Vaccination with Cathepsin L Proteinases and with Leucine Aminopeptidase Induces High Levels of Protection against Fascioliasis in Sheep

Abstract

The potential of different parasite proteinases for use as vaccine candidates against fascioliasis in sheep was studied by vaccinating animals with the cathepsin L proteinases CL1 and CL2 and with leucine aminopeptidase (LAP) purified from adult flukes. In the first trial, sheep were immunized with CL1 or CL2 and the mean protection levels obtained were 33 and 34%, respectively. Furthermore, a significant reduction in egg output was observed in sheep vaccinated either with CL1 (71%) or with CL2 (81%). The second trial was performed to determine the protective potential of the two cathepsin L proteinases assayed together, as well as in combination with LAP, and of LAP alone. The combination of CL1 and CL2 induced higher levels of protection (60%) than those produced when these enzymes were administered separately. Those sheep that received the cocktail vaccine including CL1, CL2, and LAP were significantly protected (78%) against metacercarial challenge, but vaccination with LAP alone elicited the highest level of protection (89%). All vaccine preparations induced high immunoglobulin G titers which were boosted after the challenge infection, but no correlations between antibody titers and worm burdens were found. However, the sera of those animals vaccinated with LAP contained LAP-neutralizing antibodies. Reduced liver damage, as assessed by the level of the liver enzyme gamma-glutamyl transferase, was observed in the groups vaccinated with CL1, CL2, and LAP or with LAP alone.

An enzymatically inactivated hemoglobinase fromNecator americanusinduces neutralizing antibodies against multiple hookworm species and protects dogs against heterologous hookworm infection

“…Indeed, in the Candida albicans mouse model, passive transfer of anti-protease IgG significantly decreased the yeast burden in kidneys of mice infected with C. albicans, highlighting the role of antiprotease antibodies in protection. Our work with hookworms (12,13) and studies on another blood-feeding helminth parasite, F. hepatica (36,37), are unique, however, in showing that antibodies generated to hemoglobinases probably exert their efficacy by neutralizing the catalytic activity of their target proteases. To the best of our knowledge, this is the first report describing the use of antibodies raised against a catalytically inactive protease from a parasite to inhibit the catalytic activity of its wild-type counterpart.…”

Fasciola hepatica cathepsin L suppresses sheep lymphocyte proliferation in vitro and modulates surface CD4 expression on human and ovine T cells

“…The importance of cathepsin L isoenzymes in liver fluke biology has been demonstrated in vaccine trials in ruminants. Cathepsin L molecules have shown efficacy as vaccines in cattle, sheep and rats (1,18,(37)(38)(39)(40)(41). Protection in cattle with cathepsin L vaccines against a challenge infection has varied from 38% to 69%.…”

Discovery and validation of serum biomarkers expressed over the first twelve weeks of Fasciola hepatica infection in sheep

“…Serum samples were obtained from eight male Corriedale sheep (2 years old) housed in a paddock with an artificial water supply. The animals were purchased from a fluke-free area and shown to be free of infection by fecal analysis and ELISA using F. hepatica cathepsin L1 as a specific antigen (Piacenza et al, 1999). The animals were from the control group of a vaccination trial carried out in Uruguay where eight sheep were immunized with PBS in FCA, followed 4 weeks later by Freund's incomplete adjuvant.…”