Schistosome infection stimulates host CD4(+) T helper cell and B-cell responses against a novel egg antigen, thioredoxin peroxidase

Human serum activates the tegument of female schistosomes and supports recovery from Praziquantel

Schistosomiasis is one of the most devastating parasitic disease in the world. Schistosoma spp. survive for decades within the vasculature of their human hosts. They have evolved a vast array of mechanisms to avoid the immune reaction of the host. Due to their sexual dimorphism, with the female worm lying within the gynecophoric canal of the male worm, it is the male that is exposed to the immediate environment and the soluble parts of the host’s immune response. To understand how the worms are so successful in fending off the immune attacks of the host, comparative analyses of both worm sexes in human serum (with or without Praziquantel) were performed using scanning electron microscopy, transmission electron microscopy, and immunohistochemistry. Further, gene expression analyses of tegument-specific genes were performed. Following the incubation in human serum, males and females out of pairs show morphological changes such as an altered structure of the pits below the surface and an increased number of pits per area. In addition, female schistosomes presented a marked tuft-like repulsion of their opsonized surface. The observed resistance of females to Praziquantel seemed to depend on active proteins in the human serum. Moreover, different expression profiles of tegument-specific genes indicate different functions of female_single and male_single teguments in response to human serum. Our results indicate that female schistosomes developed different evasion strategies toward the host’s immune system in comparison to males that might lead to more robustness and has to be taken into account for the development of new anti-schistosomal drugs.

Expression and serodiagnostic potential of antigen B and thioredoxin peroxidase from Taenia multiceps

Coenurosis is a serious parasitic disease of herbivorous animals caused by the metacestode of Taenia multiceps (Coenurus cerebralis). Accordingly, a significant amount of research is currently dedicated to the development of appropriate antigens for use in rapid and accurate coenurosis diagnosis kits. In the present study, antigen B (AgB) and thioredoxin peroxidase (TPx) from T. multiceps were cloned and expressed using a prokaryotic system, molecular characterization of Tm-AgB was determined by bioinformatical analyses. The serological diagnostic potentials of rTm-AgB and rTm-TPx were evaluated by indirect ELISA and compared with those of previously reported rTm-AnxB2, rTm-HSP70, and rTm-GST. The results showed that Tm-AgB is a specific lipoprotein of cestodes with good thermal stability. The ELISA assay showed that rTm-AgB exhibited a sensitivity of 95.8% and a specificity of 87.5%, indicating its strong potential for serological diagnosis of T. multiceps.

Prokaryotic Expression and Serodiagnostic Potential of Glyceraldehyde-3-Phosphate Dehydrogenase and Thioredoxin Peroxidase from Baylisascaris schroederi

Baylisascaris schroederi, a roundworm parasite of giant pandas, badly affects the health of its hosts. Diagnosis of this disease currently depends mainly on sedimentation floatation and Polymerase Chain Reaction (PCR) methods to detect the eggs. However, neither of these methods is suitable for diagnosis of early-stage panda baylisascariasis and no information on early diagnosis of this disease is available so far. Therefore, to develop an effective serologic diagnostic method, this study produced recombinant glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and thioredoxin peroxidase (Tpx) proteins from B. schroederi using a prokaryotic expression system. We determined the immunological characteristics of these proteins and their location in the parasite. Indirect enzyme-linked immunosorbent assays (ELISAs) were established to detect B. schroederi infection in giant pandas based on GAPDH and Tpx respectively. The open reading frame of the GAPDH gene (1083 bp) encoded a 39 kDa protein, while the predicted molecular weight of Tpx (588 bp) was 21.6 kDa. Western-blotting analysis revealed that both recombinant proteins could be recognized with positive serum of pandas infected with B. schroederi. Immunohistochemical staining showed that the endogenous GAPDH of B. schroederi was widely distributed in the worm while Tpx was mainly localized in the muscle, eggs, gut wall, uterus wall and hypodermis. Serological tests showed that the GAPDH-based indirect ELISA had a sensitivity of 95.83% and specificity of 100%, while the test using Tpx as the antigen had sensitivity of 75% and specificity of 91.7%. Thus, B. schroederi Tpx is unsuitable as a diagnostic antigen for baylisascariasis, but B. schroederi GAPDH is a good candidate diagnostic antigen for B. schroederi in pandas.

Schistosoma mekongi cathepsin B and its use in the development of an immunodiagnosis

Schistosomiasis mekongi is one of the most important human parasitic diseases caused by Schistosoma mekongi in South-east Asia. The endemic area is the Mekong River sub-region from Laos to Cambodia. This parasite also infects dogs and pigs which are its alternative host species. Currently, the lack of reliable rapid diagnosis makes it difficult to monitor the infection and spreading of the disease. In this study, we screened the antigens of the parasite with sera of infected mice using Western blotting and identified proteins of interest with LC-MS/MS to obtain potential candidate proteins for diagnostic development. This assay yielded 2 immunoreactive bands at molecular masses of 31 and 22kDa. The 31kDa protein was the major band identified as cathepsin B, and its gene was cloned to obtain a full cDNA sequence (SmekCatB). The cDNA consisted of 1123bp and its longest reading frame encoded for 342 amino acids with some putative post translation modifications. The recombinant SmekCatB (rSmekCatB) with hexahistidine tag at the C-terminus was expressed in Escherichia coli and purified by Ni-NTA resin under denaturing conditions. The rSmekCatB reacted with sera of S. mekongi-infected mice. Indirect ELISA using rSmekCatB as the antigen to detect mouse antibodies, revealed a sensitivity of 91.67% for schistosomiasis mekongi and the specificity of 100%. Our data suggested that SmekCatB is one of the most promising parasitic antigens that could be used for the diagnosis of S. mekongi infection.

iTRAQ-based comparative proteomic analysis of excretory-secretory proteins of schistosomula and adult worms of Schistosoma japonicum

Schistosomiasis remains a serious public health problem with 200 million people infected and 779 million people at risk worldwide. The schistosomulum and adult worm are two stages of the complex lifecycle of Schistosoma japonicum and excretory/secretory proteins (ESPs) play a major role in host-parasite interactions. In this study, iTRAQ-coupled LC-MS/MS was used to investigate the proteome of ESPs obtained from schistosomula and adult worms of S. japonicum, and 298 differential ESPs were identified. Bioinformatics analysis of differential ESPs in the two developmental stages showed that 161 ESPs upregulated in schistosomula were associated with stress responses, carbohydrate metabolism and protein degradation, whereas ESPs upregulated in adult worms were mainly related to immunoregulation and purine metabolism. Recombinant heat shock protein 70 (HSP70) and thioredoxin peroxidase (TPx), two differential proteins identified in this study, were expressed. Further studies showed that rSjHSP70 and rSjTPx stimulated macrophages expressing high levels of the anti-inflammatory factors TGF-β, IL-10 and Arg-1, and suppressed the expression of the pro-inflammatory cytokines TNF-α, IL-1β, IL-6 and iNOS in LPS-induced macrophages. This study provides new insights into the survival and development of schistosomes in the final host and helps identify vaccine candidates or new diagnostic reagents for schistosomiasis.

Specific humoral response of hosts with variable schistosomiasis susceptibility

The schistosome blood flukes are some of the largest global causes of parasitic morbidity. Further study of the specific antibody response during schistosomiasis may yield the vaccines and diagnostics needed to combat this disease. Therefore, for the purposes of antigen discovery, sera and antibody-secreting cell (ASC) probes from semi-permissive rats and sera from susceptible mice were used to screen a schistosome protein microarray. Following Schistosoma japonicum infection, rats had reduced pathology, increased antibody responses and broader antigen recognition profiles compared with mice. With successive infections, rat global serological reactivity and the number of recognized antigens increased. The local antibody response in rat skin and lung, measured with ASC probes, increased after parasite migration and contributed antigen-specific antibodies to the multivalent serological response. In addition, the temporal variation of anti-parasite serum antibodies after infection and reinfection followed patterns that appear related to the antigen driving the response. Among the 29 antigens differentially recognized by the infected hosts were numerous known vaccine candidates, drug targets and several S. japonicum homologs of human schistosomiasis resistance markers-the tegument allergen-like proteins. From this set, we prioritized eight proteins that may prove to be novel schistosome vaccine and diagnostic antigens.

Cytokine patterns in experimental schistosomiasis mansoni infected mice treated with silymarin

The purpose of this study was to determine cytokine patterns in experimental schistosomiasis mansoni infected mice treated with silymarin. The study was conducted upon 100 mice that were divided into five groups; 20 each: uninfected control group, Schistosoma mansoni infected untreated mice (infected control), infected mice treated with praziquantel (PZQ), infected mice treated with silymarin and infected mice treated with both praziquantel and silymarin. 10 mice from each group were sacrificed at 10th and 18th weeks post infection respectively. Histopathological investigations were performed. Liver sections were stained with hematoxylin-eosin and Masson's trichrome stain to evaluate changes of granuloma sizes and numbers. Serum levels of the cytokines (TNF-α, IFN-γ, IL-4 and TGF-β1) were assessed in the sera of all groups by immunoassay. The measured levels of cytokines (IFN-γ, IL-4, TNF-α, TGF-β1) were found to be significantly increased in infected mice compared to normal control. At the same time, treated groups with silymarin alone or combined with PZQ showed significant decrease in IL-4, TNF-α and TGF-β1 levels compared to infected control. On the other hand, there was a significant increase in IFN-γ level observed in all treated groups compared to infected control. In addition, the histopathological examination of the liver in the group treated with PZQ showed a reduction in the number of livers eggs granuloma at all periods of sacrification compared with the infected untreated group. However, there was more decrease in granulomas diameter in both silymarin treated group or combined with PZQ at all periods of sacrification when compared to infected untreated group. In conclusion; treatment with silymarin combined with PZQ in murine schistosomiasis could reduce hepatic fibrosis by their action on the production of pro-inflammatory cytokines.

Inhibitory effects and analysis of RNA interference on thioredoxin glutathione reductase expression in Schistosoma japonicum

Schistosomes infect around 280 million people worldwide. The worms survive in the veins of the final host, where thioredoxin glutathione reductase (TGR) activity helps the parasites to survive in the aerobic environment. In the present study, we synthesized 4 small interfering RNAs (siRNA S1, S2, S3, and S4) targeting the Schistosoma japonicum (Sj) TGR gene and used them to knockdown the TGR gene. The knockdown effects of the siRNAs on SjTGR, and the thioredoxin reductase (TrxR) activity of SjTGR, were evaluated in vitro. The results of transfection with the siRNAs via the soaking method in vitro were confirmed by flow cytometry. S2 siRNA at a final concentration of 200 nM partially inhibited the expression of SjTGR at both the transcript and protein levels in vitro. TrxR-activity was lower in worms in the S2 siRNA-treated group compared with the control groups. Further analysis revealed that purified recombinant SjTGR could remove oxygen free radicals but not H(2)O(2) directly, which may explain the incomplete effects of RNA interference on SjTGR. The results of this study indicate that SjTGR may play an important role in the clearance of oxygen free radicals and protection of S. japonicum parasites against oxidative damage.

Induction and regulation of pathogenic Th17 cell responses in schistosomiasis

Schistosomiasis is a major tropical disease caused by trematode helminths in which the host mounts a pathogenic immune response against tissue-trapped parasite eggs. The immunopathology consists of egg antigen-specific CD4 T cell-mediated granulomatous inflammation that varies greatly in magnitude in humans and among mouse strains in an experimental model. New evidence, covered in this review, intimately ties the development of severe pathology to IL-17-producing CD4 T helper (Th17) cells, a finding that adds a new dimension to the traditional CD4 Th1 vs. Th2 cell paradigm. Most examined mouse strains, in fact, develop severe immunopathology with substantial Th17 as well as Th1 and Th2 cell responses; a solely Th2-polarized response is an exception that is only observed in low-pathology strains such as the C57BL/6. The ability to mount pathogenic Th17 cell responses is genetically determined and depends on the production of IL-23 and IL-1β by antigen presenting cells following recognition of egg antigens; analyses of several F2 progenies of (high × low)-pathology strain crosses demonstrated that quantitative trait loci governing IL-17 levels and disease severity vary substantially from cross to cross. Low pathology is dominant, which may explain the low incidence of severe disease in humans; however, coinfection with intestinal nematodes can also dampen pathogenic Th17 cell responses by promoting regulatory mechanisms such as those afforded by alternatively activated macrophages and T regulatory cells. A better understanding of the pathways conducive to severe forms of schistosomiasis and their regulation should lead to interventions similar to those presently used to manage other immune-mediated diseases.

Peroxiredoxins in parasites

SIGNIFICANCE

Parasite survival and virulence relies on effective defenses against reactive oxygen and nitrogen species produced by the host immune system. Peroxiredoxins (Prxs) are ubiquitous enzymes now thought to be central to such defenses and, as such, have potential value as drug targets and vaccine antigens.

RECENT ADVANCES

Plasmodial and kinetoplastid Prx systems are the most extensively studied, yet remain inadequately understood. For many other parasites our knowledge is even less well developed. Through parasite genome sequencing efforts, however, the key players are being discovered and characterized. Here we describe what is known about the biochemistry, regulation, and cell biology of Prxs in parasitic protozoa, helminths, and fungi. At least one Prx is found in each parasite with a sequenced genome, and a notable theme is the common patterns of expression, localization, and functionality among sequence-similar Prxs in related species.

CRITICAL ISSUES

The nomenclature of Prxs from parasites is in a state of disarray, causing confusion and making comparative inferences difficult. Here we introduce a systematic Prx naming convention that is consistent between organisms and informative about structural and evolutionary relationships.

FUTURE DIRECTIONS

The new nomenclature should stimulate the crossfertilization of ideas among parasitologists and with the broader redox research community. The diverse parasite developmental stages and host environments present complex systems in which to explore the variety of roles played by Prxs, with a view toward parlaying what is learned into novel therapies and vaccines that are urgently needed.

Moonlighting by different stressors: crystal structure of the chaperone species of a 2-Cys peroxiredoxin

2-Cys peroxiredoxins (Prxs) play two different roles depending on the physiological status of the cell. They are thioredoxin-dependent peroxidases under low oxidative stress and ATP-independent chaperones upon exposure to high peroxide concentrations. These alternative functions have been associated with changes in the oligomerization state from low-(LMW) to high-molecular-weight (HMW) species. Here we present the structures of Schistosoma mansoni PrxI in both states: the LMW decamer and the HMW 20-mer formed by two stacked decamers. The latter is the structure of a 2-Cys Prx chaperonic form. Comparison of the structures sheds light on the mechanism by which chemical stressors, such as high H(2)O(2) concentration and acidic pH, are sensed and translated into a functional switch in this protein family. We also propose a model to account for the in vivo formation of long filaments of stacked Prx rings.

The redox biology of schistosome parasites and applications for drug development

Schistosomiasis caused by Schistosoma spp. is a serious public health concern, especially in sub-Saharan Africa. Praziquantel is the only drug currently administrated to treat this disease. However, praziquantel-resistant parasites have been identified in endemic areas and can be generated in the laboratory. Therefore, it is essential to find new therapeutics. Antioxidants are appealing drug targets. In order to survive in their hosts, schistosomes are challenged by reactive oxygen species from intrinsic and extrinsic sources. Schistosome antioxidant enzymes have been identified as essential proteins and novel drug targets and inhibition of the antioxidant response can lead to parasite death. Because the organization of the redox network in schistosomes is significantly different from that in humans, new drugs are being developed targeting schistosome antioxidants. In this paper the redox biology of schistosomes is discussed and their potential use as drug targets is reviewed. It is hoped that compounds targeting parasite antioxidant responses will become clinically relevant drugs in the near future.

Schistosoma mansoni: the egg, biosynthesis of the shell and interaction with the host

The schistosome eggshell is a hardened and tanned structure made from cross-linked proteins. It is synthesized within the female worm from many different kinds of proteins and glycoproteins. Once the egg is released in the circulation, the outer surface of the eggshell is exposed and hence a direct site of interaction between the parasite and the host. The major eggshell protein is p14, but about one third of the eggshell is made from common cellular proteins, some of which are known to be immunogenic. This has many consequences for parasite-host interactions. However, so far, the eggshell has gained little attention from researchers. We will discuss the structure of the eggshell and its role in granuloma formation, host factor binding and egg excretion.

Fasciola hepatica and Schistosoma mansoni: identification of common proteins by comparative proteomic analysis

It is not unusual to find common molecules among parasites of different species, genera, or phyla. When those molecules are antigenic, they may be used for developing drugs or vaccines that simultaneously target different species or genera of parasite. In the present study, we used a proteomic-based approach to identify proteins that are common to adult Fasciola hepatica and Schistosoma mansoni. Whole-worm extracts from each parasite were separated by 2-dimensional electrophoresis (2-DE), and digital images of both proteomes were superimposed using imaging software to identify proteins with identical isoelectric points and molecular weights. Protein identities were determined by mass spectrometry. Imaging and immunoblot analyses identified 28 immunoreactive proteins that are common to both parasites. Among these molecules are antioxidant proteins (thioredoxin and glutathione-S-transferase), glycolytic enzymes (glyceraldehyde 6-phosphate dehydrogenase and enolase), proteolytic enzymes (cathepsin-L and -D), inhibitors (Kunitz-type, Stefin-1), proteins with chaperone activity (heat shock protein 70 and fatty acid-binding protein), and structural proteins (calcium-binding protein, actin, and myosin). Some of the identified proteins could be used to develop drugs and vaccines against fascioliasis and schistosomiasis.

The proteome of the insoluble Schistosoma mansoni eggshell skeleton

In schistosomiasis, the majority of symptoms of the disease is caused by the eggs that are trapped in the liver. These eggs elicit an immune reaction that leads to the formation of granulomas. The eggshell, which is a rigid insoluble structure built from cross-linked proteins, is the site of direct interaction between the egg and the immune system. However, the exact protein composition of the insoluble eggshell was previously unknown. To identify the proteins of the eggshell of Schistosoma mansoni we performed LC-MS/MS analysis, immunostaining and amino acid analysis on eggshell fragments. For this, eggshell protein skeleton was prepared by thoroughly cleaning eggshells in a four-step stripping procedure of increasing strength including urea and SDS to remove all material that is not covalently linked to the eggshell itself, but is part of the inside of the egg, such as Reynold's layer, von Lichtenberg's envelope and the miracidium. We identified 45 proteins of which the majority are non-structural proteins and non-specific for eggs, but are house-keeping proteins that are present in large quantities in worms and miracidia. Some of these proteins are known to be immunogenic, such as HSP70, GST and enolase. In addition, a number of schistosome-specific proteins with unknown function and no homology to any known annotated protein were found to be incorporated in the eggshell. Schistosome-specific glycoconjugates were also shown to be present on the eggshell protein skeleton. This study also confirmed that the putative eggshell protein p14 contributes largely to the eggshell. Together, these results give new insights into eggshell composition as well as eggshell formation. Those proteins that are present at the site and time of eggshell formation are incorporated in the cross-linked eggshell and this cross-linking does no longer occur when the miracidium starts secreting proteins.

Characterization of the methionine sulfoxide reductases of Schistosoma mansoni

Schistosomiasis, also known as Bilharzia, is an infectious disease caused by several species of Schistosoma. Twenty million individuals suffer severe symptoms and 200,000 people die annually from the disease. The host responds to the presence of S. mansoni by producing reactive oxygen species that cause oxidative stress. We hypothesized that schistosomes produce antioxidants in response to oxidative stress. A known antioxidant protein is methionine sulfoxide reductase (Msr). Methionine residues can be oxidized to methionine sulfoxide in the presence of oxidizing agents, and the process is readily reversed by the action of the Msr system. Two S. mansoni MsrB genes (MsrB1 and MsrB2) were cloned and the recombinant proteins were expressed in bacteria and purified. The S. mansoni MsrB proteins contained the common conserved catalytic-and zinc-coordinating cysteines. Analysis of the proteins showed that both proteins promote the reduction of both free methionine sulfoxide (Met[O]) and dabsyl-Met(O) to free methionine (Met) and dabsyl-Met, respectively, while exhibiting differences in their specific activities toward these substrates. Using real-time polymerase-chain reaction (RT-PCR), both proteins were found to be expressed in all stages of the parasite's life cycle, with the highest level of expression of both proteins in the egg stage. This is the first description of MsrB proteins from a parasite.

Immune events associated with high level protection against Schistosoma japonicum infection in pigs immunized with UV-attenuated cercariae

Background

The vaccination of radiation-attenuated Schistosoma japonicum cercariae can induce effective protection in artiodactyl, but the immune events related to protective immunity are not fully understood. To provide a paradigm for a human recombinant antigen vaccine, we have undertaken a vaccination and challenge experiment in pigs, which was recognized as an appropriate animal model in this type of study because of their similarity to human in immunology, and investigated the relative immune events induced by the radiation-attenuated S. japonicum cercariae.

Methods and Findings

We found that pigs immunized once with 400 µw UV-irradiated cercariae exhibited 63.84% and 71.82% reductions in worm burden and hepatic eggs respectively. Protective immunity in vaccinated pigs was associated with high level productions of IgM, total IgG, IgG1 and IgG2; IgG2 was significantly increased in the acute infection. IFN-γ levels could be elicited by immunization. At week 6 post-infection, IFN-γ, IL-4 and IL-10 levels also showed a dramatic rise synchronously in vaccinated pigs. Moreover, the granzyme b, nk-lysin, ifnγ, il4 and il10 mRNA levels in early skin-draining lymph nodes of immunized pigs were higher than those in pigs with non-irradiated cercariae infection. In addition, cytotoxicity-related genes in the mesenteric lymph nodes were significantly upregulated in vaccinated pigs in the acute infection.

Conclusion/Significance

Our results demonstrated that IFN-γ and IgG2 antibody production, as well as genes related to cytotoxicity are associated with the high level protection induced by UV-irradiated Schistosoma japonicum vaccine. These findings indicated that optimal vaccination against S. japonicum required the induction of IFN-γ, IgG2 antibody related to Th1 responses and cytotoxicity effect.

IPSE/alpha-1 of Schistosoma mansoni egg induces enlargement of granuloma but does not alter Th2 balance after infection

Schistosomiasis is a parasitic disease with more than 200 million people infected worldwide. The formation of granulomas around eggs trapped in the liver is the main cause of disease morbidity. Therefore, the aim of this investigation was to characterize the immunopathological response induced by the recombinant (r) IPSE/alpha-1 egg protein in mice. Herein, we have shown that splenocytes from mice immunized with rIPSE/alpha-1 produced IFN-gamma, TNF-alpha, IL-4, IL-5 and IL-13 characterizing a mixed Th1/Th2 type of immune response. Pathological analysis of the liver revealed that there was no alteration in the number of eggs and granulomas; however, we observed an increase in granuloma area in immunized mice. Furthermore, eosinophil peroxidase assay showed that there was no alteration in the eosinophil infiltration in the liver; however, n-acetyl-beta-glucosaminidase measurement revealed an increase in macrophage activity. Despite the alteration in the profile of liver inflammatory cells in rIPSE immunized mice, the production of chemokines such as CCL2, CCL3, CCL5 and CCL11 was unaltered compared with the control group. In conclusion, IPSE/alpha-1 immunization induces a mixed Th1/Th2 type of immune response and enlargement of hepatic granuloma caused by an increased macrophage activity, but does not alter Th2 cytokines following infection.

Peroxiredoxin: a central player in immune modulation

Peroxiredoxins (Prx) are a family of anti-oxidants that protect cells from metabolically produced reactive oxygen species (ROS). The presence of these enzymes in the secretomes of many parasitic helminths suggests they provide protection against ROS released by host immune effector cells. However, we recently reported that helminth-secreted Prx also contribute to the development of Th2-responses via a mechanism involving the induction of alternatively activated macrophages. In this review, we discuss the role helminth Prx may play in modulating the immune responses of their hosts.

A comparative proteomic study of the undeveloped and developed Schistosoma mansoni egg and its contents: the miracidium, hatch fluid and secretions

The schistosome egg is the key agent responsible both for transmission of the parasite from human to molluscan host, and is the primary cause of pathogenesis in schistosomiasis. Characterisation of its proteome is a crucial step in understanding the egg's interactions with the mammalian host. We devised a scheme to isolate undeveloped eggs from mature schistosome eggs by Percoll gradient and then fractionate the mature egg into miracidial, hatch fluid and secreted protein preparations. The soluble proteins contained within the five preparations were separated by two-dimensional electrophoresis and their spot patterns compared by image analysis. Large numbers of representative spots were then excised and subjected to tandem mass spectrometry to obtain identities. In this way, the principal components of each sub-proteome were established. Chaperones were the most abundant category, with heat shock protein 70 (HSP70) dominant in the undeveloped egg and Schistosoma mansoni protein 40 (Smp-40) in the miracidium. Cytoskeletal proteins were expressed at similar levels in the undeveloped egg and miracidium, with tubulins the most abundant. The proteins of energy metabolism reflected the change from anaerobic to aerobic metabolism as the miracidium developed. None of the above categories was abundant in the hatch fluid but this peri-miracidial compartment was highly enriched for defence proteins such as thioredoxin. Hatch fluid also contained several host proteins and schistosome proteins of unknown function, highlighting its distinct nature and potentially its role. The egg secretions could not be compared with the other preparations due to their unique composition featuring the previously characterised IL-4-inducing principal of S. mansoni eggs (IPSE), Omega-1, egg secreted protein 15 (ESP15), a micro-exon gene 2 (MEG-2) protein and two members of the recently described MEG-3 family. This last preparation contains the subset of egg proteins that probably enables eggs to escape from host tissues and may also initiate granuloma formation, emphasising the need to establish fully the roles of its components in schistosome biology.

Schistosoma genomics: new perspectives on schistosome biology and host-parasite interaction

Schistosomiasis, caused mainly by Schistosoma japonicum, S. mansoni, and S. hematobium, remains one of the most prevalent and serious parasitic diseases worldwide. The blood flukes have a complex life cycle requiring adaptation for survival in fresh water as free-living forms and as parasites in snail intermediate and vertebrate definitive hosts. Functional genomics analyses, including transcriptomic and proteomic approaches, have been performed on schistosomes, in particular S. mansoni and S. japonicum, using powerful high-throughput methodologies. These investigations have not only chartered gene expression profiles across genders and developmental stages within mammalian and snail hosts, but have also characterized the features of the surface tegument, the eggshell and excretory-secretory proteomes of schistosomes. The integration of the genomic, transcriptomic, and proteomic information, together with genetic manipulation on individual genes, will provide a global insight into the molecular architecture of the biology, pathogenesis, and host-parasite interactions of the human blood flukes. Importantly, these functional genomics analyses lay a foundation on which to develop new antischistosome vaccines as well as drug targets and diagnostic markers for treatment and control of schistosomiasis.

The embryonic development of Schistosoma mansoni eggs: proposal for a new staging system

Schistosomiasis is a water-borne parasitic illness caused by neoophoran trematodes of the genus Schistosoma. Using classical histological techniques and whole-mount preparations, the present work describes the embryonic development of Schistosoma mansoni eggs in the murine host and compares it with eggs maintained under in vitro conditions. Two pre-embryonic stages occur inside the female worm: the prezygotic stage is characterized by the release of mature oocytes from the female ovary until its fertilization. The zygotic stage encompasses the migration of the zygote through the ootype, where the eggshell is formed, to the uterus. Fully formed eggs are laid still undeveloped, without having suffered any cleavage. In the outside environment, eight embryonic stages can be defined: stage 1 refers to early cleavages and the beginning of yolk fusion. Stage 2 represents late cleavage, with the formation of a stereoblastula and the onset of outer envelope differentiation. Stage 3 is defined by the elongation of the embryonic primordium and the onset of inner envelope formation. At stage 4, the first organ primordia arise. During stages 5 to 7, tissue and organ differentiation occurs (neural mass, epidermis, terebratorium, musculature, and miracidial glands). Stage 7 is characterized by the nuclear condensation of neurons of the central neural mass. Stage 8 refers to the fully formed larva, presenting muscular contraction, cilia, and flame-cell beating. This staging system was compared to a previous classification and could underlie further studies on egg histoproteomics (morphological localizome). The differentiation of embryonic structures and their probable roles in granulomatogenesis are discussed herein.

Peroxiredoxin-1 from Schistosoma japonicum functions as a scavenger against hydrogen peroxide but not nitric oxide

Three peroxiredoxins (Prxs) are expressed during most of the developmental stages in the schistosome. Prx-1 is localized on the surface of the schistosomula and adults of Schistosoma japonicum, while Prx-2 is localized in the sub-tegumental tissues, parenchyma, vitelline glands, and gut epithelium, but not on the surface of the worms. We applied RNA interference techniques to suppress the specific genes of S. japonicum Prxs. Schistosomula of S. japonicum were cultured together with long-dsRNA encoding Prx-1 and Prx-2 of S. japonicum (the soaking method). The transcription level of each Prx gene was reduced by an RNA interference (RNAi)-mediated effect specifically. Although neither Prx was the essential protein for survival of S. japonicum schistosomula, Prx-1 dsRNA-treated larvae were susceptible to hydrogen peroxide. Moreover, these larvae were also susceptible to t-butyl hydroperoxide and cumene-hydroperoxide. However, the knockdown of neither Prx-1 nor Prx-2 influenced the resistance against nitric oxide generated from DETA/NO. Prx-1 may work as a scavenger against reactive oxygen species (ROS) generated outside of the schistosomes to prevent the oxidation of the bodies and/or the attack by immune cells producing the ROS. These findings suggest that Prx-1 may become a novel target of drugs and vaccines for schistosomiasis.

Helminth 2-Cys peroxiredoxin drives Th2 responses through a mechanism involving alternatively activated macrophages

During helminth infections, alternatively activated macrophages (AAMacs) are key to promoting Th2 responses and suppressing Th1-driven inflammatory pathology. Th2 cytokines IL-4 and/or IL-13 are believed to be important in the induction and activation of AAMacs. Using murine models for the helminth infections caused by Fasciola hepatica (Fh) and Schistosoma mansoni (Sm), we show that a secreted antioxidant, peroxiredoxin (Prx), induces alternative activation of macrophages. These activated, Ym1-expressing macrophages enhanced the secretion of IL-4, IL-5, and IL-13 from naive CD4(+) T cells. Administration of recombinant FhPrx and SmPrx to wild-type and IL-4(-/-) and IL-13(-/-) mice induced the production of AAMacs. In addition, Prx stimulated the expression of markers of AAMacs (particularly, Ym1) in vitro, and therefore can act independently of IL-4/IL-13 signaling. The immunomodulatory property of Prx is not due to its antioxidant activity, as an inactive recombinant variant with active site Cys residues replaced by Gly could also induce AAMacs and Th2 responses. Immunization of mice with recombinant Prx or passive transfer of anti-Prx antibodies prior to infection with Fh not only blocked the induction of AAMacs but also the development of parasite-specific Th2 responses. We propose that Prx activates macrophages as an initial step in the induction of Th2 responses by helminth parasites and is thereby a novel pathogen-associated molecular pattern.

Thioredoxin peroxidase from Echinococcus granulosus: a candidate to extend the antigenic panel for the immunodiagnosis of human cystic echinococcosis

The currently available tests for the diagnosis of cystic echinococcosis (CE), enzyme-linked immunosorbent assay (ELISA), and immunoblotting (IB) lack sensitivity and specificity, and antigen panels need standardizing. By screening an Echinococcus granulosus cDNA library with IgG1 from patients with CE, we identified E. granulosus thioredoxin peroxidase (EgTPx). Although IB and ELISA achieved the same specificity (92%), ELISA showed higher sensitivity than IB (83% versus 42%) in determining total immunoglobulin G (IgG) specific to EgTPx in CE sera. The percentage of total IgG- and IgG1-positive sera in ELISA was equally distributed in patients with active, transitional, and inactive disease. Conversely, the percentages of IgG4-positive sera were significantly higher in sera from patients with active than inactive disease (P = 0.03). Our data suggest that adding this highly specific recombinant antigen to the standard diagnostic panel of antigens used in ELISA would increase diagnostic sensitivity. Antibodies specific to EgTPx are of potential interest in the host-parasite relationship.

Profiling Schistosoma mansoni development using serial analysis of gene expression (SAGE)

Despite the widespread use of chemotherapy and other control strategies over the past 50years, transmission rates for schistosomiasis have changed little. Regardless of the approach used, future control efforts will require a more complete understanding of fundamental parasite biology. Schistosomes undergo complex development involving an alteration of parasite generations within a mammalian and freshwater molluscan host in the completion of its lifecycle. Little is known about factors controlling schistosome development, but understanding these processes may facilitate the discovery of new control methods. Therefore, our goal in this study is to determine global developmentally regulated and stage-specific gene expression in Schistosoma mansoni using serial analysis of gene expression (SAGE). We present a preliminary analysis of genes expressed during development and sexual differentiation in the mammalian host and during early larval development in the snail host. A number of novel, differentially expressed genes have been identified, both within and between the different developmental stages found in the mammalian and snail hosts.

Antioxidant gene expression and function in in vitro-developing Schistosoma mansoni mother sporocysts: possible role in self-protection

The ability of the larval forms of Schistosoma mansoni to invade and parasitize their molluscan host, Biomphalaria glabrata, is determined by a multitude of factors. In this study we sought to elucidate the possible mechanisms by which the invading larvae are able to counteract the potentially harmful oxidative environment presented by the host upon initial miracidial infection. This was attempted by examining the gene expression profile of parasite antioxidant enzymes of the linked glutathione-(GSH) thioredoxin (Trx) redox pathway during early intramolluscan larval development. Three such enzymes, the peroxiredoxins (Prx1, Prx2 and Prx3) were examined as to their activity and sites of expression within S. mansoni miracidia and in vitro-cultured mother sporocysts. Results of these studies demonstrated that the H(2)O(2)-reducing enzymes Prx1 and 2 are upregulated during early mother sporocyst development compared to miracidia. Immunolocalization studies further indicated that Prx1 and Prx2 proteins are expressed within the apical papillae of miracidia and tegumental syncytium of sporocysts, and are released with parasite excretory-secretory proteins (ESP) during in vitro larval transformation. Removal of Prx1 and Prx2 from larval ESP by immunoabsorption significantly reduced the ability of ESP to breakdown exogenous H(2)O(2), thereby directly linking ESP Prx proteins with H(2)O(2)-scavenging activity. Moreover, exposure of live sporocysts to exogenous H(2)O(2)stimulated an upregulation of Prx1 and 2 gene expression suggesting the involvement of H(2)O(2)-responsive elements in regulating larval Prx gene expression. These data provide evidence that Prx1 and Prx2 may function in the protection of S. mansoni sporocysts during the early stages of infection.

2-Cys peroxiredoxins from Schistosoma japonicum: The expression profile and localization in the life cycle

Peroxiredoxin (Prx) is known to be an antioxidant protein that protects the organisms against various oxidative stresses and functions as a signal transductor. Here, we determined the full-length cDNA sequences of three types of Prx from an Asian blood fluke, Schistosoma japonicum: Prx-1, Prx-2 and Prx-3. According to the deduced amino acid sequences, only Prx-3 had a mitochondria-targeting sequence. Using RT-PCR, it was shown that these Prx genes were constitutively expressed in the eggs, cercariae and adult worms of the schistosome. Western blot analysis using antisera specific for each Prx revealed that all the three Prx proteins existed in these developmental stages. By immunolocalization analysis, Prx-1 existed on the surface of a miracidium and in the space between a miracidium and an eggshell. Furthermore, Prx-1 was deposited in the host tissues around the eggs. In adult worms, Prx-1 was not only expressed in the tegument, but also contained in their excretory/secretory products. The surface of the 7 day-schistosomula was stained with anti-Prx-1 antiserum. On the other hand, Prx-2 only existed inside the miracidia in eggs. In addition, Prx-2 was mainly detected in the sub-tegumental tissues, parenchyma, vitelline gland and gut epithelium of the adult worms, but was not detected in the tegument of adults and schistosomula. Taken together with previous reports by other investigators, these data suggest that Prx-1 acts to protect the parasite against the ROS produced by host immune cells, and that Prx-2 plays important roles in intracellular redox signaling and/or in the reduction of ROS generated through the hemoglobinolytic process in the digestive tract.

New perspectives on host-parasite interplay by comparative transcriptomic and proteomic analyses of Schistosoma japonicum

Schistosomiasis remains a serious public health problem with an estimated 200 million people infected in 76 countries. Here we isolated ~ 8,400 potential protein-encoding cDNA contigs from Schistosoma japonicum after sequencing circa 84,000 expressed sequence tags. In tandem, we undertook a high-throughput proteomics approach to characterize the protein expression profiles of a number of developmental stages (cercariae, hepatic schistosomula, female and male adults, eggs, and miracidia) and tissues at the host-parasite interface (eggshell and tegument) by interrogating the protein database deduced from the contigs. Comparative analysis of these transcriptomic and proteomic data, the latter including 3,260 proteins with putative identities, revealed differential expression of genes among the various developmental stages and sexes of S. japonicum and localization of putative secretory and membrane antigens, enzymes, and other gene products on the adult tegument and eggshell, many of which displayed genetic polymorphisms. Numerous S. japonicum genes exhibited high levels of identity with those of their mammalian hosts, whereas many others appeared to be conserved only across the genus Schistosoma or Phylum Platyhelminthes. These findings are expected to provide new insights into the pathophysiology of schistosomiasis and for the development of improved interventions for disease control and will facilitate a more fundamental understanding of schistosome biology, evolution, and the host-parasite interplay.

Schistosomiasis remains a major public health problem in the developing world. Schistosoma japonicum, the Oriental blood fluke, causes intestinal schistosomiasis in China and the Philippines. Knowledge of the genome and proteome of this worm should improve understanding of biomedical aspects of schistosomiasis. This study represents the first major attempt to characterize the majority of the expressed genes and proteins of a human blood fluke through rigorous, high-throughput genomic and proteomic methodologies. The findings of this study provide a unique resource of numerous schistosome genes and information on protein profiles of the different developmental stages of S. japonicum. Many of the newly discovered proteins are localized on the surface of the worm and its eggs, and they are likely to be involved in the pathogenesis of schistosomiasis. Furthermore, genetic variants found in many of these new genes likely reflect the ability of this important human pathogen to adapt and respond to environmental pressures and the capacity of the parasite to respond to anti-schistosomal therapies. Comparison of these S. japonicum genes with those from mammals and other organisms will facilitate advances in the understanding of blood fluke biology and evolution.

Redox balance mechanisms in Schistosoma mansoni rely on peroxiredoxins and albumin and implicate peroxiredoxins as novel drug targets

Schistosoma mansoni, a causative agent of schistosomiasis, resides in the hepatic portal circulation of their human host up to 30 years without being eliminated by the host immune attack. Production of an antioxidant "firewall," which would neutralize the oxidative assault generated by host immune defenses, is one proposed survival mechanism of the parasite. Schistosomes lack catalase, the main H2O2-neutralizing enzyme of many organisms, and their glutathione peroxidases are in the phospholipid class with poor reactivity toward H2O2. Evidence implicates peroxiredoxins (Prx) as providing the main enzymatic activity to reduce H2O2 in the parasite. Quantitative monitoring of Prx mRNAs during parasite life cycle indicated that Prx proteins are differentially expressed, with highest expression occurring in adult stages (oxidative resistant stages). Incubation of schistosomula with Prx1 double-stranded RNA knocked down total Prx enzymatic activity and resulted in lowered survival of cultured parasites compared with controls demonstrating that Prx are essential parasite proteins. These results represent the first report of lethal gene silencing in Schistosoma. Investigation of downstream effects of Prx silencing revealed an abrupt increase of lipid peroxides and the generation of several oxidized proteins. Using mass spectrometry, parasite albumin and actin were identified as the main oxidized proteins. Gene expression analysis showed that schistosome albumin was induced by oxidative stress. This study highlights Prx proteins as essential parasite proteins and potential new targets for anti-schistosome drug development and albumin as a novel, sacrificial oxidant scavenging protein in parasite redox regulation.

Murine immune responses to a novel schistosome egg antigen, SmEP25

Pathology in schistosomiasis consists of granuloma formation around parasite eggs. There is considerable variation in the severity of disease in individuals with schistosomiasis, which may result from differential responses to egg antigens. The egg-induced immunopathology is mediated by CD4+ T helper cells sensitised to egg antigens. In this study, cellular responses to a 25-kDa fraction of egg proteins identified a novel T-cell antigen, SmEP25. The native SmEP25 elicited significant proliferative responses as well as gamma interferon (IFN-gamma), IL-2, IL-4, and IL-5 secretion in CD4+ cells from 8.5-week infected CBA and C57BL/6 mice. In C57BL/6 mice, proliferative responses to SmEP25 were relatively stronger than those directed against the major egg antigen Sm-p40, whereas in CBA mice the reverse was found. SmEP25 elicited stronger Th2 type response than Sm-p40 in both mouse strains. By comparison, recombinant SmEP25 elicited a smaller, Th1-polarised response, with significant IFN-gamma, low levels of IL-5 and essentially no IL-4. B-cell responses to SmEP25 coincided with the start of parasite egg production and SmEP25 protein was restricted to parasite eggs. The systematic identification of T-cell-sensitising egg components will lead to a better understanding of the processes involved in granuloma formation.

An unusual surface peroxiredoxin protects invasive Entamoeba histolytica from oxidant attack

Peroxiredoxins are an important class of antioxidant enzymes found from Archaea to humans, which reduce and thereby detoxify peroxides and peroxynitrites. The major thiol-containing surface antigen of the invasive ameba, Entamoeba histolytica, is a peroxiredoxin and is likely to be important during the transition from the anaerobic environment of the large intestine to human tissues. The closely related species, Entamoeba dispar, is incapable of invasion and more sensitive to hydrogen peroxide, yet also has a peroxiredoxin. We cloned and expressed the two active recombinant enzymes and found that their activity was similar by a fluorometric stopped-flow assay, giving a Km of <10 microM for hydrogen peroxide. Three monoclonal antibodies produced to recombinant E. histolytica peroxiredoxin cross-reacted with Entamoeba dispar.E. histolytica contains as much as 50 times more peroxiredoxin than E. dispar as demonstrated by a sensitive capture ELISA. In addition, the peroxiredoxin is present largely on the outer surface of the cell, in contrast to E. dispar. This unusual peroxiredoxin localizes to the site of parasite-host cell contact where it can effectively counteract oxidants generated by host cells, thus facilitating invasion.

Expansion of CD4 T cells expressing a highly restricted TCR structure specific for a single parasite epitope correlates with high pathology in murine schistosomiasis

The hepatic immunopathology in schistosomiasis mansoni is mediated by CD4 T cells specific for egg antigens and varies considerably among mouse strains. Previous studies in high pathology C3H mice suggested that a strong T cell response was due to the recognition of an immunodominant epitope within the major egg antigen Sm-p40 (Sm-p40(234-246)). Using a panel of T cell hybridomas, we have now examined the egg antigen-specific TCR repertoire in two high pathology strains, C3H and CBA. We found that nearly half of the hybridomas responded to the Sm-p40(234-246 )epitope and, of these, nearly all expressed Valpha11.3 associated with Vbeta8. Furthermore, in response to egg antigen stimulation, transcript levels of Valpha11.3J36 (the most prevalent rearrangement expressed by Sm-p40(234-246)-specific hybridomas), increased in high pathology (CBA) but not in low pathology BALB/c strains. Our findings suggest that exacerbated schistosome egg-induced immunopathology can be driven by T cells expressing a highly restricted TCR structure specific for a single parasite epitope.

Evaluation of CD4(+)/CD8(+) status and urinary tract infections associated with urinary schistosomiasis among some rural Nigerians

BACKGROUND

Data on urinary schistosomiasis in Nigeria are mainly epidemological. The knowledge of co-infections of urinary schistosomiasis and other pathogens are important epidemiological tools for the control and health benefits of the rural dwellers. The granulomatous reactions in urinary schistosomiasis is CD4(+) dependent. The CD8(+) is cytotoxic to parasites and it is activated by CD4(+). These parameters therefore participate in the immune responses to urinary schistosomiasis.

OBJECTIVE

In this study, we evaluated the polyparasitism involving urinary schistosomiasis and urinary tract co - infections among some rural Nigerians. The CD4(+):CD8(+) ratio and status with age groups in years were also investigated.

METHODS

Parasitological investigation using ova on urine was carried out on 216 volunteers. The urine samples were examined for bacteriuria and subsequently subjected to standard microbiological urine culture. CD4(+)/CD8(+) were determined using the CD T 4 Dynabead techniques. Data were analysed using MicroSoft Excel.

RESULTS

The inhabitants with light infections of urinary schistosomiasis as indicated by <50 ova /10 ml of urine had a mean CD4(+):CD8(+) ratio of 1.57 while those with heavy infections as shown by >50 ova/10 ml of urine had a relatively lower CD4(+):CD8(+) ratio of 1.03. In all, the overall CD4+:CD8+ ratio of 1.23 was recorded with the mean CD4+ count of 257.96 cells/microL and the mean CD8(+) count of 210.45 cells/microL. Comparatively, the control uninfected subjects had a CD4(+):CD8(+) ratio of 5.97. The CD4(+) and the CD8(+) counts were correlated with the ova of S. haematobium in their urine samples at r = 0.0108 and r = 0.516 respectively. The bacteriuria, urinary schistosomiasis and urinary tract co-infections, namely: Escherichia coli, Proteus, Pseudomonas aeroginosa, Staphylococcus epidermidis and Staph. Saprophyticus were reported in the urine cultures of 48(22.0%) volunteers.

CONCLUSION

The mean overall CD4(+):CD8(+) ratio of urinary schistosomiasis infected persons is 1.23 which is above the normal CD4(+):CD8(+) ratio of 1. The CD4(+):CD8(+) ratio and counts of the urinary schistosomiasis infected inhabitants were lower than the uninfected inhabitants. The positive correlation between the CD4(+):CD8(+) and the S. haematobium ova shows a relationship which indicate an increase of the CD4(+):CD8(+) as the intensity of infection increases. We report polyparasitism of S. haematobium and urinary tracts co-infections among some rural inhabitants in Ikpeshi, Nigeria. It is therefore imperative to incorporate the management of urinary tract infections in urinary schistosomiasis control programme.

Thioredoxin peroxidase secreted by Fasciola hepatica induces the alternative activation of macrophages

Alternatively activated macrophages (AAMphi) are primarily associated with the chronic stages of parasitic infections and the development of a polarized Th2 response. We have shown that Fasciola hepatica infection of BALB/c mice induces a polarized Th2 response during both the latent and chronic stage of disease. The activation status of macrophages was analyzed in this model of helminth infection by evaluating the expression of genetic markers of alternative activation, namely, Fizz1, Ym1, and Arg1. AAMphi were recruited to the peritoneum of mice within 24 h of F. hepatica infection and after intraperitoneal injection of parasite excretory-secretory (ES) products. Administration of a recombinant antioxidant thioredoxin peroxidase (TPx), which is contained within the ES products, also induced the recruitment of AAMphi to the peritoneum. In vitro studies showed that this recombinant TPx directly converts RAW 264.7 macrophages to an alternatively activated phenotype characterized by the production of high levels of interleukin-10 (IL-10), prostaglandin E(2), corresponding with low levels of IL-12. Our data suggest that the Th2 responses induced by the helminth F. hepatica are mediated through the secretion of molecules, one of which is TPx, that induce the recruitment and alternative activation of macrophages.

The immunobiology of Th1 polarization in high-pathology schistosomiasis

Schistosomiasis is a serious global helminthic disease, in which the main immunopathology consists of a granulomatous and fibrosing reaction against tissue-trapped parasite eggs. The severity of this inflammatory process, the product of a CD4(+) T-cell-mediated immune response against parasite egg antigens, is, however, markedly uneven, both in human patients and among mouse strains in an experimental model. Severe schistosomiasis is associated with persistently elevated pro-inflammatory T-helper-1 (Th1)-type cytokines, whereas milder pathology is present when Th2 cytokines dominate. This scenario is supported by the pronounced pathology resulting from the obliteration of pathways that facilitate Th2 differentiation and by the development of more intense lesions in mouse strains that fail to downregulate the Th1 response. Genetically prone high-pathology mice have a higher proportion of CD4(+) T cells in lymph nodes and granulomas, in which the Th1 phenotype is driven by interleukin-12; they also develop a dominant repertoire against peptide 234-246 of the major Sm-p40 egg antigen, utilizing a strikingly restricted T-cell receptor structure that involves Valpha11.3beta8. In turn, low-pathology mice exhibit enhanced CD4(+) T-cell apoptosis, which contributes to limit pathology. The definition of distinctive immune profiles associated with polar forms of schistosomiasis opens opportunities for targeted immuno-intervention in individuals suffering from or at risk of severe disease.

Novel phage display-based subtractive screening to identify vaccine candidates of Brugia malayi

This study describes a novel phage display method based on an iterative subtraction strategy to identify candidate vaccine antigens of Brugia malayi. A cDNA library of the infective larval stage of B. malayi expressed on the surface of T7 phage was sequentially screened with sera samples from human subjects showing different manifestations of the disease. Antigens that selectively and specifically bind to immune sera were then enriched using a multi-step panning procedure. This strategy identified five antigens, four of which were previously reported (ALT-2, TPX-2, VAH and COX-2) and the other one was a novel cuticular collagen (Col-4). Sera from immune individuals specifically recognized all the five antigens. However, ALT-2 appeared to be the most predominantly recognized antigen by the immune sera. Therefore, it was decided to evaluate the vaccine potential of recombinant ALT-2 (rALT-2) in a mouse and jird model. The results presented show that immunization with rALT-2 conferred over 73% protection against a challenge infection in the jird model and over 64% protection in the mouse model. The present study suggests that phage display-based cDNA screening may be a powerful tool to identify candidate vaccine antigens of infectious agents.

Overview: from the horse experimentation by Prof. Akira Fujinami to paramyosin

Professor Akira Fujinami demonstrated for the first time in the world that acquired immunity might be induced against macroparasites such as schistosomes. Since then, vaccination models have been developed using various species of animals, among which the attenuated vaccine model in the mouse has been utilized mostly to clarify immune effector mechanisms and define candidate vaccine molecules. However, further studies are necessary on immune responses to defined parasite molecules in humans, because some discrepancies in immune responses still exist between animals and humans, and apparently genetic influence should be taken into consideration in such studies on defined molecules. Despite of some limitations, vaccine trials in livestock against Schistosoma japonicum may provide useful information for development of vaccines against the other human infections caused by S. mansoni or S. haematobium. In this overview, studies carried out mainly by Japanese investigators towards vaccine development will be described.

Linked thioredoxin-glutathione systems in platyhelminths

The thioredoxin and glutathione systems play a central role in thiol-disulfide redox homeostasis in many organisms by providing electrons to essential enzymes, and defence against oxidative stress. These systems have recently been characterized in platyhelminth parasites, and the emerging biochemical scenario is the existence of linked processes with the enzyme thioredoxin glutathione reductase supplying reducing equivalents to both pathways. In contrast to their hosts, conventional thioredoxin reductase and glutathione reductase enzymes appear to be absent. Analysis of published data and expressed-sequence tag databases indicates the presence of linked thioredoxin-glutathione systems in the cytosolic and mitochondrial compartments of these parasites.

Biochemical characterization of 2-Cys peroxiredoxins from Schistosoma mansoni

Peroxiredoxins are a large family of peroxidases that have important antioxidant and cell signaling functions. Genes encoding two novel 2-cysteine peroxiredoxin proteins were identified in the expressed sequence tag data base of the helminth parasite Schistosoma mansoni, a causative agent of schistosomiasis. The recombinant proteins showed peroxidase activity in vitro with a variety of hydroperoxides and used both the thioredoxin and the glutathione systems as electron donors. Steady-state kinetic analysis indicated that the new peroxiredoxins had saturable kinetics, whereas a previously identified schistosome peroxiredoxin was found to function with more typical unsaturable (ping-pong) kinetics. The catalytic efficiencies S. mansoni peroxiredoxins were similar to those for other peroxiredoxins studied (10(4)-10(5) m(-1) s(-1)). Mutagenesis of S. mansoni peroxiredoxins indicated that glutathione dependence and kinetic differences were conferred by the C-terminal alpha-helix forming 22 amino acids. This is the first report of 2-cysteine peroxiredoxins efficiently utilizing reducing equivalents from both the thioredoxin and glutathione systems. Studies to determine the resistance to oxidative inactivation, important in regulating cell signaling pathways, showed that S. mansoni possess both bacterial-like resistant and mammalian-like sensitive peroxiredoxins. The susceptibility to oxidative inactivation was conferred by the C-terminal tail containing a tyrosine-phenylalanine motif. S. mansoni is the first organism shown to possess both robust and sensitive peroxiredoxins. The ability of schistosome peroxiredoxins to use alternative electron donors, and their variable resistance to overoxidation may reflect their presence in different cellular sites and emphasizes the significant differences in overall redox balance mechanisms between the parasite and its mammalian host.

Analysis of egg antigens inducing hepatic lesions in schistosome infection

In schistosomiasis, granuloma formation to parasite eggs signals the beginning of a chronic and potentially life-threatening disease. Granulomas are strictly mediated by CD4+ T helper (Th) cells specific for egg antigens; however, the number and identity of these T cell-sensitizing molecules are largely unknown. We have used monoclonal T cell reagents as probes to track down, isolate and positively identify several egg antigens; this approach implicitly assures that the molecules of interest are T cell immunogens and, hence, potentially pathogenic. The best-studied egg component is the Sm-p40 antigen. Sm-p40 elicits a strikingly immunodominant Th-1-polarized response in C3H and CBA mice, which are characterized by severe egg-induced immunopathology. Two additional described T cell-sensitizing egg antigens are Schistosoma mansoni phosphoenolpyruvate carboxykinase (Sm-PEPCK) and thioredoxin peroxidase-1 (Sm-TPx-1). In contrast to Sm-p40, both of these molecules induce a more balanced Th-1/Th-2 response, and are relatively stronger antigens in C57BL/6 mice, which develop smaller egg granulomas. Other components, including moieties with molecular weights of 25 kDa (Sm-p25), 150/166 kDa (Sm-p155/166), and 29 kDa (Sm-GST29), are also found to stimulate specific T cells. These findings in the murine model introduce the important notion that egg antigens can vary significantly in immunogenicity according to the host's genetic background. A better knowledge of the principal immunogenic egg components is necessary to ascertain whether such responses can be manipulated for the purpose of reducing pathology.

Differential production in vitro of antigen specific IgG1, IgG3 and IgA: a study in Schistosoma haematobium infected individuals

This study has evaluated the individual control of isotype production and the influence of external signals that can be experimentally provided in vitro, in antibody responses to two different recombinant Schistosoma antigens (Sh28GST and TPx-1). Peripheral blood mononuclear cells or enriched B cell fractions obtained from S. haematobium infected Senegalese adults were induced to terminal differentiation in vitro. The production of antibody to either antigen was donor-dependent and for each donor it was antigen-dependent. Differentiation to IgG1 and IgG3 production, and possibly IgA, specific to these conserved parasite antigens could be regulated differentially in vitro. Exogenous IL-2 and IL-10 or IL-10 and TGF-beta led to the production of specific IgG3 or IgG1 and/or IgA, respectively. This is the first report on such experimentally induced differential regulation of antigen-specific IgG1 and IgG3. This may have implications in designing protocols for protein based-vaccinations aiming at eliciting antibody responses of certain protective-type isotypes.

Molecular and enzymatic characterisation of Schistosoma mansoni thioredoxin

Defense against oxidative damage can be mediated through glutathione and/or thioredoxin utilising systems. Here, we report the identification and characterisation of a thioredoxin from Schistosoma mansoni. The predicted protein has similarity to previously characterised thioredoxins including conservation of the redox active site. Recombinant six-histidine tagged schistosome thioredoxin had insulin reduction activity and supported the enzymatic function of thioredoxin reductase and thioredoxin peroxidase. By Western blotting, all mammalian stages of the schistosome lifecycle expresses thioredoxin. Thioredoxin is present in egg secretory products and antibodies against the recombinant protein produce the circumoval precipitin reaction. This is the first identification of defined antigen producing this reaction. Furthermore, thioredoxin is a novel egg immunogen as it elicits an antibody response in schistosome-infected mice. The most significant IgG production against thioredoxin occurs after parasite oviposition commences. These observations suggest that thioredoxin participates in processes vital to the parasite and may facilitate the passage and survival of eggs across inflamed host tissues.

The immunobiology of schistosomiasis

Schistosomes are parasitic worms that are a prime example of a complex multicellular pathogen that flourishes in the human host despite the development of a pronounced immune response. Understanding how the immune system deals with such pathogens is a daunting challenge. The past decade has seen the use of a wide range of new approaches to determine the nature and function of the immune response to schistosomes. Here, we attempt to summarize advances in our understanding of the immunology of schistosomiasis, with the bulk of the review reflecting the experimental focus on Schistosoma mansoni infection in mice.

The disulfide redox system of Schistosoma mansoni and the importance of a multifunctional enzyme, thioredoxin glutathione reductase

Schistosoma mansoni, a causative agent of schistosomiasis, is a major cause of human morbidity in tropical countries. Adult schistosomes, which reside in the hepatic portal system, are exposed to reactive oxygen compounds through respiration and as a result of the host immune response. To minimize oxidative stress schistosomes must possess adequate mechanisms of detoxification. Major detoxification systems rely on reducing equivalents from the disulfide oxidoreductases glutathione and thioredoxin. Therefore, maintenance of adequate levels of these thiols in a reduced form is critical. Here we show that S. mansoni possess an unusual thiol redox system centered on thioredoxin glutathione reductase. This enzyme represents an unusual fusion of a pyridine nucleotide disulfide oxidoreductase with a redox active glutaredoxin extension. Furthermore, we predict that this is a selenocysteine protein. Immunoprecipitation, western blot and inhibitor studies show that this protein has thioredoxin reductase, glutathione reductase, and glutaredoxin activities. Most importantly, we show that thioredoxin glutathione reductase appears to be the major, if not the sole enzyme for these activities in adult worms, completely replacing thioredoxin reductase and glutathione reductase. This is the first example of an organism with a redox system based exclusively on thioredoxin glutathione reductase.

The identification and characterization of new immunogenic egg components: implications for evaluation and control of the immunopathogenic T cell response in schistosomiasis

In schistosomiasis, granuloma formation to parasite eggs signals the beginning of a chronic and potentially life-threatening disease. Granulomas are strictly mediated by CD4+ T helper (Th) cells specific for egg antigens; however, the number and identity of these T cell-sensitizing molecules are largely unknown. We have used monoclonal T cell reagents derived from egg-sensitized individuals as probes to track down, isolate and positively identify several egg antigens; this approach implicitly assures that the molecules of interest are T cell immunogens and, hence, potentially pathogenic. The best studied and most abundant egg component is the Sm-p40 antigen. Sm-p40 and its peptide 234-246 elicit a strikingly immunodominant Th-1-polarized response in C3H and CBA mice, which are H-2k strains characterized by severe egg-induced immunopathology. Two additional recently described T cell-sensitizing egg antigens are Schistosoma mansoni phosphoenolpyruvate carboxykinase (Sm-PEPCK) and thioredoxin peroxidase-1 (Sm-TPx-1). In contrast to Sm-p40, both of these molecules induce a more balanced Th-1/Th-2 response, and are relatively stronger antigens in C57BL/6 mice, which develop smaller egg granulomas. Importantly, Sm-p40 and Sm-PEPCK have demonstrated immunogenicity in humans. The findings in the murine model introduce the important notion that egg antigens can vary significantly in immunogenicity according to the host's genetic background. A better knowledge of the principal immunogenic egg components is necessary to determine whether the immune responses to certain antigens can serve as indicators or predictors of the form and severity of clinical disease, and to ascertain whether such responses can be manipulated for the purpose of reducing pathology.