizing
peptides generated by the concerted activity of gut-associated
endopeptidases on host
polypeptides, thus releasing
amino acids to be used in
protein anabolism. In this study, a recombinant functional form of this homo hexameric
metallopeptidase produced in Escherichia coli was used in combination with adjuvants of different types in a vaccination trial in Corriedale sheep against experimental challenge with F. hepatica metacercariae. The experimental assay consisted of 6 groups of 10 animals; 5 of the groups (1-5) were subcutaneously inoculated at weeks 0 and 4 with 100 μg of rFhLAP mixed with Freund's complete plus incomplete adjuvant (group 1),
Alum (group 2), Adyuvac 50 (group 3),
DEAE-D (group 4) and Ribi (group 5); the adjuvant control group (group 6) received
Freund's adjuvant. Two weeks after the booster, the sheep were orally challenged with 200 metacercariae. Immunization with rFhLAP induced significant reduction in fluke burdens in all vaccinated groups: 83.8% in the Freund's group, 86.7% in the
Alum group, 74.4% in the Adyuvac 50 group, 49.8% in the Ribi group and 49.5% in the
DEAE-D group compared to the adjuvant control group. Morphometric analysis of recovered liver flukes showed no significant size modifications in the different vaccination groups. All
vaccine preparations elicited specific
IgG,
IgG1 and
IgG2 responses. This study shows that a liver fluke
vaccine based on rFhLAP combined with different adjuvants significantly reduced worm burden in a ruminant species that was high in animals that received the
enzyme along with the commercially approved adjuvants
Alum and Adyuvac 50.