O-methylated glycans from Toxocara are specific targets for antibody binding in human and animal infections

Recognition of Highly Branched N-Glycans of the Porcine Whipworm by the Immune System

Glycans are key to host-pathogen interactions, whereby recognition by the host and immunomodulation by the pathogen can be mediated by carbohydrate binding proteins, such as lectins of the innate immune system, and their glycoconjugate ligands. Previous studies have shown that excretory-secretory products of the porcine nematode parasite Trichuris suis exert immunomodulatory effects in a glycan-dependent manner. To better understand the mechanisms of these interactions, we prepared N-glycans from T. suis and both analyzed their structures and used them to generate a natural glycan microarray. With this array, we explored the interactions of glycans with C-type lectins, C-reactive protein, and sera from T. suis-infected pigs. Glycans containing LacdiNAc and phosphorylcholine-modified glycans were associated with the highest binding by most of these proteins. In-depth analysis revealed not only fucosylated LacdiNAc motifs with and without phosphorylcholine moieties but phosphorylcholine-modified mannose and N-acetylhexosamine-substituted fucose residues, in the context of maximally tetraantennary N-glycan scaffolds. Furthermore, O-glycans also contained fucosylated motifs. In summary, the glycans of T. suis are recognized by both the innate and adaptive immune systems and also exhibit species-specific features distinguishing its glycome from those of other nematodes.

Potential roles of Toxocara canis larval excretory secretory molecules in immunomodulation and immune evasion

Toxocara canis larvae invade various tissues of different vertebrate species without developing into adults in paratenic host. The long-term survival of the larvae despite exposure to the well-armed immune response is a notable achievement. The larvae modulate the immune response to help the survival of both the host and the larvae. They skew the immune response to type 2/regulatory phenotype. The outstanding ability of the larvae to modulate the host immune response and to evade the immune arms is attributed to the secretion of Toxocara excretory-secretory products (TESPs). TESPs are complex mixture of differing molecules. The present review deals with the molecular composition of the TESPs, their interaction with the host molecules, their effect on the innate immune response, the receptor recognition, the downstream signals the adaptive immunity and the repair of tissues. This review also addresses the role of TESPs molecules in the immune evasion strategy and the potential effect of the induced immunomodulation in some diseases. Identification of parasite components that influence the nematode-host interactions could enhance understanding the molecular basis of nematode pathogenicity. Furthermore, the identification of helminths molecules with immunomodulatory potential could be used in immunotherapies for some diseases.

Screening of Cystic Echinococcosis and Toxocariasis in Urmia Municipal Workers, Northwest Iran

BACKGROUND

Echinococcus granulosus and Toxocara spp., the causative agents of hydatid cyst and toxocariasis in humans and animals, are zoonotic infections with medical and veterinary significance respectively.

AIM

Herein, we aimed to investigate the seroprevalence of toxocariasis and cystic echinococcosis in Urmia municipal workers (gardeners and sweepers) in 2018 using ELISA assay.

OBJECTIVE

There is no precise report on the seroprevalence of toxocariasis and cystic echinococcosis in Urmia municipal workers using ELISA assay. Therefore, this study found an opportunity to investigate this subject.

METHODS

A total of 220 blood samples were obtained from municipal workers with an average age of 41.31 ± 9.42. Commercial anti-Toxocara canis and hydatid cyst ELISA kits were used to assess the seroprevalence rates.

RESULTS

Approximately, 14.5% and 2.3% of individuals were seropositive for toxocariasis and hydatidosis, respectively. Consuming unboiled milk and/or raw/uncooked meat and rural conditions are risk factors for toxocariasis. Regarding hydatidosis, consuming unwashed vegetables was the only statistically significant risk factor. Toxocara infection (p = 0.01), but not hydatid cyst (p = 0.05), is more prevalent among sweepers than municipal gardeners.

CONCLUSION

Due to the occupational condition of municipal workers, they are exposed to many infectious agents; thus, more researches should be done on these populations.

Toxocara canis and Toxocara cati Somatic and Excretory-Secretory Antigens Are Recognised by C-Type Lectin Receptors

Toxocara canis and Toxocara cati, the worldwide occurring intestinal roundworms of canids and felids, represent an important public health threat due to various disease manifestations in humans. Host recognition of pathogens is mediated by pattern recognition receptors (PRRs). Myeloid C-type lectin receptors (CLRs) are PRRs and recognise carbohydrate structures of various pathogens. As Toxocara excretory-secretory products (TES) are predominantly composed of glycoconjugates, they represent suitable targets for CLRs. However, the range of host-derived CLRs recognising Toxocara spp. is still unknown. Using a CLR-hFc fusion protein library, T. canis and T. cati L3 somatic antigens (TSOM) were bound by a variety of CLRs in enzyme-linked immunosorbent assay (ELISA), while their TES products interacted with macrophage galactose-type lectin-1 (MGL-1). Two prominent candidate CLRs, MGL-1 and macrophage C-type lectin (MCL), were selected for further binding studies. Immunofluorescence microscopy revealed binding of MGL-1 to the oral aperture of L3. Immunoblot experiments identified distinct protein fractions representing potential ligands for MGL-1 and MCL. To evaluate how these interactions influence the host immune response, bone marrow-derived dendritic cell (BMDC) assays were performed, showing MCL-dependent T. cati-mediated cytokine production. In conclusion, MGL-1 and MCL are promising candidates for immune modulation during Toxocara infection, deserving further investigation in the future.

The Functional Parasitic Worm Secretome: Mapping the Place of Onchocerca volvulus Excretory Secretory Products

Nematodes constitute a very successful phylum, especially in terms of parasitism. Inside their mammalian hosts, parasitic nematodes mainly dwell in the digestive tract (geohelminths) or in the vascular system (filariae). One of their main characteristics is their long sojourn inside the body where they are accessible to the immune system. Several strategies are used by parasites in order to counteract the immune attacks. One of them is the expression of molecules interfering with the function of the immune system. Excretory-secretory products (ESPs) pertain to this category. This is, however, not their only biological function, as they seem also involved in other mechanisms such as pathogenicity or parasitic cycle (molting, for example). We will mainly focus on filariae ESPs with an emphasis on data available regarding Onchocerca volvulus, but we will also refer to a few relevant/illustrative examples related to other worm categories when necessary (geohelminth nematodes, trematodes or cestodes). We first present Onchocerca volvulus, mainly focusing on the aspects of this organism that seem relevant when it comes to ESPs: life cycle, manifestations of the sickness, immunosuppression, diagnosis and treatment. We then elaborate on the function and use of ESPs in these aspects.

DC-SIGN signalling induced by Trichinella spiralis products contributes to the tolerogenic signatures of human dendritic cells

Tolerogenic dendritic cells (tolDCs) are central players in the maintenance of immune tolerance and thereby have been identified as the most favourable candidates for cell therapy of autoimmune diseases. We have recently shown that excretory-secretory products (ES L1) released by Trichinella spiralis larvae induce stable human tolDCs in vitro via Toll-like receptor 2 (TLR2) and TLR4. However, engagement of these receptors did not fully explain the tolerogenic profile of DCs. Here, we observed for the first time that dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) interacts with highly glycosylated ES L1 and contributes to the generation of ES L1-induced tolDCs. Blocking DC-SIGN interfered with the ES L1-induced higher expression of CD40 and CCR7 and the production of IL-10 and TGF-β by DCs. The cooperation of TLR2, TLR4 and DC-SIGN receptors is of importance for the capacity of DCs to prime T cell response toward Th2 and to induce expansion of CD4+CD25+Foxp3+ T cells, as well as for the production of IL-10 and TGF-β by these cells. Overall, these results indicate that induction of tolDCs by ES L1 involves engagement of multiple pattern recognition receptors namely, TLR2, TLR4 and DC-SIGN.

Excretory/Secretory Metabolome of the Zoonotic Roundworm Parasite Toxocara canis

Toxocariasis is a zoonotic disease affecting humans that is predominantly caused by Toxocara canis and T. cati, primarily parasites of dogs and cats, respectively. Toxocara generally establishes long-term infections by co-opting its host's physiological processes, while at the same time exploiting the nutritional environment. Adult stage T. canis reside in the gut of the definitive canine host where they employ a suite of strategies to combat intestinal immune responses by actively producing and releasing excretory-secretory products (ESPs). The protein component of T. canis ESPs has been widely studied, but characterisation of the non-protein ESP complement remains neglected. To characterize the secreted metabolome of Toxocara ESPs and to shed light on the parasite's metabolic processes, we profiled the ESPs of T. canis using both gas chromatography (GC) and liquid chromatography (LC) mass spectrometry approaches. We successfully identified 61 small molecules, including 41 polar metabolites, 14 medium-long chain fatty acids (MLCFAs) and six short chain fatty acids (SCFAs). We identified talose, stearic acid and isovalerate as the major compounds belonging to the polar, MLCFA and SCFA chemical classes, respectively. Most of the 61 identified metabolites appear to have been produced by T. canis via three distinct metabolic pathways - fatty acid, amino acid and carbohydrate metabolism. The majority of the identified ESPs have known biological properties, especially as immunomodulators. However, there is limited/no information on the biological roles or applications of 31 ESP biomolecules, suggesting that these may have novel activities that merit further investigation.

Human toxocariasis - A look at a neglected disease through an epidemiological 'prism'

Toxocariasis, a disease caused by infection with larvae of Toxocara canis, T. cati and/or congeners, represents clinical syndromes in humans including visceral and ocular larva migrans, neurotoxocariasis and covert/common toxocariasis. It is reported to be one of the most widespread public health and economically important zoonotic parasitic infections that humans share with dogs, wild canids, including foxes, and possibly other mammals. Humans become infected by accidental ingestion of embryonated Toxocara eggs, or larvae from tissues from domestic or wild paratenic hosts. Most infections are asymptomatic, and human disease may go unnoticed, as clinical investigation is often not pursued and/or diagnostic testing not conducted. Sometimes toxocariasis can be associated with complications, such as allergic and/or neurological disorders, possibly including cognitive or developmental delays in children. There is no anti-toxocariasis vaccine, and chemotherapy in humans varies, depending on symptoms and location of larvae, and may include the administration of albendazole or mebendazole, together with anti-inflammatory corticosteroids. Some recent studies indicate that toxocariasis is having an increased, adverse impact on human health in some, particularly underprivileged, tropical and subtropical communities around the world. Although tens of millions of people, especially children, are expected to be exposed to, or infected with Toxocara species, there is limited precise epidemiological data or information on the relationship between seropositivity and disease (toxocariasis) on a global scale. To gain an improved insight into this area, the present article reviews salient clinical aspects of human toxocariasis and the epidemiology of this disease, with particular reference to seroprevalence, and discusses future research and approaches/measures to understand and prevent/control this socioeconomically important, yet neglected zoonosis.

Cytokine production and signalling in human THP-1 macrophages is dependent on Toxocara canis glycans

The effect of Toxocara canis antigens on cytokine production by human THP-1 macrophages was studied in vitro. Toxocara Excretory–Secretory products (TES) and recombinant mucins (Tc-MUC-2, Tc-MUC-3, Tc-MUC-4, and Tc-MUC-5) as well as deglycosylated forms of these antigens were used in the study. TES products stimulated macrophages to produce the innate proinflammatory IL-1β, IL-6, and TNF-α cytokines regardless of the presence of glycans. Recombinant mucins induced glycan-dependent cytokine production. Sugar moieties led to at least 3-fold higher production of regulatory IL-10 as well as proinflammatory cytokines. The presence of glycans on mucins also affected the downstream signalling pathways in stimulated cells. The most prominent difference was noted in AKT and AMPK kinase activation. AKT phosphorylation was observed in cells stimulated with glycosylated mucins, whereas treatment with deglycosylated antigens led to AMPK phosphorylation. MAP kinase family members such as JNK and p38 and c-Jun transcription factor were phosphorylated in both cases what suggests that toll-like receptor signalling may be involved in mucin-treated macrophages. This pathway is however modified by other signalling molecules as only mucins containing intact sugars significantly induced the production of cytokines.

Toxocara vitulorum cuticle glycoproteins in the diagnosis of calves' toxocariasis

Aim:

The current study was designed to isolate and characterize Toxocara vitulorum glycoprotein antigens and then to evaluate its potency in accurate diagnosis of toxocariasis.

Materials and Methods:

T. vitulorum glycoprotein fractions were isolated using Con-A affinity chromatography. The fractions characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and immunoblot assay. Mass spectrometric analysis was used for identification of proposed structure of the N-acetylglucosamine (GlcNAc) fraction. Enzyme-linked immunosorbent assay (ELISA) was used to assess the diagnostic potential of the isolated fractions.

Results:

Surface of T. vitulorum adult worm revealed two glycoprotein fractions rich in glucose (Glc) and GlcNAc. Three bands of molecular weight 212kDa, 107 kDa, and 93 kDa were detected in Glc fraction by SDS-PAGE. These bands were also detected in GlcNAc fraction with an additional band of 49 kDa. GlcNAc fraction showed more diagnostic potency of calves’ toxocariasis; 79% than Glc fraction; 46.9% by indirect ELISA. The additional band of 49 kDa in GlcNAc fraction is probably responsible for its higher diagnostic potentials. Western blotting verified the immunoreactivity of the Glc and GlcNAc isolated fraction as they reacted with calves sera infected with toxocariasis. The proposed structure of GlcNAc fraction was Ser-Meth-Arg-O-methylated GlcNAc.

Conclusion:

GlcNAc-rich fraction of T. vitulorum can be successfully utilized in the diagnosis of calves’ toxocariasis.

Immunomodulation by Helminths: Intracellular Pathways and Extracellular Vesicles

Helminth parasites are masters at manipulating host immune responses, using an array of sophisticated mechanisms. One of the major mechanisms enabling helminths to establish chronic infections is the targeting of pattern recognition receptors (PRRs) including toll-like receptors, C-type lectin receptors, and the inflammasome. Given the critical role of these receptors and their intracellular pathways in regulating innate inflammatory responses, and also directing adaptive immunity toward Th1 and Th2 responses, recognition of the pathways triggered and/or modulated by helminths and their products will provide detailed insights about how helminths are able to establish an immunoregulatory environment. However, helminths also target PRRs-independent mechanisms (and most likely other yet unknown mechanisms and pathways) underpinning the battery of different molecules helminths produce. Herein, the current knowledge on intracellular pathways in antigen presenting cells activated by helminth-derived biomolecules is reviewed. Furthermore, we discuss the importance of helminth-derived vesicles as a less-appreciated components released during infection, their role in activating these host intracellular pathways, and their implication in the development of new therapeutic approaches for inflammatory diseases and the possibility of designing a new generation of vaccines.

Human toxocariasis

Parasitic nematodes of the genus Toxocara are socioeconomically important zoonotic pathogens. These parasites are usually directly transmitted to the human host via the faecal-oral route and can cause toxocariasis and associated complications, including allergic and neurological disorders. Although tens of millions of people are estimated to be exposed to or infected with Toxocara spp, global epidemiological information on the relationship between seropositivity and toxocariasis is limited. Recent findings suggest that the effect of toxocariasis on human health is increasing in some countries. Here we review the salient background on Toxocara and biology, summarise key aspects of the pathogenesis, diagnosis, and treatment of toxocariasis, describe what is known about its geographic distribution and prevalence, and make some recommendations for future research towards the prevention and control of this important disease.

6-OHDA-Lesioned Adult Zebrafish as a Useful Parkinson's Disease Model for Dopaminergic Neuroregeneration

Conventional mammalian models of neurodegeneration are often limited by futile axonogenesis with minimal functional recuperation of severed neurons. The emergence of zebrafish, a non-mammalian model with excellent neuroregenerative properties, may address these limitations. This study aimed to establish an adult zebrafish-based, neurotoxin-induced Parkinson's disease (PD) model and subsequently validate the regenerative capability of dopaminergic neurons (DpN). The DpN of adult male zebrafish (Danio rerio) were lesioned by microinjecting 6-hydroxydopamine (6-OHDA) neurotoxin (6.25, 12.5, 18.75, 25, 37.5, 50 and 100 mg/kg) into the ventral diencephalon (Dn). This was facilitated by an optimised protocol that utilised 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanineperchlorate (DiI) dye to precisely identify the injection site. Immunostaining was utilised to identify the number of tyrosine hydroxylase immunoreactive (TH-ir) DpN in brain regions of interest (i.e. olfactory bulb, telencephalon, preoptic area, posterior tuberculum and hypothalamus). Open tank video recordings were performed for locomotor studies. The Dn was accessed by setting the injection angle of the microinjection capillary to 60° and injection depth to 1200 μm (from the exposed brain surface). 6-OHDA (25 mg/kg) successfully ablated >85% of the Dn DpN (preoptic area, posterior tuberculum and hypothalamus) whilst maintaining a 100% survival. Locomotor analysis of 5-min recordings revealed that 6-OHDA-lesioned adult zebrafish were significantly (p < 0.0001) reduced in speed (cm/s) and distance travelled (cm). Lesioned zebrafish showed full recovery of Dn DpN 30 days post-lesion. This study had successfully developed a stable 6-OHDA-induced PD zebrafish model using a straightforward and reproducible approach. Thus, this developed teleost model poses exceptional potentials to study DpN regeneration.

Immunoglobulin M antibodies are not specific for serodiagnosis of human toxocariasis

Serodiagnosis of human toxocariasis is established by detecting serum anti-Toxocara IgG antibodies, but there is little knowledge regarding the reactivity of human IgM antibodies against the Toxocara antigens. In this study, we have evaluated the reactivity of IgM antibodies in sera from patients with toxocariasis, patients with other helminth infections, and healthy individuals, against Toxocara larval excretory-secretory (TES) antigens by enzyme-linked immunosorbent assay (ELISA) and Western blot (WB). Anti-Toxocara IgM were detected in 91.4% of sera from patients with toxocariasis, 76% of sera from patients with other helminth infections, and 45.3% of sera from healthy individuals when ELISA was used. Likewise, IgM antibodies were detected in 94.8% of sera from patients with toxocariasis, 65.3% of sera from patients with other helminth infections, and 41% of sera from healthy individuals when WB was used. This reactivity exhibited only a slight decrease when the TES antigens were deglycosylated, showing that not only glycosidic epitopes, but also peptide epitopes are involved in the recognition and binding of IgM antibodies during the immune response against the parasite. The results shown that IgM antibodies are not specific for serodiagnosis of human toxocariasis.

Isolation of a methylated mannose-binding protein from terrestrial worm Enchytraeus japonensis

To elucidate a biological role of the methylated mannose residues found in N-glycans of terrestrial worm Enchytraeus japonensis, we first synthesized 3-O-methyl mannose- and 4-O-methyl mannose-derivatives and immobilized them to Sepharose 4B beads in order to isolate the sugar-binding protein. When whole protein extracts from the worms was applied to a series of the columns immobilized with the modified and unmodified mannose-derivatives, respectively, a protein with a molecular weight of 25,000 was isolated by 4-O-methyl mannose-immobilized column chromatography, and termed as a methylated mannose-binding protein (mMBP). mMBP bound weakly to a mannose-immobilized column and moderately to a 3-O-methyl mannose-immobilized column. The N-terminal amino acid sequences of mMBP and its endoprotease-digested peptides were determined. Using the degenerate first primers synthesized based on the primary sequence, a genomic DNA fragment was isolated. Then, the second primers were synthesized based on the genomic DNA fragment, and with use of them two cDNA fragments were obtained by the 3'- and 5'-RACE methods. Finally, the third primers were synthesized based on the sequences of the two cDNA fragments and one genomic DNA fragment, and with use of them a full-length cDNA of mMBP was isolated and shown to comprise a putative 633 bp open reading frame encoding 210 amino acid residues. BLAST analysis revealed that mMBP has identities by 26 ~ 55% to several proteins including the regeneration-upregulated protein 3 from the same species. Whether mMBP is involved in the regeneration of the worm is under investigation.

Helminth glycomics - glycan repertoires and host-parasite interactions

Glycoproteins and glycolipids of parasitic helminths play important roles in biology and host-parasite interaction. This review discusses recent helminth glycomics studies that have been expanding our insights into the glycan repertoire of helminths. Structural data are integrated with biological and immunological observations to highlight how glycomics advances our understanding of the critical roles that glycans and glycan motifs play in helminth infection biology. Prospects and challenges in helminth glycomics and glycobiology are discussed.

Proteomic analysis of Toxocara canis excretory and secretory (TES) proteins

Toxocariasis is a neglected disease, and its main etiological agent is the nematode Toxocara canis. Serological diagnosis is performed by an enzyme-linked immunosorbent assay using T. canis excretory and secretory (TES) antigens produced by in vitro cultivation of larvae. Identification of TES proteins can be useful for the development of new diagnostic strategies since few TES components have been described so far. Herein, we report the results obtained by proteomic analysis of TES proteins using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach. TES fractions were separated by one-dimensional SDS-PAGE and analyzed by LC-MS/MS. The MS/MS spectra were compared with a database of protein sequences deduced from the genome sequence of T. canis, and a total of 19 proteins were identified. Classification according to the signal peptide prediction using the SignalP server showed that seven of the identified proteins were extracellular, 10 had cytoplasmic or nuclear localization, while the subcellular localization of two proteins was unknown. Analysis of molecular functions by BLAST2GO showed that the majority of the gene ontology (GO) terms associated with the proteins present in the TES sample were associated with binding functions, including but not limited to protein binding (GO:0005515), inorganic ion binding (GO:0043167), and organic cyclic compound binding (GO:0097159). This study provides additional information about the exoproteome of T. canis, which can lead to the development of new strategies for diagnostics or vaccination.

Toxocara canis glycans influence antigen recognition by mouse IgG1 and IgM antibodies

The impact of sugar moieties of Toxocara canis glycoprotein antigens on their recognition by infected mouse antibodies was investigated in this study. Native TES and recombinant Toxocara mucins generated in Pichia pastoris yeast as well as their deglycosylated forms were used in ELISA. TES and recombinant mucins were equally recognized by T. canis infected mouse IgG1 antibodies. IgM immunoglobulins predominantly recognized TES antigens. Among mucins recognition of Tc-MUC-4 was the most significant. Deglycosylation of antigens resulted in significant loss of IgM and IgG1 reactivity to TES, mucins, Tc-MUC-3 and Tc-MUC-4. The presence of sugar moieties had no influence on IgE binding to native or recombinant T. canis antigens. Our results suggest that glycans are involved in epitope formation what should be taken into consideration in production of recombinant helminth antigens for diagnostic purposes.

Novel O-linked methylated glycan antigens decorate secreted immunodominant glycoproteins from the intestinal nematode Heligmosomoides polygyrus

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Heligmosomoides polygyrus excretory–secretory (ES) proteins carry diverse N- and O-glycans, and many are O-methylated.

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A methylhexose containing O-glycan of abundant ES glycoproteins is immunodominant.

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This dominant glycan is not the immunomodulatory heat-stable ES component.

Glycan molecules from helminth parasites have been associated with diverse biological functions ranging from interactions with neighbouring host cell populations to down-modulation of specific host immunity. Glycoproteins secreted by the intestinal nematode Heligmosomoides polygyrus are of particular interest as the excretory–secretory products (termed HES) of this parasite contain both heat-labile and heat-stable components with immunomodulatory effects. We used MALDI-TOF-MS and LC–MS/MS to analyse the repertoire of N- and O-linked glycans released from Heligmosomoides polygyrus excretory–secretory products by PNGase A and F, β-elimination and hydrazinolysis revealing a broad range of structures including novel methylhexose- and methylfucose-containing glycans. Monoclonal antibodies to two immunodominant glycans of H. polygyrus, previously designated Glycans A and B, were found to react by glycan array analysis to a methyl-hexose-rich fraction and to a sulphated LacDiNAc (LDN; GalNAcβ1–4GlcNAc) structure, respectively. We also analysed the glycan repertoire of a major glycoprotein in Heligmosomoides polygyrus excretory–secretory products, VAL-2, which contains many glycan structures present in Heligmosomoides polygyrus excretory–secretory products including Glycan A. However, it was found that this set of glycans is not responsible for the heat-stable immunomodulatory properties of Heligmosomoides polygyrus excretory–secretory products, as revealed by the inability of VAL-2 to inhibit allergic lung inflammation. Taken together, these studies reveal that H. polygyrus secretes a diverse range of antigenic glycoconjugates, and provides a framework to explore the biological and immunomodulatory roles they may play within the mammalian host.

Inhibition of Haemonchus contortus larval development by fungal lectins

Background

Lectins are carbohydrate-binding proteins that are involved in fundamental intra- and extracellular biological processes. They occur ubiquitously in nature and are especially abundant in plants and fungi. It has been well established that certain higher fungi produce lectins in their fruiting bodies and/or sclerotia as a part of their natural resistance against free-living fungivorous nematodes and other pests. Despite relatively high diversity of the glycan structures in nature, many of the glycans targeted by fungal lectins are conserved among organisms of the same taxon and sometimes even among different taxa. Such conservation of glycans between free-living and parasitic nematodes is providing us with a useful tool for discovery of novel chemotherapeutic and vaccine targets. In our study, a subset of fungal lectins emanating from toxicity screens on Caenorhabditis elegans was tested for their potential to inhibit larval development of Haemonchus contortus.

Methods

The effect of Coprinopsis cinerea lectins - CCL2, CGL2, CGL3; Aleuria aurantia lectin – AAL; Marasmius oreades agglutinin - MOA; and Laccaria bicolor lectin – Lb-Tec2, on cultivated Haemonchus contortus larval stages was investigated using a larval development test (LDT). To validate the results of the toxicity assay and determine lectin binding capacity to the nematode digestive tract, biotinylated versions of lectins were fed to pre-infective larval stages of H. contortus and visualized by fluorescent microscopy. Lectin histochemistry on fixed adult worms was performed to investigate the presence and localisation of lectin binding sites in the disease-relevant developmental stage.

Results

Using an improved larval development test we found that four of the six tested lectins: AAL, CCL2, MOA and CGL2, exhibited a dose-dependent toxicity in LDT, as measured by the number of larvae developing to the L3 stage. In the case of AAL, CGL2 and MOA lectin, doses as low as 5 μg/ml caused >95 % inhibition of larval development while 40 μg/ml were needed to achieve the same inhibition by CCL2 lectin. MOA was the only lectin tested that caused larval death while other toxic lectins had larvistatic effect manifesting as L1 growth arrest. Using lectin histochemistry we demonstrate that of all lectins tested, only the four toxic ones displayed binding to the larvae’s gut and likewise were found to interact with glycans localized to the gastrodermal tissue of adults.

Conclusion

The results of our study suggest a correlation between the presence of target glycans of lectins in the digestive tract and the lectin-mediated toxicity in Haemonchus contortus. We demonstrate that binding to the structurally conserved glycan structures found in H. contortus gastrodermal tissue by the set of fungal lectins has detrimental effect on larval development. Some of these glycan structures might represent antigens which are not exposed to the host immune system (hidden antigens) and thus have a potential for vaccine or drug development. Nematotoxic fungal lectins prove to be a useful tool to identify such targets in parasitic nematodes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1032-x) contains supplementary material, which is available to authorized users.

Mucin-Type O-Glycosylation in Invertebrates

O-Glycosylation is one of the most important posttranslational modifications of proteins. It takes part in protein conformation, protein sorting, developmental processes and the modulation of enzymatic activities. In vertebrates, the basics of the biosynthetic pathway of O-glycans are already well understood. However, the regulation of the processes and the molecular aspects of defects, especially in correlation with cancer or developmental abnormalities, are still under investigation. The knowledge of the correlating invertebrate systems and evolutionary aspects of these highly conserved biosynthetic events may help improve the understanding of the regulatory factors of this pathway. Invertebrates display a broad spectrum of glycosylation varieties, providing an enormous potential for glycan modifications which may be used for the design of new pharmaceutically active substances. Here, overviews of the present knowledge of invertebrate mucin-type O-glycan structures and the currently identified enzymes responsible for the biosynthesis of these oligosaccharides are presented, and the few data dealing with functional aspects of O-glycans are summarised.

Toxocara canis mucins among other excretory-secretory antigens induce in vitro secretion of cytokines by mouse splenocytes

The effect of Toxocara larval antigens on cytokine secretion by mouse splenocytes was studied in vitro. Recombinant mucins were produced in Pichia pastoris yeast, and Toxocara excretory-secretory (TES) antigens were collected from in vitro culture of L2 larvae. Tc-MUC-2, Tc-MUC-3, Tc-MUC-4, and Tc-MUC-5 were expressed as glycoproteins and were specifically recognized by Toxocara canis-infected dog serum antibodies. Mouse splenocytes stimulated with recombinant mucins produced IL-5, IL-6, and TGF-β. Cell stimulation with whole TES products was more effective and resulted in secretion of IL-4, IL-5, IL-6, IL-10, and TGF-β and downregulation of TNF-α production. IFN-γ and IL-17 secretion was noted only after ConA treatment. Cells originating from infected animals produced significantly smaller amounts of these two cytokines compared to control cells, which suggests that Th1 and Th17 response in infected mice is strongly inhibited. However, splenocyte stimulation with both TES and ConA upregulated the production of IFN-γ and IL-17. This shows that TES antigens have strong immunomodulatory properties and are able to induce a broad range of effects on murine immune cells.

[Evaluation of a purified antigen for the diagnosis of toxocariosis]

Toxocarosis is a zoonotic disease caused by the ingestion of infective eggs of Toxocara spp. The diagnosis is based on the detection of antibodies in serum or other biological fluids. One of the current serological techniques for the diagnosis of toxocariasis is ELISA using excretory - secretory antigens of third stage larvae (ES/L3). These antigens are glycoproteins, which originate in the secretory organs of the parasite and are non species-specific. Sera from patients with other helminthiases and non- parasitic diseases were used to evaluate the specificity of ELISA using the excretory - secretory antigen (ES/L3). The reactivity of these sera was between 11 and 70%. Western blot using patients' sera revealed that the glycoprotein triplet having a molecular weight of 120 kDa was responsible for cross-reactivity. With these results, and for the purpose of purifying the antigen, ion exchange chromatography was performed. When the sera from patients with various parasitic and non-parasitic diseases were analyzed with the purified antigen ES/ L3, they were only reactive between 10 to 20%. The sensitivity of the ELISA test determined by program Epidat 3.0 for the two antigens was 100%, but the following differences in specificity were observed: 84% for the total antigen ES/L3 and 99% for purified ES/L3. Using the ES/L3 purified antigen, it can be considered that the reactive sera, with compatible symptoms correspond to patients who are or were parasitized with Toxocara canis.

Helminths: Immunoregulation and Inflammatory Diseases-Which Side Are Trichinella spp. and Toxocara spp. on?

Macropathogens, such as multicellular helminths, are considered masters of immunoregulation due to their ability to escape host defense and establish chronic infections. Molecular crosstalk between the host and the parasite starts immediately after their encounter, which influences the course and development of both the innate and adaptive arms of the immune response. Helminths can modulate dendritic cells (DCs) function and induce immunosuppression which is mediated by a regulatory network that includes regulatory T (Treg) cells, regulatory B (Breg) cells, and alternatively activated macrophages (AAMs). In this way, helminths suppress and control both parasite-specific and unrelated immunopathology in the host such as Th1-mediated autoimmune and Th2-mediated allergic diseases. However, certain helminths favour the development or exacerbation of allergic responses. In this paper, the cell types that play an essential role in helminth-induced immunoregulation, the consequences for inflammatory diseases, and the contrasting effects of Toxocara and Trichinella infection on allergic manifestations are discussed.

Toxocara canis: molecular basis of immune recognition and evasion

Toxocara canis has extraordinary abilities to survive for many years in the tissues of diverse vertebrate species, as well as to develop to maturity in the intestinal tract of its definitive canid host. Human disease is caused by larval stages invading musculature, brain and the eye, and immune mechanisms appear to be ineffective at eliminating the infection. Survival of T. canis larvae can be attributed to two molecular strategies evolved by the parasite. Firstly, it releases quantities of 'excretory-secretory' products which include lectins, mucins and enzymes that interact with and modulate host immunity. For example, one lectin (CTL-1) is very similar to mammalian lectins, required for tissue inflammation, suggesting that T. canis may interfere with leucocyte extravasation into infected sites. The second strategy is the elaboration of a specialised mucin-rich surface coat; this is loosely attached to the parasite epicuticle in a fashion that permits rapid escape when host antibodies and cells adhere, resulting in an inflammatory reaction around a newly vacated focus. The mucins have been characterised as bearing multiple glycan side-chains, consisting of a blood-group-like trisaccharide with one or two O-methylation modifications. Both the lectins and these trisaccharides are targeted by host antibodies, with anti-lectin antibodies showing particular diagnostic promise. Antibodies to the mono-methylated trisaccharide appear to be T. canis-specific, as this epitope is not found in the closely related Toxocara cati, but all other antigenic determinants are very similar between the two species. This distinction may be important in designing new and more accurate diagnostic tests. Further tools to control toxocariasis could also arise from understanding the molecular cues and steps involved in larval development. In vitro-cultivated larvae express high levels of four mRNAs that are translationally silenced, as the proteins they encode are not detectable in cultured larvae. However, these appear to be produced once the parasite has entered the mammalian host, as they are recognised by specific antibodies in infected patients. Elucidating the function of these genes, or analysing if micro-RNA translational silencing suppresses production of the proteins, may point towards new drug targets for tissue-phase parasites in humans.

How helminths use excretory secretory fractions to modulate dendritic cells

It is well known that helminth parasites have immunomodulatory effects on their hosts. They characteristically cause a skew toward T_H2 immunity, stimulate Treg cells while simultaneously inhibiting T_H1 and T_H17 responses. Additionally, they induce eosinophilia and extensive IgE release. The exact mechanism of how the worms achieve this effect have yet to be fully elucidated; however, parasite-derived secretions and their interaction with antigen presenting cells have been centrally implicated. Herein, we will review the effects of helminth excretory-secretory fractions on dendritic cells and discuss how this interaction is crucial in shaping the host response.

Synthesis, antigenicity against human sera and structure-activity relationships of carbohydrate moieties from Toxocara larvae and their analogues

Stereocontrolled syntheses of biotin-labeled oligosaccharide portions containing the Galβ1-3GalNAc core of the TES-glycoprotein antigen obtained from larvae of the parasite Toxocara and their analogues have been accomplished. Trisaccharides Fuc2Meα1-2Gal4Meβ1-3GalNAcα1-OR (A), Fucα1-2Gal4Meβ1-3GalNAcα1-OR (B), Fuc2Meα1-2Galβ1-3GalNAcα1-OR (C), Fucα1-2Galβ1-3GalNAcα1-OR (D) and a disaccharide Fuc2Meα1-2Gal4Meβ1-OR (E) (R = biotinylated probe) were synthesized by block synthesis using 5-(methoxycarbonyl)pentyl-2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl-(1→3)-2-azide-4-O-benzyl-2-deoxy-α-D-galactopyranoside as a common glycosyl acceptor. We examined the antigenicity of these five oligosaccharides by enzyme linked immunosorbent assay (ELISA). Our results demonstrate that the O-methyl groups in these oligosaccharides are important for their antigenicity and the biotinylated oligosaccharides A, B, C and E have high serodiagnostic potential to detect infections caused by Toxocara larvae.

Alternative activation of macrophages by filarial nematodes is MyD88-independent

Alternative macrophage activation is largely defined by IL-4Rα stimulation but the contribution of Toll-like receptor (TLR) signaling to this phenotype is not currently known. We have investigated macrophage activation status under Th2 conditions in the absence of the core TLR adaptor molecule, MyD88. No impairment was observed in the ability of MyD88-deficient bone marrow derived macrophages to produce or express alternative activation markers, including arginase, RELM-α or Ym1, in response to IL-4 treatment in vitro. Further, we observed no difference in the ability of peritoneal exudate cells from nematode implanted wild type (WT) or MyD88-deficient mice to produce arginase or express the alternative activation markers RELM-α or Ym1. Therefore, MyD88 is not a fundamental requirement for Th2-driven macrophage alternative activation, either in vitro or in vivo.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

TLRs, Treg, and B Cells, an Interplay of Regulation during Helminth Infection

Commonly described as masters of regulation parasitic helminth infections provide a fascinating insight into the complexity of our immune system. As with many other pathogens helminths have developed complex evasion strategies and the immune response of the host has to find a balance between eliciting severe damage to eliminate the parasite or limiting damage and thereby accepting the infection. Nevertheless, one should not forget that these infections still pose a serious public health problem and can elicit severe disfigurement or death in the individual. An interesting spin-off of helminth manipulation on host responses is the apparent prevention of autoimmune diseases or allergy although the actual mechanisms remain unclear. It is well known that Toll-like-receptors (TLR) and non-TLR PRRs play a critical role in initiating innate immune responses which in turn create appropriate adaptive immune reactions. Helminths comprise of a multitude of (glyco)-proteins and (glyco)-lipids and some have been shown to trigger TLR, or alter TLR-mediated responses. Such reactions of course alter adaptive immunity as well. This review will address the consequences of TLR-triggering by helminth antigens and the downstream effect on B cell and regulatory T cell (Treg) actions.

Modifications of glycans: biological significance and therapeutic opportunities

Carbohydrates play a central role in a wide range of biological processes. As with nucleic acids and proteins, modifications of specific sites within the glycan chain can modulate a carbohydrate's overall biological function. For example, acylation, methylation, sulfation, epimerization, and phosphorylation can occur at various positions within a carbohydrate to modulate bioactivity. Therefore, there is significant interest in identifying discrete carbohydrate modifications and understanding their biological effects. Additionally, enzymes that catalyze those modifications and proteins that bind modified glycans provide numerous targets for therapeutic intervention. This review will focus on modifications of glycans that occur after the oligomer/polymer has been assembled, generally referred to as post-glycosylational modifications.

Heligmosomoides polygyrus elicits a dominant nonprotective antibody response directed against restricted glycan and peptide epitopes

Heligmosomoides polygyrus is a widely used gastrointestinal helminth model of long-term chronic infection in mice, which has not been well-characterized at the antigenic level. We now identify the major targets of the murine primary Ab response as a subset of the secreted products in H. polygyrus excretory-secretory (HES) Ag. An immunodominant epitope is an O-linked glycan (named glycan A) carried on three highly expressed HES glycoproteins (venom allergen Ancylostoma-secreted protein-like [VAL]-1, -2, and -5), which stimulates only IgM Abs, is exposed on the adult worm surface, and is poorly represented in somatic parasite extracts. A second carbohydrate epitope (glycan B), present on both a non-protein high molecular mass component and a 65-kDa molecule, is widely distributed in adult somatic tissues. Whereas the high molecular mass component and 65-kDa molecules bear phosphorylcholine, the glycan B epitope itself is not phosphorylcholine. Class-switched IgG1 Abs are found to glycan B, but the dominant primary IgG1 response is to the polypeptides of VAL proteins, including also VAL-3 and VAL-4. Secondary Ab responses include the same specificities while also recognizing VAL-7. Although vaccination with HES conferred complete protection against challenge H. polygyrus infection, mAbs raised against each of the glycan epitopes and against VAL-1, VAL-2, and VAL-4 proteins were unable to do so, even though these specificities (with the exception of VAL-2) are also secreted by tissue-phase L4 larvae. The primary immune response in susceptible mice is, therefore, dominated by nonprotective Abs against a small subset of antigenic epitopes, raising the possibility that these act as decoy specificities that generate ineffective humoral immunity.

Glycoproteomics-based identification of cancer biomarkers

Protein glycosylation is one of the most common posttranslational modifications in mammalian cells. It is involved in many biological pathways and molecular functions and is well suited for proteomics-based disease investigations. Aberrant protein glycosylation may be associated with disease processes. Specific glycoforms of glycoproteins may serve as potential biomarkers for the early detection of disease or as biomarkers for the evaluation of therapeutic efficacy for treatment of cancer, diabetes, and other diseases. Recent technological developments, including lectin affinity chromatography and mass spectrometry, have provided researchers the ability to obtain detailed information concerning protein glycosylation. These in-depth investigations, including profiling and quantifying glycoprotein expression, as well as comprehensive glycan structural analyses may provide important information leading to the development of disease-related biomarkers. This paper describes methodologies for the detection of cancer-related glycoprotein and glycan structural alterations and briefly summarizes several current cancer-related findings.

Glycan microarray profiling of parasite infection sera identifies the LDNF glycan as a potential antigen for serodiagnosis of trichinellosis

Diagnostic methods for parasite infections still highly depend on the identification of the parasites by direct methods such as microscopic examination of blood, stool and tissue biopsies. Serodiagnosis is often carried out to complement the direct methods; however, few synthetic antigens with sufficient sensitivity and specificity are available. Here we evaluated a glycan microarray approach to select for synthetic glycan antigens that could be used for serodiagnosis of parasitic infections. Using a glycan array containing over 250 different glycan antigens, we identified GalNAcβ1-4(Fucα1-3)GlcNAc-R (LDNF) as a glycan antigen that is recognized by antibodies from Trichinella-infected individuals. We synthesized a neoglycoconjugate, consisting of five LDNF molecules covalently coupled to bovine serum albumin (BSA), and used this neoglycoconjugate as an antigen to develop a highly sensitive total-Ig ELISA for serological screening of trichinellosis. The results indicate that glycan microarrays constitute a promising technology for fast and specific identification of parasite glycan antigens to improve serodiagnosis of different parasitic infections, either using an ELISA format, or parasite-specific glycan arrays.

Glycomarkers in parasitic infections and allergy

Both helminth infections and contact with allergens result in development of a Th2 type of immune response in the affected individual. In this context, the hygiene hypothesis suggests that reduced prevalence of parasitic infections and successful vaccination strategies are causative for an increase of allergies in industrialized countries. It is therefore of interest to study glycans and their role as immunogenic structures in both parasitic infections and allergies. In the present paper we review information on the different types of glycan structure present in proteins from plant and animal food, insect venom and helminth parasites, and their role as diagnostic markers. In addition, the application of these glycan structures as immunomodulators in novel immunotherapeutic strategies is discussed.

Chronic helminth infections protect against allergic diseases by active regulatory processes

Developed countries are suffering from an epidemic rise in immunologic disorders, such as allergy-related diseases and certain autoimmunities. Several studies have demonstrated a negative association between helminth infections and inflammatory diseases (eg, allergy), providing a strong case for the involvement of helminth infections in this respect. However, some studies point in the opposite direction. The discrepancy may be explained by differences in frequency, dose, time, and type of helminth. In this review, new studies are discussed that may support the concept that chronic helminth infections in particular—but not acute infections—are associated with the expression of regulatory networks necessary for downmodulating allergic immune responses to harmless antigens. Furthermore, different components of regulatory networks are highlighted, such as the role of regulatory T and B cells, modulation of dendritic cells, early innate signals from structural cells (eg, epithelial cells), and their individual contributions to protection against allergic diseases. It is of great interest to define and characterize specific helminth molecules that have profound immunomodulatory capacities as targets for therapeutic application in the treatment or prophylaxis of allergic manifestations.

Helminths and dendritic cells: sensing and regulating via pattern recognition receptors, Th2 and Treg responses

The classical reaction of the host to helminth infections is the induction of Th2 immune responses with a regulatory component. DC, as central players in the induction and maintenance of immune responses, play a prominent role in both these processes, and in recent years considerable progress has been made in elucidating the mechanisms behind the interplay between DC and helminths. It is becoming increasingly clear that helminths modulate DC function not only via direct interactions but also indirectly via host-derived cues. Furthermore, while studies have until recently focused on receptor signaling-mediated DC modulation by helminths, evidence is emerging that DC may also respond to helminth infections by sensing stress signals or tissue damage inflicted by the worms or their products. Here, we will discuss these new insights and will link them to the origin and importance of Th2 and regulatory immune responses with respect to the survival of both parasite and host.

Worms to the rescue: can worm glycans protect from autoimmune diseases?

Autoimmune and autoinflammatory diseases represent a significant health burden, especially in Western societies. For the majority of these diseases, no cure exists. Recently, research on parasitic worms (helminths) has demonstrated great potential for whole worms, their eggs or their excretory/secretory proteins in down-regulating inflammatory responses both in vitro and in vivo, in various disease models and, in some cases, even in clinical trials. The worms are thought to induce Th2 and regulatory T cells, interfere with Toll-like receptor (TLR) signaling and to down-regulate Th17 and Th1 responses. The molecular mechanisms underlying the worms' ability to modulate the host immune response are not well understood, and many hypotheses have been proposed to explain the observed immune modulation. Increasing evidence suggests that carbohydrate structures (glycans), for example, phosphorylcholine-modified glycans or Galbeta1-4(Fucalpha1-3)GlcNAc- (Lewis X, Le(X)) containing glycans, expressed by the worms contribute to these modulating properties by their interaction with antigen presenting cells. Helminths express a broad variety of protein- and lipid-linked glycans on their surface and on secretory products. These glycans differ in amount and composition and several of these structures are species specific. However, worms also express glycan antigens that are found in a wide variety of different species. Some of these "common" worm glycans are particularly interesting with regard to regulating host responses, because they have the potential to interact with C-type lectins on dendritic cells and thereby may interfere with T-cell polarization. Helminths and helminth-derived molecules form a novel and promising group of therapeutics for autoinflammatory diseases. However, much has to be learned about the molecular mechanisms behind the helminth-mediated antiinflammatory properties. This review will describe some of the emerging evidence in selected disease areas as well as discuss the putative role of glycans in helminth-mediated immunosuppression.

Characterization of the Caenorhabditis elegans UDP-galactopyranose mutase homolog glf-1 reveals an essential role for galactofuranose metabolism in nematode surface coat synthesis

Galactofuranose (Gal(f)), the furanoic form of d-galactose produced by UDP-galactopyranose mutases (UGMs), is present in surface glycans of some prokaryotes and lower eukaryotes. Absence of the Gal(f) biosynthetic pathway in vertebrates and its importance in several pathogens make UGMs attractive drug targets. Since the existence of Gal(f) in nematodes has not been established, we investigated the role of the Caenorhabditis elegans UGM homolog glf-1 in worm development. glf-1 mutants display significant late embryonic and larval lethality, and other phenotypes indicative of defective surface coat synthesis, the glycan-rich outermost layer of the nematode cuticle. The glf homolog from the protozoan Leishmania major partially complements C. elegans glf-1. glf-1 mutants rescued by L. major glf, which behave as glf-1 hypomorphs, display resistance to infection by Microbacterium nematophilum, a pathogen of rhabditid nematodes thought to bind to surface coat glycans. To confirm the presence of Gal(f) in C. elegans, we analyzed C. elegans nucleotide sugar pools using online electrospray ionization-mass spectrometry (ESI-MS). UDP-Gal(f) was detected in wild-type animals while absent in glf-1 deletion mutants. Our data indicate that Gal(f) likely has a pivotal role in maintenance of surface integrity in nematodes, supporting investigation of UGM as a drug target in parasitic species.

Glycan gimmickry by parasitic helminths: a strategy for modulating the host immune response?

Parasitic helminths (worms) co-evolved with vertebrate immune systems to enable long-term survival of worms in infected hosts. Among their survival strategies, worms use their glycans within glycoproteins and glycolipids, which are abundant on helminth surfaces and in their excretory/ secretory products, to regulate and suppress host immune responses. Many helminths express unusual and antigenic (nonhost-like) glycans, including those containing polyfucose, tyvelose, terminal GalNAc, phosphorylcholine, methyl groups, and sugars in unusual linkages. In addition, some glycan antigens are expressed that share structural features with those in their intermediate and vertebrate hosts (host-like glycans), including Le(X) (Galbeta1-4[Fucalpha1-3]GlcNAc-), LDNF (GalNAcbeta1-4[Fucalpha1-3]GlcNAc-), LDN (GalNAcbeta1-4GlcNAc-), and Tn (GalNAcalpha1-O-Thr/Ser) antigens. The expression of host-like glycan determinants is remarkable and suggests that helminths may gain advantages by synthesizing such glycans. The expression of host-like glycans by parasites previously led to the concept of "molecular mimicry," in which molecules are either derived from the pathogen or acquired from the host to evade recognition by the host immune system. However, recent discoveries into the potential of host glycan-binding proteins (GBPs), such as C-type lectin receptors and galectins, to functionally interact with various host-like helminth glycans provide new insights. Host GBPs through their interactions with worm-derived glycans participate in shaping innate and adaptive immune responses upon infection. We thus propose an alternative concept termed "glycan gimmickry," which is defined as an active strategy of parasites to use their glycans to target GBPs within the host to promote their survival.

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.

Vaccination-induced IgG response to Galalpha1-3GalNAc glycan epitopes in lambs protected against Haemonchus contortus challenge infection

Lambs vaccinated with Haemonchus contortus excretory/secretory (ES) glycoproteins in combination with the adjuvant Alhydrogel are protected against H. contortus challenge infection. Using glycan micro-array analysis we showed that serum from such vaccinated lambs contains IgG antibodies that recognise the glycan antigen Galalpha1-3GalNAc-R and GalNAcbeta1-4(Fucalpha1-3)GlcNAc-R. Our studies revealed that H. contortus glycoproteins contain Galalpha1-3Gal-R as well as significant levels of Galalpha1-3GalNAc-R, which has not been previously reported. Extracts from H. contortus adult worms contain a galactosyltransferase acting on glycan substrates with a terminal GalNAc, indicating that the worms possess the enzymatic potential to synthesise terminal Gal-GalNAc moieties. These data illustrate that glycan micro-arrays constitute a promising technology for fast and specific analysis of serum anti-glycan antibodies in vaccination studies. In addition, this approach facilitates the discovery of novel, antigenic parasite glycan antigens that may have potential for developing glycoconjugate vaccines or utilization in diagnostics.

Exploring the immunology of parasitism--from surface antigens to the hygiene hypothesis

Helminth immunology is a field which has changed beyond recognition in the past 30 years, transformed not only by new technologies from cDNA cloning to flow cytometry, but also conceptually as our definition of host immune pathways has matured. The molecular revolution defined key nematode surface and secreted antigens, and identified candidate immunomodulators that are likely to underpin parasites' success in eluding immune attack. The immunological advances in defining cytokine networks, lymphocyte subsets and innate cell recognition have also made a huge impact on our understanding of helminth infections. Most recently, the ideas of regulatory immune cells, in particular the regulatory T cell, have again overturned older thinking, but also may explain immune hyporesponsiveness observed in chronic helminth diseases, as well as the link to reduced allergic reactions observed in human and animal infections. The review concludes with a forward look to where we may make future advances towards the final eradication of helminth diseases.

How common is human toxocariasis? Towards standardizing our knowledge

Our understanding of the global impact and cost of human toxocariasis is poor because there is insufficient clinical awareness and no clear repository for the efficacy of clinical, laboratory and treatment interventions. Uniform clinical and laboratory investigative approaches maximize disease diagnosis. International collaboration is required to develop web-based, professional educational support, surveillance questionnaires and standardized serodiagnostic criteria. Determining clinical benefits and treatment outcomes using less crossreactive antigens will enhance clinical and treatment interventions. Increased liaison will identify realistic occurrence and prevalence data and cost benefits of intervention. Web-based centres of excellence and repositories of current knowledge, which augment current veterinary and public health educational sites, should be supported. Expected outcomes should be capable of addressing the clinical and financial burdens of this treatable disease.

Four abundant novel transcript genes from Toxocara canis with unrelated coding sequences share untranslated region tracts implicated in the control of gene expression

The Toxocara canis "abundant novel transcripts" (ant) are four highly expressed products, constituting >18% of ESTs from the infective stage of this widely prevalent nematode parasite. Using 5' RACE, we determined full-length sequences for each ant gene, between 1.8 and 2.8kb. The four genes (termed ant-3, -5, -30 and -34), share no coding sequence similarity, although their 3'UTRs (untranslated regions) are homologous. Predicted ANT-5 and ANT-30 proteins show distant similarity to RNA regulatory proteins, RNA-dependent RNA polymerase and DEAH-box helicase, respectively. Surprisingly, ant-3 appears to be bi-cistronic, encoding two ORFs (ANT-3.1 and -3.2), each with a predicted N-terminal signal sequence. Antibodies raised to recombinant proteins did not react with native parasite products, indicating that protein expression did not accord with transcript abundance. However, antibody reactivity to two gene products (ANT-3.1 and ANT-34) was present in patient sera, suggesting that these proteins are synthesized later in infection. To test whether 3'UTRs may regulate expression, the ant-34 3'UTR sequence was inserted adjacent to enhanced green fluorescent protein (EGFP) for transformation of Caenorhabditis elegans. The ant-34 3'UTR greatly reduced EGFP expression, inhibiting both transcription and translation. We identified a tract in this UTR with significant sequence complementarity to the C. elegans micro-RNA lin-4. While infective stage parasites stockpile high levels of the ant transcripts, we suggest that translation is repressed, possibly by a mechanism involving 3' UTR motifs shared by the four genes.

On the hunt for helminths: innate immune cells in the recognition and response to helminth parasites

The generation of protective immunity to helminth parasites is critically dependent upon the development of a CD4(+) T helper type 2 cytokine response. However, the host-parasite interactions responsible for initiating this response are poorly understood. This review will discuss recent advances in our understanding of how helminth-derived products are recognized by innate immune cells. Specifically, interactions between helminth excretory/secretory products and host Toll-like receptors and lectins will be discussed as well as the putative functions of helminth proteases and chitin in activating and recruiting innate immune cells. In addition, the functional significance of pattern recognition by epithelial cells, granulocytes, dendritic cells and macrophages including expression of alarmins, thymic stromal lymphopoetin, interleukin (IL)-25, IL-33 and Notch ligands in the development of adaptive anti-parasite Th2 cytokine responses will be examined.