Vaccination with DNA encoding cysteine proteinase confers protective immune response to rats infected with Clonorchis sinensis

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.

Clonorchiasis and opisthorchiasis: epidemiology, transmission, clinical features, morbidity, diagnosis, treatment, and control

Clonorchis sinensis, Opisthorchis viverrini, and Opisthorchis felineus are important liver flukes that cause a considerable public health burden in eastern Asia, southeastern Asia, and eastern Europe, respectively. The life cycles are complex, involving humans, animal reservoirs, and two kinds of intermediate hosts. An interplay of biological, cultural, ecological, economic, and social factors drives transmission. Chronic infections are associated with liver and biliary complications, most importantly cholangiocarcinoma. With regard to diagnosis, stool microscopy is widely used in epidemiologic surveys and for individual diagnosis. Immunologic techniques are employed for screening purposes, and molecular techniques facilitate species differentiation in reference laboratories. The mainstay of control is preventive chemotherapy with praziquantel, usually combined with behavioral change through information, education and communication, and environmental control. Tribendimidine, a drug registered in the People's Republic of China for soil-transmitted helminth infections, shows potential against both C. sinensis and O. viverrini and, hence, warrants further clinical development. Novel control approaches include fish vaccine and biological control. Considerable advances have been made using multi-omics which may trigger the development of new interventions. Pressing research needs include mapping the current distribution, disentangling the transmission, accurately estimating the disease burden, and developing new diagnostic and treatment tools, which would aid to optimize control and elimination measures.

Liver Flukes: Clonorchis and Opisthorchis

Clonorchis sinensis, Opisthorchis viverrini and O. felineus are liver flukes of human and animal pathogens occurring across much of Europe and Asia. Nevertheless, they are often underestimated compared to other, better known neglected diseases in spite of the fact that many millions of people are infected and hundreds of millions are at risk. This is possibly because of the chronic nature of the infection and disease and that it takes several decades prior to a life-threatening pathology to develop. Several studies in the past decade have provided more information on the molecular biology of the liver flukes which clearly lead to better understanding of parasite biology, systematics and population genetics. Clonorchiasis and opisthorchiasis are characterized by a chronic infection that induces hepatobiliary inflammation, especially periductal fibrosis, which can be detected by ultrasonography. These chronic inflammations eventually lead to cholangiocarcinoma (CCA), a usually fatal bile duct cancer that develops in some infected individuals. In Thailand alone, opisthorchiasis-associated CCA kills up to 20,000 people every year and is therefore of substantial public health importance. Its socioeconomic impacts on impoverished families and communities are considerable. To reduce hepatobiliary morbidity and CCA, the primary intervention measures focus on control and elimination of the liver fluke. Accurate diagnosis of liver fluke infections in both human and other mammalian, snail and fish intermediate hosts is important for achieving these goals. While the short-term goal of liver fluke control can be achieved by praziquantel chemotherapy, a comprehensive health education package targeting school children is believed to be more beneficial for a long-term goal/solution. It is recommended that transdisciplinary research or multisectoral control approach including one health and/or eco health intervention strategy should be applied to combat the liver flukes and hence contribute to reduction of CCA in endemic areas.

Molecular Mechanisms of Clonorchis sinensis-Host Interactions and Implications for Vaccine Development

Infections caused by Clonorchis sinensis remain a significant public health challenge for both humans and animals, causing pyogenic cholangitis, cholelithiasis, cholecystitis, biliary fibrosis, and even cholangiocarcinoma. However, the strategies used by the parasite and the immunological mechanisms used by the host have not yet been fully understood. With the advances in technologies and the accumulated knowledge of host-parasite interactions, many vaccine candidates against liver flukes have been investigated using different strategies. In this review, we explore and analyze in-depth the immunological mechanisms involved in the pathogenicity of C. sinensis. We highlight the different mechanisms by which the parasite interacts with its host to induce immune responses. All together, these data will allow us to have a better understanding of molecular mechansism of host-parasite interactions, which may shed lights on the development of an effective vaccine against C. sinensis.

Prospects for liver fluke vaccines

Fasciola spp., Opisthorchis spp. and Clonorchis sinensis are common liver flukes that can cause a variety of diseases, mainly cholangiocarcinoma induced by clonorchiasis and liver damage and associated pathology induced by fascioliasis. Because these trematodes are parasites of humans and domestic animals, they have greatly affected the economy of agricultural industries and public health worldwide. Due to the emergence of drug resistance and the living habits of flukes, among other reasons, a possibility of reinfection remains even when antiparasitic drugs are used. Therefore, developing a safe, efficient and cost-effective vaccine against trematodes is an important goal. Here, we briefly describe the progress in the development of vaccines against liver flukes. Related innovations may provide effective protection against these helminths and the diseases that they cause.

Clonorchis sinensis secretory protein CsAg17 vaccine induces immune protection

Background

Clonorchiasis is endemic in East and Southeast Asian countries. For a preventive strategy against infectious diseases, vaccination is the most effective. Here, we evaluated the molecular characteristics and immune responses of CsAg17 protein from Clonorchis sinensis, and investigated its protective effects against C. sinensis challenge.

Methods

A cDNA clone encoding CsAg17 protein and containing a secretory signal peptide at the N-terminus was retrieved from the C. sinensis transcriptome bank. Recombinant CsAg17 B-cell epitope protein and cDNA vaccines were produced and their immune responses were evaluated in FVB mice. The proportional changes of CD3⁺/CD4⁺ and CD3⁺/CD8⁺ T cells were detected by flow cytometry, and immune effectors were measured by ELISA.

Results

The CsAg17 mRNA was transcribed at a higher level in C. sinensis adults than in metacercariae. The CsAg17 protein was distributed in the sperms, oral and ventral suckers, and mesenchymal tissues of C. sinensis adults. In mice challenged with C. sinensis metacercariae, vaccination with CsAg17 protein and cDNA resulted in a reduction to 64% and 69% in worm burden, respectively. Both CsAg17 protein and cDNA vaccines increased the proportion of CD3⁺/CD4⁺ and CD3⁺/CD8⁺ T cells and stimulated the production of Th1 type cytokines such as interleukin (IL)-2, IL-12, and interferon-γ, while maintaining minimum levels of Th2 cytokines. The levels of IgG specific to CsAg17 protein steeply increased in the two vaccinated groups from 2 weeks after immunization. The liver tissue retained good morphology in the mice vaccinated with CsAg17 protein or cDNA, whereas severe inflammation and large serous cysts were observed in the liver of the unvaccinated mice.

Conclusions

Vaccination with CsAg17 protein and cDNA reduced the pathological changes in the bile duct and liver, and ameliorated the worm burden via cellular and humoral immune responses. Thus, they may serve as good vaccine candidates against C. sinensis infections.

Liver Flukes: Clonorchis and Opisthorchis

Clonorchis sinensis, Opisthorchis viverrini, and O. felineus are liver flukes of human and animal pathogens occurring across much of Europe and Asia. Nevertheless, they are often underestimated compared to other, better known neglected diseases in spite of the fact that many millions of people are infected and hundreds of millions are at risk. This is possibly because of the chronic nature of the infection and disease and that it takes several decades prior to a life-threatening pathology to develop. Several studies in the past decade have provided more information on the molecular biology of the liver flukes which clearly lead to better understanding of parasite biology, systematics, and population genetics. Clonorchiasis and opisthorchiasis are characterized by a chronic infection that induces hepatobiliary inflammation, especially periductal fibrosis, which can be detected by ultrasonography. These chronic inflammations eventually lead to cholangiocarcinoma (CCA), a usually fatal bile duct cancer that develops in some infected individuals. In Thailand alone, opisthorchiasis-associated CCA kills up to 20,000 people every year and is therefore of substantial public health importance. Its socioeconomic impacts on impoverished families and communities are considerable. To reduce hepatobiliary morbidity and CCA, the primary intervention measures focus on control and elimination of the liver fluke. Accurate diagnosis of liver fluke infections in both human and other mammalian, snail and fish intermediate hosts, are important for achieving these goals. While the short-term goal of liver fluke control can be achieved by praziquantel chemotherapy, a comprehensive health education package targeting school children is believed to be more beneficial for a long-term goal/solution. It is recommended that a transdisciplinary research or multisectoral control approach including one health and/or eco health intervention strategy should be applied to combat the liver flukes, and hence contribute to reduction of cholangiocarcinoma in endemic areas.

A 21.6 kDa tegumental protein of Clonorchis sinensis induces a Th1/Th2 mixed immune response in mice

Introduction

Clonorchis sinensis is a major parasite affecting the Korea population. Despite the high infection rate and pathogenicity, very few studies have been conducted to investigate the immune responses against the proteins of C. sinensis.

Methods

In this study, in vitro immune response induced by a recombinant 21.6 kDa tegumental protein derived from C. sinensis (rCsTegu21.6) was confirmed in murine dendritic cells and T cells. For the in vivo analysis, each mouse was immunized three times. Total serum IgG and T cell cytokine production were determined by ELISA, while T cell proliferation was detected by a WST (Water‐Soluble Tetrazolium salt)‐1 assay.

Results

In vitro tests indicated that rCsTegu21.6 treatment increased the expression of surface molecules, such as CD40 (77%), CD80 (52%) and CD86 (46%), on murine dendritic cells and the secretion of cytokines (TNF‐α, IL‐6, IL‐1β, IL‐10, and IL‐12p70). Moreover, co‐culturing dendritic cells activated by rCsTegu21.6 with allogenic T cells induced T cell proliferation over time. rCsTegu21.6 also stimulated specific antibody production and cytokine secretion [IL‐2, IL‐4, and interferon (IFN)‐γ)] from T cells following immunization in vivo. Notably, rCsTegu21.6 predominantly induced IgG1 production and secretion of the Th2 cytokine IL‐4, regardless of the type of adjuvant used.

Conclusion

These results serve as a foundation for the development of tegumental protein‐based vaccines against C. sinensis.

Comparative analysis of immune effects in mice model: Clonorchis sinensis cysteine protease generated from recombinant Escherichia coli and Bacillus subtilis spores

Clonorchiasis remains a nonnegligible public health problem in endemic areas. Cysteine protease of Clonorchis sinensis (CsCP) plays indispensable roles in the parasitic physiology and pathology, and has been exploited as a promising drug and vaccine candidate. In recent years, development of spore-based vaccines against multiple pathogens has attracted many investigators' interest. In previous studies, the recombinant Escherichia coli (BL21) and Bacillus subtilis spores expressing CsCP have been successfully constructed, respectively. In this study, the immune effects of CsCP protein purified from recombinant BL21 (rCsCP) and B. subtilis spores presenting CsCP (B.s-CsCP) in Balb/c mice model were conducted with comparative analysis. Levels of specific IgG, IgG1 and IgG2a were significantly increased in sera from both rCsCP and B.s-CsCP intraperitoneally immunized mice. Additionally, recombinant spores expressing abundant fusion CsCP (0.03125 pg/spore) could strongly enhance the immunogenicity of CsCP with significantly higher levels of IgG and isotypes. Compared with rCsCP alone, intraperitoneal administration of mice with spores expressing CsCP achieved a better effect of fighting against C. sinensis infection by slowing down the process of fibrosis. Our results demonstrated that a combination of Th1/Th2 immune responses could be elicited by rCsCP, while spores displaying CsCP prominently induced Th1-biased specific immune responses, and the complex cytokine network maybe mediates protective immune responses against C. sinensis. This work further confirmed that the usage of B. subtilis spores displaying CsCP is an effective way to against C. sinensis.

Clonorchiasis

On Aug 21, 1875, James McConnell published in The Lancet his findings from a post-mortem examination of a 20-year-old Chinese man--undertaken at the Medical College Hospital in Calcutta, India--in whom he found Clonorchis sinensis in the bile ducts. Now, exactly 140 years later, we have a sound understanding of the lifecycle of this liver fluke, including key clinical, diagnostic, and epidemiological features. Developments in the so-called -omics sciences have not only advanced our knowledge of the biology and pathology of the parasite, but also led to the discovery of new diagnostic, drug, and vaccine targets. C sinensis infection is primarily related to liver and biliary disorders, especially cholangiocarcinoma. Clonorchiasis mainly occurs in east Asia, as a result of the region's social-ecological systems and deeply rooted cultural habit of consuming raw freshwater fish. The Kato-Katz technique, applied on fresh stool samples, is the most widely used diagnostic approach. Praziquantel is the treatment of choice and has been considered for preventive chemotherapy. Tribendimidine showed good safety and therapeutic profiles in phase 2 trials and warrants further investigation. Still today, the precise distribution, the exact number of infected people, subtle morbidities and pathogenesis, and the global burden of clonorchiasis are unknown. Integrated control strategies, consisting of preventive chemotherapy; information, education, and communication; environmental management; and capacity building through intersectoral collaboration should be advocated.

Molecular characterization of a cathepsin F-like protease in Trichinella spiralis

Background

Trichinellosis is a re-emerging infectious disease, caused by Trichinella spp. Cathepsin F belongs to cysteine protease that is a major virulence factor for parasitic helminths, and it may be a potential anti-helminth drug target and vaccine candidate. The aim of this study was to clone, express and identify a cathepsin F-like protease in Trichinella spiralis and to investigate its biochemical characteristics.

Methods

The full-length cDNA encoding a putative cathepsin F-like protease in T. spiralis, TsCF1, was cloned and its biochemical characterization and expression profile were analyzed. Transcription of TsCF1 at different developmental stages of T. spiralis was observed by RT-PCR. The recombinant TsCF1 protein was expressed by prokaryotic expression system and recombinant TsCF1 (rTsCF1) was analyzed by western blotting. And expression of TsCF1 at muscle larvae stage was performed by immunofluorescent technique. Molecular modeling of TsCF1 and its binding mode with E-64 and K11777 were analyzed. Enzyme activity and inhibitory test with E-64 as inhibitor were investigated by using Z-Phe-Arg-AMC as specific substrate.

Results

Sequence analysis revealed that TsCF1 ORF encodes a protein of 366 aa with a theoretical molecular weight of 41.9 kDa and an isoelectric point of 7.46. The cysteine protease conserved active site of Cys173, His309 and Asn333 were identified and cathepsin F specific motif ERFNAQ like KLFNAQ sequence was revealed in the propeptide of TsCF1. Sequence alignment analysis revealed a higher than 40 % identity with other cathepsin F from parasitic helminth and phylogenetic analysis indicated TsCF1 located at the junction of nematode and trematode. RT-PCR revealed the gene was expressed in muscle larvae, newborn larvae and adult stages. SDS-PAGE revealed the recombinant protein was expressed with the molecular weight of 45 kDa. The purified rTsCF1 was used to immunize rabbit and the immune serum could recognize a band of about 46 kDa in soluble protein of adult, muscle larvae and ES product of muscle larvae. Immunolocalization analysis showed that TsCF1 located on the cuticle and stichosome of the muscle larvae. After renaturation rTsCF1 demonstrated substantial enzyme activity to Z-Phe-Arg-AMC substrate with the optimal pH 5.5 and this activity could be inhibited by cysteine protease inhibitor E-64. Further analysis showed the kinetic parameters of rTsCF1 to be Km = 0.5091 μM and Vmax = 6.12 RFU/s μM at pH 5.5, and the IC₅₀ value of E64 was 135.50 ± 16.90 nM.

Conclusion

TsCF1 was expressed in all stages of T. spiralis and localized in the cuticle and stichosome. TsCF1 might play a role in the life cycle of T. spiralis and could be used as a potential vaccine candidate and drug target against T. spiralis infection.

Antiparasitic DNA vaccines in 21st century

Demands for effective vaccines to control parasitic diseases of humans and livestock have been recently exacerbated by the development of resistance of most pathogenic parasites to anti-parasitic drugs. Novel genomic and proteomic technologies have provided opportunities for the discovery and improvement of DNA vaccines which are relatively easy as well as cheap to fabricate and stable at room temperatures. However, their main limitation is rather poor immunogenicity, which makes it necessary to couple the antigens with adjuvant molecules. This paper review recent advances in the development of DNA vaccines to some pathogenic protozoa and helminths. Numerous studies were conducted over the past 14 years of 21st century, employing various administration techniques, adjuvants and new immunogenic antigens to increase efficacy of DNA vaccines. Unfortunately, the results have not been rewarding. Further research is necessary using more extensive combinations of antigens; alternate delivery systems and more efficient adjuvants based on knowledge of the immunomodulatory capacities of parasitic protozoa and helminths.

Detection of Clonorchis sinensis circulating antigen in sera from Chinese patients by immunomagnetic bead ELISA based on IgY

BACKGROUND

Clonorchiasis, caused by Clonorchis sinensis, is widely distributed in Southeast Asia including China. Clonorchiasis is included in control programs of neglected tropical diseases by World Health Organization (WHO) because it is one of the major health problems in most endemic areas. Diagnosis of clonorchiasis plays a key role in the control programs. However, so far, there is no satisfactory method for clonorchiasis because of low sensitivity, poor practicality and high false positivity of available diagnostic tools.

METHODOLOGY/PRINCIPAL FINDINGS

We developed an immunomagnetic bead enzyme-linked immunosorbent assay (ELISA) based on IgY (egg yolk immunoglobulin) against cysteine proteinase of C. sinensis for detection of circulating antigen in serum samples of patients infected with C. sinensis. The polyclonal IgY, coated with magnetic beads, was used as a capture antibody and a monoclonal IgG labeled with horseradish peroxidase as a detection antibody in the IgY-based immunomagnetic bead ELISA system (IgY-IMB-ELISA). The results showed that the sensitivity of IgY-IMB-ELISA was 93.3% (14 of 15) in cases of heavy infection (5000 to 9999 eggs per gram feces, i.e, EPG 5000-9999), 86.7% (13 of 15) in cases of moderate infection (EPG 1000-4999) and 75.0% (9 of 12) in cases of light infection (EPG <1000) of clonorchiasis. Together 36 of total 42 (85.7%) serum samples of human clonorchiasis gave a positive reaction. There was a significant correlation between ELISA optical density and egg counts (EPG) with a correlation coefficient of 0.83 in total 42 patients. There were no positive results in patients with trichinosis (n = 10) or cysticercosis (n = 10). Cross-reactivity was 6.7% (2 of 30) with schistosomiasis japonica and 10.0% (3 of 30) with paragonimiasis, respectively. No positive reaction was found in 20 healthy persons.

CONCLUSIONS

Our findings suggest that IgY-IMB-ELISA appears to be a sensitive and specific assay for detection of circulating antigen in human clonorchiasis.

Characterization of the secreted cathepsin B cysteine proteases family of the carcinogenic liver fluke Clonorchis sinensis

Clonorchis sinensis excretory/secretory products (ESP) have gained high attentions because of their potential to be vaccine candidates and drug targets in C. sinensis prevention. In this study, we extensively profiled the characteristics of four C. sinensis cathepsin B cysteine proteases (CsCB1, CsCB2, CsCB3, and CsCB4). Bioinformatics analysis showed all CsCBs contained signal peptides at the N-terminal. Functional domains and residues were found in CsCB sequences. We expressed four CsCBs and profiled immune responses followed by vaccine trials. Recombinant CsCBs could induce high IgG titers, indicating high immunogenicity of CsCB family. Additionally, ELISA results showed that both IgG1 and IgG2a levels apparently increased post-immunization with all four CsCBs, showing that combined Th1/Th2 immune responses were triggered by CsCB family. Both Real-time polymerase chain reaction (RT-PCR) and Western blotting confirmed that four CsCBs have distinct expression patterns in C. sinensis life stages. More importantly, we validated our hypothesis that CsCBs were C. sinensis excretory/secretory products. CsCBs could be recognized by C. sinensis-infected sera throughout the infection period, indicating that secreted CsCBs are immune triggers during C. sinensis infection. The protective effect was assessed by comparing the worm burden and egg per gram (EPG) between CsCB group and control group, showing that worm burden (P < 0.01) and EPG (P < 0.01) in CsCB2 and CsCB3 groups were significantly lower than in control group. In conclusion, we profiled secreted cathepsin B cysteine proteases family for the first time and demonstrated that all CsCB family were C. sinensis excretory/secretory products that may regulate host immune responses.

The biochemical and immunological characterization of two serpins from Clonorchis sinensis

Serpins (serine proteinase inhibitors) are evidenced to regulate numerous biological processes such as immunoregulation in parasitic helminths. The functions of serpins from Clonorchis sinensis remain unclear to date. In this study, two serpin genes, respectively denominated as CsproSERPIN and CsSERPIN2, had been selected from metacercaria cDNA library of C. sinensis. The biochemical activities of both recombinant proteins (rCsproSERPIN and rCsSERPIN2) were analyzed by assays of inhibition on some serine or cysteine proteases, the results showed that rCsproSERPIN significantly inhibited trypsin, chymotrypsin and thrombin, while rCsSERPIN2 inhibited only chymotrypsin. Moreover, cytokine and antibody measurements indicated that rats subcutaneously immunized with rCsproSERPIN and rCsSERPIN2 respectively developed a strong IFN-γ production and IgG2a levers of sera were higher than IgG1. Besides, immunoblot assays revealed that the rCsproSERPIN and rCsSERPIN2 could be recognized by the sera of rats infected with C. sinensis and the sera of rabbits immunized by excretory/secretory products. Furthermore, immunofluorescence assays illuminated the two were similarly localized in the reproductive organs such as vitelline glands, testis and eggs in adult stage. In short, all the results collectively indicated that CsproSERPIN and CsSERPIN2 might play important role in the parasite development by preventing the parasite from digestion by exogenous serine proteases, as well as CsproSERPIN and CsSERPIN2 probably involved in immunoregulation of host by inducing Th1-biased type cytokines in rats.

The tumorigenic liver fluke Opisthorchis viverrini--multiple pathways to cancer

Liver fluke infection caused by Opisthorchis viverrini is a major public health problem in Thailand and adjacent countries. In addition to infection-associated morbidity, infection with O. viverrini and the related Clonorchis sinensis are unarguable risk factors for cholangiocarcinoma (CAA, bile-duct cancer). Here we review the pathogenesis of opisthorchiasis and the association between O. viverrini infection and bile-duct cancer, focusing on the molecular parallels between wound healing, chronic inflammation, and cancer development. We review a schema for human disease progression from fluke infection, chronic opisthorchiasis, advanced periductal fibrosis, and cholangiocarcinogenesis, and present a rationale for biomarker discovery to facilitate early intervention. We conclude by addressing post-genomic advances with a view to developing new control strategies to combat this infectious cancer.

Identification and characterization of paramyosin from cyst wall of metacercariae implicated protective efficacy against Clonorchis sinensis infection

Human clonorchiasis has been increasingly prevalent in recent years and results in a threat to the public health in epidemic regions, motivating current strategies of vaccines to combat Clonorchis sinensis (C. sinensis). In this study, we identified C. sinensis paramyosin (CsPmy) from the cyst wall proteins of metacercariae by proteomic approaches and characterized the expressed recombinant pET-26b-CsPmy protein (101 kDa). Bioinformatics analysis indicated that full-length sequences of paramyosin are conserved in helminthes and numerous B-cell/T-cell epitopes were predicted in amino acid sequence of CsPmy. Western blot analysis showed that CsPmy was expressed at four life stages of C. sinensis, both cyst wall proteins and soluble tegumental components could be probed by anti-CsPmy serum. Moreover, immunolocalization results revealed that CsPmy was specifically localized at cyst wall and excretory bladder of metacercaria, as well as the tegument, oral sucker and vitellarium of adult worm. Both immunoblot and immunolocalization results demonstrated that CsPmy was highly expressed at the stage of adult worm, metacercariae and cercaria, which could be supported by real-time PCR analysis. Both recombinant protein and nucleic acid of CsPmy showed strong immunogenicity in rats and induced combined Th1/Th2 immune responses, which were reflected by continuous high level of antibody titers and increased level of IgG1/IgG2a subtypes in serum. In vaccine trials, comparing with control groups, both CsPmy protein and DNA vaccine exhibited protective effect with significant worm reduction rate of 54.3% (p<0.05) and 36.1% (p<0.05), respectively. In consistence with immune responses in sera, elevated level of cytokines IFN-γ and IL-4 in splenocytes suggested that CsPmy could induce combined cellular immunity and humoral immunity in host. Taken together, CsPmy could be a promising vaccine candidate in the prevention of C. sinensis regarding its high immunogenicity and surface localization.

41.5-kDa Cathepsin L protease from Clonorchis sinensis: expression, characterization, and serological reactivity of one excretory-secretory antigen

Cysteine proteases (CPs) were associated with the pathogenicity and excystment of Clonorchis sinensis. Most of them were potential antigens for the immunodiagnosis of clonorchiasis. More researches on CPs will let us know more about their functions, and further employ them for the development of more efficient diagnostic reagent and prevention strategies. In the current study, a full-length sequence encoding cathepsin L from C. sinensis (CsCL41.5) was identified from our adult cDNA library. Bioinformatic analysis showed that CsCL41.5 included typical motifs of cathepsin L (ERFNIN and GNFD motifs) and conserved amino acid positions which constituted the active center of the enzyme. The identity of its amino acid sequence with the cathepsin L of Schistosoma japonicum was 49.6 %. Recombinant CsCL41.5 (rCsCL41.5) was highly expressed in the form of inclusion body in Escherichia coli, and soluble rCsCL41.5 was obtained after purification and renaturation. Western blotting analysis indicated that CsCL41.5 is an excretory-secretory antigen of C. sinensis adult. Immunolocalization demonstrated that CsCL41.5 is distributed in the intestine and eggs in the uterus of adult worm, tegument of metacercaria, oral suck, and tail of cercaria. ELISA assays showed that IgG4 was the predominant IgG isotype responding to rCsCL41.5 in sera from clonorchiasis patients. The sensitivity and specificity of specific IgG4 detection with rCsCL41.5 was 62.5 % (15/24) and 81.7 % (49/60), respectively. It was concluded that there were differences in biological function, efficiency of serodiagnosis, and characterization of immune reactivity between CsCL41.5 and other CPs of C. sinensis, combining with previous studies.

Molecular characterization of cathepsin B from Clonorchis sinensis excretory/secretory products and assessment of its potential for serodiagnosis of clonorchiasis

Background

Cathepsin cysteine proteases play multiple roles in the life cycle of parasites such as food uptake, immune invasion and pathogenesis, making them valuable targets for diagnostic assays, vaccines and drugs. The purpose of this study was to identify a cathepsin B of Clonorchis sinensis (CsCB) and to investigate its diagnostic value for human helminthiases.

Results

The predicted amino acid sequence of the cathepsin B of C. sinensis shared 63%, 52%, 50% identity with that of Schistosoma japonicum, Homo sapiens and Fasciola hepatica, respectively. Sequence encoding proenzyme of CsCB was overexpressed in Escherichia coli. Reverse transcription PCR experiments revealed that CsCB transcribed in both adult worm and metacercaria of C. sinensis. CsCB was identified as a C. sinensis excretory/secretory product by immunoblot assay, which was consistent with immunohistochemical localization showing that CsCB was especially expressed in the intestine of C. sinensis adults. Both ELISA and western blotting analysis showed recombinant CsCB could react with human sera from clonorchiasis and other helminthiases.

Conclusions

Our findings revealed that secreted CsCB may play an important role in the biology of C. sinensis and could be a diagnostic candidate for helminthiases.

Clonorchis sinensis and clonorchiasis, an update

Clonorchis sinensis is the most common human liver fluke in East Asia. Several studies proved its carcinogenesis in humans and it was reclassified as a group 1 biological carcinogen in 2009. It is still actively transmitted in endemic areas of Korea, China, Russia, and Vietnam. Currently it is estimated that more than 200 million people are at risk of infection, 15-20 million people are infected and 1.5-2 million show symptoms or complications. Several molecules and genes of the fluke have been identified and characterized. Studies on its oncogenesis and omics-based findings have been especially encouraging. Diagnosis of its infection depends mainly on detection of eggs in feces but other methods have been developed. ELISA using crude extract antigen is now popular for its diagnosis. Diagnosis by detecting DNAs from eggs in feces has been developed using PCR, real-time PCR, and LAMP, which have been found sensitive and specific. Imaging diagnosis has been studied in depth and is widely used. Any evidence of clonorchiasis, such as eggs, DNAs, or images, may lead to recommendations of chemotherapy in endemic areas. Praziquantel is the major chemotherapeutic agent for clonorchiasis and recently tribendimidine was found effective and is now under investigation as a promising chemotherapeutic alternative. Sustainable control programs which include mass chemotherapy with praziquantel and education for prevention of re-infection may reduce its morbidity and eliminate its infections in endemic areas.

Cysteine proteases as potential antigens in antiparasitic DNA vaccines

Cysteine proteases in parasites are potent inducers of vertebrate host immune responses and may under certain circumstances take part in the pathogen's immune evasion strategies. These capacities place these parasite molecules as interesting candidate antigens in antiparasitic vaccines for use in vertebrates. Parasite cysteine proteases are able to skew the Th1/Th2 profile in mammals towards a response which allows sustainable parasite burdens in the host. DNA vaccines are also able to skew the Th1/Th2 profile by different administration techniques and the use of cysteine proteases in these genetic immunizations open perspectives for manipulation of the host immune response towards higher protection.

Zoonotic helminth infections with particular emphasis on fasciolosis and other trematodiases

Zoonotic infections are among the most common on earth and are responsible for >60 per cent of all human infectious diseases. Some of the most important and well-known human zoonoses are caused by worm or helminth parasites, including species of nematodes (trichinellosis), cestodes (cysticercosis, echinococcosis) and trematodes (schistosomiasis). However, along with social, epidemiological and environmental changes, together with improvements in our ability to diagnose helminth infections, several neglected parasite species are now fast-becoming recognized as important zoonotic diseases of humans, e.g. anasakiasis, several fish-borne trematodiasis and fasciolosis. In the present review, we discuss the current disease status of these primary helminth zoonotic infections with particular emphasis on their diagnosis and control. Advances in molecular biology, proteomics and the release of helminth genome-sequencing project data are revolutionizing parasitology research. The use of these powerful experimental approaches, and their potential benefits to helminth biology are also discussed in relation to the future control of helminth infections of animals and humans.

Ov-APR-1, an aspartic protease from the carcinogenic liver fluke, Opisthorchis viverrini: functional expression, immunolocalization and subsite specificity

The human liver fluke Opisthorchis viverrini is endemic in Thailand, Laos and Cambodia where long standing infection is associated with cancer of the bile ducts, cholangiocarcinoma. Here we describe a cathepsin D-like aspartic protease from the gut and other tissues in O. viverrini. Phylogenetic analysis indicated that Ov-APR-1 is cathepsin D-like, conforming with Clan AA, Family A1 of the MEROPS classification. Ov-APR-1 is expressed in the gut of the mature hermaphroditic parasite, in the reproductive tissues including the testis and immature spermatids, and the developing miracidium within the eggshell. The enzyme was also detected in the excretory/secretory products of cultured adult flukes, indicating a role in host-parasite relationships. A recombinant form of the enzyme expressed in Escherichia coli and refolded from denatured inclusion bodies underwent autocatalytic activation and demonstrated hydrolytic activity against the peptide substrate 7-methoxycoumarin-4-acetyl-GKPILFFRLK(DNP)-D-Arg-amide with a k(cat)/K(m)=1.7 x 10(4)M(-1)s(-1) and a pH optimum around pH 2.5-3.0. The recombinant enzyme digested hemoglobin and bovine serum albumin. Forty-six serum albumin peptides were detected after digestion with recombinant Ov-APR-1 and sequenced. Like many other aspartic proteases, Ov-APR-1 displayed promiscuous preferences for residues accommodated at the key subsites of the binding pocket although hydrophobic (Leu, Ala, Ile), positively charged (Lys) and bulky aromatic (Phe) residues, in that order, were preferred at P1. Similar residues were accommodated at P1' although even less selectivity was exerted at this position.

Changing patterns of serum and bile antibodies in re-infected rats with Clonorchis sinensis

Rats develop strong resistance to re-infection and super-infection by Clonorchis sinensis. The present study investigated the antibodies present in the sera and bile juice of rats that were primary infected and re-infected with C. sinensis. The serum level of specific IgG antibodies, which were elevated 2 wk of the primary infection, peaked at 4 wk and subsequently remained unchanged even during re-infection. The total IgE level in serum increased slowly from 388 ng / ml to 3,426 ng / ml beginning 2 wk after the primary infection, and remained high up to 8 wk but dropped to a normal level (259 ng / ml) after treatment. In resistant re-infected rats, the serum IgE level increased rapidly and peaked within 1 wk, whereas no increase was observed in immunosuppressed rats. The serum level of specific IgA antibodies was elevated beginning 1 wk after infection, and decreased 4 wk after treatment. The total bile IgA level unchanged during the primary infection but increased in treated and re-infected rats. The elevated levels of serum IgE and bile IgA indicate that these immunoglobulins may be correlated with the development of resistance to re-infection by C. sinensis in rats.

Characterization of cysteine proteases from the carcinogenic liver fluke, Opisthorchis viverrini

Protease activities in extracts of Opisthorchis viverrini were investigated using gelatin zymography and fluorogenic peptide substrates. Using gelatin-impregnated X-ray film, 2 microg of O. viverrini excretory-secretory products (Ov-ES) and adult somatic extract (Ov-SE) showed proteolytic activity. Zymography of both O. viverrini extracts revealed bands at approximately 30 kDa. Using fluorogenic peptide substrates, the majority of O. viverrini activity was determined to be cathepsin L-like cysteine protease (cleaved Z-Phe-Arg-aminomethylcoumarin (AMC)) whereas little or no activity was ascribable to other classes of proteases. The O. viverrini cysteine protease activity was greatest at pH 6.0 and the activity was inhibited by the class-specific inhibitors, E-64 and Z-Ala-CHN2. Chromatographic purification of O. viverrini cysteine proteases on thiol-sepharose enriched for protein(s) of approximately 30 kDa from Ov-ES and Ov-SE. The activity profile of the purified enzyme was similar to that of the cathepsin L-like activity characterized in Ov-SE and Ov-ES. Furthermore, determination of cysteine protease activity in several developmental stages of the parasite revealed the highest protease activity in metacercariae soluble extract, followed by Ov-ES, egg soluble extract, and Ov-SE. These findings demonstrated that O. viverrini has a cathepsin L-like cysteine protease(s) and suggested that abundant cysteine protease activity was present in metacercariae where the hydrolase might be involved in cyst excystation during mammalian infection.

Clonorchis sinensis: expression, characterization, immunolocalization and serological reactivity of one excretory/secretory antigen-LPAP homologue

From a Clonorchis sinensis adult cDNA plasmid library, a cDNA clone encoding a novel lysophosphatidic acid phosphatase (LPAP) homologue was isolated. The predicted molecular weight of putative protein was 48.8 kDa and the deduced amino acid sequence had 45%, 32%, and 29% identity with LPAP of Schistosoma japonicum, Danio rerio, and Homo sapiens, respectively. Prediction of signal peptide and Western blot analysis indicated that the CsLPAP homologue was an excretory-secretory antigen (ES antigen) of C. sinensis. Immunostaining revealed that the CsLPAP was markedly localized in the intestinal cecum, seminal receptacle and eggs of the adult worm. The recombinant CsLPAP showed slightly higher sensitivity (82.14%) and specificity (85.86%) than the crude worm antigen by enzyme-linked immunosorbent assay (ELISA), a result which suggested that the recombinant antigen might be valuable in the serodiagnosis of human clonorchiasis.

Molecular characterization and serodiagnosis analysis of a novel lysophospholipase from Clonorchis sinensis

A cDNA clone encoding a novel lysophospholipase with a predicted molecular weight of 25.2 kDa was isolated from a Clonorchis sinensis adult cDNA library. The enzyme activity of the recombinant protein expressed in Escherichia coli was determined using phosphatidylcholine and lysophosphatidylcholine as substrates. Western blotting analysis indicated that it belonged to excretory/secretory proteins of the adults. The sensitivity and specificity of the recombinant antigen for serodiagnosis were evaluated with immunoglobulin enzyme-linked immunosorbent assay using serum samples from 20 patients with clonorchiasis and 20 patients with schistosomiasis. The sensitivity (75%) and specificity (80%) of the recombinant protein were comparable to those of crude extracts, at 65 and 82.5%, respectively. The sensitivity of the recombinant protein was 77% using 100 serum samples of clonorchiasis patients with various parasite burden. The results suggested that the recombinant lysophospholipase protein was not a satisfactory candidate for diagnosis of clonorchiasis, although it might be an excretory/secretory protein.