Immunization with recombinant leucine aminopeptidase showed protection against Fasciola gigantica in mice

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.

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.

Partial protection with a chimeric tetraspanin-leucine aminopeptidase subunit vaccine against Opisthorchis viverrini infection in hamsters

Opisthorchiasis is a serious public health problem in East Asia and Europe. The pathology involves hepatobiliary abnormalities such as cholangitis, choledocholithiasis and tissue fibrosis that can develop into cholangiocarcinoma. Prevention of infection is difficult as multiple social and behavioral factors are involved, thus, progress on a prophylactic vaccine against opisthorchiasis is urgently needed. Opisthorchis viverrini tetraspanin-2 (Ov-TSP-2) was previously described as a potential vaccine candidate conferring partial protection against O. viverrini infections in hamsters. In this study, we generated a recombinant chimeric form of the large extracellular loop of Ov-TSP-2 and O. viverrini leucine aminopeptidase, designated rOv-TSP-2-LAP. Hamsters were vaccinated with 100 and 200 µg of rOv-TSP-2-LAP formulated with alum-CpG adjuvant via intraperitoneal injection and evaluated the level of protection against O. viverrini infection. Our results demonstrated that the number of worms recovered from hamsters vaccinated with either 100 or 200 µg of rOv-TSP-2-LAP were significantly reduced by 27% compared to the adjuvant control group. Furthermore, the average length of worms recovered from animals vaccinated with 200 μg of rOv-TSP-2-LAP was significantly shorter than those from the control adjuvant group. Immunized hamsters showed significantly increased serum levels of anti-rOv-TSP-2 IgG and IgG1 compared to adjuvant control group, suggesting that rOv-TSP-2-LAP vaccination induces a mixed Th1/Th2 immune response in hamsters. Therefore, the development of a suitable vaccine against opisthorchiasis requires further work involving new vaccine technologies to improve immunogenicity and protective efficacy.

Naltrexone; as an efficient adjuvant in induction of Th1 immunity and protection against Fasciola hepatica infection

Toxic effects of available therapeutics are major drawbacks for conventional management approaches in parasitic infections. Vaccines have provided a promising opportunity to obviate such unwanted complications. In present study, we examined immune augmenting capacities of an emerging adjuvant, Naltrexone, against Fasciola hepatica infection in BALB/c mice. Seventy BALB/c mice were divided into five experimental groups (14 mice per group) including 1- control (received PBS), 2- vaccine (immunized with F. hepatica E/S antigens), 3- Alum-vaccine (immunized with Alum adjuvant and E/S antigens), 4- NLT-vaccine (immunized with NLT adjuvant and E/S antigens), and 5- Alum-NLT-vaccine (immunized with mixed Alum-NLT adjuvant and E/S antigens). Lymphocyte stimulation index was assessed by MTT assay. Production of IFN-γ, IL-4, IgG2a and IgG1 was assessed by ELISA method. Results showed that NLT, either alone or in combination with alum, can induce immune response toward production of IFN-γ and IgG2a as representatives of Th1 immune response. Also, using this adjuvant in immunization experiment was associated with significantly high proliferative response of splenocytes/lymphocytes. Utilization of mixed Alum-NLT adjuvant revealed the highest protection rate (73.8%) in challenge test of mice infected with F. hepatica. These findings suggest the potential role of NLT as an effective adjuvant in induction of protective cellular and Th1 immune responses against fasciolosis.

Expression, Tissue Localization and Serodiagnostic Potential of Echinococcus granulosus Leucine Aminopeptidase

Echinococcus granulosus is the causative agent of cystic echinococcosis (CE), a widespread parasitic zoonosis. Leucine aminopeptidases (LAPs) of the M17 peptidase family have important functions in regulating the balance of catabolism and anabolism, cell maintenance, growth and defense. In this study, we presented a bioinformatic characterization and experimentally determined the tissue distribution characteristics of E. granulosus LAP (Eg-LAP), and explored its potential value for diagnosis of CE in sheep based on indirect ELISA. Through fluorescence immunohistochemistry, we found that Eg-LAP was present in the tegument and hooks of PSCs, the whole germinal layer and adult worm parenchymatous tissue. Western blotting results revealed that the recombinant protein could be identified using E. granulosus-infected sheep serum. The diagnostic value of this recombinant protein was assessed by indirect ELISA, and compared with indirect ELISA based on hydatid fluid antigen. The sensitivity and specificity rEgLAP-ELISA were 95.8% (23/24) and 79.09% (87/110), respectively, while using hydatid fluid as antigen showed the values 41.7% (10/24) and 65.45% (72/110). This is the first report concerning leucine aminopeptidase from E. granulosus, and the results showed that Eg-LAP belong to M17 peptidase families, and that it is involved in important biological function of E. granulosus. Furthermore, rEg-LAP is appropriate for diagnosing and monitoring CE in sheep in field. Development of a rapid test using rEg-LAP to diagnose sheep CE deserves further study.

Development of Fasciola Vaccine in an Animal Model

Fasciola hepatica and F. gigantica are the parasites that cause the zoonotic parasitic disease called fasciolosis. Although several anthelmintic drugs have been used to treat these parasitic infections, recombinant protein vaccines have been developed to overcome the anthelmintic resistance that has recently been reported in many regions of the world. These vaccines have been shown to induce high levels of immune responses and high percentages of protection in experimental and large animals. Efficacies of these vaccines suggest they could be an alternative and sustainable strategy to prevent fasciolosis in animals as well as humans in the future. The purpose of this chapter is to provide a protocol to develop a recombinant protein-based vaccine against Fasciola infection in mice. Moreover, this method can also be used as a guideline when the vaccination is performed in larger animals.

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.

Cytosolic superoxide dismutase can provide protection against Fasciola gigantica

Superoxide dismutases (SOD), antioxidant metallo-enzymes, are a part of the first line of defense in the trematode parasites which act as the chief scavengers for reactive oxygen species (ROS). A recombinant Fasciola gigantica cytosolic SOD (FgSOD) was expressed in Escherichia coli BL21 (DE3) and used for immunizing rabbits to obtain polyclonal antibodies (anti-rFgSOD). This rabbit anti-rFgSOD reacted with the native FgSOD at a molecular weight of 17.5kDa. The FgSOD protein was expressed at high level in parenchyma, caecal epithelium and egg of the parasite. The rFgSOD reacted with antisera from rabbits infected with F. gigantica metacercariae collected at 2, 5, and 7 weeks after infection, and reacted with sera of infected mice. Anti-rFgSOD exhibited cross reactivity with the other parasites' antigens, including Eurytrema pancreaticum, Cotylophoron cotylophorum, Fischoederius cobboldi, Gastrothylax crumenifer, Paramphistomum cervi, and Setaria labiato papillosa. A vaccination was performed in imprinting control region (ICR) mice by subcutaneous injection with 50μg of rFgSOD combined with Freund's adjuvant. At 2 weeks after the second boost, mice were infected with 15 metacercariae by oral route. IgG1 and IgG2a in the immune sera were determined to indicate Th2 and Th1 immune responses. It was found that the parasite burden was reduced by 45%, and both IgG1 and IgG2a levels showed correlation with the numbers of worm recoveries.

Vaccine potential of recombinant cathepsinL1G against Fasciola gigantica in mice

In this study, we characterized and investigated the vaccine potential of FgCatL1G against Fasciola gigantica infection in mice. Recombinant mature FgCatL1G (rmFgCatL1G) was expressed in Escherichia coli BL21. The vaccination was performed in Imprinting Control Region (ICR) mice (n=10) by subcutaneous injection with 50μg of rmFgCatL1G combined with Freund's adjuvant. Two weeks after the second boost, mice were infected with 15 metacercariae by the oral route. The percents of protection of rmFgCatL1G vaccine were estimated to be 56.5% and 58.3% when compared with non vaccinated-infected and adjuvant-infected controls, respectively. Antibodies in the immune sera of vaccinated mice were shown by immunoblot to react with the native FgCatL1s in the extract of all stages of parasites and rmFgCatL1H, recombinant pro - FgCatL1 (rpFgCatL1). By immunohistochemistry, the immune sera also reacted with FgCatL1s in the caecal epithelial cells of the parasites. The levels of IgG1 and IgG2a in the immune sera, which are indicative of Th2 and Th1 immune responses, were also increased with IgG1 predominating. The levels of serum glutamic oxaloacetic transaminase (SGOT) and serum glutamic pyruvic transaminase (SGPT) in rmFgCatL1G-immunized group showed no significant difference from the control groups, but pathological lesions of livers in rmFgCatL1G-immunized group showed significant decrease when compared to the control groups. This study indicates that rmFgCatL1G has a vaccine potential against F. gigantica in mice, and this potential will be tested in larger livestock animals.

Fasciola gigantica enolase is a major component of worm tegumental fraction protective against sheep fasciolosis

Infection of cattle and sheep with the parasite Fasciola gigantica is a cause of important economic losses throughout Asia and Africa. Many of the available anthelmintics have undesirable side effects, and the parasite may acquire drug resistance as a result of mass and repeated treatments of livestock. Accordingly, the need for developing a vaccine is evident. Triton-soluble surface membrane and tegumental proteins (TSMTP) of 60, 32, and 28 kDa previously shown to elicit protective immunity in mice against challenge F. gigantica infection were found to be strongly immunogenic in sheep eliciting vigorous specific antibody responses to a titer>1:16,000 as assessed by enzyme-linked immunosorbent assay. Furthermore, the 60 kDa fraction induced production of antibodies able to bind to the surface membrane of newly excysted juvenile flukes and mediate their attrition in antibody-dependent complement- and cell-mediated cytotoxicity assays, and significant (P<0.05) 40% protection of sheep against F. gigantica challenge infection. Amino acid micro sequencing of the 60 kDa-derived tryptic peptides revealed the fraction predominantly consists of F. gigantica enolase. The cDNA nucleotide and translated amino acid sequences of F. gigantica enolase showed homology of 92% and 95%, respectively to Fasciola hepatica enolase, suggesting that a fasciolosis vaccine might be effective against both tropical and temperate liver flukes.

Definitive host influences the proteomic profile of excretory/secretory products of the trematode Echinostoma caproni

Background

Echinostoma caproni is an intestinal trematode extensively used as experimental model for the study of factors that determine the course of intestinal helminth infections, since this markedly depends on the host species. Although the host-dependent mechanisms for either chronic establishment or early parasite rejection have been broadly studied, little is known regarding the parasite response against different host environments.

Methods

To identify host-dependent differentially expressed proteins, a comparative proteomic analysis of the excretory/secretory products released from E. caproni adults, isolated from hosts displaying different compatibility with this trematode, was performed.

Results

A total of 19 differential protein spots were identified (14 overexpressed in mice and 5 overexpressed in rats). The establishment of chronic infections in mice is mainly associated with the overexpression by adult worms of antioxidant and detoxifying enzymes (e.g. glutathione S-transferase, hydroxyacylglutathione hydrolase, thiopurine S-transferase, etc.) and metabolic enzymes like enolase, leucine aminopeptidase or malate dehydrogenase. However, the overexpression of cathepsin L and the structural protein actin observed in worms isolated from rats seems not to be effective for the colonization of the intestinal mucosa of this host.

Conclusions

The observed differences suggest that protein expression and/or release is modulated by the local environment generated inside the host and provide useful insights in regards to the resistance mechanisms developed by parasites to ensure their long-term survival.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1465-x) contains supplementary material, which is available to authorized users.

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

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 50μg 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.

Juvenile-specific cathepsin proteases in Fasciola spp.: their characteristics and vaccine efficacies

Fasciolosis, caused by Fasciola hepatica and Fasciola gigantica, is one of the most neglected tropical zoonotic diseases. One sustainable control strategy against these infections is the employment of vaccines that target proteins essential for parasites' invasion and nutrition acquiring processes. Cathepsin proteases are the most abundantly expressed proteins in Fasciola spp. that have been tested successfully as vaccines against fasciolosis in experimental as well as large animals because of their important roles in digestion of nutrients, invasion, and migration. Specifically, juvenile-specific cathepsin proteases are the more effective vaccines because they could block the invasion and migration of juvenile parasites whose immune evasion mechanism has not yet been fully developed. Moreover, because of high sequence similarity and identity of cathepsins from juveniles with those of adults, the vaccines can attack both the juvenile and adult stages. In this article, the characteristics and vaccine potentials of juvenile-specific cathepsins, i.e., cathepsins L and B, of Fasciola spp. were reviewed.

Protection against Fasciola gigantica infection in mice by vaccination with recombinant juvenile-specific cathepsin L

Fasciola gigantica cathepsin L1H (FgCatL1H) is one of the major cathepsin L released by juveniles of F. gigantica to aid in the invasion of host's tissues. Due to its high sequence similarity with other cathepsin L (CatL) isoforms of late stage F. gigantica, it was considered to be a good vaccine candidate that can block all CatL-mediated protease activities and affect juveniles as well as adult parasites. In this study, recombinant proFgCatL1H protein expressed in yeast, Pichia pastoris, system was mixed with Freund's adjuvants and used to subcutaneously immunize mice that were later challenged with metacercariae of F. gigantica. The percentage of worm protection in the rproFgCatL1H-vaccinated mice compared to the non-immunized and adjuvant control mice were approximately 62.7% and 66.1%, respectively. Anti-rproFgCatL1H antisera collected from vaccinated mice reacted specifically with rproFgCatL1H and other cathepsin L isoforms of F. gigantica, but the antibodies did not cross react with antigens from other trematode and nematode parasites, including Eurytrema pancreaticum, Opisthorchis viverrini, Fischoederius cobboldi, Cotylophoron cotylophorum, Gigantocotyle explanatum, Paramphistomum cervi, and Setaria labiato-papillosa. The levels of IgG1 and IgG2a in mouse sera increased significantly at two weeks after immunization and were highest during the sixth to eighth weeks after immunization. The IgG1 level was higher than IgG2a at all periods of immunization, implicating the dominance of the Th2 response. The levels of IgG1 and IgG2a in the immune sera were shown to be strongly correlated with the numbers of worm recovery, and the correlation coefficient was higher for IgG1. The levels of serum aspartate aminotransferase and alanine transaminase were significantly lower in the sera of rproFgCatL1H-vaccinated mice than in the infected control mice indicating a lower degree of liver damage. This study demonstrated a high potential of FgCatL1H vaccine, and its efficacy is currently being studied in the larger economic animals.

Identification and expression of Fasciola gigantica thioredoxin

In the present study, a cDNA encoding Trx from F. gigantica (FgTrx) was cloned by polymerase chain reaction (PCR). The sequence of FgTrx, analyzed by BLAST, SignalP, and ClustralW programs, showed 315 bp of an open reading frame (ORF), 12 bp 5'UTR, 78 bp 3'UTR, and the putative FgTrx peptide comprising of 104 amino acids, with a molecular weight of 11.68 kDa, with the active site containing five amino acids (tryptophan, cysteine, glycine, proline, cysteine) with a conserved dithiol motif from the two cysteines, and pI 5.86. The peptide had no signal sequence; hence, it was not a secreted protein. The recombinant FgTrx was expressed in Escherichia coli BL21 (DE3) and used for production for a polyclonal antibody in rabbits (anti-rFgTrx). The FgTrx protein expression, estimated by indirect ELISA using the rabbit anti-rFgTrx as probe, showed high levels in eggs, 2- and 4-week-old juveniles, and adult parasite. In a functional test, the rFgTrx exhibited specific activity that could be suppressed by an inhibitor (PX12). When tested by immunoblotting and immunohistochemistry, rabbit anti-rFgTrx reacted with natural FgTrx at a molecular weight of 11.68 kDa from eggs, metacercariae, NEJ, 2- and 4-week-old juveniles, and adult F. gigantica. The FgTrx protein was distributed at high levels in the tegument of 2- and 4-week-old juveniles, and the tegument, parenchyma, eggs, and reproductive organs of adult parasites. FgTrx may be one of the major factors acting against oxidative stresses that can damage the parasite; hence, it could be considered as a novel vaccine or drug target.