Teladorsagia circumcincta: Activation-associated secreted proteins in excretory/secretory products of fourth stage larvae are targets of early IgA responses in infected sheep

Characterisation of protective vaccine antigens from the thiol-containing components of excretory/secretory material of Ostertagia ostertagi

Previous vaccination trials have demonstrated that thiol proteins affinity purified from Ostertagia ostertagi excretory-secretory products (O. ostertagi ES-thiol) are protective against homologous challenge. Here we have shown that protection induced by this vaccine was consistent across four independent vaccine-challenge experiments. Protection is associated with reduced cumulative faecal egg counts across the duration of the trials, relative to control animals. To better understand the diversity of antigens in O. ostertagi ES-thiol we used high-resolution shotgun proteomics to identify 490 unique proteins in the vaccine preparation. The most numerous ES-thiol proteins, with 91 proteins identified, belong to the sperm-coating protein/Tpx/antigen 5/pathogenesis-related protein 1 (SCP/TAPS) family. This family includes previously identified O. ostertagi vaccine antigens O. ostertagi ASP-1 and ASP-2. The ES-thiol fraction also has numerous proteinases, representing three distinct classes, including: metallo-; aspartyl- and cysteine proteinases. In terms of number of family members, the M12 astacin-like metalloproteinases, with 33 proteins, are the most abundant proteinase family in O. ostertagi ES-thiol. The O. ostertagi ES-thiol proteome provides a comprehensive database of proteins present in this vaccine preparation and will guide future vaccine antigen discovery projects.

Ancient diversity in host-parasite interaction genes in a model parasitic nematode

Host-parasite interactions exert strong selection pressures on the genomes of both host and parasite. These interactions can lead to negative frequency-dependent selection, a form of balancing selection that is hypothesised to explain the high levels of polymorphism seen in many host immune and parasite antigen loci. Here, we sequence the genomes of several individuals of Heligmosomoides bakeri, a model parasite of house mice, and Heligmosomoides polygyrus, a closely related parasite of wood mice. Although H. bakeri is commonly referred to as H. polygyrus in the literature, their genomes show levels of divergence that are consistent with at least a million years of independent evolution. The genomes of both species contain hyper-divergent haplotypes that are enriched for proteins that interact with the host immune response. Many of these haplotypes originated prior to the divergence between H. bakeri and H. polygyrus, suggesting that they have been maintained by long-term balancing selection. Together, our results suggest that the selection pressures exerted by the host immune response have played a key role in shaping patterns of genetic diversity in the genomes of parasitic nematodes.

The role of IgA in gastrointestinal helminthiasis: A systematic review

Immunoglobulin-A (IgA) is an important mediator of immunity and has been associated with protection against several pathogens, although its role in gastrointestinal infections remains unclear. Then, the aim of this systematic review was to synthesize qualitative evidence in respect of IgA as mediator of protective immunity against gastrointestinal helminths. Following recommended guidelines, we searched for articles published between January 1990 and October 2019 that evaluated IgA levels and their association with gastrointestinal helminth infections. Twenty-five articles were included after screening 1,546 titles and abstracts, as well as reading in full 52 selected articles. Consistent associations between higher IgA levels and lower parasitological parameters were only found in mice, rats, and sheep. However, the role of IgA in other host species remains uncertain, making it difficult to create a consensus. Therefore, it is too soon to claim that IgA is an effective protective factor against gastrointestinal helminths, and further studies are still needed.

Development and evaluation of an indirect ELISA for detection of Teladorsagia circumcincta infection in sheep

Background

The gastrointestinal helminth, Teladorsagia circumcincta, is one of the major health risks and production-limiting diseases in small ruminant populations, particularly in temperate regions. With the increasing importance of disease management and recruited anthelmintic resistant types, accurate approaches are needed for the diagnosis of the infection in the host. Due to uncertain results using faecal examinations, the ELISA method was indicated for the detection of nematode antigenic materials. Despite some promising results, problems were described in terms of test specificity and cross-reactions. Therefore, this study aimed to evaluate the IgG response to worm somatic and excretory/secretory (ES) products using western blot analysis and an indirect ELISA for the detection of T. circumcincta infection in sheep.

Results

Based on the immuno-reactivity analysis, immunogenic fractions with molecular weights (MWs) of approximately 60, 75 and 100 kDa were detected in somatic content and two antigens of about 63 and 75 kDa in ES material. Accordingly, a specific product at 75 kDa had the strongest reaction and appeared as the most common antigenic protein. In ELISA, all the sera from the infected sheep revealed the OD rates above the calculated cut-off value with about two-fold greater average. Negative control samples were also specifically recognized with the mean OD rate of about 1/3 of the estimated cut-off value. The cross-reaction test, using rabbit anti-T. circumcincta IgG, did not show reactivity with the ES antigens of other prevalent nematodes including Haemonchus contortus, Protostrongylus rufescens and Marshallagia marshalli. In contrast, a strong positive reaction was observed with the somatic antigens of M. marshalli.

Conclusions

The results of this study indicated that the indirect ELISA method using the ES content enables distinguishing the T. circumcincta infected sheep with high specificity. Those antigenic ES peptides with 63 and particularly 75 kDa MWs should be further investigated due to the potential for serological diagnostic methods and immunoprotective targets in the host.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03042-1.

Characterisation of a niche-specific excretory-secretory peroxiredoxin from the parasitic nematode Teladorsagia circumcincta

Background

The primary cause of parasitic gastroenteritis in small ruminants in temperate regions is the brown stomach worm, Teladorsagia circumcincta. Host immunity to this parasite is slow to develop, consistent with the ability of T. circumcincta to suppress the host immune response. Previous studies have shown that infective fourth-stage T. circumcincta larvae produce excretory–secretory products that are able to modulate the host immune response. The objective of this study was to identify immune modulatory excretory–secretory proteins from populations of fourth-stage T. circumcincta larvae present in two different host-niches: those associated with the gastric glands (mucosal-dwelling larvae) and those either loosely associated with the mucosa or free-living in the lumen (lumen-dwelling larvae).

Results

In this study excretory–secretory proteins from mucosal-dwelling and lumen-dwelling T. circumcincta fourth stage larvae were analysed using comparative 2-dimensional gel electrophoresis. A total of 17 proteins were identified as differentially expressed, with 14 proteins unique to, or enriched in, the excretory–secretory proteins of mucosal-dwelling larvae. One of the identified proteins, unique to mucosal-dwelling larvae, was a putative peroxiredoxin (T. circumcincta peroxiredoxin 1, Tci-Prx1). Peroxiredoxin orthologs from the trematode parasites Schistosoma mansoni and Fasciola hepatica have previously been shown to alternatively activate macrophages and play a key role in promoting parasite induced Th2 type immunity. Here we demonstrate that Tci-Prx1 is expressed in all infective T. circumcincta life-stages and, when produced as a recombinant protein, has peroxidase activity, whereby hydrogen peroxide (H₂O₂) is reduced and detoxified. Furthermore, we use an in vitro macrophage stimulation assay to demonstrate that, unlike peroxiredoxins from trematode parasites Schistosoma mansoni and Fasciola hepatica, Tci-Prx1 is unable to alternatively activate murine macrophage cells.

Conclusions

In this study, we identified differences in the excretory–secretory proteome of mucosal-dwelling and lumen-dwelling infective fourth-stage T. circumcincta larvae, and demonstrated the utility of this comparative proteomic approach to identify excretory–secretory proteins of potential importance for parasite survival and/or host immune modulation.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3593-6) contains supplementary material, which is available to authorized users.

High throughput LC-MS/MS-based proteomic analysis of excretory-secretory products from short-term in vitro culture of Haemonchus contortus

Parasitic nematodes of humans, animals and plants have a major, adverse impact on global health and agricultural production worldwide. To cope with their surrounding environment in and the immune attack from the host, excretory-secretory (ES) proteins are released by nematodes to orchestrate or regulate parasite-host interactions. In the present study, we characterised the ES products from short-term (12 h) in vitro culture of different developmental stages/sexes of Haemonchus contortus (one of the most important parasitic nematodes of livestock animals worldwide) using a high throughput tandem mass-spectrometry, underpinned by the most recent genomic dataset. In total, 878 unique proteins from key developmental stages/sexes (third-stage and fourth-stage larvae, and female and male adults) were identified and quantified with high confidence. Bioinformatic analyses showed noteworthy ES protein alterations during the transition from the free-living to the parasitic phase, especially for proteins which are likely involved in nutrient digestion and acquisition as well as parasite-host interactions, such as proteolytic cascade-related peptidases, glycoside hydrolases, C-type lectins and sperm-coating protein/Tpx/antigen 5/pathogenesis related-1/Sc7 (= SCP/TAPS) proteins. Our findings provide an avenue to better explore interactive processes between the host and this highly significant parasitic nematode, to underpin the search for novel drug and vaccine targets. SIGNIFICANCE: The present study represents a comprehensive proteomic analysis of the secretome of key developmental stages/sexes of H. contortus maintained in short-term in vitro culture. High throughput LC-MS/MS analysis of ES products allowed the identification of a large repertoire of proteins (secretome) and the establishment of a new proteomic database for H. contortus. The secretome of H. contortus undergoes substantial changes during the nematode's transition from free-living to parasitic stages, suggesting a constant adaptation to different environments outside of and within the host animal. Understanding the host-parasite relationship at the molecular level could assist significantly in the development of intervention strategies (i.e. novel drugs and vaccines) against H. contortus and related nematodes.

Metazoan Parasite Vaccines: Present Status and Future Prospects

Eukaryotic parasites and pathogens continue to cause some of the most detrimental and difficult to treat diseases (or disease states) in both humans and animals, while also continuously expanding into non-endemic countries. Combined with the ever growing number of reports on drug-resistance and the lack of effective treatment programs for many metazoan diseases, the impact that these organisms will have on quality of life remain a global challenge. Vaccination as an effective prophylactic treatment has been demonstrated for well over 200 years for bacterial and viral diseases. From the earliest variolation procedures to the cutting edge technologies employed today, many protective preparations have been successfully developed for use in both medical and veterinary applications. In spite of the successes of these applications in the discovery of subunit vaccines against prokaryotic pathogens, not many targets have been successfully developed into vaccines directed against metazoan parasites. With the current increase in -omics technologies and metadata for eukaryotic parasites, target discovery for vaccine development can be expedited. However, a good understanding of the host/vector/pathogen interface is needed to understand the underlying biological, biochemical and immunological components that will confer a protective response in the host animal. Therefore, systems biology is rapidly coming of age in the pursuit of effective parasite vaccines. Despite the difficulties, a number of approaches have been developed and applied to parasitic helminths and arthropods. This review will focus on key aspects of vaccine development that require attention in the battle against these metazoan parasites, as well as successes in the field of vaccine development for helminthiases and ectoparasites. Lastly, we propose future direction of applying successes in pursuit of next generation vaccines.

Progress in the development of subunit vaccines for gastrointestinal nematodes of ruminants

The global increase in anthelmintic resistant nematodes of ruminants, together with consumer concerns about chemicals in food, necessitates the development of alternative methods of control for these pathogens. Subunit recombinant vaccines are ideally placed to fill this gap. Indeed, they are probably the only valid option for the long-term control of ruminant parasitic nematodes given the increasing ubiquity of multidrug resistance in a range of worm species across the world. The development of a subunit multicellular parasite vaccine to the point of practical application would be a groundbreaking step in the control of these important endemic infections of livestock. This review summarizes the current status of subunit vaccine development for a number of important gastrointestinal nematodes of cattle and sheep, with a focus on the limitations and problems encountered thus far, and suggestions as to how these hurdles might be overcome.

Niche-specific gene expression in a parasitic nematode; increased expression of immunomodulators in Teladorsagia circumcincta larvae derived from host mucosa

Metazoan parasites have to survive in many different niches in order to complete their life-cycles. In the absence of reliable methods to manipulate parasite genomes and/or proteomes, identification of the molecules critical for parasite survival within these niches has largely depended on comparative transcriptomic and proteomic analyses of different developmental stages of the parasite; however, changes may reflect differences associated with transition between developmental stages rather than specific adaptations to a particular niche. In this study, we compared the transcriptome of two fourth-stage larval populations of the nematode parasite, Teladorsagia circumcincta, which were of the same developmental stage but differed in their location within the abomasum, being either mucosal-dwelling (MD) or lumen-dwelling (LD). Using RNAseq, we identified 57 transcripts which were significantly differentially expressed between MD and LD larvae. Of these transcripts, the majority (54/57) were up-regulated in MD larvae, one of which encoded for an ShKT-domain containing protein, Tck6, capable of modulating ovine T cell cytokine responses. Other differentially expressed transcripts included homologues of ASP-like proteins, proteases, or excretory-secretory proteins of unknown function. Our study demonstrates the utility of niche- rather than stage-specific analysis of parasite transcriptomes to identify parasite molecules of potential importance for survival within the host.

Perusal of parasitic nematode 'omics in the post-genomic era

The advent of high-throughput, next-generation sequencing methods combined with advances in computational biology and bioinformatics have greatly accelerated discovery within biomedical research. This "post-genomics" era has ushered in powerful approaches allowing one to quantify RNA transcript and protein abundance for every gene in the genome - often for multiple conditions. Herein, we chronicle how the post-genomics era has advanced our overall understanding of parasitic nematodes through transcriptomics and proteomics and highlight some of the important advances made in each major nematode clade. We primarily focus on organisms relevant to human health, given that nematode infections significantly impact disability-adjusted life years (DALY) scores within the developing world, but we also discuss organisms of veterinary importance as well as those used as laboratory models. As such, we envision that this review will serve as a comprehensive resource for those seeking a better understanding of basic parasitic nematode biology as well as those interested in targets for vaccination and pharmacological intervention.

A preliminary proteomic characterisation of extracellular vesicles released by the ovine parasitic nematode, Teladorsagia circumcincta

Teladorsagia circumcincta is a major cause of ovine parasitic gastroenteritis in temperate climatic regions. The development of high levels of anthelmintic resistance in this nematode species challenges its future control. Recent research indicates that many parasite species release extracellular vesicles into their environment, many of which have been classified as endocytic in origin, termed exosomes. These vesicles are considered to play important roles in the intercellular communication between parasites and their hosts, and thus represent potentially useful targets for novel control strategies. Here, we demonstrate that exosome-like extracellular vesicles can be isolated from excretory-secretory (ES) products released by T. circumcincta fourth stage larvae (Tci-L4ES). Furthermore, we perform a comparative proteomic analysis of vesicle-enriched and vesicle-free Tci-L4ES. Approximately 73% of the proteins identified in the vesicle-enriched fraction were unique to this fraction, whilst the remaining 27% were present in both vesicle-enriched and vesicle-free fraction. These unique proteins included structural proteins, nuclear proteins, metabolic proteins, proteolytic enzymes and activation-associated secreted proteins. Finally, we demonstrate that molecules present within the vesicles-enriched material are targets of the IgA and IgG response in T. circumcincta infected sheep, and could potentially represent useful targets for future vaccine intervention studies.

Identification and evaluation of vaccine candidate antigens from the poultry red mite (Dermanyssus gallinae)

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Ten poultry red mite vaccine candidate antigens were identified and recombinant versions produced.

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Mite mortality was monitored after feeding on the blood from vaccinated hens.

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A ⩾1.6-fold increased risk of mite death was observed with four of the vaccine candidates (P < 0.001).

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Best candidates include: a serpin, vitellogenin, hemelipoglycoprotein and a novel protein.

An aqueous extract of the haematophagous poultry ectoparasite, Dermanyssus gallinae, was subfractionated using anion exchange chromatography. Six of these subfractions were used to immunise hens and the blood from these hens was fed, in vitro, to poultry red mites. Mite mortality following these feeds was indicative of protective antigens in two of the subfractions, with the risks of mites dying being 3.1 and 3.7 times higher than in the control group (P < 0.001). A combination of two-dimensional immunoblotting and immunoaffinity chromatography, using IgY from hens immunised with these subfractions, was used in concert with proteomic analyses to identify the strongest immunogenic proteins in each of these subfractions. Ten of the immunoreactive proteins were selected for assessment as vaccine candidates using the following criteria: intensity of immune recognition; likelihood of exposure of the antigen to the antibodies in a blood meal; proposed function and known vaccine potential of orthologous molecules. Recombinant versions of each of these 10 proteins were produced in Escherichia coli and were used to immunise hens. Subsequent in vitro feeding of mites on blood from these birds indicated that immunisation with Deg-SRP-1 (serpin), Deg-VIT-1 (vitellogenin), Deg-HGP-1 (hemelipoglycoprotein) or Deg-PUF-1 (a protein of unknown function) resulted in significantly increased risk of mite death (1.7–2.8 times higher than in mites fed blood from control hens immunised with adjuvant only, P < 0.001). The potential for using these antigens in a recombinant vaccine is discussed.

Marker genes for activation of the RNA interference (RNAi) pathway in the free-living nematode Caenorhabditis elegans and RNAi development in the ovine nematode Teladorsagia circumcincta

The nematode Teladorsagia circumcincta is a major cause of parasitic gastroenteritis in sheep in temperate regions. The development of resistance to the major anthelmintic classes used for its control is a threat to small ruminant farming sustainability. Vaccination is a potential alternative control method for this nematode. Gene datasets can be exploited to identify potential vaccine candidates and these validated further by methods such as RNA interference (RNAi) prior to vaccine trials. Previous reports indicate that RNAi in parasitic nematodes is inconsistent and, to date, there are no internal controls that indicate activation of the RNAi pathway in response to double-stranded RNA (dsRNA). The present aims were to determine whether or not the transcription levels of potential marker genes in the RNAi pathway could indicate activation of the pathway in Caenorhabditis elegans and to develop an RNAi platform in T. circumcincta. In C. elegans, transcript levels of three candidate marker genes, Ce-dcr-1 (Dicer), Ce-ego-1 (Enhancer of Glp-One family member) and Ce-rsd-3 (RNAi Spreading Defective), were analysed and results indicated that activation of the pathway had no effect on transcript levels of these genes. In T. circumcincta, two vaccine candidate genes from the Activation-associated Secreted Protein (ASP) family were targets for knockdown. RNAi experiments showed successful silencing of both targets, although inconsistencies in efficacy were observed. After testing a number of parameters that might affect variability, it was found that the length of the storage period of the larvae plays an important role in the consistency of the RNAi results.

Proteomic analysis of the excretory-secretory products from larval stages of Ascaris suum reveals high abundance of glycosyl hydrolases

BACKGROUND

Ascaris lumbricoides and Ascaris suum are socioeconomically important and widespread parasites of humans and pigs, respectively. The excretory-secretory (ES) molecules produced and presented at the parasite-host interface during the different phases of tissue invasion and migration are likely to play critical roles in the induction and development of protective immune and other host responses.

METHODOLOGY/PRINCIPAL FINDINGS

The aim of this study was to identify the ES proteins of the different larval stages (L3-egg, L3-lung and L4) by LC-MS/MS. In total, 106 different proteins were identified, 20 in L3-egg, 45 in L3-lung stage and 58 in L4. Although most of the proteins identified were stage-specific, 15 were identified in the ES products of at least two stages. Two proteins, i.e. a 14-3-3-like protein and a serpin-like protein, were present in the ES products from the three different larval stages investigated. Interestingly, a comparison of ES products from L4 with those of L3-egg and L3-lung showed an abundance of metabolic enzymes, particularly glycosyl hydrolases. Further study indicated that most of these glycolytic enzymes were transcriptionally upregulated from L4 onwards, with a peak in the adult stage, particularly in intestinal tissue. This was also confirmed by enzymatic assays, showing the highest glycosidase activity in protein extracts from adult worms gut.

CONCLUSIONS/SIGNIFICANCE

The present proteomic analysis provides important information on the host-parasite interaction and the biology of the migratory stages of A. suum. In particular, the high transcriptional upregulation of glycosyl hydrolases from the L4 stage onwards reveals that the degradation of complex carbohydrates forms an essential part of the energy metabolism of this parasite once it establishes in the small intestine.

Secretion of protective antigens by tissue-stage nematode larvae revealed by proteomic analysis and vaccination-induced sterile immunity

Gastrointestinal nematode parasites infect over 1 billion humans, with little evidence for generation of sterilising immunity. These helminths are highly adapted to their mammalian host, following a developmental program through successive niches, while effectively down-modulating host immune responsiveness. Larvae of Heligmosomoides polygyrus, for example, encyst in the intestinal submucosa, before emerging as adult worms into the duodenal lumen. Adults release immunomodulatory excretory-secretory (ES) products, but mice immunised with adult H. polygyrus ES become fully immune to challenge infection. ES products of the intestinal wall 4th stage (L4) larvae are similarly important in host-parasite interactions, as they readily generate sterile immunity against infection, while released material from the egg stage is ineffective. Proteomic analyses of L4 ES identifies protective antigen targets as well as potential tissue-phase immunomodulatory molecules, using as comparators the adult ES proteome and a profile of H. polygyrus egg-released material. While 135 proteins are shared between L4 and adult ES, 72 are L4 ES-specific; L4-specific proteins correspond to those whose transcription is restricted to larval stages, while shared proteins are generally transcribed by all life cycle forms. Two protein families are more heavily represented in the L4 secretome, the Sushi domain, associated with complement regulation, and the ShK/SXC domain related to a toxin interfering with T cell signalling. Both adult and L4 ES contain extensive but distinct arrays of Venom allergen/Ancylostoma secreted protein-Like (VAL) members, with acetylcholinesterases (ACEs) and apyrase APY-3 particularly abundant in L4 ES. Serum antibodies from mice vaccinated with L4 and adult ES react strongly to the VAL-1 protein and to ACE-1, indicating that these two antigens represent major vaccine targets for this intestinal nematode. We have thus defined an extensive and novel repertoire of H. polygyrus proteins closely implicated in immune modulation and protective immunity.

Intestinal helminth parasites are highly prevalent in humans and animals, and survive for long periods by deviating the host immune system. No vaccines are currently available to control these infections. Many helminths invade through barrier surfaces (such as the skin or the digestive tract) and develop through tissue larval stages before reaching their final niche such as the intestinal lumen. We studied the tissue larval stage of a mouse parasite, Heligmosomoides polygyrus, to test whether proteins released by this stage could elicit protective immunity, and found that they indeed constitute very effective vaccine antigens. Proteomic analysis to identify the individual proteins released by the larvae demonstrated that while many products are shared between tissue-dwelling larvae and adults occupying the intestinal lumen, larvae express higher levels of two gene families linked to immunomodulation, namely the Sushi protein family and the ShK toxin family. Antibody analysis of serum from vaccinated mice identified two major antigens recognised by the protective immune response as VAL-1 and ACE-1, which are respectively members of the venom allergen and acetylcholinesterase families. This work establishes that tissue larvae are the source of protective antigens for future vaccines, and highlights their production of two potentially immunomodulatory gene families.

Immunomodulation by helminth parasites: defining mechanisms and mediators

Epidemiological and interventional human studies, as well as experiments in animal models, strongly indicate that helminth parasitic infections can confer protection from immune dysregulatory diseases such as allergy, autoimmunity and colitis. Here, we review the immunological pathways that helminths exploit to downregulate immune responses, both against bystander specificities such as allergens and against antigens from the parasites themselves. In particular, we focus on a highly informative laboratory system, the mouse intestinal nematode, Heligmosomoides polygyrus, as a tractable model of host-parasite interaction at the cellular and molecular levels. Analysis of the molecules released in vitro (as excretory-secretory products) and their cellular targets is identifying individual parasite molecules and gene families implicated in immunomodulation, and which hold potential for future human therapy of immunopathological conditions.

An analysis of the transcriptome of Teladorsagia circumcincta: its biological and biotechnological implications

BACKGROUND

Teladorsagia circumcincta (order Strongylida) is an economically important parasitic nematode of small ruminants (including sheep and goats) in temperate climatic regions of the world. Improved insights into the molecular biology of this parasite could underpin alternative methods required to control this and related parasites, in order to circumvent major problems associated with anthelmintic resistance. The aims of the present study were to define the transcriptome of the adult stage of T. circumcincta and to infer the main pathways linked to molecules known to be expressed in this nematode. Since sheep develop acquired immunity against T. circumcincta, there is some potential for the development of a vaccine against this parasite. Hence, we infer excretory/secretory molecules for T. circumcincta as possible immunogens and vaccine candidates.

RESULTS

A total of 407,357 ESTs were assembled yielding 39,852 putative gene sequences. Conceptual translation predicted 24,013 proteins, which were then subjected to detailed annotation which included pathway mapping of predicted proteins (including 112 excreted/secreted [ES] and 226 transmembrane peptides), domain analysis and GO annotation was carried out using InterProScan along with BLAST2GO. Further analysis was carried out for secretory signal peptides using SignalP and non-classical sec pathway using SecretomeP tools. For ES proteins, key pathways, including Fc epsilon RI, T cell receptor, and chemokine signalling as well as leukocyte transendothelial migration were inferred to be linked to immune responses, along with other pathways related to neurodegenerative diseases and infectious diseases, which warrant detailed future studies. KAAS could identify new and updated pathways like phagosome and protein processing in endoplasmic reticulum. Domain analysis for the assembled dataset revealed families of serine, cysteine and proteinase inhibitors which might represent targets for parasite intervention. InterProScan could identify GO terms pertaining to the extracellular region. Some of the important domain families identified included the SCP-like extracellular proteins which belong to the pathogenesis-related proteins (PRPs) superfamily along with C-type lectin, saposin-like proteins. The 'extracellular region' that corresponds to allergen V5/Tpx-1 related, considered important in parasite-host interactions, was also identified. Six cysteine motif (SXC1) proteins, transthyretin proteins, C-type lectins, activation-associated secreted proteins (ASPs), which could represent potential candidates for developing novel anthelmintics or vaccines were few other important findings. Of these, SXC1, protein kinase domain-containing protein, trypsin family protein, trypsin-like protease family member (TRY-1), putative major allergen and putative lipid binding protein were identified which have not been reported in the published T. circumcincta proteomics analysis. Detailed analysis of 6,058 raw EST sequences from dbEST revealed 315 putatively secreted proteins. Amongst them, C-type single domain activation associated secreted protein ASP3 precursor, activation-associated secreted proteins (ASP-like protein), cathepsin B-like cysteine protease, cathepsin L cysteine protease, cysteine protease, TransThyretin-Related and Venom-Allergen-like proteins were the key findings.

CONCLUSIONS

We have annotated a large dataset ESTs of T. circumcincta and undertaken detailed comparative bioinformatics analyses. The results provide a comprehensive insight into the molecular biology of this parasite and disease manifestation which provides potential focal point for future research. We identified a number of pathways responsible for immune response. This type of large-scale computational scanning could be coupled with proteomic and metabolomic studies of this parasite leading to novel therapeutic intervention and disease control strategies. We have also successfully affirmed the use of bioinformatics tools, for the study of ESTs, which could now serve as a benchmark for the development of new computational EST analysis pipelines.

Immune modulation and modulators in Heligmosomoides polygyrus infection

The intestinal nematode parasite Heligmosomoides polygyrus bakeri exerts widespread immunomodulatory effects on both the innate and adaptive immune system of the host. Infected mice adopt an immunoregulated phenotype, with abated allergic and autoimmune reactions. At the cellular level, infection is accompanied by expanded regulatory T cell populations, skewed dendritic cell and macrophage phenotypes, B cell hyperstimulation and multiple localised changes within the intestinal environment. In most mouse strains, these act to block protective Th2 immunity. The molecular basis of parasite interactions with the host immune system centres upon secreted products termed HES (H. polygyrus excretory-secretory antigen), which include a TGF-β-like ligand that induces de novo regulatory T cells, factors that modify innate inflammatory responses, and molecules that block allergy in vivo. Proteomic and transcriptomic definition of parasite proteins, combined with biochemical identification of immunogenic molecules in resistant mice, will provide new candidate immunomodulators and vaccine antigens for future research.

SCP/TAPS proteins in helminths--where to from now?

A diverse array of proteins belonging to the SCP/TAPS 'family' has been described for various eukaryotic organisms, including parasites. Although SCP/TAPS proteins have been hypothesized to play key roles in various fundamental biological processes, such as host-pathogen interactions and defence mechanisms, there is still a limited understanding of the precise roles of these proteins. Here, we review current knowledge of key SCP/TAPS proteins of helminths and their proposed roles in parasite-host interactions. Molecular investigations of these molecules in parasites and the integration of structural and functional data could lead to new and innovative approaches for the treatment and control of parasitic diseases, with important biotechnological outcomes.

Explaining patterns of infection in free-living populations using laboratory immune experiments

The host response to different helminth species can vary and have different consequences for helminth persistence. Often these differences are generated by changes in the dynamics and intensity of the immune components against parasites with distinct life history strategies. We examined the immune response of rabbits to primary infections of the gastrointestinal nematodes Trichostrongylus retortaeformis and Graphidium strigosum under controlled conditions for 120 days post-challenge. Results showed that rabbits developed a robust and effective immune response against T. retortaeformis and abundance quickly decreased in the duodenum and was completely cleared in the remaining sections of the small intestine within 4 months. Infected individuals exhibited an initial strong inflammatory response (IFN-γ), IL-4 expression also increased and was coupled to a rapid serum and mucus IgG and IgA and eosinophilia. Strong IL-4, serum IgA and IgG responses and eosinophilia were also observed against G. strigosum. However, parasite abundance remained consistently high throughout the infection, and this was associated with relatively low mucus antibodies. These findings suggest that immunity plays a key role in affecting the abundance of these nematodes, and different immune mechanisms are involved in regulating the dynamics of each infection and their long-term persistence in free-living host populations.

Proteomic analysis of secretory products from the model gastrointestinal nematode Heligmosomoides polygyrus reveals dominance of venom allergen-like (VAL) proteins

The intestinal helminth parasite, Heligmosomoides polygyrus bakeri offers a tractable experimental model for human hookworm infections such as Ancylostoma duodenale and veterinary parasites such as Haemonchus contortus. Parasite excretory-secretory (ES) products represent the major focus for immunological and biochemical analyses, and contain immunomodulatory molecules responsible for nematode immune evasion. In a proteomic analysis of adult H. polygyrus secretions (termed HES) matched to an extensive transcriptomic dataset, we identified 374 HES proteins by LC-MS/MS, which were distinct from those in somatic extract HEx, comprising 446 identified proteins, confirming selective export of ES proteins. The predominant secreted protein families were proteases (astacins and other metalloproteases, aspartic, cysteine and serine-type proteases), lysozymes, apyrases and acetylcholinesterases. The most abundant products were members of the highly divergent venom allergen-like (VAL) family, related to Ancylostoma secreted protein (ASP); 25 homologues were identified, with VAL-1 and -2 also shown to be associated with the parasite surface. The dominance of VAL proteins is similar to profiles reported for Ancylostoma and Haemonchus ES products. Overall, this study shows that the secretions of H. polygyrus closely parallel those of clinically important GI nematodes, confirming the value of this parasite as a model of helminth infection.

A calcium-activated apyrase from Teladorsagia circumcincta: an excretory/secretory antigen capable of modulating host immune responses?

A cDNA representing the gene Teladorsagia circumcincta apyrase-1 (Tci-apy-1) was isolated, by PCR, from a T. circumcincta fourth-stage larval (L4) cDNA library. The closest orthologue of this gene is a Ca(2+)-dependent apyrase from Ostertagia ostertagi, with 92% amino acid identity across all 339 residues. Tci-apy-1 is transcribed in a stage-specific manner, the transcript being predominant in L4, detectable in the adult cDNA, but absent from eggs and infective third-stage larvae (L3). The protein, Tci-APY-1, was detected by immunoblotting in extracts of L4 nematodes and was present in excretory/secretory products from the same developmental stage. A recombinant version of Tci-APY-1 was expressed in bacteria as an active enzyme that hydrolysed nucleoside triphosphate substrates with a preference of ATP over other nucleoside triphosphates. Recombinant Tci-APY-1 hydrolysed ATP and ADP but not AMP. Apyrase activity was divalent cation-dependent, with no hydrolysis in the presence of Mg(2+), but activation in the presence of Ca(2+). Recombinant Tci-APY-1 was bound by IgG present in serum and both IgG and IgA present in abomasal mucus from trickle-infected, immune sheep but not in material derived from lambs exposed to a single infection. The potential immunomodulatory roles of this Tci-APY-1 are discussed in relation to purinergic signalling.