Immunological genomics of Brugia malayi: filarial genes implicated in immune evasion and protective immunity

Dose-Dependent Prophylactic Efficacy of Filarial Antigens Glutathione-S-Transferase and Abundant Larval Transcript-2 against Brugia malayi Challenge in Mastomys

Objective

To identify the most effective dose of filarial rBmALT-2 and rWbGST alone or in combination against B. malayi infection in vitro and in vivo.

Methods

Mastomys (n = 5-7/group) received intramuscular (i.m.) injection with three different doses (25, 50, and 100 μg) of rBmALT-2 or rWbGST, either alone or in combination with alum as the adjuvant. Protective immunity was studied by in vivo and in vitro cytotoxicity assay. To evaluate the cellular immune response, splenocyte proliferation and cytokine profile were assessed.

Results

Serological results revealed a substantial (p < 0.005) induction of IgG1, IgG2a, and IgG3 responses in vaccinated Mastomys. Mastomys immunized with 50 μg rBmALT-2 + alum induced 79-81% killing against the L3 larvae challenge in vivo and in vitro ADCC assay (p < 0.005); whereas rWbGST + alum alone or in combination with rBmALT-2 + alum induced 63-68% killing (p < 0.005) in vivo and in vitro. Antigen-specific cytokine profiles of Mastomys vaccinated with either BmALT-2, WbGST or a combination showed elevated IL-10, IL-4, and IFN-γ levels, signifying both Th1 and Th2 immune response.

Conclusions

These findings suggest that immunization of Mastomys with a 50 μg/dose of rBmALT-2 + alum four times at a 4-week interval demonstrated considerable protection against B. malayi infection.

Nematode Orthologs of Macrophage Migration Inhibitory Factor (MIF) as Modulators of the Host Immune Response and Potential Therapeutic Targets

One of the adaptations of nematodes, which allows long-term survival in the host, is the production of proteins with immunomodulatory properties. The parasites secrete numerous homologs of human immune mediators, such as macrophage migration inhibitory factor (MIF), which is a substantial regulator of the inflammatory immune response. Homologs of mammalian MIF have been recognized in many species of nematode parasites, but their role has not been fully understood. The application of molecular biology and genetic engineering methods, including the production of recombinant proteins, has enabled better characterization of their structure and properties. This review provides insight into the current state of knowledge on MIF homologs produced by nematodes, as well as their structure, enzymatic activity, tissue expression pattern, impact on the host immune system, and potential use in the treatment of parasitic, inflammatory, and autoimmune diseases.

Genome editing as control tool for filarial infections

Human filarial infections are vector-borne nematode infections, which include lymphatic filariasis, onchocerciasis, loiasis, and mansonella filariasis. With a high prevalence in developing countries, filarial infections are responsible for some of the most debilitating morbidities and a vicious cycle of poverty and disease. Global initiatives set to eradicate these infections include community mass treatments, vector control, provision of care for morbidity, and search for vaccines. However, there are growing challenges associated with mass treatments, vector control, and antifilarial vaccine development. With the emergence of genome editing tools and successful applications in other infectious diseases, the integration of genetic editing techniques in future control strategies for filarial infections would offer the best option for eliminating filarial infections. In this review, we briefly discuss the mechanisms of the three main genetic editing techniques and explore the potential applications of these powerful tools to control filarial infections.

A rapid, parasite-dependent cellular response to Dirofilaria immitis in the Mongolian jird (Meriones unguiculatus)

BACKGROUND

The Mongolian jird (Meriones unguiculatus) has long been recognized as a permissive host for the filarial parasite Brugia malayi; however, it is nonpermissive to another filarial parasite, canine heartworm (Dirofilaria immitis). By elucidating differences in the early response to infection, we sought to identify mechanisms involved in the species-specific clearance of these parasites. We hypothesized that the early clearance of D. immitis in intraperitoneal infection of the jird is immune mediated and parasite species dependent.

METHODS

Jird peritoneal exudate cells (PECs) were isolated and their attachment to parasite larvae assessed in vitro under various conditions: D. immitis and B. malayi cultured separately, co-culture of both parasites, incubation before addition of cells, culture of heat-killed parasites, and culture with PECs isolated from jirds with mature B. malayi infection. The cells attaching to larvae were identified by immunohistochemistry.

RESULTS

In vitro cell attachment to live D. immitis was high (mean = 99.6%) while much lower for B. malayi (mean = 5.56%). This species-specific attachment was also observed when both filarial species were co-cultured, with no significant change from controls (U_{(9, 14)} = 58.5, p = 0.999). When we replicated these experiments with PECs derived from jirds subcutaneously infected with B. malayi, the results were similar (99.4% and 4.72% of D. immitis and B. malayi, respectively, exhibited cell attachment). Heat-killing the parasites significantly reduced cell attachment to D. immitis (mean = 71.9%; U_{(11, 14)} = 7.5, p < 0.001) while increasing attachment to B. malayi (mean = 16.7%; U_{(9, 15)} = 20, p = 0.002). Cell attachment to both species was reduced when larvae were allowed a 24-h pre-incubation period prior to the addition of cells. The attaching cells were identified as macrophages by immunohistochemistry.

CONCLUSIONS

These results suggest a strongly species-dependent response from which B. malayi could not confer protection by proxy in co-culture. The changes in cell attachment following heat-killing and pre-incubation suggest a role for excretory/secretory products in host immune evasion and/or antigenicity. The nature of this attachment is the subject of ongoing study and may provide insight into filarial host specificity.

Modulatory functions of recombinant electron transfer flavoprotein α subunit protein from Haemonchus contortus on goat immune cells in vitro

Suppression and modulation of the host immune response to parasitic nematodes have been extensively studied. In the present study, we cloned and produced recombinant electron transfer flavoprotein α subunit (ETFα) protein from Haemonchus contortus (rHCETFα), a parasitic nematode of small ruminants, and studied the effect of this protein on modulating the immune response of goat peripheral blood mononuclear cells (PBMCs) and monocytes. Immunohistochemical tests verified that the HCETFα protein was localized mainly in the intestinal wall and on the body surface of worms. Immunoblot analysis revealed that rHCETFα was recognized by the serum of goats artificially infected with H. contortus. Immunofluorescence analysis indicated that rHCETFα bound to the surface of PBMCs. rHCETFα was co-incubated with goat PBMCs to observe the immunomodulatory effects exerted by HCETFα on proliferation, apoptosis, cytokine secretion and nitric oxide (NO) production. The results showed that rHCETFα suppressed the proliferation of goat PBMCs stimulated by concanavalin A and induced apoptosis in goat PBMCs. After rHCETFα exposure, IL-2, IL-4, IL-17A and TNF-α expression was markedly reduced, whereas secretion of TGF-β1 was significantly elevated, in goat PBMCs. Moreover, rHCETFα up-regulated NO production in a dose-dependent manner. FITC-dextran internalization assays showed that rHCETFα inhibited phagocytosis of goat monocytes. These results elucidate the interaction between parasites and hosts at the molecular level, suggest a possible immunomodulatory target and contribute to the search for innovative proteins that may be candidate targets for drugs and vaccines.

Molecular cloning, expression and characterization of aspartyl protease inhibitor from Ancylostoma ceylanicum

Aspartyl protease inhibitors (APIs) from parasitic intestinal nematodes are highly immunogenic and have been suggested as potential vaccine antigens. Ac-API-1 from Ancylostoma caninum showed strong immunogenicity and its polyclonal antibodies could specifically recognize the excretory/secretory products of adult worms. However, little is known about molecular characteristics and biological function of API from Ancylostoma ceylanicum (Ace-API). In this study, the Ace-API mature peptide coding sequence was cloned and expressed, and molecular characteristics of its full length sequence were analyzed. Ace-API cDNA was 684 bp in length, which encoded 228 amino acids. The similarity of the Ace-API amino acid sequence to Ac-API-1 and Adu-API-1 was 96.93% and 96.49%, respectively, and they clustered together in the phylogenetic tree. Escheria coli-expressed recombinant protein was mainly soluble in the supernatant of bacterial cell lysate. Western blot showed that Ace-API protein had good reactivity to the serum of infected dogs. Pepsin inhibition assay revealed that the recombinant protein had inhibitory activity on pepsin. Immunofluorescence results demonstrated that Ace-API was mainly localized to the epidermis, excretory glands, and pseudocoelomic fluid of the adult. Using the quantitative real-time PCR, the expression of Ace-api mRNA in adults was significantly higher than that in the third stage (L3) larvae. Together, these data indicate that Ace-API is secreted extracellularly by the parasite, and might play a role in protecting the parasite against the proteolytic digestion by the host proteases, which stimulate further studies to explore this protein as a potential hookworm vaccine candidate.

Characterization of a rhodanese homologue from Haemonchus contortus and its immune-modulatory effects on goat immune cells in vitro

BACKGROUND

Modulation of the host immune response by nematode parasites has been widely reported. Rhodaneses (thiosulfate: cyanide sulfurtransferases) are present in a wide range of organisms, such as archaea, bacteria, fungi, plants and animals. Previously, it was reported that a rhodanese homologue could be bound by goat peripheral blood mononuclear cells (PBMCs) in vivo.

METHODS

In the present study, we cloned and produced a recombinant rhodanese protein originating from Haemonchus contortus (rHCRD), a parasitic nematode of small ruminants. rHCRD was co-incubated with goat PBMCs to assess its immunomodulatory effects on proliferation, apoptosis and cytokine secretion.

RESULTS

We verified that the natural HCRD protein localized predominantly to the bowel wall and body surface of the parasite. We further demonstrated that serum produced by goats artificially infected with H. contortus successfully recognized rHCRD, which bound to goat PBMCs. rHCRD suppressed proliferation of goat PBMCs stimulated by concanavalin A but did not induce apoptosis in goat PBMCs. The production of TNF-α and IFN-γ decreased significantly, whereas secretion of IL-10 and TGF-β1 increased, in goat PBMCs after exposure to rHCRD. rHCRD also inhibited phagocytosis by goat monocytes. Moreover, rHCRD downregulated the expression of major histocompatibility complex (MHC)-II on goat monocytes in a dose-dependent manner, but did not alter MHC-I expression.

CONCLUSIONS

These results propose a possible immunomodulatory target that may help illuminate the interactions between parasites and their hosts at the molecular level and reveal innovative protein species as candidate drug and vaccine targets.

Characterization of a phosphotyrosyl phosphatase activator homologue of the parasitic nematode Haemonchus contortus and its immunomodulatory effect on goat peripheral blood mononuclear cells in vitro

Suppression and modulation of the host immune response to parasitic nematodes have been extensively studied. In the present study, we cloned and produced recombinant phosphotyrosyl phosphatase activator protein from Haemonchus contortus (rHCPTPA), a parasitic nematode of small ruminants, and studied the effect of this protein on modulating the immune response of goat peripheral blood mononuclear cells. Enzymatic assays revealed that rHCPTPA enhanced the p-nitrophenylphosphate phosphatase activity of bovine PP2A₁. Immunohistochemical tests verified that the HCPTPA protein was localised mainly in the bowel wall and on the body surface of worms. It was also shown that serum produced by goats artificially infected with H. contortus successfully recognised rHCPTPA, which conjugated with goat peripheral blood mononuclear cells. The rHCPTPA was then co-incubated with goat peripheral blood mononuclear cells to assess its immunomodulatory effects on proliferation, apoptosis, cytokine secretion, migration and nitric oxide production. Our results showed that rHCPTPA suppressed the proliferation of goat peripheral blood mononuclear cells stimulated by concanavalin A and induced apoptosis in goat peripheral blood mononuclear cells. After rHCPTPA exposure, IFN-γ and IL-2 expression was markedly reduced, whereas secretion of IL-10 and IL-4 was significantly elevated, in goat peripheral blood mononuclear cells. Moreover, rHCPTPA down-regulated nitric oxide production and migration of goat peripheral blood mononuclear cells in a dose-dependent manner. These results illuminate the interaction between parasites and hosts at the molecular level, suggest a possible immunomodulatory target and contribute to the search for innovative proteins that might be candidate targets for drugs and vaccines.

De novo transcriptome assembly of a facultative parasitic nematode Pelodera (syn. Rhabditis) strongyloides

Pelodera strongyloides is a generally free-living gonochoristic facultative nematode. The whole genomic sequence of P. strongyloides remains unknown but 4 small subunit ribosomal RNA (ssrRNA) gene sequences are available. This project launched a de novo transcriptome assembly with 100 bp paired-end RNA-seq reads from normal, starved and wet-plate cultured animals. Trinity assembly tool generated 104,634 transcript contigs with N50 contig being 2195 bp and average contig length at 1103 bp. Transcriptome BLASTX matching results of five nematodes (C. elegans, Strongyloides stercoralis, Necator americanus, Trichuris trichiura, and Pristionchus pacificus) were consistent with their evolutionary relationships. Sixteen genes were identified to be homologous to key elements of the C. elegans RNA interference system, such as Dicer, Argonaute, RNA-dependent RNA polymerase and double strand RNA transport proteins. In starved samples, we observed up-regulation of cuticle related genes and 3 dauer formation genes. Dauer morphology was captured with enlarged phasmid under light microscopy, and dauer and normal larvae counts in clumps had a Pearson's product-moment correlation of 0.805 with P-value = 0.0088. Our results demonstrate that P. strongyloides could be used for studying nematode-related human or pet parasitic diseases. The sequenced assembled transcriptome reported here may be useful to understand the evolution of parasitism in Nematoda.

Molecular Characterization of a Dirofilaria immitis Cysteine Protease Inhibitor (Cystatin) and Its Possible Role in Filarial Immune Evasion

Infection with canine heartworm (Dirofilaria immitis), spread via mosquito vectors, causes coughing, asthma, pneumonia, and bronchitis in humans and other animals. The disease is especially severe and often fatal in dogs and represents a serious threat to public health worldwide. Cysteine protease inhibitors (CPIs), also known as cystatins, are major immunomodulators of the host immune response during nematode infections. Herein, we cloned and expressed the cystatin Di-CPI from D. immitis. Sequence analysis revealed two specific cystatin-like domains, a Q-x-V-x-G motif, and a SND motif. Phylogenetic analysis indicates that Di-CPI is a member of the second subgroup of nematode type II cystatins. Probing of D. immitis total proteins with anti-rDi-CPI polyclonal antibody revealed a weak signal, and immunofluorescence-based histochemical analysis showed that native Di-CPI is mainly localized in the cuticle of male and female worms and the gut of male worms. Treatment of canine peripheral blood mononuclear cells (PMBCs) with recombinant Di-CPI induced a Th2-type immune response characterized by high expression of the anti-inflammatory factor interleukin-10. Proliferation assays showed that Di-CPI inhibits the proliferation of canine PMBCs by 15%. Together, the results indicate that Di-CPI might be related to cellular hyporesponsiveness in dirofilariasis and may help D. immitis to evade the host immune system.

Helminth community and host dynamics in northern bobwhites from the Rolling Plains Ecoregion, U.S.A

One hundred and sixty-one northern bobwhites (Colinus virginianus; hereafter 'bobwhite') were examined from the Rolling Plains ecoregion of Texas and western Oklahoma from 2011 to 2013. Complete necropsies yielded 13 species, of which two are new host (Gongylonema phasianella) and region (Eucoleus contortus) records and three (Dispharynx nasuta, Tetrameres pattersoni and Oxyspirura petrowi) are known to cause morbidity and mortality. Of the species found, Aulonocephalus pennula commonly occurred, Oxyspirura petrowi was intermediate in prevalence, and the remaining species were rare. Species richness was similar compared to studies from the southeastern U.S., but higher than studies from the same region. In addition, 12 of the 13 species were heteroxenous helminths, supporting the theory that heteroxenous helminths in semi-arid regions are more successful than monoxenous helminths. Prevalence and abundance of A. pennula and O. petrowi were higher in adult bobwhites than in juveniles. Abundance of A. pennula and O. petrowi was higher at southern locations compared to northern locations in the study area. Our study is the first to provide a current assessment of the bobwhite helminth community across the Rolling Plains ecoregion of the U.S.

Characterization of a secreted macrophage migration inhibitory factor homologue of the parasitic nematode Haemonchus Contortus acting at the parasite-host cell interface

Modulation and suppression of the immune response of the host by nematode parasites have been reported extensively and the migration inhibitory factor (MIF) is identified as one of the major immunomodulator. In the present study, we cloned and produced recombinant MIF protein from the small ruminant’s nematode parasite Haemonchus contortus (rHCMIF-1), and investigated its immunomodulatory effects on goat monocyte. Enzymatic assays indicated that rHCMIF-1 possessed tautomerase activity. Immunohistochemical test demonstrated that the native HCMIF-1 protein was predominantly localized at the body surface and internal surface of the worm’s gut. We demonstrated that rHCMIF-1 could be distinguished by antisera from goats experimentally infected with H. contortus and could bind by goat monocytes. The immunomodulatory effects of HCMIF-1 on cytokine secretion, MHC molecule expression, NO production and phagocytosis were observed by co-incubation of rHCMIF-1 with goat monocytes. The results showed that the interaction of rHCMIF-1 decreased the production of TNF-α, IL-1β and IL-12p40, where as, it significantly increased the secretion of IL-10 and TGF β in goat monocytes. After rHCMIF-1 exposure, the expression of MHC-II on goat monocytes was inhibited. Moreover, rHCMIF-1 could down-regulate the LPS induced NO production of goat monocytes. Phagocytotic assay by FITC-dextran internalization showed that rHCMIF-1 could inhibit the phagocytosis of goat monocytes. Our findings provided potential targetas immunoregulator, and will be helpful to elucidate the molecular basis of host–parasite interactions and search for new potential protein as vaccine and drug target candidate.

Immunoprophylaxis of multi-antigen peptide (MAP) vaccine for human lymphatic filariasis

Human lymphatic filariasis, the parasitic disease caused by the filarial nematodes Wuchereria bancrofti, Brugia malayi, and Brugia timori, is ranked as the second most complex clinical condition leading to permanent and long-term disability. The multiple antigen peptide (MAP) approach is an effective method to chemically synthesize and deliver multiple T and B cell epitopes as the constituents of a single immunogen. Here, we report on the design, chemical synthesis, and immunoprophylaxis of three epitopes that have been identified from promising vaccine candidates reported in our previous studies, constructed as MAP on an inert lysine core for human lymphatic filariasis in Jird model. Two epitopes from Thioredoxin and one epitope from Transglutaminase were constructed as MAP in an inert lysine core. The immunoprophylaxis of the synthetic vaccine construct studied in Jird models showed protective antibody (1 in 64,000 titer) and cellular immune response. Thioredoxin-Transglutaminase MAP (TT MAP) conferred a significantly high protection of 63.04% compared to control (8.5%). Multi-antigen peptide vaccine is one best approach to provide immunity against multiple antigens delivered by the complex filarial parasite.

Ecological selection of siderophore-producing microbial taxa in response to heavy metal contamination

Some microbial public goods can provide both individual and community-wide benefits, and are open to exploitation by non-producing species. One such example is the production of metal-detoxifying siderophores. Here, we investigate whether conflicting selection pressures on siderophore production by heavy metals - a detoxifying effect of siderophores, and exploitation of this detoxifying effect - result in a net increase or decrease. We show that the proportion of siderophore-producing taxa increases along a natural heavy metal gradient. A causal link between metal contamination and siderophore production was subsequently demonstrated in a microcosm experiment in compost, in which we observed changes in community composition towards taxa that produce relatively more siderophores following copper contamination. We confirmed the selective benefit of siderophores by showing that taxa producing large amounts of siderophore suffered less growth inhibition in toxic copper. Our results suggest that ecological selection will favour siderophore-mediated decontamination, with important consequences for potential remediation strategies.

Characterization of a novel aspartyl protease inhibitor from Haemonchus contortus

Background

Aspartyl protease inhibitor (API) was thought to protect intestinal parasitic nematodes from their hostile proteolytic environment. Studies on Ostertagia ostertagi, Ascaris suum and Brugia malayi indicated that aspins might play roles in nematode infection. In a recent study, proteins differentially expressed between free-living third-stage larvae (L3) and activated L3 (xL3) of Haemonchus contortus were identified by 2D-DIGE. API was found downregulated in xL3 when compared with L3. However, there was no report about the functions of H. contortus API in the parasite-host interaction. In this study, the gene encoding API from H. contortus was cloned, expressed, and part of its biological characteristics were studied.

Results

A DNA fragment of 681 bp was amplified by RT-PCR. Ninety one percent of the amino acid sequence was similar with that for aspin from O. ostertagi. The recombinant API protein was fusion-expressed with a molecular weight of 48 × 10³. Results of Western blot showed that the recombinant API could be recognized by serum from goat infected with H. contortus. It was found that API was localized exclusively in the subcutaneous tissue and epithelial cells of the gastrointestinal tract in adult H. contortus. qRT-PCR suggested that the API gene was differentially transcribed in different life-cycle stages, with the lowest level in female adults and the highest in free-living L3 larvae. Enzyme inhibition assay indicated that the recombinant API can inhibit the activity of pepsin significantly, and the optimal reaction pH and temperature were 4.0 and 37–50 °C respectively. In vitro study showed that the recombinant API could induce goat PBMCs to express IFN-γ, IL-4 and IL-10.

Conclusions

A new aspartyl protease inhibitor was cloned from H. contortus and its characteristics were studied for the first time. The results indicate that API may regulate the immune response of the host and play roles in the infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2137-1) contains supplementary material, which is available to authorized users.

Parasitic Nematode Immunomodulatory Strategies: Recent Advances and Perspectives

More than half of the described species of the phylum Nematoda are considered parasitic, making them one of the most successful groups of parasites. Nematodes are capable of inhabiting a wide variety of niches. A vast array of vertebrate animals, insects, and plants are all identified as potential hosts for nematode parasitization. To invade these hosts successfully, parasitic nematodes must be able to protect themselves from the efficiency and potency of the host immune system. Innate immunity comprises the first wave of the host immune response, and in vertebrate animals it leads to the induction of the adaptive immune response. Nematodes have evolved elegant strategies that allow them to evade, suppress, or modulate host immune responses in order to persist and spread in the host. Nematode immunomodulation involves the secretion of molecules that are capable of suppressing various aspects of the host immune response in order to promote nematode invasion. Immunomodulatory mechanisms can be identified in parasitic nematodes infecting insects, plants, and mammals and vary greatly in the specific tactics by which the parasites modify the host immune response. Nematode-derived immunomodulatory effects have also been shown to affect, negatively or positively, the outcome of some concurrent diseases suffered by the host. Understanding nematode immunomodulatory actions will potentially reveal novel targets that will in turn lead to the development of effective means for the control of destructive nematode parasites.

Effect of muramyl dipeptide and alum adjuvants on immunization with Filarial multi antigen peptide vaccine in mice model

Filarial thioredoxin and transglutaminase are enzymes that are secreted throughout the lifecycle of the parasites which are mandatory for the survival of the parasite. They are reported to be promising vaccine candidates, yet the limitation factors of these proteins to be developed as vaccines is their homology they share with the host proteins. Hence immunodominant epitopes from these proteins were constructed as peptides and immunised in mice model with Muramyl dipeptide (MDP) as adjuvant. Immunodominant epitopic portions from Filarial thioredoxin and transglutaminase which are non-homologous with host proteins were constructed as Multi Antigen Peptide (MAP) and assembled in an inert lysine core. The synthesised MAP was immunised with MDP as adjuvant in Balb/c mice model, humoral and cellular immune response were studied. Antibody titre levels for TT MAP with MDP was in par with alum as adjuvant in mice models. T cell responses of TT MAP with MDP showed a balanced TH1/TH2 response. The TH1 cytokines namely IL-2 and IFN-ɤ were also higher in TT MAP immunised groups with MDP as adjuvant whereas alum immunised groups was TH2 biased. TT MAP admixed with MDP as adjuvant proves to be safe in mice model. Further vaccination studies are underway in permissive animal models to determine the role of TT MAP with MDP as adjuvant in protective immunity against W. bancrofti and B. malayi infections.

Identifying the immunomodulatory components of helminths

Immunomodulatory components of helminths offer great promise as an entirely new class of biologics for the treatment of inflammatory diseases. Here, we discuss the emerging themes in helminth-driven immunomodulation in the context of therapeutic drug discovery. We broadly define the approaches that are currently applied by researchers to identify these helminth molecules, highlighting key areas of potential exploitation that have been mostly neglected thus far, notably small molecules. Finally, we propose that the investigation of immunomodulatory compounds will enable the translation of current and future research efforts into potential treatments for autoimmune and allergic diseases, while at the same time yielding new insights into the molecular interface of host-parasite biology.

Identification and biochemical characterization of macrophage migration inhibitory factor-2 (MIF-2) homologue of human lymphatic filarial parasite, Wuchereria bancrofti

Homologues of human macrophage migration inhibitory factor (hMIF) have been reported from vertebrates, invertebrates and prokaryotes, as well as plants. Filarial parasites produce two homologues of hMIF viz., MIF-1 and MIF-2, which play important role in the host immune modulation. Earlier, we have characterized MIF-1 (Wba-mif-1) from Wuchereria bancrofti, the major causal organism of human lymphatic filariasis. Here, we are reporting the molecular and biochemical characterization of MIF-2 from this parasite (Wba-mif-2). The complete Wba-mif-2 gene and its cDNA were amplified, cloned and sequenced. The size of Wba-mif-2 gene and cDNA were found to be 4.275 kb and 363 bp, respectively. The gene annotation revealed the presence of a large intron of 3.912 kb interspersed with two exons of 183 bp and 180 bp. The alignment of derived amino acid sequences of Wba-MIF-2 with Wba-MIF-1 showed 44% homology. The conserved CXXC oxido-reductase catalytic site present in Wba-mif-1 was found absent in Wba-mif-2 coding sequence. The amplified Wba-mif-2 cDNA was cloned into an expression vector pRSET-B and transformed into salt inducible Escherichia coli strain GJ1158. The expressed recombinant Wba-MIF-2 protein showed tautomerase activity against L-dopachrome methyl ester and the specific activity was determined to be 18.57±0.77 μmol/mg/min. Three known inhibitors of hMIF tautomerase activity significantly inhibited the tautomerase activity of recombinant Wba-MIF-2. Although the conserved CXXC oxido-reductase motif is absent in Wba-mif-2, the recombinant protein showed significant oxido-reductase activity in the insulin reduction assay, possibly because of the presence of vicinal cysteine residues.

Immune responses of B. malayi thioredoxin (TRX) and venom allergen homologue (VAH) chimeric multiple antigen for lymphatic filariasis

Although multiple vaccine strategy for lymphatic filariasis has provided tremendous hope, the choice of antigens used in combination has determined its success in the previous studies. Multiple antigens comprising key vaccine candidates from different life cycle stages would provide a promising strategy if the antigenic combination is chosen by careful screening. In order to analyze one such combination, we have used a chimeric construct carrying the well studied B. malayi antigens thioredoxin (BmTRX) and venom allergen homologue (BmVAH) as a fusion protein (TV) and evaluated its immune responses in mice model. The efficacy of fusion protein vaccine was explored in comparison with the single antigen vaccines and their cocktail. In mice, TV induced significantly high antibody titer of 1,28,000 compared to cocktail vaccine TRX+VAH (50,000) and single antigen vaccine TRX (16,000) or VAH (50,000). Furthermore, TV elicited higher level of cellular proliferative response together with elevated levels of IFN-γ, IL-4 and IL-5 indicating a Th1/Th2 balanced response. The isotype antibody profile showed significantly high level of IgG1 and IgG2b confirming the balanced response elicited by TV. Immunization with TV antigen induced high levels of both humoral and cellular immune responses compared to either cocktail or antigen given alone. The result suggests that TV is highly immunogenic in mice and hence the combination needs to be evaluated for its prophylactic potential.

Nematode-derived proteins suppress proliferation and cytokine production of antigen-specific T cells via induction of cell death

In order to establish long-lasting infections in their mammalian host, filarial nematodes have developed sophisticated strategies to dampen their host’s immune response. Proteins that are actively secreted by the parasites have been shown to induce the expansion of regulatory T cells and to directly interfere with effector T cell function. Here, we analyze the suppressive capacity of Onchocercavolvulus-derived excreted/secreted proteins. Addition of two recombinant O. volvulus proteins, abundant larval transcript-2 (OvALT-2) and novel larval transcript-1 (OvNLT-1) to cell cultures of T cell receptor transgenic CD4⁺ and CD8⁺ T cells suppressed antigen-specific stimulation in vitro. Ovalbumin-specific CD4⁺ DO11.10 and OT-II T cells that had been stimulated with their cognate antigen in the presence of OvALT-2 or OvNLT-1 displayed reduced DNA synthesis quantified by ³H-thymidine incorporation and reduced cell division quantified by CFSE dilution. Furthermore, the IL-2 and IFN-γ response of ovalbumin-specific CD8⁺ OT-I T cells was suppressed by OvALT-2 and OvNLT-1. In contrast, another recombinant O. volvulus protein, microfilariae surface-associated antigen (Ov103), did not modulate T cell activation, thus serving as internal control for non-ESP-mediated artifacts. Suppressive capacity of the identified ESP was associated with induction of apoptosis in T cells demonstrated by increased exposure of phosphatidylserine on the plasma membrane. Of note, the digestion of recombinant proteins with proteinase K did not abolish the suppression of antigen-specific proliferation although the suppressive capacity of the identified excreted/secreted products was not mediated by low molecular weight contaminants in the undigested preparations. In summary, we identified two suppressive excreted/secreted products from O. volvulus, which interfere with the function of antigen-specific T cells in vitro.

Multiplex proteomics analysis of gender-associated proteins in Brugia malayi

Gender-associated (GA) genes are important for the development and reproduction of filarial nematodes. Identification and characterization of GA genes may provide insight into major pathways and processes involved in development and reproduction. The recent completion of the Brugia malayi genome has provided a good foundation for proteomics studies. Multiplex protein labelling and two-dimensional difference in-gel electrophoresis (2D-DIGE) combined with MALDI-TOF/TOF tandem MS were used to identify GA proteins. Thirty male and 32 female associated proteins were identified in this study. Many of these GA genes have homologues in Caenorhabditis elegans (83% male and 69% female), and most of the homologues have severe RNA interference (RNAi) phenotypes (72% male and 55% female) in C. elegans. Functional analysis showed that the male-associated genes are enriched for energy production, metabolic processes and cytoskeleton, while the female-associated genes are enriched for RNA modification and transcription. GA genes encode many excreted/secreted proteins. In situ localization studies showed that GA genes are mainly expressed in reproductive organs, and this is further evidence for their involvement in reproduction. Improved understanding of the basic biology of filarial nematodes may lead to improved tools for prevention and treatment of filarial infections. This study combined proteomics, in situ hybridization (ISH) and bioinformatics in a systems biology approach to improve understanding of gender differences and key proteins involved in reproduction in filarial worms. Advanced proteomics methods and bioinformatics led to the identification of 62 GA proteins for B. malayi. ISH revealed that most of those GA genes are expressed during embryogenesis or spermatogenesis. ISH results were consistent with RNAi data for C. elegans that linked the homologues of the B. malayi proteins to gamete production and embryogenesis.

The adjuvant-free immunoprotection of recombinant filarial protein Abundant Larval Transcript-2 (ALT-2) in Mastomys coucha and the immunoprophylactic importance of its putative signal sequence

The filarial protein Abundant Larval Transcript-2 (ALT-2) of the filarial parasite Brugia malayi has been shown to produce 74% worm clearance when administered with an adjuvant. In the present study, we show that it not only induces humoral and cell-mediated immunity, but also protection up to 71% in Mastomys coucha, a permissive animal model for filariasis, even without adjuvant. This unique feature of ALT-2 protein is highly restricted to its 21 amino acid N-terminal signal sequence, the absence of which resulted in poor immune response as well as immunoprotection (49%). Moreover, ALT-2 is likely to exert immunoprotection effects in B. malayi infection by maintaining a Th1-Th2 balance, evident from higher levels of IgG1 and IgG2a as well as IL-4 and IFN-γ. An improved understanding about the role of this filarial protein in host immunity, host-parasite interaction and worm clearance will aid in the development of good immunoprophylaxis for the disease.

Stage-specific proteomic expression patterns of the human filarial parasite Brugia malayi and its endosymbiont Wolbachia

Global proteomic analyses of pathogens have thus far been limited to unicellular organisms (e.g., protozoa and bacteria). Proteomic analyses of most eukaryotic pathogens (e.g., helminths) have been restricted to specific organs, specific stages, or secretomes. We report here a large-scale proteomic characterization of almost all the major mammalian stages of Brugia malayi, a causative agent of lymphatic filariasis, resulting in the identification of more than 62% of the products predicted from the Bm draft genome. The analysis also yielded much of the proteome of Wolbachia, the obligate endosymbiont of Bm that also expressed proteins in a stage-specific manner. Of the 11,610 predicted Bm gene products, 7,103 were definitively identified from adult male, adult female, blood-borne and uterine microfilariae, and infective L3 larvae. Among the 4,956 gene products (42.5%) inferred from the genome as "hypothetical," the present study was able to confirm 2,336 (47.1%) as bona fide proteins. Analysis of protein families and domains coupled with stage-specific expression highlight the important pathways that benefit the parasite during its development in the host. Gene set enrichment analysis identified extracellular matrix proteins and those with immunologic effects as enriched in the microfilarial and L3 stages. Parasite sex- and stage-specific protein expression identified those pathways related to parasite differentiation and demonstrates stage-specific expression by the Bm endosymbiont Wolbachia as well.

Multivalent vaccine formulation with BmVAL-1 and BmALT-2 confer significant protection against challenge infections with Brugia malayi in mice and jirds

PURPOSE: Lymphatic filariasis, a mosquito-borne infection, affects 120 million people in 83 different countries. Mass drug administration is fully underway in several parts of the world to eradicate this infection by year 2020. Drugs alone are highly efficient treatments, but long-term sustainable prophylaxis requires an effective vaccine. No vaccines are available for humans and animals despite several potential candidate vaccine antigens having been identified. Brugia malayi vespid venom allergen homolog-like protein (BmVAL-1) and B. malayi abundant larval transcript (BmALT-2) are two of the most promising vaccine candidates. We evaluated various vaccination regimens consisting of DNA and protein antigens and evaluated the potential of monovalent and multivalent vaccine formulations in mice and jird animal models. METHODS: Mice and jirds were vaccinated with monovalent DNA preparations of BmVAL-1 or BmALT-2 in pVAX-1 vector or monovalent protein preparations of rBmVAL-1 and rBmALT-2 in alum using a homologous or heterologous prime boost approach. These vaccine regimens were then compared with a multivalent vaccine formulation consisting of DNA or hybrid protein formulation of the two antigens. Challenge experiments were performed with B. malayi L3 in mice and jirds to evaluate the degree of protection, and immunological parameters were determined in mice and humans to elucidate the characteristics of the protective immune responses. RESULTS: Vaccination with monovalent BmVAL-1 vaccine conferred 39% (DNA vaccine) to 54% (DNA prime and protein boost) protection in mice. A similar degree of protection was observed in jirds (50% to 52%). Monovalent BmALT-2 afforded 51% to 75% protection in mice and 58% to 79% protection in jirds. Our testing of a multivalent formulation of BmVAL-1 and BmALT-2, showed 57% to 82% protection in mice and 77% to 85% protection in jirds. A heterologous prime boost approach using the multivalent vaccine gave the highest degree of protection in both mice and jirds. Serological analysis in mice showed that BmVAL-1 vaccination induced an IgG1, IgG2a, and IgG3 antibody response, whereas BmALT-2 vaccination predominantly induced an IgG1 and IgG3 antibody response. Cytokine responses of antigen-responding cells in the spleen secreted predominantly IFN-γ and IL-5 in response to BmVAL-1, and IL-4, and IL-5 in response to BmALT-2. CONCLUSION: A multivalent vaccine formulation of BmVAL-1 and BmALT-2 given as a prime boost regimen gave significant protection against lymphatic filariasis caused by B. malayi in mice and jirds. Because putatively immune endemic normal subjects also carry protective antibodies against BmVAL-1 and BmALT-2, developing this multivalent formulation as a prophylactic vaccine against B. malayi for human and veterinary use has great potential.

Immune responses to recombinant Brugia malayi pepsin inhibitor homolog (Bm-33) in patients with human lymphatic filariaisis

Immune responses to recombinant Brugia malayi pepsin inhibitor homolog (rBm-33) were investigated in patients with human lymphatic filariasis (microfilaremics (MF) and chronic pathology (CP)) along with endemic normals (EN). Flow cytometric analysis (24 h) revealed CD4(+) T cell activation in patients (MF and CP) compared to normals (EN), with increased expression of CD69 and diminished levels of CD62L and CD127. This was associated with an elevated expression of CD154 but not CD28 and CTLA4 in CP patients. However, Bm-33-induced cytokine expression profile (IL-1β, IL-12, IL-8, IFN-γ, IL-10 and TGF-β) did not exhibit any significant difference between normals and patients at the same time point. Although CD4(+) T cell activation was observed initially in filarial patients (24 h), lymphoproliferation studies (96 h) suggested diminished proliferation compared to normals, indicating functional inactivation in the former upon prolonged antigen exposure. This indicates that rBm-33 induces an early T cell activation in MF and CP patients followed by a decreased lymphoproliferation that might contribute to immune suppression in these individuals.

The role of a Brugia malayi p38 MAP kinase ortholog (Bm-MPK1) in parasite anti-oxidative stress responses

Filariasis, caused by thread-like nematode worms, affects millions of individuals throughout the tropics and is a major cause of acute and chronic morbidity. Filarial nematodes effectively evade host immunological responses and are long lived within their hosts. Recently an emphasis has been placed on enzymatic and non-enzymatic anti-oxidant systems which counteract the generation of reactive oxygen species (ROS) by macrophages and granulocytes, a first line of defense against parasites. We have characterized an anti-oxidant pathway in the filarial parasite Brugia malayi related to the evolutionarily conserved human mitogen-activated p38 protein kinase and the Caenorhabditis elegans PMK-1 protein kinase stress pathways. We have expressed a recombinant p38/PMK-1 ortholog from B. malayi (Bm-MPK1) and have successfully activated the kinase with mammalian upstream kinases. In addition, we have demonstrated inhibition of Bm-MPK1 activity using a panel of known p38 inhibitors. Using the potent and highly selective allosteric p38 inhibitor, BIRB796, we have implicated Bm-MPK1 in a pathway which offers B. malayi protection from the effects of ROS. Our results, for the first time, describe a stress-activated protein kinase pathway within the filarial parasite B. malayi which plays a role in protecting the parasite from ROS. Inhibition of this pathway may have therapeutic benefit in treating filariasis by increasing the sensitivity of filarial parasites to ROS and other reactive intermediates.

Identification and characterization of nematode specific protective epitopes of Brugia malayi TRX towards development of synthetic vaccine construct for lymphatic filariasis

Although multi-epitope vaccines have been evaluated for various diseases, they have not yet been investigated for lymphatic filariasis. Here, we report for the first time identification of two immunodominant B epitopes (TRXP1 and TRXP2) from the antioxidant Brugia malayi thioredoxin by studying their immune responses in mice model and human subjects. TRXP1 was also found to harbor a T epitope recognized by human PBMCs and mice splenocytes. Further, the epitopic peptides were synthesized as a single peptide conjugate (PC1) and their prophylactic efficacy was tested in a murine model of filariasis with L3 larvae. PC1 conferred a significantly high protection (75.14%) (P < 0.0001) compared to control (3.7%) and recombinant TRX (63.03%) (P < 0.018) in experimental filariasis. Our results suggest that multi-epitope vaccines could be a promising strategy in the control of lymphatic filariasis.

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.

Exploring the immunology of parasitism--from surface antigens to the hygiene hypothesis

Helminth immunology is a field which has changed beyond recognition in the past 30 years, transformed not only by new technologies from cDNA cloning to flow cytometry, but also conceptually as our definition of host immune pathways has matured. The molecular revolution defined key nematode surface and secreted antigens, and identified candidate immunomodulators that are likely to underpin parasites' success in eluding immune attack. The immunological advances in defining cytokine networks, lymphocyte subsets and innate cell recognition have also made a huge impact on our understanding of helminth infections. Most recently, the ideas of regulatory immune cells, in particular the regulatory T cell, have again overturned older thinking, but also may explain immune hyporesponsiveness observed in chronic helminth diseases, as well as the link to reduced allergic reactions observed in human and animal infections. The review concludes with a forward look to where we may make future advances towards the final eradication of helminth diseases.

Identification of parasite-responsive cysteine proteases inManduca sexta

Parasites have evolved different virulence strategies to manipulate host physiological functions. The parasitoid waspCotesia congregatainduces developmental arrest and immune suppression of its Lepidopteran hostManduca sexta. In this interaction, a symbiotic virus (C. congregataBracovirus, CcBV) associated with the wasp is essential for parasitism success. The virus is injected into the host with wasp eggs and virus genes are expressed in host tissues. Among potential CcBV virulence genes, cystatins, which are tight binding inhibitors of C1A cysteine proteases, are suspected to play an important role in the interaction owing to their high level of expression. So far, however, potentialin vivotargets inM. sextaare unknown. Here, we characterized for the first time fourM. sextaC1A cysteine proteases corresponding to cathepsin L and cathepsin B and two different ‘26–29 kDa’ cysteine proteases (MsCath1 and MsCath2). Our analyses revealed that MsCath1 and MsCath2 are transcriptionally downregulated in the course of parasitism. Moreover, viral Cystatin1 and MsCath1 co-localize in the plasma following parasitism, strongly suggesting that they interact. We also show that parasitism induces a general increase of cysteine protease activity which is later controlled. The potential involvement of cysteine proteases in defense against parasitoids is discussed.

Brugia malayi excreted/secreted proteins at the host/parasite interface: stage- and gender-specific proteomic profiling

Relatively little is known about the filarial proteins that interact with the human host. Although the filarial genome has recently been completed, protein profiles have been limited to only a few recombinants or purified proteins of interest. Here, we describe a large-scale proteomic analysis using microcapillary reverse-phase liquid chromatography-tandem-mass spectrometry to identify the excretory-secretory (ES) products of the L3, L3 to L4 molting ES, adult male, adult female, and microfilarial stages of the filarial parasite Brugia malayi. The analysis of the ES products from adult male, adult female, microfilariae (Mf), L3, and molting L3 larvae identified 852 proteins. Annotation suggests that the functional and component distribution was very similar across each of the stages studied; however, the Mf contributed a higher proportion to the total number of identified proteins than the other stages. Of the 852 proteins identified in the ES, only 229 had previous confirmatory expressed sequence tags (ESTs) in the available databases. Moreover, this analysis was able to confirm the presence of 274 “hypothetical” proteins inferred from gene prediction algorithms applied to the B. malayi (Bm) genome. Not surprisingly, the majority (160/274) of these “hypothetical” proteins were predicted to be secreted by Signal IP and/or SecretomeP 2.0 analysis. Of major interest is the abundance of previously characterized immunomodulatory proteins such as ES-62 (leucyl aminopeptidase), MIF-1, SERPIN, glutathione peroxidase, and galectin in the ES of microfilariae (and Mf-containing adult females) compared to the adult males. In addition, searching the ES protein spectra against the Wolbachia database resulted in the identification of 90 Wolbachia-specific proteins, most of which were metabolic enzymes that have not been shown to be immunogenic. This proteomic analysis extends our knowledge of the ES and provides insight into the host–parasite interaction.

Human lymphatic filariasis caused by the nematode parasites Brugia malayi and Wuchereria bancrofti are a major cause of concern in tropical countries. Studies over several decades have identified various proteins of these parasites that have highlighted their role in host–parasite interactions and possible chemotherapeutic and prophylactic interventions. The availability of the parasite genome facilitates the identification of all of the proteins of the parasite that could interact with the host. In this study, we have attempted to identify the excretory-secretory proteins of the various stages of the parasite that could be maintained in vitro for a limited period utilizing a high-throughput proteomics approach. We observe and report that the parasites expend resources to secrete out various molecules that they utilize to evade the host immune system and modulate its responses. Further, this study also provides information on the predicted hypothetical proteins to be bonafide proteins and thus a catalogue of the excretory-secretory proteins towards a better understanding of the host–parasite interactions.

Characterization of immunosuppressive surface coat proteins from Steinernema glaseri that selectively kill blood cells in susceptible hosts

Surface coat proteins (SCPs) of entomopathogenic nematodes are implicated in the suppression/evasion of host immune responses, which is required for successful host colonization. Steinernema glaseri NC strain SCPs suppressed immune responses in oriental beetle larvae (Exomala orientalis), a susceptible host for S. glaseri, in a dosage-dependent manner, thus protecting Heterorhabditis bacteriophora from being killed in the same host. Melanization of H. bacteriophora decreased from 92+/-5% in the untreated check to 1+/-3% when protected by injection of 230ng of S. glaseri SCPs. As the SCPs dosage increased, freely moving H. bacteriophora increased from 3+/-4% in the untreated group to 57+/-15% with an SCPs dose of 940ng. At 2h and in the absence of SCPs, 8% and 11% of hemocytes of E. orientalis were stained by propidium iodide and Hoechst, respectively. When exposed to 300ng/microl SCPs, 70% and 96% were stained, respectively. At 6h, propidium iodide stained 37% and 92% of the hemocytes without and with SCPs, respectively. In contrast, more than 90% of the cells were stained by Hoechst with or without SCPs. As native proteins, two isolated S. glaseri SCPs had an immunosuppressive effect; they were each composed of 38kDa (PI=4.6) and 56kDa (PI=3.6) subunits. SCP peptides were sequenced using LC-MS/MS and the mass fingerprints obtained with MALDI-TOF-MS; there were no significant matches found in peptide databases, which suggests that the SCPs studied are novel proteins. Twelve cDNA sequences were derived based on short peptides and 7 of them had no significant match against the Caenorhabditis elegans protein database. One of the cDNA matched an unknown C. elegans protein and the remaining 4 cDNAs matched proteins of C. elegans and Brugia malayi.

The genome of Brugia malayi - all worms are not created equal

Filarial nematode parasites, the causative agents of elephantiasis and river blindness, undermine the livelihoods of over one hundred million people in the developing world. Recently, the Filarial Genome Project reported the draft sequence of the ~95 Mb genome of the human filarial parasite Brugia malayi - the first parasitic nematode genome to be sequenced. Comparative genome analysis with the prevailing model nematode Caenorhabditis elegans revealed similarities and differences in genome structure and organization that will prove useful as additional nematode genomes are completed. The Brugia genome provides the first opportunity to comprehensively compare the full gene repertoire of a free-living nematode species and one that has evolved as a human pathogen. The Brugia genome also provides an opportunity to gain insight into genetic basis for mutualism, as Brugia, like a majority of filarial species, harbors an endosybiotic bacterium (Wolbachia). The goal of this review is to provide an overview of the results of genomic analysis and how these observations provide new insights into the biology of filarial species.

Viral cystatin evolution and three-dimensional structure modelling: a case of directional selection acting on a viral protein involved in a host-parasitoid interaction

Background

In pathogens, certain genes encoding proteins that directly interact with host defences coevolve with their host and are subject to positive selection. In the lepidopteran host-wasp parasitoid system, one of the most original strategies developed by the wasps to defeat host defences is the injection of a symbiotic polydnavirus at the same time as the wasp eggs. The virus is essential for wasp parasitism success since viral gene expression alters the immune system and development of the host. As a wasp mutualist symbiont, the virus is expected to exhibit a reduction in genome complexity and evolve under wasp phyletic constraints. However, as a lepidopteran host pathogenic symbiont, the virus is likely undergoing strong selective pressures for the acquisition of new functions by gene acquisition or duplication. To understand the constraints imposed by this particular system on virus evolution, we studied a polydnavirus gene family encoding cyteine protease inhibitors of the cystatin superfamily.

Results

We show that cystatins are the first bracovirus genes proven to be subject to strong positive selection within a host-parasitoid system. A generated three-dimensional model of Cotesia congregata bracovirus cystatin 1 provides a powerful framework to position positively selected residues and reveal that they are concentrated in the vicinity of actives sites which interact with cysteine proteases directly. In addition, phylogenetic analyses reveal two different cystatin forms which evolved under different selective constraints and are characterized by independent adaptive duplication events.

Conclusion

Positive selection acts to maintain cystatin gene duplications and induces directional divergence presumably to ensure the presence of efficient and adapted cystatin forms. Directional selection has acted on key cystatin active sites, suggesting that cystatins coevolve with their host target. We can strongly suggest that cystatins constitute major virulence factors, as was already proposed in previous functional studies.

Effect of chemotherapeutic treatment on cytokine (IFN-gamma, IL-2, IL-4, IL-5, IL-10) gene transcription in response to specific antigens in Brugia malayi-infected Mastomys coucha

Cytokine (interferon (IFN)-gamma, interleukin (IL)-2, IL-4, IL-5, IL-10) gene transcription in response to filarial antigens was determined in peripheral blood mononuclear cells of Brugia malayi-infected Mastomys coucha in the course of untreated and chemotherapeutically abbreviated infections. Transcript levels in infected untreated animals suggest particular time courses for the various cytokines with ongoing parasite development and differing efficacies of female, male, microfilarial, and L3 antigens in inducing cytokine gene transcription. Gene transcription of both of Th1- and Th2-associated cytokines were initiated in the course of the infection in a manner that does not fit in a simple Th1-Th2 paradigm. IFN-gamma and IL-4 gene transcripts prevailed during prepatency. In case of the other cytokine genes considered in the study, transcription in general peaked around beginning of patency. During the phase of increasing microfilaremia (approximately 120-180 days p. i.) cytokine gene transcription was generally decreased. Later on, when the parasitemia had leveled off, except IFN-gamma, transcript levels often tended to increase. In chemotherapeutically treated animals, the outcome varied with the different efficacies of the drugs employed. The highly microfilaricidal cyclodepsipeptide BAY 44-4400 eliminated circulating microfilariae and partially sterilized adult worms without killing them. This kind of treatment hardly affected cytokine responses. In contrast, the therapy with Flubendazole, a selectively macrofilaricidal benzimidazole, and particularly the application of CGP 20376, a highly efficient microfilaricidal and macrofilaricidal benzthiazole, resulted in enhanced transcription of the Th1-associated IFN-gamma and IL-2 genes as well as of the Th2-associated IL-5 gene 2-3 months after treatment. IL-10 gene transcription seemed transiently increased after 1 month. There was no effect of any treatment on the IL-4 gene transcription.

Prophylactic evaluation of recombinant extracellular superoxide dismutase of Brugia malayi in jird model

The immunoscreening of Brugia malayi adult cDNA library with pooled endemic normal sera identified several seroreactive clones including, EC-SOD which contained a 612 bp insert and showed significant nucleotide and deduced amino acid sequence homologies with superoxide dismutase (SOD) of other nematode parasites. The SODs are known to play an important role in the protection of parasite against reactive oxygen species of the host. The coding region of the B. malayi EC-SOD (BmEC-SOD) was cloned and expressed in Escherichia coli followed by affinity purification on nickel agarose resin. Staining of native polyacrylamide gel for SOD activity of the expressed recombinant protein revealed that SOD activity inactivated by potassium cyanide and hydrogen peroxide but not by sodium azide, indicating presence of Cu/Zn-SOD. The rBm EC-SOD protein showed its activity over a broad range of pH.7.0-11.0. Further the immune protective activity of recombinant EC-SOD antigen was evaluated in susceptible host, jirds (gerbils) (Meriones unguiculatus) against B. malayi filarial infection. The immunized jirds showed 33.5% and 36% cytotoxicity against microfilariae and 42.8% and 45.5% cytotoxicity against infective larvae in in vitro antibody dependent cellular cytotoxicity (ADCC) assay and in in situ micropore chamber methods respectively. This study suggests that the rBm EC-SOD antigen could stimulate a partial protective immune response against microfilariae and infective larvae in experimental animals against filarial infection.

Expression of helminth genes in Leishmania: an experimental transfection system to test immunological function

Functional analysis of genes from parasitic helminths requires, at the present time, heterologous expression. We have adapted the well-characterized system of transfection in Leishmania protozoal parasites, as a means of analysing the effect of single filarial genes on the mammalian immune system. For example, testing the function of the Brugia malayi abundant larval transcript (ALT) gene-transfected Leishmania mexicana were found to be significantly more virulent in macrophages in vitro. The course of infection in vivo is also aggravated by expression of the ALT gene. Examples are also given of transgenes which reduced in vitro growth within macrophages, as well as others which exert no effect on the protozoal parasitism. Thus, Leishmania transfection provides a tractable system to analyse helminth gene function within the context of the host immune system.

A novel small heat shock protein 12.6 (HSP12.6) from Brugia malayi functions as a human IL-10 receptor binding protein

Phage display cDNA expression library of the third stage larvae (L3) of Brugia malayi was screened for identifying target(s) that bound to the human interleukin-10 receptor (huIL10R). This iterative screening identified an insert that showed significant homology to Caenorhabditis elegans HSP12.6. The gene was designated B. malayi HSP12.6 (BmHSP12.6) and has orthologues in several gastrointestinal nematode genome (Ancylostoma caninum, Ascaris lumbricoides and Ascaris suum) but the gene or gene product has not been studied further in these parasites. Structural analyses of BmHSP12.6 showed that it has a highly conserved alpha-crystallin central domain that is characteristic of other small heat shock proteins (HSPs). BmHSP12.6 has a short N-terminal domain and an unusually small C-terminal domain flanking the crystallin domain suggesting that this protein belongs to a novel class of small HSPs. BmHSP12.6 appears to be differentially transcribed with highest expression in the vertebrate stages of the parasite (L4, adult and mf) compared to its mosquito vector stage (L3). More importantly recombinant BmHSP12.6 bound to huIL10R in a dose dependent fashion and inhibited the binding of human IL-10 (huIL10) to huIL10R in vitro. rBmHSP12.6 also enhanced the growth and proliferation of MC/9 mast cells in vitro similar to huIL10. This study thus describes a novel small HSP from B. malayi that has the capacity to bind to huIL10R, block binding of huIL10 to huIL10R and function similar to huIL10.

Molecular basis of worm-induced immunomodulation

Long-term infection with parasitic worms is generally associated with an immunological phenotype that is Th2-like and anti-inflammatory. This phenotype is probably an unintentional consequence of molecular characteristics of worms (as free-living worms also express polarising molecules) in combination with deliberate attempts by the parasites, via molecular secretions, to modulate the phenotype. This review is concerned with the identity of immunomodulatory worm products, the receptors that they interact with and the signal transduction pathways that they activate. It hopes to indicate how knowledge of these factors can explain the changes in gene expression that result in the characteristic worm-induced immunological phenotype.

Brugia malayi: Effects of radiation and culture on gene expression in infective larvae

Third-stage infective larvae (L3i) of Brugia malayi are developmentally arrested in mosquitoes but must quickly adapt to a new environment when they enter mammalian hosts to initiate infections. These changes can be studied by in vitro culture of L3 (L3c) under conditions that permit molting of L3-L4. Irradiated L3 (L3ir) have stunted growth and limited lifespan in mammalian hosts, and they induce high levels of immunity to challenge infections in animal models. This study explored differences in gene expression in L3i, L3c and L3ir by expressed sequence tag EST generation and qRT-PCR. 2506 ESTs generated from cDNA libraries constructed from L3i, L3c and L3ir were grouped into 1309 gene clusters. Despite extensive prior sampling from B. malayi (>22,000 ESTs in dbEST), 73% of the L3 clusters described here are novel. Sixty-three percentage of the clusters have homology to proteins from other species including 187 specific to nematodes and 141 that have to date only been described in non-nematode species. The transcript levels of 62 candidates for up- or down-regulation in L3i, L3c and L3ir based on EST frequencies were evaluated by qRT-PCR. Twenty-eight were confirmed to have > or = 3-fold differences in expression. Genes coding for proteins believed to be involved in establishment of infection, host adaptation and targets of protective immunity were confirmed to have higher expression in L3i than in L3c. Some of the genes that were down-regulated in L3c were highly expressed in L3ir. This study provides an improved description of the adaptations that accompany the transition from L3i to L3c and the special ability of L3ir to induce protective immunity.

New perspectives on host-parasite interplay by comparative transcriptomic and proteomic analyses of Schistosoma japonicum

Schistosomiasis remains a serious public health problem with an estimated 200 million people infected in 76 countries. Here we isolated ~ 8,400 potential protein-encoding cDNA contigs from Schistosoma japonicum after sequencing circa 84,000 expressed sequence tags. In tandem, we undertook a high-throughput proteomics approach to characterize the protein expression profiles of a number of developmental stages (cercariae, hepatic schistosomula, female and male adults, eggs, and miracidia) and tissues at the host-parasite interface (eggshell and tegument) by interrogating the protein database deduced from the contigs. Comparative analysis of these transcriptomic and proteomic data, the latter including 3,260 proteins with putative identities, revealed differential expression of genes among the various developmental stages and sexes of S. japonicum and localization of putative secretory and membrane antigens, enzymes, and other gene products on the adult tegument and eggshell, many of which displayed genetic polymorphisms. Numerous S. japonicum genes exhibited high levels of identity with those of their mammalian hosts, whereas many others appeared to be conserved only across the genus Schistosoma or Phylum Platyhelminthes. These findings are expected to provide new insights into the pathophysiology of schistosomiasis and for the development of improved interventions for disease control and will facilitate a more fundamental understanding of schistosome biology, evolution, and the host-parasite interplay.

Schistosomiasis remains a major public health problem in the developing world. Schistosoma japonicum, the Oriental blood fluke, causes intestinal schistosomiasis in China and the Philippines. Knowledge of the genome and proteome of this worm should improve understanding of biomedical aspects of schistosomiasis. This study represents the first major attempt to characterize the majority of the expressed genes and proteins of a human blood fluke through rigorous, high-throughput genomic and proteomic methodologies. The findings of this study provide a unique resource of numerous schistosome genes and information on protein profiles of the different developmental stages of S. japonicum. Many of the newly discovered proteins are localized on the surface of the worm and its eggs, and they are likely to be involved in the pathogenesis of schistosomiasis. Furthermore, genetic variants found in many of these new genes likely reflect the ability of this important human pathogen to adapt and respond to environmental pressures and the capacity of the parasite to respond to anti-schistosomal therapies. Comparison of these S. japonicum genes with those from mammals and other organisms will facilitate advances in the understanding of blood fluke biology and evolution.

Identification and analysis of genes expressed in the adult filarial parasitic nematode Dirofilaria immitis

The heartworm Dirofilaria immitis is a filarial parasitic nematode infecting dogs and other mammals worldwide causing fatal complications. Here, we present the first large-scale survey of the adult heartworm transcriptome by generation and analysis of 4005 expressed sequence tags, identifying about 1800 genes and expanding the available sequence information for the parasite significantly. Brugia malayi genomic data offered the most valuable information to interpret heartworm genes, with about 70% of D. immitis genes showing significant similarities to the assembly. Comparative genomic analyses revealed both genes common to metazoans or nematodes and genes specific to filarial parasites that may relate to parasitism. Characterization of abundant transcripts suggested important roles for genes involved in energy generation and antioxidant defense in adults. In particular, we proposed that adult heartworm likely adopted an anaerobic electron transfer-based energy generation system distinct from the aerobic pathway utilized by its mammalian host, making it a promising target in developing next generation macrofilaricides and other treatments. Our survey provided novel insights into the D. immitis transcriptome and laid a foundation for further comparative studies on biology, parasitism and evolution within the phylum Nematoda.

Characterization of a Novel Filarial Serine Protease Inhibitor, Ov-SPI-1, from Onchocerca volvulus, with Potential Multifunctional Roles during Development of the Parasite

A novel filarial serine protease inhibitor (SPI) from the human parasitic nematode Onchocerca volvulus, Ov-SPI-1, was identified through the analysis of a molting third-stage larvae expressed sequence tag dataset. Subsequent analysis of the expressed sequence tag datasets of O. volvulus and other filariae identified four other members of this family. These proteins are related to the low molecular weight SPIs originally isolated from Ascaris suum where they are believed to protect the parasite from host intestinal proteases. The two Ov-spi transcripts are up-regulated in the molting larvae and adult stages of the development of the parasite. Recombinant Ov-SPI-1 is an active inhibitor of serine proteases, specifically elastase, chymotrypsin, and cathepsin G. Immunolocalization of the Ov-SPI proteins demonstrates that the endogenous proteins are localized to the basal layer of the cuticle of third-stage, molting third-stage, and fourth-stage larvae, the body channels and multivesicular bodies of third-stage larvae and the processed material found between the two cuticles during molting. In O. volvulus adult worms the Ov-SPI proteins are localized to the sperm and to eggshells surrounding the developing embryos. RNA interference targeting the Ov-spi genes resulted in the specific knockdown of the transcript levels of both Ov-spi-1 and Ov-spi-2, a loss of native proteins, and a significant reduction in both molting and viability of third-stage larvae. We suggest the Ov-SPI proteins play a vital role in nematode molting by controlling the activity of an endogenous serine protease(s). The localization data in adults also indicate that these inhibitors may be involved in other processes such as embryogenesis and spermatogenesis.

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.

A flow cytometry based method for studying embryogenesis and immune reactivity to embryogenic stages in filarial parasites

BACKGROUND

In the absence of intermediate animal hosts, the process of embryogenesis leading to fecundity of adult female filarial worms is very critical for persistence of these obligate parasites in human communities. Embryogenesis in adult female filarial parasites involves fertilization of eggs or oocytes by sperms and their subsequent development into motile microfilariae inside the uterine cavity of worms. Development of assays for monitoring embryogenesis in adult female worms is a critical requirement in filariasis research--filarial worms are known to harbour endosymbionts such as Wolbachia which play a significant role in fecundity. Tetracycline or doxycycline treatment of the infected hosts effectively eliminates the endosymbionts resulting in inhibition of embryogenesis in female worms. Currently, inhibition of embryogenesis in adult filarial worms can be monitored only by microscopic examination of in vitro harvested intrauterine stages.

METHODS

Adult female filarial worms of bovine filarial parasites, Setaria digitata were collected from the peritoneum of infected animals and intrauterine stages were harvested in culture medium and were analyzed for forward and side scatter by flowcytometry using a BD FACS Calibur. Different populations were gated, sorted and identified by phase microscopy. Binding of biotinylated lectins to intra uterine stages was monitored using FITC labeled Avidin and monitored by flow cytometry of gated populations. Similarly, binding of antibodies in human filarial sera to intrauterine stages was monitored using FITC labeled anti-human immunoglobulins.

RESULTS

The forward and side scatter for intrauterine stages delineated 3 distinct populations labeled as R1, R2 and R3. The three populations were sorted and identified to be a) fully stretched microfilariae, b) early and c) late developmental stages of eggs respectively. Lectins such as Wheat Germ agglutinin or Concanavalin-A were found to bind strongly to egg stages and less prominently to intra-uterine microfilariae. Similarly the binding of antibodies in filarial sera to the three intra-uterine stages could also be precisely quantified.

CONCLUSION

The manuscript reports a novel flow cytometry based method to monitor progression of embryogenesis in adult filarial worms. Apart from relative quantification of different intra uterine developmental stages, the assay allows quantitative binding of lectins and antibodies to each of the intrauterine stages. It may now be possible to quantify levels of antibodies in infected and immune hosts to monitor anti-fecundity immunity in filariasis--the assay can thus be used as a powerful tool for drug development and in immunological studies in human and experimental filariasis.