A preliminary proteomic survey of the in vitro excretory/secretory products of fourth-stage larval and adult Teladorsagia circumcincta

Nematode Galectin Inhibits Basophilic Leukaemia RBL-2H3 Cells Apoptosis in IgE-Mediated Activation

Mast cells are essential immune cells involved in the host's defence against gastrointestinal nematodes. To evade the immune response, parasitic nematodes produce a variety of molecules. Galectin 1, produced by Teladorsagia circumcincta (Tci-gal-1), reduces mast cell degranulation and selectively regulates mediator production and release in an IgE-dependent manner. To uncover the activity of Tci-gal-1, we have examined the effect of the protein on gene expression, protein production, and apoptosis in activated basophilic leukaemia RBL-2H3 cells. Rat RBL-2H3 cells were activated with anti-DNP IgE and DNP-HSA, and then treated with Tci-gal-1. Microarray analysis was used to examine gene expression. The levels of several apoptosis-related molecules and cytokines were determined using antibody arrays and ELISA. Early and late apoptosis was evaluated cytometrically. Degranulation of cells was determined by a β-hexosaminidase release assay. Treatment of activated RBL-2H3 cells with Tci-gal-1 resulted in inhibited apoptosis and decreased degranulation, although we did not detect significant changes in gene expression. The production of pro-apoptotic molecules, receptor for advanced glycation end products (RAGE) and Fas ligand (FasL), and the cytokines IL-9, IL-10, IL-13, TNF-α, and IL-2 was strongly inhibited. Tci-gal-1 modulates apoptosis, degranulation, and production of cytokines by activated RBL-2H3 cells without detectable influence on gene transcription. This parasite protein is crucial for modulation of the protective immune response and the inhibition of chronic inflammation driven by mast cell activity.

Secretory IgA as Biomarker for Gastrointestinal Nematodes Natural Infection in Different Breed Sheep

Specific IgA antibody has been shown to play an important role in resistance to gastrointestinal nematode (GIN) infections in sheep, particularly in Teladorsagia circumcincta parasitosis. In some breeds, negative associations have been shown between IgA levels and worm burden in experimentally infected sheep. In the present study, we have studied the relationship between IgA levels in naturally infected sheep (582 ewes in total; 193 younger than one year old and 389 older than one year old) and fecal egg count (FEC) in the Assaf, Castellana, and Churra breeds. ELISA assays were performed to measure IgA levels against the somatic antigen of T. circumcincta third larval stage (L₃) and a 203-amino-acid fragment of the protein disulfide isomerase from the same GIN species. A multilevel random intercept model was developed to predict the infection risk according to age or breed. Spearman's correlation rank was used for statistical analysis. The prediction model showed that breed was not an influential factor in this study, although the Assaf breed could be considered slightly more susceptible than the others. In addition, age affected the infection risk, with the young ewes more susceptible to infection than the adult groups, except for the Castellana breed, whose risk of infection was similar at all ages. The most significant positive association was found between FEC and IgA measured in the nasal secretions of young ewes using both antigens (Rho = 0.5; p = 0.00); the correlation of FEC with IgA in serum was moderately significant (Rho = 0.306; p = 0.00). Comparing both antigens, the protein disulfide isomerase antigen was less reactive than the somatic antigen from L₃. In conclusion, under natural conditions, specific IgA against GIN was positively associated with FEC in sheep, with nasal secretions from young animals being the sample where this association is stronger, which, therefore, could be used as a marker of infection in further studies.

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.

Teladorsagia Circumcincta Galectin-Mucosal Interactome in Sheep

Teladorsagia circumcincta is the most important gastrointestinal parasite in the livestock industry in temperate regions around the world, causing great economic losses. The infective third-stage larvae (L3) of Teladorsagia circumcincta secrete a large number of excretory-secretory (E/S) molecules, some of which are likely to play critical roles in modulating the host immune response. One of the most abundant E/S molecules is a protein termed Tci-gal-1, which has similarity to mammalian galectins. Galectins are a family of carbohydrate-binding molecules, with characteristic domain organisation and affinity for β-galactosids that mediate a variety of important cellular functions including inflammation and immune responses. To understand the role of Tci-gal-1 at the host–parasite interface, we used a proteomics pull-down approach to identify Tc-gal-1 interacting proteins from sheep abomasal scrapes and whole tissue. A total of 135 unique proteins were identified from whole abomasal tissue samples, while 89 proteins were isolated from abomasal scrape samples. Of these proteins, 63 were present in both samples. Many of the host proteins identified, such as trefoil factors and mucin-like proteins, play critical roles in the host response. The identification of Tci-gal-1 binding partners provides new insights on host–parasite interactions and could lead to the development of new control strategies.

The interaction of host and nematode galectins influences the outcome of gastrointestinal nematode infections

Galectins are a family of proteins that bind β-galactosides and play key roles in a variety of cellular processes including host defence. They have been well studied in hosts but less so in gastrointestinal nematodes. Both host and parasite galectins are present in the gastrointestinal tract following infection. Parasite galectins can both bind antibody, especially highly glycosylated IgE and be bound by antibody. Parasite galectins may act as molecular sponges that soak up antibody. Host galectins promote mast cell degranulation while parasite galectins inhibit degranulation. Host and parasite galectins can also bind mucins and influence mucus viscosity. As the protective response against gastrointestinal nematode infection is partly dependent on IgE mediated mast cell degranulation and mucus, the interactions between host and parasite galectins play key roles in determining the outcome of infection.

The production of excretory-secretory molecules from Heligmosomoides polygyrus bakeri fourth stage larvae varies between mixed and single sex cultures

Background

Excretory-secretory (ES) products are crucial in maintaining helminths in the host. Consequently, the proteins of ES are potential vaccine molecules and potential therapeutic agents for autoimmune diseases. Heligmosomoides polygyrus bakeri, a gastrointestinal parasite of mice, is a model of hookworm infection in humans. ES produced by both sexes of H. polygyrus bakeri L4 stage cultured separately shows different immunomodulatory properties than ES obtained when both sexes are cultured together. Accordingly, the objective of this study was to identify and compare the excretory-secretory molecules from single-sex and mixed cultures.

Methods

The composition of ES of male and female L4 stage nematodes in the presence (cultured together) or absence (cultured alone) of the opposite sex was examined. Proteins were identified using mass spectrometry. The functions of identified proteins were explored with Blast2GO.

Results

A total of 258 proteins derived from mixed larval culture in the presence of sex pheromones were identified, 160 proteins from pure female cultures and 172 from pure male cultures. Exposure of nematodes to the sex pheromones results in abundant production of proteins with immunomodulatory properties such as Val proteins, acetylcholinesterases, TGF-β mimic 9 and HpARI. Proteins found only in ES from mixed larval cultures were TGF-β mimics 6 and 7 as well as galectin.

Conclusions

The presence of the opposite sex strongly influences the composition of ES products, probably by chemical (pheromone) communication between individuals. However, examination of the composition of ES from various conditions gives an opportunity for searching for new potentially therapeutic compounds and anthelminthics as well as components of vaccines. Manipulation of the nematode environment might be important for the studies on the immunomodulatory potential of nematodes.

Characterization of Haemonchus contortus Excretory/Secretory Antigen (ES-15) and Its Modulatory Functions on Goat Immune Cells In Vitro

Small size excretory/secretory (ES) antigens of the Haemonchus contortus parasite have intense interest among researchers for understanding the molecular basis of helminths immune regulation in term of control strategies. Immunomodulatory roles of H. contortus ES-15 kDa (HcES-15) on host immune cells during host–parasite interactions are unknown. In this study, the HcES-15 gene was cloned and expression of recombinant protein (rHcES-15) was induced by isopropyl-ß-d-thiogalactopyranoside (IPTG). Binding activity of rHcES-15 to goat peripheral blood mononuclear cells (PBMCs) was confirmed by immunofluorescence assay (IFA) and immunohistochemical analysis showed that H. contortus 15 kDa protein localized in the outer and inner structure of the adult worm, clearly indicated as the parasite’s ES antigen. The immunoregulatory role on cytokines production, cell proliferation, cell migration, nitric oxide (NO) production, apoptosis, and phagocytosis were observed by co-incubation of rHcES-15 with goat PBMCs. The results showed that cytokines IL-4, IL-10, IL-17, the production of nitric oxide (NO), PBMCs apoptosis, and monocytes phagocytosis were all elevated after cells incubated with rHcES-15 at differential protein concentrations. We also found that IFN-γ, TGF-β1, cells proliferation and migration were significantly suppressed with the interaction of rHcES-15 protein. Our findings indicated that low molecular ES antigens of H. contortus possessed discrete immunoregulatory roles, which will help to understand the mechanisms involved in immune evasion by the parasite during host–parasite interactions.

Arginine kinase from Haemonchus contortus decreased the proliferation and increased the apoptosis of goat PBMCs in vitro

BACKGROUND

Arginine kinase (AK), an important member of phosphagen kinase family has been extensively studied in various vertebrates and invertebrates. Immunologically, AKs are important constituents of different body parts, involved in various biological and cellular functions, and considered as immune-modulator and effector for pro-inflammatory cytokines. However, immunoregulatory changes of host cells triggered by AK protein of Haemonchus contortus, a parasitic nematode of ruminants, are still unknown. The current study was focused on cloning and characterisation of Hc-AK, and its regulatory effects on cytokines level, cell migration, cell proliferation, nitric oxide production and apoptosis of goat peripheral blood mononuclear cells (PBMCs) were observed.

METHODS

The full-length sequence of the Hc-AK gene was amplified by reverse transcription-polymerase chain reaction (RT-PCR) and sub-cloned into the prokaryotic expression vector pET-32a. The biochemical characteristics of recombinant protein Hc-AK, which was purified by affinity chromatography, were performed based on the enzymatic assay. Binding of rHc-AK with PBMCs was confirmed by immunofluorescence assay (IFA). Immunohistochemical analysis was used to detect localisation of Hc-AK within adult worms sections. The immunoregulatory effects of rHc-AK on cytokine secretions, cell proliferation, cell migration, nitric oxide production and apoptosis were determined by co-incubation of rHc-AK with goat PBMCs.

RESULTS

The full-length ORF (1080 bp) of the Hc-AK gene was successfully cloned, and His-tagged AK protein was expressed in the Escherichia coli strain BL21. The recombinant protein of Hc-AK (rHc-AK) was about 58.5 kDa together with the fused vector protein of 18 kDa. The biochemical assay showed that the protein encoded by the Hc-ak exhibited enzymatic activity. Western blot analysis confirmed that the rHc-AK was recognised by the sera from rat (rat-antiHc-AK). The IFA results showed that rHc-AK could bind on the surface of goat PBMCs. Immunohistochemically, Hc-AK was localised at the inner and outer membrane as well as in the gut region of adult worms. The binding of rHc-AK to host cells increased the levels of IL-4, IL-10, IL-17, IFN-γ, nitric oxide (NO) production and cell apoptosis of goat PBMCs, whereas, TGF-β1 levels, cell proliferation and PBMCs migration were significantly decreased in a dose dependent manner.

CONCLUSIONS

Our findings suggested that rHc-AK is an important excretory and secretory (ES) protein involved in host immune responses and exhibit distinct immunomodulatory properties during interaction with goat PBMCs.

Helminth Immunomodulation in Autoimmune Disease

Helminths have evolved to become experts at subverting immune surveillance. Through potent and persistent immune tempering, helminths can remain undetected in human tissues for decades. Redirecting the immunomodulating "talents" of helminths to treat inflammatory human diseases is receiving intensive interest. Here, we review therapies using live parasitic worms, worm secretions, and worm-derived synthetic molecules to treat autoimmune disease. We review helminth therapy in both mouse models and clinical trials and discuss what is known on mechanisms of action. We also highlight current progress in characterizing promising new immunomodulatory molecules found in excretory/secretory products of helminths and their potential use as immunotherapies for acute and chronic inflammatory diseases.

Molecular and biochemical characterisation and recognition by the immune host of the enolase of the abomasal nematode parasite Teladorsagia circumcincta

A 1299 bp full length cDNA encoding Teladorsagia circumcincta enolase (TeciENO) was cloned, expressed in Escherichia coli and the recombinant protein purified and its kinetic properties determined. Helminth enolase sequences were used to construct a phylogenetic tree. The predicted protein consisted of 433 amino acids and was present as a single band of about 50 kDa on SDS-PAGE. Multiple alignments of the protein sequence of TeciENO with homologues from other helminths showed 98% similarity with Haemonchus contortus enolase, 78-95% similarity to other nematode sequences and 72-75% similarity to cestode and trematode enolases. Substrate binding sites and conserved regions were identified and were completely conserved in other homologues. The optimum pH for TeciENO activity at 25 °C was pH 7, the K_m for 2-phophoglycerate 0.09 ± 0.04 mM and the V_max was 604 ± 6 nmol min^-1 mg^-1 protein (both mean ± SD, n = 2). TeciENO activity was inhibited by 11.5% by 1 mM citrate (p < 0.001). Antibodies in both serum and saliva from field-immune, but not nematode-naïve, sheep recognised recombinant TeciENO in enzyme-linked immunosorbent assays. The recognition of the recombinant protein by antibodies generated by exposure of sheep to native enolase indicates similar antigenicity of the two proteins.

Multifunctional Thioredoxin-Like Protein from the Gastrointestinal Parasitic Nematodes Strongyloides ratti and Trichuris suis Affects Mucosal Homeostasis

The cellular redox state is important for the regulation of multiple functions and is essential for the maintenance of cellular homeostasis and antioxidant defense. In the excretory/secretory (E/S) products of Strongyloides ratti and Trichuris suis sequences for thioredoxin (Trx) and Trx-like protein (Trx-lp) were identified. To characterize the antioxidant Trx-lp and its interaction with the parasite's mucosal habitat, S. ratti and T. suis Trx-lps were cloned and recombinantly expressed. The primary antioxidative activity was assured by reduction of insulin and IgM. Further analysis applying an in vitro mucosal 3D-cell culture model revealed that the secreted Trx-lps were able to bind to monocytic and intestinal epithelial cells and induce the time-dependent release of cytokines such as TNF-α, IL-22, and TSLP. In addition, the redox proteins also possessed chemotactic activity for monocytic THP-1 cells and fostered epithelial wound healing activity. These results confirm that the parasite-secreted Trx-lps are multifunctional proteins that can affect the host intestinal mucosa.

Excretory/secretory products in the Echinococcus granulosus metacestode: is the intermediate host complacent with infection caused by the larval form of the parasite?

The genus Echinococcus consists of parasites that have a life cycle with two mammalian hosts. Their larval stage, called the hydatid cyst, develops predominantly in the liver and lungs of intermediate hosts. The hydatid cyst is the causative agent of cystic hydatid disease and the species Echinococcus granulosus, G1 haplotype, is responsible for the vast majority of cases in humans, cattle and sheep. Protein characterization in hydatid cysts is essential for better understanding of the host-parasite relationship and the fertility process of Echinococcus. The aims of this work were the identification and quantitative comparison of proteins found in hydatid fluid from fertile and infertile cysts from E. granulosus, in order to highlight possible mechanisms involved in cyst fertility or infertility. Hydatid fluid samples containing proteins from both E. granulosus and Bos taurus were analysed by LC-MS/MS. Our proteomic analysis of fertile and infertile cysts allowed identification of a total of 498 proteins, of which 153 proteins were exclusively identified in the fertile cyst, 271 in the infertile cyst, and 74 in both. Functional in silico analysis allowed us to highlight some important aspects: (i) clues about the possible existence of an "arms race" involving parasite and host responses in fertile and infertile cysts; (ii) a number of proteins in hydatid fluid without functional annotation or with possible alternative functions; (iii) the presence of extracellular vesicles such as exosomes, which was confirmed by transmission electron microscopy.

Proteomic Analysis of the Excretory and Secretory Proteins of Haemonchus contortus (HcESP) Binding to Goat PBMCs In Vivo Revealed Stage-Specific Binding Profiles

Haemonchus contortus is a parasitic gastrointestinal nematode, and its excretory and secretory products (HcESPs) interact extensively with the host cells. In this study, we report the interaction of proteins from HcESPs at different developmental stages to goat peripheral blood mononuclear cells (PBMCs) in vivo using liquid chromatography-tandem mass spectrometry. A total of 407 HcESPs that interacted with goat PBMCs at different time points were identified from a H. contortus protein database using SEQUEST searches. The L4 and L5 stages of H. contortus represented a higher proportion of the identified proteins compared with the early and late adult stages. Both stage-specific interacting proteins and proteins that were common to multiple stages were identified. Forty-seven interacting proteins were shared among all stages. The gene ontology (GO) distributions of the identified goat PBMC-interacting proteins were nearly identical among all developmental stages, with high representation of binding and catalytic activity. Cellular, metabolic and single-organism processes were also annotated as major biological processes, but interestingly, more proteins were annotated as localization processes at the L5 stage than at the L4 and adult stages. Based on the clustering of homologous proteins, we improved the functional annotations of un-annotated proteins identified at different developmental stages. Some unnamed H. contortus ATP-binding cassette proteins, including ADP-ribosylation factor and P-glycoprotein-9, were identified by STRING protein clustering analysis.

Recent Advances in Elucidating Nematode Moulting - Prospects of Using Oesophagostomum dentatum as a Model

There are major gaps in our knowledge of many molecular biological processes that take place during the development of parasitic nematodes, in spite of the fact that understanding such processes could lead to new ways of treating and controlling parasitic diseases via the disruption of one or more biological pathways in the parasites. Progress in genomics, transcriptomics, proteomics and bioinformatics now provides unique opportunities to investigate the molecular basis of key developmental processes in parasitic nematodes. The porcine nodule worm, Oesophagostomum dentatum, represents a large order (Strongylida) of socioeconomically important nematodes, and provides a useful platform for exploring molecular developmental processes, particularly given that this nematode can be grown and maintained in culture in vitro for periods longer than most other nematodes of this order. In this article, we focus on the moulting process (ecdysis) in nematodes; review recent advances in our understanding of molecular aspects of moulting in O. dentatum achieved by using integrated proteomic-bioinformatic tools and discuss key implications and future prospects for research in this area, also with respect to developing new anti-nematode interventions and biotechnological outcomes.

Excretory/secretory proteome of 14-day schistosomula, Schistosoma japonicum

Schistosomiasis remains a serious public health problem, with 200 million people infected and 779 million people at risk worldwide. The schistosomulum is the early stage of the complex lifecycle of Schistosoma japonicum in their vertebrate hosts, and is the main target of vaccine-induced protective immunity. Excretory/secretory (ES) proteins play a major role in host-parasite interactions and ES protein compositions of schistosomula of S. japonicum have not been characterized to date. In the present study, the proteome of ES proteins from 14 day schistosomula of S. japonicum was analyzed by liquid chromatography/tandem mass spectrometry and 713 unique proteins were finally identified. Gene ontology and pathway analysis revealed that identified proteins were mainly involved in carbohydrate metabolism, degradation, response to stimulus, oxidation-reduction, biological regulation and binding. Flow cytometry analysis demonstrated that thioredoxin peroxidase identified in this study had the effect on inhibiting MHCII and CD86 expression on LPS-activated macrophages. The present study provides insight into the growth and development of the schistosome in the final host and valuable information for screening vaccine candidates for schistosomiasis.

Transcriptome profiles of the protoscoleces of Echinococcus granulosus reveal that excretory-secretory products are essential to metabolic adaptation

Background

Cystic hydatid disease (CHD) is caused by the larval stages of the cestode and affects humans and domestic animals worldwide. Protoscoleces (PSCs) are one component of the larval stages that can interact with both definitive and intermediate hosts. Previous genomic and transcriptomic data have provided an overall snapshot of the genomics of the growth and development of this parasite. However, our understanding of how PSCs subvert the immune response of hosts and maintains metabolic adaptation remains unclear. In this study, we used Roche 454 sequencing technology and in silico secretome analysis to explore the transcriptome profiles of the PSCs from E. granulosus and elucidate the potential functions of the excretory-secretory proteins (ESPs) released by the parasite.

Methodology/Principal Findings

A large number of nonredundant sequences as unigenes were generated (26,514), of which 22,910 (86.4%) were mapped to the newly published E. granulosus genome and 17,705 (66.8%) were distributed within the coding sequence (CDS) regions. Of the 2,280 ESPs predicted from the transcriptome, 138 ESPs were inferred to be involved in the metabolism of carbohydrates, while 124 ESPs were inferred to be involved in the metabolism of protein. Eleven ESPs were identified as intracellular enzymes that regulate glycolysis/gluconeogenesis (GL/GN) pathways, while a further 44 antigenic proteins, 25 molecular chaperones and four proteases were highly represented. Many proteins were also found to be significantly enriched in development-related signaling pathways, such as the TGF-β receptor pathways and insulin pathways.

Conclusions/Significance

This study provides valuable information on the metabolic adaptation of parasites to their hosts that can be used to aid the development of novel intervention targets for hydatid treatment and control.

The successful infection establishment of parasites depends on their ability to combat their host's immune system while maintaining metabolic adaptation to their hosts. The mechanisms of these processes are not well understood. We used the protoscoleces (PSCs) of E. granulosus as a model system to study this complex host-parasite interaction by investigating the role of excretory-secretory proteins (ESPs) in the physiological adaptation of the parasite. Using Roche 454 sequencing technology and in silico secretome analysis, we predicted 2280 ESPs and analyzed their biological functions. Our analysis of the bioinformatic data suggested that ESPs are integral to the metabolism of carbohydrates and proteins within the parasite and/or hosts. We also found that ESPs are involved in mediating the immune responses of hosts and function within key development-related signaling pathways. We found 11 intracellular enzymes, 25 molecular chaperones and four proteases that were highly represented in the ESPs, in addition to 44 antigenic proteins that showed promise as candidates for vaccine or serodiagnostic development purposes. These findings provide valuable information on the mechanisms of metabolic adaptation in parasites that will aid the development of novel hydatid treatment and control targets.

Immune modulation by helminth parasites of ruminants: implications for vaccine development and host immune competence

Parasitic helminths reside in immunologically-exposed extracellular locations within their hosts, yet they are capable of surviving for extended periods. To enable this survival, these parasites have developed complex and multifaceted mechanisms to subvert or suppress host immunity. This review summarises current knowledge of immune modulation by helminth parasites of ruminants and the parasite-derived molecules involved in driving this modulation. Such immunomodulatory molecules have considerable promise as vaccine targets, as neutralisation of their function is predicted to enhance anti-parasite immunity and, as such, current knowledge in this area is presented herein. Furthermore, we summarise current evidence that, as well as affecting parasite-specific immunity, immune modulation by these parasites may also affect the ability of ruminant hosts to control concurrent diseases or mount effective responses to vaccination.

Harnessing the helminth secretome for therapeutic immunomodulators

Helminths are the largest and most complex pathogens to invade and live within the human body. Since they are not able to outpace the immune system by rapid antigen variation or faster cell division or retreat into protective niches not accessible to immune effector mechanisms, their long-term survival depends on influencing and regulating the immune responses away from the mode of action most damaging to them. Immunologists have focused on the excretory and secretory products that are released by the helminths, since they can change the host environment by modulating the immune system. Here we give a brief overview of the helminth-associated immune response and the currently available helminth secretome data. We introduce some major secretome-derived immunomodulatory molecules and describe their potential mode of action. Finally, the applicability of helminth-derived therapeutic proteins in the treatment of allergic and autoimmune inflammatory disease is discussed.

Ortleppascaris sp. and your host Rhinella marina: A proteomic view into a nematode-amphibian relationship

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Rhinella marina is a synanthropic amphibian that offers great possibilities for the study of parasite–host relations.

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A complex protein profile, including neuroendocrine proteins indicating intense stress in the liver of the host.

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Important aspects of the host’s immune response plasticity are shown.

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This study contributes to knowledge of the biochemical aspects of the helminth–host interface.

The success of the helminth–host relationship depends on a biochemical molecular arsenal. Perhaps the proteome is the largest and most important set of this weaponry, in which the proteins have a crucial role in vital processes to the parasite/host relationship, from basic metabolism and energy production to complex immune responses. Nowadays, the bioproducts expressed by the parasites are under the “spotlight” of immunoassays and biochemical analysis in helminthology, especially in proteomic analysis, which has provided valuable information about the physiology of the infecting agent. Looking into this point of view, why not turn to the infected agent as well? This study characterised the proteomic profile of fluid-filled fibrous cysts of encapsulated Ortleppascaris sp. larvae in the hepatic parenchyma of their intermediate host, the amphibian Rhinella marina. The proteins were separated by two-dimensional electrophoresis and identified by MS with the aid of Peptide Mass Fingerprint. A total of 54 molecules were analysed in this system, revealing a complex protein profile with molecules related to basic metabolic processes of the parasite, energy production, oxi-reduction and oxidative stress processes as well as molecules related to the host response. This study contributes to proteomic studies of protein markers of the development, infectivity, virulence and co-existence of helminths and their hosts.

Proteomic analysis of Mecistocirrus digitatus and Haemonchus contortus intestinal protein extracts and subsequent efficacy testing in a vaccine trial

BACKGROUND

Gastrointestinal nematode infections, such as Haemonchus contortus and Mecistocirrus digitatus, are ranked in the top twenty diseases affecting small-holder farmers' livestock, yet research into M. digitatus, which infects cattle and buffalo in Asia is limited. Intestine-derived native protein vaccines are effective against Haemonchus, yet the protective efficacy of intestine-derived M. digitatus proteins has yet to be determined.

METHODOLOGY/PRINCIPAL FINDINGS

A simplified protein extraction protocol (A) is described and compared to an established method (B) for protein extraction from H. contortus. Proteomic analysis of the H. contortus and M. digitatus protein extracts identified putative vaccine antigens including aminopeptidases (H11), zinc metallopeptidases, glutamate dehydrogenase, and apical gut membrane polyproteins. A vaccine trial compared the ability of the M. digitatus extract and two different H. contortus extracts to protect sheep against H. contortus challenge. Both Haemonchus fractions (A and B) were highly effective, reducing cumulative Faecal Egg Counts (FEC) by 99.19% and 99.89% and total worm burdens by 87.28% and 93.64% respectively, compared to the unvaccinated controls. There was no effect on H. contortus worm burdens following vaccination with the M. digitatus extract and the 28.2% reduction in cumulative FEC was not statistically significant. However, FEC were consistently lower in the M. digitatus extract vaccinates compared to the un-vaccinated controls from 25 days post-infection.

CONCLUSIONS/SIGNIFICANCE

Similar, antigenically cross-reactive proteins are found in H. contortus and M. digitatus; this is the first step towards developing a multivalent native vaccine against Haemonchus species and M. digitatus. The simplified protein extraction method could form the basis for a locally produced vaccine against H. contortus and, possibly M. digitatus, in regions where effective cold chains for vaccine distribution are limited. The application of such a vaccine in these regions would reduce the need for anthelmintic treatment and the resultant selection for anthelmintic resistant parasites.

Proteomic profile of Ortleppascaris sp.: A helminth parasite of Rhinella marina in the Amazonian region

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We have characterized somatic proteins of a helminth parasite of a synanthropic amphibian from Amazonian region.

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As37, an immunoreactive antigen considered a target for antihelminthic vaccines was found.

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We found virulence factors which are evolutionarily conserved and are potential factors for anti-parasitic interventions.

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This study brings a new approach for host–parasite research by using a amphibian as an animal model.

Ortleppascaris sp. is a helminth that, in its larval stage, infects the liver parenchyma of the amphibian Rhinella marina, resulting in severe physiological and pathological changes. This study used a proteomic approach to determine the overall profile of proteins expressed in a somatic extract from the nematodes to investigate the relationship between the parasite and its host. A total of 60 abundant proteins were selected from the two-dimensional electrophoresis, identified by peptide mass fingerprinting, and grouped based on their Gene Ontology by the biological processes in which they are potentially involved. Important helminthic derivatives, such as the immunoreactive As37 antigen, guanylyl cyclases, proteolytic enzymes, and other proteins conserved among different parasites, were identified through homology. This study represents a new approach to helminth-related proteomic studies using an amphibian animal model. Furthermore, this study identified protein markers that are important to the host–parasite relationship and the viability, development, infectivity, and virulence of helminths.

Analysis of the transcriptome of adult Dictyocaulus filaria and comparison with Dictyocaulus viviparus, with a focus on molecules involved in host-parasite interactions

Parasitic nematodes cause diseases of major economic importance in animals. Key representatives are species of Dictyocaulus (=lungworms), which cause bronchitis (=dictyocaulosis, commonly known as "husk") and have a major adverse impact on the health of livestock. In spite of their economic importance, very little is known about the immunomolecular biology of these parasites. Here, we conducted a comprehensive investigation of the adult transcriptome of Dictyocaulus filaria of small ruminants and compared it with that of Dictyocaulus viviparus of bovids. We then identified a subset of highly transcribed molecules inferred to be linked to host-parasite interactions, including cathepsin B peptidases, fatty-acid and/or retinol-binding proteins, β-galactoside-binding galectins, secreted protein 6 precursors, macrophage migration inhibitory factors, glutathione peroxidases, a transthyretin-like protein and a type 2-like cystatin. We then studied homologues of D. filaria type 2-like cystatin encoded in D. viviparus and 24 other nematodes representing seven distinct taxonomic orders, with a particular focus on their proposed role in immunomodulation and/or metabolism. Taken together, the present study provides new insights into nematode-host interactions. The findings lay the foundation for future experimental studies and could have implications for designing new interventions against lungworms and other parasitic nematodes. The future characterisation of the genomes of Dictyocaulus spp. should underpin these endeavours.

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.

In-depth proteomic and glycomic analysis of the adult-stage Cooperia oncophora excretome/secretome

Cooperia oncophora is one of the most common intestinal parasitic nematodes in cattle worldwide. To date, C. oncophora infections are treated using broad-spectrum anthelmintics. However, during the past decade, reports of anthelmintic resistance in this parasite species have emerged worldwide, necessitating new avenues for its control, possibly through vaccination. In this frame, we analyzed the adult-stage C. oncophora excretome/secretome (ES), covering both the protein and glycan components, since this fraction constitutes the primary interface between parasite and host and may hold potential vaccine candidates. Two-dimensional gel electrophoretic separation of the ES material enabled the MALDI-TOF mass spectrometry (MS)-directed identification of 12 distinct proteins, grouped in three separate molecular weight fractions: (i) a high molecular weight fraction consisting of a double-domain activation-associated secreted protein (ASP), (ii) a midmolecular weight fraction predominantly containing a single-domain ASP, a thioredoxin peroxidase and innexin, and (iii) a low molecular weight protein pool essentially holding two distinct low molecular weight antigens. Further MS-driven glycan analysis mapped a variety of N-glycans to the midmolecular weight single-domain ASP, with Man6GlcNAc2 oligomannosyl glycans as the major species. The predominance of the nonglycosylated double-domain ASP in the high-molecular weight fraction renders it ideal for advancement toward vaccine trials and development.

Insights into the immuno-molecular biology of Angiostrongylus vasorum through transcriptomics--prospects for new interventions

Angiostrongylus vasorum is a metastrongyloid nematode of dogs and other canids of major clinical importance in many countries. In order to gain first insights into the molecular biology of this worm, we conducted the first large-scale exploration of its transcriptome, and predicted essential molecules linked to metabolic and biological processes as well as host immune responses. We also predicted and prioritized drug targets and drug candidates. Following Illumina sequencing (RNA-seq), 52.3 million sequence reads representing adult A. vasorum were assembled and annotated. The assembly yielded 20,033 contigs, which encoded proteins with 11,505 homologues in Caenorhabditis elegans, and additional 2252 homologues in various other parasitic helminths for which curated data sets were publicly available. Functional annotation was achieved for 11,752 (58.6%) proteins predicted for A. vasorum, including peptidases (4.5%) and peptidase inhibitors (1.6%), protein kinases (1.7%), G protein-coupled receptors (GPCRs) (1.5%) and phosphatases (1.2%). Contigs encoding excretory/secretory and immuno-modulatory proteins represented some of the most highly transcribed molecules, and encoded enzymes that digest haemoglobin were conserved between A. vasorum and other blood-feeding nematodes. Using an essentiality-based approach, drug targets, including neurotransmitter receptors, an important chemosensory ion channel and cysteine proteinase-3 were predicted in A. vasorum, as were associated small molecular inhibitors/activators. Future transcriptomic analyses of all developmental stages of A. vasorum should facilitate deep explorations of the molecular biology of this important parasitic nematode and support the sequencing of its genome. These advances will provide a foundation for exploring immuno-molecular aspects of angiostrongylosis and have the potential to underpin the discovery of new methods of intervention.

Molecular and biochemical characterisation of arginine kinases in Haemonchus contortus and Teladorsagia circumcincta

Full length cDNA encoding arginine kinases (AK) were cloned from Teladorsagia circumcincta (TcAK) and Haemonchus contortus (HcAK). The TcAK and HcAK cDNA (1080 bp) encoded 360 amino acid proteins. The predicted amino acid sequence showed 99% similarity with each other and 94% with a Caenorhabditis elegans AK. Soluble N-terminal His-tagged AK proteins were expressed in Escherichia coli strain BL21, purified and characterised. All binding sites were completely conserved in both proteins. The recombinant TcAK and HcAK had very similar kinetic properties: K(m) arginine was 0.35 mM, K(m) ATP was 0.8-0.9 mM and the pH optima were pH 7.5. Arginine analogues strongly inhibited recombinant enzyme activities (up to 80%), whilst other amino acids decreased activities by a maximum of 20%. TcAK and HcAK are potential vaccine candidates because of the strong antigenicity of invertebrate phosphagens and kinases and presence in metabolically active parts of the worm.

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.

Helminth secretome database (HSD): a collection of helminth excretory/secretory proteins predicted from expressed sequence tags (ESTs)

Background

Helminths are important socio-economic organisms, responsible for causing major parasitic infections in humans, other animals and plants. These infections impose a significant public health and economic burden globally. Exceptionally, some helminth organisms like Caenorhabditis elegans are free-living in nature and serve as model organisms for studying parasitic infections. Excretory/secretory proteins play an important role in parasitic helminth infections which make these proteins attractive targets for therapeutic use. In the case of helminths, large volume of expressed sequence tags (ESTs) has been generated to understand parasitism at molecular level and for predicting excretory/secretory proteins for developing novel strategies to tackle parasitic infections. However, mostly predicted ES proteins are not available for further analysis and there is no repository available for such predicted ES proteins. Furthermore, predictions have, in the main, focussed on classical secretory pathways while it is well established that helminth parasites also utilise non-classical secretory pathways.

Results

We developed a free Helminth Secretome Database (HSD), which serves as a repository for ES proteins predicted using classical and non-classical secretory pathways, from EST data for 78 helminth species (64 nematodes, 7 trematodes and 7 cestodes) ranging from parasitic to free-living organisms. Approximately 0.9 million ESTs compiled from the largest EST database, dbEST were cleaned, assembled and analysed by different computational tools in our bioinformatics pipeline and predicted ES proteins were submitted to HSD.

Conclusion

We report the large-scale prediction and analysis of classically and non-classically secreted ES proteins from diverse helminth organisms. All the Unigenes (contigs and singletons) and excretory/secretory protein datasets generated from this analysis are freely available. A BLAST server is available at http://estexplorer.biolinfo.org/hsd, for checking the sequence similarity of new protein sequences against predicted helminth ES proteins.

Parasites, proteomes and systems: has Descartes' clock run out of time?

Systems biology aims to integrate multiple biological data types such as genomics, transcriptomics and proteomics across different levels of structure and scale; it represents an emerging paradigm in the scientific process which challenges the reductionism that has dominated biomedical research for hundreds of years. Systems biology will nevertheless only be successful if the technologies on which it is based are able to deliver the required type and quality of data. In this review we discuss how well positioned is proteomics to deliver the data necessary to support meaningful systems modelling in parasite biology. We summarise the current state of identification proteomics in parasites, but argue that a new generation of quantitative proteomics data is now needed to underpin effective systems modelling. We discuss the challenges faced to acquire more complete knowledge of protein post-translational modifications, protein turnover and protein-protein interactions in parasites. Finally we highlight the central role of proteome-informatics in ensuring that proteomics data is readily accessible to the user-community and can be translated and integrated with other relevant data types.

Anthelmintic metabolism in parasitic helminths: proteomic insights

Anthelmintics are the cornerstone of parasitic helminth control. Surprisingly, understanding of the biochemical pathways used by parasitic helminths to detoxify anthelmintics is fragmented, despite the increasing global threat of anthelmintic resistance within the ruminant and equine industries. Reductionist biochemistry has likely over-estimated the enzymatic role of glutathione transferases in anthelmintic metabolism and neglected the potential role of the cytochrome P-450 superfamily (CYPs). Proteomic technologies offers the opportunity to support genomics, reverse genetics and pharmacokinetics, and provide an integrated insight into both the cellular mechanisms underpinning response to anthelmintics and also the identification of biomarker panels for monitoring the development of anthelmintic resistance. To date, there have been limited attempts to include proteomics in anthelmintic metabolism studies. Optimisations of membrane, post-translational modification and interaction proteomic technologies in helminths are needed to especially study Phase I CYPs and Phase III ABC transporter pumps for anthelmintics and their metabolites.

Excretory/secretory products from in vitro-cultured Echinococcus granulosus protoscoleces

Cystic hydatid disease (CHD) is caused by infection with Echinococcus granulosus metacestodes and affects humans and livestock. Proteins secreted or excreted by protoscoleces, pre-adult worms found in the metacestode, are thought to play fundamental roles in the host-parasite relationship. In this work, we performed an LC-MS/MS proteomic analysis of the excretory-secretory products obtained from the first 48 h of an in vitro culture of the protoscoleces. We identified 32 proteins, including 18 that were never detected previously in metacestode proteomic studies. Among the novel identified excretory-secretory products are antigenic proteins, such as EG19 and P-29 and a calpain protease. We also identified other important protoscolex excretory-secretory products, such as thioredoxin peroxidase and 14-3-3 proteins, which are potentially involved in evasion mechanisms adopted by parasites to establish infection. Several intracellular proteins were found in the excretory-secretory products, revealing a set of identified proteins not previously thought to be exposed at the host-parasite interface. Additionally, immunological analyses established the antigenic profiles of the newly identified excretory-secretory products and revealed, for the first time, the in vitro secretion of the B antigen by protoscoleces. Considering that the excretory-secretory products obtained in vitro might reflect the products released and exposed to the host in vivo, our results provide valuable information on parasite survival strategies in adverse host environments and on the molecular mechanisms underpinning CHD immunopathology.

In silico secretome analysis approach for next generation sequencing transcriptomic data

BACKGROUND

Excretory/secretory proteins (ESPs) play a major role in parasitic infection as they are present at the host-parasite interface and regulate host immune system. In case of parasitic helminths, transcriptomics has been used extensively to understand the molecular basis of parasitism and for developing novel therapeutic strategies against parasitic infections. However, none of transcriptomic studies have extensively covered ES protein prediction for identifying novel therapeutic targets, especially as parasites adopt non-classical secretion pathways.

RESULTS

We developed a semi-automated computational approach for prediction and annotation of ES proteins using transcriptomic data from next generation sequencing platforms. For the prediction of non-classically secreted proteins, we have used an improved computational strategy, together with homology matching to a dataset of experimentally determined parasitic helminth ES proteins. We applied this protocol to analyse 454 short reads of parasitic nematode, Strongyloides ratti. From 296231 reads, we derived 28901 contigs, which were translated into 20877 proteins. Based on our improved ES protein prediction pipeline, we identified 2572 ES proteins, of which 407 (1.9%) proteins have classical N-terminal signal peptides, 923 (4.4%) were computationally identified as non-classically secreted while 1516 (7.26%) were identified by homology to experimentally identified parasitic helminth ES proteins. Out of 2572 ES proteins, 2310 (89.8%) ES proteins had homologues in the free-living nematode Caenorhabditis elegans and 2220 (86.3%) in parasitic nematodes. We could functionally annotate 1591 (61.8%) ES proteins with protein families and domains and establish pathway associations for 691 (26.8%) proteins. In addition, we have identified 19 representative ES proteins, which have no homologues in the host organism but homologous to lethal RNAi phenotypes in C. elegans, as potential therapeutic targets.

CONCLUSION

We report a comprehensive approach using freely available computational tools for the secretome analysis of NGS data. This approach has been applied to S. ratti 454 transcriptomic data for in silico excretory/secretory proteins prediction and analysis, providing a foundation for developing new therapeutic solutions for parasitic infections.

Proteomic analysis of excretory-secretory products of Heligmosomoides polygyrus assessed with next-generation sequencing transcriptomic information

The murine parasite Heligmosomoides polygyrus is a convenient experimental model to study immune responses and pathology associated with gastrointestinal nematode infections. The excretory-secretory products (ESP) produced by this parasite have potent immunomodulatory activity, but the protein(s) responsible has not been defined. Identification of the protein composition of ESP derived from H. polygyrus and other relevant nematode species has been hampered by the lack of genomic sequence information required for proteomic analysis based on database searches. To overcome this, a transcriptome next generation sequencing (RNA-seq) de novo assembly containing 33,641 transcripts was generated, annotated, and used to interrogate mass spectrometry (MS) data derived from 1D-SDS PAGE and LC-MS/MS analysis of ESP. Using the database generated from the 6 open reading frames deduced from the RNA-seq assembly and conventional identification programs, 209 proteins were identified in ESP including homologues of vitellogenins, retinol- and fatty acid-binding proteins, globins, and the allergen V5/Tpx-1-related family of proteins. Several potential immunomodulators, such as macrophage migration inhibitory factor, cysteine protease inhibitors, galectins, C-type lectins, peroxiredoxin, and glutathione S-transferase, were also identified. Comparative analysis of protein annotations based on the RNA-seq assembly and proteomics revealed processes and proteins that may contribute to the functional specialization of ESP, including proteins involved in signalling pathways and in nutrient transport and/or uptake. Together, these findings provide important information that will help to illuminate molecular, biochemical, and in particular immunomodulatory aspects of host-H. polygyrus biology. In addition, the methods and analyses presented here are applicable to study biochemical and molecular aspects of the host-parasite relationship in species for which sequence information is not available.

Gastrointestinal (GI) nematode infections are major causes of human and animal disease. Much of their morbidity is associated with establishment of chronic infections in the host, reflecting the deployment of mechanisms to evade and modulate the immune response. The molecules responsible for these activities are poorly known. The proteins released from nematode species as excretory-secretory products (ESP) have potent immunomodulatory effects. The murine parasite Heligmosomoides bakeri (polygyrus) has served as a model to understand several aspects related to GI nematode infections. Here, we aimed to identify the protein components of H. polygyrus ESP through a proteomic approach, but the lack of genomic sequence information for this organism limited our ability to identify proteins by relying on comparisons between experimental and database-predicted mass spectra. To overcome these difficulties, we used transcriptome next-generation sequencing and several bioinformatic tools to generate and annotate a sequence assembly for this parasite. We used this information to support the protein identification process. Among the 209 proteins identified, we delineated particular processes and proteins that define the functional specialization of ESP. This work provides valuable data to establish a path to identify and understand particular parasite proteins involved in the orchestration of immune evasion events.

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.

Comprehensive proteomic profiling of adult Angiostrongylus costaricensis, a human parasitic nematode

Angiostrongylus costaricensis is a nematode helminth that causes an intestinal acute inflammatory process known as abdominal angiostrongyliasis, which is a poorly understood human disease occurring in Latin America. Our aim was to study the proteomic profiles of adult parasites focusing on immunogenic proteins. Total cellular extracts from both genders showed similar 2-DE profiles, with 60% of all protein spots focused between pH 5-7 and presenting molecular masses from 20.1 to 66 kDa. A total of 53 different dominant proteins were identified in our dataset and were mainly associated with the following over-represented Gene Ontology Biological Process terms: "macromolecule metabolic process", "developmental process", "response to stress", and "biological regulation". Female and male immunoblots showed similar patterns of reactive proteins. Immunoreactive spots identified by MALDI-PSD were found to represent heat shock proteins, a putative abnormal DAuer Formation family member, and galectins. To date, very few biochemical analyses have focused on the nematode Angiostrongylus costaricensis. As such, our results contribute to a better understanding of its biology and the mechanisms underlying the host-parasite relationship associated with this species. Moreover, our findings represent a first step in the search for candidate proteins for diagnostic assays and the treatment of this parasitic infection.

Proteomic analysis of Strongyloides stercoralis L3 larvae

Strongyloidiasis can be perpetuated by autoinfection with the filariform larvae L3, causing asymptomatic chronic infections and creating a population of carriers, affecting not only developing countries. So far, very little is known about the proteins that interact with the human host, and few proteins from the infective Strongyloides stercoralis L3 have been characterized. Here, we report results obtained from a proteomic analysis of the proteins from S. stercoralis L3 larvae obtained from patients. Since the genome of S. stercoralis is not yet available, we used proteomic analysis to identify 26 different proteins, 13 of them released by short digestion with trypsin, which could represent surface-associated proteins. The present work extends our knowledge of host-parasite interactions by identifying proteins that could be of interest in the development of diagnostic tools, vaccines, or treatments for a neglected disease like strongyloidiasis.

Secretome: clues into pathogen infection and clinical applications

The secretome encompasses the complete set of gene products secreted by a cell. Recent studies on secretome analysis reveal that secretory proteins play an important role in pathogen infection and host-pathogen interactions. Excretory/secretory proteins of pathogens change the host cell environment by suppressing the immune system, to aid the proliferation of infection. Identifying secretory proteins involved in pathogen infection will lead to the discovery of potential drug targets and biomarkers for diagnostic applications.

Teladorsagia circumcincta: survival of adults in vitro is enhanced by the presence of a mammalian cell line

Adult Teladorsagia circumcincta survival and motility in vitro was examined in a range of different cell culture media, supplements and gas mixes. Under optimum conditions, worms survived for 14 days, exhibiting high motility for 9 days and egg production for 72 h. Optimum conditions involved co-culture of worms with a HeLa cell line in a supplemented cell medium (CEM) and an atmosphere containing 10% CO(2), 5% O(2) 85% N(2), 65% humidity at 37 degrees C. The incubation medium consisted of Minimum Essential Medium with 10% fetal calf serum, 1% non-essential amino acids, 1% glutamax and 1% penicillin-neomycin-streptomycin cocktail mix. Compared with optimum conditions, incubation in CEM alone, cell conditioned CEM, RPMI alone, Medium 199 alone, reduced CO(2) or O(2), or when cells were replaced with Escherichia coli, both survival and motility were reduced. Optimum conditions for adult T. circumcincta maintenance for culture, anthelmintic testing or generation of excretory/secretory products are described.

Helminth immunoregulation: the role of parasite secreted proteins in modulating host immunity

Helminths are masterful immunoregulators. A characteristic feature of helminth infection is a Th2-dominated immune response, but stimulation of immunoregulatory cell populations, such as regulatory T cells and alternatively activated macrophages, is equally common. Typically, Th1/17 immunity is blocked and productive effector responses are muted, allowing survival of the parasite in a "modified Th2" environment. Drug treatment to clear the worms reverses the immunoregulatory effects, indicating that a state of active suppression is maintained by the parasite. Hence, research has focussed on "excretory-secretory" products released by live parasites, which can interfere with every aspect of host immunity from initial recognition to end-stage effector mechanisms. In this review, we survey our knowledge of helminth secreted molecules, and summarise current understanding of the growing number of individual helminth mediators that have been shown to target key receptors or pathways in the mammalian immune system.

Roles of galectins in infection

Galectins, which were first characterized in the mid-1970s, were assigned a role in the recognition of endogenous ('self') carbohydrate ligands in embryogenesis, development and immune regulation. Recently, however, galectins have been shown to bind glycans on the surface of potentially pathogenic microorganisms, and function as recognition and effector factors in innate immunity. Some parasites subvert the recognition roles of the vector or host galectins to ensure successful attachment or invasion. This Review discusses the role of galectins in microbial infection, with particular emphasis on adaptations of pathogens to evasion or subversion of host galectin-mediated immune responses.

Interaction of hookworm 14-3-3 with the forkhead transcription factor DAF-16 requires intact Akt phosphorylation sites

Background

Third-stage infective larvae (L3) of hookworms are in an obligatory state of developmental arrest that ends upon entering the definitive host, where they receive a signal that re-activates development. Recovery from the developmentally arrested dauer stage of Caenorhabditis elegans is analogous to the resumption of development during hookworm infection. Insulin-like signaling (ILS) mediates recovery from arrest in C. elegans and activation of hookworm dauer L3. In C. elegans, phosphorylation of the forkhead transcription factor DAF-16 in response to ILS creates binding cites for the 14-3-3 protein Ce-FTT-2, which translocates DAF-16 out of the nucleus, resulting in resumption of reproductive development.

Results

To determine if hookworm 14-3-3 proteins play a similar role in L3 activation, hookworm FTT-2 was identified and tested for its ability to interact with A. caninum DAF-16 in vitro. The Ac-FTT-2 amino acid sequence was 91% identical to the Ce-FTT-2, and was most closely related to FTT-2 from other nematodes. Ac-FTT-2 was expressed in HEK 293T cells, and was recognized by an antibody against human 14-3-3β isoform. Reciprocal co-immunoprecipitations using anti-epitope tag antibodies indicated that Ac-FTT-2 interacts with Ac-DAF-16 when co-expressed in serum-stimulated HEK 293T cells. This interaction requires intact Akt consensus phosphorylation sites at serine107 and threonine312, but not serine381. Ac-FTT-2 was undetectable by Western blot in excretory/secretory products from serum-stimulated (activated) L3 or adult A. caninum.

Conclusion

The results indicate that Ac-FTT-2 interacts with DAF-16 in a phosphorylation-site dependent manner, and suggests that Ac-FTT-2 mediates activation of L3 by binding Ac-DAF-16 during hookworm infection.

Excretory/secretory proteome of the adult developmental stage of human blood fluke, Schistosoma japonicum

Schistosomes are the causative agents of schistosomiasis, one of the most prevalent and serious of the parasitic diseases that currently infects approximately 200 million people worldwide. Schistosome excretory/secretory (ES) proteins have been shown to play important roles in modulating mammalian host immune systems. In our current study, we performed a global proteomics identification of the ES proteins from adult worms of Schistosoma japonicum, one of the three major schistosome species. Our results unambiguously identified 101 proteins, including 53 putatively secreted proteins. By quantitative analysis, we revealed fatty acid-binding protein as a major constituent of the in vitro ES proteome. Strikingly the heat shock proteins HSP70s, HSP90, and HSP97 constituted the largest protein family in the ES proteome, implying a central role for these proteins in immunomodulation in the host-parasite relationship. Other important S. japonicum ES proteins included actins, 14-3-3, aminopeptidase, enolase, and glyceraldehyde-3-phosphate dehydrogenase, some of which have been considered as viable vaccine candidates and therapeutic targets. A comparison with previous studies suggests that 48.5% of S. japonicum ES proteins are common to other parasite ES products, indicating that the molecular mechanisms involved in evading the host immune response may be conserved across different parasites. Interestingly seven host proteins, including antimicrobial protein CAP18, immunoglobulins, and a complement component, were identified among in vitro S. japonicum ES products likely originating from the schistosome tegument or gut, indicating that host innate and acquired immune systems could defend against schistosome invasion. Our present study represents the first attempt at profiling S. japonicum ES proteins, provides an insight into host-parasite interactions, and establishes a resource for the development of diagnostic agents and vaccines for the control of schistosomiasis.

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

SUMMARY

Infection of the snail, Biomphalaria glabrata, by the free-swimming miracidial stage of the human blood fluke, Schistosoma mansoni, and its subsequent development to the parasitic sporocyst stage is critical to establishment of viable infections and continued human transmission. We performed a genome-wide expression analysis of the S. mansoni miracidia and developing sporocyst using Long Serial Analysis of Gene Expression (LongSAGE). Five cDNA libraries were constructed from miracidia and in vitro cultured 6- and 20-day-old sporocysts maintained in sporocyst medium (SM) or in SM conditioned by previous cultivation with cells of the B. glabrata embryonic (Bge) cell line. We generated 21 440 SAGE tags and mapped 13 381 to the S. mansoni gene predictions (v4.0e) either by estimating theoretical 3' UTR lengths or using existing 3' EST sequence data. Overall, 432 transcripts were found to be differentially expressed amongst all 5 libraries. In total, 172 tags were differentially expressed between miracidia and 6-day conditioned sporocysts and 152 were differentially expressed between miracidia and 6-day unconditioned sporocysts. In addition, 53 and 45 tags, respectively, were differentially expressed in 6-day and 20-day cultured sporocysts, due to the effects of exposure to Bge cell-conditioned medium.

Proteomic analysis of excretory/secretory products released by Teladorsagia circumcincta larvae early post-infection

Teladorsagia circumcincta is an important parasitic nematode of domestic small ruminants. Drug resistance in this species is common so alternative methods of control are required. As animals develop immunity to T. circumcincta, vaccination is a valid option. Little is known about the antigens that play a role in stimulating immunity at this host/parasite interface. As responses generated between 1 and 5 dpi are known to affect development of these nematodes in their gastric niche, we focused on proteins released during the early stages of infection. To identify molecules potentially involved in immunity, we undertook a proteomics analysis of proteins released from larvae harvested at 1-, 3- and 5-days post-infection (dpi). This analysis produced peptide sequence data that was used to search information available in T. circumcincta expressed sequence tag (EST) databases and enabled identification of a number of excretory/secretory (ES) proteins. Immunoblots were performed to assess the relative molecular weight of ES antigens that were targets of local IgA responses in mucus from sheep rendered immune to infection. ELISA was performed to assess antigen-specific mucus IgA levels in individual sheep. These experiments provided preliminary evidence that the proteins identified in the larval secretome were subject to these antibody responses.

Parasitic helminths: a pharmacopeia of anti-inflammatory molecules

Infection with parasitic helminths takes a heavy toll on the health and well-being of humans and their domestic livestock, concomitantly resulting in major economic losses. Analyses have consistently revealed bioactive molecules in extracts of helminths or in their excretory/secretory products that modulate the immune response of the host. It is our view that parasitic helminths are an untapped source of immunomodulatory substances that, in pure form, could become new drugs (or models for drug design) to treat disease. Here, we illustrate the range of immunomodulatory molecules in selected parasitic trematodes, cestodes and nematodes, their impact on the immune cells in the host and how the host may recognize these molecules. There are many examples of the partial characterization of helminth-derived immunomodulatory molecules, but these have not yet translated into new drugs, reflecting the difficulty of isolating and fully characterizing proteins, glycoproteins and lipid-based molecules from small amounts of parasite material. However, this should not deter the investigator, since analytical techniques are now being used to accrue considerable structural information on parasite-derived molecules, even when only minute quantities of tissue are available. With the introduction of methodologies to purify and structurally-characterize molecules from small amounts of tissue and the application of high throughput immunological assays, one would predict that an assessment of parasitic helminths will yield a variety of novel drug candidates in the coming years.

Improved insights into the transcriptomes of the human hookworm Necator americanus--fundamental and biotechnological implications

Hookworms of humans are blood-feeding parasitic nematodes of major socio-economic significance in a wide range of countries. They cause a neglected tropical disease (NTD) called "hookworm disease" (=necatoriasis and/or ancylostomiasis). Necator americanus is the most widely distributed hookworm of humans and is a leading cause of iron deficiency anaemia, which can cause physical and mental retardation and deaths in children as well as adverse maternal-foetal outcomes. Currently, there is a significant focus on the development of new approaches for the prevention and control of hookworms in humans. Technological advances are underpinning the discovery of drug and vaccine targets through insights into the molecular biology and genomics of these parasites and their relationship with the human host. In spite of the widespread socio-economic impacts of human necatoriasis, molecular datasets for N. americanus are scant, limiting progress in molecular research. The present article explores all currently available EST datasets for adult and larval stages of N. americanus using a semi-automated bioinformatic pipeline. In the current repertoire of molecules now available, some have been or are being considered as candidate vaccines against N. americanus. Among others, the most abundant sets of molecules relate to the pathogenesis-related protein (PRP) superfamily, comprising various members, such as the Ancylostoma-secreted or activation-associated proteins (ASPs) and the kunitz-type proteins, both of which are inferred to play key roles in the interplay between N. americanus and the human host. Understanding the molecular biology of these and other novel molecules discovered could have important implications for finding new ways of disrupting the pathways that they are involved in, and should facilitate the identification of new drug and vaccine targets. Also, the bioinformatic prediction of the essentiality of genes and gene products as well as molecular network connectivity of nematode-specific genes, together with sequencing by 454 technology, are likely to assist in the genomic discovery efforts in the very near future, to also underpin fundamental, molecular research of hookworms.