Molecular cross-talk in host-parasite relationships: the intriguing immunomodulatory role of Echinococcus antigen B in cystic echinococcosis

Modulatory actions of Echinococcus granulosus antigen B on macrophage inflammatory activation

Cestodes use own lipid-binding proteins to capture and transport hydrophobic ligands, including lipids that they cannot synthesise as fatty acids and cholesterol. In E. granulosus s.l., one of these lipoproteins is antigen B (EgAgB), codified by a multigenic and polymorphic family that gives rise to five gene products (EgAgB8/1-5 subunits) assembled as a 230 kDa macromolecule. EgAgB has a diagnostic value for cystic echinococcosis, but its putative role in the immunobiology of this infection is still poorly understood. Accumulating research suggests that EgAgB has immunomodulatory properties, but previous studies employed denatured antigen preparations that might exert different effects than the native form, thereby limiting data interpretation. This work analysed the modulatory actions on macrophages of native EgAgB (nEgAgB) and the recombinant form of EgAg8/1, which is the most abundant subunit in the larva and was expressed in insect S2 cells (rEgAgB8/1). Both EgAgB preparations were purified to homogeneity by immunoaffinity chromatography using a novel nanobody anti-EgAgB8/1. nEgAgB and rEgAgB8/1 exhibited differences in size and lipid composition. The rEgAgB8/1 generates mildly larger lipoproteins with a less diverse lipid composition than nEgAgB. Assays using human and murine macrophages showed that both nEgAgB and rEgAgB8/1 interfered with in vitro LPS-driven macrophage activation, decreasing cytokine (IL-1β, IL-6, IL-12p40, IFN-β) secretion and ·NO generation. Furthermore, nEgAgB and rEgAgB8/1 modulated in vivo LPS-induced cytokine production (IL-6, IL-10) and activation of large (measured as MHC-II level) and small (measured as CD86 and CD40 levels) macrophages in the peritoneum, although rEgAgB8/1 effects were less robust. Overall, this work reinforced the notion that EgAgB is an immunomodulatory component of E. granulosus s.l. Although nEgAgB lipid's effects cannot be ruled out, our data suggest that the EgAgB8/1 subunit contributes to EgAgB´s ability to regulate the inflammatory activation of macrophages.

EgCF mediates macrophage polarisation by influencing the glycolytic pathway

Human cystic echinococcosis (CE) is a zoonotic disorder triggered by the larval stage of Echinococcus granulosus (E. granulosus) and predominantly occurred in the liver and lungs. The M2 macrophage level is considerably elevated among the liver of patients with hepatic CE and performs an integral function in liver fibrosis. However, the mechanism of CE inducing polarisation of macrophage to an M2 phenotype is unknown. In this study, macrophage was treated with E. granulosus cyst fluid (EgCF) to explore the mechanism of macrophage polarisation. Consequently, the expression of the M2 macrophage and production of anti-inflammatory cytokines increased after 48 h treatment by EgCF. In addition, EgCF promoted polarisation of macrophage to an M2 phenotype by inhibiting the expression of transcriptional factor hypoxia-inducible factor 1-alpha (HIF-1α), which increased the expression of glycolysis-associated genes, including hexokinase 2 (HK2) and pyruvate kinase 2 (PKM2). The HIF-1α agonist ML228 also inhibited the induction of macrophage to an M2 phenotype by EgCF in vitro. Our findings indicate that E. granulosus inhibits glycolysis by suppressing the expression of HIF-1α.

Characterization of protein cargo of Echinococcus granulosus extracellular vesicles in drug response and its influence on immune response

BACKGROUND

The Echinococcus granulosus sensu lato species complex causes cystic echinococcosis, a zoonotic disease of medical importance. Parasite-derived small extracellular vesicles (sEVs) are involved in the interaction with hosts intervening in signal transduction related to parasite proliferation and disease pathogenesis. Although the characteristics of sEVs from E. granulosus protoscoleces and their interaction with host dendritic cells (DCs) have been described, the effect of sEVs recovered during parasite pharmacological treatment on the immune response remains unexplored.

METHODS

Here, we isolated and characterized sEVs from control and drug-treated protoscoleces by ultracentrifugation, transmission electron microscopy, dynamic light scattering, and proteomic analysis. In addition, we evaluated the cytokine response profile induced in murine bone marrow-derived dendritic cells (BMDCs) by qPCR.

RESULTS

The isolated sEVs, with conventional size between 50 and 200 nm, regardless of drug treatment, showed more than 500 cargo proteins and, importantly, 20 known antigens and 70 potential antigenic proteins, and several integral-transmembrane and soluble proteins mainly associated with signal transduction, immunomodulation, scaffolding factors, extracellular matrix-anchoring, and lipid transport. The identity and abundance of proteins in the sEV-cargo from metformin- and albendazole sulfoxide (ABZSO)-treated parasites were determined by proteomic analysis, detecting 107 and eight exclusive proteins, respectively, which include proteins related to the mechanisms of drug action. We also determined that the interaction of murine BMDCs with sEVs derived from control parasites and those treated with ABZSO and metformin increased the expression of pro-inflammatory cytokines such as IL-12 compared to control cells. Additionally, protoscolex-derived vesicles from metformin treatments induced the production of IL-6, TNF-α, and IL-10. However, the expression of IL-23 and TGF-β was downregulated.

CONCLUSIONS

We demonstrated that sEV-cargo derived from drug-treated E. granulosus protoscoleces have immunomodulatory functions, as they enhance DC activation towards a type 1 pro-inflammatory profile against the parasite, and therefore support the proposal of a new approach for the prevention and treatment of secondary echinococcosis.

Apoptosis as a Potential Target to Arrest and Survival of Hydatid Cyst

Background

Hydatidosis is a serious and life-threatening disease that may lead to the death of the host if diagnosed and treated improperly. Apoptosis has been investigated as a mechanism of host innate immunity in suppressing parasites and also the survival of cysts in the human body. The present study investigates the process and role of apoptosis caused by a host cell or parasite in hydatid cysts.

Materials and Methods

Survey cytotoxic effect and apoptotic mortality of hydatid-treated lymphocytes were investigated. Also, to determine the mechanism of apoptosis in host and parasite, the mean gene expressions of Bcl-2, Bax, Caspase 3 in hydatid-treated lymphocytes, and Fas-L gene in the laminated-germinal layer of fertile and infertile hydatid cysts were evaluated.

Results

The viability of fertile and infertile hydatid fluid-treated lymphocytes was significantly different compared with the control group. Flow cytometry also showed apoptotic cells. Bax mean gene expression was significantly different between fertile and infertile treated lymphocytes. However, there was no significant difference in the mean expression of Caspase 3, and Bcl-2 genes in these two groups. Although the expression of the Fas-L gene in infertile cysts was higher than in fertile cysts, the result was not significant.

Conclusion

It seems that hydatid cyst fluid may induce apoptosis in lymphocytes so that, hydatid cysts can escape from the immune system and stay alive. On the other hand, the results represent the possible immune path of host apoptosis against the parasite as one of the important routes in infertility of hydatid cysts.

Targeted and non-targeted proteomics to characterize the parasite proteins of Echinococcus multilocularis metacestodes

The larval stage of the cestode Echinococcus multilocularis is the causative agent of alveolar echinococcosis. To investigate the biology of these stages and to test novel compounds, metacestode cultures represent a suitable in vitro model system. These metacestodes are vesicles surrounded by an envelope formed by the vesicle tissue (VT), which is formed by the laminated and germinal layer, and filled with vesicle fluid (VF). We analyzed the proteome of VF and VT by liquid chromatography tandem mass spectrometry (LC-MS/MS) and identified a total of 2,954 parasite proteins. The most abundant protein in VT was the expressed conserved protein encoded by EmuJ_000412500, followed by the antigen B subunit AgB8/3a encoded by EmuJ_000381500 and Endophilin B1 (protein p29). In VF, the pattern was different and dominated by AgB subunits. The most abundant protein was the AgB8/3a subunit followed by three other AgB subunits. In total, the AgB subunits detected in VF represented 62.1% of the parasite proteins. In culture media (CM), 63 E. multilocularis proteins were detected, of which AgB subunits made up 93.7% of the detected parasite proteins. All AgB subunits detected in VF (encoded by EmuJ_000381100-700, corresponding to AgB8/2, AgB8/1, AgB8/4, AgB8/3a, AgB8/3b, and AgB8/3c) were also found in CM, except the subunit encoded by EmuJ_000381800 (AgB8/5) that was very rare in VF and not detected in CM. The relative abundance of the AgB subunits in VF and CM followed the same pattern. In VT, only the subunits EmuJ_000381500 (AgB8/3a) and EmuJ_000381200 (AgB8/1) were detected among the 20 most abundant proteins. To see whether this pattern was specific to VF from in vitro cultured metacestodes, we analyzed the proteome of VF from metacestodes grown in a mouse model. Here, the AgB subunits encoded by EmuJ_000381100-700 constituted the most abundant proteins, namely, 81.9% of total protein, with the same order of abundance as in vitro. Immunofluorescence on metacestodes showed that AgB is co-localized to calcareous corpuscles of E. multilocularis. Using targeted proteomics with HA-tagged EmuJ_000381200 (AgB8/1) and EmuJ_000381100 (AgB8/2), we could show that uptake of AgB subunits from CM into VF occurs within hours.

Proteomic characterization of Echinococcus granulosus sensu stricto, Taenia hydatigena and Taenia multiceps metacestode cyst fluids

Cystic echinococcosis (CE) diagnosis by means of serological assays is hampered by the presence of parasites closely related to Echinococcus granulosus sensu lato (s.l.), responsible of the zoonotic disease and with which share cross-reacting antigens. Thus, improvements on the characterization of Echinococcus specific antigens expressed in the larval stage are required, in order to provide useful information for the development of immunological assays for the serodiagnosis of CE in sheep. Here, the proteome of the hydatid cyst fluids (HFs) of Echinococcus granulosus (hydatid fluid, EgHF) and other ovine parasites cyst fluids (CFs), Taenia hydatigena (ThCF) and Taenia multiceps (TmCF) were analyzed by a shotgun proteomic approach. Parasite and host protein profiles in the three types of cyst fluids were characterized and compared. Among the identified proteins, differential parasitic markers with serodiagnostic potential, due to their well-known immunoreactivity in human, included Ag5, AgB proteins, 8-kDa glycoproteins, hydatid disease diagnostic antigen P29 and major egg antigen P40. In particular, seven proteoforms of AgB and 8-kDa glycoprotein resulted to be the most promising diagnostic biomarkers, as they might predict CE in ovine and discriminate between different types of parasites.

Microcyst fluid promotes the migration and invasion of fibroblasts in the adventitial layer of alveolar echinococcosis

Alveolar echinococcosis (AE) caused by Echinococcus multilocularis (E. multilocularis), characterized by lesions composed of an aggregate of microcysts embedded in a granulomatous host's reaction. The periphery of parasite granulomas often additionally displays fibrotic reactions of varying intensity, in which E. multilocularis microenvironment fibroblasts (EMFs) laid down collagen. However, the regulation of EMFs by the infiltration of E. multilocularis microcyst fluid (MF) into granulomas remains poorly defined. This study aimed to investigate the effect of MF on migration and invasion of primary isolated EMFs cells. A mouse model of secondary infection with AE was established, and the model construction was evaluated by HE staining. EMFs were cultured in primary by tissue block adherency method. The isolated cells were identified by qPCR, immunofluorescence and Western blot. Then CCK-8 assay, cell migration/invasion assay and flow cytometry were performed to detect the effects of MF on the proliferation, migration, invasion and cell cycle of EMFs, respectively. The expressions of MMP2 and MMP9 at mRNA and protein levels in EMFs were detected by RT-qPCR and Western blot. The effect of PI3K-Akt signal transduction pathway on regulating the expression of MMPs expression was assessed by Western blot. As indicated from the results, EMFs were successfully isolated from the E. multilocularis microenvironment and identified as myofibroblasts. MF significantly facilitated the proliferation and cell cycle progression of EMFs. In addition, MF significantly improved the migration and invasion of EMFs. MF was further confirmed to up-regulate mRNA and protein expressions of MMP2 and MMP9 in EMFs, which was related to the activation of the PI3K-Akt signaling pathway. The present study demonstrates that MF can promote the migration and invasion of EMFs cells significantly, which might be via activating PI3K-Akt signaling pathway.

Cattle co-infection of Echinococcus granulosus and Fasciola hepatica results in a different systemic cytokine profile than single parasite infection

E. granulosus is a cestode that causes Cystic Echinococcosis (CE), a zoonotic disease with worldwide presence. The immune response generated by the host against the metacestode induces a permissive Th2 response, as opposed to pro-inflammatory Th1 response. In this view, mixed Th2 and regulatory responses allow parasite survival. Overall, larval Echinococcus infections induce strong regulatory responses. Fasciola hepatica, another common helminth parasite, represents a major infection in cattle. Co-infection with different parasite species in the same host, polyparasitism, is a common occurrence involving E. granulosus and F. hepatica in cattle. ‘While it is known that infection with F. hepatica also triggers a polarized Th2/Treg immune response, little is reported regarding effects on the systemic immune response of this example of polyparasitism. F. hepatica also triggers immune responses polarized to the Th2/ Treg spectrum. Serum samples from 107 animals were analyzed, and were divided according to their infection status and Echinococcal cysts fertility. Cytokines were measured utilizing a Milliplex Magnetic Bead Panel to detect IFN-γ, IL-1, IL-2, IL-4, IL-6, IL-10, IL-12 and IL-18. Cattle infected only with F. hepatica had the highest concentration of every cytokine analyzed, with both 4.24 and 3.34-fold increases in IL-10 and IL-4, respectively, compared to control animals, followed by E. granulosus and F. hepatica co-infected animals with two-fold increase in IL-10 and IL-4, compared to control animals, suggesting that E. granulosus co-infection dampens the cattle Th2/Treg immune response against F. hepatica. When considering Echinococcal cyst fertility and systemic cytokine concentrations, fertile cysts had higher IFN-γ, IL-6 and IL-18 concentrations, while infertile cysts had higher IL-10 concentrations. These results show that E. granulosus co-infection lowers Th1 and Th2 cytokine serological concentration when compared to F. hepatica infection alone. E. granulosus infections show no difference in IFN-γ, IL-1, IL-2, IL-6 and IL-18 levels compared with control animals, highlighting the immune evasion mechanisms of this cestode.

Outcomes of Radiotherapy for Osseous Echinococcosis of Meriones meridianus

Background

Osseous cyst echinococcosis (CE) is an infectious disease that causes disability and deformity in patients, yet there is still no satisfactory treatment. Focusing on the feasibility and prognosis of radiotherapy as an adjuvant or palliative treatment for osseous CE, this study investigated the outcome of Meriones meridianus with osseous CE after radiotherapy.

Methods

The study utilized a comparison control group design with three groups of gerbils, and 240 osseous CE gerbils were randomly divided into control, 40Gy/5times, and 50Gy/5times groups. Different doses of radiotherapy were given to the gerbils, and then, the effects of radiotherapy on gerbils and lesions were observed at 3 and 6 months after radiotherapy. Statistical analysis was done using χ² test, unpaired t-test, and one-way ANOVA.

Results

Significant changes (P < 0.05) were achieved between the three groups in terms of seven parameters at 3 and 6 months, including the number of dead gerbils and lesion sites with ulceration and infection, number of dead scolices, protein content, Ca2+ concentration, the maximum diameter of lesion site, and wet weight of cysts. Except for the number of dead gerbils and lesion sites with ulceration and infection, all other parameters were observed a big difference between 3 months and 6 months in the 50Gy/5times group.

Conclusion

Radiotherapy at a dose of 50 Gy has inhibitory and therapeutic effects on osseous CE in gerbils, and radiotherapy could probably be a treatment option for persistent or recurrent osseous CE.

Recent advances on innate immune pathways related to host-parasite cross-talk in cystic and alveolar echinococcosis

Cystic echinococcosis (CE) and alveolar echinococcosis (AE) are life-threatening parasitic infections worldwide caused by Echinococcus granulosus (sensu lato) and E. multilocularis, respectively. Very little is known about the factors affecting innate susceptibility and resistance to infection with Echinococcus spp. Although benzimidazolic drugs against CE and AE have definitively improved the treatment of these cestodes; however, the lack of successful control campaigns, including the EG95 vaccine, at a continental level indicates the importance of generating novel therapies. This review represents an update on the latest developments in the regulatory functions of innate immune pathways such as apoptosis, toll-like receptors (TLRs), and inflammasomes against CE and AE. We suggest that apoptosis can reciprocally play a bi-functional role among the host-Echinococcus metabolite relationships in suppressive and survival mechanisms of CE. Based on the available information, further studies are needed to determine whether the orchestrated in silico strategy for designing inhibitors and interfering RNA against anti-apoptotic proteins and TLRs would be effective to improve new treatments as well as therapeutic vaccines against the E. granulosus and E. multilocularis.

Antigen B from Echinococcus granulosus is a novel ligand for C-reactive protein

Antigen B (EgAgB) is a phosphatidylcholine (PC)-rich lipoprotein of Echinococcus granulosus s.l. larva, potentially capable of modulating the activation of various myeloid cells, including macrophages. As C-reactive protein (CRP) can act as an innate receptor with ability to bind the phosphocholine moiety of PC in lipoproteins, we investigated whether EgAgB and CRP could interact during cystic echinococcosis infection (CE), and how CRP binding could affect the modulation activities exerted by EgAgB on macrophages. To that end, we firstly investigated the occurrence of CRP induction during human CE. We found that 61% of CE patients, but none of healthy donors, exhibited serum CRP levels higher than 10 mg/mL, suggesting that CRP can be induced during the chronic phase of CE. Furthermore, human CRP was capable of binding specifically to EgAgB with high affinity (0.6 ± 0.1 nM); this binding was Ca²⁺ -dependent and involved the phosphocholine moiety of PC, but not EgAgB8/1, EgAgB8/2 or EgAgB8/3 apolipoproteins. Finally, CRP presence altered the modulation exerted by EgAgB on the cytokine response of LPS-activated macrophages. Overall, our results suggest that CRP presence during CE may contribute to a complex scenario of interactions between EgAgB and myeloid cells, influencing the cytokine response induced during macrophage activation.

Antigen B from Echinococcus granulosus enters mammalian cells by endocytic pathways

Background

Cystic hydatid disease is a zoonosis caused by the larval stage (hydatid) of Echinococcus granulosus (Cestoda, Taeniidae). The hydatid develops in the viscera of intermediate host as a unilocular structure filled by the hydatid fluid, which contains parasitic excretory/secretory products. The lipoprotein Antigen B (AgB) is the major component of E. granulosus metacestode hydatid fluid. Functionally, AgB has been implicated in immunomodulation and lipid transport. However, the mechanisms underlying AgB functions are not completely known.

Methodology/Principal findings

In this study, we investigated AgB interactions with different mammalian cell types and the pathways involved in its internalization. AgB uptake was observed in four different cell lines, NIH-3T3, A549, J774 and RH. Inhibition of caveolae/raft-mediated endocytosis causes about 50 and 69% decrease in AgB internalization by RH and A549 cells, respectively. Interestingly, AgB colocalized with the raft endocytic marker, but also showed a partial colocalization with the clathrin endocytic marker. Finally, AgB colocalized with an endolysosomal tracker, providing evidence for a possible AgB destination after endocytosis.

Conclusions/Significance

The results indicate that caveolae/raft-mediated endocytosis is the main route to AgB internalization, and that a clathrin-mediated entry may also occur at a lower frequency. A possible fate for AgB after endocytosis seems to be the endolysosomal system. Cellular internalization and further access to subcellular compartments could be a requirement for AgB functions as a lipid carrier and/or immunomodulatory molecule, contributing to create a more permissive microenvironment to metacestode development and survival.

Antigen B (AgB) is an oligomeric lipoprotein highly abundant in Echinococcus granulosus hydatid fluid. AgB has already been characterized as an immunomodulatory protein, capable of inducing a permissive immune response to parasite development. Also, an important role in lipid acquisition is attributed to AgB, because it has been found associated to different classes of host lipids. However, the mechanisms of interaction employed by AgB to perform its functions remain undetermined. In this study, we demonstrate that mammalian cells are able to internalize E. granulosus AgB in culture and found that specific mechanisms of endocytosis are involved. Our results extend the understanding of AgB biological role indicating cellular internalization as a mechanism of interaction, which in turn, may represent a target to intervention.

Evaluation of Echinococcus granulosus recombinant EgAgB8/1, EgAgB8/2 and EPC1 antigens in the diagnosis of cystic echinococcosis in buffaloes

Three recombinant proteins of Echinococcus granulosus including two antigen B sub-units EgAgB8/1 and EgAgB8/2 and Echinococcus protoscolex calcium binding protein 1 (EPC1) were expressed in prokaryotic expression vectors. The diagnostic potential of these three recombinant proteins was evaluated in the detection of cystic echinococcosis in buffaloes in IgG-ELISA. The EgAgB8/1 and EgAgB8/2 recombinant proteins reacted fairly with the hydatid infected buffaloes with sensitivity of 75.0% and 78.6%, respectively and specificity of 75.8% while EPC1 recombinant protein showed higher sensitivity (89.3%) but lower specificity (51.5%). Cross-reactivity of these three antigens was assayed with buffalo sera naturally infected with Explanatum explanatum, Paramphistomum epiclitum, Gastrothylax spp., Fasciola gigantica and Sarcocystis spp. EgAgB8/1 and EPC1 antigens cross-reacted with all these sera while EgAgB8/2 showed no cross-reaction with Sarcocystis spp. and reacted with some of the E. explanatum infected buffalo sera. This study explores the potential of three hydatid antigens viz. EgAgB8/1, EgAgB8/2 and EPC1 for their diagnostic potential in buffaloes positive for cystic echinococcosis.

Liver cystic echinococcosis and human host immune and autoimmune follow-up: A review

Cystic echinococcosis (CE) is an infectious disease caused by the larvae of parasite Echinococcus granulosus (E. granulosus). To successfully establish an infection, parasite release some substances and molecules that can modulate host immune functions, stimulating a strong anti-inflammatory reaction to carry favor to host and to reserve self-survival in the host. The literature was reviewed using MEDLINE, and an open access search for immunology of hydatidosis was performed. Accumulating data from animal experiments and human studies provided us with exciting insights into the mechanisms involved that affect all parts of immunity. In this review we used the existing scientific data and discuss how these findings assisted with a better understanding of the immunology of E. granulosus infection in man. The aim of this study is to point the several facts that challenge immune and autoimmune responses to protect E. granulosus from elimination and to minimize host severe pathology. Understanding the immune mechanisms of E. granulosus infection in an intermediate human host will provide, we believe, a more useful treatment with immunomodulating molecules and possibly better protection from parasitic infections. Besides that, the diagnosis of CE has improved due to the application of a new molecular tool for parasite identification by using of new recombinant antigens and immunogenic peptides. More studies for the better understanding of the mechanisms of parasite immune evasion is necessary. It will enable a novel approach in protection, detection and improving of the host inflammatory responses. In contrast, according to the "hygiene hypothesis", clinical applications that decrease the incidence of infection in developed countries and recently in developing countries are at the origin of the increasing incidence of both allergic and autoimmune diseases. Thus, an understanding of the immune mechanisms of E. granulosus infection is extremely important.

Comparison of Echinococcus multilocularis and Echinococcus granulosus hydatid fluid proteome provides molecular strategies for specialized host-parasite interactions

Alveolar and cystic echinococcoses, caused by the metacestodes of Echinococcus multilocularis and E. granulosus, are prevalent in several regions and invoke deleterious zoonotic helminthiases. Hydatid fluid (HF), which contains proteinaceous and non-proteinaceous secretions of the parasite- and host-derived components, critically affects the host-parasite interplay and disease progression. We conducted HF proteome profiling of fully mature E. multilocularis vesicle (nine months postinfection) and E. granulosus cyst (stage 2). We identified 120 and 153 proteins, respectively, in each fluid. Fifty-six and 84 proteins represented distinct species; 44 and 66 were parasites, and 12 and 18 were host-derived proteins. The five major parasite protein populations, which included antigen B isoforms, metabolic enzymes, proteases and inhibitors, extracellular matrix molecules (ECMs), and developmental proteins, were abundantly distributed in both fluids and also exclusively in one sample or the other. Carbohydrate-metabolizing enzymes were enriched in E. granulosus HF. In the E. multilocularis HF, proteins that constitute ECMs, which might facilitate adhesion and cytogenesis, were highly expressed. Those molecules had physical and functional relationships along with their biochemical properties through protein-protein interaction networks. Twelve host-derived proteins were largely segregated to serum components. The major proteins commonly and uniquely detected in these HFs and their symbiotic interactome relationships might reflect their biological roles in similar but distinct modes of maturation, invasion, and the longevity of the parasites in the hosts.

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.

Characterisation of Antigen B Protein Species Present in the Hydatid Cyst Fluid of Echinococcus canadensis G7 Genotype

The larva of cestodes belonging to the Echinococcus granulosus sensu lato (s.l.) complex causes cystic echinococcosis (CE). It is a globally distributed zoonosis with significant economic and public health impact. The most immunogenic and specific Echinococcus-genus antigen for human CE diagnosis is antigen B (AgB), an abundant lipoprotein of the hydatid cyst fluid (HF). The AgB protein moiety (apolipoprotein) is encoded by five genes (AgB1-AgB5), which generate mature 8 kDa proteins (AgB8/1-AgB8/5). These genes seem to be differentially expressed among Echinococcus species. Since AgB immunogenicity lies on its protein moiety, differences in AgB expression within E. granulosus s.l. complex might have diagnostic and epidemiological relevance for discriminating the contribution of distinct species to human CE. Interestingly, AgB2 was proposed as a pseudogene in E. canadensis, which is the second most common cause of human CE, but proteomic studies for verifying it have not been performed yet. Herein, we analysed the protein and lipid composition of AgB obtained from fertile HF of swine origin (E. canadensis G7 genotype). AgB apolipoproteins were identified and quantified using mass spectrometry tools. Results showed that AgB8/1 was the major protein component, representing 71% of total AgB apolipoproteins, followed by AgB8/4 (15.5%), AgB8/3 (13.2%) and AgB8/5 (0.3%). AgB8/2 was not detected. As a methodological control, a parallel analysis detected all AgB apolipoproteins in bovine fertile HF (G1/3/5 genotypes). Overall, E. canadensis AgB comprised mostly AgB8/1 together with a heterogeneous mixture of lipids, and AgB8/2 was not detected despite using high sensitivity proteomic techniques. This endorses genomic data supporting that AgB2 behaves as a pseudogene in G7 genotype. Since recombinant AgB8/2 has been found to be diagnostically valuable for human CE, our findings indicate that its use as antigen in immunoassays could contribute to false negative results in areas where E. canadensis circulates. Furthermore, the presence of anti-AgB8/2 antibodies in serum may represent a useful parameter to rule out E. canadensis infection when human CE is diagnosed.

Cystic echinococcosis (CE), a worldwide-spread zoonosis, affects livestock mammals and humans with significant economic and public health impact. It is caused by the infection with the larva of cestodes belonging to Echinococcus granulosus complex, a series of parasite species with preference for different hosts. Among them, Echinococcus canadensis larva uses mainly camels, goats and pigs as hosts. Species/genotypes belonging to E. canadensis are considered the second most common cause of human CE, but its contribution may be underestimated since causes asymptomatic or more benign infections than other E. granulosus complex species. The most relevant antigen for CE diagnosis is a lipoprotein called antigen B (AgB). AgB antigenicity is linked to its protein moiety that is encoded by several genes. One of these genes, AgB2, seems to be differentially expressed within E. granulosus complex. Using high sensitivity proteomic tools we analysed the composition of AgB obtained from E. canadensis larva, detecting the protein products of all AgB genes, except AgB2. Since AgB subunits have been widely used as antigens in immunoassays for human CE diagnosis, our results indicate that using AgB2 protein product in these assays may lead to false-negative results, particularly in geographical areas where E. canadensis species/genotypes circulate.

Biochemical Characterization of Echinococcus multilocularis Antigen B3 Reveals Insight into Adaptation and Maintenance of Parasitic Homeostasis at the Host-Parasite Interface

Alveolar echinococcosis (AE) caused by Echinococcus multilocularis metacestode is frequently associated with deleterious zoonotic helminthiasis. The growth patterns and morphological features of AE, such as invasion of the liver parenchyme and multiplication into multivesiculated masses, are similar to those of malignant tumors. AE has been increasingly detected in several regions of Europe, North America, Central Asia, and northwestern China. An isoform of E. multilocularis antigen B3 (EmAgB3) shows a specific immunoreactivity against patient sera of active-stage AE, suggesting that EmAgB3 might play important roles during adaptation of the parasite to hosts. However, expression patterns and biochemical properties of EmAgB3 remained elusive. The protein profile and nature of component proteins of E. multilocularis hydatid fluid (EmHF) have never been addressed. In this study, we conducted proteome analysis of EmHF of AE cysts harvested from immunocompetent mice. We observed the molecular and biochemical properties of EmAgB3, including differential transcription patterns of paralogous genes, macromolecular protein status by self-assembly, distinct oligomeric states according to individual anatomical compartments of the worm, and hydrophobic ligand-binding protein activity. We also demonstrated tissue expression patterns of EmAgB3 transcript and protein. EmAgB3 might participate in immune response and recruitment of essential host lipids at the host-parasite interface. Our results might contribute to an in depth understanding of the biophysical and biological features of EmAgB3, thus providing insights into the design of novel targets to control AE.

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.

Echinococcus granulosus Antigen B binds to monocytes and macrophages modulating cell response to inflammation

BACKGROUND

Antigen B (EgAgB) is an abundant lipoprotein released by the larva of the cestode Echinococcus granulosus into the host tissues. Its protein moiety belongs to the cestode-specific family known as hydrophobic ligand binding protein (HLBP), and is encoded by five gene subfamilies (EgAgB8/1-EgAgB8/5). The functions of EgAgB in parasite biology remain unclear. It may play a role in the parasite's lipid metabolism since it carries host lipids that E. granulosus is unable to synthesise. On the other hand, there is evidence supporting immuno-modulating activities in EgAgB, particularly on innate immune cells. Both hypothetical functions might involve EgAgB interactions with monocytes and macrophages, which have not been formally analysed yet.

METHODS

EgAgB binding to monocytes and macrophages was studied by flow cytometry using inflammation-recruited peritoneal cells and the THP-1 cell line. Involvement of the protein and phospholipid moieties in EgAgB binding to cells was analysed employing lipid-free recombinant EgAgB subunits and phospholipase D treated-EgAgB (lacking the polar head of phospholipids). Competition binding assays with plasma lipoproteins and ligands for lipoprotein receptors were performed to gain information about the putative EgAgB receptor(s) in these cells. Arginase-I induction and PMA/LPS-triggered IL-1β, TNF-α and IL-10 secretion were examined to investigate the outcome of EgAgB binding on macrophage response.

RESULTS

Monocytes and macrophages bound native EgAgB specifically; this binding was also found with lipid-free rEgAgB8/1 and rEgAgB8/3, but not rEgAgB8/2 subunits. EgAgB phospholipase D-treatment, but not the competition with phospholipid vesicles, caused a strong inhibition of EgAgB binding activity, suggesting an indirect contribution of phospholipids to EgAgB-cell interaction. Furthermore, competition binding assays indicated that this interaction may involve receptors with affinity for plasma lipoproteins. At functional level, the exposure of macrophages to EgAgB induced a very modest arginase-I response and inhibited PMA/LPS-mediated IL-1β and TNF-α secretion in an IL-10-independent manner.

CONCLUSION

EgAgB and, particularly its predominant EgAgB8/1 apolipoprotein, are potential ligands for monocyte and macrophage receptors. These receptors may also be involved in plasma lipoprotein recognition and induce an anti-inflammatory phenotype in macrophages upon recognition of EgAgB.

Exosomes and Other Extracellular Vesicles: The New Communicators in Parasite Infections

Extracellular vesicles (EVs) have emerged as a ubiquitous mechanism for transferring information between cells and organisms across all three kingdoms of life. In addition to their roles in normal physiology, vesicles also transport molecules from pathogens to hosts and can spread antigens as well as infectious agents. Although initially described in the host-pathogen context for their functions in immune surveillance, vesicles enable multiple modes of communication by, and between, parasites. Here we review the literature demonstrating that EVs are secreted by intracellular and extracellular eukaryotic parasites, as well as their hosts, and detail the functional properties of these vesicles in maturation, pathogenicity and survival. We further describe the prospects for targeting or exploiting these complexes in therapeutic and vaccine strategies.

A protective effect of the laminated layer on Echinococcus granulosus survival dependent on upregulation of host arginase

The role of nitric oxide (NO) in host defense against Echinococcus granulosus larvae was previously reported. However, NO production by NOS2 (inducible NO synthase) is counteracted by the expression of Arginase. In the present study, our aim is to evaluate the involvement of the laminated layer (external layer of parasitic cyst) in Arginase induction and the protoscoleces (living and infective part of the cyst) survival. Our in vitro results indicate that this cystic compound increases the Arginase activity in macrophages. Moreover, C-type lectin receptors (CLRs) with specificity for mannan and the TGF-β are implicated in this effect as shown after adding Mannan and Anti-TGFβ. Interestingly, the laminated layer increases protoscoleces survival in macrophages-parasite co-cultures. Our results indicate that the laminated layer protects E. granulosus against the NOS2 protective response through Arginase pathway, a hallmark of M2 macrophages.

Impairment of dendritic cell function and induction of CD4(+)CD25(+)Foxp3(+) T cells by excretory-secretory products: a potential mechanism of immune evasion adopted by Echinococcus granulosus

Background

Cystic echinococcosis, caused by infection with Echinococcus granulosus, is one of the most widespread zoonotic helminth diseases. Modulation of host responses is an important strategy used by helminth parasites to promote infection. To better understand the mechanisms adopted by E. granulosus to escape host immune responses, we investigated the effects of excretory–secretory products (ES) and adult worm antigen (AWA) derived from adult E. granulosus on murine bone marrow-derived dendritic cells (BMDC).

Results

Compared with lipopolysaccharide (LPS), AWA, but not ES, induced BMDC maturation or stimulated BMDC cytokine production and co-stimulatory molecule expression (CD40, CD80 and MHC class II). Furthermore, ES-treated BMDCs pulsed with ovalbumin exhibited reduced co-stimulatory molecule expression in comparison with untreated BMDC, even in the presence of the strong Th1 inducer, CpG. Moreover, we detected the effects of ES-treated DC on T cell activation by an in vitro T cell priming assay. We observed that ES-treated BMDC co-cultured with DO11.10 transgenic CD4⁺ T cells induced the generation of CD4⁺CD25⁺Foxp3⁺ T cells. In addition, in contrast to AWA-treated BMDCs, which had markedly induced IFN-γ secretion and reduced of IL-4 levels in co-cultured T cells, ES-treated BMDCs did not modify their capacity to stimulate IFN-γ or IL-4 production by T cells.

Conclusions

We conclude that ES of adult E. granulosus inhibited DC function, impaired the development of Th1 cells induced by CpG, and induced CD4⁺CD25⁺Foxp3⁺ regulatory T cells in an IL-10-independent manner.

Recent advances in Echinococcus genomics and stem cell research

Alveolar and cystic echinococcosis, caused by the metacestode larval stages of the tapeworms Echinococcus multilocularis and Echinococcus granulosus, respectively, are life-threatening diseases and very difficult to treat. The introduction of benzimidazole-based chemotherapy, which targets parasite β-tubulin, has significantly improved the life-span and prognosis of echinococcosis patients. However, benzimidazoles show only parasitostatic activity, are associated with serious adverse side effects and have to be administered for very long time periods, underlining the need for new drugs. Very recently, the nuclear genomes of E. multilocularis and E. granulosus have been characterised, revealing a plethora of data for gaining a deeper understanding of host-parasite interaction, parasite development and parasite evolution. Combined with extensive transcriptome analyses of Echinococcus life cycle stages these investigations also yielded novel clues for targeted drug design. Recent years also witnessed significant advancements in the molecular and cellular characterisation of the Echinococcus 'germinative cell' population, which forms a unique stem cell system that differs from stem cells of other organisms in the expression of several genes associated with the maintenance of pluripotency. As the only parasite cell type capable of undergoing mitosis, the germinative cells are central to all developmental transitions of Echinococcus within the host and to parasite expansion via asexual proliferation. In the present article, we will briefly introduce and discuss recent advances in Echinococcus genomics and stem cell research in the context of drug design and development. Interestingly, it turns out that benzimidazoles seem to have very limited effects on Echinococcus germinative cells, which could explain the high recurrence rates observed after chemotherapeutic treatment of echinococcosis patients. This clearly indicates that future efforts into the development of parasitocidal drugs should also target the parasite's stem cell system.

Lipid-free antigen B subunits from echinococcus granulosus: oligomerization, ligand binding, and membrane interaction properties

Background

The hydatid disease parasite Echinococcus granulosus has a restricted lipid metabolism, and needs to harvest essential lipids from the host. Antigen B (EgAgB), an abundant lipoprotein of the larval stage (hydatid cyst), is thought to be important in lipid storage and transport. It contains a wide variety of lipid classes, from highly hydrophobic compounds to phospholipids. Its protein component belongs to the cestode-specific Hydrophobic Ligand Binding Protein family, which includes five 8-kDa isoforms encoded by a multigene family (EgAgB1-EgAgB5). How lipid and protein components are assembled into EgAgB particles remains unknown. EgAgB apolipoproteins self-associate into large oligomers, but the functional contribution of lipids to oligomerization is uncertain. Furthermore, binding of fatty acids to some EgAgB subunits has been reported, but their ability to bind other lipids and transfer them to acceptor membranes has not been studied.

Methodology/Principal Findings

Lipid-free EgAgB subunits obtained by reverse-phase HPLC were used to analyse their oligomerization, ligand binding and membrane interaction properties. Size exclusion chromatography and cross-linking experiments showed that EgAgB8/2 and EgAgB8/3 can self-associate, suggesting that lipids are not required for oligomerization. Furthermore, using fluorescent probes, both subunits were found to bind fatty acids, but not cholesterol analogues. Analysis of fatty acid transfer to phospholipid vesicles demonstrated that EgAgB8/2 and EgAgB8/3 are potentially capable of transferring fatty acids to membranes, and that the efficiency of transfer is dependent on the surface charge of the vesicles.

Conclusions/Significance

We show that EgAgB apolipoproteins can oligomerize in the absence of lipids, and can bind and transfer fatty acids to phospholipid membranes. Since imported fatty acids are essential for Echinococcus granulosus, these findings provide a mechanism whereby EgAgB could engage in lipid acquisition and/or transport between parasite tissues. These results may therefore indicate vulnerabilities open to targeting by new types of drugs for hydatidosis therapy.

Echinococcus granulosus is a causative agent of hydatidosis, a parasitic disease that affects humans and livestock with significant economic and public health impact worldwide. Antigen B (EgAgB), an abundant product of E. granulosus larvae, is a lipoprotein that carries a wide variety of lipids, including fatty acids and cholesterol. As E. granulosus is unable to synthesize these lipids, EgAgB likely plays an important role in parasite metabolism, participating in both the acquisition of host lipids and their distribution between parasite tissues. The protein component of EgAgB consists of 8 kDa subunits encoded by separate genes. However, the biochemical properties of EgAgB subunits, particularly their ability to bind and transfer lipids, are poorly known. Herein, using in vitro assays, we found that EgAgB subunits were capable of oligomerizing in the absence of lipids and to bind fatty acids, but not cholesterol. Moreover, EgAgB subunits showed the ability to transfer fatty acids to artificial phospholipid membranes. These results indicate new points of attack at which the parasite might be vulnerable to drugs.

Alteration of immunoproteome profile of Echinococcus granulosus hydatid fluid with progression of cystic echinococcosis

BACKGROUND

Cystic echinococcosis (CE), caused by Echinococcus granulosus metacestode, invokes a serious public health concern. Early diagnosis has great impacts on reduction of disability-adjusted life years. Several antigen B-related molecules (EgAgB; EgAgB1-5) are known to be immunopotent, but detection of EgAgB is variable in many patients and may not allow reliable interpretation of its immunological relevance. More importantly, the immunoproteome profile of hydatid fluid (HF) has not been addressed.

METHODS

We conducted a proteome analysis of the HF of a single fertile cyst of CE1 and CE2 stages through two-dimensional electrophoresis (2-DE). Each protein spot was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). We subsequently determined the immunoproteome profile employing patient sera of entire disease spectrum from CE1 to CE5 stages.

RESULTS

We identified 40 parasite proteins, of which EgAgB (28 spots) and antigen 5 (EgAg5; 5 molecules) were abundant. EgAgB proteoforms constituted the majority, mostly EgAgB1 (24 spots), followed by EgAgB2 and EgAgB4 (2 spots each). EgAgB3 was detected only by liquid chromatography-MS/MS. EgAgB5 was not recognized. We also detected 38 host proteins, which were largely composed of serum components, antioxidant/xenobiotic enzymes, and enzymes involved in carbohydrate metabolism. CE1 and CE2 HF exhibited comparable spotting patterns, but CE2 HF harbored greater amounts of EgAgB and EgAg5 complexes. CE sera demonstrated complicated immune recognition patterns according to the disease progression; CE2 and CE3 stages exhibited strong antibody responses against diverse EgAgB and EgAg5 proteoforms, while CE1, CE4, and CE5 stages mainly reacted to EgAg5 and cathepsin B. Patient sera of alveolar echinococcosis (AE) cross-reacted with diverse EgAgB isoforms (36%). EgAg5 and cathepsin B also demonstrated cross-reactions with sera from neurocysticercosis and sparganosis.

CONCLUSIONS

Our results demonstrated that detection of a single defined molecule may not properly diagnose CE, since specific immunodominant epitopes changed as the disease progresses. Immunoproteome analysis combined with imaging studies may be practical in the differential diagnosis of CE from AE and other cystic lesions, as well as for staging CE, which are pertinent to establish appropriate patient management.

Sero-epidemiological value of some hydatid cyst antigen in diagnosis of human cystic echinococcosis

Cystic echinococcosis (CE) is a severe zoonotic disease which affects both human and animals. The disease has a considerable economic and social impact, because it has numerous complications leading to important disabilities and even death. CE is a widespread chronic endemic helminthic disease caused by infection with metacestodes of tapeworm Echinococcus granulosus. This study was conducted to diagnosis human CE by hydatid cyst antigens from camels and sheep. Hydatid fluid and protoscoleces crude antigens corresponding to camel and sheep were resolute by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions and the protein bands of different antigens were exposed to infected patients serum CE through western blot (WB) assay. The camel hydatid fluid antigen revealed five polypeptide bands of 18-98.8 kDa by SDS-PAGE while sheep hydatid fluid antigen revealed four polypeptide bands of 20-100 kDa. Immune reactive bands were obtained through WB ranged from 25 to 125 kDa. The study showed prominent immune reactive bands of 92, 52.2 and 35.7 kDa which may helpful in diagnosis of human CE.

Immunoblotting with human native antigen shows stage-related sensitivity in the serodiagnosis of hepatic cystic echinococcosis

The diagnosis of hepatic cystic echinococcosis is based on ultrasonography and confirmed by serology. However, no biological marker of cyst viability is currently available implying years-long patient follow-up, which is not always feasible in endemic areas. We characterized the performance of an immunoblotting test based on human hydatid cyst fluid with particular regard to its ability to distinguish between cyst stages. Sera from patients with cysts in different stages showed distinctive band pattern recognition. Most importantly, the test discriminated in 80% of cases CE3a from CE3b transitional cysts, known to have different viability profiles. Interestingly, we observed a rapid change in band pattern recognition of sera from one patient at time points when his cyst passed from active to transitional to inactive stages. Further identification of different antigens expressed by different cyst stages will support the development of diagnostic tools that could early define cyst viability, to guide clinical decision making, and shorten patient follow-up.

Protein arrays as tool for studies at the host-pathogen interface

Pathogens and parasites encode a wide spectrum of multifunctional proteins interacting to and modifying proteins in host cells. However, the current lack of a reliable method to unveil the protein-protein interactions (PPI) at the host-pathogen interface is retarding our understanding of many important pathogenic processes. Thus, the identification of proteins involved in host-pathogen interactions is important for the elucidation of virulence determinants, mechanisms of infection, host susceptibility and/or disease resistance. In this sense, proteomic technologies have experienced major improvements in recent years and protein arrays are a powerful and modern method for studying PPI in a high-throughput format. This review focuses on these techniques analyzing the state-of-the-art of proteomic technologies and their possibilities to diagnose and explore host-pathogen interactions. Major technical advancements, applications and protocol concerns are presented, so readers can appreciate the immense progress achieved and the current technical options available for studying the host-pathogen interface. Finally, future uses of this kind of array-based proteomic tools in the fight against infectious and parasitic diseases are discussed.

Strategies of Echinococcus species responses to immune attacks: implications for therapeutic tool development

Echinococcus species have been studied as a model to investigate parasite-host interactions. Echinococcus spp. can actively communicate dynamically with a host to facilitate infection, growth and proliferation partially via secretion of molecules, especially in terms of harmonization of host immune attacks. This review systematically outlines our current knowledge of how the Echinococcus species have evolved to adapt to their host's microenvironment. This understanding of parasite-host interplay has implications in profound appreciation of parasite plasticity and is informative in designing novel and effective tools including vaccines and drugs for the treatment of echinococcosis and other diseases.

A transcriptomic analysis of Echinococcus granulosus larval stages: implications for parasite biology and host adaptation

Background

The cestode Echinococcus granulosus - the agent of cystic echinococcosis, a zoonosis affecting humans and domestic animals worldwide - is an excellent model for the study of host-parasite cross-talk that interfaces with two mammalian hosts. To develop the molecular analysis of these interactions, we carried out an EST survey of E. granulosus larval stages. We report the salient features of this study with a focus on genes reflecting physiological adaptations of different parasite stages.

Methodology/Principal Findings

We generated ∼10,000 ESTs from two sets of full-length enriched libraries (derived from oligo-capped and trans-spliced cDNAs) prepared with three parasite materials: hydatid cyst wall, larval worms (protoscoleces), and pepsin/H⁺-activated protoscoleces. The ESTs were clustered into 2700 distinct gene products. In the context of the biology of E. granulosus, our analyses reveal: (i) a diverse group of abundant long non-protein coding transcripts showing homology to a middle repetitive element (EgBRep) that could either be active molecular species or represent precursors of small RNAs (like piRNAs); (ii) an up-regulation of fermentative pathways in the tissue of the cyst wall; (iii) highly expressed thiol- and selenol-dependent antioxidant enzyme targets of thioredoxin glutathione reductase, the functional hub of redox metabolism in parasitic flatworms; (iv) candidate apomucins for the external layer of the tissue-dwelling hydatid cyst, a mucin-rich structure that is critical for survival in the intermediate host; (v) a set of tetraspanins, a protein family that appears to have expanded in the cestode lineage; and (vi) a set of platyhelminth-specific gene products that may offer targets for novel pan-platyhelminth drug development.

Conclusions/Significance

This survey has greatly increased the quality and the quantity of the molecular information on E. granulosus and constitutes a valuable resource for gene prediction on the parasite genome and for further genomic and proteomic analyses focused on cestodes and platyhelminths.

Cestodes are a neglected group of platyhelminth parasites, despite causing chronic infections to humans and domestic animals worldwide. We used Echinococcus granulosus as a model to study the molecular basis of the host-parasite cross-talk during cestode infections. For this purpose, we carried out a survey of the genes expressed by parasite larval stages interfacing with definitive and intermediate hosts. Sequencing from several high quality cDNA libraries provided numerous insights into the expression of genes involved in important aspects of E. granulosus biology, e.g. its metabolism (energy production and antioxidant defences) and the synthesis of key parasite structures (notably, the one exposed to humans and livestock intermediate hosts). Our results also uncovered the existence of an intriguing set of abundant repeat-associated non-protein coding transcripts that may participate in the regulation of gene expression in all surveyed stages. The dataset now generated constitutes a valuable resource for gene prediction on the parasite genome and for further genomic and proteomic studies focused on cestodes and platyhelminths. In particular, the detailed characterization of a range of newly discovered genes will contribute to a better understanding of the biology of cestode infections and, therefore, to the development of products allowing their efficient control.

Induction of T helper 1 response by immunization of BALB/c mice with the gene encoding the second subunit of Echinococcus granulosus antigen B (EgAgB8/2)

A pre-designed plasmid containing the gene encoding the second subunit of Echinococcus granulosus AgB8 (EgAgB8/2) was used to study the effect of the immunization route on the immune response in BALB/c mice. Mice were immunized with pDRIVEEgAgB8/ 2 or pDRIVE empty cassette using the intramuscular (i.m.), intranasal (i.n.) or the epidermal gene gun (g.g.) routes. Analysis of the antibody response and cytokine data revealed that gene immunization by the i.m. route induced a marked bias towards a T helper type 1 (Th1) immune response as characterized by high IFN-γ gene expression and a low IgG1/IgG2a reactivity index (R.I.) ratio of 0.04. The i.n. route showed a moderate IFN-γ expression but a higher IgG1/IgG2a R.I. ratio of 0.25 indicating a moderate Th1 response. In contrast, epidermal g.g. immunization induced a Th2 response characterized by high IL-4 expression and the highest IgG1/IgG2a R.I. ratio of 0.58. In conclusion, this study showed the advantage of genetic immunization using the i.m. route and i.n. over the epidermal g.g. routes in the induction of Th1 immunity in response to E. granulosus AgB gene immunization.

Immunogenetics of human echinococcosis

Susceptibility and resistance to human Echinococcus infection and disease, although poorly understood, appear to reflect a complex interaction of parasite and host immunological and genetic factors. Disease stage, progression, and prognosis following treatment appear to be strongly influenced by cytokine and antibody profiles, and more recent evidence has suggested an important role of dendritic cells (DCs) and T regulatory cells (Tregs) in immunomodulation. Microarrays have supported these findings, highlighting both known and novel pathways involved in chronic murine disease. Genetic studies to date have been few and with limited success. Advanced genomic approaches, such as genome-wide association studies (GWAS), may provide further insight to identify the relevant pathways involved, thereby facilitating a new approach for the development of new clinical therapies.

Granulocytes in helminth infection -- who is calling the shots?

Helminths are parasitic organisms that can be broadly described as “worms” due to their elongated body plan, but which otherwise differ in shape, development, migratory routes and the predilection site of the adults and larvae. They are divided into three major groups: trematodes (flukes), which are leaf-shaped, hermaphroditic (except for blood flukes) flatworms with oral and ventral suckers; cestodes (tapeworms), which are segmented, hermaphroditic flatworms that inhabit the intestinal lumen; and nematodes (roundworms), which are dioecious, cylindrical parasites that inhabit intestinal and peripheral tissue sites. Helminths exhibit a sublime co-evolution with the host´s immune system that has enabled them to successfully colonize almost all multicellular species present in every geographical environment, including over two billion humans. In the face of this challenge, the host immune system has evolved to strike a delicate balance between attempts to neutralize the infectious assault versus limitation of damage to host tissues. Among the most important cell types during helminthic invasion are granulocytes: eosinophils, neutrophils and basophils. Depending on the specific context, these leukocytes may have pivotal roles in host protection, immunopathology, or facilitation of helminth establishment. This review provides an overview of the function of granulocytes in helminthic infections.

Cestode genomics - progress and prospects for advancing basic and applied aspects of flatworm biology

Characterization of the first tapeworm genome, Echinococcus multilocularis, is now nearly complete, and genome assemblies of E. granulosus, Taenia solium and Hymenolepis microstoma are in advanced draft versions. These initiatives herald the beginning of a genomic era in cestodology and underpin a diverse set of research agendas targeting both basic and applied aspects of tapeworm biology. We discuss the progress in the genomics of these species, provide insights into the presence and composition of immunologically relevant gene families, including the antigen B- and EG95/45W families, and discuss chemogenomic approaches toward the development of novel chemotherapeutics against cestode diseases. In addition, we discuss the evolution of tapeworm parasites and introduce the research programmes linked to genome initiatives that are aimed at understanding signalling systems involved in basic host-parasite interactions and morphogenesis.

Echinococcus granulosus antigen B structure: subunit composition and oligomeric states

BACKGROUND

Antigen B (AgB) is the major protein secreted by the Echinococcus granulosus metacestode and is involved in key host-parasite interactions during infection. The full comprehension of AgB functions depends on the elucidation of several structural aspects that remain unknown, such as its subunit composition and oligomeric states.

METHODOLOGY/PRINCIPAL FINDINGS

The subunit composition of E. granulosus AgB oligomers from individual bovine and human cysts was assessed by mass spectrometry associated with electrophoretic analysis. AgB8/1, AgB8/2, AgB8/3 and AgB8/4 subunits were identified in all samples analyzed, and an AgB8/2 variant (AgB8/2v8) was found in one bovine sample. The exponentially modified protein abundance index (emPAI) was used to estimate the relative abundance of the AgB subunits, revealing that AgB8/1 subunit was relatively overrepresented in all samples. The abundance of AgB8/3 subunit varied between bovine and human cysts. The oligomeric states formed by E. granulosus AgB and recombinant subunits available, rAgB8/1, rAgB8/2 and rAgB8/3, were characterized by native PAGE, light scattering and microscopy. Recombinant subunits showed markedly distinct oligomerization behaviors, forming oligomers with a maximum size relation of rAgB8/3>rAgB8/2>rAgB8/1. Moreover, the oligomeric states formed by rAgB8/3 subunit were more similar to those observed for AgB purified from hydatid fluid. Pressure-induced dissociation experiments demonstrated that the molecular assemblies formed by the more aggregative subunits, rAgB8/2 and rAgB8/3, also display higher structural stability.

CONCLUSIONS/SIGNIFICANCE

For the first time, AgB subunit composition was analyzed in samples from single hydatid cysts, revealing qualitative and quantitative differences between samples. We showed that AgB oligomers are formed by different subunits, which have distinct abundances and oligomerization properties. Overall, our findings have significantly contributed to increase the current knowledge on AgB expression and structure, highlighting issues that may help to understand the parasite adaptive response during chronic infection.

Excretory/secretory-products of Echinococcus multilocularis larvae induce apoptosis and tolerogenic properties in dendritic cells in vitro

BACKGROUND

Alveolar echinococcosis, caused by Echinococcus multilocularis larvae, is a chronic disease associated with considerable modulation of the host immune response. Dendritic cells (DC) are key effectors in shaping the immune response and among the first cells encountered by the parasite during an infection. Although it is assumed that E.multilocularis, by excretory/secretory (E/S)-products, specifically affects DC to deviate immune responses, little information is available on the molecular nature of respective E/S-products and their mode of action.

METHODOLOGY/PRINCIPAL FINDINGS

We established cultivation systems for exposing DC to live material from early (oncosphere), chronic (metacestode) and late (protoscolex) infectious stages. When co-incubated with Echinococcus primary cells, representing the invading oncosphere, or metacestode vesicles, a significant proportion of DC underwent apoptosis and the surviving DC failed to mature. In contrast, DC exposed to protoscoleces upregulated maturation markers and did not undergo apoptosis. After pre-incubation with primary cells and metacestode vesicles, DC showed a strongly impaired ability to be activated by the TLR ligand LPS, which was not observed in DC pre-treated with protoscolex E/S-products. While none of the larvae induced the secretion of pro-inflammatory IL-12p70, the production of immunosuppressive IL-10 was elevated in response to primary cell E/S-products. Finally, upon incubation with DC and naïve T-cells, E/S-products from metacestode vesicles led to a significant expansion of Foxp3+ T cells in vitro.

CONCLUSIONS

This is the first report on the induction of apoptosis in DC by cestode E/S-products. Our data indicate that the early infective stage of E. multilocularis is a strong inducer of tolerance in DC, which is most probably important for generating an immunosuppressive environment at an infection phase in which the parasite is highly vulnerable to host attacks. The induction of CD4+CD25+Foxp3+ T cells through metacestode E/S-products suggests that these cells fulfill an important role for parasite persistence during chronic echinococcosis.

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

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

Host-parasite relationship in cystic echinococcosis: an evolving story

The larval stage of Echinococcus granulosus causes cystic echinococcosis, a neglected infectious disease that constitutes a major public health problem in developing countries. Despite being under constant barrage by the immune system, E. granulosus modulates antiparasite immune responses and persists in the human hosts with detectable humoral and cellular responses against the parasite. In vitro and in vivo immunological approaches, together with molecular biology and immunoproteomic technologies, provided us exciting insights into the mechanisms involved in the initiation of E. granulosus infection and the consequent induction and regulation of the immune response. Although the last decade has clarified many aspects of host-parasite relationship in human cystic echinococcosis, establishing the full mechanisms that cause the disease requires more studies. Here, we review some of the recent developments and discuss new avenues in this evolving story of E. granulosus infection in man.

Development and evaluation of flow through technique for diagnosis of cystic echinococcosis in sheep

A novel in vitro flow through technique was developed and evaluated for immunodiagnosis of cystic echinococcosis in sheep using hydatid specific non-cross reactive 8-kDa protein. The 8-kDa protein was prepared from hydatid cyst fluid by DEAE-Sepharose fast flow anion exchange chromatography. In this flow through technique, the 8-kDa antigen was coated on the nitrocellulose membrane of flow through device. Protein A colloidal gold was used as detector. The evaluation of the technique was performed by comparing 150 known positive hydatid serum and known negative serum collected from sheep. The test was shown to be high sensitivity and specificity that were closely correlated with those of EITB. Furthermore the immunofiltration-based assay is rapid (2 min) and easy to perform with no requirement of special skill, reagent and instrumentation. This suggests the flow through technique is an acceptance alternative to be used in clinical laboratories lacking specialized equipments as well as large scale screening of cystic echinococcosis both in the field with animal and human populations.

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.

The Echinococcus granulosus antigen B gene family comprises at least 10 unique genes in five subclasses which are differentially expressed

BACKGROUND

Antigen B (EgAgB) is a major protein produced by the metacestode cyst of Echinococcus granulosus, the causative agent of cystic hydatid disease. This protein has been shown to play an important role in modulating host immune responses, although its precise biological function still remains unknown. It is generally accepted that EgAgB is comprised of a gene family of five subfamilies which are highly polymorphic, but the actual number of genes present is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Based on published sequences for the family, we designed specific primers for each subfamily and used PCR to amplify them from genomic DNA isolated from individual mature adult worms (MAW) taken from an experimentally infected dog in China and individual larval protoscoleces (PSC) excised from a single hydatid cyst taken from an Australian kangaroo. We then used real-time PCR to measure expression of each of the genes comprising the five EgAgB subfamilies in all life-cycle stages including the oncosphere (ONC).

CONCLUSIONS/SIGNIFICANCE

Based on sequence alignment analysis, we found that the EgAgB gene family comprises at least ten unique genes. Each of the genes was identical in both larval and adult E. granulosus isolates collected from two geographical areas (different continents). DNA alignment comparisons with EgAgB sequences deposited in GenBank databases showed that each gene in the gene family is highly conserved within E. granulosus, which contradicts previous studies claiming significant variation and polymorphism in EgAgB. Quantitative PCR analysis revealed that the genes were differentially expressed in different life-cycle stages of E. granulosus with EgAgB3 expressed predominantly in all stages. These findings are fundamental for determining the expression and the biological function of antigen B.

Human cystic echinococcosis: old problems and new perspectives

Cystic echinococcosis (CE) is a widespread chronic endemic helminthic disease caused by infection with metacestodes of the tapeworm Echinococcus granulosus. CE affects humans and has a worldwide prevalence of approximately six million. In this review, we discuss current findings in diagnosis and clinical management of CE and new concepts relating to E. granulosus molecules that directly modulate the host immune responses favouring a strong anti-inflammatory response and perpetuating parasite survival in the host. New insights into the molecular biology of E. granulosus will improve considerably our knowledge of the disease and will provide new potential therapeutic applications to treat or prevent inflammatory immune-mediated disease.

Relative expression of antigen B coding gene of bubaline isolates of Echinococcus granulosus in fertile and sterile cysts

This article communicates the relative quantification of five isoforms of antigen B (AgB) of Echinococcus granulosus. Relative expression of the AgB was quantified in active and inactive cysts. Cysts with germinal membrane, clear cyst fluid and protoscoleces showed uniform expression of the five isoforms and were utilized as control. Relative expression of AgB1 was the highest in cysts, where calcification has initiated. AgB2 and AgB4 were expressed more in fertile cysts irrespective of the condition of germinal membrane. The lowest expression of AgB3 was seen in calcified cysts. The relative expression of AgB5 could not be correlated with respect to the condition of the cyst because AgB5 is typically expressed by the adult stage of the parasite.

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

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