Vaccine potential of recombinant pro- and mature cathepsinL1 against fasciolosis gigantica in mice

Abstract In Fasciola gigantica cathepsin L1 (CatL1) is a family of predominant proteases that is expressed in caecal epithelial cells and secreted into the excretory-secretory products (ES). CatL1 isotypes are expressed in both early and late stages of the life cycle and the parasites use them for migration and digestion. Therefore, CatL1 is a plausible target for vaccination against this parasite. Recombinant pro- F.gigantica CatL1 (rproFgCatL1) and recombinant mature F.gigantica CatL1 (rmatFgCatL1) were expressed in Escherichia coli BL21. The vaccination was performed in Imprinting Control Region (ICR) mice ( n  = 10) by subcutaneous injection with 50 μg of rproFgCatL1 and rmatFgCatL1 combined with Freund’s adjuvant. Two weeks after the second boost, mice were infected with 15 metacercariae by the oral route. The level of protection of rproFgCatL1 and rmatFgCatL1 vaccines was estimated to be 39.1, 41.7% and 44.9, 47.2% when compared with non vaccinated-infected and adjuvant-infected controls, respectively. Antibodies in the immune sera of vaccinated mice were shown by immuno-blotting to react with the native FgCatL1 in the extract of newly excysted juveniles (NEJ), 4-week-old juveniles and the ES products of 4 week-old juveniles. By determining the levels of IgG1 and IgG2a in the immune sera, which are indicative of Th2 and Th1 immune response, respectively, it was found that both Th1 and Th2 responses were significantly increased in rproFgCatL1- and rmatFgCatL1-immunized groups compared with the control groups, with higher levels of Th2 (IgG1) than Th1 (IgG2a). The levels of serum aspartate aminotransferase (AST) and alanine transaminase (ALT) in rmatFgCatL1-immunized group showed a significant decrease when compared to rproFgCatL1-immunized group, indicating that rmatFgCatL1-vaccinated mice had reduced liver parenchyma damage. The pathological lesions of liver in vaccinated groups were significantly decreased when compared with control groups. This study indicates that rFgCatL1 has a potential as a vaccine candidate against F. gigantica in mice, and this potential will be tested in ruminants.