Vaccination with
fatty acid-binding proteins (FABPs) from Fasciola hepatica has been shown to confer significant levels of protection against challenge
infection in mice, rabbits, and sheep. A recombinant 15-kDa FABP (rFh15) has been purified and also shown to be an immunoprotective molecule. From the rFh15 molecule sequence 2, 12- and 10-mer putative
T-cell epitopes were identified, the first an Fh15Ta of amino acid sequence IKMVSSLKTKIT, and the second an Fh15Tb of amino acid sequence VKAVTTLLKA. The synthesized
oligonucleotides were cloned individually into a pGEX-2TK expression vector. The overexpressed fusion
protein was affinity purified using
glutathione S-transferase (GST) by competitive elution with excess
reduced glutathione. These GST fusion
proteins were emulsified in
Freund adjuvant for rabbit immunizations or further purified as
peptides after digestion with
thrombin. The purified 12- and 10-mer
peptides were either emulsified in
Freund adjuvant for immunizations in rabbits or used in an adjuvant-adaptation (ADAD) system, followed by challenge
infection with F. hepatica metacercariae in mice and rabbits. In vaccinated-challenged rabbits, the highest levels of protection were found in those treated with GST-
epitopes (Fh15Ta 48.2% and Fh15Tb 59.1% reduction, respectively), as compared to GST-immunized controls. Moreover, those immunized with Fh15Ta had higher (84%) numbers of immature flukes as compared with Fh15Tb (41%) or GST alone (64%). The rabbits immunized with the putative
T-cell epitopes in adjuvant had a 13% reduction in flukes in those with Fh15Ta and also were highest with immature flukes (46%). In vaccinated mice challenged with a lethal number of metacercariae, both CD-1 and BALB/c mice treated with complete ADAD-GST-Ta had the highest (40%) survival rates of all groups by 47 days postinfection. Thus the Fh15Ta and Fh15Tb
polypeptide epitopes warrant further study as a potential
vaccine against F. hepatica. Antibody isotype studies in mice revealed a mixed Thl/Th2 response to vaccination.