Characterization of the immunosuppressive environment induced by larval Echinococcus granulosus during chronic experimental infection

The larval stage of Echinococcus granulosus causes the chronic infection known as cystic echinococcosis, deploying strong inhibitory mechanisms on host immune responses. Using experimental intraperitoneal infection in C57BL/6 mice, we carried out an in-depth analysis of the local changes in macrophage populations associated with chronic infection. In addition, we analyzed T cells and relevant soluble mediators. Infected animals showed an increase in local cell numbers, mostly accounted for by eosinophils, T cells, and macrophages. Within macrophage populations, the largest increases in cell numbers corresponded to resident large peritoneal macrophages (LPM). Monocyte recruitment appeared to be active, as judged by the increased number of monocytes and cells in the process of differentiation towards LPM, including small (SPM) and converting peritoneal macrophages (CPM). In contrast, we found no evidence of macrophage proliferation. Infection induced the expression of M2 markers in SPM, CPM, and LPM. It also enhanced the expression of the co-inhibitor PD-L1 in LPM, SPM, and CPM and induced the co-inhibitor PD-L2 in SPM and CPM. Therefore, local macrophages acquire M2-like phenotypes with probable suppressive capacities. Regarding T cells, infection induced an increase in the percentage of CD4+ cells that are PD-1+, which represent a potential target of suppression by PD-L1+/PD-L2+ macrophages. In possible agreement, CD4+ T cells from infected animals showed blunted proliferative responses to in vitro stimulation with anti-CD3. Further evidence of immune suppression in the parasite vicinity arose from the observation of an expansion in FoxP3+ CD4+ regulatory T cells and increases in the local concentrations of the anti-inflammatory cytokines TGF-β and IL-1Ra.

Mucins Shed from the Laminated Layer in Cystic Echinococcosis Are Captured by Kupffer Cells via the Lectin Receptor Clec4F

Cystic echinococcosis is caused by the larval stages (hydatids) of cestode parasites belonging to the species cluster Echinococcus granulosus sensu lato, with E. granulosus sensu stricto being the main infecting species. Hydatids are bladderlike structures that attain large sizes within various internal organs of livestock ungulates and humans. Hydatids are protected by the massive acellular laminated layer (LL), composed mainly of mucins. Parasite growth requires LL turnover, and abundant LL-derived particles are found at infection sites in infected humans, raising the question of how LL materials are dealt with by the hosts. In this article, we show that E. granulosus sensu stricto LL mucins injected into mice are taken up by Kupffer cells, the liver macrophages exposed to the vascular space. This uptake is largely dependent on the intact mucin glycans and on Clec4F, a C-type lectin receptor which, in rodents, is selectively expressed in Kupffer cells. This uptake mechanism operates on mucins injected both in soluble form intravenously (i.v.) and in particulate form intraperitoneally (i.p.). In mice harboring intraperitoneal infections by the same species, LL mucins were found essentially only at the infection site and in the liver, where they were taken up by Kupffer cells via Clec4F. Therefore, shed LL materials circulate in the host, and Kupffer cells can act as a sink for these materials, even when the parasite grows in sites other than the liver.

Immunology of a unique biological structure: the Echinococcus laminated layer

The larval stages of the cestode parasites belonging to the genus Echinococcus grow within internal organs of humans and a range of animal species. The resulting diseases, collectively termed echinococcoses, include major neglected tropical diseases of humans and livestock. Echinococcus larvae are outwardly protected by the laminated layer (LL), an acellular structure that is unique to this genus. The LL is based on a fibrillar meshwork made up of mucins, which are decorated by galactose-rich O-glycans. In addition, in the species cluster termed E. granulosus sensu lato, the LL features nano-deposits of the calcium salt of myo-inositol hexakisphosphate (Insp6). The main purpose of our article is to update the immunobiology of the LL. Major recent advances in this area are (i) the demonstration of LL "debris" at the infection site and draining lymph nodes, (ii) the characterization of the decoy activity of calcium Insp6 with respect to complement, (iii) the evidence that the LL mucin carbohydrates interact specifically with a lectin receptor expressed in Kupffer cells (Clec4F), and (iv) the characterization of what appear to be receptor-independent effects of LL particles on dendritic cells and macrophages. Much information is missing on the immunology of this intriguing structure: we discuss gaps in knowledge and propose possible avenues for research.

Quillaja brasiliensis saponin-based nanoparticulate adjuvants are capable of triggering early immune responses

Commercially available saponins are extracted from Quillaja saponaria barks, being Quil A® the most widely used. Nanoparticulate immunostimulating complexes (ISCOMs or ISCOMATRIX) formulated with these, are able to stimulate strong humoral and cellular immune responses. Recently, we formulated novel ISCOMs replacing QuilA® by QB-90 (IQB-90), a Quillaja brasiliensis leaf-extracted saponin fraction, and reported that IQB-90 improved antigen uptake, and induced systemic and mucosal antibody production, and T-cell responses. However, its mechanism of action remains unclear. In this study we provide a deeper insight into the immune stimulatory properties of QB-90 and ISCOMATRIX-like based on this fraction (IMXQB-90). We show herein that, when used as a viral vaccine adjuvant, QB-90 promotes an "immunocompetent environment". In addition, QB-90 and IMXQB-90 induce immune-cells recruitment at draining-lymph nodes and spleen. Subsequently, we prove that QB-90 or IMXQB-90 stimulated dendritic cells secret IL-1β by mechanisms involving Caspase-1/11 and MyD88 pathways, implying canonical inflammasome activation. Finally, both formulations induce a change in the expression of cytokines and chemokines coding genes, many of which are up-regulated. Findings reported here provide important insights into the molecular and cellular mechanisms underlying the adjuvant activity of Q. brasiliensis leaf-saponins and its respective nanoparticles.

Particles from the Echinococcus granulosus laminated layer inhibit IL-4 and growth factor-driven Akt phosphorylation and proliferative responses in macrophages

Proliferation of macrophages is a hallmark of inflammation in many type 2 settings including helminth infections. The cellular expansion is driven by the type 2 cytokine interleukin-4 (IL-4), as well as by M-CSF, which also controls homeostatic levels of tissue resident macrophages. Cystic echinococcosis, caused by the tissue-dwelling larval stage of the cestode Echinococcus granulosus, is characterised by normally subdued local inflammation. Infiltrating host cells make contact only with the acellular protective coat of the parasite, called laminated layer, particles of which can be ingested by phagocytic cells. Here we report that a particulate preparation from this layer (pLL) strongly inhibits the proliferation of macrophages in response to IL-4 or M-CSF. In addition, pLL also inhibits IL-4-driven up-regulation of Relm-α, without similarly affecting Chitinase-like 3 (Chil3/Ym1). IL-4-driven cell proliferation and up-regulation of Relm-α are both known to depend on the phosphatidylinositol (PI3K)/Akt pathway, which is dispensable for induction of Chil3/Ym1. Exposure to pLL in vitro inhibited Akt activation in response to proliferative stimuli, providing a potential mechanism for its activities. Our results suggest that the E. granulosus laminated layer exerts some of its anti-inflammatory properties through inhibition of PI3K/Akt activation and consequent limitation of macrophage proliferation.

Parasite molecules and host responses in cystic echinococcosis

Cystic echinococcosis is the infection by the larvae of cestode parasites belonging to the Echinococcus granulosus sensu lato species complex. Local host responses are strikingly subdued in relation to the size and persistence of these larvae, which develop within mammalian organs as 'hydatid cysts' measuring up to tens of cm in diameter. In a context in which helminth-derived immune-suppressive, as well as Th2-inducing, molecules garner much interest, knowledge on the interactions between E. granulosus molecules and the immune system lags behind. Here, we discuss what is known and what are the open questions on E. granulosus molecules and structures interacting with the innate and adaptive immune systems, potentially or in demonstrated form. We attempt a global biological approach on molecules that have been given consideration primarily as protective (Eg95) or diagnostic antigens (antigen B, antigen 5). We integrate glycobiological information, which traverses the discussions on antigen 5, the mucin-based protective laminated layer and immunologically active preparations from protoscoleces. We also highlight some less well-known molecules that appear as promising candidates to possess immune-regulatory activities. Finally, we point out gaps in the molecular-level knowledge of this infectious agent that hinder our understanding of its immunology.

The laminated layer: Recent advances and insights into Echinococcus biology and evolution

The laminated layer is the unique mucin-based extracellular matrix that protects Echinococcus larvae, and thus to an important extent, shapes host-parasite relationships in the larval echinococcoses. In 2011, we published twin reviews summarizing what was known about this structure. Since then, important advances have been made. Complete genomes and some RNAseq data are now available for E. multilocularis and E. granulosus, leading to the inference that the E. multilocularis LL is probably formed by a single type of mucin backbone, while a second apomucin subfamily additionally contributes to the E. granulosus LL. Previously suspected differences between E. granulosus and E. multilocularis in mucin glycan size have been confirmed and pinned down to the virtual absence of Galβ1-3 chains in E. multilocularis. The LL carbohydrates from both species have been found to interact selectively with the Kupffer cell receptor expressed in rodent liver macrophages, highlighting the ancestral adaptations to rodents as intermediate hosts and to the liver as infection site. Finally, LL particles have been shown to possess carbohydrate-independent mechanisms profoundly conditioning non-liver-specific dendritic cells and macrophages. These advances are discussed in an integrated way, and in the context of the newly determined phylogeny of Echinococcus and its taenid relatives.

Understanding the laminated layer of larval Echinococcus II: immunology

The laminated layer (LL) is the massive carbohydrate-rich structure that protects Echinococcus larvae, which cause cystic echinococcosis (hydatid disease) and alveolar echinococcosis. Increased understanding of the biochemistry of the LL is allowing a more informed analysis of its immunology. The LL not only protects the parasite against host attack but also shapes the overall immune response against it. Because of its dense glycosylation, it probably contains few T-cell epitopes, being important instead in T-cell independent antibody responses. Crucially, it is decoded in non-inflammatory fashion by innate immunity, surely contributing to the strong immune-regulation observed in Echinococcus infections. Defining the active LL molecular motifs and corresponding host innate receptors is a feasible and promising goal in the field of helminth-derived immune-regulatory molecules.

Understanding the laminated layer of larval Echinococcus I: structure

Echinococcus larvae are protected by a massive carbohydrate-rich acellular structure, called the laminated layer. In spite of being widely considered the crucial element of these host-parasite interfaces, the laminated layer has been historically poorly understood. In fact, it is still often called 'chitinous', 'hyaline' or 'cuticular' layer, or said to be composed of polysaccharides. However, over the past few years the laminated layer was found to be comprised of mucins bearing defined galactose-rich carbohydrates, and accompanied, in the case of Echinococcus granulosus, by calcium inositol hexakisphosphate deposits. In this review, the architecture and biosynthesis of this unusual structure is discussed at depth in terms of what is known and what needs to be discovered.

Studies on the structural mucins of the Echinococcus granulosus laminated layer

The larvae of the cestodes belonging to the genus Echinococcus are outwardly protected by the laminated layer (LL), a crucial but poorly understood carbohydrate-rich acellular structure. Carbohydrate structural data strongly suggest that the main components of the LL are mucins. The most massive LL in the genus is featured by E. granulosus, agent of cystic hydatid disease. No appropriate methods existed to date for the solubilisation of the E. granulosus LL and the electrophoretic visualisation of its proposed structural mucins. We report that reduction of disulphides greatly aids LL disassembly, resulting in almost full solubilisation in combination with moderate sonication. The structural mucins can then be visualised by agarose electrophoresis and blotting with galactose-binding lectins, which also react strongly with the LL in tissue sections. A substantial portion of the material migrates as if positively charged; since the LL glycans are neutral, this may correspond to mucins with cationic peptide backbones.

The major surface carbohydrates of the Echinococcus granulosus cyst: mucin-type O-glycans decorated by novel galactose-based structures

The cestodes constitute important but understudied human and veterinary parasites. Their surfaces are rich in carbohydrates, on which very little structural information is available. The tissue-dwelling larva (hydatid cyst) of the cestode Echinococcus granulosus is outwardly protected by a massive layer of carbohydrate-rich extracellular matrix, termed the laminated layer. The monosaccharide composition of this layer suggests that its major carbohydrate components are exclusively mucin-type O-glycans. We have purified these glycans after their release from the crude laminated layer and obtained by MS and NMR the complete structure of 10 of the most abundant components. The structures, between two and six residues in length, encompass a limited number of biosynthetic motifs. The mucin cores 1 and 2 are either nondecorated or elongated by a chain of Galpbeta1-3 residues. This chain can be capped by a single Galpalpha1-4 residue, such capping becoming more dominant with increasing chain size. In addition, the core 2 N-acetylglucosamine residue is in cases substituted with the disaccharide Galpalpha1-4Galpbeta1-4, giving rise to the blood P(1)-antigen motif. Larger, also related, glycans exist, reaching at least 18 residues in size. The glycans described are related but larger than those previously described from an Echinococcus multilocularis mucin [Hulsmeier, A. J., et al. (2002) J. Biol. Chem. 277, 5742-5748]. Our results reveal that the E. granulosus cyst exposes to the host only a few different major carbohydrate motifs. These motifs are composed essentially of galactose units and include the elongation by (Galpbeta1-3)(n) and the capping by Galpalpha1-4, novel in animal mucin-type O-glycans.

Characterization of the carcinoma-associated Tk antigen in helminth parasites

Expression of Tk antigen, a truncated carbohydrate antigen, was examined in helmith parasites. Using the monoclonal antibody LM389, this antigen was detected in extracts from Taenia hydatigena, Mesocestoides vogae (syn corti), and Taenia crassiceps. No reactivity was observed in Thysanosoma spp., Dipylidium caninum, Fasciola hepatica, and Nyppostrongylus brasiliensis. On the basis of their electrophoretic mobility, different patterns of Tk-bearing glycoproteins were observed among T. hydatigena, M. corti and T. crassiceps by immunoblotting, with certain components resolved as broad bands typical of mucin-like glycoproteins. Most Tk-reactive material remained in the 0.6 N perchloric acid-soluble fraction, confirming that Tk epitopes are carried by mucin-type glycoproteins. Immunohistochemical analysis revealed that in T. hydatigena, Tk antigen is mainly expressed in the tegument, whereas in M. corti the reactivity was principally observed in the subtegumental parenchyma. The presence of a novel tumor-associated carbohydrate antigen in invertebrates, contributes to strengthen the notion that truncated mucin-type O-glycosylation is a normal phenomenon in parasitic worms and may help identify new biological characteristics of helminth parasites.

Characterization of myo-inositol hexakisphosphate deposits from larval Echinococcus granulosus

The abundant metabolite myo-inositol hexakisphosphate (InsP6) can form vesicular deposits with cations, a widespread phenomenon in plants also found in the cestode parasite, Echinococcus granulosus. In this organism, the deposits are exocytosed, accumulating in a host-exposed sheath of extracellular matrix termed the laminated layer. The formation and mobilization of InsP6 deposits, which involve precipitation and solubilization reactions, respectively, cannot yet be rationalized in quantitative chemical terms, as the solids involved have not been formally described. We report such a description for the InsP6 deposits from E. granulosus, purified as the solid residue left by mild alkaline digestion of the principal mucin component of the laminated layer. The deposits are largely composed of the compound Ca5H2L.16H2O (L representing fully deprotonated InsP6), and additionally contain Mg2+ (6-9% molar ratio with respect to Ca2+), but not K+. Calculations employing recently available chemical constants show that the precipitation of Ca5H2L.16H2O is predicted by thermodynamics in secretory vesicle-like conditions. The deposits appear to be similar to microcrystalline solids when analysed under the electron microscope; we estimate that each crystal comprises around 200 InsP6 molecules. We calculate that the deposits increase, by three orders of magnitude, the surface area available for adsorption of host proteins, a salient ability of the laminated layer. The major inositol phosphate in the deposits, other than InsP6, is myo-inositol (1,2,4,5,6) pentakisphosphate, or its enantiomer, inositol (2,3,4,5,6) pentakisphosphate. The compound appears to be a subproduct of the intracellular pathways leading to the synthesis and vesicular accumulation of InsP6, rather than arising from extracellular hydrolysis of InsP6.

Unique precipitation and exocytosis of a calcium salt of myo-inositol hexakisphosphate in larval Echinococcus granulosus

The ubiquitous intracellular molecule myo-inositol hexakisphosphate (IP6) is present extracellularly in the hydatid cyst wall (HCW) of the parasitic cestode Echinococcus granulosus. This study shows that extracellular IP6 is present as its solid calcium salt, in the form of deposits that are observed, at the ultrastructural level, as naturally electron dense granules some tens of nanometers in diameter. The presence of a calcium salt of IP6 in these structures was determined by two different electron microscopy techniques: (i) the analysis of the spatial distribution of phosphorus and calcium in the outer, acellular layer of the HCW (the laminated layer, LL) through electron energy loss spectroscopy, and (ii) the observation, by transmission electron microscopy, of HCW that were selectively depleted of IP6 by treatment with EGTA or phytase, an enzyme that catalyses the dephosphorylation of IP6. The deposits of the IP6-Ca(II) salt are also observed inside membrane vesicles in cells of the germinal layer (the inner, cellular layer of the HCW), indicating that IP6 precipitates with calcium within a cellular vesicular compartment and is then secreted to the LL. Thus, much as in plants (that produce vesicular IP6 deposits), the existence of transporters for IP6 or its precursors in internal membranes is needed to explain the compound's cellular localisation in E. granulosus.

Production and characterization of monoclonal antibodies against excretory/secretory products of adult Echinococcus granulosus, and their application to coproantigen detection

Two IgM murine monoclonal antibodies (MAbs), EgC1 and EgC3, were produced against the excretory/secretory (E/S) products of Echinococcus granulosus adult worms. Immunoblotting revealed that both predominantly recognized a 50 kDa antigen in the somatic extract and an 85 kDa component in the E/S products. Immunolocalization showed that both MAbs reacted with the tegument of the parasite, and additionally EgC3 reacted with parenchyma and the tegument lining the external surface of the reproductive organs. A coproantigen capture ELISA was developed using a rabbit polyclonal antibody against E/S products from adult tapeworms as catching antibodies, and each one of MAbs as detecting antibody. The assays detected seven out of eight (EgC1), and eight out of eight (EgC3) experimentally infected dogs (worm burdens ranging from 61 to 57,500), using heat-treated samples obtained at prepatent period, and none (n=8) of helminth-free samples. Time course analysis showed that, after a 12-25 days lag, coproantigen levels rose above cut off O.D. values and typically peaked around 30 days post-infection (DPI) at the end of the experiment. One dog experimentally infected with Taenia hydatigena metacestodes was slightly detected as positive at different time points after 30 DPI. Both MAbs showed a similar pattern of recognition, but T. hydatigena antigens were undetectable for a longer period, and reached lower O.D. values with EgC1. Interestingly, fecal samples from two experimentally infected dogs with Echinococcus multilocularis were not recognized by the EgC1 assay, suggesting a potential value as species-specific diagnostic tool.

Mucin-type O-glycosylation in helminth parasites from major taxonomic groups: evidence for widespread distribution of the Tn antigen (GalNAc-Ser/Thr) and identification of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase activity

This article focuses on the initiation pathway of mucin-type O-glycosylation in helminth parasites. The presence of the GalNAc-O-Ser/Thr structure, also known as Tn antigen, a truncated determinant related to aberrant glycosylation in mammal cells, and the activity of the UDP-GalNAc:polypeptide N-acetyl-galactosaminyltransferase (ppGaNTase), the enzyme responsible for its synthesis, were studied in species from major taxonomic groups. Tn reactivity was determined in extracts from Taenia hydatigena, Mesocestoides corti, Fasciola hepatica, Nippostrongylus brasiliensis, and Toxocara canis using the monoclonal antibody 83D4. The Tn determinant was revealed in all preparations, and multiple patterns of Tn-bearing glycoproteins were observed by immunoblotting. Additionally, the first evidence that helminth parasites express ppGaNTase activity was obtained. This enzyme was studied in extracts from Echinococcus granulosus, F. hepatica, and T. canis by measuring the incorporation of UDP-(3H)GalNAc to both deglycosylated ovine syalomucin (dOSM) and synthetic peptide sequences derived from tandem repeats of human mucins. Whereas significant levels of ppGaNTase activity were detected in all the extracts when dOSM was used as a multisite acceptor, it was only observed in F. hepatica and E. granulosus extracts when mucin-derived peptides were used, suggesting that T. canis ppGaNTase enzyme(s) may represent a member of the gene family with a more restricted specificity for worm O-glycosylation motifs. The widespread expression of Tn antigen, capable of evoking both humoral and cellular immunity, strongly suggests that simple mucin-type O-glycosylation does not constitute an aberrant phenomenon in helminth parasites.

The toxicity of praziquantel against Mesocestoides vogae (syn. corti) tetrathyridia can be assessed using a novel in vitro system

We recently standardised Mesocestoides vogae (syn. corti) tetrathyridia cultures in the presence of sodium taurocholate. Parasite clustering and segmentation were observed as taurocholate-dependent effects in biphasic and monophasic media, respectively, and both were inhibited by a specific minimum inhibitory concentration (m.i.c.) of the cestocidal drugs albendazol and praziquantel. In the present study, we analysed the relationship between clustering inhibition and drug toxicity using praziquantel and a mouse experimental infection. In an "in vitro-in vivo" trial, a significant (ANOVA, P<0.05) reduction was observed in the infectivity of tetrathyridia previously cultured with praziquantel m.i.c. (0.06 micro g/ml) for 10 days. In an "in vivo-in vitro" trial, the clustering of tetrathyridia recovered from mice treated with praziquantel was found to be markedly reduced: 22%, compared with 83% cluster-containing wells of parasites from control mice. These results show that the outcome of infection and the suppression of taurocholate-induced clustering provide consistent indications of praziquantel toxicity against M. vogae, an observation confirmed by histological studies. The easily recorded clustering inhibition of M. vogae tetrathyridia in biphasic medium is a potentially useful system for the assessment of drug toxicity against cestode larvae.

Characterization of carbohydrates of adult Echinococcus granulosus by lectin-binding analysis

The identification of lectin-binding structures in adult worms of Echinococcus granulosus was carried out by lectin fluorescence; the distribution of carbohydrates in parasite glycoconjugates was also studied by lectin blotting. The lectins with the most ample recognition pattern were ConA, WGA, and PNA. ConA showed widespread reactivity in tegument and parenchyma components, including the reproductive system, suggesting that mannose is a highly expressed component of the adult glycans. Although reproductive structures appeared to be rich in N-acetyl-D-glucosamine (GlcNAc)-N-acetyl neuraminic acid (NeuAc) and galactose (Gal) as demonstrated by their strong reactivity with WGA and PNA, respectively, some differences were observed in their labeling patterns. This was very clear in the case of the vagina, which only reacted with WGA. Furthermore, WGA and ConA both had reactivity with the excretory canals. RCA, the other Gal binding lectin used, only reacted with the tegument, suggesting that widespread PNA reactivity with the reproductive system is related to the presence of the D-Gal-beta-(1,3)D-GalNAc terminal structure. UEA I failed to bind to any parasite tissues as determined by lectin fluorescence, whereas DBA and SBA showed a very faint staining of the tegument. However, in transferred glycans, N-acetyl-D-galactosamine (GalNAc) and fucose (Fuc) containing glycoproteins were distinctly detected.

Mucin-type O-glycosylation in Fasciola hepatica: characterisation of carcinoma-associated Tn and sialyl-Tn antigens and evaluation of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase activity

Simple mucin-type cancer-associated O-glycan structures, such as the Tn antigen (GalNAc-O-Ser/Thr), are expressed by certain helminth parasites. These antigens are involved in several types of receptor-ligand interactions, and they are potential targets for immunotherapy. The aim of this work was to study the initiation pathway of mucin-type O-glycosylation in Fasciola hepatica, performing a biochemical and immunohistochemical characterisation of Tn and sialyl-Tn antigens, and evaluating the ppGaNTase activity, which catalyses the first step in O-glycan biosynthesis. Using ELISA, both Tn and sialyl-Tn antigens were detected predominantly in the somatic and deoxycholate extracts. Immunofluorescence analysis revealed that Tn antigen is preferentially expressed in testis, while sialyl-Tn glycoproteins were more widely distributed, being present in parenchymal cells, basal membrane of the tegument, and apical surface of epithelial cells lining the caeca. On the basis of their electrophoretic mobility, Tn glycoproteins were resolved as six components of 10, 37, 76, 125, 170 and 205 kDa, and sialyl-Tn components showed an apparent molecular mass of 28 and 32 kDa, and two broad bands of 90-110 and 170-190 kDa. The observation that only the 76 kDa Tn-glycoprotein remained in the 0.6 N perchloric acid-soluble fraction suggests that it could be a good candidate for mucin characterisation in this parasite. The ppGaNTase activity showed its maximal activity at pH 7-7.5 and 37 degrees C, showing that Mn(2+) was the best divalent cation activator. Using a panel of nine synthetic peptides as acceptor substrates, we found that F. hepatica ppGaNTase was able to glycosylate both threonines and serines, the best substrates being the peptides derived from the tandem repeat region of human mucins (MUC2 and MUC6), and from Trypanosoma cruzi and Trypanosoma brucei glycoproteins. The results reported here constitute the first evidence on O-glycosylation pathways in F. hepatica, and may help to identify new biological characteristics of this parasite as well as of the host-parasite relationship.

O-glycosylation in Echinococcus granulosus: identification and characterization of the carcinoma-associated Tn antigen

In the present work we demonstrate that the cancer-associated O-glycosylated Tn antigen (GalNAc-O-Ser/Thr) is expressed by the cestode Echinococcus granulosus. This antigen was detected in both larval and adult worm extracts, with the highest specific activity observed in the adult excretion/secretion preparation. Histochemical analysis showed that Tn is preferentially expressed in the parenchyma in both parasite stages and the external part of tegument in adult worms. A similar pattern was observed for sialyl-Tn, a related O-linked antigen. Tn glycoproteins from protoscoleces were resolved by SDS-PAGE in two main components of 43 and 49 kDa. After purification, this material was reactive with lectins which bind GlcNAc/sialic acid, GalNAc, and T antigen. In a preliminary evaluation, high levels of Tn antigen were detected in serum samples from patients with hydatid cyst, suggesting that the measure of Tn in serum could be a biomarker of this disease, although extensive work is necessary in order to determine the clinical usefulness of this assay. The results reported here, the first evidence of O-glycosylation pathways in E. granulosus and the presence of Tn antigen in cestodes, suggest that the evaluation of O-glycosylated antigens might give new insights in the host-parasite relationship.