Induction of protective immunity in cattle against infection with Fasciola hepatica by vaccination with cathepsin L proteinases and with hemoglobin

Abstract

Two cathepsin L proteinases, cathepsin L1 and cathepsin L2, secreted by liver flukes may be involved in tissue penetration, nutrition, and protection from immune attack. To ascertain the immunoprophylactic potential of these proteinases, and of another molecule, liver fluke hemoglobin (Hb), we performed vaccine trials in cattle. In the first vaccine trial various doses of cathepsin L1 were tested. The mean protection level obtained was 53.7%. In a second vaccine trial cathepsin L1 and Hb elicited 42.5 and 43.8% protection levels, respectively, while a combination of the two molecules induced a significantly higher level of protection (51.9%). Cathepsin L2 was not examined alone; however, vaccination of cattle with a combination of cathepsin L2 and Hb elicited the highest level of protection (72.4%). The animals that received cathepsin L1-Hb or cathepsin L2-Hb showed reduced liver damage as assessed by serum glutamic dehydrogenase and gamma-glutamyl transferase levels. Furthermore, a reduced viability was observed for fluke eggs recovered from all vaccine groups. This anti-embryonation effect of vaccination was particularly evident in the group that received cathepsin L2-Hb where >98% of the eggs recovered did not embryonate to miracidia. Although all vaccine preparations induced high antibody titers which were boosted following the challenge infection, there was no correlation between antibody titers and protection. The results of these trials demonstrate that cathepsin Ls and Hb could form the basis of a molecular vaccine that would not only reduce parasite burden but would also prevent transmission of liver fluke disease.

The Sigma Class Glutathione Transferase from the Liver Fluke Fasciola hepatica

“…Therefore, based on the immunisation with FhGST-S1 showing an early response reducing hepatica damage, could be considered for inclusion into a multivalent vaccine against Fasciolosis. In addition, in light of our findings showing FhGST-S1 to be highly prominent in egg production and the egg itself, as with previous vaccination trials [67], it will be important to investigate the ability of eggs voided from vaccinated animals to embryonate. The potential to reduce pasture contamination by inhibiting egg embryonation, combined with the demonstrated reduction in liver damage, warrants further exploration using rFhGST-S1 as a vaccine candidate.…”

“…A promising aspect of producing anti-helminth vaccines is developing multivalent vaccines. In many cases the greatest protection from challenge is by vaccinating with a combination of Fasciola antigens [66,67]. Therefore, based on the immunisation with FhGST-S1 showing an early response reducing hepatica damage, could be considered for inclusion into a multivalent vaccine against Fasciolosis.…”

Dose-response inhibition of proteolytic activity by a cysteine protease inhibitor in a murine model of fasciolosis

“…There seems to be a close relationship between the rate of proteolysis and the course of infection, showing that cysteine proteases are an important factor in the in vivo pathological effects of the parasite. The fact that E-64 strongly inhibited proteolysis caused by F. hepatica in liver is an encouraging finding, as mortality due to fasciolosis in sheep is a direct consequence of liver pathology caused by migrating flukes (Dalton et al 1996).…”

“…Gall bladders from all mice were dissected and eggs were recovered and counted from decanted bile after five washes. The eggs were incubated at 22°C for 14 days (Dalton et al 1996). After this period, the eggs were observed in order to estimate the percentage of miracidial development.…”

“…Hence, there is always a need for new chemotherapeutic agents against this trematode species. The cysteine proteases of F. hepatica represent attractive targets for chemotherapy development, as these enzymes play key roles in the life cycle of the parasite, such as evasion of host-defense mechanisms (Carmona et al 1993), tissue invasion (Dalton and Heffernan 1989;Berasain et al 1997), feeding (Yamasaki et al 1989;Smith et al 1993), and egg output (Dalton et al 1996). Incubation of F. hepatica metabolic products with low-molecular-weight inhibitors abolished -thiol protease activity (Dalton and Heffernan 1989).…”