Fasciola gigantica
cathepsin L1H (FgCatL1H) is one of the major
cathepsin L released by juveniles of F. gigantica to aid in the invasion of host's tissues. Due to its high sequence similarity with other
cathepsin L (CatL)
isoforms of late stage F. gigantica, it was considered to be a good
vaccine candidate that can block all CatL-mediated
protease activities and affect juveniles as well as adult parasites. In this study, recombinant proFgCatL1H
protein expressed in yeast, Pichia pastoris, system was mixed with Freund's adjuvants and used to subcutaneously immunize mice that were later challenged with metacercariae of F. gigantica. The percentage of worm protection in the rproFgCatL1H-vaccinated mice compared to the non-immunized and adjuvant control mice were approximately 62.7% and 66.1%, respectively. Anti-rproFgCatL1H
antisera collected from vaccinated mice reacted specifically with rproFgCatL1H and other
cathepsin L isoforms of F. gigantica, but the
antibodies did not cross react with
antigens from other trematode and nematode parasites, including Eurytrema pancreaticum, Opisthorchis viverrini, Fischoederius cobboldi, Cotylophoron cotylophorum, Gigantocotyle explanatum, Paramphistomum cervi, and Setaria labiato-papillosa. The levels of
IgG1 and
IgG2a in mouse sera increased significantly at two weeks after immunization and were highest during the sixth to eighth weeks after immunization. The
IgG1 level was higher than
IgG2a at all periods of immunization, implicating the dominance of the Th2 response. The levels of
IgG1 and
IgG2a in the
immune sera were shown to be strongly correlated with the numbers of worm recovery, and the correlation coefficient was higher for
IgG1. The levels of serum
aspartate aminotransferase and
alanine transaminase were significantly lower in the sera of rproFgCatL1H-vaccinated mice than in the infected control mice indicating a lower degree of liver damage. This study demonstrated a high potential of FgCatL1H
vaccine, and its efficacy is currently being studied in the larger economic animals.