Cloning and expression of the major secreted cathepsin B-like protein from juvenile Fasciola hepatica and analysis of immunogenicity following liver fluke infection

Qualitative analysis of Fasciola gigantica excretory and secretory products coimmunoprecipitated with buffalo secondary infection sera shows dissimilar components from primary infection sera

Buffaloes cannot mount a robust adaptive immune response to secondary infection by Fasciola gigantica. Even if excretory and secretory products (ESPs) exhibit potent immunoregulatory effects during primary infection, research on ESPs in secondary infection is lacking, even though the ESP components that are excreted/secreted during secondary infection are unknown. Therefore, qualitative analysis of ESP during secondary infection was performed and compared with that of primary infection to deepen the recognition of secondary infection and facilitate immunoregulatory molecules screening. Buffaloes were divided into three groups: A (n = 3, noninfected), B (n = 3, primary infection) and C (n = 3, secondary infection). Buffaloes in the primary (0 weeks post infection; wpi) and secondary (-4 and 0 wpi) infection groups were infected with 250 metacercariae by oral administration. Then, sera were collected from groups at different wpi, and interacting proteins were precipitated by coimmunoprecipitation (Co-IP), qualitatively analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and annotated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses to infer their potential functions. In group C, 324 proteins were identified, of which 76 proteins were consistently identified across 7 time points (1, 3, 6, 8, 10, 13, and 16 wpi). Compared with 87 proteins consistently identified in group B, 22 proteins were identified in group C. Meanwhile, 34 proteins were only identified in group C compared to 200 proteins identified in group B. Protein pathway analysis indicated that these proteins were mainly involved in the cellular processes and metabolism of F. gigantica. Among them, 14-3-3θ was consistently identified in group C and may be involved in various cellular processes and innate immune signalling pathways. Members of the HSP family were identified in both groups B and C and may function in both primary and secondary infection processes. The proteins discovered in the present study will help to deepen the understanding of the molecular interactions between F. gigantica and buffalo during secondary infection and facilitate the identification of new potential immunoregulatory molecules.

Trichinella spiralis cathepsin B bound and degraded host's intestinal type I collagen

Trichinellosis is a zoonotic parasitic disease that poses threats to human health, the meat industry, food safety, and huge financial losses. The critical stage of Trichinella spiralis (T. spiralis) infection is the invasion of intestinal larvae into the host's intestinal epithelial cells (IECs). T. spiralis Cathepsin B (TsCB) specifically interacts with IECs to facilitate the invasion of larvae. This study aims to look at how TsCB affects mouse IECs. TsCB was successfully cloned, expressed, and characterized, demonstrating its natural cysteine protease hydrolysis activity. A total of 140 proteins that interact with rTsCB were identified by GST pull-down combined with LC-MS/MS, including type I collagen, an essential component of the host's intestinal epithelial barrier system and intimately related to intestinal epithelial damage. TsCB transcription and expression levels rise, whereas type I collagen in the host's intestinal mucosa declines when the T. spiralis larvae invaded. Besides, it was discovered that TsCB bound to and degraded type I collagen of the host's intestine. This research can serve as a foundation for clarifying how T. spiralis invades the host's intestinal barrier and might provide information on potential targets for the creation of novel treatments to treat parasite illnesses.

Advances in diagnostic approaches to Fasciola infection in animals and humans: An overviews

Fasciolosis, caused by Fasciola hepatica and F. gigantica, is an impediment to the livestock industry’s expansion and has a massively negative socio-economic impact due to its widespread prevalence in livestock. It is a waterborne zoonosis affecting human populations in the countries where rural economies are associated with livestock rearing. Conventional diagnosis of Fasciola infection is done by detecting parasite eggs in the faeces of infected animals or by immunological methods. Accurate and quick immunodiagnosis of Fasciola infection in animals and humans is based on the detection of antibodies and specific antigens expressed in the prepatent stage of the parasite. Both molecular and serodiagnostic tests developed thus far have enhanced the reliability of Fasciola diagnosis in both man and animals but are not widely available in resource-poor nations. A pen-side diagnostic test based on a lateral flow assay or a DNA test like loop-mediated isothermal amplification (LAMP) would be simple, fast, and cost-effective, enabling clinicians to treat animals in a targeted manner and avoid the development of drug resistance to the limited flukicides. This review focuses on the recent advances made in the diagnosis of this parasite infection in animals and humans.

An evolutionary molecular adaptation of an unusual stefin from the liver fluke Fasciola hepatica redefines the cystatin superfamily

Fasciolosis is a worldwide parasitic disease of ruminants and an emerging human disease caused by the liver fluke Fasciola hepatica. The cystatin superfamily of cysteine protease inhibitors is composed of distinct families of intracellular stefins and secreted true cystatins. FhCyLS-2 from F. hepatica is an unusual member of the superfamily, where our sequence and 3D structure analyses in this study revealed that it combines characteristics of both families. The protein architecture demonstrates its relationship to stefins, but FhCyLS-2 also contains the secretion signal peptide and disulfide bridges typical of true cystatins. The secretion status was confirmed by detecting the presence of FhCyLS-2 in excretory/secretory products, supported by immunolocalization. Our high-resolution crystal structure of FhCyLS-2 showed a distinct disulfide bridging pattern and functional reactive center. We determined that FhCyLS-2 is a broad specificity inhibitor of cysteine cathepsins from both the host and F. hepatica, suggesting a dual role in the regulation of exogenous and endogenous proteolysis. Based on phylogenetic analysis that identified several FhCyLS-2 homologues in liver/intestinal foodborne flukes, we propose a new group within the cystatin superfamily called cystatin-like stefins.

The Zoonotic Helminth Parasite Fasciola hepatica: Virulence-Associated Cathepsin B and Cathepsin L Cysteine Peptidases Secreted by Infective Newly Excysted Juveniles (NEJ)

Simple Summary

Fasciolosis, caused by the worm parasite Fasciola hepatica (liver fluke), is a global disease of farm animals and a neglected disease of humans. Infection arises from the ingestion of resistant metacercariae that contaminate vegetation. Within the intestine, the parasite excysts as an active larvae, the newly excysted juvenile (NEJ), that borrows through the intestinal wall to infect the host and migrates to the liver. NEJ release, tissue penetration and migration are facilitated by enzymes secreted by the parasite, namely, cathepsin B1 (FhCB1), cathepsin B2 (FhCB2), cathepsin B3 (FhCB3) and cathepsin L3 (FhCL3). While our knowledge of these enzymes is growing, we have yet to understand why the parasites require all four of them to invade the host. In this study, we produced functional recombinant forms of these enzymes and demonstrated that they vary greatly in terms of activity, optimal pH and substrate specificity, suggesting that, combined, these enzymes provide the parasite with an efficient digestion system for different host tissues and molecules. We also identified several compounds that inhibited the activity of these enzymes, but did not affect the ability of the larvae to excyst or survive. However, this does not exclude these enzymes as targets for development of drugs or vaccines.

Abstract

Fasciolosis caused by Fasciola hepatica is a major global disease of livestock and an important neglected helminthiasis of humans. Infection arises when encysted metacercariae are ingested by the mammalian host. Within the intestine, the parasite excysts as a newly excysted juvenile (NEJ) that penetrates the intestinal wall and migrates to the liver. NEJ excystment and tissue penetration are facilitated by the secretion of cysteine peptidases, namely, cathepsin B1 (FhCB1), cathepsin B2 (FhCB2), cathepsin B3 (FhCB3) and cathepsin L3 (FhCL3). While our knowledge of these peptidases is growing, we have yet to understand why multiple enzymes are required for parasite invasion. Here, we produced functional recombinant forms of these four peptidases and compared their physio-biochemical characteristics. Our studies show great variation of their pH optima for activity, substrate specificity and inhibitory profile. Carboxy-dipeptidase activity was exhibited exclusively by FhCB1. Our studies suggest that, combined, these peptidases create a powerful hydrolytic cocktail capable of digesting the various host tissues, cells and macromolecules. Although we found several inhibitors of these enzymes, they did not show potent inhibition of metacercarial excystment or NEJ viability in vitro. However, this does not exclude these peptidases as targets for future drug or vaccine development.

Diagnosis of sheep fasciolosis caused by Fasciola hepatica using cathepsin L enzyme-linked immunosorbent assays (ELISA)

Fasciolosis, a global parasitic disease of agricultural livestock, is caused by the liver fluke Fasciola hepatica. Management and strategic control of fasciolosis on farms depends on early assessment of the extent of disease so that control measures can be implemented quickly. Traditionally, this has relied on the detection of eggs in the faeces of animals, a laborious method that lacks sensitivity, especially for sub-clinical infections, and identifies chronic infections only. Enzyme linked immunosorbent assays (ELISA) offer a quicker and more sensitive serological means of diagnosis that could detect early acute infection before significant liver damage occurs. The performance of three functionally-active recombinant forms of the major F. hepatica secreted cathepsins L, rFhCL1, rFhCL2, rFhCL3, and a cathepsin B, rFhCB3, were evaluated as antigens in an indirect ELISA to serologically diagnose liver fluke infection in experimentally and naturally infected sheep. rFhCL1 and rFhCL3 were the most effective of the four antigens detecting fasciolosis in sheep as early as three weeks after experimental infection, at least five weeks earlier than both coproantigen and faecal egg tests. In addition, the rFhCL1 and rFhCL3 ELISAs had a very low detection limit for liver fluke in lambs exposed to natural infection on pastures and thus could play a major role in the surveillance of farms and a 'test and treat' approach to disease management. Finally, antibodies to all three cathepsin L proteases remain high throughout chronic infection but decline rapidly after drug treatment with the flukicide, triclabendazole, implying that the test may be adapted to trace the effectiveness of drug treatment.

Recent Developments in Recombinant Proteins for Diagnosis of Human Fascioliasis

Fascioliasis is an important neglected tropical disease that causes severe injury to the bile ducts and liver. Therefore, a rapid and accurate method for detection of Fasciola hepatica infection plays a vital role in early treatment. Currently, the diagnosis of fascioliasis is mainly conducted via serological tests using the excretory/secretory (E/S) products, which might cross-react with antigens from other helminth parasitic diseases. Hence, the development of serodiagnosis test using recombinant antigens may contribute to differentiate fascioliasis from other helminth infections. In the past 20 years, many attempts have been made to exert different F. hepatica recombinant antigens to obtain a well-established standard assay with high accuracy. In this review, we address recent studies that refer to the development of serodiagnosis tests for diagnosis of human fascioliasis based on the candidate recombinant antigens produced by different approaches. Meanwhile, in the present review, some main factors have been highlighted to improve the accuracy of diagnostic tests such as the effect of refolding methods to recover antigens' tertiary structure as well as applying a mixture of recombinant antigens with the highest sensitivity and specificity to improve the accuracy of diagnostic tests.

Proteases and pseudoproteases in parasitic arthropods of clinical importance

Parasitic arthropods feed on blood or skin tissue and share comparable repertoires of proteases involved in haematophagy, digestion, egg development and immunity. While proteolytically active proteases of multiple classes dominate, an increasing number of pseudoproteases have been discovered that have no proteolytic function but are pharmacologically active biomolecules, evolved to carry out alternative functions as regulatory, antihaemostatic, anti-inflammatory or immunomodulatory compounds. In this review, we provide an overview of proteases and pseudoproteases from clinically important arthropod parasites. Many of these act in central biological pathways of parasite survival and host-parasite interaction and may be potential targets for therapeutic interventions.

Isoforms of Cathepsin B1 in Neurotropic Schistosomula of Trichobilharzia regenti Differ in Substrate Preferences and a Highly Expressed Catalytically Inactive Paralog Binds Cystatin

Schistosomula (the post-infective stages) of the neurotropic schistosome Trichobilharzia regenti possess multiple isoforms of cathepsin B1 peptidase (TrCB1.1-TrCB1.6) with involvement in nutrient digestion. The comparison of substrate preferences of TrCB1.1 and TrCB1.4 showed that TrCB1.4 had a very narrow substrate specificity and after processing it was less effective toward protein substrates when compared to TrCB1.1. Self-processing of both isoforms could be facilitated by sulfated polysaccharides due to a specific binding motif in the pro-sequence. Trans-activation by heterologous enzymes was also successfully employed. Expression profiling revealed a high level of transcription of genes encoding the enzymatically inactive paralogs TrCB1.5 and TrCB1.6. The transcription level of TrCB1.6 was comparable with that of TrCB1.1 and TrCB1.2, the most abundant active isoforms. Recombinant TrCB1.6wt, a wild type paralog with a Cys29-to-Gly substitution in the active site that renders the enzyme inactive, was processed by the active TrCB1 forms and by an asparaginyl endopeptidase. Although TrCB1.6wt lacked hydrolytic activity, endopeptidase, but not dipeptidase, activity could be restored by mutating Gly29 to Cys29. The lack of exopeptidase activity may be due to other mutations, such as His110-to-Asn in the occluding loop and Asp224-to-Gly in the main body of the mature TrCB1.6, which do not occur in the active isoforms TrCB1.1 and TrCB1.4 with exopeptidase activity. The catalytically active enzymes and the inactive TrCB1.6 paralog formed complexes with chicken cystatin, thus supporting experimentally the hypothesis that inactive paralogs could potentially regulate the activity of the active forms or protect them from being inhibited by host inhibitors. The effect on cell viability and nitric oxide production by selected immune cells observed for TrCB1.1 was not confirmed for TrCB1.6. We show here that the active isoforms of TrCB1 have different affinities for peptide substrates thereby facilitating diversity in protein-derived nutrition for the parasite. The inactive paralogs are unexpectedly highly expressed and one of them retains the ability to bind cystatins, likely due to specific mutations in the occluding loop and the enzyme body. This suggests a role in sequestration of inhibitors and protection of active cysteine peptidases.

The Effects of pH and Temperature on Cysteine Protease (Cathepsin B) Activity in Miracidia and Eggs of Fasciola hepatica

BACKGROUND

Fascioliasis is a worldwide zoonotic disease caused by the trematodes Fasciola hepatica in humans and animals. Proteases are essential for the survival of parasites and have important activities such as penetration, tissue migration, and egg hatching. This study was conducted to analyze cysteine protease of the miracidia and eggs of F. hepatica, and to assess the effects of pH and temperature on the proteases activity and stability.

METHODS

Adults F. hepatica were isolated from infected livers and were morphologically identified in 2018. Eggs collected from the adults and incubated in distilled water at 28 °C for 16 d to produce miracidia. The extract was collected from miracidia and eggs. A substrate for cathepsin B (Z-Arg-Arg-Pna) was used to assess the enzyme activity at different (2-12) pH levels. After homogenization, protein level was measured with Bradford method. Estimation of optimum temperature and pH was performed in the temperature range of 10-90 ° C and pH values from 2-12.

RESULTS

The highest activity of the miracidia and eggs enzyme extracts for Z-Arg-Arg-pNA was at pH 4. The miracidia extract was most stable at neutral pH and the eggs extract was most stable in acidic pH. The optimum temperature activity for both stages was 40 °C. These proteases were stable up to 40 °C.

CONCLUSION

Upon the importance of pH and temperature in the life cycle of F. hepatica, the current findings can be used for induction of some modifications in pH and preventing the activity of the enzymes for decrement of the efficacy of miracidia penetration into the intermediate snails and egg hatching of this zoonotic parasite.

Generation of a single-chain variable fragment phage display antibody library from naïve mice panned against Fasciola hepatica antigens

Monoclonal antibodies have a wide range of applications in basic and applied research as well as in the medical and pharmaceutical industries. Phage display antibody libraries offer an alternative to hybridoma technology for the generation of monoclonal antibodies and can be applied to high-throughput screening and facilitate the generation of novel antibodies. Despite their utility in several fields of research there has been limited application of antibody libraries in the study of trematode parasites. Fasciola hepatica causes considerable loss to the agriculture sector and is also a human pathogen. The parasite's excretory/secretory material contains numerous molecules that facilitate its invasion and survival within the mammalian host, including cathepsin B and L proteases. F. hepatica cathepsin B2 is expressed during the initial weeks of infection and has suspected roles in immune evasion and as a digestive enzyme in the parasite's gut; it is considered a good target for vaccination or therapeutic inhibitors. In this study, we produced a single-chain variable fragment (scFv) phage display library from naïve mice. The library was used to identify several scFv that can bind to antigens from adult F. hepatica homogenate, and a scFv that can bind to F. hepatica cathepsin B2. The results highlight the potential applicability of such a library to facilitate the study of F. hepatica and other parasites. This is the first report of the application of a naïve phage display antibody library to the study of F. hepatica.

A proteomic comparison of excretion/secretion products in Fasciola hepatica newly excysted juveniles (NEJ) derived from Lymnaea viatrix or Pseudosuccinea columella

The characteristics of parasitic infections are often tied to host behavior. Although most studies have investigated definitive hosts, intermediate hosts can also play a role in shaping the distribution and accumulation of parasites. This is particularly relevant in larval stages, where intermediate host's behavior could potentially interfere in the molecules secreted by the parasite into the next host during infection. To investigate this hypothesis, we used a proteomic approach to analyze excretion/secretion products (ESP) from Fasciola hepatica newly excysted juveniles (NEJ) derived from two intermediate host species, Lymnaea viatrix and Pseudosuccinea columella. The two analyzed proteomes showed differences in identity, abundance, and functional classification of the proteins. This observation could be due to differences in the biological cycle of the parasite in the host, environmental aspects, and/or host-dependent factors. Categories such as protein modification machinery, protease inhibitors, signal transduction, and cysteine-rich proteins showed different abundance between samples. More specifically, differences in abundance of individual proteins such as peptidyl-prolyl cis-trans isomerase, thioredoxin, cathepsin B, cathepsin L, and Kunitz-type inhibitors were identified. Based on the differences identified between NEJ ESP samples, we can conclude that the intermediate host is a factor influencing the proteomic profile of ESP in F. hepatica.

Evaluation of a Commercial Enzyme-Linked Immunosorbent Assay Kit and In-House Fasciola gigantica Cysteine Proteinases-Based Enzyme-Linked Immunosorbent Assays for Diagnosis of Human Fascioliasis

Fascioliasis, caused by Fasciola hepatica and Fasciola gigantica infection, is a major food-borne trematodiasis in many places of the world, with the central region of Vietnam being reported as a highly endemic area. Stool examination for Fasciola eggs is not a sensitive method, and immunodiagnostic methods are preferable. We investigated various enzyme-linked immunosorbent assays (ELISAs) to evaluate their efficacy for fascioliasis diagnosis. Test sera used are primarily screened using an ELISA kit produced in Vietnam (VN kit; Viet Sinh Chemical Producing & Trading Co. Ltd., Ho Chi Minh City, Vietnam): Seropositive individuals having symptoms compatible with fascioliasis were regarded as clinically diagnosed fascioliasis cases. A commercial Fasciola IgG ELISA kit from Diagnostic Automation/Cortez Diagnostics, Inc. (USA kit; Woodland Hills, CA), which has been commonly used in Vietnam, was assessed and compared with in-house ELISA systems, including a cystatin-capture (CC) ELISA using crude worm extract (CWE) and an indirect ELISA using a synthetic peptide Ac-TPTCHWECQVGYNKTYDEE-NHMe designed from the F. gigantica cathepsin B (FgCB5) molecule. The USA kit was suitable for routine diagnosis after recalibration of the manufacturer's suggested cutoff point. Cystatin-capture ELISA with CWE provided good sensitivity and specificity with perfect agreement to the results of the USA kit. In dot-blot ELISA, recombinant FgCB5 reacted more strongly with human antisera than did other F. gigantica antigens tested. Enzyme-linked immunosorbent assay using the synthetic peptide fragment of the FgCB5 exhibited nearly 80% sensitivity and specificity, but the test results showed low agreement with CC-ELISA or the USA kit. In conclusion, the commercially available Fasciola IgG ELISA kit from the United States and the in-house CC ELISA using CWE are suitable for practical diagnosis for fascioliasis.

Proteomic analysis of Fasciola gigantica excretory and secretory products (FgESPs) interacting with buffalo serum of different infection periods by shotgun LC-MS/MS

Fasciolosis, caused by Fasciola hepatica and Fasciola gigantica, is an important zoonotic disease in the world. It affects livestock, especially for sheep and cattle, causing major economic loss due to morbidity and mortality. Although the excretory and secretory products (ESPs) of F. hepatica have been relatively well studied, little is known about the interaction between the ESP and host, and the mechanism of the key proteins involved in interaction. In this study, buffaloes were infected by Fasciola gigantica, and infection serum was collected at three different periods (42dpi, 70dpi, and 98dpi). The interaction proteins were pulled down with three different period serum by Co-IP assay, respectively, and then identified by LC-MS/MS analysis. A number of proteins were identified; some of them related to the biological function of the parasite, while most of them the functions were unknown. For the annotated proteins, 13, 5, and 7 proteins were pulled down by the infected serum in 42dpi, 70dpi, and 98dpi, respectively, and 18 proteins could be detected in all three periods. Among them, 13 belong to the cathepsin family, 4 proteins related to glutathione S-transferase, and 3 proteins are calcium-binding protein; other proteins related to catalytic activity and cellular process. This study could provide new insights into the central role played by ESPs in the protection of F. gigantica from the host immune response. At the same time, our research provided material for further studies about the interaction between F. gigantica and host.

Intranasal delivery of a formulation containing stage-specific recombinant proteins of Fasciola hepatica cathepsin L5 and cathepsin B2 triggers an anti-fecundity effect and an adjuvant-mediated reduction in fluke burden in sheep

Fasciola hepatica infection continues to be a major problem in the agriculture sector, particularly in sheep and cattle. Cathepsin L and B proteases are major components of the excretory/secretory material of the parasite, and their roles in several important aspects of parasite invasion and survival has led to their use as targets in rational vaccine design. Previous studies in rats demonstrated that the use of stage-specific antigens, cathepsin B2 and cathepsin L5, as part of a multivalent vaccine, was able to confer significant protection against challenge. In the present study, recombinant versions of cathepsin L5 and cathepsin B2 produced in yeast were used in combination to vaccinate sheep. Intramuscular and intranasal forms of administration were applied, and sheep were subsequently challenged with 150 F. hepatica metacercariae. Intramuscular vaccination was able to induce a strong systemic antibody response against both antigens, but failed to confer significant protection. Conversely, no elevated antibody response was detected against the vaccine antigens following nasal vaccination; however, a reduction in parasite egg viability (>92%) and a statistically significant (p = 0.006), predominantly adjuvant-mediated reduction in worm burdens was observed.

Phylogenetic relationships, stage-specific expression and localisation of a unique family of inactive cysteine proteases in Sarcoptes scabiei

Background

Scabies is worldwide one of the most common, yet neglected, parasitic skin infections, affecting a wide range of mammals including humans. Limited treatment options and evidence of emerging mite resistance against the currently used drugs drive our research to explore new therapeutic candidates. Previously, we discovered a multicopy family of genes encoding cysteine proteases with their catalytic sites inactivated by mutation (SMIPP-Cs). This protein family is unique in parasitic scabies mites and is absent in related non-burrowing mites. We postulated that the SMIPP-Cs have evolved as an adaptation to the parasitic lifestyle of the scabies mite. To formulate testable hypotheses for their functions and to propose possible strategies for translational research we investigated whether the SMIPP-Cs are common to all scabies mite varieties and where within the mite body as well as when throughout the parasitic life-cycle they are expressed.

Results

SMIPP-C sequences from human, pig and dog mites were analysed bioinformatically and the phylogenetic relationships between the SMIPP-C multi-copy gene families of human, pig and dog mites were established. Results suggest that amplification of the SMIPP-C genes occurred in a common ancestor and individual genes evolved independently in the different mite varieties. Recombinant human mite SMIPP-C proteins were produced and used for murine polyclonal antibody production. Immunohistology on skin sections from human patients localised the SMIPP-Cs in the mite gut and in mite faeces within in the epidermal skin burrows. SMIPP-C transcription into mRNA in different life stages was assessed in human and pig mites by reverse transcription followed by droplet digital PCR (ddPCR). High transcription levels of SMIPP-C genes were detected in the adult female life stage in comparison to all other life stages.

Conclusions

The fact that the SMIPP-Cs are unique to three Sarcoptes varieties, present in all burrowing life stages and highly expressed in the digestive system of the infective adult female life stage may highlight an essential role in parasitism. As they are excreted from the gut in scybala they presumably are able to interact or interfere with host proteins present in the epidermis.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2862-0) contains supplementary material, which is available to authorized users.

Functional characterization of single-domain cystatin-like cysteine proteinase inhibitors expressed by the trematode Fasciola hepatica

Cystatins are small, phylogenetically conserved proteins that are tight-binding inhibitors of cysteine proteinases. The liver fluke Fasciola hepatica uses a diverse set of cysteine proteinases of the papain superfamily for host invasion, immune evasion and nutrition, but little is known about the regulation of these enzymes. The aim of this work is to characterize the cystatin repertoire of F. hepatica. For this purpose, we first surveyed the available sequence databases, identifying three different F. hepatica single-domain cystatins. In agreement with the in silico predictions, at least three small proteins with cysteine proteinase binding activity were identified. Phylogenetic analyses showed that the three cystatins (named FhStf-1, -2 and -3) are members of the I25A subfamily (stefins). Whereas FhStf-1 grouped with classical stefins, FhStf-2 and 3 fell in a divergent stefin subgroup unusually featuring signal peptides. Recombinant rFhStf-1, -2 and -3 had potent inhibitory activity against F. hepatica cathepsin L cysteine proteinases but differed in their capacity to inhibit mammalian cathepsin B, L and C. FhStf-1 was localized in the F. hepatica reproductive organs (testes and ovary), and at the surface lamella of the adult gut, where it may regulate cysteine proteinases related with reproduction and digestion, respectively. FhStf-1 was also detected among F. hepatica excretion-secretion (E/S) products of adult flukes. This suggests that it is secreted by non-classical secretory pathway and that it may interact with host lysosomal cysteine proteinases.

The cathepsin S cysteine proteinase of the burrowing nematode Radopholus similis is essential for the reproduction and invasion

BACKGROUND

The nematode Radopholus similis is an important migratory endoparasite of plants. Cysteine proteinases such as cathepsin S (CPS) play key roles during embryonic development, invasion, and pathogenesis in nematodes and many other animal parasites. This study was designed to investigate the molecular characterization and functions of a cathepsin S protease in R. similis and to find new targets for its control.

RESULTS

Rs-CPS of R. similis, Hg-CPS of Heterodera glycines and Ha-CPS of H. avenae are closely genetically related and share the same branch of the phylogenetic tree. Rs-cps is a multi-copy gene that is expressed in the esophageal glands, ovaries, testes, vas deferens, and eggs of R. similis. Rs-cps mRNA transcripts are expressed at varying levels during all developmental stages of R. similis. Rs-cps expression was highest in females. The neurostimulant octopamine did not significantly enhance the ingestion of the dsRNA soaking solution by R. similis but instead had a detrimental effect on nematode activity. The dsRNA soaking solution diffused into the body of R. similis not only through the esophageal lumen but also through the amphids, excretory duct, vagina, anus and cloacal orifice. We confirmed that RNAi significantly suppressed the expression level of Rs-cps and reproductive capability and pathogenicity of R. similis.

CONCLUSIONS

Our results demonstrate that Rs-cps plays important roles in the reproduction, parasitism and pathogenesis of R. similis and could be used as a new potential target for controlling plant parasitic nematodes.

Fasciola gigantica cathepsin B5 is an acidic endo- and exopeptidase of the immature and mature parasite

Cysteine proteases of the liver fluke Fasciola have been described as essential molecules in the infection process of the mammalian host. Destinct cathepsin Bs, which are already expressed in the metacercarial stage and released by the newly excysted juvenile are major actors in this process. Following infection their expression is stopped and the proteins will not be detectable any longer after the first month of development. On the contrary, the novel cathepsin B5 of Fasciola gigantica (FgCB5) described in this work was also found expressed in later juvenile stages and the mature worm. Like all previously described Fasciola family members it was located in the cecal epithelium of the parasite. Western blot analysis of adult antigen preparations detected procathepsin B5 in crude worm extract and in small amounts in the ES product. In support of these data, the sera of infected rabbits and mice were reactive with recombinant FgCB5 in Western blot and ELISA. Biochemical analysis of yeast-expressed FgCB5 revealed that it has properties of a lysosomal hydrolase optimized for activity at acid pH and that it is able to efficiently digest a broad spectrum of host proteins. Unlike previously characterized Fasciola family members FgCB5 carries a histidine doublet in the occluding loop equivalent to residues His110 and His111 of human mature cathepsin B and consequently showed substantial carboxydipeptidyl activity which depends on these two residues.

Activating the cathepsin B1 of a parasite: a major route with alternative pathways?

With a major leap in a long running saga, Jilkova and colleagues, in this issue of Structure, provide structural and biochemical evidence for a role of sulfated polysaccharides in the activation of parasite digestive proteases.

Cathepsin B Cysteine Proteinase is Essential for the Development and Pathogenesis of the Plant Parasitic Nematode Radopholus similis

Radopholus similis is an important plant parasitic nematode which severely harms many crops. Cathepsin B is present in a wide variety of organisms, and plays an important role in many parasites. Understanding cathepsin B of R. similis would allow us to find new targets and approaches for its control. In this study, we found that Rs-cb-1 mRNA was expressed in esophageal glands, intestines and gonads of females, testes of males, juveniles and eggs in R. similis. Rs-cb-1 expression was the highest in females, followed by juveniles and eggs, and was the lowest in males. The maximal enzyme activity of Rs-CB-1 was detected at pH 6.0 and 40 °C. Silencing of Rs-cb-1 using in vitro RNAi (Soaking with dsRNA in vitro) not only significantly inhibited the development and hatching of R. similis, but also greatly reduced its pathogenicity. Using in planta RNAi, we confirmed that Rs-cb-1 expression in nematodes were significantly suppressed and the resistance to R. similis was significantly improved in T2 generation transgenic tobacco plants expressing Rs-cb-1 dsRNA. The genetic effects of in planta RNAi-induced gene silencing could be maintained in the absence of dsRNA for at least two generations before being lost, which was not the case for the effects induced by in vitro RNAi. Overall, our results first indicate that Rs-cb-1 plays key roles in the development, hatching and pathogenesis of R. similis, and that in planta RNAi is an effective tool in studying gene function and genetic engineering of plant resistance to migratory plant parasitic nematodes.

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.

Fasciola hepatica fatty acid binding protein induces the alternative activation of human macrophages

The liver fluke Fasciola hepatica is a highly evolved parasite that uses sophisticated mechanisms to evade the host immune response. The immunosuppressive capabilities of the parasite have been associated with antigens secreted through the parasite's tegument, called excretory-secretory products (ESPs). Proteomic studies have identified the fatty acid binding protein (FABP) as one of molecules present in the parasite ESPs. Although FABP has been investigated for potential use in the development of vaccines against fascioliasis, its direct interaction with cells of immune system has not been studied. In this study, FABP was purified in native form from soluble extracts of F. hepatica adult flukes using a combination of molecular sieving chromatography and preparative isoelectric focusing. The immunological effect of the purified protein, termed Fh12, was assayed in vitro using monocyte-derived macrophages (MDM) obtained from healthy human donors. Results from the assay indicate that Fh12 produced a significantly increased arginase expression and activity and induced the expression of chitinase-3-like protein (CHI3L1). The assay also showed that Fh12 downregulated the production of nitric oxide (NO) and the expression of nitric oxide synthase (NOS2). This indicates that Fh12 induced the production of alternatively activated macrophages (AAMϕ). The results also demonstrated the ability of Fh12 to downregulate the secretion of the proinflammatory and inflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin-12 (IL-12), and IL-1βB, even after stimulation with lipopolysaccharide (LPS), as well as its ability to stimulate the overexpression of IL-10. These results suggest a potent anti-inflammatory role for Fh12, which could occur via targeting of Toll-like receptor 4 (TLR4).

Novel cathepsin B and cathepsin B-like cysteine protease of Naegleria fowleri excretory-secretory proteins and their biochemical properties

Naegleria fowleri causes a lethal primary amoebic meningoencephalitis (PAM) in humans and experimental animals, which leads to death within 7-14 days. Cysteine proteases of parasites play key roles in nutrient uptake, excystment/encystment, host tissue invasion, and immune evasion. In this study, we cloned N. fowleri cathepsin B (nfcpb) and cathepsin B-like (nfcpb-L) genes from our cDNA library of N. fowleri. The full-length sequences of genes were 1,038 and 939 bp (encoded 345 and 313 amino acids), and molecular weights were 38.4 and 34 kDa, respectively. Also, nfcpb and nfcpb-L showed a 56 and 46 % identity to Naegleria gruberi cathepsin B and cathepsin B-like enzyme, respectively. Recombinant NfCPB (rNfCPB) and NfCPB-L (rNfCPB-L) proteins were expressed by the pEX5-NT/TOPO vector that was transformed into Escherichia coli BL21, and they showed 38.4 and 34 kDa bands on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis using their respective antibodies. Proteolytic activity of refolded rNfCPB and rNfCPB-L was maximum at a pH of 4.5, and the most effective substrate was Z-LR-MCA. rNfCPB and rNfCPB-L showed proteolytic activity for several proteins such as IgA, IgG, IgM, collagen, fibronectin, hemoglobin, and albumin. These results suggested that NfCPB and NfCPB-L cysteine protease are important components of the N. fowleri ESP, and they may play important roles in host tissue invasion and immune evasion as pathogens that cause N. fowleri PAM.

Neurological and ocular fascioliasis in humans

Fascioliasis is a food-borne parasitic disease caused by the trematode species Fasciola hepatica, distributed worldwide, and Fasciola gigantica, restricted to given regions of Africa and Asia. This disease in humans shows an increasing importance, which relies on its recent widespread emergence related to climate and global changes and also on its pathogenicity in the invasive, biliary, and advanced chronic phases in the human endemic areas, mainly of developing countries. In spite of the large neurological affection capacity of Fasciola, this important pathogenic aspect of the disease has been pronouncedly overlooked in the past decades and has not even appear within the numerous reviews on the parasitic diseases of the central nervous system. The aim of this wide retrospective review is an in-depth analysis of the characteristics of neurological and ocular fascioliasis caused by these two fasciolid species. The terms of neurofascioliasis and ophthalmofascioliasis are restricted to cases in which the direct affection of the central nervous system or the eye by a migrant ectopic fasciolid fluke is demonstrated by an aetiological diagnosis of recovered flukes after surgery or spontaneous moving-out of the fluke through the orbit. Cases in which the ectopic fluke is not recovered and the symptoms cannot be explained by an indirect affection at distance may also be included in these terms. Neurofascioliasis and ophthalmofascioliasis cases are reviewed and discussed. With regard to fascioliasis infection giving an indirect rise to neurological affection, the distribution and frequency of cases are analysed according to geography, sex, and age. Minor symptoms and major manifestations are discussed. Three main types of cases are distinguished depending on the characteristics of their manifestations: genuine neurological, meningeal, and psychiatric or neuropsychic. The impressive symptoms and signs appearing in each type of these cases are included. Brain examination techniques and neuroimaging useful for the diagnosis of neurological cases are exposed. Within fascioliasis infection indirectly causing ocular manifestations, case distribution and frequency are similarly analysed. A short analysis is devoted to clarify the first reports of a human eye infection. The affection of related and close organs is discussed by differentiating between cases of the dorsal spine, pulmonary manifestations, heart and vessel affection, findings in blood vessels, skin and dermatologic reactions, cases of ectopic mature flukes, and upper body locations. The clinical complexity of the puzzling polymorphisms, the disconcerting multifocality of the manifestations, and their changes along the evolution of the disease in the same patient, as well as the differences between the clinical pictures shown by different patients, are highlighted. The many syndromes involved are enumerated. The pathogenic and physiological mechanisms underlying neurofascioliasis and ophthalmofascioliasis caused by ectopic flukes and the physiopathogenic processes indirectly affecting the central nervous system and causing genuine neurological, meningeal, psychiatric, and ocular manifestations are discussed. The diagnosis of neurological and ophthalmologic fascioliasis is analysed in depth, including clinical and paraclinical diagnosis, eosinophilia in the blood and cerebrospinal fluid, differential diagnosis from other parasitic infections such as helminthiases and myiases, an update of human fascioliasis diagnosis, and fluke and/or fluke egg recovery by surgery. Diagnostic analyses with faecal and blood samples for fascioliasis patients are updated. Therapy for patients with major neurological manifestations includes both antiparasitic treatments and anti-inflammatory therapeutics. Prognosis in fascioliasis patients with neurological manifestations is discussed, with emphasis on sequelae and fatal cases, and the care of patients with ophthalmologic manifestations is added. Conclusions indicate that neurological cases are overlooked in human fascioliasis endemic areas and also in developing countries in general. In remote zones, rural health centres and small hospitals in or near the human endemic areas do not dispose of the appropriate equipments for neurological analyses. Moreover, physicians may not be aware about the potential relationship between liver fluke infection and neurological implications, and such cases may therefore remain misdiagnosed, even in developed countries. Priority should henceforth be given to the consideration of neurological and ocular affection in human endemic areas, and efforts should be implemented to assess their characteristics and frequency. Their impact should also be considered when estimating the global burden of fascioliasis.

The mitochondrial genome and a 60-kb nuclear DNA segment from Naegleria fowleri, the causative agent of primary amoebic meningoencephalitis

Naegleria fowleri is a unicellular eukaryote causing primary amoebic meningoencephalitis, a neuropathic disease killing 99% of those infected, usually within 7-14 days. Naegleria fowleri is found globally in regions including the US and Australia. The genome of the related nonpathogenic species Naegleria gruberi has been sequenced, but the genetic basis for N. fowleri pathogenicity is unclear. To generate such insight, we sequenced and assembled the mitochondrial genome and a 60-kb segment of nuclear genome from N. fowleri. The mitochondrial genome is highly similar to its counterpart in N. gruberi in gene complement and organization, while distinct lack of synteny is observed for the nuclear segments. Even in this short (60-kb) segment, we identified examples of potential factors for pathogenesis, including ten novel N. fowleri-specific genes. We also identified a homolog of cathepsin B; proteases proposed to be involved in the pathogenesis of diverse eukaryotic pathogens, including N. fowleri. Finally, we demonstrate a likely case of horizontal gene transfer between N. fowleri and two unrelated amoebae, one of which causes granulomatous amoebic encephalitis. This initial look into the N. fowleri nuclear genome has revealed several examples of potential pathogenesis factors, improving our understanding of a neglected pathogen of increasing global importance.

Specificity of a coproantigen ELISA test for fasciolosis: lack of cross-reactivity with Paramphistomum cervi and Taenia hydatigena

A commercial coproantigen ELISA test for fasciolosis, based on the use of MM3 monoclonal antibody for antigen capture, was investigated for possible cross-reactivity with Paramphistomum cervi, a trematode that commonly infects cattle and sheep grazing in fluke-infested pasture in Ireland. Histological sections of adult and immature Fasciola hepatica and P cervi were incubated with MM3 monoclonal antibody, and its binding to tissue-localised coproantigen was subsequently visualised by immunocytochemistry. In a related study, the soluble antigenic fractions derived from homogenates of P cervi adults and Taenia hydatigena metacestodes were tested for cross-reactivity with MM3 monoclonal antibody in an antigen-capture ELISA, using known F hepatica-positive and F hepatica-negative ovine faecal samples as natural controls. It was found that, while intense immunocytochemical labelling was located over the gastrodermis and gut contents of adult and immature F hepatica, sections of adult and immature P cervi were unlabelled. In the ELISA tests, the soluble fractions of F hepatica reacted strongly with MM3 monoclonal antibody, but those of P cervi and T hydatigena gave negative results. These findings support the specificity of the coproantigen ELISA test for fasciolosis in areas where paramphistomosis and cysticercosis are liable to occur singly or as coinfections with F hepatica.

Evaluation of the immune responses induced by four targeted DNA vaccines encoding the juvenile liver fluke antigen, cathepsin B in a mouse model

Background

Liver fluke can infect cattle and sheep, and is also emerging as a human pathogen in developing countries. Cathepsin B (Cat B2) is a major cysteine protease secreted by the juvenile flukes. To enhance the immune responses of Cat B2, the cDNA sequence was fused with four different DNA vaccine vectors. The induced cellular and antibody responses were compared in vaccinated mice.

Methods

The following recombinant DNA vaccine constructs were constructed: empty vector VR1012 as negative control, cytoplasmic construct pVR1012 Cat B2, secretory construct pVR1020 Cat B2, chemokine-fused construct pMCP3 Cat B2 and lymph node targeting construct pCTLA-4 Cat B2. Plasmids were constructed using standard procedures, and positive constructs screened and selected using restriction digestion analysis followed by sequence analysis. The constructs were then tested in Cos-7 cells for in vitro expression, which was analysed using immunoblotting. Subsequently, female BALB/c mice were immunised with DNA constructs as vaccines. Elicited antibody responses were measured using ELISA. The ratio between IgG1 and IgG2a antibody responses was estimated among different vaccine groups. IgG antibody avidity assay was performed and the relative avidity index was calculated. The induced cytokine production from splenocytes of vaccinated animals was estimated using ELISPOT.

Results

DNA vaccine constructs carrying Cat B2 were expressed in Cos-7 cell lines and encoded protein was recognised using western blotting using rat anti- cathepsin B antibody. DNA vaccines elicited high Cat B2- specific IgG, IgG1, IgE and also modest IgG2a antibody responses. Cat B2 specific IL-4 T cell responses were also observed in Cat B2 vaccinated mice. The comparison of immunogenic potential in each of these constructs was demonstrated as enhanced antibody responses on the lymph-node targeting vector pCTLA-4 Cat B2, the high antibody avidity of chemo-attractant pMCP3 Cat B2 and stronger T cellular responses of non-secretory DNA vaccine pVR1012 Cat B2 in vaccinated animals.

Conclusion

This study showed that the targeting DNA vaccine strategies enhanced specific immune responses to juvenile fluke Cat B2. The results of our current study have demonstrated that a gene-based vaccine as an immunotherapeutic approach to combat Fasciola infection may be feasible.

Characterization and expression of cathepsin B2 in Fasciola gigantica

Fasciola gigantica cathepsin B belongs to a family of cysteine proteases which is involved in invasion of host tissues. In this study, the recombinant cathepsin B2 (rFgCatB2), synthesized in Pichia pastoris, showed enzymatic activity on a fluorometric substrate Z-Phe-Arg-AMC and gelatin. Furthermore, this recombinant enzyme could degrade IgG and type I collagen. Mouse antiserum against rFgCatB2 reacted with the native FgCatB2 in whole body (WB) extracts of metacercariae (MET), newly excysted juveniles (NEJ) and 2week-old juveniles, but not in 3, 4 week-old juveniles and adult flukes. Immunolocalization showed the presence of cathepsin B2 only in the caecal epithelium of MET, NEJ and 2 week-old juveniles. Co-localization of FgCatB2 and a prominent antigen of NEJ, FgCatB3, revealed that these proteins were expressed at the same regions in the caecal epithelium. Anti-rFgCatB2 showed no cross reaction with the other parasites' antigens by Western blotting. These findings suggest that CatB2 is expressed only in early stages of the parasite and may be involved in digestion of host connective tissues and evasion of the host immune system during their penetration and migration. Thus, CatB2 could be considered as an immunodiagnostic and vaccine candidate for fasciolosis.

Fasciola hepatica saposin-like protein-2-based ELISA for the serodiagnosis of chronic human fascioliasis

An indirect enzyme-linked immunosorbent assay (ELISA) was developed and evaluated for its diagnostic ability to detect human IgG antibodies against Fasciola hepatica saposin-like protein-2. The assay was compared with an indirect ELISA with excretory-secretory products (FhES) from adult F. hepatica. In an analysis of the sera of 37 patients infected with F. hepatica, 40 patients with other parasitic infections, and 50 healthy controls, the sensitivity of both ELISA assays was 100%. However, the FhSAP2-based ELISA was more specific (95.6%) than the FhES-ELISA (91.9%). These results demonstrated that FhSAP2 can be used in the serodiagnosis of chronic human fascioliasis with the additional advantage of being relatively cheap and easy to produce. Studies are in progress to evaluate this FhSAP2-ELISA assay in a large-scale prevalence surveys in endemic areas.

Innate and adaptive resistance of Indonesian Thin Tail sheep to liver fluke: a comparative analysis of Fasciola gigantica and Fasciola hepatica infection

In the current study, three independent trials directly compared Fasciola gigantica and Fasciola hepatica infection of ITT sheep. In all trials, F. hepatica infection resulted in higher worm burden recoveries and greater physiological damage to ITT sheep. Developmental differences of the two Fasciola species were also observed during the first twelve weeks of a primary infection, where the migration and growth of F. hepatica was more rapid than F. gigantica. Various immunological blood parameters were measured and indicated similar kinetics in the humoral and cellular responses during the time course of infection with each Fasciola species. In contrast to F. hepatica infection, we demonstrate an innate and adaptive comparative ability of ITT sheep to resist the early stages of infection with F. gigantica infection. Unraveling the mechanisms leading to this differential resistance may potentially lead to new methods for the control of fasciolosis and other human liver flukes.

Cathepsins B1 and B2 of Trichobilharzia SPP., bird schistosomes causing cercarial dermatitis

Trichobilharzia regenti and T. szidati are schistosomes that infect birds. although T. regenti/T. szidati can only complete their life cycle in specific bird hosts (waterfowl), their larvae-cercariae are able to penetrate, transform and then migrate as schistosomula in nonspecific hosts (e.g., mouse, man). Peptidases are among the key molecules produced by these schistosomes that enable parasite invasion and survival within the host and include cysteine peptidases such as cathepsins B1 and B2. These enzymes are indispensable bio-catalysts in a number of basal biological processes and host-parasite interactions, e.g., tissue invasion/migration, nutrition and immune evasion. Similar biochemical and functional characteristics were observed for cathepsins B1 and B2 in bird schistosomes (T. regenti, T. szidati) and also for their homologs in human schistosomes (Schistosoma mansoni, S. japonicum). Therefore, data obtained in the research of bird schistosomes can also be exploited for the control of human schistosomes such as the search for targets of novel chemotherapeutic drugs and vaccines.

Standardisation of a coproantigen reduction test (CRT) protocol for the diagnosis of resistance to triclabendazole in Fasciola hepatica

A sheep trial was performed to standardise a coproantigen reduction test (CRT) protocol for the diagnosis of resistance to triclabendazole (TCBZ) in Fasciola hepatica). The CRT employs the BIO K201 Fasciola coproantigen ELISA (Bio-X Diagnostics, Jemelle, Belgium) to test for the presence of F. hepatica coproantigens in a faecal sample. If it is coproantigen-positive, the CRT protocol recommends that faecal samples are re-tested for coproantigens at 14 days post-treatment (dpt), with negative testing at this point indicating TCBZ success. Initial work aimed to confirm the sensitivity of the BIO K201 ELISA for Fasciola infection and investigate whether coproantigens represent a robust reduction marker of TCBZ efficacy. Thirty-eight, indoor-reared sheep were artificially infected with F. hepatica isolates known to be susceptible (Cullompton) and resistant (Sligo) to TCBZ action, respectively. Treatment was administered at 12 weeks post-infection (wpi), with 2 sheep groups, infected with each isolate, culled at 2 and 4 weeks post-treatment (wpt), respectively. Necropsy was performed to confirm treatment efficacy. Individual faecal samples were collected twice-weekly throughout the trial period. Additional work focused on the effect of temperature on faecal sample collection and storage. Faecal samples collected from sheep positive for F. hepatica infection were sub-sampled and left at room temperature. Individual sub-samples were tested by ELISA on consecutive days and these readings compared to the original test result on the day of collection. In addition, ELISA values were compared between faecal sub-samples prepared on the day of sampling and post storage at -20°C. Also, an immunocytochemical study was performed to determine the tissue site of origin of the coproantigen protein in the fluke. Results showed that the BIO K201 ELISA was sensitive for Fasciola coproantigens, with coproantigens detectable from 5 wpi onwards. The suitability of coproantigens as a diagnostic marker of TCBZ efficacy was supported by the absence and presence of coproantigens in TCBZ-treated Cullompton (TCBZ-susceptible) and Sligo (TCBZ-resistant) F. hepatica infections at 2 and 4 wpt, respectively. Study results suggest that low to moderate temperature has little, if any, impact on coproantigen stability in faecal samples, but that higher temperatures may have. Immunolabelling for the coproantigen showed that it was specific to the gastrodermal cells of both adult and juvenile flukes.

Blunting the knife: development of vaccines targeting digestive proteases of blood-feeding helminth parasites

Proteases are pivotal to parasitism, mediating biological processes crucial to worm survival including larval migration through tissue, immune evasion/modulation and nutrient acquisition by the adult parasite. In haematophagous parasites, many of these proteolytic enzymes are secreted from the intestine (nematodes) or gastrodermis (trematodes) where they act to degrade host haemoglobin and serum proteins as part of the feeding process. These proteases are exposed to components of the immune system of the host when the worms ingest blood, and therefore present targets for the development of anti-helminth vaccines. The protective effects of current vaccine antigens against nematodes that infect humans (hookworm) and livestock (barber's pole worm) are based on haemoglobin-degrading intestinal proteases and act largely as a result of the neutralisation of these proteases by antibodies that are ingested with the blood-meal. In this review, we survey the current status of helminth proteases that show promise as vaccines and describe their vital contribution to a parasitic existence.

Cathepsin B proteases of flukes: the key to facilitating parasite control?

Cysteine proteases are important virulence factors for parasites. This review will focus on the cathepsin B proteases of trematodes (also known as flukes) which are abundant in juvenile and immature flukes. Recent research, primarily in Fasciola, using inhibitors, RNA interference (RNAi) and vaccination studies indicates that cathepsin Bs play a key role in the biology of trematodes. As these proteases are largely expressed by infective parasite stages, their inactivation by chemotherapy or vaccination will greatly reduce the damage wrought by flukes as they invade host tissues. This validates cathepsin Bs as key strategic targets for fluke control.

Comparative analysis of two fatty acid binding proteins fromFasciola gigantica

Fatty acid binding proteins are considered to be promising vaccine candidates against trematodiasis. In order to provide additional information about their function inFasciola giganticawe performed a comparative analysis of FgFABP1 and FgFABP3, two isoforms with quite different isoelectric points of 4·9 and 9·9 and 67% sequence identity. Both are expressed in the juvenile and adult parasite but differ in their tissue-specific distribution. In addition, the sequence of FABP3 is identical inF. hepaticaandF. giganticaindicating the protein's functional importance in this genus. Immune sera produced against soluble recombinant FgFABPs reacted with 14 kDa antigens in crude worm, soluble egg, cirrus sac extracts, and excretion/secretion product. Both FgFABPs were located in the parenchyma of the parasite but in addition, FgFABP1 was abundant in testes and spermatozoa while FgFABP3 was abundant in vitelline cells, eggs, and caecal epithelium. Mass spectrometry identified FgFABP1 and FgFABP3 in the ES product whereas only FgFABP3 was identified in egg extract. Serum samples of an experimentally infected rabbit reacted from week 6 post-infection with FgFABP3 and from week 12 with FgFABP1 while sera of infected sheep were not reactive. The results suggest differences in the biological functions of these 2 isoforms and differences in the host/parasite interaction that should be considered for their potential as vaccines against fascioliasis.

In situ immunolocalization and stage-dependent expression of a secretory serine protease in Leishmania donovani and its role as a vaccine candidate

Proteases have been found to play essential roles in many biological processes, including the pathogenesis of leishmaniasis. Most parasites rely on their intracellular and extracellular protease repertoire to invade and multiply in mammalian host cells. However, few studies have addressed serine proteases in Leishmania and their role in host pathogenesis. Here we report the intracellular distribution of a novel L. donovani secretory serine protease in the flagellar pocket, as determined by immunogold labeling. Flow cytometry and confocal immunofluorescence analysis revealed that the expression of the protease diminishes sequentially from virulent to attenuated strains of this species and is also highly associated with the metacyclic stage of L. donovani promastigotes. The level of internalization of parasites treated with the anti-115-kDa antibody into host macrophages was significantly reduced from that of non-antibody-treated parasites, suggesting that this serine protease probably plays a role in the infection process. In vivo studies confirmed that this serine protease is a potential vaccine candidate. Altogether, the 115-kDa serine protease might play vital roles in L. donovani pathogenesis and hence could be recognized as a potential candidate for drug design.

Quantitation of cytokine mRNA by real-time RT-PCR during a vaccination trial in a rabbit model of fascioliasis

Use of the rabbit as disease model has long been hampered by a lack of immunological assays specific to this species. In the present study we developed a SYBR Green-based, real-time RT-PCR protocol to quantitate cytokine mRNA in freshly harvested rabbit peripheral mononuclear cells. The method was validated in the course of a vaccination trial in which animals vaccinated with the recombinant antigen FhSAP2 were challenged with Fasciola hepatica metacercariae. Changes in the levels of rabbit interleukin (IL)-2, IL-4, IL-6, IL-10, tumor necrosis factor-alpha (TNFalpha), and interferon-gamma (IFNgamma) mRNA were determined. Messenger RNA from the universally expressed housekeeping gene GAPDH was used as an amplification control and allowed for correction of variations in the efficiencies of RNA extraction and reverse transcription. Rabbits vaccinated with FhSAP2 showed an 83.3% reduction in liver fluke burden after challenge infection when compared to non-vaccinated controls. All cytokine mRNAs were found at detectable levels; however, the levels of IFNgamma, TNFalpha, IL-2 and IL-10 were significantly higher in the vaccinated group compared to the non-vaccinated group. These results suggest that protection conferred by FhSAP2 protein could be associated with a mixed Th1/Th2 immune response in which Th1 cytokines are dominant. The real-time RT-PCR method described herein can be a useful tool for monitoring changes in basic immune functions in the rabbit model of fascioliasis and may also aid in studies of human diseases for which the rabbit is an important experimental model.

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.

A major cathepsin B protease from the liver fluke Fasciola hepatica has atypical active site features and a potential role in the digestive tract of newly excysted juvenile parasites

The newly excysted juvenile (NEJ) stage of the Fasciola hepatica lifecycle occurs just prior to invasion into the wall of the gut of the host, rendering it an important target for drug development. The cathepsin B enzymes from NEJ flukes have recently been demonstrated to be crucial to invasion and migration by the parasite. Here we characterize one of the cathepsin B enzymes (recombinant FhcatB1) from NEJ flukes. FhcatB1 has biochemical properties distinct from mammalian cathepsin B enzymes, with an atypical preference for Ile over Leu or Arg residues at the P(2) substrate position and an inability to act as an exopeptidase. FhcatB1 was active across a broad pH range (optimal activity at pH 5.5-7.0) and resistant to inhibition by cystatin family inhibitors from sheep and humans, suggesting that this enzyme would be able to function in extracellular environments in its mammalian hosts. It appears, however, that the FhcatB1 protease functions largely as a digestive enzyme in the gut of the parasite, due to the localization of a specific, fluorescently labeled inhibitor with an Ile at the P(2) position. Molecular modelling and dynamics were used to predict the basis for the unusual substrate specificity: a P(2) Ile residue positions the substrate optimally for interaction with catalytic residues of the enzyme, and the enzyme lacks an occluding loop His residue crucial for exopeptidase activity. The unique features of the enzyme, particularly with regard to its specificity and likely importance to a vital stage of the parasite's life cycle, make it an excellent target for therapeutic inhibitors or vaccination.

An integrated transcriptomics and proteomics analysis of the secretome of the helminth pathogen Fasciola hepatica: proteins associated with invasion and infection of the mammalian host

To infect their mammalian hosts, Fasciola hepatica larvae must penetrate and traverse the intestinal wall of the duodenum, move through the peritoneum, and penetrate the liver. After migrating through and feeding on the liver, causing extensive tissue damage, the parasites move to their final niche in the bile ducts where they mature and produce eggs. Here we integrated a transcriptomics and proteomics approach to profile Fasciola secretory proteins that are involved in host-pathogen interactions and to correlate changes in their expression with the migration of the parasite. Prediction of F. hepatica secretory proteins from 14,031 expressed sequence tags (ESTs) available from the Wellcome Trust Sanger Centre using the semiautomated EST2Secretome pipeline showed that the major components of adult parasite secretions are proteolytic enzymes including cathepsin L, cathepsin B, and asparaginyl endopeptidase cysteine proteases as well as novel trypsin-like serine proteases and carboxypeptidases. Proteomics analysis of proteins secreted by infective larvae, immature flukes, and adult F. hepatica showed that these proteases are developmentally regulated and correlate with the passage of the parasite through host tissues and its encounters with different host macromolecules. Proteases such as FhCL3 and cathepsin B have specific functions in larvae activation and intestinal wall penetration, whereas FhCL1, FhCL2, and FhCL5 are required for liver penetration and tissue and blood feeding. Besides proteases, the parasites secrete an array of antioxidants that are also highly regulated according to their migration through host tissues. However, whereas the proteases of F. hepatica are secreted into the parasite gut via a classical endoplasmic reticulum/Golgi pathway, we speculate that the antioxidants, which all lack a signal sequence, are released via a non-classical trans-tegumental pathway.

Type I cystatin (stefin) is a major component of Fasciola gigantica excretion/secretion product

In the present study we describe type 1 cystatin, a cysteine protease inhibitor, as a major released antigen of the tropical liver fluke Fasciola gigantica (FgStefin-1). Immunohistochemical analysis showed that FgStefin-1 is abundant in (a) tissue of tegumental type, including oral and ventral sucker, pharynx, genital atrium, metraterm, cirrus and (b) the intestinal epithelium. Faint staining was observed in the epithelia of ovary and proximal uterus. Immunoblots showed the presence of FgStefin-1 in the parasite's excretion/secretion (ES) product and immunodepletion demonstrated that FgStefin-1 herein is partially complexed with cathepsin L. Furthermore, quantitation of FgStefin-1 in comparison to cathepsin L in ES product and crude worm extract of adults supports a major external function of FgStefin-1 with an estimated 50% being released in at least equimolar amounts to cathepsin L. Sera of an experimentally infected rabbit reacted with recombinant FgStefin-1 starting 8 weeks postinfection. Activity analyses of recombinant FgStefin-1 showed nanomolar inhibition constants for mammalian cathepsin B, L, and S cysteine proteases and released cysteine proteases of the parasite. The protein is active over a wide pH range and is heat stable. Our results suggest protective functions of FgStefin-1, regulating intracellular cysteine protease activity, and possibly protection against extracellular proteolytic damage to the parasite's intestinal and tegumental surface proteins. Considering inhibition kinetics and previously demonstrated immunomodulatory properties of cystatin in parasitic nematodes a comparable function of FgStefin-1 is suggested and is at present under investigation.

Plasmodium chabaudi: expression of active recombinant chabaupain-1 and localization studies in Anopheles sp

Plasmodium cysteine proteases have been shown to be immunogenic and are being used as malaria potential serodiagnostic markers and vaccine targets. Genes encoding two Plasmodium chabaudi cysteine proteases chabaupain-1 (CP-1) and chabaupain-2 (CP-2) were identified and further expressed in Escherichia coli. Solubilisation of recombinant CP-1 and CP-2 was achieved by decreasing the temperature of induction. Anopheles gambiae tissues infected with Plasmodium were analyzed by Western blotting using the anti-CP-1 antibody showing that CP-1 is only present in the A. gambiae midguts being absent from other infected mosquito biological material. Anti-CP-1 anti-serum recognized a 30 kDa band in P. chabaudi, Plasmodium berghei and Plasmodium yoelii lysates but does not recognize the recombinant CP-2 extracts suggesting high antibody specificity.

Vaccination against fasciolosis by a multivalent vaccine of stage-specific antigens

Liver flukes produce cathepsin B and cathepsin L in their excretory-secretory material. These proteases are proposed to be key virulence factors for parasite infection, and are therefore targets for vaccination. Cathepsin B is predominately released in the juvenile stage of the life cycle, while different cathepsin L's are released throughout the cycle. Three proteases (cathepsin L5, cathepsin L1g and cathepsin B) were expressed in yeast from cDNA clones isolated from adult, metacercariae and newly excysted juvenile flukes respectively. Each was used singly or in combination to vaccinate rats that were subsequently challenged with Fasciola hepatica metercercariae. Each protein induced an immune response, and all groups vaccinated with recombinant protein yielded significantly fewer and smaller flukes than the control group. Maximal protection of 83% was seen in the group vaccinated with cathepsin B and cathepsin L5 in combination.