Potential of recombinant 2-Cys peroxiredoxin protein as a vaccine for Fasciola gigantica infection

Combination Vaccines of Fasciola gigantica Saposin-like Protein-2 and Leucine Aminopeptidase

Saposin-like protein-2 (SAP-2) and leucine aminopeptidase (LAP) are major proteins involved in the digestive process of Fasciola gigantica (Fg). Both SAP-2 and LAP are highly expressed in F. gigantica; therefore, they could be vaccine candidates for fasciolosis. The aims of this study are (1) to observe the tissue expression of F. gigantica SAP-2 (FgSAP-2) and F. gigantica LAP (FgLAP) in F. gigantica by indirect immunofluorescence technique under confocal microscopy and (2) to test the vaccine potentials of individual and combined recombinant (r) FgSAP-2 and rFgLAP against F. gigantica in Imprinting Control Region (ICR) mice (n = 10 per group). By indirect immunofluorescence-confocal microscopy, FgSAP-2 and FgLAP were localized in the caecal epithelium but at different sites: FgSAP-2 appeared in small granules that are distributed in the middle and lower parts of the cytoplasm of epithelial cells, while FgLAP appeared as a line or zone in the apical cytoplasm of caecal epithelial cells. For vaccine testing, the percent protection of combined rFgSAP-2 and rFgLAP vaccines against F. gigantica was at 80.7 to 81.4% when compared with aluminum hydroxide (alum) adjuvant and unimmunized controls, respectively. The levels of IgG1 and IgG2a in the sera were significantly increased in single and combine vaccinated groups compared with the control groups. Vaccinated mice showed reduced liver damage when compared with control groups. This study indicates that the combined rFgSAP-2 and rFgLAP vaccine had a higher vaccine potential than a single vaccine. These results support the further testing and application of this combined vaccine against F. gigantica infection in farmed livestock animals.

Proteomic analysis of exosome-like vesicles from Fasciola gigantica adult worm provides support for new vaccine targets against fascioliasis

BACKGROUND

Extracellular vesicles (EVs) released by helminths play an important role in parasite-host communication. However, little is known about the characteristics and contents of the EVs of Fasciola gigantica, a parasitic flatworm that causes tropical fascioliasis. A better understanding of EVs released by F. gigantica will help elucidate the mechanism of F. gigantica-host interaction and facilitate the search for new vaccine candidates for the control and treatment of fascioliasis.

METHODS

Two different populations of EVs (15k EVs and 100k EVs) were purified from adult F. gigantica culture media by ultracentrifugation. The morphology and size of the purified EVs were determined by transmission electron microscopy (TEM) and by the Zetasizer Nano ZSP high performance particle characterization system. With the aim of identifying diagnostic markers or potential vaccine candidates, proteins within the isolated 100k EVs were analyzed using mass spectrometry-based proteomics (LC-MS/MS). Mice were then vaccinated with excretory/secretory products (ESPs; depleted of EVs), 15k EVs, 100k EVs and recombinant F. gigantica heat shock protein 70 (rFg-HSP70) combined with alum adjuvant followed by challenge infection with F. gigantica metacercariae. Fluke recovery and antibody levels were used as measures of vaccine protection.

RESULTS

TEM analysis and nanoparticle tracking analysis indicated the successful isolation of two subpopulations of EVs (15k EVs and 100k EVs) from adult F. gigantica culture supernatants using differential centrifugation. A total of 755 proteins were identified in the 100k EVs. Exosome biogenesis or vesicle trafficking proteins, ESCRT (endosomal sorting complex required for transport) pathway proteins and exosome markers, heat shock proteins and 14-3-3 proteins were identified in the 100k EVs. These results indicate that the isolated 100k EVs were exosome-like vesicles. The functions of the identified proteins may be associated with immune regulation, immune evasion and virulence. Mice immunized with F. gigantica ESPs, 15k EVs, 100k EVs and rFg-HSP70 exhibited a reduction in fluke burden of 67.90%, 60.38%, 37.73% and 56.6%, respectively, compared with the adjuvant control group. The vaccination of mice with F. gigantica 100k EVs, 15k EVs, ESP and rFg-HSP70 induced significant production of specific immunoglobulins in sera, namely IgG, IgG1 and IgG2a.

CONCLUSION

The results of this study suggest that proteins within the exosome-like vesicles of F. gigantica have immunomodulatory, immune evasion and virulence functions. This knowledge may lead to new strategies for immunotherapy, vaccination and the diagnosis of fascioliasis.

The combined recombinant cathepsin L1H and cathepsin B3 vaccine against Fasciola gigantica infection

Protections against Fasciola gigantica infection in mice immunized with the individual and combined cathepsin L1H and cathepsin B3 vaccines were assessed. The vaccines comprised recombinant (r) pro-proteins of cathepsin L1H and B3 (rproFgCatL1H and rproFgCatB3) and combined proteins which were expressed in Pichia pastoris. The experimental trials were performed in ICR mice (n = 10 per group) by subcutaneous injection with 50 μg of the recombinant proteins combined with Alum or Freund's adjuvants. At two weeks after the third immunization, mice were infected with 15 F. gigantica metacercariae per mouse by oral route. The percents of protection of rproFgCatL1H, rproFgCatB3 and combined vaccines against F. gigantica were approximately 58.8 to 75.0% when compared with adjuvant-infected control. These protective effects were similar among groups receiving vaccines with Alum or Freund's adjuvants. By determining the levels of IgG1 and IgG2a in the immune sera, which are indicative of Th1 and Th2 immune responses, it was found that both Th1 and Th2 humoral immune responses were significantly increased in vaccinated groups compared with the control groups, with higher levels of IgG1 (Th2) than IgG2a (Th1). Mice in vaccinated groups showed reduction in liver pathological lesions when compared with control groups. This study indicates that the combined rproFgCatB3 and rproFgCatL1H vaccine had a high protective potential than a single a vaccine, with Alum and Freund's adjuvants showing similar level of protection. These results can serve as guidelines for the testing of this F. gigantica vaccine in larger economic animals.