Vaccine potential of recombinant cathepsin B against Fasciola gigantica

- rFgCatB2 and rFgCatB3 expressed in P. pastoris were used to immunize mice to evaluate the protection against F. gigantica.
- Mice immunized with both recombinant proteins exhibited percent of protection at 60% for rFgCatB2 and 66% for rFgCatB3.
- Immunization by both antigens induced continuously increasing levels of IgG1 and IgG2a with a higher level of IgG1 isotype.
- The higher the levels of IgG1 and IgG2a were correlated with the lower the numbers of worm recoveries.

In Fasciola gigantica, cathepsin Bs, especially cathepsin B2 and B3 are expressed in early juvenile stages, and are proposed to mediate the invasion of host tissues. Thus they are thought to be the target vaccine candidates that can block the invasion and migration of the juvenile parasite. To evaluate their vaccine potential, the recombinant cathepsin B2 (rFgCatB2) and cathepsin B3 (rFgCatB3) were expressed in yeast, Pichia pastoris, and used to immunize mice in combination with Freund's adjuvant to evaluate the protection against the infection by F. gigantica metacercariae, and the induction of immune responses. Mice immunized with both recombinant proteins exhibited high percent of parasite reduction at 60% for rFgCatB2 and 66% for rFgCatB3. Immunization by both antigens induced continuously increasing levels of IgG1 and IgG2a with a higher level of IgG1 isotype, indicating the mixed Th1/Th2 responses with Th2 predominating. When examined individually, the higher levels of IgG1 and IgG2a were correlated with the lower numbers of worm recoveries. Thus, both cathepsin B2 and cathepsin B3 are plausible vaccine candidates whose potential should be further tested in large economic animals.