Immunogenic glycoconjugates implicated in parasitic nematode diseases

Enhanced mucosal response in sheep harbouring βA beta-globin against haemonchosis

Association between ovine β-globin polymorphisms and resistance against haemonchosis was described and related to the mechanism of high oxygen affinity βA ➔ βC switch during anaemia, but there are no studies regarding the involved local host responses. Phenotypic parameters and local responses were evaluated in sheep from two β-globin haplotypes naturally infected with Haemonchus contortus. Morada Nova lambs were monitored at 63, 84 and 105 days of age for faecal egg counts and packed cell volume (PCV) under natural infection with H. contortus. At 210 days of age, lambs of Hb-AA and Hb-BB β-globin haplotypes were euthanised, and the fundic region of abomasum was sampled for evaluation of microscopic lesions and relative expression of genes related to immune, mucin and lectin activities. Lambs harbouring the βA allele presented an improved resistance/resilience against clinical haemonchosis, showing higher PCV during infection. Hb-AA animals presented increased eosinophilia in the abomasum compared to Hb-BB animals, accompanied by higher Th2 profile, mucin and lectin activity transcripts, while the inflammatory response was increased in Hb-BB animals. This is the first report to demonstrate an enhanced local response in the primary site of H. contortus infection related to βA allele of β-globin haplotype.

Unraveling cross-reactivity of anti-glycan IgG responses in filarial nematode infections

Parasitic nematodes responsible for filarial diseases cause chronic disablement in humans worldwide. Elimination programs have substantially reduced the rate of infection in certain areas, but limitations of current diagnostics for population surveillance have been pointed out and improved assays are needed to reach the elimination targets. While serological tests detecting antibodies to parasite antigens are convenient tools, those currently available are compromised by the occurrence of antibodies cross-reactive between nematodes, as well as by the presence of residual antibodies in sera years after treatment and clearance of the infection. We recently characterized the N-linked and glycosphingolipid derived glycans of the parasitic nematode Brugia malayi and revealed the presence of various antigenic structures that triggered immunoglobulin G (IgG) responses in infected individuals. To address the specificity of IgG binding to these glycan antigens, we screened microarrays containing Brugia malayi glycans with plasma from uninfected individuals and from individuals infected with Loa loa, Onchocerca volvulus, Mansonella perstans and Wuchereria bancrofti, four closely related filarial nematodes. IgG to a restricted subset of cross-reactive glycans was observed in infection plasmas from all four species. In plasma from Onchocerca volvulus and Mansonella perstans infected individuals, IgG binding to many more glycans was additionally detected, resulting in total IgG responses similar to the ones of Brugia malayi infected individuals. For these infection groups, Brugia malayi, Onchocerca volvulus and Mansonella perstans, we further studied the different IgG subclasses to Brugia malayi glycans. In all three infections, IgG1 and IgG2 appeared to be the major subclasses involved in response to glycan antigens. Interestingly, in Brugia malayi infected individuals, we observed a marked reduction in particular in IgG2 to parasite glycans post-treatment with anthelminthic, suggesting a promising potential for diagnostic applications. Thus, we compared the IgG response to a broad repertoire of Brugia malayi glycans in individuals infected with various filarial nematodes. We identified broadly cross-reactive and more specific glycan targets, extending the currently scarce knowledge of filarial nematode glycosylation and host anti-glycan antibody response. We believe that our initial findings could be further exploited to develop disease-specific diagnostics as part of an integrated approach for filarial disease control.

Boronic Acid-Functionalized Two-Dimensional MoS2 at Biointerfaces

While noncovalent interactions at two-dimensional nanobiointerfaces are extensively investigated, less knowledge about covalent interactions at this interface is available. In this work, boronic acid-functionalized 2D MoS₂ was synthesized and its covalent multivalent interactions with bacteria and nematodes were investigated. Polymerization of glycidol by freshly exfoliated MoS₂ and condensation of 2,5-thiophenediylbisboronic acid on the produced platform resulted in boronic acid-functionalized 2D MoS₂. The destructive interactions between 2D MoS₂ and bacteria as well as nematodes were significantly amplified by boronic acid functional groups. Because of the high antibacterial and antinematodal activities of boronic acid-functionalized 2D MoS₂, its therapeutic efficacy for diabetic wound healing was investigated. The infected diabetic wounds were completely healed 10 days after treatment with boronic acid-functionalized 2D MoS₂, and a normal structure for recovered tissues including different layers of skin, collagen, and blood vessels was detected.

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

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

Comparative analysis of excretory-secretory antigens of Anisakis simplex, Pseudoterranova decipiens and Contracaecum osculatum regarding their applicability for specific serodiagnosis of human anisakidosis based on IgG-ELISA

Serodiagnosis of human anisakidosis is presently hampered by the current lack of standardised serological assays that allow sensitive and specific detection of Anisakidae-specific antibodies in human patients. In the present study, we comparatively evaluated the diagnostic value (by IgG-ELISA) of excretory-secretory antigens (ESAgs) of Anisakis simplex, Pseudoterranova decipiens and Contracaecum osculatum, representing the most frequently found genera responsible for human infection. In addition, we tested also a mix of the three ES preparations (Mix-ESAgs) as well as two recombinant allergens of A. simplex, rAni s 1 and rAni s 7. ES antigen from C. osculatum yielded the best diagnostic performance in IgG-ELISA-based serodiagnosis of the Spanish anisakidosis patients investigated in this study (relative serodiagnostic sensitivity 100%; specificity 89%) as compared to A. simplex ES-antigen (93% versus 57%) and P. decipiens (67% versus 93%) or a mix of the three ES antigens (100% versus 44%), respectively. Cross-reactions of C. osculatum ES antigen with serum-antibodies from patients suffering from other helminth infections were rare and were exclusively found with few sera from toxocariasis, ascariasis, and filariasis patients. The two recombinant allergens rAni s 1 and rAni s 7 did not prove sufficiently sensitive and specific in order to justify a further evaluation of these antigens regarding their suitability in IgG-ELISA-based serodiagnosis of human anisakidosis. In conclusion, the C. osculatum-ESAg-ELISA remains as key candidate to be further assessed for the serodiagnosis of symptomatic anisakidosis in different endemic regions.

Galectin-3 in M2 Macrophages Plays a Protective Role in Resolution of Neuropathology in Brain Parasitic Infection by Regulating Neutrophil Turnover

Macrophages/microglia with M2-activation phenotype are thought to play important anti-inflammatory and tissue reparative functions in the brain, yet the molecular bases of their functions in the CNS remain to be clearly defined. In a preclinical model of neurocysticercosis using brain infection with a parasite Mesocestoides corti, we previously reported the presence of large numbers of M2 cells in the CNS. In this study using female mice, we report that M2 macrophages in the parasite-infected brain display abundant galectin-3 expression. Disease severity was increased in Galectin-3^-/- mice correlating with increased neurological defects, augmented cell death and, importantly, massive accumulation of neutrophils and M2 macrophages in the CNS of these mice. Because neutrophil clearance by efferocytosis is an important function of M2 macrophages, we investigated a possible role of galectin-3 in this process. Indeed, galectin-3-deficient M2 macrophages exhibited a defect in efferocytic clearance of neutrophils in vitro Furthermore, adoptive transfer of M2 macrophages from galectin-3-sufficient WT mice reduced neutrophilia in the CNS and ameliorated disease severity in parasite-infected Galectin-3^-/- mice. Together, these results demonstrate, for the first time, a novel role of galectin-3 in M2 macrophage function in neutrophil turnover and resolution of inflammatory pathology in the CNS. This likely will have implications in neurocysticercosis and neuroinflammatory diseases.SIGNIFICANCE STATEMENT Macrophages/microglia with M1-activation phenotype are thought to promote CNS pathology, whereas M2-anti-inflammatory phenotype promote CNS repair. However, the mechanisms regulating M2 cell-protective functions in the CNS microenvironment are undefined. The current study reports that helminth infection of the brain induces an increased expression of galectin-3 in M2 macrophages accumulated in the CNS. Using multiple experimental models in vivo and in vitro, they show that galectin-3 in M2 macrophages functions to clear neutrophils accumulated in the CNS. Importantly, galectin-3 in M2 macrophages plays a central role in the containment of neuropathology and disease severity. These results provide a direct mechanistic evidence of the protective function of M2 macrophages in the CNS.

Toxoplasma gondii tachyzoite-extract acts as a potent immunomodulator against allergic sensitization and airway inflammation

Epidemiological and experimental studies have shown an inverse relationship between infections with certain parasites and a reduced incidence of allergic diseases. We and others have shown that infection with Toxoplasma gondii prevents the development of allergy in mice. To establish whether this beneficial effect could be recapitulated by soluble products of this parasite, we tested an extract derived from T. gondii tachyzoites. Immunization of BALB/c mice with tachyzoites lysate antigen (TLA) elicited mixed Th1/Th2 responses. When TLA was applied together with the sensitizing ovalbumin (OVA), the development of allergic airway inflammation was reduced, with decreased airway hyperresponsiveness associated with reduced peribronchial and perivascular cellular infiltration, reduced production of OVA-specific Th2 cytokines in lungs and spleens and reduced levels of serum OVA-specific IgG1 as well as IgE-dependent basophil degranulation. Of note, TLA retained its immunomodulatory properties, inducing high levels of IL-6, TNFα, IL-10 and IL-12p70 in bone marrow-derived dendritic cells after heat-inactivation or proteinase K-treatment for disruption of proteins, but not after sodium metaperiodate-treatment that degrades carbohydrate structures, suggesting that carbohydrates may play a role in immunomodulatory properties of TLA. Here we show that extracts derived from parasites may replicate the benefits of parasitic infection, offering new therapies for immune-mediated disorders.

Antibody response to glycan antigens of hydatid cyst fluid, laminated layer and protoscolex of Echinococcus granulosus

Background: Hydatid disease is characterized by long-term growth of hydatid cysts in the human. The glycan antigens have an important role in the immunology of hydatid cyst. In this study immunological reaction of host sera to different glycan antigens of the cyst, has been investigated.

Methods: The antibody responses were tested to glycoprotein and glycolipid of the laminated layer (LL), cyst fluid (CF) and protoscolex (PS) antigens of E. Granulosus using ELISA and western immunoblotting tests. Thin-layer chromatography and ß-elimination were used for glycan purification.

Results: Both hydatid cyst and normal human sera reacted with hydatid cyst fluid, protoscolices, laminated layer, glycoprotein and glycolipid antigens. The most antigen-antibody reaction was related to CF and PS antigens, and LL antigens had the minimal reaction with the sera. Thin layer chromatography (TLC) of the antigens showed presence of many glycan bands in the laminated layer.

Conclusion: The parasite may elaborate different glycan antigens in LL to evade host immune response.

A Phosphorylcholine-Containing Glycolipid-like Antigen Present on the Surface of Infective Stage Larvae of Ascaris spp. Is a Major Antibody Target in Infected Pigs and Humans

BACKGROUND

The pig parasite Ascaris suum plays and important role in veterinary medicine and represents a suitable model for A. lumbricoides, which infects over 800 million people. In pigs, continued exposure to Ascaris induces immunity at the level of the gut, protecting the host against migrating larvae. The objective of this study was to identify and characterize parasite antigens targeted by this local immune response that may be crucial for parasite invasion and establishment and to evaluate their protective and diagnostic potential.

METHODOLOGY/PRINCIPAL FINDINGS

Pigs were immunized by trickle infection for 30 weeks, challenged with 2,000 eggs at week 32 and euthanized two weeks after challenge. At necropsy, there was a 100% reduction in worms recovered from the intestine and a 97.2% reduction in liver white spots in comparison with challenged non-immune control animals. Antibodies purified from the intestinal mucus or from the supernatant of cultured antibody secreting cells from mesenteric lymph nodes of immune pigs were used to probe L3 extracts to identify antibody targets. This resulted in the recognition of a 12kDa antigen (As12) that is actively shed from infective Ascaris L3. As12 was characterized as a phosphorylcholine-containing glycolipid-like antigen that is highly resistant to different enzymatic and chemical treatments. Vaccinating pigs with an As12 fraction did not induce protective immunity to challenge infection. However, serological analysis using sera or plasma from experimentally infected pigs or naturally infected humans demonstrated that the As12 ELISA was able to detect long-term exposure to Ascaris with a high diagnostic sensitivity (98.4% and 92%, respectively) and specificity (95.5% and 90.0%) in pigs and humans, respectively.

CONCLUSIONS/SIGNIFICANCE

These findings show the presence of a highly stage specific, glycolipid-like component (As12) that is actively secreted by infectious Ascaris larvae and which acts as a major antibody target in infected humans and pigs.

Pan-phylum Comparison of Nematode Metabolic Potential

Nematodes are among the most important causative pathogens of neglected tropical diseases. The increased availability of genomic and transcriptomic data for many understudied nematode species provides a great opportunity to investigate different aspects of their biology. Increasingly, metabolic potential of pathogens is recognized as a critical determinant governing their development, growth and pathogenicity. Comparing metabolic potential among species with distinct trophic ecologies can provide insights on overall biology or molecular adaptations. Furthermore, ascertaining gene expression at pathway level can help in understanding metabolic dynamics over development. Comparison of biochemical pathways (or subpathways, i.e. pathway modules) among related species can also retrospectively indicate potential mistakes in gene-calling and functional annotation. We show with numerous illustrative case studies that comparisons at the level of pathway modules have the potential to uncover biological insights while remaining computationally tractable. Here, we reconstruct and compare metabolic modules found in the deduced proteomes of 13 nematodes and 10 non-nematode species (including hosts of the parasitic nematode species). We observed that the metabolic potential is, in general, concomitant with phylogenetic and/or ecological similarity. Varied metabolic strategies are required among the nematodes, with only 8 out of 51 pathway modules being completely conserved. Enzyme comparison based on topology of metabolic modules uncovered diversification between parasite and host that can potentially guide therapeutic intervention. Gene expression data from 4 nematode species were used to study metabolic dynamics over their life cycles. We report unexpected differential metabolism between immature and mature microfilariae of the human filarial parasite Brugia malayi. A set of genes potentially important for parasitism is also reported, based on an analysis of gene expression in C. elegans and the human hookworm Necator americanus. We illustrate how analyzing and comparing metabolism at the level of pathway modules can improve existing knowledge of nematode metabolic potential and can provide parasitism related insights. Our reconstruction and comparison of nematode metabolic pathways at a pan-phylum and inter-phylum level enabled determination of phylogenetic restrictions and differential expression of pathways. A visualization of our results is available at http://nematode.net and the program for identification of module completeness (modDFS) is freely available at SourceForge. The methods reported will help biologists to predict biochemical potential of any organism with available deduced proteome, to direct experiments and test hypotheses.

We reconstructed metabolic pathways of 23 organisms including 13 nematode species, using their complete deduced protein coding sequences and compared them to 10 non-nematodes. We observed that metabolic potential availability is concomitant with phylogenetic and/or ecological similarity, with the exceptions providing interesting case studies. We also studied changes in metabolic profiles under different developmental stages of 4 nematode species using stage-specific transcriptomic data. A comparison of the variation patterns in these profiles led to recognition of modules that share metabolic profiles at various life-cycle stages or during development. The undertaken analysis improved genome annotation and the obtained results provided insight into parasitism, resulting in identification of taxonomically-restricted pathways and enzymes that may provide new mechanisms for control of nematode infections.

Carbohydrates as allergens

Complex carbohydrates are effective inducers of Th2 responses, and carbohydrate antigens can stimulate the production of glycan-specific antibodies. In instances where the antigen exposure occurs through the skin, the resulting antibody production can contain IgE class antibody. The glycan-stimulated IgE may be non-specific but may also be antigen specific. This review focuses on the production of cross-reactive carbohydrate determinants, the recently identified IgE antibody response to a mammalian oligosaccharide epitope, galactose-alpha-1,3-galactose (alpha-gal), as well as discusses practical implications of carbohydrates in allergy. In addition, the biological effects of carbohydrate antigens are reviewed in setting of receptors and host recognition.

The effect of glycosylation of antigens on the antibody responses against Echinostoma caproni (Trematoda: Echinostomatidae)

In the present study, we analyse the effect of glycosylation in Echinostoma caproni (Trematoda: Echinostomatidae) antigens in antibody responses against the parasite in experimentally infected mice. It has been previously demonstrated that the mouse is a host of high compatibility with E. caproni and develops elevated responses of IgG, IgG1, IgG3 and IgM as a consequence of the infection, though the role of glycans in these responses remains unknown. To this purpose, the responses generated in mice against non-treated excretory/secretory antigens of E. caproni were compared with those observed after N-deglycosylation, O-deglycosylation and double deglycosylation of the antigens by indirect ELISA and western blot. Our results suggest that E. caproni-expressed glycans play a major role in the modulation of the immune responses. The results obtained indicate that IgG subclass responses generated in mice against E. caproni are essentially due to glycoproteins and may affect the Th1/Th2 biasing. The reactivity significantly decreased after any of the deglycosylation treatments and the N-glycans appears to be of greater importance than O-glycans. Interestingly, the IgM response increased after N-deglycosylation suggesting that carbohydrates may mask peptide antigens.

The molecular basis of peanut allergy

Peanut allergens can trigger a potent and sometimes dangerous immune response in an increasing number of people. The molecular structures of these allergens form the basis for understanding this response. This review describes the currently known peanut allergen structures and discusses how modifications both enzymatic and non-enzymatic affect digestion, innate immune recognition, and IgE interactions. The allergen structures help explain cross-reactivity among allergens from different sources, which is useful in improving patient diagnostics. Surprisingly, it was recently noted that similar short peptide sequences among unrelated peanut allergens could also be a source of cross-reactivity. The molecular features of peanut allergens continue to inform predictions and provide new research directions in the study of allergic disease.

Novel expression of Haemonchus contortus vaccine candidate aminopeptidase H11 using the free-living nematode Caenorhabditis elegans

With the problem of parasitic nematode drug resistance increasing, vaccine development offers an alternative sustainable control approach. For some parasitic nematodes, native extracts enriched for specific proteins are highly protective. However, recombinant forms of these proteins have failed to replicate this protection. This is thought to be due to differences in glycosylation and/or conformation between native and recombinant proteins. We have exploited the free-living nematode Caenorhabditis elegans to examine its suitability as an alternative system for recombinant expression of parasitic nematode vaccine candidates. We focussed on Haemonchus contortus aminopeptidase H11 glycoprotein, which is enriched in a gut membrane fraction capable of inducing significant protection against this important ovine gastrointestinal nematode. We show that H. contortus H11 expressed in C. elegans is enzymatically active and MALDI mass spectrometry identifies similar di- and tri-fucosylated structures to those on native H11, with fucose at the 3- and/or 6-positions of the proximal GlcNAc. Some glycan structural differences were observed, such as lack of LDNF. Serum antibody to native H11 binds to C. elegans recombinant H11 and most of the antibody to rH11 or native H11 is directed to glycan moieties. Despite these similarities, no reduction in worm burden or faecal egg count was observed following immunisation of sheep with C. elegans-expressed recombinant H11 protein. The findings suggest that the di- and tri-fucosylated N-glycans expressed on rH11 do not contribute to the protective effect of H11 and that additional components present in native H11-enriched extract are likely required for enhancing the antibody response necessary for protection.

Changes in Heligmosomoides polygyrus glycoprotein pattern by saponins impact the BALB/c mice immune response

Saponins of marigold (Calendula officinalis), in particular derivatives of 3-O-monoglucuronide of oleanolic acid, are able to reduce infectivity of Heligmosomoides polygyrus in mice. The purpose of this study was to understand the immune activation provoked by third-stage larvae exposed to marigold glucuronides. We also examined the pattern of glycosylation of larval antigens which appeared to be crucial for induction of cytokine production in BALB/c mice; higher concentrations of IL-6, IFN-γ, IL-10 and TNF-α were observed in serum or intestine one week post infection. Three weeks later, in the chronic phase of infection, cells in culture were able to produce IL-6, IFN-γ, TNF-α and IL-17. Restimulation of cells with H. polygyrus antigen resulted in reduced production of IL-6, and TNF-α. The pattern of cytokine production co-existed with reduced expression of terminal glucose, α-linked mannose, N-acetyl-galactosamine, β-galactose, N-acetyl-glucosamine and α-fucose in several protein bands. Galactose, as a new terminal carbohydrate residue appeared in 20-24kDa protein bands. The number of immunogenic epitopes in parasitic antigens was reduced; only three protein bands of 56, 26 and 12kDa were recognized by IgG1. These studies provide a model system to find the glycosylated molecules expressed on nematodes that improve establishment and survival and characterize cytokine production in mice infected with larvae exposed to saponin. Identification of these molecules is the first step in the recognition of key antigenic epitopes able to induce protective or tolerogenic immune responses.

N- and o-glycosylation of a commercial bovine whey protein product

Bovine whey protein products are used as a base ingredient in infant formulas to optimize the amino acid pattern to a more human-like composition. Although the protein composition of bovine milk has been studied in detail, glycosylation details of commercial whey protein products are missing. To this end, both the N- and O-glycans of such a protein concentrate were sequentially released, the N-glycans enzymatically and the O-glycans chemically (reducing and nonreducing conditions). For the structural analysis of the N- and O-glycans a combination of MALDI-TOF-MS, one-dimensional (1)H NMR spectroscopy, Wisteria floribunda agglutinin affinity chromatography, HPAEC-PAD profiling, and HPLC-FD profiling (2-aminobenzamide derivatives), together with exoglycosidase treatments, were used. A mixture of over 60 N-glycans and 10 O-glycans was characterized, giving a detailed insight into the glycosylation of a bovine whey protein product, Deminal 90, which is applied as an ingredient for infant formulas.

Synthetic studies on glycosphingolipids from protostomia phyla: synthesis of glycosphingolipids and related carbohydrate moieties from the parasite Schistosoma mansoni

Stereocontrolled syntheses of three neutral glycosphingolipids and six oligosaccharide derivatives found from the parasite Schistosoma mansoni have been accomplished. A pentasaccharide glycosphingolipid β-D-Galp-(1→4)-[α-L-Fucp-(1→3)]-β-D-GlcpNAc-(1→3)-β-D-GalpNAc-(1→4)-β-D-Glcp-(1↔1)-Cer (1), two hexasaccharide glycosphingolipids α-L-Fucp-(1→3)-β-D-Galp-(1→4)-[α-L-Fucp-(1→3)]-β-D-GlcpNAc-(1→3)-β-D-GalpNAc-(1→4)-β-D-Glcp-(1↔1)-Cer (2) and β-D-Galp-(1→4)-[α-L-Fucp-(1→3)]-β-D-GlcpNAc-(1→3)-β-D-GlcpNAc-(1→3)-β-D-GalpNAc-(1→4)-β-D-Glcp-(1↔1)-Cer (3), together with their non-reducing end tri- and tetrasaccharides, β-D-Galp-(1→4)-[α-L-Fucp-(1→3)]-β-D-GlcpNAcOR (4) and α-L-Fucp-(1→3)-β-D-Galp-(1→4)-[α-L-Fucp-(1→3)]-β-D-GlcpNAcOR (5), were synthesized by block synthesis. Moreover, non-reducing end oligosaccharides of schistosomal glycosphingolipids, β-D-GalpNAc-(1→4)-[α-L-Fucp-(1→3)]-β-D-GlcpNAcOR (6), α-L-Fucp-(1→3)-β-D-GalpNAc-(1→4)-[α-L-Fucp-(1→3)]-β-D-GlcpNAcOR (7), α-L-Fucp-(1→3)-β-D-GalpNAc-(1→4)-[α-L-Fucp-(1→2)-α-L-Fucp-(1→3)]-β-D-GlcpNAcOR (8) and α-L-Fucp-(1→3)-β-D-GalpNAc-(1→4)-[α-L-Fucp-(1→2)-α-L-Fucp-(1→2)-α-L-Fucp-(1→3)]-β-D-GlcpNAcOR (9) [R=2-(trimethylsilyl)ethyl], were synthesized as probes to explore their diagnostic potential to detect schistosomiasis from patients' sera.

Phage-display library biopanning as a novel approach to identifying nematode vaccine antigens

Infections with parasitic nematodes are of significant welfare and economic importance worldwide, and because of the emergence of anthelmintic resistance, this has lead to alternative methods of parasite control being required. Vaccination offers a feasible alternative control, and the majority of research has focused on the production of recombinant versions of native antigens previously identified as protective in vaccinated animals. Attempts at the production of protective recombinant subunit vaccines have been hindered, however, as these antigens have invariably failed to replicate the same level of protective immune response as seen with the native versions. It has been proposed that these failures are owing to the fact that the recombinant proteins do not contain the appropriate post-translational modifications to retain the protective capacity of the native molecules. In this review, we discuss a novel approach to vaccine antigen identification through the application of random peptide phage-display libraries and their use to identify peptide sequences that potentially mimic the structure(s) of antigenic epitopes. This area of research is still relatively novel with respect to parasites, and the current state of the art will be discussed here.

Use of Wisteria floribunda agglutinin affinity chromatography in the structural analysis of the bovine lactoferrin N-linked glycosylation

BACKGROUND

Over the years, the N-glycosylation of both human and bovine lactoferrin (LF) has been studied extensively, however not all aspects have been studied in as much detail. Typically, the bovine LF complex-type N-glycans include certain epitopes, not found in human LF N-glycans, i.e. Gal(α1-3)Gal(β1-4)GlcNAc (αGal), GalNAc(β1-4)GlcNAc (LacdiNAc), and N-glycolylneuraminic acid (Neu5Gc). The combined presence of complex-type N-glycans, with αGal, LacdiNAc, LacNAc [Gal(β1-4)GlcNAc], Neu5Ac (N-acetylneuraminic acid), and Neu5Gc epitopes, and oligomannose-type N-glycans complicates the high-throughput analysis of such N-glycoprofiles highly.

METHODS

For the structural analysis of enzymatically released N-glycan pools, containing both LacNAc and LacdiNAc epitopes, a prefractionation protocol based on Wisteria floribunda agglutinin affinity chromatography was developed. The sub pools were analysed by MALDI-TOF-MS and HPLC-FD profiling, including sequential exoglycosidase treatments.

RESULTS

This protocol separates the N-glycan pool into three sub pools, with (1) free of LacdiNAc epitopes, (2) containing LacdiNAc epitopes, partially shielded by sialic acid, and (3) containing LacdiNAc epitopes, without shielding by sialic acid. Structural analysis by MALDI-TOF-MS and HPLC-FD showed a complex pattern of oligomannose-, hybrid-, and complex-type di-antennary structures, both with, and without LacdiNAc, αGal and sialic acid.

CONCLUSIONS

Applying the approach to bovine LF has led to a more detailed N-glycome pattern, including LacdiNAc, αGal, and Neu5Gc epitopes, than was shown in previous studies.

GENERAL SIGNIFICANCE

Bovine milk proteins contain glycosylation patterns that are absent in human milk proteins; particularly, the LacdiNAc epitope is abundant. Analysis of bovine milk serum proteins is therefore excessively complicated. The presented sub fractionation protocol allows a thorough analysis of the full scope of bovine milk protein glycosylation. This article is part of a Special Issue entitled Glycoproteomics.

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.

High-sensitivity O-glycomic analysis of mice deficient in core 2 {beta}1,6-N-acetylglucosaminyltransferases

Core 2 β1,6-N-acetylglucosaminyltransferase (C2GnT), which exists in three isoforms, C2GnT1, C2GnT2 and C2GnT3, is one of the key enzymes in the O-glycan biosynthetic pathway. These isoenzymes produce core 2 O-glycans and have been correlated with the biosynthesis of core 4 O-glycans and I-branches. Previously, we have reported mice with single and multiple deficiencies of C2GnT isoenzyme(s) and have evaluated the biological and structural consequences of the loss of core 2 function. We now present more comprehensive O-glycomic analyses of neutral and sialylated glycans expressed in the colon, small intestine, stomach, kidney, thyroid/trachea and thymus of wild-type, C2GnT2 and C2GnT3 single knockouts and the C2GnT1-3 triple knockout mice. Very high-quality data have emerged from our mass spectrometry techniques with the capability of detecting O-glycans up to at least 3500 Da. We were able to unambiguously elucidate the types of O-glycan core, branching location and residue linkages, which allowed us to exhaustively characterize structural changes in the knockout tissues. The C2GnT2 knockout mice suffered a major loss of core 2 O-glycans as well as glycans with I-branches on core 1 antennae especially in the stomach and the colon. In contrast, core 2 O-glycans still dominated the O-glycomic profile of most tissues in the C2GnT3 knockout mice. Analysis of the C2GnT triple knockout mice revealed a complete loss of both core 2 O-glycans and branched core 1 antennae, confirming that the three known isoenzymes are entirely responsible for producing these structures. Unexpectedly, O-linked mannosyl glycans are upregulated in the triple deficient stomach. In addition, our studies have revealed an interesting terminal structure detected on O-glycans of the colon tissues that is similar to the RM2 antigen from glycolipids.

Antibody isotype analysis of malaria-nematode co-infection: problems and solutions associated with cross-reactivity

BACKGROUND

Antibody isotype responses can be useful as indicators of immune bias during infection. In studies of parasite co-infection however, interpretation of immune bias is complicated by the occurrence of cross-reactive antibodies. To confidently attribute shifts in immune bias to the presence of a co-infecting parasite, we suggest practical approaches to account for antibody cross-reactivity. The potential for cross-reactive antibodies to influence disease outcome is also discussed.

RESULTS

Utilising two murine models of malaria-helminth co-infection we analysed antibody responses of mice singly- or co-infected with Plasmodium chabaudi chabaudi and Nippostrongylus brasiliensis or Litomosoides sigmodontis. We observed cross-reactive antibody responses that recognised antigens from both pathogens irrespective of whether crude parasite antigen preparations or purified recombinant proteins were used in ELISA. These responses were not apparent in control mice. The relative strength of cross-reactive versus antigen-specific responses was determined by calculating antibody titre. In addition, we analysed antibody binding to periodate-treated antigens, to distinguish responses targeted to protein versus carbohydrate moieties. Periodate treatment affected both antigen-specific and cross-reactive responses. For example, malaria-induced cross-reactive IgG1 responses were found to target the carbohydrate component of the helminth antigen, as they were not detected following periodate treatment. Interestingly, periodate treatment of recombinant malaria antigen Merozoite Surface Protein-119 (MSP-119) resulted in increased detection of antigen-specific IgG2a responses in malaria-infected mice. This suggests that glycosylation may have been masking protein epitopes and that periodate-treated MSP-119 may more closely reflect the natural non-glycosylated antigen seen during infection.

CONCLUSIONS

In order to utilize antibody isotypes as a measure of immune bias during co-infection studies, it is important to dissect antigen-specific from cross-reactive antibody responses. Calculating antibody titre, rather than using a single dilution of serum, as a measure of the relative strength of the response, largely accomplished this. Elimination of the carbohydrate moiety of an antigen that can often be the target of cross-reactive antibodies also proved useful.

Immunomodulation by phosphocholine--biosynthesis, structures and immunological implications of parasitic PC-epitopes

Phosphocholine (PC) as a small haptenic molecule present on antigens of parasites can provoke various effects on immune cells leading to immunomodulation of the host's immune system. This immunomodulation not only allows long-term persistence but also prevents severe pathology due to down-regulation of cellular immune responses. Additionally, PC plays an important role for development and fertility of the parasites. To fully understand the mechanisms of immunomodulation the detailed knowledge of the biosynthesis of the PC-epitopes, their molecular structure and biological function has to be elucidated. The implication of parasite-specific transferases in the biosynthesis of the PC-epitopes and the sensitivity of parasites towards disruption of the choline metabolism offers new perspectives for the development of anti-parasitic drugs and therapies. Furthermore, the immunomodulation provoked by PC-epitopes preventing inflammatory reactions may be useful in the treatment of inflammatory diseases. This review summarizes the current knowledge on the biosynthesis of PC-epitopes, their structures and immunological implications.

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.

Differential release and phagocytosis of tegument glycoconjugates in neurocysticercosis: implications for immune evasion strategies

Neurocysticercosis (NCC) is an infection of the central nervous system (CNS) by the metacestode of the helminth Taenia solium. The severity of the symptoms is associated with the intensity of the immune response. First, there is a long asymptomatic period where host immunity seems incapable of resolving the infection, followed by a chronic hypersensitivity reaction. Since little is known about the initial response to this infection, a murine model using the cestode Mesocestoides corti (syn. Mesocestoides vogae) was employed to analyze morphological changes in the parasite early in the infection. It was found that M. corti material is released from the tegument making close contact with the nervous tissue. These results were confirmed by infecting murine CNS with ex vivo–labeled parasites. Because more than 95% of NCC patients exhibit humoral responses against carbohydrate-based antigens, and the tegument is known to be rich in glycoconjugates (GCs), the expression of these types of molecules was analyzed in human, porcine, and murine NCC specimens. To determine the GCs present in the tegument, fluorochrome-labeled hydrazides as well as fluorochrome-labeled lectins with specificity to different carbohydrates were used. All the lectins utilized labeled the tegument. GCs bound by isolectinB4 were shed in the first days of infection and not resynthesized by the parasite, whereas GCs bound by wheat germ agglutinin and concavalinA were continuously released throughout the infectious process. GCs bound by these three lectins were taken up by host cells. Peanut lectin-binding GCs, in contrast, remained on the parasite and were not detected in host cells. The parasitic origin of the lectin-binding GCs found in host cells was confirmed using antibodies against T. solium and M. corti. We propose that both the rapid and persistent release of tegumental GCs plays a key role in the well-known immunomodulatory effects of helminths, including immune evasion and life-long inflammatory sequelae seen in many NCC patients.

Neurocysticercosis (NCC) is a disease caused by the larval form of a tapeworm parasite that preferentially migrates to the brain. It is characterized by a long asymptomatic period thought to result from the parasite's ability to evade host immunity. To date, the mechanisms of host–parasite interaction before symptoms develop remain unknown. In this study we evaluate by multiple immunofluorescent techniques distinct stages of the infection, making use of a murine model that closely resembles the disease process observed in humans. We discovered that the array of molecules secreted by the parasite varies according to the phase of infection studied. Early in infection, the parasite permanently sheds distinct molecules, allowing a rapid establishment in the brain. As the infection ensues, the continuous release of different molecules appears to facilitate the persistence of the parasite by downregulating molecules involved in its recognition and destruction. Loss of such molecules when the parasite dies after drug treatment may explain sudden inflammatory responses in patients. Characterization of these molecules will lead to advances in our understanding of the complex immunoregulatory mechanisms used by parasites and to new approaches for therapeutic strategies.

Expression and purification of an active cysteine protease of Haemonchus contortus using Caenorhabditis elegans

Many proteolytic enzymes of parasitic nematodes have been identified as possible targets of control. Testing these as vaccine or drug targets is often difficult due to the problems of expressing proteases in a correctly folded, active form in standard expression systems. In an effort to overcome these difficulties we have tested Caenorhabditis elegans as an expression system for a Haemonchus contortus cathepsin L cysteine protease, Hc-CPL-1. Recombinant Hc-CPL-1 with a polyhistidine tag added to the C-terminal was expressed in an active and glycosylated form in C. elegans. Optimal expression was obtained expressing Hc-cpl-1 under control of the promoter of the homologous C. elegans cpl-1 gene. The recombinant protein was purified from liquid cultures by nickel chelation chromatography in sufficient amounts for vaccination studies to be carried out. This study provides proof of principle that active, post-translationally modified parasitic nematode proteases can be expressed in C. elegans and this approach can be extended for expression of known protective antigens.

Antibodies elicited by the bovine lungworm, Dictyocaulus viviparus, cross-react with platelet-activating factor

Parasite N-glycans may play an important role in helminth infections. As antibodies from Dictyocaulus viviparus-infected calves strongly react with N-glycans, we investigated the characteristics of the major immunodominant glycoprotein (GP300) of this parasite. Probing of worm extracts with various lectins demonstrated unique binding of GP300 to wheat germ agglutinin. Analysis of lectin-purified GP300 revealed that the glycan was substituted with phosphorylcholine and reacted with the phosphorylcholine-specific antibody TEPC-15. Competitive enzyme-linked immunosorbent assay with GP300-coated plates and GP300-specific immunoglobulin G (IgG) in conjunction with free phosphorylcholine or TEPC-15 demonstrated that antibodies from infected calves recognized phosphorylcholine on GP300. Additional assays showed that these antibodies cross-reacted with the phosphorylcholine moiety present on platelet-activating factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine), a proinflammatory mediator of the host. Heavily infected calves contained high levels of serum GP300-specific IgG1 but low levels of IgA and IgG2 and showed a reduced influx of eosinophils in the lungs, all consistent with a neutralization of PAF activity. In conclusion, we demonstrated that D. viviparus infection elicits GP300-specific antibodies that cross-react with PAF and may neutralize PAF function, thus limiting the development of a protective response as well as parasite-induced host pathology.

Three surface antigens dominate the mucosal antibody response to gastrointestinal L3-stage strongylid nematodes in field immune sheep

Although gastrointestinal nematode parasites are a major human and veterinary health problem, little is known about how the host is sometimes able to mount an effective immune rejection response. In previous work, we identified a carbohydrate larval surface antigen (CarLA) as the target of mucosal antibodies that can elicit rejection of Trichostrongylus colubriformis L3s in sheep. Here we characterise the natural mucosal antibody responses to L3s from three major strongylid gastrointestinal parasites of sheep, Trichostrongylus colubriformis, Haemonchus contortus and Teladorsagia circumcincta. The mucosal antibody repertoire of naturally field-immune sheep was displayed on bacteriophage as single-chain antibodies (scFvs) and phage were selected for the ability to bind to the surface of living L3s of the three nematode species. All nematode-binding scFvs were found to recognize one of three different antigen classes that are each found in the three strongylid species. These three antigen classes appear to represent all of the major antigens recognized on Western blots by pooled mucosal antibodies from field-immune sheep. One of the antigen classes is a heterogeneous, high molecular weight molecule that is protease-sensitive. The scFvs recognizing this surface antigen also recognize a similar antigen in all strongylids tested. A second antigen class is a protease-insensitive, low molecular weight antigen found only in sheaths and scFvs recognizing this antigen cross-react with a similar molecule found in all strongylids tested. The third surface antigen class is CarLA and all of the anti-CarLA scFvs obtained from the field-immune sheep repertoire were specific to L3s of only one species and often recognized only a subset of the worms. Thus three different L3-stage surface antigens, two that lack a protein component, dominate the natural mucosal antibody response to L3-stage gastrointestinal strongylid nematodes in sheep.

Lack of galectin-3 involvement in murine intestinal nematode and schistosome infection

Many parasitic helminths produce large quantities of glycosylated proteins, some if which are believed to be involved in the skewing towards the dominant Th2 response observed during helminth infection. Galectin-3 is a member of a family of lectin-binding proteins produced by many different types of immune cells, including macrophages. Galectin-3 recognizes the GalNAcbeta1-4GlcNAc (LDN) epitope present on many helminth antigens, including those of the schistosome eggs. Here we show that galectin-3 is not involved in the development of the Th2 response nor in schistosome granuloma formation. Galectin-3-deficient mice were able to expel the gastrointestinal nematode Trichuris muris at the same speed as wild-type mice. Expulsion of T. muris is known to be dependent on a Th2 immune response and galectin-3-deficient mice showed no defect in their ability to produce Th2 cytokines or in their antibody responses, compared to wild-type mice. Furthermore, galectin-3-deficient mice were also able to mount a Th2 response to Schistosoma mansoni infection and they exhibited normal hepatic granuloma formation. The data presented here demonstrate that galectin-3 is not a critical component in the development of Th2 responses during helminth infection in vivo, nor is it essential for schistosome egg granuloma formation.

N-glycans of the porcine nematode parasite Ascaris suum are modified with phosphorylcholine and core fucose residues

In recent years, the glycoconjugates of many parasitic nematodes have attracted interest due to their immunogenic and immunomodulatory nature. Previous studies with the porcine roundworm parasite Ascaris suum have focused on its glycosphingolipids, which were found, in part, to be modified by phosphorylcholine. Using mass spectrometry and western blotting, we have now analyzed the peptide N-glycosidase A-released N-glycans of adults of this species. The presence of hybrid bi- and triantennary N-glycans, some modified by core alpha1,6-fucose and peripheral phosphorylcholine, was demonstrated by LC/electrospray ionization (ESI)-Q-TOF-MS/MS, as was the presence of paucimannosidic N-glycans, some of which carry core alpha1,3-fucose, and oligomannosidic oligosaccharides. Western blotting verified the presence of protein-bound phosphorylcholine and core alpha1,3-fucose, whereas glycosyltransferase assays showed the presence of core alpha1,6-fucosyltransferase and Lewis-type alpha1,3-fucosyltransferase activities. Although, the unusual tri- and tetrafucosylated glycans found in the model nematode Caenorhabditis elegans were not found, the vast majority of the N-glycans found in A. suum represent a subset of those found in C. elegans; thus, our data demonstrate that the latter is an interesting glycobiological model for parasitic nematodes.

The role of protein glycosylation in allergy

The asparagine-linked carbohydrate moieties of plant and insect glycoproteins are the most abundant environmental immune determinants. They are the structural basis of what is known as cross-reactive carbohydrate determinants (CCDs). Despite some structural variation, the two main motifs are the xylose and the core-3-linked fucose, which form the essential part of two independent epitopes. Plants contain both epitopes, insect glycoproteins only fucose. These epitopes and other fucosylated determinants are also found in helminth parasites where they exert remarkable immunomodulatory effects. About 20% or more of allergic patients generate specific anti-glycan IgE, which is often accompanied by IgG. Even though antibody-binding glycoproteins are widespread in pollens, foods and insect venoms, CCDs do not appear to cause clinical symptoms in most, if not all patients. When IgE binding is solely due to CCDs, a glycoprotein allergen thus can be rated as clinical irrelevant allergen. Low binding affinity between IgE and plant N-glycans now drops out as a plausible explanation for the benign nature of CCDs. This rather may result from blocking antibodies induced by an incidental 'immune therapy' ('glyco-specific immune therapy') exerted by everyday contact with plant materials, e.g. fruits or vegetables. The need to detect and suppress anti-CCD IgE without interference from peptide epitopes can be best met by artificial glycoprotein allergens. Hydroxyproline-linked arabinose (single beta-arabinofuranosyl residues) has been identified as a new IgE-binding carbohydrate epitope in the major mugwort allergen. However, currently the occurrence of this O-glycan determinant appears to be rather restricted.

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

The parasitic helminth Toxocara canis is a widely distributed nematode of mammals. Larval parasites, which infect a wide range of hosts including mice and humans, export glycosylated macromolecules bearing novel methylated oligosaccharide structures, similar to the mammalian blood group antigen H but bearing one or two O-methylated substitutions on the terminal fucose and subterminal galactose residues. We have studied the reactivity of synthetic forms of these glycans to parasite-specific antibodies and mammalian immune system lectins. Murine antibodies, generated to T. canis infection, predominantly recognise the mono-O-methylated form with the beta-configuration of the GalNAc residue (MoMbeta), and antibodies are entirely IgM isotype. The mAb Tcn-2 reproduces this pattern, and shows little reactivity to either the alpha isomer (MoMalpha) or the di-O-methylated form (DiM). Antibodies generated to helminth infections other than T. canis were unreactive with the glycans, except antibodies to other members of the Toxocara genus. Hence, the carbohydrate structures represent immunogenic, genus-specific antigens. Antibodies from human toxocariasis patients are reactive with the same sugars, although preferentially towards DiM. Sera from unrelated helminth infections do not react, confirming the status of these structures as Toxocara-specific glycans. The human dendritic cell lectin, DC-SIGN, was found to bind both Toxocara excretory/secretory products and mammalian blood group antigen H3. However, DC-SIGN did not bind the synthetic glycans, indicating additional non-methylated carbohydrates may also play a role in the interaction between T. canis and its host.

Antigens for the immunodiagnosis of Echinococcus granulosus infection: An update

The taeniid tapeworm Echinococcus granulosus is the causative agent of the echinococcal disease, an important zoonosis with worldwide distribution. Accurate immunodiagnosis of the infection requires highly specific and sensitive antigens to be used in immunodiagnostic assays. The choice of an appropriate source of antigenic material is a crucial point in the improvement of the diagnostic features of tests, and must be based on the developmental stage of the parasite and the host. The most common antigenic sources used for the immunodiagnosis of echinococcal disease are hydatid cyst fluid, somatic extracts and excretory-secretory products from protoscoleces or adults of E. granulosus. Hydatid cyst fluid is the antigenic source of reference for immunodiagnosis of human hydatidosis, which is mainly based on the detection of antigens B and 5. Somatic extracts have been widely used in the serodiagnosis for E. granulosus infection in dogs and ruminant intermediate hosts, although in the last few years the detection of excretory-secretory products of the worm in faeces (coproantigens) have become the most reliable method for the detection of the parasite in the definitive host. This review emphasizes recent advances in the identification and characterization of novel antigens with potential for the immunodiagnosis of echinococcal disease. Progress in recombinant technologies and synthetic peptides are also discussed. The paper highlights the need to search for new antigenic components with high diagnostic sensitivity and specificity, a fact that remains a crucial task in the improvement of the immunodiagnosis of the disease.

Schistosome glycans and innate immunity

Schistosome glycans induce characteristic innate immune responses in the infected host. The molecular aspects of these responses, the pathways and receptors as well as the schistosome glycans and glycoconjugates involved, form an area of intense research. The relevant schistosome glycan elements and the possible mechanisms through which they act on the innate immune system are discussed in this review.

Helminth parasites--masters of regulation

Immune regulation by parasites is a global concept that includes suppression, diversion, and conversion of the host immune response to the benefit of the pathogen. While many microparasites escape immune attack by antigenic variation or sequestration in specialized niches, helminths appear to thrive in exposed extracellular locations, such as the lymphatics, bloodstream, or gastrointestinal tract. We review here the multiple layers of immunoregulation that have now been discovered in helminth infection and discuss both the cellular and the molecular interactions involved. Key events among the host cell population are dominance of the T-helper 2 cell (Th2) phenotype and the selective loss of effector activity, against a background of regulatory T cells, alternatively activated macrophages, and Th2-inducing dendritic cells. Increasingly, there is evidence of important effects on other innate cell types, particularly mast cells and eosinophils. The sum effect of these changes to host reactivity is to create an anti-inflammatory environment, which is most favorable to parasite survival. We hypothesize therefore that parasites have evolved specific molecular strategies to induce this conducive landscape, and we review the foremost candidate immunomodulators released by helminths, including cytokine homologs, protease inhibitors, and an intriguing set of novel products implicated in immune suppression.

Molecular Basis of Anti-horseradish Peroxidase Staining in Caenorhabditis elegans

Cross-reactivity with anti-horseradish peroxidase antiserum is a feature of many glycoproteins from plants and invertebrates; indeed staining with this reagent has been used to track neurons in Drosophila melanogaster and Caenorhabditis elegans. Although in insects the evidence indicates that the cross-reaction results from the presence of core alpha1,3-fucosylated N-glycans, the molecular basis for anti-horseradish peroxidase staining in nematodes has been unresolved to date. By using Western blots of wild-type and mutant C. elegans extracts in conjunction with specific inhibitors, we show that the cross-reaction is due to core alpha1,3-fucosylation. Of the various mutants examined, one with a deletion of the fut-1 (K08F8.3) gene showed no reaction to anti-horseradish peroxidase; the molecular phenotype was rescued by injection of either the K08F8 cosmid or the fut-1 open reading frame under control of the let-858 promoter. Furthermore, expression of fut-1 cDNA in Pichia and insect cells in conjunction with antibody staining, high pressure liquid chromatography, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry analyses showed that FUT-1 is a core alpha1,3-fucosyltransferase with an unusual substrate specificity. It is the only core fucosyltransferase in plants and animals described to date that does not require the prior action of N-acetylglucosaminyltransferase I.

Antigenic glycans in parasitic infections: implications for vaccines and diagnostics

Infections by parasitic protozoans and helminths are a major world-wide health concern, but no vaccines exist to the major human parasitic diseases, such as malaria, African trypanosomiasis, amebiasis, leishmaniasis, schistosomiasis, and lymphatic filariasis. Recent studies on a number of parasites indicate that immune responses to parasites in infected animals and humans are directed to glycan determinants within cell surface and secreted glycoconjugates and that glycoconjugates are important in host-parasite interactions. Because of the tremendous success achieved recently in generating carbohydrate-protein conjugate vaccines toward microbial infections, such as Haemophilus influenzae type b, there is renewed interest in defining parasite-derived glycans in the prospect of developing conjugate vaccines and new diagnostics for parasitic infections. Parasite-derived glycans are compelling vaccine targets because they have structural features that distinguish them from mammalian glycans. There have been exciting new developments in techniques for glycan analysis and the methods for synthesizing oligosaccharides by chemical or combined chemo-enzymatic approaches that now make it feasible to generate parasite glycans to test as vaccine candidates. Here, we highlight recent progress made in elucidating the immunogenicity of glycans from some of the major human and animal parasites, the potential for developing conjugate vaccines for parasitic infections, and the possible utilization of these novel glycans in diagnostics.

Loss of srf-3-encoded nucleotide sugar transporter activity in Caenorhabditis elegans alters surface antigenicity and prevents bacterial adherence

During the establishment of a bacterial infection, the surface molecules of the host organism are of particular importance, since they mediate the first contact with the pathogen. In Caenorhabditis elegans, mutations in the srf-3 locus confer resistance to infection by Microbacterium nematophilum, and they also prevent biofilm formation by Yersinia pseudotuberculosis, a close relative of the bubonic plague agent Yersinia pestis. We cloned srf-3 and found that it encodes a multitransmembrane hydrophobic protein resembling nucleotide sugar transporters of the Golgi apparatus membrane. srf-3 is exclusively expressed in secretory cells, consistent with its proposed function in cuticle/surface modification. We demonstrate that SRF-3 can function as a nucleotide sugar transporter in heterologous in vitro and in vivo systems. UDP-galactose and UDP-N-acetylglucosamine are substrates for SRF-3. We propose that the inability of Yersinia biofilms and M. nematophilum to adhere to the nematode cuticle is due to an altered glycoconjugate surface composition of the srf-3 mutant.

Both free-living and parasitic nematodes induce a characteristic Th2 response that is dependent on the presence of intact glycans

Infection with parasitic nematodes is characterized by the induction of a profound type 2 immune response. We have studied the role of glycans in the induction of the skewed type 2 response by antigens of the parasitic nematode Brugia malayi as well as the free-living nematode Caenorhabditis elegans. Lymph node cells from BALB/c mice immunized with soluble extracts of the two nematodes showed distinct antigen-specific proliferation and cytokine production; however, both nematodes induced antigen-specific interleukin 4 (IL-4) production, demonstrating that the induction of a biased type 2 response is not unique to parasitic nematodes. Sodium periodate-treated soluble extracts of both nematodes consistently induced significantly less IL-4 production than the respective mock-treated extracts, indicating that glycans play a critical role in the induction of the Th2 immune response by these nematodes. The glycan-dependent induction of the Th2-potentiating cytokine IL-4 occurs by 72 h postinoculation. Our data suggest that glycan determinants common to nematodes act as ligands, displaying distinct molecular patterns that trigger the immune system to launch a biased Th2 immune response upon exposure to these organisms or their products. Further, the similarity of our findings to those for Schistosoma mansoni egg antigen is striking considering the enormous phylogenetic distance between nematodes and trematodes. These data thus have important implications for how the mammalian host responds to widely divergent metazoan invaders and suggest that the powerful C. elegans model system can be used to address these questions.

Expansion of NK cells with reduction of their inhibitory Ly-49A, Ly-49C, and Ly-49G2 receptor-expressing subsets in a murine helminth infection: contribution to parasite control

Natural killer cell-associated direct cytotoxicity and cytokine production are crucial mechanisms for early innate host resistance against viruses, bacteria, or protozoa. The engagement of inhibitory NK cell receptors can influence host responses to viruses. However, these receptors have not been investigated to date in parasitic infections, and little is known about the role of NK cells in the defense against helminths. Therefore, we have correlated the frequencies of cells expressing the pan-NK marker DX5 and subsets bearing inhibitory Ly-49 receptors with worm survival and cytokine production during infection with Litomosoides sigmodontis in BALB/c mice (H2(d)), the only fully permissive model of filariasis. A marked influx of DX5(+)/CD3(-) NK cells and DX5(+)/CD3(+) T cells into the pleural cavity, where the parasites were located, was observed. The frequency of pleural NK cells expressing the H2(d)-reactive inhibitory receptors Ly-49A, Ly-49C, or Ly-49G2 declined most strongly compared with spleen and blood. In the peripheral blood, longitudinal analysis revealed an early and stable reduction of Ly-49C(+) and Ly-49G2(+) NK cells, a subsequent significant increase of the entire NK cell and DX5(+)/CD3(+) T cell populations, and a reduction in the Ly-49A(+) subset. The in vivo depletion of NK cells strongly enhanced the worm load and influenced IL-4 and IL-5 plasma levels. These data demonstrate a new role for NK cells in the host defense against filariae and, for the first time, alterations of Ly-49 receptor-expressing NK cell subsets in a parasitic infection.

Structural analysis and antibody response to the extracellular glutathione S-transferases from Onchocerca volvulus

Onchocerca volvulus is a human pathogenic filarial parasite which, like other parasitic nematodes, is capable of surviving in an immunologically competent host by employing a variety of immune evasion strategies and defense mechanisms including the detoxification and repair mechanisms of the glutathione S-transferases (GSTs). In this study we analyzed the glycosylation pattern and the immunological properties of extracellular O. volvulus GST1a and -1b (OvGST1a and -1b). The enzymes differ in only 10 amino acids, and both are glycoproteins that have cleavable signal peptides and unusual N-terminal extensions. These characteristics have not been described for other GSTs so far. Mass spectrometry analyses indicate that both enzymes carry high-mannose type oligosaccharides on at least four glycosylation sites. Glycosylation sites 1 to 3 of OvGST1a (OvGST1b sites 2 to 4) are occupied by truncated N-glycans (Man(2)GlcNAc2 to Man(5)GlcNAc(2)), and N glycosylation site 4 of OvGST1a (OvGST1b site 5) carries Man(5)GlcNAc2 to Man(9)GlcNAc(2). To analyze the capacity of these secretory GSTs to stimulate host immune responses, we studied the antibody responses of onchocerciasis patients against the native affinity-purified OvGST1a and -1b. By enzyme-linked immunosorbent assay we showed that OvGST1a and -1b are immunodominant antigens, with less than 7% nonresponder patients. A direct comparison of the antibody responses to the glycosylated and deglycosylated forms demonstrates the high immunogenicity of the N-glycans. Analyses of the antibody responses to the unusual N-terminal extension show an enhanced recognition of this portion by patients as opposed to recognition of the recombinant protein without extension.

Schistosome glycoconjugates in host-parasite interplay

Schistosomes are digenetic trematodes which cause schistosomiasis, also known as bilharzia, one of the main parasitic infections in man. In tropical and subtropical areas an estimated 200 million people are infected and suffer from the debilitating effects of this chronic disease. Schistosomes live in the blood vessels and strongly modulate the immune response of their host to be able to survive the hostile environment that they are exposed to. It has become increasingly clear that glycoconjugates of schistosome larvae, adult worms and eggs play an important role in the evasion mechanisms that schistosomes utilise to withstand the immunological measures of the host. Upon infection, the host mounts innate as well as adaptive immune responses to antigenic glycan elements, setting the immunological scene characteristic for schistosomiasis. In this review we summarise the structural data now available on schistosome glycans and provide data and ideas regarding the role that these glycans play in the various aspects of the glycobiology and immunology of schistosomiasis.

Mass spectrometric strategies: providing structural clues for helminth glycoproteins

Here we review current knowledge of helminth glycans and introduce parasitologists to the power of the mass spectrometric techniques that have been largely responsible for defining their carbohydrate moieties. A brief overview of glycosylation in other eukaryotes is presented, with a focus on mammalian glycosylation, to facilitate understanding of how parasite structures might be recognized as 'self' or 'foreign' by the immune system of the host.

Studies on the immunoglobulin E responses to Teladorsagia circumcincta in sheep: purification of a major high molecular weight allergen

Studies on the immunoglobulin (Ig)E immune responses to the gastric nematode, Teladorsagia circumcincta, have demonstrated a major high molecular weight allergen (HMWTc). Cross reactive allergens of similar MW were demonstrated for Trichostrongylus colubriformis and Cooperia curticei, but not for Haemonchus contortus. Purification of HMWTc was achieved by gel-filtration chromatography, and nonreducing SDS-PAGE and Western blot analysis revealed two closely associated bands with a molecular weight of approximately 140-150 kDa. Reduction showed four IgE reactive bands of 120, 50, 45 and 30 kDa, and deglycosylation abrogated the immunoreactivity of the 120 and 30 kDa bands. Ultrastructural immunolocalization by electron microscopy revealed that the IgE reactivity was confined to the cuticular surface of the infective (L3) larvae. ELISA studies to determine the IgE anti-HMWTc responses in lambs during their first grazing season, demonstrated significantly higher IgE antibody in lambs with low accumulative faecal egg count (FEC) compared to animals with high accumulative FEC. These studies provide evidence for a protective function of IgE antibody in Teladorsagia infections in lambs.

Selective expression of different fucosylated epitopes on two distinct sets of Schistosoma mansoni cercarial O-glycans: identification of a novel core type and Lewis X structure

The glycobiology of Schistosoma mansoni is dominated by developmentally regulated expression of various fucosylated structures, most notably the Lewis X epitope and a multifucosylated sequence, Fuc alpha1-->2Fuc alpha1-->, in its various forms. For the infective cercarial stage, Lewis X has been structurally identified on glycosphingolipids and N-glycans of total glycoprotein extracts, and a population of multifucosylated glycoproteins were found to carry a unique terminal sequence, +/-Fuc alpha1-->2Fuc alpha1-->[3GalNAc beta1-->4(Fuc alpha1-->2Fuc alpha1--> 2Fuc alpha1-->3) GlcNAc beta1-->3Gal alpha1-->](n), on their O-glycans. Using a mass spectrometry approach coupled with chromatographic separation, sequential exoglycosidase digestion, periodate oxidation, and other chemical derivatization, we demonstrate that Lewis X could also be carried on the cercarial O-glycans, but the two distinctive sets of fucosylated epitopes were conjugated to two different core structures. Lewis X, lacNAc, or single GlcNAc was found to attach directly to the -->3Gal beta1-->3GalNAc core and indirectly via another beta-Gal residue branching off from C6 of the reducing end GalNAc to give a biantennary-like structure. The -->3(+/-Gal beta1-->6)Gal beta1-->3(-->3Gal beta1-->6)GalNAc core thus characterized represents a novel core type for O-glycans. In contrast, the previously characterized multifucosylated terminal sequences were carried on conventional type 1 and 2 cores. The smallest structures of the reductively released O-glycans were defined as GalNAc beta1-->4GlcNAc beta1-->3Gal beta1-->3GalNAcitol with a total of two to four fucoses attached to the terminal lacdiNAc. alpha-Galactosylation of the nonreducing terminal beta-GalNAc instead of fucose capping leads to further elongation with another lacdiNAc unit that could also extend directly from C6 of the reducing end GalNAc and similarly elongated or terminated.