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

Anti-schistosomal immunity to core xylose/fucose in N-glycans

Schistosomiasis is a globally prevalent, debilitating disease that is poorly controlled by chemotherapy and for which no vaccine exists. While partial resistance in people may develop over time with repeated infections and treatments, some animals, including the brown rat (Rattus norvegicus), are only semi-permissive and have natural protection. To understand the basis of this protection, we explored the nature of the immune response in the brown rat to infection by Schistosoma mansoni. Infection leads to production of IgG to Infection leads to production of IgG to parasite glycoproteins parasite glycoproteins with complex-type N-glycans that contain a non-mammalian-type modification by core α2-Xylose and core α3-Fucose (core Xyl/Fuc). These epitopes are expressed on the surfaces of schistosomula and adult worms. Importantly, IgG to these epitopes can kill schistosomula by a complement-dependent process in vitro. Additionally, sera from both infected rhesus monkey and infected brown rat were capable of killing schistosomula in a manner inhibited by glycopeptides containing core Xyl/Fuc. These results demonstrate that protective antibodies to schistosome infections in brown rats and rhesus monkeys include IgG responses to the core Xyl/Fuc epitopes in surface-expressed N-glycans, and raise the potential of novel glyco-based vaccines that might be developed to combat this disease.

A new antigen detection ELISA for the diagnosis of Strongyloides infection

Serodiagnosis is an essential component of the laboratory diagnosis of Strongyloides infection and is usually performed using an indirect IgG antibody test. A direct antigen detection method can complement the IgG assay, particularly for detecting early infection and post-treatment follow-up. In the present study, a recombinant scFv monoclonal antibody against NIE recombinant protein (rMAb23) that we had previously produced was used to develop a Strongyloides antigen detection ELISA (SsAg-ELISA). The assay is based on detecting immune complexes of circulating NIE antigens bound to Strongyloides-specific IgG antibodies. The optimized ELISA parameters were 10 µg/mL of rMAb23 coated on microtitre plate wells, 2% skim milk as blocking reagent, 1:100 serum dilution, and 1:1000 goat anti-human IgG F(ab')2 conjugated to horseradish peroxidase. Four groups of serum samples were used, i.e., Strongyloides-positive serum samples categorized into Groups IA and IB; the former were from probable chronic infections and the latter from probable early/acute infections. Strongyloides-negative samples comprising Groups II (healthy samples) and III (other infections); the latter were from eleven different types of other parasitic infections. The receiver operating characteristic (ROC) curve showed an area under the curve (AUC) of 1.00, cut-off optical density (OD₄₀₅) of 0.5002, and 100% diagnostic sensitivity and specificity. The results of the commercial IgG-ELISA and SsAg-ELISA from Group IA were found to be moderately correlated (r = 0.416; p < 0.05). Notably, ANOVA showed that the average ODs₄₀₅ of Group 1B were significantly higher (p < 0.05) than Group 1A, indicating that the assay may be useful to differentiate early and chronic infection. In conclusion, the developed SsAg-ELISA showed good diagnostic potential, and it merits further evaluation.

Revisiting the Schistosoma japonicum life cycle transcriptome for new insights into lung schistosomula development

Schistosome parasites are complex trematode blood flukes responsible for the disease schistosomiasis; a global health concern prevalent in many tropical and sub-tropical countries. While established transcriptomic databases are accessed ad hoc to facilitate studies characterising specific genes or gene families, a more comprehensive systematic updating of gene annotation and survey of the literature to aid in annotation and context is rarely addressed. We have reanalysed an online transcriptomic dataset originally published in 2009, where seven life cycle stages of Schistosoma japonicum were examined. Using the online pathway analysis tool Reactome, we have revisited key data from the original study. A key focus of this study was to improve the interpretation of the gene expression profile of the developmental lung-stage schistosomula, since it is one of the principle targets for worm elimination. Highly enriched transcripts, associated with lung schistosomula, were related to a number of important biological pathways including host immune evasion, energy metabolism and parasitic development. Revisiting large transcriptomic databases should be considered in the context of substantial new literature. This approach could aid in the improved understanding of the molecular basis of parasite biology. This may lead to the identification of new targets for diagnosis and therapies for schistosomes, and other helminths.

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.

Immunofluorescent Localization of Proteins in Schistosoma mansoni

Immunofluorescence allows the detection, visualization, and localization of proteins by using the ability of antibodies to firmly bind to specific antigens. Proteins must be accessible to thorough interaction with the specific antibodies. Different immune evasion mechanisms of parasites are directed to hamper or prevent access of antibodies to critical proteins or virulence factors. The blood fluke Schistosoma mansoni would not survive a day in the host blood capillaries if antibodies were able to readily bind to proteins located at the surface and mediate its attrition and demise by the complement system and/or the FcγR- or FcαR-bearing leukocytes. The worm surface is the area of parasite-host interaction and the route to critical nutrients, but is selectively permeable, allowing access of nutrient molecules but not host antibodies. Gentle procedures, which, however, are not commonly in use in vivo, are required to increase the permeability of the parasite outer membrane shield to just allow access of specific antibodies and identify and localize the proteins at the apical surface. Robust methods involving acetone, methanol, and Triton X-100 treatment lead to disintegration of the dual lipid bilayer cover with exposure of the proteins located in the tegument beneath. Internal proteins may not be accessed except following cryostat or paraffin sectioning. Accordingly, vaccine-induced specific antibodies to the apical surface or tegument proteins are unable to harm intact parasites. Specific antibodies to surface membrane proteins may only add to the action of administered or endo schistosomicides via acceleration of killing and interference with repair of severely and lightly impacted parasites, respectively. Therefore, careful immunofluorescent localization of S. mansoni proteins is important for devising the different control strategies against infection.

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

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

Quantitative multiplexed proteomics of Taenia solium cysts obtained from the skeletal muscle and central nervous system of pigs

In human and porcine cysticercosis caused by the tapeworm Taenia solium, the larval stage (cysts) can infest several tissues including the central nervous system (CNS) and the skeletal muscles (SM). The cyst’s proteomics changes associated with the tissue localization in the host tissues have been poorly studied. Quantitative multiplexed proteomics has the power to evaluate global proteome changes in response to different conditions. Here, using a TMT-multiplexed strategy we identified and quantified over 4,200 proteins in cysts obtained from the SM and CNS of pigs, of which 891 were host proteins. To our knowledge, this is the most extensive intermixing of host and parasite proteins reported for tapeworm infections.Several antigens in cysticercosis, i.e., GP50, paramyosin and a calcium-binding protein were enriched in skeletal muscle cysts. Our results suggested the occurrence of tissue-enriched antigen that could be useful in the improvement of the immunodiagnosis for cysticercosis. Using several algorithms for epitope detection, we selected 42 highly antigenic proteins enriched for each tissue localization of the cysts. Taking into account the fold changes and the antigen/epitope contents, we selected 10 proteins and produced synthetic peptides from the best epitopes. Nine peptides were recognized by serum antibodies of cysticercotic pigs, suggesting that those peptides are antigens. Mixtures of peptides derived from SM and CNS cysts yielded better results than mixtures of peptides derived from a single tissue location, however the identification of the ‘optimal’ tissue-enriched antigens remains to be discovered. Through machine learning technologies, we determined that a reliable immunodiagnostic test for porcine cysticercosis required at least five different antigenic determinants.

Human and porcine cysticercosis caused by Taenia solium is a parasite disease still endemic in developing countries. The cysts can be located in different host tissues, including different organs of the central nervous system and the skeletal muscles. The molecular mechanisms associated with the tissue localization of the cysts are not well understood. Here, we described the proteome changes of the cysts obtained from different host tissues from infected pigs using quantitative multiplex proteomics. We explored the diversity of host proteins identified in the cyst’s protein extracts and we also explored the immune-localization of several host-related proteins within the cysts, and propose their possible function. We identified several proteins and antigens enriched for a given tissue localization. Several synthetic peptides designed from these tissue-enriched antigens were tested trough ELISA. Using a combination of peptide mixtures and machine learning technologies we were able to distinguish non cysticercotic and cysticercotic pig’s sera. The tissue-enriched proteins/antigens could be useful for the development of improved immuno-diagnostic tests capable of discriminate the tissue-localization of the cysts.

Schistosoma mansoni Infection of Mice, Rats and Humans Elicits a Strong Antibody Response to a Limited Number of Reduction-Sensitive Epitopes on Five Major Tegumental Membrane Proteins

Schistosomiasis is a major disease of the developing world for which no vaccine has been successfully commercialized. While numerous Schistosoma mansoni worm antigens have been identified that elicit antibody responses during natural infections, little is known as to the identities of the schistosome antigens that are most prominently recognized by antibodies generated through natural infection. Non-reducing western blots probed with serum from schistosome-infected mice, rats and humans on total extracts of larval or adult schistosomes revealed that a small number of antigen bands predominate in all cases. Recognition of each of these major bands was lost when the blots were run under reducing condition. We expressed a rationally selected group of schistosome tegumental membrane antigens in insect host cells, and used the membrane extracts of these cells to unambiguously identify the major antigens recognized by S. mansoni infected mouse, rat and human serum. These results revealed that a limited number of dominant, reduction-sensitive conformational epitopes on five major tegumental surface membrane proteins: SmTsp2, Sm23, Sm29, SmLy6B and SmLy6F, are primary targets of mouse, rat and human S. mansoni infection sera antibodies. We conclude that, Schistosoma mansoni infection of both permissive (mouse) and non-permissive (rat) rodent models, as well as humans, elicit a dominant antibody response recognizing a limited number of conformational epitopes on the same five tegumental membrane proteins. Thus it appears that neither infecting schistosomula nor mature adult schistosomes are substantively impacted by the robust circulating anti-tegumental antibody response they elicit to these antigens. Importantly, our data suggest a need to re-evaluate host immune responses to many schistosome antigens and has important implications regarding schistosome immune evasion mechanisms and schistosomiasis vaccine development.

Schistosomiasis is caused by blood flukes residing in the veins of infected individuals and afflicts millions of people in the developing world. The schistosome worms can remain healthy in the bloodstream for more than 10 years, implying an extraordinary ability to evade host immune damage. Scientists are seeking to understand immune evasion so as to find weaknesses in defenses that can be exploited in the development of effective vaccines. Here we investigate the normal antibody response to schistosomes during infection of mice, rats and humans, and show for the first time that this response is highly skewed to the recognition of a small number of proteins present at the worm surface. Surprisingly, these abundant antibodies recognize their targets only when the proteins retain their native conformations, stabilized by the presence of intramolecular disulfide bridges. Because of this conformational-dependence, these antibodies have remained undetected in prior studies in which antibody binding assays were routinely performed in a reducing environment that destroys disulfide bridges. The routine presence of these antibodies within the serum of schistosome infected patients and animals raises new and interesting questions as to their possible role in immune evasion, and has significant implications for schistosomiasis vaccine development.

Using the local immune response from the natural buffalo host to generate an antibody fragment library that binds the early larval stages of Schistosoma japonicum

Antibodies isolated from the local draining inguinal lymph node of field exposed-water buffaloes following challenge with Schistosoma japonicum cercariae showed high reactivity towards S. japonicum antigen preparations and bound specifically to formaldehyde-fixed S. japonicum schistosomules. Using this specific local immune response we produced a series of single-chain antibody Fv domain libraries from the same lymph nodes. Removal of phage that cross reacted with epitopes on adult parasites yielded a single-chain antibody Fv domain-phage library that specifically bound to whole formaldehyde-fixed and live S. japonicum schistosomules. DNA sequencing indicated clear enrichment of the single-chain antibody Fv domain library for buffalo B-cell complementarity determining regions post-selection for schistosomule binding. This study also revealed that long heavy chain complementarity determining regions appear to be an important factor when selecting for antibody binding fragments against schistosomule proteins. The selected single-chain antibody Fv domain-phage were used to probe a schistosome-specific protein microarray, which resulted in the recognition of many proteins expressed across all schistosome life-cycle stages. Following absorption to adult worms, the single-chain antibody Fv domain-phage library showed significantly reduced binding to most proteins, whilst two proteins (NCBI GenBank accession numbers AY915878 and AY815196) showed increased binding. We have thus developed a unique set of host derived single-chain antibody Fv domains comprising buffalo B-cell variable regions that specifically bind to early S. japonicum life-stages.

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.

Structural and functional characterization of a novel scFv anti-HSP60 of Strongyloides sp

Phage display is a powerful technology that selects specific proteins or peptides to a target. We have used Phage Display to select scFv (single-chain variable fragment) clones from a combinatorial library against total proteins of Strongyloides venezuelensis. After scFv characterization, further analysis demonstrated that this recombinant fragment of antibody was able to bind to an S. venezuelensis antigenic fraction of ~65 kDa, present in the body periphery and digestive system of infective larvae (L3), as demonstrated by immunofluorescence. Mass spectrometry results followed by bioinformatics analysis showed that this antigenic fraction was a heat shock protein 60 (HSP60) of Strongyloides sp. The selected scFv was applied in serodiagnosis by immune complexes detection in serum samples from individuals with strongyloidiasis using a sandwich enzyme-linked immunosorbent assay (ELISA), showing sensitivity of 97.5% (86.84–99.94), specificity of 98.81 (93.54–99.97), positive likelihood ratio of 81.60 and an area under the curve of 0.9993 (0.9973–1.000). Our study provided a novel monoclonal scFv antibody fragment which specifically bound to HSP60 of Strongyloides sp. and was applied in the development of an innovative serodiagnosis method for the human strongyloidiasis.

Drug-induced exposure of Schistosoma mansoni antigens SmCD59a and SmKK7

Background

Schistosomiasis is a serious health problem especially in developing countries and affects more than 243 million people. Only few anthelmintic drugs are available up to now. A major obstacle for drug treatment is the different developmental stages and the varying host compartments during worm development. Anthelmintic drugs have been tested mainly on adult schistosomes or freshly transformed cercariae. Knowledge concerning the larval stages is lacking.

Methodology/Principal Findings

In this study, we used in vitro-grown schistosomula (aged between 2 to 14 days) to investigate drug effects of the three anthelmintics praziquantel, artemether, and oxamniquine. Further, we analyzed the antibody accessibility of two exemplary schistosome antigens SmCD59a and SmKK7, before and after drug treatment. Our results demonstrated that praziquantel applied at a concentration of 1 μM inhibited development of all life stages. Application of 10 μM praziquantel led to dramatic morphological changes of all schistosomula. Artemether at 1 and 10 μM had differential effects depending on whether it was applied to 2-day as compared to 7- and 14-day schistosomula. While 2-day schistosomula were not killed but inhibited from further development, severe morphological damage was seen in 7- and 14-day schistosomula. Oxamniquine (1 and 10 μM) led to severe morphological impairment in all life stages. Analyzing the accessibility of the antigens SmCD59a and SmKK7 before drug treatment showed no antibody binding on living intact schistosomula. However, when schistosomula were treated with anthelmintics, both antigens became exposed on the larvae. Oxamniquine turned out to be most effective in promoting antibody binding to all schistosomula stages.

Conclusion

This study has revealed marked differences in anthelmintic drug effects against larvae. Drug treatment increases surface antigen presentation and renders larvae accessible to antibody attack.

Schistosomiasis is one of the major parasitic diseases in developing countries and still causes 200,000 deaths per year. Mass drug administration programs with praziquantel, the drug of choice against schistosomiasis, are currently undertaken in Sub-Saharan Africa. Praziquantel, although efficient against adult worms, fails to cure early infection. The complex developmental stages of schistosomes and migration through varying host compartments with different local drug concentration are a challenge for drug treatment. After infecting their mammalian host, schistosomula traverse through skin and the vasculature of lung, liver and intestines. During their migration, they develop from larvae to paired adults in approximately 4 to 5 weeks. So far, drug effects have been analyzed on adult worms or freshly transformed schistosomula only. Information about the effects on the larval stages is lacking. We were able to transfer the larval development of the first three weeks into the culture dish. This tool can be used for the analysis of drug effects against schistosomula and for investigation of the accessibility, expression and localization of antigens. Rendering the parasite’s larvae vulnerable to the host’s immune system by increasing antigen presentation is an important aspect of drug activity. We demonstrate on in vitro-cultured Schistosoma mansoni larvae, that SmCD59a and SmKK7, as examples for hidden antigens, become accessible to antibodies following drug treatment.

Characterisation of a secretory serine protease inhibitor (SjB6) from Schistosoma japonicum

BACKGROUND

Proteins belonging to the serine protease inhibitor (serpin) superfamily play essential physiological roles in many organisms. In pathogens, serpins are thought to have evolved specifically to limit host immune responses by interfering with the host immune-stimulatory signals. Serpins are less well characterised in parasitic helminths, although some are thought to be involved in mechanisms associated with host immune modulation. In this study, we cloned and partially characterised a secretory serpin from Schistosoma japonicum termed SjB6, these findings provide the basis for possible functional roles.

METHODS

SjB6 gene was identified through database mining of our previously published microarray data, cloned and detailed sequence and structural analysis and comparative modelling carried out using various bioinformatics and proteomics tools. Gene transcriptional profiling was determined by real-time PCR and the expression of native protein determined by immunoblotting. An immunological profile of the recombinant protein produced in insect cells was determined by ELISA.

RESULTS

SjB6 contains an open reading frame of 1160 base pairs that encodes a protein of 387 amino acid residues. Detailed sequence analysis, comparative modelling and structural-based alignment revealed that SjB6 contains the essential structural motifs and consensus secondary structures typical of inhibitory serpins. The presence of an N-terminal signal sequence indicated that SjB6 is a secretory protein. Real-time data indicated that SjB6 is expressed exclusively in the intra-mammalian stage of the parasite life cycle with its highest expression levels in the egg stage (p < 0.0001). The native protein is approximately 60 kDa in size and recombinant SjB6 (rSjB6) was recognised strongly by sera from rats experimentally infected with S. japonicum.

CONCLUSIONS

The significantly high expression of SjB6 in schistosome eggs, when compared to other life cycle stages, suggests a possible association with disease pathology, while the strong reactivity of sera from experimentally infected rats against rSjB6 suggests that native SjB6 is released into host tissue and induces an immune response. This study presents a comprehensive demonstration of sequence and structural-based analysis of a secretory serpin from a trematode and suggests SjB6 may be associated with important functional roles in S. japonicum, particularly in parasite modulation of the host microenvironment.

An immunomics approach to schistosome antigen discovery: antibody signatures of naturally resistant and chronically infected individuals from endemic areas

Schistosomiasis is a neglected tropical disease that is responsible for almost 300,000 deaths annually. Mass drug administration (MDA) is used worldwide for the control of schistosomiasis, but chemotherapy fails to prevent reinfection with schistosomes, so MDA alone is not sufficient to eliminate the disease, and a prophylactic vaccine is required. Herein, we take advantage of recent advances in systems biology and longitudinal studies in schistosomiasis endemic areas in Brazil to pilot an immunomics approach to the discovery of schistosomiasis vaccine antigens. We selected mostly surface-derived proteins, produced them using an in vitro rapid translation system and then printed them to generate the first protein microarray for a multi-cellular pathogen. Using well-established Brazilian cohorts of putatively resistant (PR) and chronically infected (CI) individuals stratified by the intensity of their S. mansoni infection, we probed arrays for IgG subclass and IgE responses to these antigens to detect antibody signatures that were reflective of protective vs. non-protective immune responses. Moreover, probing for IgE responses allowed us to identify antigens that might induce potentially deleterious hypersensitivity responses if used as subunit vaccines in endemic populations. Using multi-dimensional cluster analysis we showed that PR individuals mounted a distinct and robust IgG1 response to a small set of newly discovered and well-characterized surface (tegument) antigens in contrast to CI individuals who mounted strong IgE and IgG4 responses to many antigens. Herein, we show the utility of a vaccinomics approach that profiles antibody responses of resistant individuals in a high-throughput multiplex approach for the identification of several potentially protective and safe schistosomiasis vaccine antigens.

Schistosomiasis is a neglected tropical disease that kills as many as 300,000 people each year. Mass drug administration is widely used to control schistosomiasis, but fails to prevent rapid reinfection in endemic areas. There is a desperate need for a prophylactic vaccine; however, very few candidates have been developed. Herein, we take advantage of recent advances in systems biology and longitudinal studies in schistosomiasis endemic areas to pilot an immunomics approach to the discovery of vaccine antigens. The emerging field of immunomics enables the determination of an “antibody signature” to a pathogen proteome for both resistant and susceptible individuals. We constructed the first protein microarray for a multi-cellular pathogen and probed it with sera from naturally resistant vs. susceptible individuals from a high transmission area in Northeastern Brazil. Using multi-dimensional cluster analysis, we showed that resistant individuals mounted a distinct and robust IgG1 antibody signature to a small set of newly discovered and well-characterized surface antigens in contrast to infected individuals. This antigen discovery strategy can lead to identification of several potentially protective and safe schistosomiasis vaccine antigens.

Identification of a vaccine against schistosomiasis using bioinformatics and molecular modeling tools

Schistosomiasis is a serious public health problem in Brazil and worldwide. Although the drugs used to treatment schistosomiasis are effective, the disease continues to expand in all endemic countries due to constant reinfection, poor sanitation, and the lack of effective programs for disease control. However, advances generated through genome projects have provided important information that has improved the understanding of the biology of this parasite. These advances, associated with the advent of bioinformatic analysis, are becoming an important tool in reverse vaccinology. Through database access to the DNA and protein sequences of Schistosoma mansoni and the use of bioinformatics programs, fourteen epitopes were identified. Five epitopes were obtained from proteins whose immunogenic potential had already been assessed in other studies (KP), and nine whose immunogenic potential is unknown (UP). To improve stimulation of the host immune system, the selected epitopes were modeled with a sugar moiety. After this addition, all of the epitopes showed structures similar to those observed in the native proteins, but only eleven of the peptides presented thermodynamically stable structures. Prediction analysis and molecular modeling showed that the glycopeptides presented here are important targets in the search for a vaccine against schistosomiasis. Additionally, they suggest that these molecules may be used in immunological assays to evaluate the level of protection, the effect on pathology reduction and the profile of cytokines and antibodies induced by them.

Adaptive radiation within the vaccine target tetraspanin-23 across nine Schistosoma species from Africa

High levels of polymorphism in DNA sequences of tetraspanin-23 (TSP-23) were revealed within and between nine different species of Schistosoma from Africa including Schistosoma mansoni, Schistosoma rodhaini, Schistosoma margrebowiei, Schistosoma mattheei, Schistosoma intercalatum, Schistosoma haematobium, Schistosoma guineensis, Schistosoma curassoni and Schistosoma bovis. The greatest levels of diversity coincided with evidence of positive selection (d(N)/d(S)>1) within regions that code for extracellular loops of TSP-23 believed to interact with the host immune system. Kolaskar and Tongaonkar antigenicity predictions of protein sequences were compared across species and high levels of variation in antigenicity were also identified with each species which possessed their own unique antigenic profile. Phylogenetic analysis of TSP-23 proteins suggested evidence of convergent evolution in antigenic lineages as no true inter-species phylogenetic relationships were seen. This could be indicative of host-specific evolution of antigens in different species of schistosomes, a factor that should be considered carefully when developing vaccine targets.

Efficacy and mechanism of action of arachidonic acid in the treatment of hamsters infected with Schistosoma mansoni or Schistosoma haematobium

We have recently shown that in vitro and in vivo exposure of Schistosoma mansoni and Schistosoma haematobium to 5-10mM arachidonic acid (ARA) induces parasite surface membrane disintegration and eventual attrition. Here we report on the optimum ARA dose and post-infection treatment time for maximum schistosome demise in hamsters. A series of four experiments for each schistosome species indicated that oral administration of ARA after patency led to a highly significant (P<0.02 to <0.001) reduction in worm burden accompanied by a significant (P<0.05) decrease in worm egg load. ARA-mediated attrition in vivo appeared to be associated with high titres of serum antibodies to tegumental antigens. In support, serum antibodies from patently infected and ARA-treated hamsters readily bound to the surface membrane of ARA-exposed adult worms, as judged by indirect membrane immunofluorescence. More importantly, addition of serum antibodies and peripheral blood mononuclear cells significantly enhanced ARA-mediated adult worm attrition in vitro. These data together show that the schistosomicidal effect of ARA in laboratory animals is enhanced by immune effectors and is highly efficacious and entirely safe.

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.