Origin, kinetics of circulation and fate in vivo of the major excretory-secretory product of Acanthocheilonema viteae

Epigenetic changes induced by parasitic worms and their excretory-secretory products

Parasitic worms are pathogens of major medical and veterinary importance. They have evolved highly effective and sophisticated strategies of immune system manipulation, typically involving actively excreted/secreted (E-S) products. These molecules dampen and regulate the host immune responses that would otherwise result in parasite expulsion, thereby enabling the worms to survive in the host for many years, and they can also help prevent the potentially serious tissue damage that the worms can induce. Reflecting these E-S product-associated anti-inflammatory activities, there is also increasing evidence that parasitic worms and their products may serendipitously protect against allergic and autoimmune conditions and in addition, comorbidities of ageing that are associated with inflammatory responses, like type 2 diabetes and obesity. Research in this area has to date generally focused on identifying the cellular and effector targets of immunomodulation induced by the worm E-S products. However, increasing evidence that they can induce stably imprinted phenotypes of haematopoietic and stromal cells which promote their long-lasting survival has recently ignited interest in the ability of the molecules to epigenetically rewire cells to 'resolve and repair' phenotypes. Here, we review and discuss these new data in the context of their potential for exploitation in identifying novel gene signatures for the development of advanced and safe therapeutics for chronic inflammatory diseases.

The allure of targets for novel drugs

The challenges of bringing new medicines to patients have been extensively discussed and debated, including consideration of the contribution that academic laboratories can make. At the University of Strathclyde, drug discovery has been a continuing focal activity since the 1960s, and in the past 30 years, the author has led or contributed to many projects of different character and for diverse diseases. A feature common to these projects is the extension of concepts of molecular and biological targets in drug discovery research. In mechanistic terms, these have included compounds that are activators and not inhibitors, and in particular multitargeted compounds. With respect to relevance to disease, schizophrenia, pulmonary disfunction, autoimmune, and infectious disease are most relevant. These projects are discussed in the context of classical medicinal chemistry and more recent concepts in and approaches to drug discovery.

Helminth-derived biomacromolecules as therapeutic agents for treating inflammatory and infectious diseases: What lessons do we get from recent findings?

Despite the tremendous progress in healthcare sectors, a number of life-threatening infectious, inflammatory, and autoimmune diseases are continuously challenging mankind throughout the globe. In this context, recent successes in utilizing helminth parasite-derived bioactive macromolecules viz. glycoproteins, enzymes, polysaccharides, lipids/lipoproteins, nucleic acids/nucleotides, and small organic molecules for treating various disorders primarily resulted from inflammation. Among the several parasites that infect humans, helminths (cestodes, nematodes, and trematodes) are known as efficient immune manipulators owing to their explicit ability to modulate and modify the innate and adaptive immune responses of humans. These molecules selectively bind to immune receptors on innate and adaptive immune cells and trigger multiple signaling pathways to elicit anti-inflammatory cytokines, expansion of alternatively activated macrophages, T-helper 2, and immunoregulatory T regulatory cell types to induce an anti-inflammatory milieu. Reduction of pro-inflammatory responses and repair of tissue damage by these anti-inflammatory mediators have been exploited for treating a number of autoimmune, allergic, and metabolic diseases. Herein, the potential and promises of different helminths/helminth-derived products as therapeutic agents in ameliorating immunopathology of different human diseases and their mechanistic insights of function at cell and molecular level alongside the molecular signaling cross-talks have been reviewed by incorporating up-to-date findings achieved in the field.

Lead optimisation efforts on a molecular prototype of the immunomodulatory parasitic protein ES-62

The immunomodulatory property of some parasitic helminths is well documented. The glycoprotein ES-62 from the nematode, acanthocheilonema viteae has been found to possess immunomodulatory properties. Two small molecule analogues (SMA’s) of ES-62 (S3 and S5) were found to mimic its immunomodulatory properties in vivo and were active in animal models of allergic, inflammatory and autoimmune diseases. In this work, new efforts were made to further optimise the activities of compound S3 by making small but directed structural changes. A variety of analogues based on the S3 prototype were simulated by making variations at one position and then screened in silico. The best compounds were selected based on predicted physiochemical properties and medicinal chemistry indices and synthesised. Structural elucidation was done via HNMR, LCMS, FTIR and HRESIMS. The predicted properties were evaluated by HPLC method. A total of 11 novel molecules were synthesised and characterised. Significant correlation was obtained between the predicted physicochemical properties and their HPLC retention times (RT) for eight of our novel compounds. This suggests that these compounds may behave in a physiological environment as closely as computationally predicted. This entails, lesser host toxicity while maintaining good or better activities compared to the earlier prototype. They hence provide a good opportunity for development of drugs for immune conditions such as asthma, inflammation and autoimmune diseases.

Helminth Glycans at the Host-Parasite Interface and Their Potential for Developing Novel Therapeutics

Helminths are parasitic worms that have successfully co-evolved with their host immune system to sustain long-term infections. Their successful parasitism is mainly facilitated by modulation of the host immune system via the release of excretory-secretory (ES) products covered with glycan motifs such as Lewis X, fucosylated LDN, phosphorylcholine and tyvelose. Evidence is accumulating that these glycans play key roles in different aspects of helminth infection including interactions with immune cells for recognition and evasion of host defences. Moreover, antigenic properties of glycans can be exploited for improving the efficacy of anti-helminthic vaccines. Here, we illustrate that glycans have the potential to open new avenues for the development of novel biopharmaceuticals and effective vaccines based on helminth glycoproteins.

Mini Review: Structure and Function of Nematode Phosphorylcholine-Containing Glycoconjugates

An unusual aspect of the biology of nematodes is the covalent attachment of phosphorylcholine (PC) to carbohydrate in glycoconjugates. Investigation of the structure of these molecules by ever-increasingly sophisticated analytical procedures has revealed that PC is generally in phosphodiester linkage with C6 of N-acetylglucosamine (GlcNAc) in both N-type glycans and glycosphingolipids. Up to five PC groups have been detected in the former, being located on both antenna and core GlcNAc. The PC donor for transfer to carbohydrate appears to be phosphatidylcholine but the enzyme responsible for transfer remains to be identified. Work primarily involving the PC-containing Acanthocheilonema viteae secreted product ES-62, has shown that the PC attached to nematode N-glycans possesses a range of immunomodulatory properties, subverting for example, pro-inflammatory signalling in various immune system cell-types including lymphocytes, mast cells, dendritic cells and macrophages. This has led to the generation of PC-based ES-62 small molecule analogues (SMAs), which mirror the parent molecule in preventing the initiation or progression of disease in mouse models of a number of human conditions associated with aberrant inflammatory responses. These include rheumatoid arthritis, systemic lupus erythematosus and lung and skin allergy such that the SMAs are considered to have widespread therapeutic potential.

Human filariasis-contributions of the Litomosoides sigmodontis and Acanthocheilonema viteae animal model

Filariae are vector-borne parasitic nematodes that are endemic worldwide, in tropical and subtropical regions. Important human filariae spp. include Onchocerca volvulus, Wuchereria bancrofti and Brugia spp., and Loa loa and Mansonella spp. causing onchocerciasis (river blindness), lymphatic filariasis (lymphedema and hydrocele), loiasis (eye worm), and mansonelliasis, respectively. It is estimated that over 1 billion individuals live in endemic regions where filarial diseases are a public health concern contributing to significant disability adjusted life years (DALYs). Thus, efforts to control and eliminate filarial diseases were already launched by the WHO in the 1970s, especially against lymphatic filariasis and onchocerciasis, and are mainly based on mass drug administration (MDA) of microfilaricidal drugs (ivermectin, diethylcarbamazine, albendazole) to filarial endemic areas accompanied with vector control strategies with the goal to reduce the transmission. With the United Nations Sustainable Development Goals (SDGs), it was decided to eliminate transmission of onchocerciasis and stop lymphatic filariasis as a public health problem by 2030. It was also requested that novel drugs and treatment strategies be developed. Mouse models provide an important platform for anti-filarial drug research in a preclinical setting. This review presents an overview about the Litomosoides sigmodontis and Acanthocheilonema viteae filarial mouse models and their role in immunological research as well as preclinical studies about novel anti-filarial drugs and treatment strategies.

Development of Acanthocheilonema viteae in Meriones shawi: Absence of microfilariae and production of active ES-62

AIMS

ES-62 is a well-studied anti-inflammatory molecule secreted by L4-adult stage Acanthocheilonema viteae. We maintain the life cycle of A viteae using Meriones libycus as the definitive host. Here, we investigated whether the full life cycle could be maintained, and functional ES-62 produced, in a related jird species-Meriones shawi.

METHODS AND RESULTS

Adult worms were produced in comparable numbers in the two species, but very few microfilariae (MF) were observed in the M shawi bloodstream. M shawi ES-62 produced ex vivo was functional and protective in a mouse model of arthritis. Myeloid-derived cells from naïve and infected jirds of both species were compared with respect to ROS production and osteoclast generation, and some differences between the two species in both the absence and presence of infection were observed.

CONCLUSIONS

The life cycle of A viteae cannot be successfully completed in M shawi jirds but L3 stage worms develop to adulthood and produce functional ES-62. Preliminary investigation into jird immune responses suggests that infection can differentially modulate myeloid responses in the two species. However, species-specific reagents are required to understand the complex interplay between A viteae and its host and to explain the lack of circulating MF in infected M shawi jirds.

Site-specific glycoproteomic characterization of ES-62: The major secreted product of the parasitic worm Acanthocheilonema viteae

ES-62 is the major secreted product of the parasitic filarial nematode Acanthocheilonema viteae and has potent anti-inflammatory activities as a consequence of posttranslational decoration by phosphorylcholine (PC). Previously, we showed that ES-62’s PC was attached to N-linked glycans, and using fast atom bombardment mass spectrometry, we characterized the structure of the glycans. However, it was unknown at this time which of ES-62’s four potential N-glycosylation sites carries the PC-modified glycans. In the present study, we now employ more advanced analytical tools—nano-flow liquid chromatography with high-definition electrospray mass spectrometry—to show that PC-modified glycans are found at all four potential N-glycosylation sites. Also, our earlier studies showed that up to two PC groups were detected per glycan, and we are now able to characterize N-glycans with up to five PC groups. The number per glycan varies in three of the four glycosylation sites, and in addition, for the first time, we have detected PC on the N-glycan chitobiose core in addition to terminal GlcNAc. Nevertheless, the majority of PC is detected on terminal GlcNAc, enabling it to interact with the cells and molecules of the immune system. Such expression may explain the potent immunomodulatory effects of a molecule that is considered to have significant therapeutic potential in the treatment of certain human allergic and autoimmune conditions.

Small Molecule Analogues of the parasitic worm product ES-62 interact with the TIR domain of MyD88 to inhibit pro-inflammatory signalling

ES-62 is a protein secreted by the parasitic worm Acanthocheilonema viteae that is anti-inflammatory by virtue of covalently attached phosphorylcholine. Previously we have reported that drug-like Small Molecule Analogues (SMAs) of its phosphorylcholine moiety can mimic ES-62 in protecting against disease development in certain mouse models of autoimmune and allergic conditions, due to them causing partial degradation of the TLR/IL-1R adaptor MyD88. We have now taken a molecular modelling approach to investigating the mechanism underlying this effect and this predicts that the SMAs interact directly with the MyD88 TIR domain. Further support for this is provided by assay of LPS-induced MyD88/NF-κB-driven secreted alkaline phosphatase (SEAP) reporter activity in commercially-available stably transfected (TLR4-MD2-NF-κB-SEAP) HEK293 cells, as SMA12b-mediated inhibition of such SEAP activity is blocked by its pre-incubation with recombinant MyD88-TIR domain. Direct binding of SMA12b to the TIR domain is also shown to inhibit homo-dimerization of the adaptor, an event that can explain the observed degradation of the adaptor and inhibition of subsequent downstream signalling. Thus, these new data identify initial events by which drug-like ES-62 SMAs, which we also demonstrate are able to inhibit cytokine production by human cells, homeostatically maintain "safe" levels of MyD88 signalling.

Helminth Immunomodulation in Autoimmune Disease

Helminths have evolved to become experts at subverting immune surveillance. Through potent and persistent immune tempering, helminths can remain undetected in human tissues for decades. Redirecting the immunomodulating "talents" of helminths to treat inflammatory human diseases is receiving intensive interest. Here, we review therapies using live parasitic worms, worm secretions, and worm-derived synthetic molecules to treat autoimmune disease. We review helminth therapy in both mouse models and clinical trials and discuss what is known on mechanisms of action. We also highlight current progress in characterizing promising new immunomodulatory molecules found in excretory/secretory products of helminths and their potential use as immunotherapies for acute and chronic inflammatory diseases.

Crystal structure of N,N-dimethyl-2-[(4-methyl-benz-yl)sulfon-yl]ethanamine

In the crystal, the title compound, C12H19NO2S, has a disordered structure with two equally populated conformations of the amine fragment. A pair of weak C-H⋯O inter-molecular inter-actions between the CH2 and SO2 groups gives a one-dimensional supra-molecular structure that propagates through translation along the a-axis direction.

Prophylactic and therapeutic treatment with a synthetic analogue of a parasitic worm product prevents experimental arthritis and inhibits IL-1β production via NRF2-mediated counter-regulation of the inflammasome

Rheumatoid arthritis (RA) remains a debilitating autoimmune condition as many patients are refractory to existing conventional and biologic therapies, and hence successful development of novel treatments remains a critical requirement. Towards this, we now describe a synthetic drug-like small molecule analogue, SMA-12b, of an immunomodulatory parasitic worm product, ES-62, which acts both prophylactically and therapeutically against collagen-induced arthritis (CIA) in mice. Mechanistic analysis revealed that SMA-12b modifies the expression of a number of inflammatory response genes, particularly those associated with the inflammasome in mouse bone marrow-derived macrophages and indeed IL-1β was the most down-regulated gene. Consistent with this, IL-1β was significantly reduced in the joints of mice with CIA treated with SMA-12b. SMA-12b also increased the expression of a number of genes associated with anti-oxidant responses that are controlled by the transcription factor NRF2 and critically, was unable to inhibit expression of IL-1β by macrophages derived from the bone marrow of NRF2(-/-) mice. Collectively, these data suggest that SMA-12b could provide the basis of an entirely novel approach to fulfilling the urgent need for new treatments for RA.

Unraveling the Hygiene Hypothesis of helminthes and autoimmunity: origins, pathophysiology, and clinical applications

BACKGROUND

The Hygiene Hypothesis (HH) attributes the dramatic increase in autoimmune and allergic diseases observed in recent decades in Western countries to the reduced exposure to diverse immunoregulatory infectious agents. This theory has since largely been supported by strong epidemiological and experimental evidence.

DISCUSSION

The analysis of these data along with the evolution of the Western world's microbiome enable us to obtain greater insight into microorganisms involved in the HH, as well as their regulatory mechanisms on the immune system. Helminthes and their derivatives were shown to have a protective role. Helminthes' broad immunomodulatory properties have already begun to be exploited in clinical trials of autoimmune diseases, including inflammatory bowel disease, multiple sclerosis, rheumatoid arthritis, and type-1 diabetes.

SUMMARY

In this review, we will dissect the microbial actors thought to be involved in the HH as well as their immunomodulatory mechanisms as emphasized by experimental studies, with a particular attention on parasites. Thereafter, we will review the early clinical trials using helminthes' derivatives focusing on autoimmune diseases.

Helminth therapy or elimination: epidemiological, immunological, and clinical considerations

Deworming is rightly advocated to prevent helminth-induced morbidity. Nevertheless, in affluent countries, the deliberate infection of patients with worms is being explored as a possible treatment for inflammatory diseases. Several clinical trials are currently registered, for example, to assess the safety or efficacy of Trichuris suis ova in allergies, inflammatory bowel diseases, multiple sclerosis, rheumatoid arthritis, psoriasis, and autism, and the Necator americanus larvae for allergic rhinitis, asthma, coeliac disease, and multiple sclerosis. Studies in animals provide strong evidence that helminths can not only downregulate parasite-specific immune responses, but also modulate autoimmune and allergic inflammatory responses and improve metabolic homoeostasis. This finding suggests that deworming could lead to the emergence of inflammatory and metabolic conditions in countries that are not prepared for these new epidemics. Further studies in endemic countries are needed to assess this risk and to enhance understanding of how helminths modulate inflammatory and metabolic pathways. Studies are similarly needed in non-endemic countries to move helminth-related interventions that show promise in animals, and in phase 1 and 2 studies in human beings, into the therapeutic development pipeline.

Small molecule analogues of the immunomodulatory parasitic helminth product ES-62 have anti-allergy properties

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Small molecule analogues of the helminth immunomodulator ES-62 have been produced.

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Two analogues inhibit mast cell functions and prevent airway hypersensitivity.

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The analogues are drug-like and could be considered for treatment of human allergy.

ES-62, a glycoprotein secreted by the filarial nematode Acanthocheilonema viteae, exhibits anti-inflammatory properties by virtue of covalently attached phosphorylcholine moieties. Screening of a library of ES-62 phosphorylcholine-based small molecule analogues (SMAs) revealed that two compounds, termed 11a and 12b, mirrored the helminth product both in inhibiting mast cell degranulation and cytokine responses in vitro and in preventing ovalbumin-induced Th2-associated airway inflammation and eosinophil infiltration of the lungs in mice. Furthermore, the two SMAs inhibited neutrophil infiltration of the lungs when administered therapeutically. ES-62-SMAs 11a and 12b thus represent starting points for novel drug development for allergies such as asthma.

Designing anti-inflammatory drugs from parasitic worms: a synthetic small molecule analogue of the Acanthocheilonema viteae product ES-62 prevents development of collagen-induced arthritis

In spite of increasing evidence that parasitic worms may protect humans from developing allergic and autoimmune diseases and the continuing identification of defined helminth-derived immunomodulatory molecules, to date no new anti-inflammatory drugs have been developed from these organisms. We have approached this matter in a novel manner by synthesizing a library of drug-like small molecules based upon phosphorylcholine, the active moiety of the anti-inflammatory Acanthocheilonema viteae product, ES-62, which as an immunogenic protein is unsuitable for use as a drug. Following preliminary in vitro screening for inhibitory effects on relevant macrophage cytokine responses, a sulfone-containing phosphorylcholine analogue (11a) was selected for testing in an in vivo model of inflammation, collagen-induced arthritis (CIA). Testing revealed that 11a was as effective as ES-62 in protecting DBA/1 mice from developing CIA and mirrored its mechanism of action in downregulating the TLR/IL-1R transducer, MyD88. 11a is thus a novel prototype for anti-inflammatory drug development.

Growth factors and chemotactic factors from parasitic helminths: molecular evidence for roles in host-parasite interactions versus parasite development

For decades molecular helminthologists have been interested in identifying proteins expressed by the parasite that have roles in modulating the host immune response. In some cases, the aim was targeting parasite-derived orthologues of mammalian cytokines and growth factors known to have functions in immune modulation. In others, novel proteins without homology to mammalian cytokines were isolated by investigating effects of purified worm extracts on various immunological processes. Often, the role parasite-derived growth factors play in worm development was ignored. Here, we review growth factors and chemotactic factors expressed by parasitic helminths and discuss their recognised and potential roles in immunomodulation and/or parasite development.

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

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

Immunomodulatory activity and therapeutic potential of the filarial nematode secreted product, ES-62

ES-62 is a protein that is actively secreted by filarial nematodes during parasitism of the vertebrate host. The molecule is able to directly interact with a number of cells of the immune system including B-lymphocytes, dendritic cells, macrophages and mast cells. Interaction appears to be dependent on complexing with TLR4 and results in modulation of the activity of a number of signal transduction molecules including MAP kinases, PI-3 kinase and NF-kappaB. Immunomodulatory activity of ES-62 appears to be largely due to the presence of phosphorylcholine (PC) moieties covalently attached to N-type glycans. The net effect of ES-62's interaction with the immune system is the generation of an anti-inflammatory immunological phenotype. As a consequence of this, ES-62 demonstrates striking drug-like activity in models of disease associated with aberrant inflammation, in particular those associated with autoimmunity and allergy.

Filarial nematode secreted product ES-62 is an anti-inflammatory agent: therapeutic potential of small molecule derivatives and ES-62 peptide mimetics

1. The 'hygiene hypothesis' postulates that the recent increased incidence of allergic or autoimmune diseases (e.g. asthma, type I diabetes) in the West reflects an absence of appropriate priming of the immune response by infectious agents, such as parasitic worms, during childhood. 2. Consistent with this, it has long been recognized that several autoimmune disorders, such as rheumatoid arthritis (RA), a T helper (Th) 1-mediated autoimmune disease characterized by excess production of pro-inflammatory cytokines, such as tumour necrosis factor-alpha, exhibit reduced incidence and severity in geographical regions with high parasite load, suggesting that environmental factors may subtly alter disease progression. 3. Infection with worms also appears to suppress Th2-biased inflammatory disorders, such as asthma, because there also appears to be an inverse correlation between parasite load and atopy. This is perhaps more surprising, given that helminths often induce strong Th2-type immune responses characterized by release of specific cytokines, such as interleukin (IL)-4, IL-5 and IL-13. 4. Therefore, these findings suggest that the co-evolution of helminths with hosts, which has resulted in the ability of worms to modulate inflammatory responses in order to promote parasite survival, may also have generated a predisposition for the host to develop autoimmunity and allergy in the absence of infection. 5. The mechanisms underlying such immunomodulation are not clear, but appear to involve the release of parasite-derived molecules that allow the worms to modulate or evade the host immune response by a number of mechanisms, including skewing of cytokine responses and the induction of T regulatory cells. 6. In the present review we discuss the properties of one such filarial nematode-derived immunomodulatory molecule, namely ES-62, its anti-inflammatory action and the therapeutic potential of small molecule derivatives and peptides that mimic its action.

Immunomodulatory effect of various anti-parasitics: a review

This paper reviews the immunomodulatory effects (immunosuppression or immunoactivation) of various anthelmintics including levamisole, fenvalerate, dieldrin, carbofuran, aminocarb, thiabendazole, fenbendazole, oxfendazole and ivermectin. The induced modulation of immune function may occur via direct and/or indirect mechanisms. The immunomodulatory effects of these anti-parasitics have been studied in a variety of bacterial (e.g. brucellosis, salmonellosis, paratuberculosis, mastitis), viral (e.g. infectious bovine rhinotracheitis, Herpes, foot and mouth disease), parasitic (e.g. onchocerciasis, coccidiosis, ascariasis, schistosomiasis) and neoplastic diseases. Some antiparasitics have also been used to boost immunity in a number of human diseases including leprosy, Hodgkin's disease, rheumatoid arthritis, and in adjuvanted therapy of colorectal cancer. The ability to stimulate the immune response of animals offers a new means of disease intervention. Future research on immunomodulatory effects of anti-parasitics, for humans and domestic farm animals, will provide additional methods of treating immunosuppressed subjects. The immunopotentiating or immunosuppressing activity of anti-parasitics will dictate whether co-administration of vaccines and anthelmintics or administration of vaccines during the window of immunoactivation is justified or not.

Subversion of immune cell signal transduction pathways by the secreted filarial nematode product, ES-62

Filarial nematodes achieve longevity within the infected host by suppressing and modulating the host immune response. To do this, the worms actively secrete products that have been demonstrated to possess immunomodulatory properties. In this article we discuss the immunomodulatory effects of the phosphorylcholine-containing filarial nematode secreted glycoprotein ES-62. In particular we describe how it modulates intracellular signal transduction pathways in a number of different cells of the immune system, in particular B-lymphocytes, T-lymphocytes, macrophages and dendritic cells.

Lack of immunological cross-reactivity between parasite-derived and recombinant forms of ES-62, a secreted protein of Acanthocheilonema viteae

The longevity of filarial nematodes is dependent on secreted immunomodulatory products. Previous investigation of one such product, ES-62, has suggested a critical role for post-translationally attached phosphorylcholine (PC) moieties. In order to further investigate this, ES-62 lacking PC was produced, using the Pichia pastoris recombinant gene expression system. Unlike parasite-derived ES-62, which is tetrameric the recombinant material was found to consist of a mixture of apparently stable tetramers, dimers and monomers. Nevertheless, the recombinant protein was considered to be an adequate PC-free ES-62 as it was recognized by existing antisera against the parasite-derived protein. However, subsequent to this, recognition of parasite-derived ES-62 by antibodies produced against the recombinant protein was found to be absent. In an attempt to explain this, recombinant ES-62 was subjected to structural analysis and was found to (i) contain 3 changes in amino acid composition; (ii) demonstrate significant alterations in glycosylation; (iii) show major differences in protein secondary structure. The effects of these alterations in relation to the observed change in immunogenicity were investigated and are discussed. The data presented clearly show that recognition by existing antibodies is insufficient proof that recombinant proteins can be used to mimic parasite-derived material in studies on nematode immunology and vaccination.

Signalling mechanisms underlying subversion of the immune response by the filarial nematode secreted product ES-62

Secretion of immunomodulatory molecules is a key strategy employed by pathogens to enable their survival in host organisms. For example, arthropod-transmitted filarial nematodes, which achieve longevity within the infected host by suppressing and modulating the host immune response, produce excretory-secretory (ES) products that have been demonstrated to possess immunomodulatory properties. In this review we discuss the immunomodulatory effects of the phosphorylcholine-containing filarial nematode-secreted glycoprotein ES-62 and describe the intracellular signal transduction pathways it targets to achieve these effects.

Structure and synthesis of nematode phosphorylcholine-containing glycoconjugates

Infection with filarial nematodes produces a chronic, long-lasting illness with adult worms able to survive within human hosts for up to 15 years. A contributor to the longevity of these parasites is the presence of phosphorylcholine (PC) on components of the worms' molecular secretions (ES). PC on ES modulates host immune responses towards an anti-inflammatory phenotype thereby generating an environment favourable for parasite survival. PC is attached to nematode ES via a covalent association with carbohydrate, which, although well-documented in bacteria and fungi, is absent from humans, making it an ideal target for the development of novel drugs. In order to produce such drugs it is first necessary to understand the structure and synthesis of nematode PC-glycans. ES-62 is the major PC-ES-product ofAcanthocheilonema viteaeand is a homologue of PC-ES found in human filarial nematodes. We have studied the structure and biosynthesis of PC-glycans of ES-62 by a combination of pulse-chase experiments, experiments involving the use of inhibitors of each of intracellular trafficking, oligosaccharide processing and phospholipid biosynthesis and various forms of mass spectrometry. Our indications indicate that PC is transferred in the lumen of the medial Golgi to an N-type glycan consisting of a trimannosyl core with or without core fucosylation bearing between 1 and 4 N-acetyl glucosamine residues. The structure of the PC-N-glycans found in ES-62 appears to be conserved amongst filarial nematodes in that it has additionally been identified inOnchocerca volvulusandO. gibsoni. Also, similar structures have been found in non-filarial parasitic nematodes and in the free-living nematodeCaenorhabditis elegans. Finally, PC has also been recently found attached to the carbohydrate moieties of nematode glycosphingolipids and the structure of these will also be considered.

ES-62, a filarial nematode-derived immunomodulator with anti-inflammatory potential

Arthropod-transmitted filarial nematodes can survive for in excess of a decade via modulation of the vertebrate host immune system. Although human infection can result in very severe pathology, most infected individuals show remarkably little evidence of this. Analysis of the anti-nematode response indicates that apparently pathology-free individuals have an anti-inflammatory immunological phenotype and it has been suggested that this favours maintenance of host good health. It is considered that parasite-derived molecular secretions contribute to the anti-inflammatory phenotype and we have thus investigated the properties of a filarial nematode glycoprotein secreted in some abundance, ES-62. This molecule shows a plethora of immunomodulatory activities that can be classified as anti-inflammatory. It has been observed in a number of studies that several autoimmune disorders including rheumatoid arthritis (RA) exhibit reduced incidence and severity in geographic regions in which filarial nematodes are transmitted to humans. Furthermore, it has been speculated that these two observations are linked although molecular explanations for such an association have not been forthcoming. Although the aetiology of RA remains unknown a majority of data are consistent with it being mediated via excess pro-inflammatory cytokine production. Given that ES-62 is anti-inflammatory, we hypothesised that it might be able to counter the pathology associated with diseases like RA. Indeed, we found that exposure to ES-62 prevented initiation of collagen-induced arthritis (CIA) in a murine model and also suppressed progression of established disease. Ex vivo analyses demonstrated that these effects correlated with inhibition of TNF-alpha production and inhibition of collagen-specific TH-1 responses. The nematode product was also able to suppress pro-inflammatory cytokine release in vitro in synovial cells derived from RA patients. ES-62 thus constitutes a pathogen-derived immunomodulator with significant therapeutic potential.

Stage-specific and species-specific differences in the production of the mRNA and protein for the filarial nematode secreted product, ES-62

Previous studies have shown that the secreted phosphorylcholine-containing glycoprotein of filarial nematodes, ES-62, is only present in the post-infective life-cycle stages, but that the mRNA is transcribed throughout the worm's life-cycle. The aim of this current study was to investigate whether the presence or absence of protein expression simply reflects differences in mRNA abundance. To this end, we investigated the relative abundance of ES-62 using TaqMan real time RT-PCR, in different life-cycle stages of 2 model filarial nematode parasites, Acanthocheilonema viteae and Brugia pahangi. For B. pahangi, microfilariae, infective larvae and adult worms were each found to have approximately similar levels of ES-62 mRNA. However, the corresponding stages of A. viteae differed greatly from each other with a pattern of increased mRNA production with maturation. As a rule A. viteae had higher levels of ES-62 mRNA than B. pahangi, and this was particularly noticeable in the adult stage where the difference was approximately 3500-fold higher. However, this significant difference in mRNA abundance was not reflected in the quantity of ES-62 protein secreted by the adult worms of each species, as A. viteae only secreted approximately 3 times as much ES-62 as B. pahangi. Thus, overall, the results obtained from this study indicate that ES-62 protein production does not solely reflect mRNA levels, and also suggest that the 2 nematodes may employ different mechanisms for regulating protein production.

Hyporesponsiveness of murine B lymphocytes exposed to the filarial nematode secreted product ES-62 in vivo

ES-62 is a phosphorylcholine (PC)-containing glycoprotein secreted by filarial nematodes, parasites of vertebrates including humans. We have previously demonstrated that pre-exposure to this molecule in vitro interferes with subsequent B-cell receptor (BCR)-dependent activation of murine splenic B lymphocytes. To investigate the significance of this during filarial nematode infection, we now employ mice exposed to ES-62, at concentrations equivalent to those found for PC-containing molecules in the bloodstream of parasitized humans, via release from implanted osmotic pumps. Using this approach, we reveal that splenic and lymph node mononuclear cells, and also purified splenic B cells recovered from these mice have reduced ability ex vivo to proliferate in response to BCR ligation. The effect on BCR-induced proliferation was further investigated with respect to elucidating the mechanism of action of the parasite product and was shown to be associated with impaired signal transduction affecting the ErkMAPkinase pathway. Also, it was found that ES-62 did not act by promoting apoptosis or by priming for apoptosis following subsequent stimulation, but rather, appeared to render cells hyporesponsive to stimulation. ES-62 is thus shown for the first time to be a potent modulator of B lymphocyte function in vivo at a concentration relevant to natural filarial nematode infection. This finding considerably strengthens the idea that ES-62 plays a role in evasion of the immune response during parasitism.

Immunomodulatory properties of Ascaris suum glycosphingolipids - phosphorylcholine and non-phosphorylcholine-dependent effects

Immunomodulatory properties of phosphorylcholine (PC)-containing glycosphingolipids from Ascaris suum were investigated utilizing immune cells from BALB/c mice. Proliferation of splenic B cells induced either via F(ab')2 fragments of anti-murine Ig (anti-Ig) or LPS was significantly reduced when the glycosphingolipids were present in the culture medium. However whereas the LPS-mediated effect was dependent on the PC moiety of the glycosphingolipids, the result generated when using anti-Ig was not. Analysis of cell cycle status and mitochondrial potential indicated that the combination of the glycosphingolipids and anti-Ig reduced B cell proliferation, at least in part, by inducing apoptosis. Consistent with the observed suppression of B cell activation/cell cycle progression, investigation of the effect of glycosphingolipid pre-exposure on mitogenic B cell signal transduction pathways activated by anti-Ig, revealed a PC-independent inhibitory effect on dual (thr/tyr) phosphorylation and activation of ErkMAPKinase. The glycosphingolipids were also investigated for their inhibitory effect on LPS/IFN-gamma induced Th1/pro-inflammatory cytokine production by peritoneal macrophages. It was found that IL-12 p40 production was inhibited and in an apparently PC-dependent manner. Overall these data indicate that PC-containing glycosphingolipids of A. suum appear to have at least two immunomodulatory constituents - PC and an as yet unknown component.

A filarial nematode-secreted phosphorylcholine-containing glycoprotein uncouples the B cell antigen receptor from extracellular signal-regulated kinase-mitogen-activated protein kinase by promoting the surface Ig-mediated recruitment of Src homology 2 domain-containing tyrosine phosphatase-1 and Pac-1 mitogen-activated kinase-phosphatase

Unraveling the molecular mechanisms by which filarial nematodes, major human pathogens in the tropics, evade the host immune system remains an elusive goal. We have previously shown that excretory-secretory product-62 (ES-62), a homologue of phosphorylcholine-containing molecules that are secreted by human parasites and which is active in rodent models of filarial infection, is able to polyclonally activate certain protein tyrosine kinase and mitogen-activating protein kinase signal transduction elements in B lymphocytes. Such activation mediates desensitization of subsequent B cell Ag receptor (BCR) ligation-induced activation of extracellular signal-regulated kinase-mitogen-activated protein (ErkMAP) kinase and ultimately B cell proliferation. We now show that the desensitization is due to ES-62 targeting two major regulatory sites of B cell activation. Firstly, pre-exposure to ES-62 primes subsequent BCR-mediated recruitment of SHP-1 tyrosine phosphatase to abolish recruitment of the RasErkMAP kinase cascade via the Igalphabeta-ShcGrb2Sos adaptor complex interactions. Secondly, any ongoing ErkMAP kinase signaling in ES-62-primed B cells is terminated by the MAP kinase phosphatase, Pac-1 that is activated consequently to challenge via the BCR.

Presence of phosphorylcholine on a filarial nematode protein influences immunoglobulin G subclass response to the molecule by an interleukin-10-dependent mechanism

The filarial nematode product ES-62 contains phosphorylcholine (PC) covalently attached to N-linked glycans. ES-62 induced high levels of immunoglobulin G1 (IgG1) antibodies, but no IgG2a, to non-PC epitopes of the molecule following subcutaneous injection into BALB/c mice. Conversely, mice given ES-62 lacking PC demonstrated significant production of both IgG subclasses. Thus, PC appears to block production of IgG2a antibodies to other epitopes on the parasite molecule. A role for interleukin-10 (IL-10) in this effect was shown by the ability of IL-10(-/-) mice to make an IgG2a antibody response to non-PC epitopes of ES-62.

Phosphorylcholine substituents in nematodes: structures, occurrence and biological implications

Phosphorylcholine (PC), a small haptenic molecule, is found in a wide variety of prokaryotic organisms, i. e. bacteria, and in eukaryotic parasites such as nematodes, as well as in fungi. Linked to parasite-specific glycoprotein glycans or glycolipids, it is assumed to be responsible for a variety of immunological effects, including invasion mechanisms and long-term persistence of parasites within the host. Numerous reports have indicated various effects of PC-substituted molecules derived from parasitic nematodes on signal transduction pathways in B and T lymphocytes, displaying a highly adapted and profound modulation of the immune system by these parasites. The Nematoda, comprising parasitic and free-living species, can be regarded as promising prototypic systems for structural analyses, immunological studies and biosynthetic investigations. In this context, Ascaris suum, the pig parasitic nematode, is an ideal organism for immunological studies and an excellent source for obtaining large amounts of PC-substituted (macro)molecules. Caenorhabditis elegans, as a completely genome-sequenced species and expressing parasite analogous PC-substituted structures, together with the possibility for easy in vitro cultivation, represents a conceptual model for biosynthetic studies, whereas filarial parasites represent important model systems for human pathogens, especially in developing countries. This review summarises current knowledge on the tissue-specific expression of PC epitopes, structural data of glycoprotein glycans and glycosphingolipids bearing this substituent and biological implications for the immune systems of the respective hosts.

Immunomodulatory properties of a phosphorylcholine-containing secreted filarial glycoprotein

ES-62 is a phosphorylcholine (PC)-containing glycoprotein which is secreted by the rodent filarial nematode Acanthocheilonema viteae. A homologue exists in the human filarial nematode Brugia malayi and indeed PC is found attached to glycoproteins of many, if not all, filarial species. At concentrations equivalent to those found for PC-containing molecules in the bloodstream of parasitized humans, ES-62 is able to polyclonally activate certain protein tyrosine kinase and mitogen-activating protein kinase signal-transduction elements in B and T lymphocytes following in-vitro exposure. Although this interaction is insufficient to cause lymphocyte proliferation per se, it serves to desensitize the cells to subsequent activation of the phosphoinositide-3-kinase, protein kinase C and Ras mitogen-activating protein kinase pathways and hence also to proliferation via the antigen receptors. The active component of ES-62 appears to be PC, as the results obtained with ES-62 are broadly mimicked by PC conjugated to BSA or PC alone. Although PC can also be shown to desensitize B cells following in-vivo administration, not all cells are affected, as it is still possible to generate an antibody response. Dissection of this response indicates that it is of the Th2 type.

Molecular cloning and demonstration of an aminopeptidase activity in a filarial nematode glycoprotein

ES-62 is an abundant phosphorylcholine-containing secreted glycoprotein of the filarial nematode Acanthocheilonema viteae. Using an antiserum directed against the parasite molecule, 3 cDNAs of size, approximately 1.5-1.6 kbp were isolated from an A. viteae expression library. Sequence analysis in combination with N-terminal amino acid sequencing of purified ES-62 revealed that each clone contained a full-length cDNA for ES-62 corresponding to 474 amino acid residues but differed in their 5' and 3' untranslated regions. Characterisation of the 5' end of ES-62 mRNA using 5' rapid amplification of cDNA ends showed that it coded for a signal sequence. Several tryptic peptides were independently sequenced using quadruple-time-of-flight mass spectrometry and used to confirm the cDNA sequence. The mature protein was found to contain three potential N-linked glycosylation sites. Comparison of the derived amino acid sequence of ES-62 with the SwissProt database identified a sequence (between amino acid residues approximately 250 and 350 of mature ES-62) with significant similarity to several bacterial/fungal aminopeptidases. Incubation of ES-62 with leucine-7-amino-4-methylcoumarin as substrate confirmed that ES-62 possessed aminopeptidase activity.

Structural studies of N-glycans of filarial parasites. Conservation of phosphorylcholine-substituted glycans among species and discovery of novel chito-oligomers

N-Type glycans containing phosphorylcholine (PC-glycans), unusual structures found in the important human pathogens filarial nematodes, represent a novel target for chemotherapy. Previous work in our laboratories produced compositional information on the PC-glycan of ES-62, a secreted protein of the rodent parasite Acanthocheilonema viteae. In particular, we established using fast atom bombardment mass spectrometry (MS) analysis that PC was attached to a glycan with a trimannosyl core, with and without core fucosylation, carrying between one and four additional N-acetylglucosamine residues. In the present study, we demonstrate that this structure is conserved among filarial nematodes, including the parasite of humans, Onchocerca volvulus, for which new drugs are most urgently sought. Furthermore, by employing a variety of procedures, including collision-activated dissociation MS-MS analysis and matrix-assisted laser desorption MS analysis, we reveal that surprisingly, filarial nematodes also contain N-linked glycans, the antennae of which are composed of chito-oligomers. To our knowledge, this is the first report of such structures in a eukaryotic glycoprotein.

Phosphorylcholine: friend or foe of the immune system?

Phosphorylcholine (PC) is a structural component of a variety of prokaryotic and eukaryotic pathogens. In some cases, PC in infectious agents can benefit the infected host due to its targeting by both the innate and adaptive immune responses. However, as discussed here, PC exhibits a surprising range of immunomodulatory properties that might be to the detriment of the host.

Induction of signalling anergy via the T-cell receptor in cultured Jurkat T cells by pre-exposure to a filarial nematode secreted product

Filarial nematodes constitute major causes of morbidity in the Tropics. The worms have a life-span exceeding five years, a longevity which is considered to reflect at least in part, their ability to interfere with host lymphocyte responsiveness. To date the molecular mechanisms underlying this ability have not been defined but we now demonstrate that ES-62, a phosphorylcholine (PC)-containing glycoprotein released by the rodent filarial parasite Acanthocheilonema viteae, is able to render Jurkat T cells anergic to intracellular signalling via the antigen receptor (TCR). In particular, ES-62 acts by modulating activation of the tyrosine kinases Fyn, Lck and ZAP-70 leading to selective disruption of TCR coupling to the phospholipase D, protein kinase C, phosphoinositide-3-kinase and RasMAPkinase signalling cascades. These cascades are key elements in the transduction of transcriptional and proliferative signals following ligation of TCR. As PC-containing secreted products (PC-ES) are also released by human filarial parasites, our data suggest that PC-ES may play a role in the induction of T lymphocyte hyporesponsiveness observed during filarial infections.

A Phosphorylcholine-Containing Filarial Nematode-Secreted Product Disrupts B Lymphocyte Activation by Targeting Key Proliferative Signaling Pathways

Filarial nematodes infect more than 100 million people in the tropics, causing elephantiasis, chronic skin lesions, and blindness. The parasites are long-lived as a consequence of being able to evade the host immune system, but an understanding of the molecular mechanisms underlying this evasion remains elusive. In this study, we demonstrate that ES-62 (2 μg/ml), a phosphorylcholine (PC)-containing glycoprotein released by the rodent filarial parasite Acanthocheilonema viteae, is able to polyclonally activate certain protein tyrosine kinase and mitogen-activating protein kinase signal-transduction elements in B lymphocytes. Although this interaction is insufficient to cause B lymphocyte proliferation per se, it serves to desensitize the cells to subsequent activation of the phosphoinositide-3-kinase and Ras mitogen-activating protein kinase pathways, and hence also to proliferation, via the Ag receptor. The active component of ES-62 appears to be PC, a molecule recently shown to act as an intracellular signal transducer, as the results obtained with ES-62 are broadly mimicked by PC alone. As PC-containing secreted products (PC-ES) are also released by human filarial parasites, our data suggest that PC-ES, by interfering with B cell function, could play a role in prolonging filarial infection in parasitized individuals.

Characterisation of the phosphorylcholine-containing N-linked oligosaccharides in the excretory-secretory 62 kDa glycoprotein of Acanthocheilonema viteae

The major excretory-secretory product of the rodent filarial nematode Acanthocheilonema viteae is a 62 kDa glycoprotein (ES-62), which has phosphorylcholine, attached to the N-linked carbohydrates. In this paper, we describe structural studies of N-glycans released from ES-62 by peptide N-glycosidase F. Three major classes of N-glycan structures were observed: high mannose type structures; those which had been fully trimmed to the trimannosyl core and were sub-stoichiometrically fucosylated; and those with a trimannosyl core, with and without core fucosylation, carrying between one and four additional N-acetylglucosamine resides. Of the three classes of glycans, only the last was found to be substituted with detectable levels of phosphorylcholine. The implications of these results with respect to the probable glycosylation pathways operating in A. viteae are discussed.

Studies on the site and mechanism of attachment of phosphorylcholine to a filarial nematode secreted glycoprotein

We have recently shown that the immunomodulatory substance phosphorylcholine (PC) is covalently attached to ES-62, a major secreted protein of the filarial nematode parasite Acanthocheilonema viteae, via an N-linked glycan. Linkage of PC to N-glycans is previously unreported, and hence we have investigated the biochemical events underlying it. PC addition was found by pulse-chase experiments to be a fairly early event during intracellular transport, occurring within 40-60 min of protein synthesis. Biosynthetic labeling/immunoprecipitation experiments revealed that addition of PC to ES-62 was blocked by (i) brefeldin A, an inhibitor of trafficking of newly synthesized proteins from the endoplasmic reticulum (ER) to the Golgi, (ii) 1-deoxynorijirimycin, an inhibitor of glucosidase activity in the ER, and (iii) 1-deoxymannojirimycin, an inhibitor of mannosidase I in the cis Golgi. Swainsonine, an inhibitor of mannosidase II in the medial Golgi, did not affect PC addition. Taken together these data indicate that PC attachment is a post-ER event which is dependent on generation of an appropriate substrate during oligosaccharide processing. Furthermore, they strongly suggest that PC addition takes place in the medial Golgi and that the substrate for addition is the 3-linked branch of Man5GlcNAc3 or Man3GLcNAc3.

Antigens with application toward immune control of blood-feeding parasitic nematodes

This review considers progress toward immune control of nematode parasites that feed on mammalian host blood. Approaches to identify relevant parasite antigens include use of irradiated larvae, somatic antigens, metabolites, enzymes and gut antigens. Because significant immune protection has more recently been achieved using gut antigens of the blood-feeding parasite Haemonchus contortus, these antigens are considered in greater detail. Issues discussed are implications of gut antigens in immune control, potential mechanisms involved in this immunity, biochemical characteristics of gut antigens and potential application of gut antigens to immune control of other blood-feeding nematodes.

Trichinella spiralis: light microscope monoclonal antibody localization and immunochemical characterization of phosphorylcholine and other antigens in the muscle larva

A panel of monoclonal antibodies was used to examine the structure of the muscle larva of Trichinella spiralis under the light microscope. Immunofluorescence and, in some cases, immunoperoxidase staining were used. All four antibodies reacted with the cuticle of the organism, although differences in the staining pattern were observed for some of these. Interestingly, all the antibodies also reacted with the stichosome. One of the antibodies (Ts2Ab) is specific for the hapten, phosphorylcholine. In a binding assay, this antibody also reacted with extracts of Trichuris suis, Ascaris suum, and Fasciolopsis buski, but not with extracts derived from Cysticercus cellulosae, Candida albicans, Salmonella typhi, or Escherichia coli. This crossreactivity was confirmed microscopically in which the cuticle, oviduct and eggs of T. suis, the cuticle, muscle cells, and eggs of A. suum, and the cuticle and vitelline glands of F. buski were seen to be clearly stained by the antibody. In addition, Ts2Ab also reacted with the cuticle and stichosome of the adult T. spiralis worm. In Western blot analysis, Ts2Ab recognized a 43-kDa antigen from T. spiralis muscle larvae extracts, while a previously studied antibody (7C2C5Ab) identified four major antigens (48.5, 47, 43, and 39 kDa) in this preparation. Similar results were obtained when the 24-hr excretory-secretory (ES) antigens of T. spiralis were immunoblotted with the antibodies, although the reactivity shown by Ts2Ab was relatively weak. With the 72-hr ES material, on the other hand, major antigens of lower mol wt (44, 28, and 25 kDa) were revealed by 7C2C5Ab, and no reactivity was seen with Ts2Ab. However, this antigen preparation reacted well with both antibodies in an enzyme-linked immunoassay. Taken together, the findings suggest that the 72-hr ES antigens probably result from extensive degradation of material originally secreted or excreted by the worm. Similar binding studies on the 24-hr ES preparation indicated that this source may be relatively rich in 7C2C5Ab-reactive epitopes and relatively poor in the antigen identified by Ts2Ab. Other studies performed demonstrated that the antigens recognized by these two antibodies were distinct and physically unassociated.

Association between circulating antigen and parasite load in a model filarial system, Acanthocheilonema viteae in jirds

Jirds (Meriones libycus) were infected with various numbers of Acanthocheilonema viteae L3 stage parasites. During the course of the ensuing 16 weeks, blood samples were collected at 2 weekly intervals and the amount of the major parasite excretory-secretory product (E-S 62) and antibodies directed against it measured. After 16 weeks, animals were sacrificed and the size of the mature worm burden established. In spite of interaction between E-S 62 and host antibody, a statistically significant relationship was found to exist between the amount of E-S 62 present in the bloodstream and the size of the parasite load. It is suggested that the detectable antigen level is more influenced by the size of the worm burden than the presence of antibody and that antibody is only likely to affect adversely antigen measurement in situations where the amount released is relatively low. Examples of this are early in infection and in low-level infections. These ideas are discussed in relation to the development and assessment of serological assays which attempt to predict parasite burden in human filarial infections.