A family of galectins from Haemonchus contortus

Characterization of a novel galectin in Sarcoptes scabiei and its role in regulating macrophage functions

Sarcoptes scabiei (S. scabiei) endangers human and other mammalian health. There has been limited research into S. scabiei pathogenic mechanisms and the immunological interaction between S. scabiei and hosts. Galectins have critical roles in biological processes such as cell adhesion, signal transduction, and immune response mediation. Galectins of S. scabiei (SsGalectins) were cloned, expressed, and identified, and their transcriptional levels in S. scabiei were measured at various developmental stages. Fluorescent tissue localization was performed on SsGalectins of S. scabiei and scabies skin. A mouse AD model was constructed to evaluate the effect of rSsGalectins on skin pathogenic changes. Quantitative polymerase chain reaction and enzyme-linked immunoassay were used to identify macrophage polarization-related components and investigate the immunoregulatory effect of rSsGalectins on mouse macrophages. The results demonstrated that the S. scabiei infection causes macrophage infiltration in the scabies skin. The rSsGalectins displayed strong reactogenicity, and distinct genes of the SsGalectins were differently expressed in different developmental stages of S. scabiei. Fluorescence tissue localization revealed that the SsGalectins were mainly in the mouthparts, intestines, and body surface. Additionally, S. scabiei could secrete SsGalectins into the infected skin, proving that SsGalectins were excretion and secretion proteins of S. scabiei. In the mouse atopic dermatitis model, cutaneous macrophage infiltration and inflammation increase after rSsGalectins injection. Simultaneously, when rSsGalectins acted on bone marrow-derived macrophages, M1 macrophage-related polarization factors IL-1β, IL-6, and inducible nitric oxide synthase all increased, demonstrating that rSsGalectins can induce M1 polarization and produce pro-inflammatory cytokines. In conclusion, the SsGalectins are involved in the pathogenic process of S. scabiei by regulating the polarization of host macrophages to the M1 type when S. scabiei invade the host and promoting the incidence and development of the host's inflammatory response. This study offers fresh light on the pathogenic process of scabies mites, investigates the immunological interaction mechanism between S. scabiei and the host, and offers new insights into S. scabiei prevention and therapy.

Structural, molecular, functional and immunological characterization of Wuchereria bancrofti-galectin

Galectins regulate growth and differentiation of immune cells and inflammation through their carbohydrate-binding function in humans, while also play a role in parasite survival. This study focused on the galectin of lymphatic filarial parasite Wuchereria bancrofti (Wb-Gal). The multiple sequence alignment with other galectins showed that the Wb-Gal belonged to galactoside binding lectin family, particularly tandem repeat type galectin-9. A homology model of Wb-Gal was developed in the I-TASser server using high similarity 3D structures with a quality score of 89.5. Molecular docking and dynamics studies revealed that the CCRD and NCRD of Wb-Gal bind with galactose and lactose. Further, Wb-Gal was cloned into the pET28 vector, expressed in E. coli Rosetta strain and purified by affinity chromatography. In the hemagglutination assays, the rWb-Gal bound to lactose, galactose, and glucose. Indirect Enzyme-Linked Immunosorbent Assay (ELISA) using different clinical filarial sera showed that the IgG and IgM response was against Wb-Gal x very high in all filarial clinical groups, whereas the IgA and IgG2 response was minimum to negligible. There was an enhanced response of IgG1 and IgG4 antibodies in Microfilaremics (MF) cases compared to Chronic Pathology (CP) and Endemic Normal (EN) individuals. Interestingly, the IgE response was comparatively higher in EN than MF and CP. These studies show that Wb-Gal is a member of the lectin family of proteins binding to different carbohydrates and may have an important role in the pathophysiology of filarial infection which needs to be investigated in greater detail.

Brugia malayi galectin 2 is a tandem-repeat type galectin capable of binding mammalian polysaccharides

Galectins are among the most abundant excretory/secretory (ES) products of filarial worms, but their role in filarial biology is poorly understood. Galectin-2 (Lec-2), a major component of Brugia malayi extracellular vesicles, is released by filarial worms, and was recently identified in the serum of persons with loiasis. We therefore sought to clone and characterize Lec-2, and to develop reagents to examine its potential as a biomarker and its role in parasite biology. We cloned and expressed recombinant B. malayi Lec-2 (rBmLec-2), generated a Lec-2-specific monoclonal antibody (4B4), and used it to confirm the presence of Lec-2 in B. malayi ES products and whole worm lysate. We show that Lec-2 is absent in B. malayi oocytes, and increases in concentration as embryos mature. Recombinant BmLec-2 hemagglutinates rabbit red blood cells at concentrations less than 1 μg/mL, and this is abrogated by single amino acid substitutions in the predicted carbohydrate recognition domains. rBmLec-2 binds multiple LacNAc oligosaccharides on a mammalian carbohydrate array. Sera from 17/23 (78 %) persons with microfilaremic loiasis and 4/10 (40 %) persons with bancroftian filariasis had detectable antibody to Lec-2 by western blot. Our studies confirm the functionality of BmLec-2 and indicate anti-Lec-2 antibody responses are common in persons with filariasis. These studies set the stage for further examination of the role of Lec-2 in filarial biology and in filarial-host interactions.

Comparative characterization of two galectins excreted-secreted from intestine-dwelling parasitic versus free-living females of the soil-transmitted nematode Strongyloides

Helminths are complex pathogens that ensure their long-term survival by influencing the immune responses of their host. Excretory/secretory products (ESP) can exert immunoregulatory effects which foster parasite survival. Galectins represent a widespread group of β-galactoside-binding proteins which are involved in a multitude of biological processes operative in parasite-host interaction. We had earlier identified seven galectins in Strongyloides ratti, four of them detected in the ESP of distinct developmental stages of the parasite. In the present report, we focused on the characterization of two of them, Sr-galectin-1 (Sr-Gal-1) and Sr-galectin-3 (Sr-Gal-3). While Sr-Gal-3 expression was strongest in parasitic females, Sr-Gal-1 was predominantly expressed in free-living females. Both proteins were cloned and recombinantly expressed in an E. coli expression system. Their glycan-binding activity was verified by haemagglutination and glycan array analysis. Furthermore, primary immunological activities of the Sr-galectins were initially investigated by the application of an in vitro mucosal 3D-culture model, comprising of mucosa-associated epithelial and dendritic cells. The Sr-galectins stimulated preferentially the release of the type 2 cytokines thymic stromal lymphopoietin and IL-22, a first indication for immunoregulatory activity. In addition, the Sr-galectins dose-dependently fostered cell migration. Our results confirm the importance of these carbohydrate-binding proteins in host-parasite-interaction by indicating possible interaction with the host mucosa-associated cells.

Potential immunological markers for diagnosis of human strongyloidiasis using heterologous antigens

Strongyloides venezuelensis is a parasitic nematode of rodents that is frequently used to obtain heterologous antigens for immunological diagnosis of human strongyloidiasis. The aim of this study was to identify antigens from filariform larvae of S. venezuelensis for immunodiagnosis of human strongyloidiasis. Soluble and membrane fractions from filariform larvae of S. venezuelensis were obtained in phosphate saline (SS and SM) and in Tris-HCl buffer (TS and TM), and were analysed by Western blotting. Different antigenic components were recognized by IgG antibodies from the sera of strongyloidiasis patients. Highest recognition was observed for a 30-40 kDa mass range present in all antigenic fractions. The band encompassing this mass range was then excised and subjected to mass spectrometry for protein identification. Immunoreactive proteins identified in the soluble fractions corresponded to metabolic enzymes, whereas cytoskeletal proteins and galectins were more abundant in the membrane fractions. These results represent the first approach towards identification of S. venezuelensis antigens for use in immunodiagnostic assays for human strongyloidiasis.

Harnessing the helminth secretome for therapeutic immunomodulators

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

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

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

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.

Characterization of a galectin-like activity from the parasitic nematode, Haemonchus contortus, which modulates ovine eosinophil migration in vitro

The development of eosinophilia is a characteristic feature of helminth infection, although the exact nature of the interaction between eosinophils and parasites remains to be fully defined. Previously, it has been reported that Haemonchus contortus and other nematodes produce eosinophil-specific chemoattractants. This paper describes studies aimed at isolating and identifying the factor(s) responsible. Initial studies showed that soluble extracts of infective larvae (L3) of H. contortus provoked a chemokinetic, rather than chemotactic, response in ovine bone marrow eosinophils in vitro. This activity was inhibited by lactose to a markedly greater extent than sucrose suggesting a galectin-like identity. Lactose affinity chromatography of soluble H. contortus extracts resulted in the isolation a specific bound fraction which retained biological activity. SDS-PAGE gel electrophoresis indicated a single Coomassie-stained band at between 31 and 41kDa. Subsequent, mass spectrometric analysis confirmed that the bound fraction contained a mixture of nematode galectins. The results confirm that H. contortus larvae produce several galectin-like proteins, at least one of which demonstrates eosinophil chemokinetic activity in vitro. The possibility of the parasite-derived factor mimicking the mammalian galectin-9, a known eosinophil chemokine, is discussed.

Identification of immuno-reactive proteins from a sheep gastrointestinal nematode, Trichostrongylus colubriformis, using two-dimensional electrophoresis and mass spectrometry

Gastrointestinal nematode infections of livestock animals are prevalent and costly problems worldwide. Currently, infections are controlled by anthelmintic chemicals but increasing drug resistance has prompted research interest to shift towards alternative methods of control such as vaccine development and selection of worm-resistant animals. The present study analyses proteins from Trichostrongylus colubriformis infective L3s that are recognised by IgG of immune sheep. Following protein separation via two-dimensional electrophoresis and Western blot probing with plasma from sheep resistant to T. colubriformis, mass spectrometry-based proteomic analyses were used to identify immuno-reactive protein spots. We were able to identify 28 immune targets, including aspartyl protease inhibitor, enolase, chaperone proteins, galectin, glycolytic enzymes, kinase, phosphatase and structural muscle proteins such as myosin, paramyosin, calponin and DIM-1. The data suggest that immune responses to T. colubriformis are dispersed over a relatively large number of parasite antigens, including several cytoplasmically expressed proteins. The results have new implications for understanding the molecular mechanisms that underpin host-parasite interaction during gastrointestinal nematode infections.

The second glutamic acid in the C-terminal CRD affects the carbohydrate-binding properties of recombinant galectins of Haemonchus contortus

The effects of the second glutamic acid (E) in the C-terminal CRDs on the hemagglutination and lactose-binding characteristics of the recombinant galectins of nematode Haemonchus contortus were observed using two isoforms of recombinant galectins as models, and the sugar-binding abilities of the N-terminal and C-terminal CRDs of the galectins were also compared. The second E in the CRD, WGNEER, of Hco-GAL-m was mutated to glycine acid (G) and resulted in a recombinant galectin (MG mutate) with a CRD of WGNEGR, identical to that of Hco-GAL-f. The G in Hco-GAL-f CRD, WGNEGR, was mutated to E and produced a recombinant galectin (FE mutate) equal to that of Hco-GAL-m. At the same time, the CRDs of the N-terminal (FNh,MNh) and C-terminal (FCh,MCh) of Hco-GAL-f, Hco-GAL-m were amplified by PCR. The abilities of carbohydrate binding and hemagglutination of the four galectins and the four CRDs were analysed, respectively, by alpha-lactose-agarose affinity chromatography and hemagglutination assay. The results showed that Hco-GAL-m and FE mutate bound effectively to alpha-lactose-agarose compared to Hco-GAL-f and MG mutate, which almost could not bind to the conjugate column. The hemagglutinating abilities of the Hco-GAL-m and FE mutate to human B type red blood cells were similar and were nearly two times higher than that of the Hco-GAL-f and MG mutate. The hemagglutinating ability of the MCh was five times to that of the MNh and FNh and almost two times to that of the FCh. The binding ability of the MCh and FCh were significantly reduced compared to that of the Hco-GAL-m and FE mutate, but still remained. As for the MNh and FNh, no elution peak was observed in the lactose-agarose affinity chromatography. These results suggested that the second amino acid E in the C-terminal CRD motif of H. contortus galectin was involved in carbohydrate binding and hemagglutination, and C-terminal CRDs had stronger carbohydrate ability than N-terminal CRDs.

Recombinant galectins of male and female Haemonchus contortus do not hemagglutinate erythrocytes of their natural host

Recombinant galectins of female and male adult worms of Haemonchus contortus were expressed in Escherichia coli and their hemagglutinating activities to human and different animal erythrocytes were analyzed. The results showed that female and male galectins could be highly expressed in E. coli using a temperature-sensitive plasmid, with the recombinant protein being mainly appeared in inclusion bodies. Hemagglutinating activity assays showed that both of the galectins hemagglutinated human A, B, O type, dog, rabbit, chicken and mouse erythrocytes at the high concentration of 40 microg/well, but did not hemagglutinate erythrocytes of the natural host of H. contortus, the goat. Sugar inhibition assays confirmed that, out of eight sugars tested, only lactose was effective to inhibit agglutination of human type B erythrocytes by the recombinant galectins.

The innate allergenicity of helminth parasites

Helminth parasites are well known to induce an immune response in their hosts characterised by elevated IgE, peripheral blood or local tissue eosinophilia, and in some cases, intestinal mastocytosis. This immunological response has a strong T-helper 2 (Th2) cytokine bias and is reminiscent of the immunological constellation found in allergic diseases. However, the molecular forces driving the Th2 response to helminth parasites are still not understood. By using the human hookworm parasite Necator americanus as an example, the authors of the current article propose that in the course of its life cycle, this parasite becomes innately allergenic through the secretion of a molecular array designed to promote tissue migration and homing, feeding and survival against immunological attack. This complex array comprises proteases, lectins and other classes of molecules. Subsequent immunological and physiological events seemingly protect the host from both the allergic sequelae of exposure to environmental allergens and, moreover, from the parasite itself.

DNA immunization with Na+-K+ ATPase (Sseat-6) induces protective immunity to larval Strongyloides stercoralis in mice

Strongyloides stercoralis causes chronic asymptomatic infections which can be maintained in the human host for many decades. Identification and treatment of S. stercoralis-infected individuals is required because immunosuppression can lead to fatal hyperinfection. In this study, human immunoglobulin G (IgG) that had previously been shown to transfer protective immunity to mice was used to identify potential protective antigens. Three antigens or genes from S. stercoralis larvae were identified as tropomyosin (Sstmy-1), Na+-K+ ATPase (Sseat-6), and LEC-5 (Sslec-5). The genes were cloned into plasmids for DNA immunization, and mice were immunized intradermally with the three plasmids individually in combination with a plasmid containing murine granulocyte-macrophage colony-stimulating factor. Only Na+-K+ ATPase induced a significant reduction in larval survival after DNA immunization. Immunization with a combination of all three plasmids, including Na+-K+ ATPase, did not induce protective immunity. Serum from mice immunized with DNA encoding Na+-K+ ATPase was transferred to naive mice and resulted in partial protective immunity. Therefore, DNA immunization with Na+-K+ ATPase induces protective immunity in mice, and it is the first identified vaccine candidate against infection with larval S. stercoralis.

Progress and new technologies for developing vaccines against gastrointestinal nematode parasites of sheep

Despite the identification of highly effective native antigens for vaccination against Haemonchus contortus, particularly 'hidden' antigens derived from the intestine of adult worms, to date similar efficacy has not been shown with recombinant antigens. In addition, progress towards identification of protective antigens from other sheep gastrointestinal (GI) nematode species is limited. Coupled with this is an incomplete understanding of the mechanism of natural immunity to GI nematodes, making selection of appropriate immunization strategies and adjuvants for evaluation of candidate 'natural' antigens problematic. The current explosion in new high-throughput technologies, arising from human studies, for analysis of the genome, transcriptome, proteome and glycome offers the opportunity to gain a better understanding of the molecular pathways underlying pathogen biology, the host immune system and the host-pathogen interaction. An overview is provided on how these technologies can be applied to parasite research and how they may aid in overcoming some of the current problems in development of commercial vaccines against GI nematode parasites.

Genomic and genetic research on bursate nematodes: significance, implications and prospects

Molecular genetic research on parasitic nematodes (order Strongylida) is of major significance for many fundamental and applied areas of medical and veterinary parasitology. The advent of gene technology has led to some progress for this group of nematodes, particularly in studying parasite systematics, drug resistance and population genetics, and in the development of diagnostic assays and the characterisation of potential vaccine and drug targets. This paper gives an account of the molecular biology and genetics of strongylid nematodes, mainly of veterinary socio-economic importance, indicates the implications of such research and gives a perspective on genome research for this important parasite group, in light of recent technological advances and knowledge of the genomes of other metazoan organisms.