Characterisation and expression of the Fasciola gigantica cathepsin L gene

An update on proteases and protease inhibitors from trematodes

Trematodes, a class of parasitic flatworms, are responsible for a variety of devastating diseases in humans and animals, with schistosomiasis and fascioliasis being prominent examples. Trematode proteolytic systems involved in the host-parasite interaction have emerged as key contributors to the success of trematodes in establishing and maintaining infections. This review concentrates on diverse proteases and protease inhibitors employed by trematodes and provides an update on recent advances in their molecular-level characterization, with a focus on function, structure, and therapeutic target potential.

Exploiting Comparative Omics to Understand the Pathogenic and Virulence-Associated Protease: Anti-Protease Relationships in the Zoonotic Parasites Fasciola hepatica and Fasciola gigantica

The helminth parasites, Fasciola hepatica and Fasciola gigantica, are the causative agents of fasciolosis, a global and economically important disease of people and their livestock. Proteases are pivotal to an array of biological processes related to parasitism (development, feeding, immune evasion, virulence) and therefore their action requires strict regulation by parasite anti-proteases (protease inhibitors). By interrogating the current publicly available Fasciola spp. large sequencing datasets, including several genome assemblies and life cycle stage-specific transcriptome and proteome datasets, we reveal the complex profile and structure of proteases and anti-proteases families operating at various stages of the parasite's life cycle. Moreover, we have discovered distinct profiles of peptidases and their cognate inhibitors expressed by the parasite stages in the intermediate snail host, reflecting the different environmental niches in which they move, develop and extract nutrients. Comparative genomics revealed a similar cohort of peptidase inhibitors in F. hepatica and F. gigantica but a surprisingly reduced number of cathepsin peptidases genes in the F. gigantica genome assemblies. Chromosomal location of the F. gigantica genes provides new insights into the evolution of these gene families, and critical data for the future analysis and interrogation of Fasciola spp. hybrids spreading throughout the Asian and African continents.

Effectiveness of Fasciola gigantica excretory-secretory and recombinant cathepsin L antigens for rapid diagnosis of human fascioliasis using immunochromatographic devices

Fascioliasis, a food- and water-borne trematodiasis, has been identified as a public health threat by the World Health Organization, with millions of people estimated to be infected or at risk of infection worldwide. We developed an immunochromatographic test (ICT) as a point-of-care (POC) tool for the rapid serodiagnosis of human fascioliasis caused by Fasciola gigantica and evaluated their diagnostic ability. Two tests were developed using antigens from adult F. gigantica excretory-secretory (ES) product and recombinant F. gigantica cathepsin L (rFgCL). Sera from 12 patients with parasitologically proven fascioliasis caused by F. gigantica, 18 with clinically suspected fascioliasis, 65 with other parasitic infections, and 30 healthy controls were used. Using a cutoff of > 0.5 for antibody detection, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the ES-based ICT method were 100%, 98.9% 96.8%, 100%, and 99.2%, respectively, and those of the rFgCL-based ICT method were 86.7%, 93.7%, 81.3%, 95.7%, and 92.0%, respectively. The concordance between the two methods was 91.2%. Tests using F. gigantica ES and rFgCL antigens can be employed quickly and easily as POC diagnostic tools. They can be used to support the clinical diagnosis of human fascioliasis gigantica and in large-scale surveys in endemic areas throughout tropical regions without necessitating additional facilities or ancillary supplies.

The cathepsin-like cysteine peptidases of trematodes of the genus Fasciola

Fasciolosis caused by trematode parasites of the genus Fasciola is a global disease of livestock, particularly cattle, sheep, water buffalo and goats. It is also a major human zoonosis with reports suggesting that 2.4-17 million people are infected worldwide, and 91.1 million people currently living at risk of infection. A unique feature of these worms is their reliance on a family of developmentally-regulated papain-like cysteine peptidases, termed cathepsins. These proteolytic enzymes play central roles in virulence, infection, tissue migration and modulation of host innate and adaptive immune responses. The availability of a Fasciola hepatica genome, and the exploitation of transcriptomic and proteomic technologies to probe parasite growth and development, has enlightened our understanding of the cathepsin-like cysteine peptidases. Here, we clarify the structure of the cathepsin-like cysteine peptidase families and, in this context, review the phylogenetics, structure, biochemistry and function of these enzymes in the host-parasite relationship.

RNA interference in Fasciola gigantica: Establishing and optimization of experimental RNAi in the newly excysted juveniles of the fluke

Fasciolosis caused by Fasciola gigantica is a neglected tropical disease but a constraint on the growth and productivity of cattle, buffaloes and sheep in the tropical countries of Asia and Africa. Resistance to commonly used anthelmintics in Fasciola has increased the need to search for alternative therapeutic targets. RNA interference is the current tool of choice in the search for such targets in Fasciola. The susceptibility of juvenile Fasciola hepatica to double stranded (ds) RNA induced RNAi has been established but in F. gigantica a single preliminary report on RNAi induced mRNA transcript knockdown is available. Here we optimized conditions for RNAi in the liver fluke F.gigantica targeting six genes including superoxide dismutase (SOD), σ class of glutathione-s-transferase (GST), cathepsin (Cat) L1-D, Cat B1, Cat B2 and Cat B3 that showed robust transcriptional silencing of the targets following exposure of the newly excysted juveniles (NEJs) to long (170–223 nt) dsRNA. Knockdown was shown to be concentration dependent with significant mRNA transcript suppression occurring at 5 ng / μl that showed further suppression with the increase in the dsRNA concentration. The dsRNA induced persistent silencing of the mRNA transcript of SOD and σGST up to 15 days of observation. Delivery of the long dsRNA and siRNA to the newly excysted juveniles by soaking method was found to be efficient by tracking the uptake and diffusion of Cy³ labelled siRNA and long dsRNA in the flukes. Off-target effects of dsRNA trigger on some of the non-target genes were detected in the present investigation on RNAi in F. gigantica. The dsRNA induced superoxide dismutase protein suppression while impact of RNAi on other target proteins was not studied. There is no in vitro culture system for prolonged survival of the F. gigantica and in the present study in vitro maintenance of the NEJs is reported for a period of 3 weeks. The present study is the first attempt on optimization of RNAi protocols in F. gigantica where long dsRNA allowed for an efficient and persistent gene silencing, opening prospects for functional validation of putative vaccine and therapeutic targets in this neglected parasite.

RNA interference (RNAi) is a powerful method for selectively silencing genes for the validation of potential targets for drug and vaccine development. The susceptibility of juvenile Fasciola hepatica to double stranded (ds) RNA induced RNAi has been established but in F. gigantica a single report of a preliminary study on knockdown of a single gene transcript exists. In the absence of other tools of reverse genetics, RNAi occupies a centre stage in the validation of gene functions in Fasciola species. This study focuses on F.gigantica, an economically important veterinary parasite with a zoonotic potential. Here in this study, we optimized a set of simple methods for triggering RNAi in the F. gigantica juvenile liver fluke, which shows that a robust transcriptional suppression can be readily achieved across all targets tested and with protein suppression confirmed in one of the targets. These studies also highlight the need for developing an in vitro maintenance system for the fluke for validation of the RNAi protocols. These findings are important for researchers aiming to employ RNAi in investigations of liver fluke biology and target validation.

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.

Molecular and immunological characterization of cathepsin L-like cysteine protease of Paragonimus pseudoheterotremus

Cathepsin L is a cysteine protease belonging to the papain family. In parasitic trematodes, cathepsin L plays essential roles in parasite survival and host-parasite interactions. In this study, cathepsin L of the lung fluke Paragonimus pseudoheterotremus (PpsCatL) was identified and its molecular biological and immunological features characterized. A sequence analysis of PpsCatL showed that the gene encodes a 325-amino-acid protein that is most similar to P. westermani cathepsin L. The in silico three-dimensional structure suggests that PpsCatL is a pro-enzyme that becomes active when the propeptide is cleaved. A recombinant pro-PpsCatL lacking the signal peptide (rPpsCatL), with a molecular weight of 35 kDa, was expressed in E. coli and reacted with P. pseudoheterotremus-infected rat sera. The native protein was detected in crude worm antigens and excretory-secretory products and was localized in the cecum and in the lamellae along the intestinal tract of the adult parasite. Enzymatic activity of rPpsCatL showed that the protein could cleave the fluorogenic substrate Z-Phe-Arg-AMC after autocatalysis but was inhibited with E64. The immunodiagnostic potential of the recombinant protein was evaluated with an enzyme-linked immunosorbent assay (ELISA) and suggested that rPpsCatL can detect paragonimiasis with high sensitivity and specificity (100 and 95.6 %, respectively). This supports the further development of an rPpsCatL-ELISA as an immunodiagnostic tool.

Immunodiagnosis of Fasciola gigantica Infection Using Monoclonal Antibody-Based Sandwich ELISA and Immunochromatographic Assay for Detection of Circulating Cathepsin L1 Protease

BACKGROUND

Tropical fasciolosis caused by Fasciola gigantica infection is one of the major diseases infecting ruminants in the tropical regions of Africa and Asia including Thailand. Parasitological diagnosis of fasciolosis is often unreliable and possesses low sensitivity. Therefore, the detection of circulating parasite antigens is thought to be a better alternative for diagnosis of fasciolosis, as it reflects the real parasite burden.

METHODS

In this study, we have produced a monoclonal antibody (MoAb) against recombinant F. gigantica cathepsin L1 (rFgCatL1), and developed both sandwich enzyme-linked immunosorbent assay (sandwich ELISA) and immunochromatographic (IC) test for rapid detection of circulating cathepsin L1 protease (CatL1) in the sera from mice experimentally and cattle naturally infected with Fasciola gigantica. MoAb 4E3 and biotinylated rabbit anti-recombinant CatL1 antibody were selected due to their high reactivities and specificities.

RESULTS

The lower detection limits of sandwich ELISA and IC test were 3 pg/ml and 0.256 ng/ml, respectively. Sandwich ELISA and IC test could detect F. gigantica infection from day 1 to 35 post infection. In experimental mice, the sensitivity, specificity and accuracy were 95%, 100% and 98.6% (for sandwich ELISA), and 93%, 100% and 98.2% (for IC test), while in natural cattle they were 98.3%, 100% and 99.5% (for sandwich ELISA), and 96.7%, 100% and 99.1% (for IC test).

CONCLUSIONS

These two assay methods showed high efficiencies and precisions for diagnosis of fasciolosis by F. gigantica.

Mucosal expression signatures of two Cathepsin L in channel catfish (Ictalurus punctatus) following bacterial challenge

The mucosal surfaces of fish are the first line of host defense against various pathogens. The mucosal immune responses are the most critical events to prevent pathogen attachment and invasion. Cathepsins are a group of peptidases that involved in different levels of immune responses, but the knowledge of the roles of Cathepsin in mucosal immune responses against bacterial infection are still lacking. Therefore, in the present study we characterized the Cathepsin L gene family in channel catfish, and profiled their expression levels after challenging with two different Gram-negative bacterial pathogens. Here, two Cathepsin L genes were identified from channel catfish and were designated CTSL1a and CTSL.1. Comparing to other fish species, the catfish CTSL genes are highly conserved in their structural features. Phylogenetic analysis was conducted to confirm the identification of CTSL genes. Expression analysis revealed that the CTSL genes were ubiquitously expressed in all tested tissues. Following infection, the CTSL genes were significantly induced at most timepoints in mucosal tissues. But the expression patterns varied depending on both pathogen and tissue types, suggesting that CTSL genes may exert disparate functions or exhibit distinct tissue-selective roles in mucosal immune responses. Our findings here, clearly revealed the key roles of CTSL in catfish mucosal immunity; however, further studies are needed to expand functional characterization and examine whether CTSL may also play additional physiological roles in catfish mucosal tissues.

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.

Molecular cloning and characterization of cathepsin L from freshwater mussel, Cristaria plicata

Cathepsin L is one of the crucial enzyme superfamilies and involved in the immune responses. The Cathepsin L cDNA and genome of Cristaria plicata（CpCL） was cloned from the hemocytes using degenerate primers by the rapid amplification of cDNA ends (RACE) PCR. The genomic DNA was 9353 bp long and had a total of six introns and seven exons. The full-length cDNA of CpCL was 1144 bp, the cDNA contained a 5' untranslated region (UTR) of 34 nucleotides, the 3' UTR of 108 bp with a canonical polyadenylation signal sequence AATAAA and a polyA tail, and an open reading frame (ORF) of 1002 bp, encoding 333 amino acid residues with 37.65 kDa predicted molecular weight. The theoretical isoelectric point was 8.61. The prepro-cathepsin L was consisted of a typical signal peptide (Met1-Gly20), a pro-region peptide (Leu21-Glu116) and a mature peptide (Tyr117-Val333). Many members of the papain family possessed of a proline residue at position 2 in the mature enzymem, this was also observed in CpCL. The preproprotein included an oxyanion hole (Gln 135), the active center formed by Cys141, His280 and Asn 300, the potential N-glycosylation site (Asn38, Asn 113 and Asn 272) and the conserved GCXGG motifs, which was characteristic of cathepsin, the conserved ERWNIN and GNFD motifs, which were characteristic for cathepsin L. Homology analysis revealed that the CpCL shared 49-87% identity to other known cathepsin L sequences. The phylogenetic tree showed that the CpCL clustered with the invertebrate cathepsin L cysteine proteases, and was closely related to the cathepsin L of Hyriopsis cumingii. The expression of CpCL mRNA was detected in hepatopancreas, hemocytes, mantle, gills and adductor muscle, and the higher expression level was in hepatopancreas. After A. hydrophila stimulation, the expression of the CpCL mRNA was up-regulated in hemocytes and hepatopancreas, and the expression level was significantly lower in gill than one after PBS challenge group.

Production and characterization of a monoclonal antibody against recombinant cathepsin L1 of Fasciola gigantica

Monoclonal antibodies (MoAbs) against a recombinant cathepsin L1 of Fasciola gigantica (rFgCatL1) were produced in vitro by fusion of BALB/c mice spleen cells immunized with rFgCatL1 and mouse myeloma cells. Reactivity and specificity of these MoAbs were evaluated by indirect ELISA and immunoblotting techniques. Seven MoAb clones were selected from the stable hybridoma clones, namely 1E10, 1F5, 3D11, 4B10, 4D3, 4E3 and 5E7. Clones 1E10, 1F5 and 3D11 were IgM, whereas clones 4B10, 4D3, 4E3 and 5E7 were IgG1. All MoAbs had kappa light chain isotypes. All MoAbs reacted with rCatL1 at molecular weight (MW) 30kDa and with the native CatL1 at MW 27kDa in whole body (WB) extracts of metacercariae (Met), newly excysted juveniles (NEJ), 1, 3, 5-week-old juveniles (Ju), adult WB and adult excretory-secretory (ES) fractions, but not with adult tegumental antigens (TA). All of these MoAbs showed no cross-reactions with antigens of other parasites commonly found in ruminants and human, including Paramphistomum cervi, Eurytrema pancreaticum, Gigantocotyle explanatum, Schistosoma spindale, Schistosoma mansoni, Moniezia benedeni, Avitellina centripunctata, Trichuris sp., Haemonchus placei and Setaria labiato-papillosa. Localization of CatL1 in each developmental stages of F. gigantica by immunoperoxidase technique, using these MoAbs as probes, indicated that CatL1 was present at high concentration in the caecal epithelium and caecal lumen of metacercariae, NEJ, 1, 3, 5-week-old juveniles and adult fluke. This finding indicated that CatL1 is a copiously expressed parasite protein that is released into the ES, thus CatL1 and its MoAb could be a good candidate for immunodiagnosis of fasciolosis in ruminant and human.

Molecular characterization and expression analysis of four cathepsin L genes in the razor clam, Sinonovacula constricta

Cathepsin L (CTSL) is a lysosomal cysteine protease involved in immune responses in vertebrates. However, few studies exist regarding the role of cathepsin L in bivalves. In this study, we isolated and characterized four cathepsin L genes from the razor clam Sinonovacula constricta, referred to as CTSL1, CTSL2, CTSL3 and CTSL4. These four genes contained typical papain-like cysteine protease structure and enzyme activity sites with ERWNIN-like and GNFD-like motifs in the proregion domain and an oxyanion hole (Gln) and a catalytic triad (Cys, His and Asn) in the mature domain. Expression analysis of the four transcripts revealed a tissue-specific pattern with high expression of CTSL1 and CTSL3 in liver and gonad tissues and high expression of CTSL2 and CTSL4 in liver and gill tissues. During the developmental stages, the four transcripts showed the highest expression in the juvenile stage; however, CTSL3 had a much higher expression level than the other three transcripts during embryogenesis. The four transcripts showed significant changes in expression as early as 4 h or 8 h after infection with Vibrio anguillarum. The fact that bacterial infection can induce expression of the four CTSL transcripts suggests that these transcripts are important components of the innate immunity system of the clam.

Edible vaccines against veterinary parasitic diseases--current status and future prospects

Protection of domestic animals against parasitic infections remains a major challenge in most of the developing countries, especially in the surge of drug resistant strains. In this circumstance vaccination seems to be the sole practical strategy to combat parasites. Most of the presently available live or killed parasitic vaccines possess many disadvantages. Thus, expression of parasitic antigens has seen a continued interest over the past few decades. However, only a limited success was achieved using bacterial, yeast, insect and mammalian expression systems. This is witnessed by an increasing number of reports on transgenic plant expression of previously reported and new antigens. Oral delivery of plant-made vaccines is particularly attractive due to their exceptional advantages. Moreover, the regulatory burden for veterinary vaccines is less compared to human vaccines. This led to an incredible investment in the field of transgenic plant vaccines for veterinary purpose. Plant based vaccine trials have been conducted to combat various significant parasitic diseases such as fasciolosis, schistosomosis, poultry coccidiosis, porcine cycticercosis and ascariosis. Besides, passive immunization by oral delivery of antibodies expressed in transgenic plants against poultry coccidiosis is an innovative strategy. These trials may pave way to the development of promising edible veterinary vaccines in the near future. As the existing data regarding edible parasitic vaccines are scattered, an attempt has been made to assemble the available literature.

Rapid identification of lymnaeid snails and their infection with Fasciola gigantica in Thailand

Freshwater snails of the family Lymnaeidae are the intermediate hosts of the liver fluke Fasciola worldwide. While distinct species have been identified at the molecular level in other parts of the world such data have not been published for Thailand. In this study we collected Lymnaeidae from different localities across Thailand and analyzed their 16S rDNA sequences as a molecular signature for classification. In addition to the ubiquitous Radix rubiginosa, we have confirmed the presence of Austropeplea viridis and Radix swinhoei, for the latter of which the ribosomal rDNA sequences are reported for the first time, in North-Thailand. Based on the obtained 16S rDNA data three primer pairs were designed that allowed rapid identification of these snail species by PCR. To determine their infection status, PCR primers for F.gigantica cathepsin L were used in parallel with the snail 16S rDNA species-specific primers in multiplex PCR analyses. Western blot analysis of total snail protein with a monoclonal anti-F.gigantica cathepsin L antibody confirmed positive cathepsin L PCR results. The developed diagnostic PCR will be of use in risk assessment for transmission of fascioliasis in Thailand.

Identification, expression and immunolocalization of cathepsin B3, a stage-specific antigen expressed by juvenile Fasciola gigantica

To identify antigens that could potentially be developed as vaccines against Fasciola gigantica, somatic antigens were analyzed by immunoprecipitation using pooled sera from rats infected with F. gigantica metacercariae. A prominent antigen of the newly excysted juveniles (NEJ), cathepsin B3 protease (FgCatB3), was identified by N-terminal sequencing and PCR screening of a cDNA library. Recombinant FgCatB3 (rFgCatB3) was expressed in Pichia pastoris, and shown to catalyse the digestion of gelatin, the fluorometric substrate Z-Phe-Arg-AMC and native fibronectin, suggesting that this enzyme may be involved in digesting host connective tissues during the fluke's penetration and migration in the host. Rabbit polyclonal sera against rFgCatB3 was produced and used to determine the distribution of the native cathepsin B3 protease in various developmental stages of F. gigantica. By Western blotting, cathepsin B3 was detected in the whole body (WB) extract of metacercariae and NEJ but not in 4-week-old juveniles or adult parasites which confirmed the stage-specific characteristics of cathepsin B3. Immunolocalization of cathepsin B3 protease in each parasite stage showed that high levels of FgCatB3 were present in the caecal epithelium of the metacercariae and NEJ. The differential distribution of FgCatB3 in the different life cycle stages suggests that this protease is functionally important for the juvenile stage of F. gigantica.

Cloning, site-directed mutagenesis and expression of cathepsin L-like cysteine protease from Uronema marinum (Ciliophora: Scuticociliatida)

A cysteine protease gene (ScCtL) homologous to the cathepsin L genes was isolated from a cDNA library of the scuticociliate parasite (Uronema marinum). To express the ScCtL recombinant protein in heterologous system, 17 codons were redesigned to conform to the standard eukaryotic genetic code using PCR-based site-directed mutagenesis. The synthetic U. marinum procathepsin L (proScCtL) was expressed at high levels in E. coli BL21 (DE3) with pGEX-4T-1 vector, and successfully refolded and purified into a functional and enzymatically active form. The optimal pH for protease activity was found to be 4.5. Like any typical cysteine protease, the enzyme was inhibited by E-64 and leupeptin. A dot-blot immunoassay was conducted in an attempt to determine the reaction abilities and sensitivity of the anti-proScCtL polyclonal antibody to the cytosol and to the membrane fraction from the scuticociliate. Our results suggest that the biochemical characteristics of the recombinant ciliate proScCtL protein are similar to that of the cathepsin L-like cysteine protease, and that the PCR-based site-direct mutated ciliate gene was successfully expressed in a biochemically active form.

Cathepsin L cysteine proteinase in the diagnosis of bovine Fasciola gigantica infection

Cathepsin L cysteine proteinase from Fasciola gigantica was evaluated for its potential in the early prepatent detection of this helminth infection in bovine calves. Five cross-bred bovine calves were experimentally infected with 400 metacercariae/calf and evaluated for anti-cathepsin L antibody response. F. gigantica infection in these calves could be detected 4 weeks post-infection using an ELISA, dipstick ELISA and Western blotting with 100% sensitivity. The antigen was also used to detect F. gigantica field infection in cattle, by screening 256 sera of these animals by an ELISA, which demonstrated an overall infection rate of 26.95%. Preliminary studies showed that F. gigantica cathepsin L cysteine proteinase does not cross-react with Paramphistomum epiclitum, Gigantocotyle explanatum and hydatid cyst antigens. However, extensive studies on the cross-reactivity of this antigen with related helminth parasites of cattle and buffaloes are required, before this antigen can be considered suitable for immuno-diagnosis of fasciolosis in these ruminants.

Cathepsin L1, the Major Protease Involved in Liver Fluke (Fasciola hepatica) Virulence

The secretion and activation of the major cathepsin L1 cysteine protease involved in the virulence of the helminth pathogen Fasciola hepatica was investigated. Only the fully processed and active mature enzyme can be detected in medium in which adult F. hepatica are cultured. However, immunocytochemical studies revealed that the inactive procathepsin L1 is packaged in secretory vesicles of epithelial cells that line the parasite gut. These observations suggest that processing and activation of procathepsin L1 occurs following secretion from these cells into the acidic gut lumen. Expression of the 37-kDa procathepsin L1 in Pichia pastoris showed that an intermolecular processing event within a conserved GXNXFXD motif in the propeptide generates an active 30-kDa intermediate form. Further activation of the enzyme was initiated by decreasing the pH to 5.0 and involved the progressive processing of the 37 and 30-kDa forms to other intermediates and finally to a fully mature 24.5 kDa cathepsin L with an additional 1 or 2 amino acids. An active site mutant procathepsin L, constructed by replacing the Cys(26) with Gly(26), failed to autoprocess. However, [Gly(26)]procathepsin L was processed by exogenous wild-type cathepsin L to a mature enzyme plus 10 amino acids attached to the N terminus. This exogenous processing occurred without the formation of a 30-kDa intermediate form. The results indicate that activation of procathepsin L1 by removal of the propeptide can occur by different pathways, and that this takes place within the parasite gut where the protease functions in food digestion and from where it is liberated as an active enzyme for additional extracorporeal roles.

Molecular expression of a cysteine proteinase of Clonorchis sinensis and its application to an enzyme-linked immunosorbent assay for immunodiagnosis of clonorchiasis

We produced a recombinant cysteine proteinase of Clonorchis sinensis and tested its value as an antigen for serologic diagnosis of C. sinensis infections. The predicted amino acid sequence of the cysteine proteinase of C. sinensis was 58, 48, and 40% identical to those of cathepsin L cysteine proteinases from Paragonimus westermani, Schistosoma japonicum, and Fasciola hepatica, respectively. Western blotting analysis showed that sera from patients infected with C. sinensis strongly reacted with the recombinant protein and that sera from patients infected with S. japonicum weakly reacted with the recombinant protein. Antibody against the recombinant protein stained proteins migrating at about 37 and 28 kDa in C. sinensis adult worm crude extracts. Immunostaining revealed that the cysteine proteinase of C. sinensis was located in the intestinal epithelial cells of the adult parasite and in intrauterine eggs. The specificity and sensitivity of the recombinant antigen or C. sinensis adult worm crude extracts were assessed by an enzyme-linked immunosorbent assay (ELISA) using serum samples from humans infected with different parasites, including 50 patients with clonorchiasis, and negative controls. The sensitivities of the ELISA with the recombinant antigen and C. sinensis adult worm crude extracts were 96 and 88%, respectively. The specificities of the ELISA with the recombinant antigen and C. sinensis adult worm crude extracts were 96.2 and 100%, respectively. The results suggested that the recombinant cysteine proteinase-based ELISA could provide a highly sensitive and specific assay for diagnosis of clonorchiasis.

Role of the tegument and gut in nutrient uptake by parasitic platyhelminths

The ease of procuring nutrient is probably the main selection pressure that drives and maintains the host–parasite relationship. The feeding activities of the ectoparasitic monogeneans exhibit similarities with the predatory turbellarians, with certain monopisthocotylean members feeding by means of a protrusible pharynx. These parasites degrade fish skin by secreting enzymes extracorporeally, but most of the digestion is carried out intracellularly in cells lining a well-differentiated gut. Some polyopisthocotylean monogeneans, however, living within the vascularized gill chamber, took advantage of the availability of a more highly nutritious, consistent, and renewable diet in the form of blood, and this represented a major step in the evolution of endoparasitism. Blood provides a rich source of carbohydrates for the production of energy and amino acids and fatty acids for the synthesis of parasite molecules and for egg production. The external surfaces of all parasitic flatworms depart from turbellarian character and are composed of a multifunctional syncytial tegument that is permeable to a variety of small organic solutes. Glucose and amino acid transporter molecules situated in the tegumental surface and basal membranes of trematodes and cestodes function in the uptake of these molecules and their distribution to the parasite tissues. Cestodes are bereft of any vestige of a gut, but their tegument has become elaborated into a highly efficient digestive–absorptive layer that competes with the vertebrate mucosa for nutrients. The patterns of energy metabolism in adult flatworm parasites are generally anaerobic and based on glycogen, with abbreviated metabolic pathways and the loss of biosynthetic capacities. In contrast to the tegument, the role of the gut is to digest host macromolecules and subsequently absorb the soluble products. However, the switch to blood as the major source of nutrient necessitated development of a means of overcoming the problems of blood clotting, attack by immune effector mechanisms, and the intracellular accumulations of haematin pigment. Digenean trematode, in contrast to monogeneans, digest blood extracellularly and their secretions include molecules capable of lysing erythrocytes and preventing blood clotting. Digestion of the ingested proteins is generally rapid, involving a range of cathepsin-like cysteine and aspartic proteases, which reduce the blood meal to absorbable peptides that are most likely further catabolized to amino acids by intracellular aminopeptidases. The parasites dispose of accumulated haematin by simply emptying the contents of their blind-ended gut.

Fasciola hepatica cathepsin L-like proteases: biology, function, and potential in the development of first generation liver fluke vaccines

Fasciola hepatica secretes cathepsin L proteases that facilitate the penetration of the parasite through the tissues of its host, and also participate in functions such as feeding and immune evasion. The major proteases, cathepsin L1 (FheCL1) and cathepsin L2 (FheCL2) are members of a lineage that gave rise to the human cathepsin Ls, Ks and Ss, but while they exhibit similarities in their substrate specificities to these enzymes they differ in having a wider pH range for activity and an enhanced stability at neutral pH. There are presently 13 Fasciola cathepsin L cDNAs deposited in the public databases representing a gene family of at least seven distinct members, although the temporal and spatial expression of each of these members in the developmental stage of F. hepatica remains unclear. Immunolocalisation and in situ hybridisation studies, using antibody and DNA probes, respectively, show that the vast majority of cathepsin L gene expression is carried out in the epithelial cells lining the parasite gut. Within these cells the enzyme is packaged into secretory vesicles that release their contents into the gut lumen for the purpose of degrading ingested host tissue and blood. Liver flukes also express a novel multi-domain cystatin that may be involved in the regulation of cathepsin L activity. Vaccine trials in both sheep and cattle with purified native FheCL1 and FheCL2 have shown that these enzymes can induce protection, ranging from 33 to 79%, to experimental challenge with metacercariae of F. hepatica, and very potent anti-embryonation/hatch rate effects that would block parasite transmission. In this article we review the vaccine trials carried out over the past 8 years, the role of antibody and T cell responses in mediating protection and discuss the prospects of the cathepsin Ls in the development of first generation recombinant liver fluke vaccines.

Helminth vaccines: from mining genomic information for vaccine targets to systems used for protein expression

The control of helminth diseases of people and livestock continues to rely on the widespread use of anti-helminthic drugs. However, concerns with the appearance of drug resistant parasites and the presence of pesticide residues in food and the environment, has given further incentive to the goal of discovering molecular vaccines against these pathogens. The exponential rate at which gene and protein sequence information is accruing for many helminth parasites requires new methods for the assimilation and analysis of the data and for the identification of molecules capable of inducing immunological protection. Some promising vaccine candidates have been discovered, in particular cathepsin L proteases from Fasciola hepatica, aminopeptidases from Haemonchus contortus, and aspartic proteases from schistosomes and hookworms, all of which are secreted into the host tissues or into the parasite intestine where they play important roles in host-parasite interactions. Since secreted proteins, in general, are exposed to the immune system of the host they represent obvious candidates at which vaccines could be targeted. Therefore, in this article, we consider the potential values and uses of algorithms for characterising cDNAs amongst the collated helminth genomic information that encode secreted proteins, and methods for their selective isolation and cloning. We also review the variety of prokaryotic and eukaryotic cell expression systems that have been employed for the production and downstream purification of recombinant proteins in functionally active form, and provide an overview of the parameters that must be considered if these recombinant proteins are to be commercialised as vaccine therapeutics in humans and/or animals.