Human antibody responses of patients living in endemic areas for schistosomiasis to the tegumental protein Sm29 identified through genomic studies

Novel immunomic technologies for schistosome vaccine development

Schistosomiasis remains one of the most common human helminthiases, despite the availability of an effective drug against the causative parasites. Drug treatment programmes have several limitations, and it is likely that a vaccine is required for effective control. While decades of vaccine development have seen the discovery and testing of several candidate antigens, none have shown consistent and acceptable high levels of protection. The migrating larval stages are susceptible to immunity, however few larval-specific antigens have been discovered. Therefore, there is a need to identify novel larval-specific antigens, which may prove to be more efficacious than existing targets. Immunomics, a relatively new field developed to cope with the recent large influx of biological information, holds promise for the discovery of vaccine targets, and this review highlights some immunomic approaches to schistosome vaccine development. Firstly, a method to focus on the immune response elicited by the important and vulnerable larval stage is described, which allows a targeted study of the immunome at different tissue sites. Then, two high-throughput arrays are discussed for the identification of protein and carbohydrate antigens. It is anticipated that these approaches will progress vaccine development against the schistosomes, as well as other parasites.

Schistosoma japonicum UDP-glucose 4-epimerase protein is located on the tegument and induces moderate protection against challenge infection

Schistosomiasis is an important global public health problem, as millions of people are at risk of acquiring this infection. An ideal method for sustainable control of schistosomiasis is using a vaccine alone or in combination with drugs. In the present study, we cloned the SjGALE gene and generated the expression product in E. coli. The expression level of SjGALE during different developmental stages of S. japonicum was evaluated by real-time RT-PCR and western blotting. Immunolocalization indicated that the protein was mainly located on the tegument of the parasite. Infection of rSjGALE-immunized mice demonstrated a 34% and 49% reduction of the mean worm burden and liver egg burden, respectively, in two independent experiments, indicating immune protection. The liver egg count from each female adult worm was significantly reduced by 63% in the two trials. The cytokine profile and IgG isotype analysis demonstrated the induction of a Th1 immune profile in response to immunization with this protein, further suggesting protection against infection. In conclusion, these findings indicated that SjGALE is a potential vaccine against S. japonicum.

Schistosoma japonicum calcium-binding tegumental protein SjTP22.4 immunization confers praziquantel schistosomulumicide and antifecundity effect in mice

A family of platyhelminth tegument-specific proteins comprising of one or two calcium ion binding EF-hand and a dynein light chain-like domain, termed tegumental proteins, are considered as candidates of vaccine. In this study, we cloned and characterized SjTP22.4, a novel membrane-anchored tegumental protein in Schistosoma japonicum with theoretic MW of 22.4. The recombinant SjTP22.4 could be recognized by S. japonicum infected sera. Immunofluorescence revealed that this protein is not only located on the surface of tegument of adult and schistosomulum and cercaria, but also in the parenchymatous tissues and intestinal epithelium. Circular dichroism (CD) measurement demonstrated rSjTP22.4 had Ca(2+)-binding ability. The rSjTP22.4 vaccination without adjuvants produced comparable high level of antibody with that of immunization with adjuvants together indicated it was an antigen of strong antigenicity. The level of IgG1 is much higher than that of IgG2a and IgE is nearly negative in S. japonicum-infected and rSjTP22.4 immunized mice. In cercaria challenge experiment, mice vaccinated with SjTP22.4 showed no reduction in adult burden and egg production, comparing with the control mice, but 41% decrease in egg mature rate and 32% reduction in liver egg granuloma area. However, the SjTP22.4 immunized mice that received praziquantel treatment at 10d post infection caused 26% reduction in adult burden and 53% decrease in egg mature rate, comparing with the control mice only received praziquantel treatment. In conclusion, SjTP22.4 is a valuable vaccine candidate for S. japonicum of anti-pathogenesis and anti-transmission effect and plays a synergetic role in praziquantel to kill schistosomulum.

Recent advances in Schistosoma genomics

Schistosome research has entered the genomic era with the publications reporting the Schistosoma mansoni and Schistosoma japonicum genomes. Schistosome genomics is motivated by the need for new control tools. However, much can also be learned about the biology of Schistosoma, which is a tractable experimental model. In this article, we review the recent achievements in the field of schistosome research and discuss future perspectives on genomics and how it can be integrated in a usable format, on the genetic mapping and how it has improved the genome assembly and provided new research approaches, on how epigenetics provides interesting insights into the biology of the species and on new functional genomics tools that will contribute to the understanding of the function of genes, many of which are parasite- or taxon specific.

Abundance of tegument surface proteins in the human blood fluke Schistosoma mansoni determined by QconCAT proteomics

The schistosome tegument provides a major interface with the host blood stream in which it resides. Our recent proteomic studies have identified a range of proteins present in the complex tegument structure, and two models of protective immunity have implicated surface proteins as mediating antigens. We have used the QconCAT technique to evaluate the relative and absolute amounts of tegument proteins identified previously. A concatamer comprising R- or K-terminated peptides was generated with [(13)C(6)] lysine/arginine amino acids. Two tegument surface preparations were each spiked with the purified SmQconCAT as a standard, trypsin digested, and subjected to MALDI ToF-MS. The absolute amounts of protein in the biological samples were determined by comparing the areas under the pairs of peaks, separated by 6m/z units, representing the light and heavy peptides derived from the biological sample and SmQconCAT, respectively. We report that aquaporin is the most abundant transmembrane protein, followed by two phosphohydrolases. Tetraspanin Tsp-2 and Annexin-2 are also abundant but transporters are scarce. Sm200 surface protein comprised the bulk of the GPI-anchored fraction and likely resides in the secreted membranocalyx. Two host IgGs were identified but in amounts much lower than their targets. The findings are interpreted in relation to the models of protective immunity.

Vaccinomics for the major blood feeding helminths of humans

Approximately one billion people are infected with hookworms and/or blood flukes (schistosomes) in developing countries. These two parasites are responsible for more disability adjusted life years lost than most other neglected tropical diseases (NTDs), and together, are second only to malaria. Although anthelmintic drugs are effective and widely available, they do not protect against reinfection, resistant parasites are likely to emerge, and mass drug administration programs are unsustainable. Therefore, there is a pressing need for the development of vaccines against these parasites. In recent years, there have been major advances in our understanding of hookworms and schistosomes at the molecular level through the use of "omics" technologies. The secretomes of these parasites have been characterized using transcriptomics, genomics, proteomics, and newly developed gene manipulation and silencing techniques, and the proteins of interest are now the target of novel antigen discovery approaches, notably immunomics. This research has resulted in the discovery, development, and early stage clinical trials of subunit vaccines against hookworms and schistosomes.

Parasite annexins--new molecules with potential for drug and vaccine development

In the last few years, annexins have been discovered in several nematodes and other parasites, and distinct differences between the parasite annexins and those of the hosts make them potentially attractive targets for anti-parasite therapeutics. Annexins are ubiquitous proteins found in almost all organisms across all kingdoms.Here, we present an overview of novel annexins from parasitic organisms, and summarize their phylogenetic and biochemical properties, with a view to using them as drug or vaccine targets. Building on structural and biological information that has been accumulated for mammalian and plant annexins, we describe a predicted additional secondary structure element found in many parasite annexins that may confer unique functional properties, and present a specific antigenic epitope for use as a vaccine.

Developing vaccines to combat hookworm infection and intestinal schistosomiasis

Hookworm infection and schistosomiasis rank among the most important health problems in developing countries. Both cause anaemia and malnutrition, and schistosomiasis also results in substantial intestinal, liver and genitourinary pathology. In sub-Saharan Africa and Brazil, co-infections with the hookworm, Necator americanus, and the intestinal schistosome, Schistosoma mansoni, are common. The development of vaccines for these infections could substantially reduce the global disability associated with these helminthiases. New genomic, proteomic, immunological and X-ray crystallographic data have led to the discovery of several promising candidate vaccine antigens. Here, we describe recent progress in this field and the rationale for vaccine development.

Schistosoma mansoni host-exposed surface antigens characterized by sera and recombinant antibodies from schistosomiasis-resistant rats

Antibodies from Schistosoma mansoni-infected rats, unlike mice, show a higher titer for schistosome apical tegumental antigens compared with non-apical membrane antigens. These antibodies bind to the surface of living lung-stage worms and to formaldehyde-fixed adult worms. We produced a single-chain antibody Fv domain (scFv) phage library displaying the antibody repertoire of rats highly immune to schistosome infection and we selected for scFvs that recognize the host-exposed surface of worms. Five unique rat scFvs (Teg1, Teg4, Teg5, Teg20 and Teg37) were obtained which recognize schistosome surface epitopes. Each of the scFvs recognizes the surface of living schistosomula and lung-stage schistosomules and/or the surface of formaldehyde-fixed adult worms. None of these scFvs reproducibly stained living adult worms. This suggests that a change occurs during the transition from lung schistosomules to 4-week adults such that at least some surface antigens, although remaining on the surface in living adult worms, can no longer be immunologically stained. Teg1 and Teg4 scFvs both recognize specific bands on Western blots. No bands were observed for the other three scFvs, suggesting that these scFvs may recognize non-protein or conformationally-dependent epitopes. Teg1 was unambiguously identified as recognizing the S. mansoni tetraspanin antigen, SmTSP-2, within the large extracellular domain. Teg4 recognizes a 35kDa band tentatively identified as Sm29 by proteomic analysis. These scFvs can now be used to characterize schistosome epitopes at the host-parasite interface, to target worms in vivo, and to study the mechanisms by which these worms naturally evade immune damage to the tegument within permissive hosts.

Functional genes and proteins of Clonorchis sinensis

During the past several decades, researches on parasite genetics have progressed from biochemical and serodiagnostic studies to protein chemistry, molecular biology, and functional gene studies. Nowadays, bioinformatics, genomics, and proteomics approaches are being applied by Korean parasitology researchers. As for Clonorchis sinensis, investigations have been carried out to identify its functional genes using forward and reverse genetic approaches and to characterize the biochemical and biological properties of its gene products. The authors review the proteins of cloned genes, which include antigenic proteins, physiologic and metabolic enzymes, and the gene expression profile of Clonorchis sinensis.

Schistosoma mansoni Stomatin like protein-2 is located in the tegument and induces partial protection against challenge infection

Background

Schistosomiasis affects more than 200 million individuals worldwide, with a further 650 million living at risk of infection, constituting a severe health problem in developing countries. Even though an effective treatment exists, it does not prevent re-infection, and the development of an effective vaccine still remains the most desirable means of control for this disease.

Methodology/Principal Findings

Herein, we report the cloning and characterization of a S. mansoniStomatin-like protein 2 (SmStoLP-2). In silico analysis predicts three putative sites for palmitoylation (Cys11, Cys61 and Cys330), which could contribute to protein membrane association; and a putative mitochondrial targeting sequence, similar to that described for human Stomatin-like protein 2 (HuSLP-2). The protein was detected by Western blot with comparable levels in all stages across the parasite life cycle. Fractionation by differential centrifugation of schistosome tegument suggested that SmStoLP-2 displays a dual targeting to the tegument membranes and mitochondria; additionally, immunolocalization experiments confirm its localization in the tegument of the adult worms and, more importantly, in 7-day-old schistosomula. Analysis of the antibody isotype profile to rSmStoLP-2 in the sera of patients living in endemic areas for schistosomiasis revealed that IgG1, IgG2, IgG3 and IgA antibodies were predominant in sera of individuals resistant to reinfection as compared to those susceptible. Next, immunization of mice with rSmStoLP-2 engendered a 30%–32% reduction in adult worm burden. Protective immunity in mice was associated with specific anti-rSmStoLP-2 IgG1 and IgG2a antibodies and elevated production of IFN-γ and TNF-α, while no IL-4 production was detected, suggesting a Th1-predominant immune response.

Conclusions/Significance

Data presented here demonstrate that SmStoLP-2 is a novel tegument protein located in the host-parasite interface. It is recognized by different subclasses of antibodies in patients resistant and susceptible to reinfection and, based on the data from murine studies, shows protective potential against schistosomiasis. These results indicate that SmStoLP-2 could be useful in a combination vaccine.

Schistosomiasis is a parasitic disease causing serious chronic morbidity in tropical countries. Together with the publication of the transcriptome database, a series of new vaccine candidates were proposed based on their functional classification. However, the prediction of vaccine candidates from sequence information or even by proteomics or microarrays data is somewhat speculative and there remains the considerable task of functional analysis of each new gene/protein. In this study, we present the characterization of one of these molecules, a stomatin like protein 2 (SmStoLP-2). Sequence analysis predicts signals that could contribute to protein membrane association and mitochondrial targeting, which was confirmed by differential extractions of schistosome tegument membranes and mitochondria. Additionally, confocal microscope analysis showed SmStoLP-2 present in the tegument of 7-day-old schistosomula and adult worms. Studies in patients living in endemic areas for schistosomiasis revealed high levels of IgG1, IgG2, IgG3 and IgA anti-SmStoLP-2 antibodies in individuals resistant to reinfection. Recombinant SmStoLP-2 protein, when used as vaccine, induced significant levels of protection in mice. This reduction in worm burden was associated with a typical Th1-type immune response. These results indicate that SmStoLP-2 could be useful in association with other antigens for the composition of a vaccine against schistosomiasis.

Schistosoma mansoni antigens modulate the allergic response in a murine model of ovalbumin-induced airway inflammation

Schistosoma mansoni infection has been associated with protection against allergies. The mechanisms underlying this association may involve regulatory cells and cytokines. We evaluated the immune response induced by the S. mansoni antigens Sm22.6, PIII and Sm29 in a murine model of ovalbumin (OVA)-induced airway inflammation. BALB/c mice were sensitized with subcutaneously injected OVA-alum and challenged with aerolized OVA. Mice were given three doses of the different S. mansoni antigens. Lung histopathology, cellularity of bronchoalveolar lavage (BAL) and eosinophil peroxidase activity in lung were evaluated. Immunoglobulin (Ig)E levels in serum and cytokines in BAL were also measured. Additionally, we evaluated the frequency of CD4+forkhead box P3 (FoxP3)+ T cells in cultures stimulated with OVA and the expression of interleukin (IL)-10 by these cells. The number of total cells and eosinophils in BAL and the levels of OVA-specific IgE were reduced in the immunized mice. Also, the levels of IL-4 and IL-5 in the BAL of mice immunized with PIII and Sm22.6 were decreased, while the levels of IL-10 were higher in mice immunized with Sm22.6 compared to the non-immunized mice. The frequency of CD4+FoxP3+ T cells was higher in the groups of mice who received Sm22.6, Sm29 and PIII, being the expression of IL-10 by these cells only higher in mice immunized with Sm22.6. We concluded that the S. mansoni antigens used in this study are able to down-modulate allergic inflammatory mediators in a murine model of airway inflammation and that the CD4+FoxP3+ T cells, even in the absence of IL-10 expression, might play an important role in this process.

Anti-schistosomal intervention targets identified by lifecycle transcriptomic analyses

Background

Novel methods to identify anthelmintic drug and vaccine targets are urgently needed, especially for those parasite species currently being controlled by singular, often limited strategies. A clearer understanding of the transcriptional components underpinning helminth development will enable identification of exploitable molecules essential for successful parasite/host interactions. Towards this end, we present a combinatorial, bioinformatics-led approach, employing both statistical and network analyses of transcriptomic data, for identifying new immunoprophylactic and therapeutic lead targets to combat schistosomiasis.

Methodology/Principal Findings

Utilisation of a Schistosoma mansoni oligonucleotide DNA microarray consisting of 37,632 elements enabled gene expression profiling from 15 distinct parasite lifecycle stages, spanning three unique ecological niches. Statistical approaches of data analysis revealed differential expression of 973 gene products that minimally describe the three major characteristics of schistosome development: asexual processes within intermediate snail hosts, sexual maturation within definitive vertebrate hosts and sexual dimorphism amongst adult male and female worms. Furthermore, we identified a group of 338 constitutively expressed schistosome gene products (including 41 transcripts sharing no sequence similarity outside the Platyhelminthes), which are likely to be essential for schistosome lifecycle progression. While highly informative, statistics-led bioinformatics mining of the transcriptional dataset has limitations, including the inability to identify higher order relationships between differentially expressed transcripts and lifecycle stages. Network analysis, coupled to Gene Ontology enrichment investigations, facilitated a re-examination of the dataset and identified 387 clusters (containing 12,132 gene products) displaying novel examples of developmentally regulated classes (including 294 schistosomula and/or adult transcripts with no known sequence similarity outside the Platyhelminthes), which were undetectable by the statistical comparisons.

Conclusions/Significance

Collectively, statistical and network-based exploratory analyses of transcriptomic datasets have led to a thorough characterisation of schistosome development. Information obtained from these experiments highlighted key transcriptional programs associated with lifecycle progression and identified numerous anti-schistosomal candidate molecules including G-protein coupled receptors, tetraspanins, Dyp-type peroxidases, fucosyltransferases, leishmanolysins and the netrin/netrin receptor complex.

Despite the implementation of focused and well-funded chemotherapeutic control initiatives over the last decade, schistosomiasis remains a significant cause of morbidity and mortality within countries of the developing world. There is, therefore, an urgent need for the rapid translation of genomic information into viable vaccines or new drug classes capable of eradicating the parasitic schistosome worms responsible for this neglected tropical disease. In our effort to identify potential targets for novel chemotherapeutic and immunoprophylactic interventions, we detail a combined bioinformatics approach, comprising exploratory statistical and network analyses, to thoroughly describe the transcriptional progression of Schistosoma mansoni across three environmental niches. Our results indicate that, although schistosomes are masters at host deception and survival, there are numerous exploitable candidate molecules displaying either differential or constitutive expression throughout the parasite's lifecycle. Importantly, some of these transcripts represent gene families not commonly found outside—or expanded within—the phylum Platyhelminthes, and thus represent priority targets. Many of the candidates identified herein will be subjected to ongoing and future hypothesis-led functional investigations. The completion of such specific examinations ultimately will contribute to the successful development of novel control strategies useful in the alleviation of schistosome-induced immunopathologies, morbidities and mortalities.

Sm21.6 a novel EF-hand family protein member located on the surface of Schistosoma mansoni adult worm that failed to induce protection against challenge infection but reduced liver pathology

Schistosomiasis continues to be a significant public health problem that affects 200 million people worldwide. This is one of the most important parasitic diseases, and one whose effective control is unlikely in the absence of a vaccine. In this study, we have isolated a cDNA clone encoding the Schistosoma mansoni Sm21.6 protein that has 45% and 44% identity with Sm22.6 and Sj21.7 EF-hand containing antigens, respectively. Confocal microscopy analysis revealed that Sm21.6 is a membrane-associated protein localized on the S. mansoni adult worm. Mouse immunization with rSm21.6 induced a mixed Th1/Th2 cytokine profile and no protection against infection. However, vaccination with rSm21.6 reduced by 28% of liver granuloma numbers, 21% of granuloma area and 34% of fibrosis. Finally, rSm21.6 was recognized by sera from individuals resistant to reinfection compared with patients susceptible to reinfection and this molecule should be further studied as potential biomarker for disease resistance. In conclusion, Sm21.6 is a new tegument protein from S. mansoni that plays an important role in reducing pathology induced by parasite infection.

Recent advances in vaccine research against schistosomiasis in Brazil

Schistosomiasis continues to be a significant public health problem in tropical countries such as Brazil. Even though drug treatment in endemic areas has been shown to be efficient for controlling morbidity, it does not reduce prevalence due to constant reinfections. Therefore, a long-term disease control strategy is needed combining mass chemotherapy with a protective vaccine. Although the field of vaccine development has experienced more failures than successes, encouraging results have been obtained in recent years using defined recombinant derived Schistosoma mansoni antigens. This article primarily reviews the progress in the development of a vaccine against S. mansoni in Brazil. We discuss here different forms of vaccine tested in Brazil in pre-clinical trials and immunologic studies performed with patients in endemic areas of schistosomiasis. Lastly, we reviewed the S. mansoni genomic projects developed in the country and the recent advances in the identification of new molecules with potential as vaccine targets.

Schistosoma mansoni tegument protein Sm29 is able to induce a Th1-type of immune response and protection against parasite infection

Background

Schistosomiasis continues to be a significant public health problem. This disease affects 200 million people worldwide and almost 800 million people are at risk of acquiring the infection. Although vaccine development against this disease has experienced more failures than successes, encouraging results have recently been obtained using membrane-spanning protein antigens from the tegument of Schistosoma mansoni. Our group recently identified Sm29, another antigen that is present at the adult worm tegument surface. In this study, we investigated murine cellular immune responses to recombinant (r) Sm29 and tested this protein as a vaccine candidate.

Methods and Findings

We first show that Sm29 is located on the surface of adult worms and lung-stage schistosomula through confocal microscopy. Next, immunization of mice with rSm29 engendered 51%, 60% and 50% reduction in adult worm burdens, in intestinal eggs and in liver granuloma counts, respectively (p<0.05). Protective immunity in mice was associated with high titers of specific anti-Sm29 IgG1 and IgG2a and elevated production of IFN-γ, TNF-α and IL-12, a typical Th1 response. Gene expression analysis of worms recovered from rSm29 vaccinated mice relative to worms from control mice revealed a significant (q<0.01) down-regulation of 495 genes and up-regulation of only 22 genes. Among down-regulated genes, many of them encode surface antigens and proteins associated with immune signals, suggesting that under immune attack schistosomes reduce the expression of critical surface proteins.

Conclusion

This study demonstrates that Sm29 surface protein is a new vaccine candidate against schistosomiasis and suggests that Sm29 vaccination associated with other protective critical surface antigens is the next logical strategy for improving protection.

Schistosomiasis is the most important human helminth infection in terms of morbidity and mortality. Although the efforts to develop a vaccine against this disease have experienced failures, a new generation of surface antigens revealed by proteomic studies changed this scenario. Our group has characterized the protein Sm29 described previously as one of the most exposed and expressed antigens in the outer tegument of Schistosoma mansoni. Studies in patients living in endemic areas for schistosomiasis revealed high levels of IgG1 and IgG3 anti-Sm29 in resistant individuals. In this study, confocal microscope analysis showed Sm29 present in the surface of lung-stage schistosoluma and adult worms. Recombinant Sm29, when used as vaccine candidate, induced high levels of protection in mice. This protection was associated with a typical Th1 immune response and reduction of worm burden, liver granulomas and in intestinal eggs. Further, microarray analysis of worms recovered from vaccinated mice showed significant down-regulation of several genes encoding previously characterized vaccine candidates and/or molecules exposed on the surface, suggesting an immune evasion strategy of schistosomes under immune attack. These results demonstrated that Sm29 as one of the important antigens with potential to compose a vaccine against schistosomiasis.

Can schistosomiasis really be consigned to history without a vaccine?

Recently, considerable enthusiasm has been expressed for expanding and combining control efforts for neglected tropical diseases (NTDs). While these efforts are laudable, the drugs in question require repeated mass administration for indefinite periods of time, and their use to achieve eradication is fraught with challenges. Mass drug administration is unlikely to be effective in isolation, and should not proceed without concurrent control methods, such as vaccines. Schistosomiasis is one of the most important NTDs, and one whose effective control is unlikely in the absence of improved sanitation and a vaccine. Recent advances in biotechnologies have enhanced antigen discovery and new molecules that show promise as recombinant vaccines are being reported. Funding bodies supporting research into the control of schistosomiasis should invest not only in mass drug administration but also in the development of new control strategies, including the development of vaccines.

Current status of vaccines for schistosomiasis

Schistosomiasis, caused by trematode blood flukes of the genus Schistosoma, is recognized as the most important human helminth infection in terms of morbidity and mortality. Infection follows direct contact with freshwater harboring free-swimming larval (cercaria) forms of the parasite. Despite the existence of the highly effective antischistosome drug praziquantel (PZQ), schistosomiasis is spreading into new areas, and although it is the cornerstone of current control programs, PZQ chemotherapy does have limitations. In particular, mass treatment does not prevent reinfection. Furthermore, there is increasing concern about the development of parasite resistance to PZQ. Consequently, vaccine strategies represent an essential component for the future control of schistosomiasis as an adjunct to chemotherapy. An improved understanding of the immune response to schistosome infection, both in animal models and in humans, suggests that development of a vaccine may be possible. This review considers aspects of antischistosome protective immunity that are important in the context of vaccine development. The current status in the development of vaccines against the African (Schistosoma mansoni and S. haematobium) and Asian (S. japonicum) schistosomes is then discussed, as are new approaches that may improve the efficacy of available vaccines and aid in the identification of new targets for immune attack.

Aluminum hydroxide associated to Schistosoma mansoni 22.6 kDa protein abrogates partial protection against experimental infection but not alter interleukin-10 production

The need to develop a vaccine against schistosomiasis led several researches and our group to investigate proteins from Schistosoma mansoni as vaccine candidates. Sm22.6 is a protein from S. mansoni that shows high identity with Sj22.6 and Sh22.6 (79 and 91%, respectively). These proteins are associated with high levels of IgE and protection to reinfection. Previously, we have shown that Sm22.6 induced a partial protection of 34.5% when used together with Freund's adjuvant and produced a Th0 type of immune response with interferon-g and interleukin-4. In this work, mice were immunized with Sm22.6 alone or with aluminum hydroxide adjuvant and high levels of IgG, IgG1, and IgG2a were measured. Unfortunately, no protection was detected. Since IL-10 is a modulating cytokine in schistosomiasis, we also observed a high level of this molecule in splenocytes of vaccinated mice. In conclusion, we did not observe the adjuvant effect of aluminum hydroxide associated with rSm22.6 in protective immunity.

Patterns of gene expression in schistosomes: localization by whole mount in situ hybridization

As a consequence of comprehensive transcriptome analysis followed by sequencing and draft assembly of the genome, the emphasis of schistosome research is shifting from the identification of genes to the characterization of their functions and interactions. Developmental biologists have long used whole mount in situ hybridization (WISH) to determine gene expression patterns, as a vital tool for formulating and testing hypotheses about function. This paper describes the application of WISH to the study of gene expression in larval and adult schistosomes. Fixed worms were permeablized by proteinase K treatment for hybridization with digoxygenin-labelled RNA probes, with binding being detected by alkaline phosphatase-coupled anti-digoxygenin antibodies, and BM Purple substrate. Discrete staining patterns for the transcripts of the molecules Sm29, cathepsin L, antigen 10.3 and chorion were observed in the tegument cell bodies, gut epithelium, oesophageal gland and vitelline lobules, respectively, of adult worms. Transcripts of the molecules SGTP4, GP18-22 and cathepsin L were localized to tegument cell bodies and embryonic gut, respectively, of lung schistosomula. We also showed that Fast Red TR fluorescent substrate can refine the pattern of localization permitting use of confocal microscopy. We believe that method of WISH will find broad application, in synergy with other emerging post-genomic techniques, such as RNA interference, to studies focused at increasing our molecular understanding of schistosomes.

Molecular cloning and identification of a novel Clonorchis sinensis gene encoding a tegumental protein

The tegumental membrane of platyhelminth parasites is of crucial importance for modulation of the host response and parasite survival. A cDNA encoding a novel tegumental protein 20.8 kDa (TP20.8) was found by large-scale sequencing of a Clonorchis sinensis cDNA library. This new cDNA was 755 bp long containing an open reading frame of 555 bp, which encoded a 20.8-kDa protein with an isoelectric point of 4.33. The deduced amino acid sequence exhibits 40 and 37% identity to Schistosoma japonicum sj20.8 and Schistosoma mansoni Sm 20.8, respectively. TP20.8 transcripts were detected in the adult worm and metacercariae cDNA libraries of C. sinensis but not in the egg. Recombinant C. sinensis TP20.8 protein was produced and purified from Escherichia coli BL21. Using specific anti-recombinant TP20.8 protein sera, the TP20.8 protein was immunohistochemically localized to the outer-surface membrane of C. sinensis. The specificity and sensitivity of the recombinant antigen for serologic diagnosis was assessed by enzyme-linked immunosorbent assay using serum from 100 patients with clonorchiasis, 20 patients with schistosomiasis, and 30 negative controls. The sensitivity was 68%, and the specificity was 84%. The antigen was less useful for the serodiagnosis of clonorchiasis with IgG.

Schistosome membrane proteins as vaccines

Schistosomes are parasitic blood flukes that infect approximately 200 million people and are arguably the most important human helminth in terms of mortality. The outermost surface of intra-mammalian stages of the parasite, the tegument, is the key to the parasite's success, but it is also generally viewed as the most susceptible target for vaccines and drugs. Over the past 2 years the proteome of the Schistosoma mansoni tegument has been investigated and these studies revealed surprisingly few proteins that are predicted to be accessible to the host immune response, namely proteins with at least one membrane-spanning domain. However, of this handful of proteins, some are showing great promise as recombinant vaccines against schistosomiasis at a pre-clinical level. In particular, the tetraspanin family of integral membrane proteins appears to be abundantly represented in the tegument, and convergent data using the mouse vaccine model and correlates of protective immunity in naturally exposed people suggests that this family of membrane proteins offer great promise for schistosomiasis vaccines. With the recent advances in schistosome genomics and proteomics, a new suite of potential vaccine antigens are presented and these warrant detailed investigation and appropriate funding over the next few years.