The schistosome in the mammalian host: understanding the mechanisms of adaptation

Can antibody conjugated nanomicelles alter the prospect of antibody targeted therapy against schistosomiasis mansoni?

BACKGROUND

CLA (conjugated linoleic acid)-mediated activation of the schistosome tegument-associated sphingomyelinase and consequent disruption of the outer membrane might allow host antibodies to access the apical membrane antigens. Here, we investigated a novel approach to enhance specific antibody delivery to concealed surface membrane antigens of Schistosoma mansoni utilising antibody-conjugated-CLA nanomicelle technology.

METHODOLOGY/PRINCIPAL FINDINGS

We invented and characterised an amphiphilic CLA-loaded whey protein co-polymer (CLA-W) as an IV injectable protein nanocarrier. Rabbit anti-Schistosoma mansoni infection (anti-SmI) and anti-Schistosoma mansoni alkaline phosphatase specific IgG antibodies were purified from rabbit sera and conjugated to the surface of CLA-W co-polymer to form antibody-conjugated-CLA-W nanomicelles (Ab-CLA-W). We investigated the schistosomicidal effects of CLA-W and Ab-CLA-W in a mouse model of Schistosoma mansoni against early and late stages of infection. Results showed that conjugation of nanomicelles with antibodies, namely anti-SmI, significantly enhanced the micelles' schistosomicidal and anti-pathology activities at both the schistosomula and adult worm stages of the infection resulting in 64.6%-89.9% reductions in worm number; 72.5-94% and 66.4-85.2% reductions in hepatic eggs and granulomas, respectively. Treatment induced overall improvement in liver histopathology, reducing granuloma size and fibrosis and significantly affecting egg viability. Indirect immunofluorescence confirmed CLA-W-mediated antigen exposure on the worm surface. Electron microscopy revealed extensive ultrastructural damage in worm tegument induced by anti-SmI-CLA-W.

CONCLUSION/SIGNIFICANCE

The novel antibody-targeted nano-sized CLA delivery system offers great promise for treatment of Schistosoma mansoni infection and control of its transmission. Our in vivo observations confirm an immune-mediated enhanced effect of the schistosomicidal action of CLA and hints at the prospect of nanotechnology-based immunotherapy, not only for schistosomiasis, but also for other parasitic infections in which chemotherapy has been shown to be immune-dependent. The results propose that the immunodominant reactivity of the anti-SmI serum, Schistosoma mansoni fructose biphosphate aldolase, SmFBPA, merits serious attention as a therapeutic and vaccine candidate.

Excretory/Secretory Products from Schistosoma japonicum Eggs Alleviate Ovalbumin-Induced Allergic Airway Inflammation

INTRODUCTION

Excretory/secretory products (ESPs) derived from helminths have been reported to effectively control allergic inflammation, which have better therapeutic prospects than live parasite infections. However, it remains unknown whether ESPs from schistosome eggs can protect against allergies, despite reports alleging that schistosome infection could alleviate disordered allergic inflammation.

METHOD

In the present study, we investigated the protective effects of ESPs from Schistosoma japonicum eggs (ESP-SJE) on asthmatic inflammation. Firstly, we successfully established an allergic airway inflammation model in mice by alum-adjuvanted ovalbumin (OVA) sensitization and challenge. ESP-SJE were administered intraperitoneally on days -1 and 13 (before sensitization), on day 20 (before challenge), and on days 21-24 (challenge phase).

RESULTS

The results showed that ESP-SJE treatment significantly reduced the infiltration of inflammatory cells, especially eosinophils into the lung tissue, inhibited the production of the total and OVA-specific IgE during OVA-sensitized and -challenged phases, respectively, and suppressed the secretion of Th2-type inflammatory cytokines (IL-4). Additionally, ESP-SJE treatment significantly upregulated the regulatory T cells (Tregs) in the lung tissue during OVA challenge. Furthermore, using liquid chromatography-mass spectrometry analysis and Treg induction experiments in vitro, we might identify nine potential therapeutic proteins against allergic inflammation in ESP-SJE. The targets of these candidate proteins included glutathione S-transferase, egg protein CP422 precursor, tubulin alpha-2/alpha-4 chain, actin-2, T-complex protein 1 subunit beta, histone H₄, whey acidic protein core region, and molecular chaperone HtpG.

CONCLUSION

Taken together, the results discussed herein demonstrated that ESP-SJE could significantly alleviate OVA-induced asthmatic inflammation in a murine model, which might be mediated by the upregulation of Treg in lung tissues that may be induced by the potential modulatory proteins. Therefore, potential proteins in ESP-SJE might be the best candidates to be tested for therapeutic application of asthma, thus pointing out to a possible new therapy for allergic airway inflammation.

Pattern recognition receptor signaling and innate immune responses to schistosome infection

Schistosomiasis remains to be a significant public health problem in tropical and subtropical regions. Despite remarkable progress that has been made in the control of the disease over the past decades, its elimination remains a daunting challenge in many countries. This disease is an inflammatory response-driven, and the positive outcome after infection depends on the regulation of immune responses that efficiently clear worms and allow protective immunity to develop. The innate immune responses play a critical role in host defense against schistosome infection and pathogenesis. Initial pro-inflammatory responses are essential for clearing invading parasites by promoting appropriate cell-mediated and humoral immunity. However, elevated and prolonged inflammatory responses against the eggs trapped in the host tissues contribute to disease progression. A better understanding of the molecular mechanisms of innate immune responses is important for developing effective therapies and vaccines. Here, we update the recent advances in the definitive host innate immune response to schistosome infection, especially highlighting the critical roles of pattern recognition receptors and cytokines. The considerations for further research are also provided.

Dynamic miRNA profile of host T cells during early hepatic stages of Schistosoma japonicum infection

Schistosomes undergo complicated migration in final hosts during infection, associated with differential immune responses. It has been shown that CD4⁺ T cells play critical roles in response to Schistosoma infections and accumulated documents have indicated that miRNAs tightly regulate T cell activity. However, miRNA profiles in host T cells associated with Schistosoma infection remain poorly characterized. Therefore, we undertook the study and systematically characterized T cell miRNA profiles from the livers and blood of S. japonicum infected C57BL/6J mice at 14- and 21-days post-infection. We observed 508 and 504 miRNAs, in which 264 miRNAs were co-detected in T cells isolated from blood and livers, respectively. The comparative analysis of T cell miRNAs from uninfected and infected C57BL/6J mice blood showed that miR-486b-5p/3p expression was significantly downregulated and linked to various T cell immune responses and miR-375-5p was highly upregulated, associated with Wnt signaling and pluripotency, Delta notch signaling pathways, etc. Whereas hepatic T cells showed miR-466b-3p, miR-486b-3p, miR-1969, and miR-375 were differentially expressed compared to the uninfected control. The different expressions of some miRNAs were further corroborated in isolated T cells from mice and in vitro cultured EL-4 cells treated with S. japonicum worm antigens by RT-qPCR and similar results were found. In addition, bioinformatics analysis combined with RT-qPCR validation of selected targets associated with the immune system and parasite-caused infectious disease showed a significant increase in the expression of Ctla4, Atg5, Hgf, Vcl and Arpc4 and a decreased expression of Fermt3, Pik3r1, Myd88, Nfkbie, Ppp1r12a, Ppp3r1, Nfyb, Atg12, Ube2n, Tyrobp, Cxcr4 and Tollip. Overall, these results unveil the comprehensive repertoire of T cell miRNAs during S. japonicum infection, suggesting that the circulatory (blood) and liver systems have distinct miRNAs landscapes that may be important for regulating T cell immune response. Altogether, our findings indicated a dynamic expression pattern of T cell miRNAs during the hepatic stages of S. japonicum infection.

Schistosomiasis mansoni: A new therapeutic target for ubiquinol, a natural inhibitor of neutral magnesium-dependent sphingomyelinase in murine model

Constituting the host-parasite interface and playing a censorious role in host immune response modulation and parasite survival, tegument represents a crucial target for many antischistosomal drugs. Sphingomyelin forms a stable outer leaflet of tegumental membrane-lipid bilayer. Neutral magnesium‏-dependent sphingomyelinase (Mg²⁺-nSMase) is a key enzyme in sphingomyelin breakdown was identified in schistosomes. We investigated the in vivo efficacy of ubiquinol, a natural inhibitor of Mg²⁺-nSMase, in free and niosomes-encapsulated forms, through five-day and 15-day regimens on the early and late Schistosoma mansoni parasitic stages, respectively, compared to PZQ. Oral administration of 300 mg/kg/day ubiquinol-encapsulated niosomes (U-N) showed significant deterioration of the parasitic growth and development in the term of reduction of lung schistosomula burden (39.12%), adult worm burden (50.81%), hepatic and intestinal tissue-egg counts (80.89% and 75.54%, respectively). PZQ and free ubiquinol regimens reported reductions in lung schistosomula counts (45.36% and 22.90%, respectively) and total worm burdens of 86.28% and 24.58%, respectively. U-N therapy revealed worms de-pairing and remarkable diminution in female worms' perimeters and fecundity. Scanning electron microscope revealed disruption of tegumental ridges with excessive longitudinal corrugation. Transmission electron microscope showed testicular and ovarian parenchymal degeneration, signs of immaturity and cell apoptosis. Indirect immunofluorescence assay approved parasite's tegumental changes. Remarkable reduction of granulomas size with amelioration of hepatic pathology and fibrosis were assumed to be attributed to the anti-inflammatory and anti-oxidant properties of ubiquinol. These findings with the drug safety profile suggest that U-N could be a promising candidate for a new antischistosomal drug development.

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.

Transcriptome of the parasitic flatworm Schistosoma mansoni during intra-mammalian development

Schistosomes are parasitic blood flukes that survive for many years within the mammalian host vasculature. How the parasites establish a chronic infection in the hostile bloodstream environment, whilst evading the host immune response is poorly understood. The parasite develops morphologically and grows as it migrates to its preferred vascular niche, avoiding or repairing damage from the host immune system. In this study, we investigated temporal changes in gene expression during the intra-mammalian development of Schistosoma mansoni. RNA-seq data were analysed from parasites developing in the lung through to egg-laying mature adult worms, providing a comprehensive picture of in vivo intra-mammalian development. Remarkably, genes involved in signalling pathways, developmental control, and adaptation to oxidative stress were up-regulated in the lung stage. The data also suggested a potential role in immune evasion for a previously uncharacterised gene. This study not only provides a large and comprehensive data resource for the research community, but also reveals new directions for further characterising host-parasite interactions that could ultimately lead to new control strategies for this neglected tropical disease pathogen.

Heat shock protein 70 (Hsp70) in Schistosoma mansoni and its role in decreased adult worm sensitivity to praziquantel

Schistosoma mansoni is the most common species causing schistosomiasis. It has a complex life cycle involving a vertebrate definitive host and a snail intermediate host of the genus Biomphalaria. Each stage encounters a plethora of environmental stresses specially heat stress. Another sort of stress arises from repeated exposure of the parasite to praziquantel (PZQ), the only drug used for treatment, which leads to the development of resistance in the fields and the labs. Heat shock protein 70 (Hsp70) is found in different developmental stages of S. mansoni. It is immunogenic and regulate cercarial invasion besides its chaperone function. In the Biomphalaria/S. mansoni interaction, epigenetic modulations of the Hsp70 gene underscore the susceptibility phenotype of the snail. Hsp70 is up-regulated in adult S. mansoni with decreased sensitivity to PZQ. This could be due to the induction of oxidative and endoplasmic reticulum stress, induction of apoptosis, exposure to the stressful drug pressure and increase influx of calcium ions. Up-regulation of Hsp70 might help the worm to survive the schistosomicidal effect of the drug mainly by dealing with misfolded proteins, inhibition of apoptosis, induction of autophagy, up-regulation of the P-glycoprotein transporter and attenuation of the signalling from G protein coupled receptors.

Long-term ethanol intake causes morphological changes in Schistosoma mansoni adult worms in mice

Schistosoma mansoni adult worms are extensively challenged by reactive oxygen species from intrinsic sources. However, the effects of extrinsic sources such as ethanol have not been looked at in schistosomes. We examined adult worms recovered from ethanol-consuming mice by light (LM), confocal (CM) and scanning electron microscopy (SEM) to address this question. Schistosomiasis-infected mice were orally gavaged with 18% (v/v) ethanol from 35 to 63 days post-infection, when they were euthanized. CM examination revealed reduced germ cells density (-36%, p = 0.0001) and sperm density (-58%, p = 0.0001) in testicular lobes, and immature cells in seminal vesicle compared to unexposed control worms. Female worms showed reduced density of vitellin glands (-71%, p = 0.0001), maturation of oocytes (-7%, p = 0.0071) and reduced spermatozoa density (-23%, p = 0.0002) within the seminal receptacle. SEM revealed remarkable damages in male's tegument, including tubercles flattening, tegumental peeling and erosive lesions. Given that lipids are present in reproductive system and tegument, our results suggest that phenotypic changes are due to ethanol-induced lipid peroxidation. To the best of our knowledge, this is the first report revealing the biological action of ethanol intake on adult schistosomes in vivo.

Glycans in the roles of parasitological diagnosis and host-parasite interplay

The investigation of the glycan repertoire of several organisms has revealed a wide variation in terms of structures and abundance of glycan moieties. Among the parasites, it is possible to observe different sets of glycoconjugates across taxa and developmental stages within a species. The presence of distinct glycoconjugates throughout the life cycle of a parasite could relate to the ability of that organism to adapt and survive in different hosts and environments. Carbohydrates on the surface, and in excretory-secretory products of parasites, play essential roles in host-parasite interactions. Carbohydrate portions of complex molecules of parasites stimulate and modulate host immune responses, mainly through interactions with specific receptors on the surface of dendritic cells, leading to the generation of a pattern of response that may benefit parasite survival. Available data reviewed here also show the frequent aspect of parasite immunomodulation of mammalian responses through specific glycan interactions, which ultimately makes these molecules promising in the fields of diagnostics and vaccinology.

Rational selection of immunodominant and preserved epitope Sm043300e from Schistosoma mansoni and design of a chimeric molecule for biotechnological purposes

Human schistosomiasis is a neglected tropical disease of great importance in public health. A large number of people are infected with schistosomiasis, making vaccine development and effective diagnosis important control strategies. A rational epitope prediction workflow using Schistosoma mansoni hypothetical proteins was previously presented by our group, and an improvement to that approach is presented here. Briefly, immunodominant epitopes from parasite membrane proteins were predicted by reverse vaccinology strategy with additional in silico analysis. Furthermore, epitope recognition was evaluated using sera of individuals infected with S. mansoni. The epitope that stood out in both in silico and in vitro assays was used to compose a rational chimeric molecule to improve immune response activation. Out of 2185 transmembrane proteins, four epitopes with high binding affinities for human and mouse MHCII molecules were selected through computational screening. These epitopes were synthesized to evaluate their ability to induce TCD4+ lymphocyte proliferation in mice. Sm204830e and Sm043300e induced significant TCD4+ proliferation. Both epitopes were submitted to enzyme-linked immunosorbent assay to evaluate their recognition by IgG antibodies from the sera of infected individuals, and epitope Sm043300 was significantly recognized in most sera samples. Epitope Sm043300 also showed good affinity for human MHCII molecules in molecular docking, and its sequence is curiously highly conserved in four S. mansoni proteins, all of which are described as G-protein-coupled receptors. In addition, we have demonstrated the feasibility of incorporating this epitope, which showed low similarity to human sequences, into a chimeric molecule. The stability of the molecule was evaluated by molecular modeling aimed at future molecule production for use in diagnosis and vaccination trials.

Suppression of VAMP2 Alters Morphology of the Tegument and Affects Glucose uptake, Development and Reproduction of Schistosoma japonicum

Schistosomiasis caused by schsitosomes is a serious global public health concern. The tegument that surrounds the worm is critical to the schistosomes survival. The tegument apical membrane undergoes a continuous process of rupture and repair owing to membranous vacuoles fusing with the plasma membrane. Vesicle-associated membrane protein 2 (VAMP2), a member of soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNAREs) is required for membrane fusion. Here, we used RNA interference (RNAi) to knock down the expression of VAMP2 of Schistosoma japonicum (SjVAMP2), and both real-time PCR and western blot analysis confirmed the suppression of this molecule, as well as the suppression of the transcript levels of schistosome glucose transporters (SGTP1 and SGTP4), and insulin receptors (SjIR1 and SjIR2). SjVAMP2-suppressed worms exhibited a lower viability, and phenotypic alterations were also observed in the tegument. Moreover, the glucose consumption of SjVAMP2-suppressed worms decreased significantly in 4 and 6 days, respectively, as well as a significant reduction in egg production. We also observed a significant reduction in worm burden and hepatic eggs burden in two independent RNAi experiment in vivo, and minor pathological changes in mice treated with SjVAMP2 specific small interfering (si)RNA. These findings reveal that SjVAMP2 may play important roles in the maintenance of tegument, glucose uptake, worm development and egg production in schistosomes.

Antiparasitic activity of menadione (vitamin K3) against Schistosoma mansoni in BABL/c mice

Schistosomiasis is one of the neglected tropical diseases affecting nearly quarter of a billion people in economically challenged tropical and subtropical countries of the world. Praziquantel (PZQ) is the only drug currently available to treat this parasitic disease in spite being ineffective against juvenile worms and concerns about developing resistance to treat reinfections. Our earlier in vitro viability studies demonstrated significant antiparasitic activity of menadione (MEN) (vitamin K₃) against Schistosoma mansoni adult worms. To gain insight into plausible mechanism of antischistosomal activity of MEN, its effect on superoxide anion levels in adult worms were studied in vitro which showed significant increases in both female and male worms. Further confirmation of the deleterious morphological changes in their teguments and organelles were obtained by ultrastructural analysis. Genotoxic and cytotoxic studies in male Swiss mice indicated that MEN was well tolerated at the oral dose of 500mg/kg using the criteria of MNPCE frequency and PCE/RBC ratio in the bone marrow of infected animals. The in vivo antiparasitic activity of MEN was conducted in female BALB/c mice infected with S. mansoni and significant reductions (P<0.001) in total worm burden were observed at single oral doses of 40 and 400mg/kg (48.57 and 61.90%, respectively). Additionally, MEN significantly reduced (P<0.001) the number of eggs in the liver of infected mice by 53.57 and 58.76%, respectively. Similarly, histological analysis of the livers showed a significant reduction (P<0.001) in the diameter of the granulomas. Since MEN is already in use globally as an over-the-counter drug for a variety of common ailments and a dietary supplement with a safety record in par with similar products when used in recommended doses, the above antiparasitic results which compare reasonably well with PZQ, make a compelling case for considering MEN to treat S. mansoni infection in humans.

Biochemical and biophysical methodologies open the road for effective schistosomiasis therapy and vaccination

BACKGROUND

Schistosomiasis caused by blood-dwelling flukes, namely Schistosoma mansoni and Schistosoma haematobium is a severe debilitating disease, widespread in sub-Saharan Africa, the Middle East, and South America. Developing and adult worms are unscathed by the surrounding immune effectors and antibodies because the parasite is protected by a double lipid bilayer armor which allows access of nutrients, while binding of specific antibodies is denied.

SCOPE OF REVIEW

Fluorescence recovery after bleaching, extraction of surface membrane cholesterol by methyl-β-cyclodextrin, inhibition and activation of sphingomyelin biosynthesis and hydrolysis, and elastic incoherent and quasi-elastic neutron scattering approaches have helped to clarify the basic mechanism of this immune evasion, and showed that sphingomyelin (SM) molecules in the worm apical lipid bilayer form with surrounding water molecules a tight hydrogen bond barrier. Viability of the parasite and permeability of the outer shield are controlled by equilibrium between SM biosynthesis and activity of a tegument-associated neutral sphingomyelinase (nSMase).

MAJOR CONCLUSIONS

Excessive nSMase activation by polyunsaturated fatty acids (PUFA), such as arachidonic acid (ARA) leads to disruption of the SM molecules and associated hydrogen bond network, with subsequent access of host antibodies and immune effectors to the outer membrane and eventual parasite death.

GENERAL SIGNIFICANCE

ARA was predicted and shown to be a potent schistosomicide in vitro and in vivo in experimental animals and in children. Additionally, it was advocated that schistosomiasis vaccine candidates should be selected uniquely among excretory-secretory products of developing worms, as contrary to cytosolic and surface membrane antigens, they are able to activate the effector functions of the host antibodies and toxic molecules. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo".

A quantitative proteomic analysis of the tegumental proteins from Schistosoma mansoni schistosomula reveals novel potential therapeutic targets

The tegument of Schistosoma mansoni plays an integral role in host-parasite interactions, particularly during the transition from the free-living cercariae to the intra-mammalian schistosomula stages. This developmental period is characterised by the transition from a trilaminate surface to a heptalaminate tegument that plays key roles in immune evasion, nutrition and excretion. Proteins exposed at the surface membranes of newly transformed schistosomula are therefore thought to be prime targets for the development of new vaccines and drugs for schistosomiasis. Using a combination of tegumental labelling and high-throughput quantitative proteomics, more than 450 proteins were identified on the apical membrane of S. mansoni schistosomula, of which 200 had significantly regulated expression profiles at different stages of schistosomula development in vitro, including glucose transporters, sterols, heat shock proteins, antioxidant enzymes and peptidases. Current vaccine antigens were identified on the apical membrane (Sm-TSP-1, calpain) or sub-tegumental (Sm-TSP-2, Sm29) fractions of the schistosomula, displaying localisation patterns that, in some cases, differ from that in the adult stage fluke. This work provides the first known in-depth proteomic analysis of the surface-exposed proteins in the schistosomula tegument, and some of the proteins identified are clear targets for the generation of new vaccines and drugs against schistosomiasis.

Structure-function analysis of apical membrane-associated molecules of the tegument of schistosome parasites of humans: prospects for identification of novel targets for parasite control

Neglected tropical diseases are a group of some 17 diseases that afflict poor and predominantly rural people in developing nations. One significant disease that contributes to substantial morbidity in endemic areas is schistosomiasis, caused by infection with one of five species of blood fluke belonging to the trematode genus Schistosoma. Although there is one drug available for treatment of affected individuals in clinics, or for mass administration in endemic regions, there is a need for new therapies. A prominent target organ of schistosomes, either for drug or vaccine development, is the peculiar epithelial syncytium that forms the body wall (tegument) of this parasite. This dynamic layer is maintained and organized by concerted activity of a range of proteins, among which are the abundant tegumentary annexins. In this review, we will outline advances in structure-function analyses of these annexins, as a means to understanding tegument cell biology in host-parasite interaction and their potential exploitation as targets for anti-schistosomiasis therapies.

Deciphering the glycogenome of schistosomes

Schistosoma mansoni and other Schistosoma sp. are multicellular parasitic helminths (worms) that infect humans and mammals worldwide. Infection by these parasites, which results in developmental maturation and sexual differentiation of the worms over a period of 5–6 weeks, induces antibodies to glycan antigens expressed in surface and secreted glycoproteins and glycolipids. There is growing interest in defining these unusual parasite-synthesized glycan antigens and using them to understand immune responses, their roles in immunomodulation, and in using glycan antigens as potential vaccine targets. A key problem in this area, however, has been the lack of information about the enzymes involved in elaborating the complex repertoire of glycans represented by the schistosome glycome. Recent availability of the nuclear genome sequences for Schistosoma sp. has created the opportunity to define the glycogenome, which represents the specific genes and cognate enzymes that generate the glycome. Here we describe the current state of information in regard to the schistosome glycogenome and glycome and highlight the important classes of glycans and glycogenes that may be important in their generation.

Biomarkers for schistosomiasis: towards an integrative view of the search for an effective diagnosis

Human schistosomiasis, caused mainly by Schistosoma mansoni, S. japonicum, and S. hematobium, remains a prevalent and serious parasitic disease worldwide. Although it is a debilitating disease, a lack of sensitive methods for the precise diagnosis of active infection cases is important to prevent morbidity. The optimization of new diagnostic approaches may be accomplished by the selection of specific markers. In that manner, markers can be satisfactorily used for detection of different phases of infection, as acute and chronic phases, pre-patent and post-patent phases and after chemotherapy, improving the efficiency of methods. For that purpose, proteomics and glycomics analyses have been performed in schistosomes, in particular S. mansoni, using powerful high-throughput methodologies. These investigations have not only chartered protein, o-glycan and n-glycan profiles across developmental stages within mammalian host, but are also leading to the characterization of features of the surface tegument, the eggshell and excretory-secretory proteomes of schistosomes.

Glycoconjugates in host-helminth interactions

Helminths are multicellular parasitic worms that comprise a major class of human pathogens and cause an immense amount of suffering worldwide. Helminths possess an abundance of complex and unique glycoconjugates that interact with both the innate and adaptive arms of immunity in definitive and intermediate hosts. These glycoconjugates represent a major untapped reservoir of immunomodulatory compounds, which have the potential to treat autoimmune and inflammatory disorders, and antigenic glycans, which could be exploited as vaccines and diagnostics. This review will survey current knowledge of the interactions between helminth glycans and host immunity and highlight the gaps in our understanding which are relevant to advancing therapeutics, vaccine development, and diagnostics.

Comparative study of transcriptome profiles of mechanical- and skin-transformed Schistosoma mansoni schistosomula

Schistosome infection begins with the penetration of cercariae through healthy unbroken host skin. This process leads to the transformation of the free-living larvae into obligate parasites called schistosomula. This irreversible transformation, which occurs in as little as two hours, involves casting the cercaria tail and complete remodelling of the surface membrane. At this stage, parasites are vulnerable to host immune attack and oxidative stress. Consequently, the mechanisms by which the parasite recognises and swiftly adapts to the human host are still the subject of many studies, especially in the context of development of intervention strategies against schistosomiasis infection. Because obtaining enough material from in vivo infections is not always feasible for such studies, the transformation process is often mimicked in the laboratory by application of shear pressure to a cercarial sample resulting in mechanically transformed (MT) schistosomula. These parasites share remarkable morphological and biochemical similarity to the naturally transformed counterparts and have been considered a good proxy for parasites undergoing natural infection. Relying on this equivalency, MT schistosomula have been used almost exclusively in high-throughput studies of gene expression, identification of drug targets and identification of effective drugs against schistosomes. However, the transcriptional equivalency between skin-transformed (ST) and MT schistosomula has never been proven. In our approach to compare these two types of schistosomula preparations and to explore differences in gene expression triggered by the presence of a skin barrier, we performed RNA-seq transcriptome profiling of ST and MT schistosomula at 24 hours post transformation. We report that these two very distinct schistosomula preparations differ only in the expression of 38 genes (out of ∼11,000), providing convincing evidence to resolve the skin vs. mechanical long-lasting controversy.

Schistosomiasis is an endemic parasitic disease affecting ∼200 million people in the most socioeconomically deprived regions of the world. Human infection occurs during water contact where free-living larvae called cercariae penetrate host skin and become parasitic organisms called schistosomula. This stage represents the first encounter of the parasites with the host and is also regarded as one of the most vulnerable stages of the parasite's life cycle. Therefore, schistosomula are the focus of many studies, many of which look at changes in the expression of genes as a way of understanding the process of infection, identifying potential drug targets and vaccine candidates. Because collecting enough parasitic material from natural infections is not possible for certain types of studies (for example, gene expression studies), a mechanical transformation of the cercariae into schistosomula is often used instead and assumed as a good proxy for the natural transformation process. However, the equivalency of gene expression profiles between naturally transformed parasites and the mechanically transformed counterparts has never been studied. In this report, we analyse differences in gene expression patterns between these two different parasite preparations and provide enough data to resolve a long-lasting controversy.

Morphological and morphometric study of cercariae and adult worms of Schistosoma mansoni (SLM strain) isolated from infected mice

In northeastern Brazil, the schistosomiasis is historically endemic and considered as a public health problem. The Schistosoma mansoni São Lourenço da Mata (SLM-PE, Brazil) strain was used in several paper already published; however, morphological and morphometric studies about this strain was never done. In this work, scanning electron microscopy (SEM) was used in morphological and morphometric analysis of cercariae and adult worms. Cercariae were obtained from Biomphalaria glabrata snails and adult worms from mice, both infected by the S. mansoni SLM strain, fixed and prepared for SEM. The results showed that cercariae of S. mansoni measures 254.9 μm of length. The bodies are covered by spines, with a ventral sucker, an oral sucker with sensory receivers, and a pair of penetration glands in the head. The area of tail and body and the distance between suckers were 3,011.77, 1,530.32, and 42.9 μm, respectively. Adult worms of S. mansoni were divided into three main regions: the anterior, medial, and posterior, besides the gynecophoral canal in males. The measure of adult worms of S. mansoni was 4 mm males and 5 mm females. The anterior region length of the male was 470 μm and of the female 271 μm. All the parameters were assayed in ten samples. The morphometric values found in the SLM strain were smaller than other S. mansoni strains described in the literature as well as other helminths. This is the first morphological and morphometric study with the SLM strain of S. mansoni being extremely important for improving control strategies and life quality of the local population.

Virulence factors of schistosomes

This review considers whether the products of schistosomes in the mammalian host can be considered as virulence factors. These include: the cercarial secretions used in infection, those of the migrating schistosomulum, surface-exposed proteins of adult worms in the portal system and their gut vomitus in the context of immune evasion, secretions of the egg facilitating its escape from gut tissues and micro-exon gene products.

Schistosoma mansoni: a method for inducing resistance to praziquantel using infected Biomphalaria glabrata snails

To elucidate the mechanisms of antischistosoma resistance, drug-resistant Schistosoma mansoni laboratory isolates are essential. We developed a new method for inducing resistance to praziquantel (PZQ) using successive drug treatments of Biomphalaria glabrata snails infected with S. mansoni. Infected B. glabrata were treated three times with 100 mg/kg PZQ for five consecutive days with a one-week interval between them. After the treatment, the cercariae (LE-PZQ) produced from these snails and the LE strains (susceptible) were used to infect mice. Forty-five days after infection, mice were treated with 200, 400 or 800 mg/kg PZQ. Thirty days post-treatment, we observed that the mean number of worms recovered by perfusion was significantly higher in the group of mice infected with the LE-PZQ isolate treated with 200 and 400 mg/kg in comparison to the LE strain with the same treatment. Moreover, there was a significant difference between the ED50 (effective dose required to kill 50% of the worms) of the LE-PZQ isolate (362 mg/kg) and the LE strain (68 mg/kg). In the in vitro assays, the worms of the LE-PZQ isolate were also less susceptible to PZQ. Thus, the use of infected snails as an experimental model for development of resistance to S. mansoni is effective, fast, simple and cheap.

Occurrence of a conserved domain in ATP diphosphohydrolases from pathogenic organisms associated to antigenicity in human parasitic diseases

A polypeptide (r78-117) belonging to the potato apyrase was identified as a conserved domain shared with apyrase-like proteins from distinct pathogenic organisms, and was obtained as a 6xHis tag polypeptide (r-Domain B). By ELISA, high IgG, and IgG1 and IgG2a subtypes levels were detected in BALB/c mice pre-inoculated with r-Domain B. In Schistosoma mansoni adult worm or Leishmania (V.) braziliensis promastigote preparation, anti-r-Domain B antibodies inhibit 22-72% of the phosphohydrolytic activities and when immobilized on Protein A-Sepharose immunoprecipitate 42-91% of them. Western blots of the immunoprecipitated resin-antibody-antigen complexes identified bands of mw similar to those predicted for parasite proteins. Total IgG and subclasses of patients with leishmaniasis or schistosomiasis exhibited cross-immunoreactivity with r-Domain B. Therefore, the domain B within both S. mansoni SmATPDase 2 (r156-195) and L. (V.) braziliensis NDPase (r83-122) are potentially involved in the host immune response, and also seem to be conserved during host and parasites co-evolution.

Migrating Schistosoma japonicum schistosomula induce an innate immune response and wound healing in the murine lung

The migrating schistosomulum is an important stage of the schistosome lifecycle and represents a key target for elimination of infection by natural and vaccine-induced host immune responses. To gain a better understanding of how schistosomes initiate a primary host immune response we have characterised the host lung response to migrating Schistosoma japonicum schistosomula using a combination of histopathology, microarray analysis and real-time PCR. Our findings indicate that the early pulmonary response to these migrating larvae is characteristic of innate inflammation and wound healing. This response is associated with significant up-regulation of several genes with immunoregulatory function including Ch25h, Hmox1 and Retnla which may act to control the nature or magnitude of the inflammatory response to the migrating schistosomula, promoting both parasite and host survival. These findings contribute to our understanding of host-parasite interactions associated with schistosome and, especially, S. japonicum infection, and may aid the future design of novel vaccines that target the lung stage schistosomulum.

Identification of phage display peptides with affinity for the tegument of Schistosoma japonicum schistosomula

Peptides, bound to the tegument of live Schistosoma japonicum schistosomula, were differentially screened by phage display in vitro using three rounds of reverse absorption and bio-panning. Three M13 phage peptides were isolated and identified by determination of their recovery rate, immunohistochemical localization, immunoblot analysis, and their anti-schistosomal effects in vivo and in vitro. Of the three, M13 phage peptide ZL4 (MppZL4, YSGLQDSSLRLR, 1.4kDa, pI 8.8) bound to the tegument of mechanically transformed schistosomula and to other developmental stages of S. japonicum from the mammalian host. By contrast, MppZL4 did not bind to the surface of cercariae. To further examine its binding properties, MppZL4 was conjugated to Rhodamine B (RhB-YSGLQDSSLRLR, RhB-ZL4) and a peptide control (RhB-AIPYFSGILQWR, RhB-12P) was similarly synthesized. The binding capacities of RhB-ZL4 to the surface membrane of S. japonicum schistosomula in vitro and of S. japonicum adult worms in vivo were examined and revealed specificity for binding. When examined for anti-parasite activity, both MppZL4 and RhB-ZL4 exhibited a potent schistosomicidal effect in vitro. Further MppZL4 also affected the growth and development of schistosomula in vivo. These findings extend previous studies showing that phage display techniques can recover polypeptides that bind specifically to living schistosomes and, moreover, that these bound peptides have the potential to inhibit key physiological processes in these parasites. Our findings suggest further that ectogenic polypeptides, which can bind to the tegument of S. japonicum, might be adapted as vectors to deliver experimental probes and/or pharmacologically relevant compounds to the schistosome tegument, including drugs and immunological mediators.

The S. mansoni glycoprotein ω-1 induces Foxp3 expression in NOD mouse CD4⁺ T cells

Immunization with Schistosoma mansoni soluble antigen preparations protects non-obese diabetic (NOD) mice against the development of type 1 diabetes. These preparations have long been known to induce Th2 responses in vitro and in vivo. Recently, two separate groups have reported that ω-1, a well-characterized glycoprotein in S. mansoni soluble egg antigens (SEA), which with IL-4 inducing principle of S. mansoni eggs (IPSE/α-1) is one of the two major glycoproteins secreted by live eggs, is a major SEA component responsible for this effect. We found that ω-1 induces Foxp3 as well as IL-4 expression when injected in vivo. We confirmed that ω-1 conditions DCs to drive Th2 responses and further demonstrated that ω-1 induces Foxp3(+) T cells from NOD mouse naïve T cells. In contrast, IPSE/α-1 did not drive Foxp3 responses. The in vitro development of Foxp3-expressing T cells by ω-1 was TGF-β- and retinoic acid-dependent. Our work, therefore, identifies ω-1 as an important factor for the induction of Foxp3(+) T cells by SEA in NOD mice.

Enzymatic activity and immunolocalization of Schistosoma mansoni and Schistosoma haematobium neutral sphingomyelinase

We predicted, and provided evidence for, the existence of a schistosome tegument-associated Mg(2+)-dependent neutral sphingomyelinase (nSMase), which controls hydrolysis of surface membrane sphingomyelin molecules, thus allowing nutrients, but not host antibodies, to access proteins at the host-parasite interface. While a putative nSMase was identified in a recent Schistosoma mansoni genome sequencing and analysis study, our report is the first to measure nSMase enzymatic activity in Triton X-100-solubilized surface membrane (Sup 1) and whole worm soluble (SWAP) molecules of male and female S. mansoni and Schistosoma haematobium. Neutral, but no acidic, sphingomyelinase activity was readily detectable by the amplex red sphingomyelinase assay, and increased with incubation time and protein amount. Like nSMase family members, the schistosome nSMase activity was significantly (P<0.05 to <0.0001) enhanced by unsaturated fatty acids and phosphatidyl serine and significantly (P<0.01) decreased following exposure to the nSMase specific inhibitor GW4869. Peptides based on the published sequence of S. mansoni putative nSMase and used in a multiple antigen peptide form induced the generation of specific antibodies, which readily bound to the immunogen and to the cognate protein in Sup 1 and SWAP. Immunofluorescence studies suggested the parasite nSMase is located in the worm tegument and gut lining. Studies using RNA interference are in progress to define nSMase role in larval and adult worm surface membrane antigen exposure and unsaturated fatty acid-mediated attrition.

Schistosoma mansoni Infections in young children: when are schistosome antigens in urine, eggs in stool and antibodies to eggs first detectable?

Background

In Uganda, control of intestinal schistosomiasis with preventive chemotherapy is typically focused towards treatment of school-aged children; the needs of younger children are presently being investigated as in lakeshore communities very young children can be infected. In the context of future epidemiological monitoring, we sought to compare the detection thresholds of available diagnostic tools for Schistosoma mansoni and estimate a likely age of first infection for these children.

Methods and Findings

A total of 242 infants and preschool children (134 boys and 108 girls, mean age 2.9 years, minimum 5 months and maximum 5 years) were examined from Bugoigo, a well-known disease endemic village on Lake Albert. Schistosome antigens in urine, eggs in stool and host antibodies to eggs were inspected to reveal a general prevalence of 47.5% (CI₉₅ 41.1–54.0%), as ascertained by a positive criterion from at least one diagnostic method. Although children as young as 6 months old could be found infected, the average age of infected children was between 3¼–3¾ years, when diagnostic techniques became broadly congruent.

Conclusion

Whilst different assays have particular (dis)advantages, direct detection of eggs in stool was least sensitive having a temporal lag behind antigen and antibody methods. Setting precisely a general age of first infection is problematic but if present Ugandan policies continue, a large proportion of infected children could wait up to 3–4 years before receiving first medication. To better tailor treatment needs for this younger ageclass, we suggest that the circulating cathodic antigen urine dipstick method to be used as an epidemiological indicator.

In sub-Saharan Africa, intestinal schistosomiasis is a debilitating disease caused by a worm infection. To arrest disease progression, de-worming medications are given out, often en masse, to school-aged children. In Uganda, however, much younger children can be infected, and in lakeshore communities both infants and pre-school children can already show signs and symptoms of intestinal schistosomiasis. To change de-worming practices, further information on the occurrence of infections in these younger is needed for evidence-based decision making. Our study applied current methods of disease diagnosis to better define the ‘age of first infection’ and estimate general infection prevalence within a disease-endemic village. Up to 50% of young children were clearly shown to have schistosomiasis and could likely wait up to 3–4 years before obtaining first treatment if present de-worming policies are not changed. In the context of identifying future treatment needs, we propose that antigen detection methods are most suitable.

A cytochrome b561 with ferric reductase activity from the parasitic blood fluke, Schistosoma japonicum

BACKGROUND

Iron has an integral role in numerous cellular reactions and is required by virtually all organisms. In physiological conditions, iron is abundant in a largely insoluble ferric state. Ferric reductases are an essential component of iron uptake by cells, reducing iron to the soluble ferrous form. Cytochromes b561 (cyts-b561) are a family of ascorbate reducing transmembrane proteins found in most eukaryotic cells. The identification of the ferric reductase duodenal cytochrome b (dcytb) and recent observations that other cyts-b561 may be involved in iron metabolism have opened novel perspectives for elucidating their physiological function.

METHODOLOGY/PRINCIPAL FINDINGS

Here we have identified a new member of the cytochrome b561 (Sjcytb561) family in the pathogenic blood fluke Schistosoma japonicum that localises to the outer surface of this parasitic trematode. Heterologous expression of recombinant Sjcyt-b561 in a Saccharomyces cerevisiae mutant strain that lacks plasma membrane ferrireductase activity demonstrated that the molecule could rescue ferric reductase activity in the yeast.

SIGNIFICANCE/CONCLUSIONS

This finding of a new member of the cytochrome b561 family further supports the notion that a ferric reductase function is likely for other members of this protein family. Additionally, the localisation of Sjcytb561 in the surface epithelium of these blood-dwelling schistosomes contributes further to our knowledge concerning nutrient acquisition in these parasites and may provide novel targets for therapeutic intervention.

Use of fluorescent probes as a useful tool to identify resistantSchistosoma mansoniisolates to praziquantel

The use of chemotherapy on a mass scale in endemic areas may lead to the appearance of resistant isolates through the mechanism of selective drug pressure. Studies have demonstrated that praziquantel (PZQ) is able to inhibit the excretory activity and to cause tegumental damage inSchistosoma mansoniadult worms. The use of the probe resorufin to evaluate excretory activity, as well as the probe Hoechst 33258 to detect tegumental damage in adult worms, may represent a method to identify resistant (or less susceptible) isolates. The purpose of the present work was to compare the changes caused by PZQ in the function of the excretory system and in the integrity of the tegument of adult worms from the LE isolate (susceptible to PZQ) and the LE-PZQ isolate (less susceptible to PZQ). Worms from the isolate LE-PZQ showed less severe tegumental lesions, in bothin vitroandin vivoexperiments, detected by labelling with Hoechst 33258 and continued to have a functional excretory system as shown by labelling with resorufinin vitro.

Pathways for the influx of molecules into cercariae of Schistosoma mansoni during skin penetration

It has been observed that fluorescent membrane-impermeant molecules can enter the cercariae as they penetrate mouse skin. The hypothesis to be tested was that such molecules, which included Lucifer Yellow and a variety of fluorescent dextrans, entered the parasite through the nephridiopore and excretory tubules as well as through the surface membrane. FITC-labelled poly-L-lysine (molecular weight 10 kDa), added at 4°C during syringe transformation, was found to enter the nephridiopore and labelled the excretory bladder and sometimes the excretory tubules. This finding indicates that macromolecules (10 kDa) can enter the nephridiopore. It was found that linoleic acid (a normal constituent of skin) greatly stimulated uptake of Lucifer Yellow and dextrans into the excretory/subtegumental region of 2-h-old schistosomula. This correlated with an increased uptake of membrane-impermeant propidium iodide at 37°C. Since increased uptake of propidium iodide occurs when membranes become permeable, the surface membrane could also be a pathway of transport of the membrane-impermeant molecules into the schistosomulum.

Do schistosomes grow old? A confocal laser scanning microscopy study

Infected hosts progressively decrease egg output during the chronic phase of Schistosoma mansoni infection. Ageing may be a factor that results in a progressive decrease in the ability to reproduce. This study was performed to gain insight into the effects of ageing on adult schistosomes, using confocal laser scanning microscopy. Adult worms were recovered from experimentally infected Nectomys squamipes (water rat). Viable eggs were voided in the faeces for 65 weeks and, thereafter, only unviable eggs were eliminated. The rat died after 70 weeks in captivity. Recovered worms (six males and one female) were prepared for confocal microscopy and images were obtained with an LSM 510–ZETA laser confocal microscope. The overall morphology of the adult worms (suckers and tegument) and reproductive organs were the focus of this work. The suckers, ovary, vitellaria and oocytes appeared to be apparently normal. The ootype was formed by flattened cells and unclear nuclei, suggesting that the mechanism for eggshell production by the ootype during organogenesis might have been impaired. Testicular lobes showed empty areas around the germinative cells. Male adult worms showed flaccid musculature of the dorsal surface. Taken together, the present results provided several indications of infertility in older male and female schistosomes.

Exposed proteins of the Schistosoma japonicum tegument

The ability of the mammalian blood fluke Schistosoma japonicum to survive in the inhospitable environment of the mammalian bloodstream can be attributed, at least in part, to its host-exposed outer surface, called the tegument. The tegument is a dynamic organ and is involved in nutrition, immune evasion and modulation, excretion, osmoregulation and signal transduction. Given its importance for parasite survival, proteins exposed to the host at the surface of the tegument are ideal targets for the development of vaccines and drugs. By biotinylating live adult worms and using a combination of OFFGEL electrophoresis and tandem mass spectrometry 54 proteins were identified as putatively host-exposed in S. japonicum. These included glucose transport proteins, an amino permease, a leucine aminopeptidase and a range of transporters, heat shock proteins and novel immune-active proteins. Members of the tetraspanin protein family and a homologue of Sm 29, a tegument membrane protein from Schistosoma mansoni, both effective vaccine antigens in S. mansoni, were also identified. The fate of labelled surface proteins was monitored over time using electron microscopy and revealed that biotinylated proteins were rapidly internalised from the surface of the tegument and trafficked into the cytoplasmic bridges that connect the distal cytoplasm of the tegument to the underlying cell bodies. The results reported herein dramatically increase the number of S. japonicum proteins known to be exposed to the host and, hence, those of interest as therapeutic targets. The ability of the parasite to rapidly internalise proteins at its surface has implications for the development of vaccines and may explain how these parasites are able to avoid the host immune system for long periods of time.

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.

Immune effector mechanisms against schistosomiasis: looking for a chink in the parasite's armour

A recombinant antigen vaccine against Schistosoma mansoni remains elusive, in part because the parasite deploys complex defensive and offensive strategies to combat immune attack. Nevertheless, research on rodent and primate models has shown that schistosomes can be defeated when appropriate responses are elicited. Acquired protection appears to involve protracted inhibition of larval migration or key molecular processes at the adult surfaces, not rapid cytolytic killing mechanisms. A successful vaccine will likely require a cocktail of antigens rather than a single recombinant protein. In addition, ways need to be found of keeping the immune system on permanent alert, either to achieve adequate inhibition of protein function in adults, or because a trickle of incoming parasites does not amplify the secondary response.

Development of Schistosoma mansoni in the laboratory rat analyzed by light and confocal laser scanning microscopy

The kinetic of maturation (schistogram) of Schistosoma mansoni worms grown in laboratory rats was studied by light and confocal laser scanning microscopy. Infected rats with the BH strain were weekly euthanized 3-9weeks pi. Recovered flukes stained with hydrochloric carmine were preserved as whole-mounts and analyzed by confocal and brightfield microscopy. Worms displayed varying degrees of maturation of the reproductive system at weeks 3-6. Male worms showed complete maturation of the reproductive system at week 6, while female worms completed their maturation at week 7. Males presented few tubercles in tegument in all weeks. Despite the presence of a developing embryo within the ootype, no uterine egg was found. The schistogram in rats follows a pattern similar to that observed in mice hosts.

Correlative and dynamic imaging of the hatching biology of Schistosoma japonicum from eggs prepared by high pressure freezing

BACKGROUND

Schistosome eggs must traverse tissues of the intestine or bladder to escape the human host and further the life cycle. Escape from host tissues is facilitated by secretion of immuno-reactive molecules by eggs and the formation of an intense strong granulomatous response by the host which acts to exclude the egg into gut or bladder lumens. Schistosome eggs hatch on contact with freshwater, but the mechanisms of activation and hatching are poorly understood. In view of the lack of knowledge of the behaviour of egg hatching in schistosomes, we undertook a detailed dynamic and correlative study of the hatching biology of Schistosoma japonicum.

METHODOLOGY/PRINCIPAL FINDINGS

Hatching eggs of S. japonicum were studied using correlative light and electron microscopy (EM). The hatching behaviour was recorded by video microscopy. EM preparative methods incorporating high pressure freezing and cryo-substitution were used to investigate ultrastructural features of the miracidium and extra-embryonic envelopes in pre-activated and activated eggs, and immediately after eggshell rupture. Lectin cytochemistry was performed on egg tissues to investigate subcellular location of specific carbohydrate groups.

CONCLUSIONS/SIGNIFICANCE

The hatching of S. japonicum eggs is a striking phenomenon, whereby the larva is liberated explosively while still encapsulated within its sub-shell envelopes. The major alterations that occur in the egg during activation are scission of the outer envelope-eggshell boundary, autolysis of the cellular inner envelope, and likely hydration of abundant complex and simple polysaccharides in the lacunal space between the miracidial larva and surrounding envelopes. These observations on hatching provide insight into the dynamic activity of the eggs and the biology of schistosomes within the host.