Saposin-like protein 2 has an immunodiagnostic potential for detecting Fasciolosis gigantica

A novel Thioredoxin-related protein 14 from Fasciola gigantica has an immunodiagnostic potential for fasciolosis

In the definitive host, a trematode parasite can survive and evade the damage by reactive oxygen species that are generated from its metabolism and the host immune cells. Several anti-oxidant proteins are found in Fasciola spp. which play essential roles in cellular redox balance. One of them is thioredoxin-related protein 14 (TRP14) that has a highly conserved WCPDC motif and serves as a disulfide reductase-like thioredoxin (Trx). In the present study, a cDNA encoding TRP14 from F. gigantica (FgTRP14) was selected and cloned by immunoscreening with a rabbit infected serum. Phylogenetic analysis was performed by MEGA X program showed that FgTRP14 was most highly related to the Fasciola hepatica. Immunoblotting analysis of the polyclonal antibody rabbit serum against recombinant FgTRP14 (rFgTRP14) revealed that the molecular weight of natural FgTRP14 was at 14 kDa from metacercariae, NEJ, 4-week old juvenile and adult stage. The native FgTRP14 was expressed in caecal epithelial cells and preferentially localized on the cells' surface lamellae of adult stage. By sandwich ELISA assay, the circulating FgTRP14 could be recognized in sera of experimentally F. gigantica metacercariae infection in mice. The native FgTRP14 in the excretory-secretory (ES) and whole body (WB) of adult F. gigantica were detected at the concentrations 6.3 ng/ml, and 45 ng/ml, respectively. Therefore, it could be considered for immunodiagnostic candidate for fasciolosis.

Monoclonal antibody against Fasciola gigantica glutathione peroxidase and their immunodiagnosis potential for fasciolosis

Glutathione peroxidases (GPx), major antioxidant enzymes, secreted by Fasciola spp., are important for the parasite evasion and protection against the host's immune responses. In the present study, a monoclonal antibody (MoAb) against recombinant F. gigantica glutathione peroxidase (rFgGPx) was produced by hybridoma technique using spleen cells from BALB/c mice immunized with rFgGPx. This MoAb (named 7B8) is IgG1 with κ light chains, and it reacted specifically with rFgGPx at a molecular weight 19 kDa as shown by immunoblotting, and reacted with the native FgGPx in the extracts of whole body (WB), metacercariae, newly excysted juveniles (NEJs), 4 week-old juveniles and adult F. gigantica as shown by indirect ELISA. It did not cross react with antigens in WB fractions from other adult trematodes, including Fischoederius cobboldi, Paramphistomum cervi, Setaria labiato-papillosa, Eurytrema pancreaticum, Gastrothylax crumenifer and Gigantocotyle explanatum. By immunolocalization, MoAb against rFgGPx reacted with the native protein in the tegument, vitelline cells, and eggs of adult F. gigantica. In addition, the sera from mice experimentally infected with F. gigantica were tested positive by this indirect sandwich ELISA. This result indicated that FgGPx is an abundantly expressed parasite protein that is secreted into the tegumental antigens (TA), therefore, FgGPx and its MoAb may be used for immunodiagnosis of both early and late fasciolosis gigantica in animals and humans.

Characterization and vaccine potential of Fasciola gigantica saposin-like protein 1 (SAP-1)

The recombinant Fasciola gigantica Saposin-like protien-1 (rFgSAP-1) was cloned by polymerase chain reaction (PCR) from NEJ cDNA, expressed in Escherichia coli BL21 (DE3) and used for production of a polyclonal antibody in rabbits (anti-rFgSAP-1). By immunoblotting and immunohistochemistry, rabbit IgG anti-rFgSAP-1 reacted with rFgSAP-1 at a molecular weight 12kDa, but not with rFgSAP-2. The rFgSAP-1 reacted with antisera from mouse infected with F. gigantica metacercariae collected at 2, 4, and 6 weeks after infection. The FgSAP-1 protein was expressed at a high level in the caecal epithelium of metacercariae and NEJs. The vaccination was performed in Imprinting Control Region (ICR) mice (n=10) by subcutaneous injection with 50μg of rFgSAP-1 combined with Alum adjuvant. Two weeks after the second boost, mice were infected with 15 metacercariae per mouse by the oral route. The percents protection of rFgSAP-1 vaccine were estimated to be 73.2% and 74.3% when compared with non vaccinated-infected and adjuvant-infected controls, respectively. The levels of IgG1 and IgG2a specific to rFgSAP-1 in the immune sera, which are indicative of Th2 and Th1 immune responses, were inversely and significantly correlated with the numbers of worm recoveries. The rFgSAP-1-vaccinated mice showed significantly reduced levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and liver damage. These indicated that rFgSAP-1 has strong potential as a vaccine candidate against F. gigantica, whose efficacy will be studied further in large economic animals including cattle, sheep, and goat.