Proteins secreted by the parasitic nematode Nippostrongylus brasiliensis act as adjuvants for Th2 responses

Differentiation and Regulation of Bovine Th2 Cells In Vitro

Bovine Th2 cells have usually been characterized by IL4 mRNA expression, but it is unclear whether their IL4 protein expression corresponds to transcription. We found that grass-fed healthy beef cattle, which had been regularly exposed to parasites on the grass, had a low frequency of IL4+ Th2 cells during flow cytometry, similar to animals grown in feedlots. To assess the distribution of IL4+ CD4+ T cells across tissues, samples from the blood, spleen, abomasal (draining), and inguinal lymph nodes were examined, which revealed limited IL4 protein detection in the CD4+ T cells across the examined tissues. To determine if bovine CD4+ T cells may develop into Th2 cells, naïve cells were stimulated with anti-bovine CD3 under a Th2 differentiation kit in vitro. The cells produced primarily IFNγ proteins, with only a small fraction (<10%) co-expressing IL4 proteins. Quantitative PCR confirmed elevated IFNγ transcription but no significant change in IL4 transcription. Surprisingly, GATA3, the master regulator of IL4, was highest in naïve CD4+ T cells but was considerably reduced following differentiation. To determine if the differentiated cells were true Th2 cells, an unbiased proteomic assay was carried out. The assay identified 4212 proteins, 422 of which were differently expressed compared to those in naïve cells. Based on these differential proteins, Th2-related upstream components were predicted, including CD3, CD28, IL4, and IL33, demonstrating typical Th2 differentiation. To boost IL4 expression, T cell receptor (TCR) stimulation strength was reduced by lowering anti-CD3 concentrations. Consequently, weak TCR stimulation essentially abolished Th2 expansion and survival. In addition, extra recombinant bovine IL4 (rbIL4) was added during Th2 differentiation, but, despite enhanced expansion, the IL4 level remained unaltered. These findings suggest that, while bovine CD4+ T cells can respond to Th2 differentiation stimuli, the bovine IL4 pathway is not regulated in the same way as in mice and humans. Furthermore, Ostertagia ostertagi (OO) extract, a gastrointestinal nematode in cattle, inhibited signaling via CD3, CD28, IL4, and TLRs/MYD88, indicating that external pathogens can influence bovine Th2 differentiation. In conclusion, though bovine CD4+ T cells can respond to IL4-driven differentiation, IL4 expression is not a defining feature of differentiated bovine Th2 cells.

Microbial Components and Effector Molecules in T Helper Cell Differentiation and Function

The mammalian intestines harbor trillions of commensal microorganisms composed of thousands of species that are collectively called gut microbiota. Among the microbiota, bacteria are the predominant microorganism, with viruses, protozoa, and fungi (mycobiota) making up a relatively smaller population. The microbial communities play fundamental roles in the maturation and orchestration of the immune landscape in health and disease. Primarily, the gut microbiota modulates the immune system to maintain homeostasis and plays a crucial role in regulating the pathogenesis and pathophysiology of inflammatory, neuronal, and metabolic disorders. The microbiota modulates the host immune system through direct interactions with immune cells or indirect mechanisms such as producing short-chain acids and diverse metabolites. Numerous researchers have put extensive efforts into investigating the role of microbes in immune regulation, discovering novel immunomodulatory microbial species, identifying key effector molecules, and demonstrating how microbes and their key effector molecules mechanistically impact the host immune system. Consequently, recent studies suggest that several microbial species and their immunomodulatory molecules have therapeutic applicability in preclinical settings of multiple disorders. Nonetheless, it is still unclear why and how a handful of microorganisms and their key molecules affect the host immunity in diverse diseases. This review mainly discusses the role of microbes and their metabolites in T helper cell differentiation, immunomodulatory function, and their modes of action.

The IL-25-dependent tuft cell circuit driven by intestinal helminths requires macrophage migration inhibitory factor (MIF)

Macrophage migration inhibitory factor (MIF) is a key innate immune mediator with chemokine- and cytokine-like properties in the inflammatory pathway. While its actions on macrophages are well-studied, its effects on other cell types are less understood. Here we report that MIF is required for expansion of intestinal tuft cells during infection with the helminth Nippostrongylus brasiliensis. MIF-deficient mice show defective innate responses following infection, lacking intestinal epithelial tuft cell hyperplasia or upregulation of goblet cell RELMβ, and fail to expand eosinophil, type 2 innate lymphoid cell (ILC2) and macrophage (M2) populations. Similar effects were observed in MIF-sufficient wild-type mice given the MIF inhibitor 4-IPP. MIF had no direct effect on epithelial cells in organoid cultures, and MIF-deficient intestinal stem cells could generate tuft cells in vitro in the presence of type 2 cytokines. In vivo the lack of MIF could be fully compensated by administration of IL-25, restoring tuft cell differentiation and goblet cell expression of RELM-β, demonstrating its requirement upstream of the ILC2-tuft cell circuit. Both ILC2s and macrophages expressed the MIF receptor CXCR4, indicating that MIF may act as an essential co-factor on both cell types to activate responses to IL-25 in helminth infection.

Nematode ascarosides attenuate mammalian type 2 inflammatory responses

Animal proof-of-concept studies have shown that roundworms have a protective effect against immune-dysregulated disorders, but it has been difficult to study in human trials without individual nematode-derived molecules to develop and test. We discovered that ascarosides, molecules that are secreted by diverse nematodes, suppress asthma in a rodent model via modulation of expression of Il33, a key epithelial cytokine for induction of type 2 immunity, in addition to decreasing memory-type pathogenic Th2 cells and ILC2s and increasing the Il10-expressing subpopulation of interstitial macrophages in the lung. Thus, ascarosides suppress type 2 immune response by affecting both innate and adaptive immunity and could define a potent class of small molecule drugs to treat allergic airway diseases.

Mounting evidence suggests that nematode infection can protect against disorders of immune dysregulation. Administration of live parasites or their excretory/secretory (ES) products has shown therapeutic effects across a wide range of animal models for immune disorders, including asthma. Human clinical trials of live parasite ingestion for the treatment of immune disorders have produced promising results, yet concerns persist regarding the ingestion of pathogenic organisms and the immunogenicity of protein components. Despite extensive efforts to define the active components of ES products, no small molecules with immune regulatory activity have been identified from nematodes. Here we show that an evolutionarily conserved family of nematode pheromones called ascarosides strongly modulates the pulmonary immune response and reduces asthma severity in mice. Screening the inhibitory effects of ascarosides produced by animal-parasitic nematodes on the development of asthma in an ovalbumin (OVA) murine model, we found that administration of nanogram quantities of ascr#7 prevented the development of lung eosinophilia, goblet cell metaplasia, and airway hyperreactivity. Ascr#7 suppressed the production of IL-33 from lung epithelial cells and reduced the number of memory-type pathogenic Th2 cells and ILC2s in the lung, both key drivers of the pathology of asthma. Our findings suggest that the mammalian immune system recognizes ascarosides as an evolutionarily conserved molecular signature of parasitic nematodes. The identification of a nematode-produced small molecule underlying the well-documented immunomodulatory effects of ES products may enable the development of treatment strategies for allergic diseases.

Intestinal helminth infection transforms the CD4+ T cell composition of the skin

Intestinal helminth parasites can alter immune responses to vaccines, other infections, allergens and autoantigens, implying effects on host immune responses in distal barrier tissues. We herein show that the skin of C57BL/6 mice infected with the strictly intestinal nematode Heligmosomoides polygyrus contain higher numbers of CD4⁺ T cells compared to the skin of uninfected controls. Accumulated CD4⁺ T cells were H. polygyrus-specific T_H2 cells that skewed the skin CD4⁺ T cell composition towards a higher T_H2/T_H1 ratio which persisted after worm expulsion. Accumulation of T_H2 cells in the skin was associated with increased expression of the skin-homing chemokine receptors CCR4 and CCR10 on CD4⁺ T cells in the blood and mesenteric lymph nodes draining the infected intestine and was abolished by FTY720 treatment during infection, indicating gut-to-skin trafficking of cells. Remarkably, skin T_H2 accumulation was associated with impaired capacity to initiate IFN-γ recall responses and develop skin-resident memory cells to mycobacterial antigens, both during infection and months after deworming therapy. In conclusion, we show that infection by a strictly intestinal helminth has long-term effects on immune cell composition and local immune responses to unrelated antigens in the skin, revealing a novel process for T cell colonisation and worm-mediated immunosuppression in this organ.

Hookworm infection: Toward development of safe and effective peptide vaccines

Hookworms are hematophagous nematode parasites that have infected a billion people worldwide. Anthelmintic drugs have limited efficacy and do not prevent reinfection. Therefore, prophylactic vaccines are in high demand. Whole parasite vaccines are allergic and unsafe; thus, research into subunit vaccines has been warranted. A comprehensive overview of protein or peptide subunit vaccines' safety, protective efficacy, and associated immune responses is provided herein. The differences between the immune responses against hookworm infection by patients from epidemic versus nonepidemic areas are discussed in detail. Moreover, the different immunologic mechanisms of protection are discussed, including those that rely on allergic and nonallergic humoral and antibody-dependent cellular responses. The allergic and autoimmune potential of hookworm antigens is also explored, as are the immunoregulatory responses induced by the hookworm secretome. The potential of oral mucosal immunizations has been overlooked. Oral immunity against hookworms is a long-lived and safer immune response that is associated with elimination of infection and protective against reinfections. However, the harsh conditions of the gastrointestinal environment necessitates special oral delivery systems to unlock vaccines' protective potential. The potential for development of safer and more effective peptide- and protein-based anthelmintic vaccines is explored herein.

The Functional Parasitic Worm Secretome: Mapping the Place of Onchocerca volvulus Excretory Secretory Products

Nematodes constitute a very successful phylum, especially in terms of parasitism. Inside their mammalian hosts, parasitic nematodes mainly dwell in the digestive tract (geohelminths) or in the vascular system (filariae). One of their main characteristics is their long sojourn inside the body where they are accessible to the immune system. Several strategies are used by parasites in order to counteract the immune attacks. One of them is the expression of molecules interfering with the function of the immune system. Excretory-secretory products (ESPs) pertain to this category. This is, however, not their only biological function, as they seem also involved in other mechanisms such as pathogenicity or parasitic cycle (molting, for example). We will mainly focus on filariae ESPs with an emphasis on data available regarding Onchocerca volvulus, but we will also refer to a few relevant/illustrative examples related to other worm categories when necessary (geohelminth nematodes, trematodes or cestodes). We first present Onchocerca volvulus, mainly focusing on the aspects of this organism that seem relevant when it comes to ESPs: life cycle, manifestations of the sickness, immunosuppression, diagnosis and treatment. We then elaborate on the function and use of ESPs in these aspects.

IL-17A both initiates, via IFNγ suppression, and limits the pulmonary type-2 immune response to nematode infection

Nippostrongylus brasiliensis is a well-defined model of type-2 immunity but the early lung-migrating phase is dominated by innate IL-17A production. In this study, we confirm previous observations that Il17a-KO mice infected with N. brasiliensis exhibit an impaired type-2 immune response. Transcriptional profiling of the lung on day 2 of N. brasiliensis infection revealed an increased Ifng signature in Il17a-KO mice confirmed by enhanced IFNγ protein production in lung lymphocyte populations. Depletion of early IFNγ rescued type-2 immune responses in the Il17a-KO mice demonstrating that IL-17A-mediated suppression of IFNγ promotes type-2 immunity. Notably, later in infection, once the type-2 response was established, IL-17A limited the magnitude of the type-2 response. IL-17A regulation of type-2 immunity was lung-specific and infection with Trichuris muris revealed that IL-17A promotes a type-2 immune response in the lung even when infection is restricted to the intestine. Together our data reveal IL-17A as a major regulator of pulmonary type-2 immunity such that IL-17A supports early development of a protective type-2 response by suppression of IFNγ but subsequently limits excessive type-2 responses. A failure of this feedback loop may contribute to conditions such as severe asthma, characterised by combined elevation of IL-17 and type-2 cytokines.

A core set of venom proteins is released by entomopathogenic nematodes in the genus Steinernema

Parasitic helminths release molecular effectors into their hosts and these effectors can directly damage host tissue and modulate host immunity. Excreted/secreted proteins (ESPs) are one category of parasite molecular effectors that are critical to their success within the host. However, most studies of nematode ESPs rely on in vitro stimulation or culture conditions to collect the ESPs, operating under the assumption that in vitro conditions mimic actual in vivo infection. This assumption is rarely if ever validated. Entomopathogenic nematodes (EPNs) are lethal parasites of insects that produce and release toxins into their insect hosts and are a powerful model parasite system. We compared transcriptional profiles of individual Steinernema feltiae nematodes at different time points of activation under in vitro and in vivo conditions and found that some but not all time points during in vitro parasite activation have similar transcriptional profiles with nematodes from in vivo infections. These findings highlight the importance of experimental validation of ESP collection conditions. Additionally, we found that a suite of genes in the neuropeptide pathway were downregulated as nematodes activated and infection progressed in vivo, suggesting that these genes are involved in host-seeking behavior and are less important during active infection. We then characterized the ESPs of activated S. feltiae infective juveniles (IJs) using mass spectrometry and identified 266 proteins that are released by these nematodes. In comparing these ESPs with those previously identified in activated S. carpocapsae IJs, we identified a core set of 52 proteins that are conserved and present in the ESPs of activated IJs of both species. These core venom proteins include both tissue-damaging and immune-modulating proteins, suggesting that the ESPs of these parasites include both a core set of effectors as well as a specialized set, more adapted to the particular hosts they infect.

Immune response markers in sera of children infected with Giardia duodenalis AI and AII subassemblages

In this study, we evaluated serum markers of immune responses in children infected with G. duodenalis and compared them with the characterized parasite isolates. The reactivity indexes (RI) of IgG (1.503 ± 0.819) and IgA (2.308 ± 1.935) antibodies were significantly higher (P < 0.001) in infected children than in non-infected children. There were also statistically significantly higher serum levels (P < 0.05) of IFN-γ (393.10 ± 983.90 pg/mL) as well as serum (30.03 ± 10.92 μmol/L) and saliva nitric oxid derivatives (NO_x) (192.4 ± 151.2 μmol/L) in children infected with G. duodenalis compared to the group of non-parasitized children (127.4 ± 274.30 pg/mL; 25.82 ± 7.74 μmol/L and 122.5 ± 105.90 μmol/L, respectively). Regarding the characterized genetic variants of G. duodenalis and the immune response profiles, no differences were observed in terms of antibody reactivity or levels of serum cytokine and NO_x among children infected with AI or AII subassemblages. The elevated levels of IFN-γ and NO_x indicate that G. duodenalis intestinal infection in humans induces a cellular immune response detectable at the systemic level. Moreover, no significant differences in the antibody reactivity profile or the cytokine and NO_x production in the sera of children infected with AI or AII G. duodenalis variants were observed, suggesting that subtypes of the parasite do not influence the immune response profile.

Immunology: The Neuronal Pathway to Mucosal Immunity

Type 2 immunity at mucosal surfaces is thought to be initiated by type 2 innate lymphoid cells. New studies report that these cells are themselves activated by the neuropeptide neuromedin U, produced by cholinergic neurons in the gut and in airways.

Helminth Antigen-Conditioned Dendritic Cells Generate Anti-Inflammatory Cd4 T Cells Independent of Antigen Presentation via Major Histocompatibility Complex Class II

A recently identified feature of the host response to infection with helminth parasites is suppression of concomitant disease. Dendritic cells (DCs) exposed to antigens from the tapeworm Hymenolepis diminuta significantly reduce the severity of dinitrobenzene sulfonic acid-induced colitis in mice. Here we elucidate mechanisms underlying this cellular immunotherapy. We show a requirement for Ccr7 expression on transferred H. diminuta antigen-treated (HD)-DCs, suggesting that homing to secondary lymphoid tissues is important for suppression of colitis. Furthermore, sodium metaperiodate-sensitive helminth-derived glycans are required to drive the anti-colitic response in recipient mice. Induction of Th2-type cytokines and Gata-3⁺Cd4⁺ cells in secondary lymphoid tissues is dependent on major histocompatibility complex class II (MHC II) protein expression on transferred DCs, although remarkably, transfer of MHC II^-/- HD-DCs still attenuated dinitrobenzene sulfonic acid-induced colitis in recipient mice. Moreover, transfer of Cd4⁺ splenic T cells retrieved from mice administered MHC II^-/- HD-DCs suppressed dinitrobenzene sulfonic acid-induced colitis in recipient mice. Our studies reveal that HD-DCs can suppress colitis via an alternative MHC II-independent pathway that involves, in part, mobilization of T-cell responses. These data support the utility of HD-DCs in blocking colitis, revealing a requirement for Ccr7 and providing for HD-DC autologous immunotherapy for disease in which MHC II expression and/or function is compromised.

Hookworm excretory/secretory products modulate immune responses to heterologous and species-specific antigens

Approximately one billion people are currently infected with hookworm. Despite its high prevalence and the concomitant immune suppression seen in infected individuals, little research has been performed on the mechanism of immunosuppression by hookworm. Our study focused on characterizing mechanisms utilized by hookworm to suppress the host immune response. Splenocytes and draining lymph node cells from mice injected with hookworm excretory/secretory (ES) proteins showed decreased proliferation in response to both heterologous and species-specific antigens while also having increased nitric oxide secretion. Analysis by fluorescence-activated cell sorting revealed that mice injected with ES had reduced percentages of CD4⁺ T cells indicating potential effects of ES proteins on lymphocyte homeostasis. Antibody and cytokine response analyses demonstrated that immunization with ES proteins decreased IgG and IgG1 levels, also decreased interleukin (IL-)-4 and increased IL-12 and interferon-gamma (IFN-γ) cytokine production suggesting impairment of B-cell activation and a shift towards a nonhealing IL-12 directed T helper-1 immune response. Together, these data demonstrate for the first time that host immunosuppression by hookworms is orchestrated by ES proteins and provide mechanisms underlying the shift towards a nonhealing Th-1 profile as seen in humans suffering from hookworm infection.

Interleukin-5 Mediates Parasite-Induced Protection against Experimental Autoimmune Encephalomyelitis: Association with Induction of Antigen-Specific CD4+CD25+ T Regulatory Cells

Objective

To examine if the protective effect of parasite infection on experimental autoimmune encephalomyelitis (EAE) was due to interleukin (IL)-5, a cytokine produced by a type-2 response that induces eosinophilia. We hypothesize that, in parasite infections, IL-5 also promotes expansion of antigen-specific T regulatory cells that control autoimmunity.

Methods

Nippostrongylus brasiliensis larvae were used to infect Lewis rats prior to induction of EAE by myelin basic protein. Animals were sham treated, or given blocking monoclonal antibodies to interleukin 4 or 5 or to deplete CD25⁺ T cells. Reactivity of CD4⁺CD25⁺ T regulatory cells from these animals was examined.

Results

Parasite-infected hosts had reduced severity and length of EAE. The beneficial effect of parasitic infection was abolished with an anti-IL-5 or an anti-CD25 monoclonal antibody (mAb), but not anti-IL-4 mAb. Parasite-infected animals with EAE developed antigen-specific CD4⁺CD25⁺ T regulatory cells earlier than EAE controls and these expressed more Il5ra than controls. Treatment with IL-5 also reduced the severity of EAE and induced Il5ra expressing CD4⁺CD25⁺ T regulatory cells.

Interpretation

The results of this study suggested that IL-5 produced by the type-2 inflammatory response to parasite infection promoted induction of autoantigen-specific CD25⁺Il5ra⁺ T regulatory cells that reduced the severity of autoimmunity. Such a mechanism may explain the protective effect of parasite infection in patients with multiple sclerosis where eosinophilia is induced by IL-5, produced by the immune response to parasites.

Molecular cloning and characterization of protein disulfide isomerase of Brugia malayi, a human lymphatic filarial parasite

Lymphatic filariasis results in an altered lymphatic system and the abnormal enlargement of body parts, causing pain, serious disability and social stigma. Effective vaccines are still not available nowadays, drugs against the disease is required. Protein disulfide isomerase (PDI) is an essential catalyst of the endoplasmic reticulum which is involved in folding and chaperone activities in different biological systems. Here, we report the enzymatic characterization of a Brugia malayi Protein disulfide isomerase (BmPDI), which was expressed and purified from Escherichia coli BL21 (DE3). Western blotting analysis showed the recombinant BmPDI could be recognized by anti-BmPDI Rabbit serum. The rBmPDI exhibited an optimum activity at pH 8 and 40 °C. The enzyme was inhibited by aurin and PDI inhibitor. Recombinant BmPDI showed interaction with recombinant Brugia malayi calreticulin (rBmCRT). The three-dimensional model for BmPDI and BmCRT was generated by homology modelling. A total of 25 hydrogen bonds were found to be formed between two interfaces. There are 259 non-bonded contacts present in the BmPDI-BmCRT complex and 12 salt bridges were formed in the interaction.

Local amplifiers of IL-4Rα-mediated macrophage activation promote repair in lung and liver

The type 2 immune response controls helminth infection and maintains tissue homeostasis but can lead to allergy and fibrosis if not adequately regulated. We have discovered local tissue-specific amplifiers of type 2-mediated macrophage activation. In the lung, surfactant protein A (SP-A) enhanced interleukin-4 (IL-4)-dependent macrophage proliferation and activation, accelerating parasite clearance and reducing pulmonary injury after infection with a lung-migrating helminth. In the peritoneal cavity and liver, C1q enhancement of type 2 macrophage activation was required for liver repair after bacterial infection, but resulted in fibrosis after peritoneal dialysis. IL-4 drives production of these structurally related defense collagens, SP-A and C1q, and the expression of their receptor, myosin 18A. These findings reveal the existence within different tissues of an amplification system needed for local type 2 responses.

Parasite excretory-secretory products and their effects on metabolic syndrome

Obesity, one of the main causes of metabolic syndrome (MetS), is an increasingly common health and economic problem worldwide, and one of the major risk factors for developing type 2 diabetes and cardiovascular disease. Chronic, low-grade inflammation is associated with MetS and obesity. A dominant type 2/anti-inflammatory response is required for metabolic homoeostasis within adipose tissue: during obesity, this response is replaced by infiltrating, inflammatory macrophages and T cells. Helminths and certain protozoan parasites are able to manipulate the host immune response towards a TH2 immune phenotype that is beneficial for their survival, and there is emerging data that there is an inverse correlation between the incidence of MetS and helminth infections, suggesting that, as with autoimmune and allergic diseases, helminths may play a protective role against MetS disease. Within this review, we will focus primarily on the excretory-secretory products that the parasites produce to modulate the immune system and discuss their potential use as therapeutics against MetS and its associated pathologies.

Effect of ivermectin on allergy-type manifestations in occult strongyloidiasis

BACKGROUND

The immunomodulatory effects of helminths have been well described. However, there is a relative lack of literature regarding the link between parasites and allergic diseases. A number of patients with allergic symptoms have positive serologic test results for Strongyloides stercoralis.

OBJECTIVE

To identify patients with allergy-type symptoms and coexisting Strongyloides infection and to analyze the effect of Strongyloides eradication therapy with ivermectin on these symptoms.

METHODS

The medical records of our allergy clinic sites were reviewed for Strongyloides test results between January 2011 and October 2014. Each allergy-type symptom was assessed separately with regard to improvement after ivermectin therapy.

RESULTS

Among the 1,446 patients who had Strongyloides serologic tests ordered, 127 (8.8%) had positive test results. Eighty-four patients had follow-up data regarding allergy-type symptoms after ivermectin treatment. Among these, 52 patients (61.9%) reported skin-related problems (pruritus, urticaria, angioedema, and/or rash). Forty-nine patients (58.3%) had asthma, and 73.8% had allergic rhinoconjunctivitis. Although respiratory symptoms typically did not respond to ivermectin treatment, 24 of 48 patients (50%) with skin symptoms reported a significant subjective improvement of symptoms after ivermectin treatment. Peripheral eosinophil counts significantly decreased after ivermectin treatment from 450 to 200/μL (P < .001).

CONCLUSION

Serologic testing for strongyloides may be indicated for patients with allergy-type symptoms and a suggestive exposure history. Patients with strongyloidiasis and primarily cutaneous symptoms experienced significant symptomatic improvement after ivermectin therapy.

Comprehensive Transcriptome Meta-analysis to Characterize Host Immune Responses in Helminth Infections

Helminth infections affect more than a third of the world’s population. Despite very broad phylogenetic differences among helminth parasite species, a systemic Th2 host immune response is typically associated with long-term helminth infections, also known as the “helminth effect”. Many investigations have been carried out to study host gene expression profiles during helminth infections. The objective of this study is to determine if there is a common transcriptomic signature characteristic of the helminth effect across multiple helminth species and tissue types. To this end, we performed a comprehensive meta-analysis of publicly available gene expression datasets. After data processing and adjusting for study-specific effects, we identified ~700 differentially expressed genes that are changed consistently during helminth infections. Functional enrichment analyses indicate that upregulated genes are predominantly involved in various immune functions, including immunomodulation, immune signaling, inflammation, pathogen recognition and antigen presentation. Down-regulated genes are mainly involved in metabolic process, with only a few of them are involved in immune regulation. This common immune gene signature confirms previous observations and indicates that the helminth effect is robust across different parasite species as well as host tissue types. To the best of our knowledge, this study is the first comprehensive meta-analysis of host transcriptome profiles during helminth infections.

Many studies have been conducted to understand the immune modulatory effects in helminth infections. To determine whether there is a common transcriptomic signature characteristic of the helminth effect, we performed a comprehensive meta-analysis of publicly available gene expression datasets. The results revealed a distinct pattern of gene expression that is consistent across multiple helminth species and host tissue types, with upregulated genes dominated by those involved in immune regulation, Th2 immunity and inflammatory responses.

Novel O-linked methylated glycan antigens decorate secreted immunodominant glycoproteins from the intestinal nematode Heligmosomoides polygyrus

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Heligmosomoides polygyrus excretory–secretory (ES) proteins carry diverse N- and O-glycans, and many are O-methylated.

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A methylhexose containing O-glycan of abundant ES glycoproteins is immunodominant.

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This dominant glycan is not the immunomodulatory heat-stable ES component.

Glycan molecules from helminth parasites have been associated with diverse biological functions ranging from interactions with neighbouring host cell populations to down-modulation of specific host immunity. Glycoproteins secreted by the intestinal nematode Heligmosomoides polygyrus are of particular interest as the excretory–secretory products (termed HES) of this parasite contain both heat-labile and heat-stable components with immunomodulatory effects. We used MALDI-TOF-MS and LC–MS/MS to analyse the repertoire of N- and O-linked glycans released from Heligmosomoides polygyrus excretory–secretory products by PNGase A and F, β-elimination and hydrazinolysis revealing a broad range of structures including novel methylhexose- and methylfucose-containing glycans. Monoclonal antibodies to two immunodominant glycans of H. polygyrus, previously designated Glycans A and B, were found to react by glycan array analysis to a methyl-hexose-rich fraction and to a sulphated LacDiNAc (LDN; GalNAcβ1–4GlcNAc) structure, respectively. We also analysed the glycan repertoire of a major glycoprotein in Heligmosomoides polygyrus excretory–secretory products, VAL-2, which contains many glycan structures present in Heligmosomoides polygyrus excretory–secretory products including Glycan A. However, it was found that this set of glycans is not responsible for the heat-stable immunomodulatory properties of Heligmosomoides polygyrus excretory–secretory products, as revealed by the inability of VAL-2 to inhibit allergic lung inflammation. Taken together, these studies reveal that H. polygyrus secretes a diverse range of antigenic glycoconjugates, and provides a framework to explore the biological and immunomodulatory roles they may play within the mammalian host.

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.

Parasites-allergy paradox: Disease mediators or therapeutic modulators

The noticeable phenomenon of an increased frequency of immune-inflammatory disorders, in the industrialized world, has led to the implication of parasitic infections in the pathophysiology of these diseases. Most of the studies investigated the infection connection to allergy have centered on helminthes. Parasitic helminthes are a group of metazoans that are evolutionary diverse, yet converge to evolve common modes of immunomodulation. Helminth immunoregulation is mainly mediated by a regulatory response including Treg and Breg cells with alternatively-activated macrophages. There is increasing evidence for a causal relationship between helminth infection and allergic hyporesponsiveness, however, conflicting data are still generating. The helminth immunoregulation seems to be species-specific and phase-specific. It depends on the stage of the clinical disease which correlates with a corresponding parasitic stage (egg, larva or mature adult). Here, we review the cellular and molecular mechanisms utilized by helminthes to manipulate the immune system and the consequent bystander immunomodulatory responses toward environmental allergens. We especially focus on parasitic species and molecules involved in the modulation of allergic disorders and summarize the experimental and clinical trials using them as therapeutic agents. We also discuss the potentials and obstacles, for helminthes and/or their derived molecules, to emerge as novel therapeutic modalities.

A truncated fragment of Ov-ASP-1 consisting of the core pathogenesis-related-1 (PR-1) domain maintains adjuvanticity as the full-length protein

The Onchocerca volvulus activation-associated secreted protein-1 (Ov-ASP-1) has good adjuvanticity for a variety of antigens and vaccines, probably due to its ability activate antigen-processing cells (APCs). However, the functional domain of Ov-ASP-1 as an adjuvant is not clearly defined. Based on the structural prediction of this protein family, we constructed a 16-kDa recombinant protein of Ov-ASP-1 that contains only the core pathogenesis-related-1 (PR-1) domain (residues 10-153), designated ASPPR. We found that ASPPR exhibits adjuvanticity similar to that of the full-length Ov-ASP-1 (residues 10-220) for various antigens, including ovalbumin (OVA), HBsAg protein antigen, and the HIV peptide 5 (Pep5) antigen, but it is more suitable for vaccine design in ASPPR-antigen fusion proteins, and more stable in PBS than Ov-ASP-1 stored at -70 °C. These results suggest that ASPPR might be the functional region of Ov-ASP-1 as an adjuvant, and therefore could be developed as an adjuvant for human use.

Chitinase-like proteins promote IL-17-mediated neutrophilia in a tradeoff between nematode killing and host damage

Enzymatically inactive chitinase-like proteins (CLPs) such as BRP-39, Ym1 and Ym2 are established markers of immune activation and pathology, yet their functions are essentially unknown. We found that Ym1 and Ym2 induced the accumulation of neutrophils through the expansion of γδ T cell populations that produced interleukin 17 (IL-17). While BRP-39 did not influence neutrophilia, it was required for IL-17 production in γδ T cells, which suggested that regulation of IL-17 is an inherent feature of mouse CLPs. Analysis of a nematode infection model, in which the parasite migrates through the lungs, revealed that the IL-17 and neutrophilic inflammation induced by Ym1 limited parasite survival but at the cost of enhanced lung injury. Our studies describe effector functions of CLPs consistent with innate host defense traits of the chitinase family.

Induction of regulatory cells by helminth parasites: exploitation for the treatment of inflammatory diseases

Helminth parasites are highly successful pathogens, chronically infecting a quarter of the world's population, causing significant morbidity but rarely causing death. Protective immunity and expulsion of helminths is mediated by T-helper 2 (Th2) cells, type 2 (M2) macrophages, type 2 innate lymphoid cells, and eosinophils. Failure to mount these type 2 immune responses can result in immunopathology mediated by Th1 or Th17 cells. Helminths have evolved a wide variety of approaches for immune suppression, especially the generation of regulatory T cells and anti-inflammatory cytokines interleukin-10 and transforming growth factor-β. This is a very effective strategy for subverting protective immune responses to prolong their survival in the host but has the bystander effect of modulating immune responses to unrelated antigens. Epidemiological studies in humans have shown that infection with helminth parasites is associated with a low incidence of allergy/asthma and autoimmunity in developing countries. Experimental studies in mice have demonstrated that regulatory immune responses induced by helminth can suppress Th2 and Th1/Th17 responses that mediate allergy and autoimmunity, respectively. This has provided a rational explanation of the 'hygiene hypothesis' and has also led to the exploitation of helminths or their immunomodulatory products in the development of new immunosuppressive therapies for inflammatory diseases in humans.

Production and analysis of immunomodulatory excretory-secretory products from the mouse gastrointestinal nematode Heligmosomoides polygyrus bakeri

Heligmosomoides polygyrus bakeri (Hpb) infection in mice is a convenient model for studying the pathophysiology and immunology of gastrointestinal (GI) helminth infection. Hpb infection suppresses immune responses to bystander antigens and unrelated pathogens, and it slows the progression and modifies the outcome of immune-mediated diseases. Hpb-derived excretory-secretory (ES) products potently modulate CD4(+) helper T cell (TH) responses by inducing regulatory T cells, tolerogenic dendritic cells (DCs) and immunoregulatory cytokines. This observation has spiked interest in identifying the immunomodulatory molecules, especially proteins, in ES products from Hpb and other GI nematodes for development as novel therapies to treat individuals with immune-mediated diseases, such as inflammatory bowel diseases (IBDs). In this protocol, we describe how to (i) maintain Hpb in the laboratory for experimental infections, (ii) collect adult worms from infected mice to generate ES products and (iii) evaluate the modulatory effects of ES products on toll-like receptor (TLR) ligand-induced maturation of CD11c(+) DCs. The three major sections of the PROCEDURE can be used independently, and they require ∼6, 10 and 27 h, respectively. Although other methods use a modified Baermann apparatus to collect Hpb adult worms, we describe a method that involves dissection of adult worms from intestinal tissue. The protocol will be useful to investigators studying the host-parasite interface and identifying and analyzing helminth-derived molecules with therapeutic potential.

Secreted proteomes of different developmental stages of the gastrointestinal nematode Nippostrongylus brasiliensis

Hookworms infect more than 700 million people worldwide and cause more morbidity than most other human parasitic infections. Nippostrongylus brasiliensis (the rat hookworm) has been used as an experimental model for human hookworm because of its similar life cycle and ease of maintenance in laboratory rodents. Adult N. brasiliensis, like the human hookworm, lives in the intestine of the host and releases excretory/secretory products (ESP), which represent the major host-parasite interface. We performed a comparative proteomic analysis of infective larval (L3) and adult worm stages of N. brasiliensis to gain insights into the molecular bases of host-parasite relationships and determine whether N. brasiliensis could indeed serve as an appropriate model for studying human hookworm infections. Proteomic data were matched to a transcriptomic database assembled from 245,874,892 Illumina reads from different developmental stages (eggs, L3, L4, and adult) of N. brasiliensis yielding∼18,426 unigenes with 39,063 possible isoform transcripts. From this analysis, 313 proteins were identified from ESPs by LC-MS/MS-52 in the L3 and 261 in the adult worm. Most of the proteins identified in the study were stage-specific (only 13 proteins were shared by both stages); in particular, two families of proteins-astacin metalloproteases and CAP-domain containing SCP/TAPS-were highly represented in both L3 and adult ESP. These protein families are present in most nematode groups, and where studied, appear to play roles in larval migration and evasion of the host's immune response. Phylogenetic analyses of defined protein families and global gene similarity analyses showed that N. brasiliensis has a greater degree of conservation with human hookworm than other model nematodes examined. These findings validate the use of N. brasiliensis as a suitable parasite for the study of human hookworm infections in a tractable animal model.

In silico and in vitro studies on the protein-protein interactions between Brugia malayi immunomodulatory protein calreticulin and human C1q

Filarial parasites modulate effective immune response of their host by releasing a variety of immunomodulatory molecules, which help in the long persistence of the parasite within the host. The present study was aimed to characterize an immunomodulatory protein of Brugia malayi and its interaction with the host immune component at the structural and functional level. Our findings showed that Brugia malayi Calreticulin (BmCRT) is responsible for the prevention of classical complement pathway activation via its interaction with the first component C1q of the human host. This was confirmed by inhibition of C1q dependent lysis of immunoglobulin-sensitized Red Blood Cells (S-RBCs). This is possibly the first report which predicts CRT-C1q interaction on the structural content of proteins to explain how BmCRT inhibits this pathway. The molecular docking of BmCRT-C1q complex indicated that C1qB chain (IgG/M and CRP binding sites on C1q) played a major role in the interaction with conserved and non-conserved regions of N and P domain of BmCRT. Out of 37 amino acids of BmCRT involved in the interaction, nine amino acids (Pro(126), Glu(132), His(147), Arg(151), His(153), Met(154), Lys(156), Ala(196) and Lys(212)) are absent in human CRT. Both ELISA and in silico analysis showed the significant role of Ca(+2) in BmCRT-HuC1q complex formation and deactivation of C1r2-C1s2. Molecular dynamics studies of BmCRT-HuC1q complex showed a deviation from ∼ 0.4 nm to ∼ 1.0 nm. CD analyses indicated that BmCRT is composed of 49.6% α helix, 9.6% β sheet and 43.6% random coil. These findings provided valuable information on the architecture and chemistry of BmCRT-C1q interaction and supported the hypothesis that BmCRT binds with huC1q at their targets (IgG/M, CRP) binding sites. This interaction enables the parasite to interfere with the initial stage of host complement activation, which might be helpful in parasites establishment. These results might be utilized for help in blocking the C1q/CRT interaction and preventing parasite infection.

Antibody and cytokine responses to Giardia excretory/secretory proteins in Giardia intestinalis-infected BALB/c mice

The humoral and cellular responses against excretory/secretory proteins and soluble extracts of Giardia intestinalis were evaluated in the course of experimental G. intestinalis infection in BALB/c mice. Production of IgG1, IgG2a, IgA, and IgE antibodies against excreted/secreted proteins and soluble extract was detected after infection by G. intestinalis. Specific IgA antibody against E/S proteins and soluble extract form intestinal fluids in infected mice was detected by ELISA. The Western blotting identified proteins of 30, 58, 63, and 83 kDa for IgA and IgG, respectively. High proliferation rate in vitro of spleen cell and secretion of interleukin-4 (IL-4) at 21 days p.i. after stimulation with excreted/secreted proteins and low proliferative response in the presence of soluble extract in infected BALB/c mice was observed. High production of interferon gamma (IFN-γ) and interleukin-5 (IL-5) at the time of decreasing cyst output (14-21 days p.i.) in infected mice was recorded, suggesting the important role of these cytokines in the control of the infection. Interestingly, progressive and gradual increase of the interleukin-10 after stimulation with both preparations was recorded from 7 days until 28 days after infection, indicating the possible regulatory effect of these antigens on the immune response during Giardia infection. Therefore, the infection by Giardia duodenalis stimulates a mixed response Th1 and Th2, mainly stimulated by excretory/secretory antigens. The immunogenicity of these antigens may be a suitable for identification of the proteins related with the effective immune response in the course of infection by G. duodenalsis.

The skin is an important bulwark of acquired immunity against intestinal helminths

IL-4–producing basophils promote the trapping of N. brasiliensis in the skin during secondary infection, a process critical for limiting the spread of infection to the lungs.

Once animals have experienced a helminthic infection, they often show stronger protective immunity against subsequent infections. Although helminthic infections are well known to elicit Th2-type immune responses, it remains ill-defined where and how acquired protection is executed. Here we show that skin-invading larvae of the intestinal helminth Nippostrongylus brasiliensis are surrounded by skin-infiltrating cells and are prevented from migrating out of infected skin during the second but not the first infection. B cell– or IgE receptor FcεRI–deficient mice showed impaired larval trapping in the skin. Selective ablation of basophils, but not mast cells, abolished the larval trapping, leading to increased worm burden in the lung and hence severe lung injury. Skin-infiltrating basophils produced IL-4 that in turn promoted the generation of M2-type macrophages, leading to the larval trapping in the skin through arginase-1 production. Basophils had no apparent contribution to worm expulsion from the intestine. This study thus reveals a novel mode of acquired antihelminth immunity, in which IgE-armed basophils mediate skin trapping of larvae, thereby limiting lung injury caused by larval migration.

A serpin released by an entomopathogen impairs clot formation in insect defense system

Steinernema carpocapsae is an entomopathogenic nematode widely used for the control of insect pests due to its virulence, which is mainly attributed to the ability the parasitic stage has to overcome insect defences. To identify the mechanisms underlying such a characteristic, we studied a novel serpin-like inhibitor (sc-srp-6) that was detected in a transcriptome analysis. Recombinant Sc-SRP-6 produced in Escherichia coli had a native fold of serpins belonging to the α-1-peptidase family and exhibited inhibitory activity against trypsin and α-chymotrypsin with Ki of 0.42×10⁻⁷ M and 1.22×10⁻⁷ M, respectively. Functional analysis revealed that Sc-SRP-6 inhibits insect digestive enzymes, thus preventing the hydrolysis of ingested particles. Moreover, Sc-SRP-6 impaired the formation of hard clots at the injury site, a major insect defence mechanism against invasive pathogens. Sc-SRP-6 does not prevent the formation of clot fibres and the activation of prophenoloxidases but impairs the incorporation of the melanin into the clot. Binding assays showed a complex formation between Sc-SRP-6 and three proteins in the hemolymph of lepidopteran required for clotting, apolipophorin, hexamerin and trypsin-like, although the catalytic inhibition occurred exclusively in trypsin-like. This data allowed the conclusion that Sc-SRP-6 promotes nematode virulence by inhibiting insect gut juices and by impairing immune clot reaction.

Development of CD4 T Cell Dependent Immunity Against N. brasiliensis Infection

Of all the microbial infections relevant to mammals the relationship between parasitic worms and what constitutes and regulates a host protective immune response is perhaps the most complex and evolved. Nippostrongylus brasiliensis is a tissue migrating parasitic roundworm of rodents that exemplifies many of the salient features of parasitic worm infection, including parasite development through sequential larval stages as it migrates through specific tissue sites. Immune competent hosts respond to infection by N. brasiliensis with a rapid and selective development of a profound Th2 immune response that appears able to confer life long protective immunity against reinfection. This review details how the lung can be the site of migrating nematode immune killing and the gut a site of rapid immune mediated clearance of worms. Furthermore it appears that N. brasiliensis induced responses in the lung are sufficient for conferring immunity in lung and gut while infection of the gut only confers immunity in the gut. This review also covers the role of IL-4, STAT6, and the innate cytokines IL-25, IL-33, and thymic stromal lymphopoietin in the generation of CD4-mediated immunity against N. brasiliensis reinfection and discusses what cytokines might be involved in mediated killing or expulsion of helminth parasites.

New Allergens of Relevance in Tropical Regions: The Impact of Ascaris lumbricoides Infections

One of the many aspects of the relationships between parasite infections and allergic diseases is the possibility that allergens from parasites enhance the T_H2 responses, especially IgE production, in allergic diseases such as asthma. In this review we discuss about the allergenic composition of the nematode Ascaris lumbricoides and their potential impact on allergy sensitization and asthma pathogenesis and prevalence in populations living in the tropics and naturally exposed to both, mite allergens and helminth infections.

Helminths: Immunoregulation and Inflammatory Diseases-Which Side Are Trichinella spp. and Toxocara spp. on?

Macropathogens, such as multicellular helminths, are considered masters of immunoregulation due to their ability to escape host defense and establish chronic infections. Molecular crosstalk between the host and the parasite starts immediately after their encounter, which influences the course and development of both the innate and adaptive arms of the immune response. Helminths can modulate dendritic cells (DCs) function and induce immunosuppression which is mediated by a regulatory network that includes regulatory T (Treg) cells, regulatory B (Breg) cells, and alternatively activated macrophages (AAMs). In this way, helminths suppress and control both parasite-specific and unrelated immunopathology in the host such as Th1-mediated autoimmune and Th2-mediated allergic diseases. However, certain helminths favour the development or exacerbation of allergic responses. In this paper, the cell types that play an essential role in helminth-induced immunoregulation, the consequences for inflammatory diseases, and the contrasting effects of Toxocara and Trichinella infection on allergic manifestations are discussed.

Immunomodulation by helminth parasites: defining mechanisms and mediators

Epidemiological and interventional human studies, as well as experiments in animal models, strongly indicate that helminth parasitic infections can confer protection from immune dysregulatory diseases such as allergy, autoimmunity and colitis. Here, we review the immunological pathways that helminths exploit to downregulate immune responses, both against bystander specificities such as allergens and against antigens from the parasites themselves. In particular, we focus on a highly informative laboratory system, the mouse intestinal nematode, Heligmosomoides polygyrus, as a tractable model of host-parasite interaction at the cellular and molecular levels. Analysis of the molecules released in vitro (as excretory-secretory products) and their cellular targets is identifying individual parasite molecules and gene families implicated in immunomodulation, and which hold potential for future human therapy of immunopathological conditions.

Type 2 innate immunity in helminth infection is induced redundantly and acts autonomously following CD11c(+) cell depletion

Infection with gastrointestinal helminths generates a dominant type 2 response among both adaptive (Th2) and innate (macrophage, eosinophil, and innate lymphoid) immune cell types. Two additional innate cell types, CD11c(high) dendritic cells (DCs) and basophils, have been implicated in the genesis of type 2 immunity. Investigating the type 2 response to intestinal nematode parasites, including Heligmosomoides polygyrus and Nippostrongylus brasiliensis, we first confirmed the requirement for DCs in stimulating Th2 adaptive immunity against these helminths through depletion of CD11c(high) cells by administration of diphtheria toxin to CD11c.DOG mice. In contrast, responsiveness was intact in mice depleted of basophils by antibody treatment. Th2 responses can be induced by adoptive transfer of DCs, but not basophils, exposed to soluble excretory-secretory products from these helminths. However, innate type 2 responses arose equally strongly in the presence or absence of CD11c(high) cells or basophils; thus, in CD11c.DOG mice, the alternative activation of macrophages, as measured by expression of arginase-1, RELM-α, and Ym-1 (Chi3L3) in the intestine following H. polygyrus infection or in the lung following N. brasiliensis infection, was unaltered by depletion of CD11c-expressing DCs and alveolar macrophages or by antibody-mediated basophil depletion. Similarly, goblet cell-associated RELM-β in lung and intestinal tissues, lung eosinophilia, and expansion of innate lymphoid ("nuocyte") populations all proceeded irrespective of depletion of CD11c(high) cells or basophils. Thus, while CD11c(high) DCs initiate helminth-specific adaptive immunity, innate type 2 cells are able to mount an autonomous response to the challenge of parasite infection.

The adjuvanticity of an O. volvulus-derived rOv-ASP-1 protein in mice using sequential vaccinations and in non-human primates

Adjuvants potentiate antigen-specific protective immune responses and can be key elements promoting vaccine effectiveness. We previously reported that the Onchocerca volvulus recombinant protein rOv-ASP-1 can induce activation and maturation of naïve human DCs and therefore could be used as an innate adjuvant to promote balanced Th1 and Th2 responses to bystander vaccine antigens in mice. With a few vaccine antigens, it also promoted a Th1-biased response based on pronounced induction of Th1-associated IgG2a and IgG2b antibody responses and the upregulated production of Th1 cytokines, including IL-2, IFN-γ, TNF-α and IL-6. However, because it is a protein, the rOv-ASP-1 adjuvant may also induce anti-self-antibodies. Therefore, it was important to verify that the host responses to self will not affect the adjuvanticity of rOv-ASP-1 when it is used in subsequent vaccinations with the same or different vaccine antigens. In this study, we have established rOv-ASP-1's adjuvanticity in mice during the course of two sequential vaccinations using two vaccine model systems: the receptor-binding domain (RBD) of SARS-CoV spike protein and a commercial influenza virus hemagglutinin (HA) vaccine comprised of three virus strains. Moreover, the adjuvanticity of rOv-ASP-1 was retained with an efficacy similar to that obtained when it was used for a first vaccination, even though a high level of anti-rOv-ASP-1 antibodies was present in the sera of mice before the administration of the second vaccine. To further demonstrate its utility as an adjuvant for human use, we also immunized non-human primates (NHPs) with RBD plus rOv-ASP-1 and showed that rOv-ASP-1 could induce high titres of functional and protective anti-RBD antibody responses in NHPs. Notably, the rOv-ASP-1 adjuvant did not induce high titer antibodies against self in NHPs. Thus, the present study provided a sound scientific foundation for future strategies in the development of this novel protein adjuvant.

CD4+ T helper 2 cells--microbial triggers, differentiation requirements and effector functions

Over the past 10 years we have made great strides in our understanding of T helper cell differentiation, expansion and effector functions. Within the context of T helper type 2 (Th2) cell development, novel innate-like cells with the capacity to secrete large amounts of interleukin-5 (IL-5), IL-13 and IL-9 as well as IL-4-producing and antigen-processing basophils have (re)-emerged onto the type 2 scene. To what extent these new players influence αβ+  CD4+  Th2 cell differentiation is discussed throughout this appraisal of the current literature. We highlight the unique features of Th2 cell development, highlighting the three necessary signals, T-cell receptor ligation, co-stimulation and cytokine receptor ligation. Finally, putting these into context, microbial and allergenic properties that trigger Th2 cell differentiation and how these influence Th2 effector function are discussed and questioned.

Protective immunity against the gastrointestinal nematode Nippostrongylus brasiliensis requires a broad T-cell receptor repertoire

The parasitic gastrointestinal nematode Nippostrongylus brasiliensis induces massive expansion of T helper type 2 (Th2) cells in the lung and small intestine. Th2 cells are a major source of interleukin-4 and interleukin-13, two cytokines that appear essential for rapid worm expulsion. It is unclear whether all Th2 cells induced during infection are pathogen-specific because Th2 cells might also be induced by parasite-derived superantigens or cytokine-mediated bystander activation. Bystander Th2 polarization could explain the largely unspecific B-cell response during primary infection. Furthermore, it is not known whether protective immunity depends on a polyclonal repertoire of T-cell receptor (TCR) specificities. To address these unresolved issues, we performed adoptive transfer experiments and analysed the TCR-Vβ repertoire before and after infection of mice with the helminth N. brasiliensis. The results demonstrate that all Th2 cells were generated by antigen-specific rather than superantigen-driven or cytokine-driven activation. Furthermore, we show that worm expulsion was impaired in mice with a limited repertoire of TCR specificities, indicating that a polyclonal T-cell response is required for protective immunity.

IgE cross-reactivity between Ascaris lumbricoides and mite allergens: possible influences on allergic sensitization and asthma

Nematode infections such as Ascariasis are important health problems in underdeveloped countries, most of them located in the tropics where environmental conditions also promote the perennial co-exposure to high concentrations of domestic mite allergens. Allergic diseases are common, and most of patients with asthma exhibit a predominant and strong IgE sensitization to mites. It is unknown whether co-exposure to Ascaris lumbricoides and the domestic mites Blomia tropicalis and Dermatophagoides pteronyssinus potentiates Th2 responses and IgE sensitization, thereby modifying the natural history of allergy. Recently, we obtained experimental evidence of a high cross-reactivity between the allergenic extracts of these invertebrates, involving well-known allergens such as tropomyosin and glutathione transferases. There is indirect evidence suggesting that the clinical impact of these findings may be important. In this review, we discuss the potential role of this cross-reactivity on several aspects of allergy in the tropics that have been a focus of a number of investigations, some of them with controversial results.

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.

Chronic helminth infection promotes immune regulation in vivo through dominance of CD11cloCD103- dendritic cells

Gastrointestinal helminth infections are extremely prevalent in many human populations and are associated with downmodulated immune responsiveness. In the experimental model system of Heligmosomoides polygyrus, a chronic infection establishes in mice, accompanied by a modulated Th2 response and increased regulatory T cell (Treg) activity. To determine if dendritic cell (DC) populations in the lymph nodes draining the intestine are responsible for the regulatory effects of chronic infection, we first identified a population of CD11c(lo) nonplasmacytoid DCs that expand after chronic H. polygyrus infection. The CD11c(lo) DCs are underrepresented in magnetic bead-sorted preparations and spared from deletion in CD11c-diptheria toxin receptor mice. After infection, CD11c(lo) DCs did not express CD8, CD103, PDCA, or Siglec-H and were poorly responsive to TLR stimuli. In DC/T cell cocultures, CD11c(lo) DCs from naive and H. polygyrus-infected mice could process and present protein Ag, but induced lower levels of Ag-specific CD4(+) T cell proliferation and effector cytokine production, and generated higher percentages of Foxp3(+) T cells in the presence of TGF-β. Treg generation was also dependent on retinoic acid receptor signaling. In vivo, depletion of CD11c(hi) DCs further favored the dominance of the CD11c(lo) DC phenotype. After CD11c(hi) DC depletion, effector responses were inhibited dramatically, but the expansion in Treg numbers after H. polygyrus infection was barely compromised, showing a significantly higher regulatory/effector CD4(+) T cell ratio compared with that of CD11c(hi) DC-intact animals. Thus, the proregulatory environment of chronic intestinal helminth infection is associated with the in vivo predominance of a newly defined phenotype of CD11c(lo) tolerogenic DCs.

Helminth secretions induce de novo T cell Foxp3 expression and regulatory function through the TGF-β pathway

Foxp3-expressing regulatory T (T reg) cells have been implicated in parasite-driven inhibition of host immunity during chronic infection. We addressed whether parasites can directly induce T reg cells. Foxp3 expression was stimulated in naive Foxp3⁻ T cells in mice infected with the intestinal helminth Heligmosomoides polygyrus. In vitro, parasite-secreted proteins (termed H. polygyrus excretory-secretory antigen [HES]) induced de novo Foxp3 expression in fluorescence-sorted Foxp3⁻ splenocytes from Foxp3-green fluorescent protein reporter mice. HES-induced T reg cells suppressed both in vitro effector cell proliferation and in vivo allergic airway inflammation. HES ligated the transforming growth factor (TGF) β receptor and promoted Smad2/3 phosphorylation. Foxp3 induction by HES was lost in dominant-negative TGF-βRII cells and was abolished by the TGF-β signaling inhibitor SB431542. This inhibitor also reduced worm burdens in H. polygyrus-infected mice. HES induced IL-17 in the presence of IL-6 but did not promote Th1 or Th2 development under any conditions. Importantly, antibody to mammalian TGF-β did not recognize HES, whereas antisera that inhibited HES did not affect TGF-β. Foxp3 was also induced by secreted products of Teladorsagia circumcincta, a related nematode which is widespread in ruminant animals. We have therefore identified a novel pathway through which helminth parasites may stimulate T reg cells, which is likely to be a key part of the parasite's immunological relationship with the host.

Antibody and cytokine responses in BALB/c mice immunized with the excreted/secreted proteins of Giardia intestinalis: the role of cysteine proteases

The mechanisms involved in the induction of the immune response in humans or experimental hosts infected with Giardia intestinalis are not well understood. The results of previous studies indicate that the parasite induces a mixed Th1/Th2 response and that, in experimentally infected mice, the parasite's excreted/secreted (E/S) proteins contain cysteine proteases that are recognised by the murine immune system. In the present study, the possible effects of the E/S proteases of G. intestinalis on the host's humoral and cellular immune responses were investigated in BALB/c mice immunized with the parasite's E/S proteins. High titres of specific IgG(1), IgG(2a) and IgE antibodies were detected after immunization with native E/S proteins. Spleen cells stimulated with such proteins in vitro showed a significant antigen-specific proliferative response accompanied by the production of high concentrations of interleukin-4 (IL-4), interleukin-5 (IL-5) and interleukin-10 (IL-10) but little secretion of interferon-gamma (IFN-gamma). When, before use, the proteases in the E/S proteins were inhibited, by heat treatment or the addition of E-64, they elicited much lower titres of specific IgG(1) and IgE in mice while, in splenocytes in vitro, they triggered much lower production of IL-4, IL-5 and IL-10 and reduced antigen-specific proliferation. Since E-64 only inhibits cysteine proteases, these results indicate that the excreted/secreted cysteine proteases of G. intestinalis may be involved in the induction and regulation of a specific immune response in the infected host.

Presence of intestinal helminths decreases T helper type 1 responses in tuberculoid leprosy patients and may increase the risk for multi-bacillary leprosy

Resistance to intracellular pathogens such as Mycobacterium leprae is dependent upon an effective T helper type 1 (Th1)-type immune response. On the other hand, intestinal helminths are known to subvert the host's immune response towards to either a Th2-type immune response or a regulatory T cell up-regulation, which may affect the host's ability to mount an effective response to mycobacteria. Here, we report a significant association between intestinal helminth infections and lepromatous leprosy [odds ratio (OR), 10.88; confidence interval (CI) 95%: 4.02-29.4; P<0.001]. We also observed that the frequency of intestinal helminths correlated strongly with the mycobacterial index (r=0.982, P<0.01). Corroborating with our hypothesis, intracellular levels of interferon-gamma were decreased significantly in leprosy patients co-infected with intestinal helminths when compared to leprosy patients without worms. Conversely, lepromatous leprosy patients with intestinal worms produced higher levels of both interleukin (IL)-4 and IL-10. Our results suggest that a pre-existing infection by intestinal helminths may facilitate the establishment of M. leprae infection or its progression to more severe forms of leprosy.

daf-7-related TGF-beta homologues from Trichostrongyloid nematodes show contrasting life-cycle expression patterns

The transforming growth factor-beta (TGF-beta) gene family regulates critical processes in animal development, and plays a crucial role in regulating the mammalian immune response. We aimed to identify TGF-beta homologues from 2 laboratory model nematodes (Heligmosomoides polygyrus and Nippostrongylus brasiliensis) and 2 major parasites of ruminant livestock (Haemonchus contortus and Teladorsagia circumcincta). Parasite cDNA was used as a template for gene-specific PCR and RACE. Homologues of the TGH-2 subfamily were isolated, and found to differ in length (301, 152, 349 and 305 amino acids respectively), with variably truncated N-terminal pre-proteins. All contained conserved C-terminal active domains (>85% identical over 115 amino acids) containing 9 cysteine residues, as in C. elegans DAF-7, Brugia malayi TGH-2 and mammalian TGF-beta. Surprisingly, only the H. contortus homologue retained a conventional signal sequence, absent from shorter proteins of other species. RT-PCR assays of transcription showed that in H. contortus and N. brasiliensis expression was maximal in the infective larval stage, and very low in adult worms. In contrast, in H. polygyrus and T. circumcincta, tgh-2 transcription is higher in adults than infective larvae. The molecular evolution of this gene family in parasitic nematodes has diversified the pre-protein and life-cycle expression patterns of TGF-beta homologues while conserving the structure of the active domain.