Parasite-induced Th2 polarization is associated with down-regulated dendritic cell responsiveness to Th1 stimuli and a transient delay in T lymphocyte cycling

Intestinal helminth infection impairs vaccine-induced T cell responses and protection against SARS-CoV-2

Although vaccines have reduced COVID-19 disease burden, their efficacy in helminth infection endemic areas is not well characterized. We evaluated the impact of infection by Heligmosomoides polygyrus bakeri (Hpb), a murine intestinal hookworm, on the efficacy of an mRNA vaccine targeting the Wuhan-1 spike protein of SARS-CoV-2. Although immunization generated similar B cell responses in Hpb-infected and uninfected mice, polyfunctional CD4+ and CD8+ T cell responses were markedly reduced in Hpb-infected mice. Hpb-infected and mRNA vaccinated mice were protected against the ancestral SARS-CoV-2 strain WA1/2020, but control of lung infection was diminished against an Omicron variant compared to animals immunized without Hpb infection. Helminth mediated suppression of spike-specific CD8+ T cell responses occurred independently of STAT6 signaling, whereas blockade of IL-10 rescued vaccine-induced CD8+ T cell responses. In mice, intestinal helminth infection impairs vaccine induced T cell responses via an IL-10 pathway and compromises protection against antigenically shifted SARS-CoV-2 variants.

Measuring the Manipulation of T Helper Immune Responses by Schistosoma mansoni

Schistosoma mansoni uses different mechanisms to escape its host's immunity. Understanding the ability of memory T cells to withstand this pathogen's manipulation is important for the development of effective vaccines against this immunomodulatory pathogen. In this study, ovalbumin (OVA) transgenic S. mansoni is used as a tool to investigate whether fully differentiated Th1, Th2 and Th17 cells are able to withstand pathogen manipulation. Naïve T cells from OT-II T cell receptor transgenic mice with a specificity for OVA were differentiated into Th1, Th2, and Th17 polarised memory cells in vitro. These cells were adoptively transferred into recipient mice to investigate whether these polarised immune memory T cells are resilient in the face of pathogen-mediated manipulation. After transferring memory cells, mice were challenged with OVA-transduced S. mansoni eggs as well as wild-type controls. The in vitro differentiated Th1, Th2 and Th17 memory cells continued to produce the same cytokines when challenged by OVA-expressing S. mansoni eggs as to these they produced when transferred in vivo, suggesting that the Th phenotypes of the memory T cells remains unaltered in the face of stimulation by S. mansoni. The ability of memory T cells to remain resilient to manipulation by the parasite suggests that vaccines might be able to produce immune memory responses able to withstand S. mansoni immune manipulation and hence protect the host from infection.

Aeroallergens Exacerbate Histoplasma capsulatum Infection

Allergens such as house dust mites (HDM) and papain induce strong Th2 responses, including elevated IL-4, IL-5, and IL-13 and marked eosinophilia in the airways. Histoplasma capsulatum is a dimorphic fungal pathogen that induces a strong Th1 response marked by IFN-γ and TNF-α production, leading to rapid clearance in nonimmunocompromised hosts. Th1 responses are generally dominant and overwhelm the Th2 response when stimuli for both are present, although there are instances when Th2 stimuli downregulate a Th1 response. We determined if the Th2 response to allergens prevents the host from mounting a Th1 response to H. capsulatum in vivo. C57BL/6 mice exposed to HDM or papain and infected with H. capsulatum exhibited a dominant Th2 response early, characterized by enhanced eosinophilia and elevated Th2 cytokines in lungs. These mice manifested exacerbated fungal burdens, suggesting that animals skewed toward a Th2 response by an allergen are less able to clear the H. capsulatum infection despite an intact Th1 response. In contrast, secondary infection is not exacerbated by allergen exposure, indicating that the memory response may suppress the Th2 response to HDM and quickly clear the infection. In conclusion, an in vivo skewing toward Th2 by allergens exacerbates fungal infection, even though there is a concurrent and unimpaired Th1 response to H. capsulatum.

Schistosoma Infection and Schistosoma-Derived Products Modulate the Immune Responses Associated with Protection against Type 2 Diabetes

Studies on parasite-induced immunoregulatory mechanisms could contribute to the development of new therapies for inflammatory diseases such as type 2 diabetes (T2D), which is a chronic inflammatory disease characterized by persistent elevated glucose levels due to insulin resistance. The association between previous Schistosoma infection and T2D has been confirmed—Schistosoma infection and Schistosoma-derived products modulate the immune system, including innate and acquired immune responses, contributing to T2D disease control. Schistosoma infections and Schistosoma-derived molecules affect the immune cell composition in adipose tissue, dampening inflammation and improving glucose tolerance. This protective role includes the polarization of immune cells to alternatively activated macrophages, dendritic cells, eosinophils, and group 2 innate lymphoid cells. Furthermore, Schistosoma infection and Schistosoma products are effective for the treatment of T2D, as they increase the number of type 2 helper T cells (Th2) and regulatory T cells (Tregs) and decrease type 1 helper T cells (Th1) and type 17 helper T cells (Th17) cells. Thus, our aim was to comprehensively review the mechanism through which Schistosoma infection and Schistosoma products modulate the immune response against T2D.

Susceptibility of dendritic cells from individuals with schistosomiasis to infection by Leishmania braziliensis

Coinfection with leishmaniasis and schistosomiasis has been associated with increased time to healing of cutaneous lesions of leishmaniasis. The objective of this study was to evaluate the effect of Leishmania braziliensis infection on co-cultures of monocyte-derived dendritic cells (MoDCs) with autologous lymphocytes from patients with schistosomiasis and patients with cutaneous leishmaniasis. MoDCs were differentiated from peripheral blood monocytes, isolated by magnetic beads, infected with L. braziliensis, and co-cultured with autologous lymphocytes. Expression of HLA-DR, CD1a, CD83, CD80, CD86, CD40, and the IL-10 receptor (IL-10R) on MoDCs as well as CD28, CD40L, CD25, and CTLA-4 on lymphocytes were evaluated by flow cytometry. The production of the cytokines IL-10, TNF, IL-12p40, and IFN-γ were evaluated by sandwich ELISA of the culture supernatant. The infectivity evaluation was performed by light microscopy after concentration of cells by cytospin and Giemsa staining. It was observed that the frequency of MoDCs expressing CD83, CD80, and CD86 as well as the MFI of HLA-DR were smaller in the group of patients with schistosomiasis compared to the group of patients with leishmaniasis. On the other hand, the frequency of IL-10R on MoDCs was higher in patients with schistosomiasis than in patients with leishmaniasis. CD4⁺ and CD8⁺ T lymphocytes from patients with schistosomiasis presented a lower frequency of CD28 and a higher frequency of CTLA-4 compared to lymphocytes from patients with leishmaniasis. Levels of IL-10 were higher in the supernatants of co-cultures from individuals with schistosomiasis compared to those with leishmaniasis. However, levels of TNF, IL-12p40, and IFN-γ were lower in the group of individuals with schistosomiasis. Regarding the frequency of MoDCs infected by L. braziliensis after 72h in culture, it was observed that higher frequencies of cells from patients with schistosomiasis were infected compared to cells from patients with leishmaniasis. It was concluded that MoDCs from patients with schistosomiasis are more likely to be infected by L. braziliensis, possibly due to a lower degree of activation and a regulatory profile.

Type I interferon is required for T helper (Th) 2 induction by dendritic cells

Type 2 inflammation is a defining feature of infection with parasitic worms (helminths), as well as being responsible for widespread suffering in allergies. However, the precise mechanisms involved in T helper (Th) 2 polarization by dendritic cells (DCs) are currently unclear. We have identified a previously unrecognized role for type I IFN (IFN‐I) in enabling this process. An IFN‐I signature was evident in DCs responding to the helminth Schistosoma mansoni or the allergen house dust mite (HDM). Further, IFN‐I signaling was required for optimal DC phenotypic activation in response to helminth antigen (Ag), and efficient migration to, and localization with, T cells in the draining lymph node (dLN). Importantly, DCs generated from Ifnar1^−/− mice were incapable of initiating Th2 responses in vivo. These data demonstrate for the first time that the influence of IFN‐I is not limited to antiviral or bacterial settings but also has a central role to play in DC initiation of Th2 responses.

Yeast-expressed recombinant As16 protects mice against Ascaris suum infection through induction of a Th2-skewed immune response

Background

Ascariasis remains the most common helminth infection in humans. As an alternative or complementary approach to global deworming, a pan-anthelminthic vaccine is under development targeting Ascaris, hookworm, and Trichuris infections. As16 and As14 have previously been described as two genetically related proteins from Ascaris suum that induced protective immunity in mice when formulated with cholera toxin B subunit (CTB) as an adjuvant, but the exact protective mechanism was not well understood.

Methodology/Principal findings

As16 and As14 were highly expressed as soluble recombinant proteins (rAs16 and rAs14) in Pichia pastoris. The yeast-expressed rAs16 was highly recognized by immune sera from mice infected with A. suum eggs and elicited 99.6% protection against A. suum re-infection. Mice immunized with rAs16 formulated with ISA720 displayed significant larva reduction (36.7%) and stunted larval development against A. suum eggs challenge. The protective immunity was associated with a predominant Th2-type response characterized by high titers of serological IgG1 (IgG1/IgG2a > 2000) and high levels of IL-4 and IL-5 produced by restimulated splenocytes. A similar level of protection was observed in mice immunized with rAs16 formulated with alum (Alhydrogel), known to induce mainly a Th2-type immune response, whereas mice immunized with rAs16 formulated with MPLA or AddaVax, both known to induce a Th1-type biased response, were not significantly protected against A. suum infection. The rAs14 protein was not recognized by A. suum infected mouse sera and mice immunized with rAs14 formulated with ISA720 did not show significant protection against challenge infection, possibly due to the protein’s inaccessibility to the host immune system or a Th1-type response was induced which would counter a protective Th2-type response.

Conclusions/Significance

Yeast-expressed rAs16 formulated with ISA720 or alum induced significant protection in mice against A. suum egg challenge that associates with a Th2-skewed immune response, suggesting that rAS16 could be a feasible vaccine candidate against ascariasis.

Roundworms (Ascaris) infect more than 700 million people living in poverty worldwide and cause malnutrition and physical and mental developmental delays in children. As an alternative or complementary approach to global deworming, a pan-anthelminthic vaccine is under development that targets ascariasis in addition to other human intestinal nematode infections. Towards this goal, two Ascaris suum antigens, As16 and As14, were expressed in Pichia pastoris as recombinant proteins. Mice immunized with rAs16 formulated with ISA720 adjuvant produced significant larva reduction (36.7%) and stunted larval development against A. suum egg challenge. The protection was associated with predominant Th2-type responses characterized by high levels of serological IgG1 (IgG1/IgG2a > 2,000) and Th2 cytokines, IL-4 and IL-5. A similar level of protection was observed in mice immunized with rAs16 formulated with alum that induces mainly a Th2-type immune response, whereas mice immunized with rAs16 formulated with MPLA or AddaVax, both inducing major Th1-type responses, were not significantly protected against A. suum infection. High-yield expression of rAs16 in yeast will allow for large-scale manufacture, and its protective efficacy when formulated with alum suggests its suitability as a vaccine candidate.

Different populations of CD11b+ dendritic cells drive Th2 responses in the small intestine and colon

T-helper 2 (Th2) cell responses defend against parasites. Although dendritic cells (DCs) are vital for the induction of T-cell responses, the DC subpopulations that induce Th2 cells in the intestine are unidentified. Here we show that intestinal Th2 responses against Trichuris muris worms and Schistosoma mansoni eggs do not develop in mice with IRF-4-deficient DCs (IRF-4^f/f CD11c-cre). Adoptive transfer of conventional DCs, in particular CD11b-expressing DCs from the intestine, is sufficient to prime S. mansoni-specific Th2 responses. Surprisingly, transferred IRF-4-deficient DCs also effectively prime S. mansoni-specific Th2 responses. Egg antigens do not induce the expression of IRF-4-related genes. Instead, IRF-4^f/f CD11c-cre mice have fewer CD11b⁺ migrating DCs and fewer DCs carrying parasite antigens to the lymph nodes. Furthermore, CD11b⁺CD103⁺ DCs induce Th2 responses in the small intestine, whereas CD11b⁺CD103⁻ DCs perform this role in the colon, revealing a specific functional heterogeneity among intestinal DCs in inducing Th2 responses.

T helper 2 (Th2) cell responses are essential for immunity against parasites, but how Th2 response is modulated in the gut is still unclear. Here the authors show that distinct dendritic cell subsets distinguishable by CD11b, CD103 and IRF4 function in the small intestine or colon to promote Th2 responses.

Parasitic infection as a potential therapeutic tool against rheumatoid arthritis

Parasites, which are a recently discovered yet ancient dweller in human hosts, remain a great public health burden in underdeveloped countries, despite preventative efforts. Rheumatoid arthritis is a predominantly cosmopolitan health problem with drastic morbidity rates, although encouraging progress has been achieved regarding treatment. However, although various types of methods and agents have been applied clinically, their broad usage has been limited by their adverse effects and/or high costs. Sustained efforts have been exerted on the 'hygiene hypothesis' since the 1870s. The immunosuppressive nature of parasitic infections may offer potential insight into therapeutic strategies for rheumatoid arthritis, in which the immune system is overactivated. An increasing number of published papers are focusing on the preventive and/or curative effect of various parasitic infection on rheumatoid arthritis from experimental studies to large-scale epidemiological studies and clinical trials. Therefore, the present review aimed to provide a general literature review on the possible beneficial role of parasitic infection on rheumatoid arthritis.

Molecular events by which dendritic cells promote Th2 immune protection in helmith infection

Helminth parasites are a major cause of global infectious diseases, affecting nearly one quarter of the world's population. The common feature of helminth infections is to skew the immune system towards a T-helper 2 (Th2) response that helps to control disease. Dendritic cells (DCs), which are professional antigen-presenting cells, play a critical role for Th2 skewing against helminth parasites. However, the molecular mechanisms by which helminth antigens activate DCs for Th2 polarization have not yet been clearly defined. This review provides a focused update on the major role of DCs for inducing and/or enhancing Th2 immune responses in helminthic infection and will discuss the main signalling-dependent and independent mechanisms by which helminth antigens activate DCs for Th2 skewing.

Dendritic cells in lung immunopathology

Dendritic cells (DCs) lie at the heart of the innate immune system, specialised at recognising danger signals in many forms including foreign material, infection or tissue damage and initiating powerful adaptive immune and inflammatory responses. In barrier sites such as the lung, the instrumental role that DCs play at the interface between the environment and the host places them in a pivotal position in determining the severity of inflammatory disease. The past few years has seen a significant increase in our fundamental understanding of the subsets of DCs involved in pulmonary immunity, as well as the mechanisms by which they are activated and which they may use to coordinate downstream inflammation and pathology. In this review, we will summarise current understanding of the multi-faceted role that DCs play in the induction, maintenance and regulation of lung immunopathology, with an emphasis on allergic pulmonary disease.

MGL Receptor and Immunity: When the Ligand Can Make the Difference

C-type lectin receptors (CLRs) on antigen-presenting cells (APCs) facilitate uptake of carbohydrate antigens for antigen presentation, modulating the immune response in infection, homeostasis, autoimmunity, allergy, and cancer. In this review, we focus on the role of the macrophage galactose type C-type lectin (MGL) in the immune response against self-antigens, pathogens, and tumor associated antigens (TAA). MGL is a CLR exclusively expressed by dendritic cells (DCs) and activated macrophages (MØs), able to recognize terminal GalNAc residues, including the sialylated and nonsialylated Tn antigens. We discuss the effects on DC function induced throughout the engagement of MGL, highlighting the importance of the antigen structure in the modulation of immune response. Indeed modifying Tn-density, the length, and steric structure of the Tn-antigens can result in generating immunogens that can efficiently bind to MGL, strongly activate DCs, mimic the effects of a danger signal, and achieve an efficient presentation in HLA classes I and II compartments.

A central role for hepatic conventional dendritic cells in supporting Th2 responses during helminth infection

Dendritic cells (DCs) are the key initiators of T-helper (Th) 2 immune responses against the parasitic helminth Schistosoma mansoni. Although the liver is one of the main sites of antigen deposition during infection with this parasite, it is not yet clear how distinct DC subtypes in this tissue respond to S. mansoni antigens in vivo, or how the liver microenvironment might influence DC function during establishment of the Th2 response. In this study, we show that hepatic DC subsets undergo distinct activation processes in vivo following murine infection with S. mansoni. Conventional DCs (cDCs) from schistosome-infected mice upregulated expression of the costimulatory molecule CD40 and were capable of priming naive CD4(+) T cells, whereas plasmacytoid DCs (pDCs) upregulated expression of MHC class II, CD86 and CD40 but were unable to support the expansion of either naive or effector/memory CD4(+) T cells. Importantly, in vivo depletion of pDCs revealed that this subset was dispensable for either maintenance or regulation of the hepatic Th2 effector response during acute S. mansoni infection. Our data provides strong evidence that S. mansoni infection favors the establishment of an immunogenic, rather than tolerogenic, liver microenvironment that conditions cDCs to initiate and maintain Th2 immunity in the context of ongoing antigen exposure.

IL-4-Producing Dendritic Cells Induced during Schistosoma japonica Infection Promote Th2 Cells via IL-4-Dependent Pathway

Although dendritic cells (DCs) have been widely demonstrated to play essential roles in initiation of Th2 responses in helminth infections and allergic reactions, the mechanisms remain uncertain largely because DCs do not produce IL-4. In present investigation, we have uncovered a novel subset of DCs from mice infected with Th2-provoking pathogens Schistosoma japonica, which independently promoted Th2 cells via IL-4-dependent pathway. These DCs contained similar levels of IL-4 mRNA and higher levels of IL-12p40 mRNA comparing to basophils, correlating to their Th2-promoting and Th1-promoting dual polarization capacities. Characterized by expression of FcεRI(+), these DCs were induced independent of T cells. Further investigations revealed that Th2-promoting FcεRI(+) DCs were monocyte-derived inflammatory DCs, which were sufficient to induce Th2 cells in vivo. Egg Ags together with GM-CSF or IL-3 alone were able to stimulate the generation of Th2-promoting FcεRI(+) DCs from bone marrow cells in vitro. To our knowledge, our data for the first time demonstrate that IL-4-producing DCs are induced under some Th2-provoking situations, and they should play important roles in initiation of Th2 response.

Involvement of CD300a Phosphatidylserine Immunoreceptor in Aluminum Salt Adjuvant-Induced Th2 Responses

Aluminum salt (alum) has been widely used for vaccinations as an adjuvant. Alum not only enhances immunogenicity but also induces Th2 cell immune responses. However, the mechanisms of how alum enhances Th2 cell immune responses have been controversial. In an experimental allergic airway inflammation model, in which alum in conjunction with OVA Ag was i.p. injected for immunization, we found that apoptotic cells and inflammatory dendritic cells (iDC) expressing CD300a, an inhibitory immunoreceptor for phosphatidylserine (PS), significantly increased in number in the peritoneal cavity after the immunization. In contrast, apoptotic cells and iDCs were scarcely observed in the peritoneal cavity after injection of OVA alone. In CD300a-deficient mice, eosinophil infiltration in bronchoalveolar lavage fluid, serum IgE levels, and airway hyperreactivity were significantly decreased after immunization with alum plus OVA compared with wild-type mice. In vitro, iDCs purified from CD300a-deficient mice after the immunization induced significantly less IL-4 production from OT-II naive CD4(+) T cells after coculture with OVA Ag. CD300a expressed on iDCs bound PS on apoptotic cells in the peritoneal cavity after injection of OVA plus alum. Blocking CD300a interaction with PS by injection of a neutralizing anti-CD300a Ab resulted in inhibition of the development of allergic airway inflammation. These results suggest that CD300a is involved in alum-induced Th2 skewing.

Prospects for Vector-Based Gene Silencing to Explore Immunobiological Features of Schistosoma mansoni

Schistosomiasis is a prevalent, socioeconomically important disease of humans caused by parasites of the genus Schistosoma (schistosomes or blood flukes). Currently, more than 200 million people worldwide are infected with schistosomes. Despite major research efforts, there is only one drug routinely used for effective treatment, and no vaccine is available to combat schistosomiasis. The purpose of the present article is to (1) provide a background on the parasites and different forms of disease; (2) describe key immunomolecular aspects of disease induced in the host; and (3) critically appraise functional genomic methods employed to explore parasite biology, parasite-host interactions and disease at the molecular level. Importantly, the article also describes the features and advantages of lentiviral delivery of artificial microRNAs to silence genes. It also discusses the first successful application of such an approach in schistosomes, in order to explore the immunobiological role of selected target proteins known to be involved in egg-induced disease. The lentiviral transduction system provides exciting prospects for future, fundamental investigations of schistosomes, and is likely to have broad applicability to other eukaryotic pathogens and infectious diseases. The ability to achieve effective and stable gene perturbation in parasites has major biotechnological implications, and might facilitate the development of radically new methods for the treatment and control of parasitic diseases.

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.

Priming dendritic cells for th2 polarization: lessons learned from helminths and implications for metabolic disorders

Nearly one quarter of the world's population is infected with helminth parasites. A common feature of helminth infections is the manifestation of a type 2 immune response, characterized by T helper 2 (Th2) cells that mediate anti-helminth immunity. In addition, recent literature describes a close association between type 2 immune responses and wound repair, suggesting that a Th2 response may concurrently mediate repair of parasite-induced damage. The molecular mechanisms that govern Th2 responses are poorly understood, although it is clear that dendritic cells (DCs), which are the most efficient antigen-presenting cells in the immune system, play a central role. Here, we review the molecular mechanisms by which DCs polarize Th2 cells, examining both helminth antigens and helminth-mediated tissue damage as Th2-inducing triggers. Finally, we discuss the implication of these findings in the context of metabolic disorders, as recent literature indicates that various aspects of the Th2-associated inflammatory response contribute to metabolic homeostasis.

The Differentiation of CD4(+) T-Helper Cell Subsets in the Context of Helminth Parasite Infection

Helminths are credited with being the major selective force driving the evolution of the so-called “type 2” immune responses in vertebrate animals, with their size and infection strategies presenting unique challenges to the immune system. Originally, type 2 immune responses were defined by the presence and activities of the CD4⁺ T-helper 2 subset producing the canonical cytokines IL-4, IL-5, and IL-13. This picture is now being challenged by the discovery of a more complex pattern of CD4⁺ T-helper cell subsets that appear during infection, including Tregs, Th17, Tfh, and more recently, Th22, Th9, and ThGM. In addition, a clearer view of the mechanisms by which helminths and their products selectively prime the CD4⁺ T-cell subsets is emerging. In this review, we have focused on recent data concerning the selective priming, differentiation, and functional role of CD4⁺ T-helper cell subsets in the context of helminth infection. We argue for a re-evaluation of the original Th2 paradigm and discuss how the observed plasticity of the T-helper subsets may enable the parasitized host to achieve an appropriate compromise between elimination, tissue repair, containment, and pathology.

A mouse model of HIES reveals pro- and anti-inflammatory functions of STAT3

Mutations of STAT3 underlie the autosomal dominant form of hyperimmunoglobulin E syndrome (HIES). STAT3 has critical roles in immune cells and thus, hematopoietic stem cell transplantation (HSCT), might be a reasonable therapeutic strategy in this disease. However, STAT3 also has critical functions in nonhematopoietic cells and dissecting the protean roles of STAT3 is limited by the lethality associated with germline deletion of Stat3. Thus, predicting the efficacy of HSCT for HIES is difficult. To begin to dissect the importance of STAT3 in hematopoietic and nonhematopoietic cells as it relates to HIES, we generated a mouse model of this disease. We found that these transgenic mice recapitulate multiple aspects of HIES, including elevated serum IgE and failure to generate Th17 cells. We found that these mice were susceptible to bacterial infection that was partially corrected by HSCT using wild-type bone marrow, emphasizing the role played by the epithelium in the pathophysiology of HIES.

Effect of helminth-induced immunity on infections with microbial pathogens

Helminth infections are ubiquitous worldwide and can trigger potent immune responses that differ from and potentially antagonize host protective responses to microbial pathogens. In this Review we focus on the three main killers in infectious disease-AIDS, tuberculosis and malaria-and critically assesses whether helminths adversely influence host control of these diseases. We also discuss emerging concepts for how M2 macrophages and helminth-modulated dendritic cells can potentially influence the protective immune response to concurrent infections. Finally, we present evidence advocating for more efforts to determine how and to what extent helminths interfere with the successful control of specific concurrent coinfections.

The effect of different adjuvants on immune parameters and protection following vaccination of sheep with a larval-specific antigen of the gastrointestinal nematode, Haemonchus contortus

It has recently been recognised that vaccine adjuvants play a critical role in directing the nature of a vaccine induced effector response. In the present study, several adjuvants were evaluated for their ability to protect sheep after field vaccination with the larval-specific Haemonchus contortus antigen, HcsL3. Using a suboptimal antigen dose, aluminium adjuvant was shown to reduce the cumulative faecal egg counts (cFEC) and worm burden by 23% and 25% respectively, in agreement with a previous study. The addition of Quil A to the aluminium-adjuvanted vaccine brought cFEC back to control levels. Vaccination with the adjuvant DEAE-dextran almost doubled the protection compared to the aluminium-adjuvanted vaccine resulting in 40% and 41% reduction in cFEC and worm counts compared to controls. Examination of skin responses following i.d. injection of exsheathed L3, revealed that cFEC was negatively correlated with wheal size and tissue eosinophils for the DEAE-dextran and aluminium-adjuvanted groups respectively. These studies have for the first time shown the potential of DEAE-dextran adjuvant for helminth vaccines, and discovered significant cellular correlates of vaccine-induced protection.

The schistosoma granuloma: friend or foe?

Infection of man with Schistosoma species of trematode parasite causes marked chronic morbidity. Individuals that become infected with Schistosomes may develop a spectrum of pathology ranging from mild cercarial dermatitis to severe tissue inflammation, in particular within the liver and intestines, which can lead to life threatening hepatosplenomegaly. It is well established that the etiopathology during schistosomiasis is primarily due to an excessive or unregulated inflammatory response to the parasite, in particular to eggs that become trapped in various tissue. The eggs forms the foci of a classical type 2 granulomatous inflammation, characterized by an eosinophil-rich, CD4⁺ T helper (Th) 2 cell dominated infiltrate with additional infiltration of alternatively activated macrophages (M2). Indeed the sequela of the type 2 perioval granuloma is marked fibroblast infiltration and development of fibrosis. Paradoxically, while the granuloma is the cause of pathology it also can afford some protection, whereby the granuloma minimizes collateral tissue damage in the liver and intestines. Furthermore, the parasite is exquisitely reliant on the host to mount a granulomatous reaction to the eggs as this inflammatory response facilitates the successful excretion of the eggs from the host. In this focused review we will address the conundrum of the S. mansoni granuloma acting as both friend and foe in inflammation during infection.

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.

Helminth infections and host immune regulation

Helminth parasites infect almost one-third of the world's population, primarily in tropical regions. However, regions where helminth parasites are endemic record much lower prevalences of allergies and autoimmune diseases, suggesting that parasites may protect against immunopathological syndromes. Most helminth diseases are spectral in nature, with a large proportion of relatively asymptomatic cases and a subset of patients who develop severe pathologies. The maintenance of the asymptomatic state is now recognized as reflecting an immunoregulatory environment, which may be promoted by parasites, and involves multiple levels of host regulatory cells and cytokines; a breakdown of this regulation is observed in pathological disease. Currently, there is much interest in whether helminth-associated immune regulation may ameliorate allergy and autoimmunity, with investigations in both laboratory models and human trials. Understanding and exploiting the interactions between these parasites and the host regulatory network are therefore likely to highlight new strategies to control both infectious and immunological diseases.

Transient deficiency of dendritic cells results in lack of a merozoite surface protein 1-specific CD4 T cell response during peak Plasmodium chabaudi blood-stage infection

Splenic dendritic cells are crucial for controlling the immune response to malaria by initiating a CD4 gamma interferon (IFN-γ) response early in a blood-stage infection, which contributes to parasite clearance as well as to acute-stage immunopathology. CD8(-) CD11c(high) dendritic cells have been described previously to be important antigen-presenting cells for induction of these CD4 T cell responses in the spleens of Plasmodium chabaudi-infected mice. However, when isolated during the period of maximum parasitemia and shortly thereafter, the dendritic cells transiently lose their ability to stimulate T cells, recovering only as the parasitemia is controlled. This loss of a CD4 T cell response is also observed in vivo during this part of the infection. CD4 T cells from a T cell receptor-transgenic mouse recognizing a peptide of merozoite surface protein 1 (MSP1) injected into BALB/c mice during peak parasitemia proliferate poorly, and very few cells produce IFN-γ and interleukin-2 (IL-2), compared with transgenic T cells injected earlier in the blood-stage infection. CD8(-) dendritic cells at day 10 can process and present peptides on major histocompatibility complex (MHC) class II with an efficiency similar to that of dendritic cells from earlier in infection. The failure of the day 10 dendritic cells to activate MSP1-specific CD4 T cells fully in vitro is associated with reduced expression of CD86 and lower production of IL-12 rather than with induction of inhibitory DC receptors or production of IL-10.

Paradoxical associations between soil-transmitted helminths and Plasmodium falciparum infection

Evidence on the comorbidity between soil-transmitted helminth infections and malaria is scarce and divergent. This study explored the interactions between soil-transmitted helminth infections and uncomplicated falciparum malaria in an endemic area of Colombia. A paired case-control study matched by sex, age and location in Tierralta, Cordoba, was done between January and September 2010. The incident cases were 68 patients with falciparum malaria and 178 asymptomatic controls. A questionnaire was used to gather information on sociodemographic variables. Additionally physical examinations were carried out, stool samples were analysed for intestinal parasites and blood samples for Ig E concentrations. We found associations between infection with hookworm (OR: 4.21; 95% CI: 1.68-11.31) and Ascaris lumbricoides (OR 0.43; 95% CI: 0.18-1.04) and the occurrence of falciparum malaria. The effects of soil-transmitted helminths on the occurrence of malaria were found to be paradoxical. While hookworm is a risk factor, A. lumbricoides has a protective effect. The findings suggest that, in addition to the comorbidity, the presence of common determinants of soil-transmitted helminth infections and malaria could also exist. While the biological mechanisms involved are not clear, public health policies aimed at the control of their common social and environmental determinants are suggested.

Dose-dependent response of dendritic cells to 7-thia-8-oxo-guanosine and its modulation by polyinosinic:polycytidylic acid

Targeting the endosomal Toll-like receptors (TLRs) by specific agonists seems to be a promising tool for stimulation of the immunogenicity of dendritic cells (DCs). Since the functional outcome upon the engagement of TLRs may be different, the aim of our study was to examine if and how different concentrations of 7-thia-8-oxo-guanosine (7-TOG), a selective TLR7 agonist, influence differentiation, maturation and functions of human monocyte-derived DCs (MoDCs) and if its effects on MoDCs could be modulated by co-ligation of TLR3. Immature MoDCs were treated with different concentrations of 7-TOG (25, 100 and 250 μmol/L) alone, or together with polyinosinic:polycytidylic acid, Poly (I:C) (10 ng/mL), a selective TLR3 agonist, for an additional 48 h. We showed that the highest concentration of 7-TOG stimulated the differentiation, maturation and allostimulatory capability of MoDCs. These changes were accompanied by an increased production of interleukin 12 (IL-12) and induction of T helper (Th)1 and Th17 immune responses. Both Th responses were significantly augmented by additional stimulation of MoDCs with Poly (I:C). The treatment of MoDCs with the intermediate concentration of 7-TOG resulted in the up-regulation of co-stimulatory molecule (CD86) and increased production of IL-1β and IL-6 by MoDCs, followed by the stimulation of the Th17 immune response. The lowest concentration of 7-TOG down-regulated the expression of CD40 on MoDCs and potentiated the Th2 immune response. The Th2 response was not significantly modulated by additional treatment of MoDCs with Poly (I:C), but this combination of TLR3/TLR7 agonists also stimulated both Th1 and Th17 responses. In conclusion, our results show that 7-TOG influences the phenotype and functions of MoDCs in a dose-dependent manner and suggests that fine-tuned signaling through TLR7 may be modified by the engagement of TLR3, resulting in a different outcome of immune response.

Cellular networks controlling Th2 polarization in allergy and immunity

In contrast to the development of Th1 (type 1 T helper cells), Th17 and Treg (regulatory T cells), little is known of the mechanisms governing Th2 development, which is important for immunity to helminths and for us to understand the pathogenesis of allergy. A picture is emerging in which mucosal epithelial cells instruct dendritic cells to promote Th2 responses in the absence of IL-12 (interleukin 12) production and provide instruction through thymic stromal lymphopoieitin (TSLP) or granulocyte-macrophage colony stimulating factor (GM-CSF). At the same time, allergens, helminths and chemical adjuvants elicit the response of innate immune cells like basophils, which provide more polarizing cytokines and IL-4 and reinforce Th2 immunity. This unique communication between cells will only be fully appreciated if we study Th2 immunity in vivo and in a tissue-specific context, and can only be fully understood if we compare several models of Th2 immune response induction.

Proteomic identification of IPSE/alpha-1 as a major hepatotoxin secreted by Schistosoma mansoni eggs

Background

Eggs deposited in the liver of the mammalian host by the blood fluke parasite, Schistosoma mansoni, normally drive a T-helper-2 (Th2)-mediated granulomatous response in immune-competent mice. By contrast, in mice deprived of T-cells and incapable of producing granulomata, egg-secreted proteins (ESP) induce acute hepatic injury and death. Previous work has shown that one such ESP, the T2 ribonuclease known as omega-1, is hepatotoxic in vivo in that specific antisera to omega-1 prevent hepatocyte damage.

Methodology/Principal Findings

Using an in vitro culture system employing mouse primary hepatocytes and alanine transaminase (ALT) activity as a marker of heptocyte injury, we demonstrated that S. mansoni eggs, egg-secreted proteins (ESP), soluble-egg antigen (SEA), and omega-1 are directly hepatotoxic and in a dose-dependent manner. Depletion of omega-1 using a monoclonal antibody abolished the toxicity of pure omega-1 and diminished the toxicity in ESP and SEA by 47 and 33%, respectively. Anion exchange chromatography of ESP yielded one predominant hepatotoxic fraction. Proteomics of that fraction identified the presence of IPSE/alpha-1 (IL-4 inducing principle from S. mansoni eggs), a known activator of basophils and inducer of Th2-type responses. Pure recombinant IPSE/alpha-1 also displayed a dose-dependent hepatotoxicity in vitro. Monoclonal antibody depletion of IPSE/alpha-1 abolished the latter's toxicity and diminished the total toxicity of ESP and SEA by 32 and 35%, respectively. Combined depletion of omega-1 and IPSE/alpha-1 diminished hepatotoxicity of ESP and SEA by 60 and 58% respectively.

Conclusions

We identified IPSE/alpha-1 as a novel hepatotoxin and conclude that both IPSE/alpha-1 and omega-1 account for the majority of the hepatotoxicity secreted by S. mansoni eggs.

The flatworm disease, schistosomiasis, is a major public health problem in sub-Saharan Africa, South America and East Asia. A hallmark of infection with Schistosoma mansoni is the immune response to parasite eggs trapped in the liver and other organs. This response involves an infiltration of cells that surround the parasite egg forming a “granuloma.” In mice deprived of T-cells, this granulomatous response is lacking, and toxic products released by eggs quickly cause liver damage and death. Thus the granulomata protect the host from toxic egg products. Only one hepatotoxic molecule, omega-1, has been described to date. We set out to identify other S. mansoni egg hepatotoxins using liver cells grown in culture. We first showed that live eggs, their secretions, and pure omega-1 are toxic. Using a physical separation technique to prepare fractions from whole egg secretions, we identified the presence of IPSE/alpha-1, a protein that is known to strongly influence the immune system. We showed that IPSE/alpha-1 is also hepatotoxic, and that toxicity of both omega-1 and IPSE/alpha-1 can be prevented by first mixing the proteins with specific neutralizing antibodies. Both proteins constitute the majority of hepatotoxicity released by eggs.

Triggering receptor expressed on myeloid cells (TREM)-1 participates in Schistosoma mansoni inflammatory responses

Inflammatory responses to microbial products are amplified by a pathway mediated by triggering a receptor expressed on the myeloid cells (TREM)-1. Relatively a few studies have been performed to investigate the role of TREM-1 in macrophage activation in response to parasitic infection. In this study, we delineate the role of the innate immunoreceptor TREM-1 in the parasite Schistosoma mansoni infection model from early to late (chronic) phases of infection. Flow cytometry analysis revealed gradual increase in the production of TREM-1 protein on CD11b(+) myeloid cells, with maximum production at 5 weeks p.i. Similar results in the pattern of TREM-1 mRNA expressions in splenic CD11b(+) cells from infected mice were obtained by real-time PCR. However, unlike in spleen, the TREM-1 mRNA expression in liver tissue showed no significant increase throughout the infection, including periods of maximum production of parasite eggs. Administration of schistosoma egg homogenate antigen to stimulate J774A.1 cells inhibited TREM-1 expression on the surface, indicating that some substances of the Schistosma eggs may inhibit the expression of TREM-1 on macrophages, lowering the macrophage-mediated inflammatory response of infected hosts.

Gene expression analysis of dendritic cells that prevent diabetes in NOD mice: analysis of chemokines and costimulatory molecules

We have demonstrated previously that BM-derived DCs can prevent diabetes development and halt progression of insulitis in NOD mice, the mouse model of type 1 diabetes. The DC population that was most effective in this therapy had a mature phenotype, expressed high levels of costimulatory molecules, and secreted low levels of IL-12p70. The protective DC therapy induced Treg and Th2 cells in vitro and in vivo. Microarray analysis of therapeutic and nontherapeutic DC populations revealed differences in the expression of OX40L, CD200, Ym-1, CCL2, and CCL5, which could play important roles in the observed DC-mediated therapy. The unique pattern of costimulatory molecules and chemokines expressed by the therapeutic DCs was confirmed by flow cytometry and ELISA. Using a novel cell-labeling and (19)F NMR, we observed that the chemokines secreted by the therapeutic DCs altered the migration of diabetogenic Th1 cells in vivo and attracted Th2 cells. These results suggest that the therapeutic function of DCs is mediated by a combination of costimulatory and chemokine properties that results in the attraction of diabetogenic Th1 and the induction of Th2 and/or Treg differentiation.

Schistosoma mansoni egg glycoproteins and C-type lectins of host immune cells: molecular partners that shape immune responses

Schistosome eggs and egg-derived molecules are potent immunomodulatory agents. There is increasing evidence that the interplay between egg glycoproteins and host C-type lectins plays an important role in shaping immune responses during schistosomiasis. As most experiments in this field so far have been performed using complex protein/glycoprotein mixtures or synthetic model glycoconjugates, it is still largely unclear which individual moieties of schistosome eggs are immunologically active. In this review we will discuss molecular aspects of Schistosoma mansoni egg glycoproteins, their interactions with C-type lectins, and the relevance to schistosome egg immunobiology.

Basophils induce Th2 immunity: is this final answer?

Despite that basophils represent less than 0.5% of circulating leukocytes, recent studies have begun to unveil their potent immunoregulatory functions, i.e., induction of Th2 immunity. It is believed that basophils are capable of doing so primarily by secreting key Th2-inducing cytokines, namely IL-4 and Thymic Stromal Lymphopoietin (TSLP), and by functioning as professional antigen presenting cells. However, we have recently demonstrated that Th2 immunity can develop in the absence of basophils or IL-4 during helminth infection. In this review, how basophils may (and may not) contribute to the development of Th2 immunity in vivo is discussed.

Mouse neutrophils are professional antigen-presenting cells programmed to instruct Th1 and Th17 T-cell differentiation

Neutrophils play a major role in the innate immune system and are normally considered to be short-lived effector cells that exert anti-microbial activity and sometimes immunopathology. Here, we show that these cells possess an additional function as professional antigen-presenting cells capable of priming a T(h)1- and T(h)17-acquired immune response. Using flow cytometry, fluorescence microscopy and western blotting, we show that mouse neutrophils express MHC class II and co-stimulatory molecules CD80 and CD86 after T-cell co-incubation. Neutrophils pulsed with ovalbumin (OVA) process and present peptide antigen to OVA-specific T cells in an MHC class II-dependent manner. Importantly, we demonstrate that neutrophils can prime antigen-specific T(h)1 and T(h)17 immune responses even without the addition of exogenous cytokines to cell cultures.

Inflammatory dendritic cells--not basophils--are necessary and sufficient for induction of Th2 immunity to inhaled house dust mite allergen

It is unclear how Th2 immunity is induced in response to allergens like house dust mite (HDM). Here, we show that HDM inhalation leads to the TLR4/MyD88-dependent recruitment of IL-4 competent basophils and eosinophils, and of inflammatory DCs to the draining mediastinal nodes. Depletion of basophils only partially reduced Th2 immunity, and depletion of eosinophils had no effect on the Th2 response. Basophils did not take up inhaled antigen, present it to T cells, or express antigen presentation machinery, whereas a population of FceRI⁺ DCs readily did. Inflammatory DCs were necessary and sufficient for induction of Th2 immunity and features of asthma, whereas basophils were not required. We favor a model whereby DCs initiate and basophils amplify Th2 immunity to HDM allergen.

Peroxiredoxin: a central player in immune modulation

Peroxiredoxins (Prx) are a family of anti-oxidants that protect cells from metabolically produced reactive oxygen species (ROS). The presence of these enzymes in the secretomes of many parasitic helminths suggests they provide protection against ROS released by host immune effector cells. However, we recently reported that helminth-secreted Prx also contribute to the development of Th2-responses via a mechanism involving the induction of alternatively activated macrophages. In this review, we discuss the role helminth Prx may play in modulating the immune responses of their hosts.

Functional impairment of human myeloid dendritic cells during Schistosoma haematobium infection

Chronic Schistosoma infection is often characterized by a state of T cell hyporesponsiveness of the host. Suppression of dendritic cell (DC) function could be one of the mechanisms underlying this phenomenon, since Schistosoma antigens are potent modulators of dendritic cell function in vitro. Yet, it remains to be established whether DC function is modulated during chronic human Schistosoma infection in vivo. To address this question, the effect of Schistosoma haematobium infection on the function of human blood DC was evaluated. We found that plasmacytoid (pDC) and myeloid DC (mDC) from infected subjects were present at lower frequencies in peripheral blood and that mDC displayed lower expression levels of HLA-DR compared to those from uninfected individuals. Furthermore, mDC from infected subjects, but not pDC, were found to have a reduced capacity to respond to TLR ligands, as determined by MAPK signaling, cytokine production and expression of maturation markers. Moreover, the T cell activating capacity of TLR-matured mDC from infected subjects was lower, likely as a result of reduced HLA-DR expression. Collectively these data show that S. haematobium infection is associated with functional impairment of human DC function in vivo and provide new insights into the underlying mechanisms of T cell hyporesponsiveness during chronic schistosomiasis.

Differential requirements for IL-4/STAT6 signalling in CD4 T-cell fate determination and Th2-immune effector responses

Improved analytical tools have revealed that the development and expression of a Th2 immune response can be broken down into distinct stages with respect to the cytokine microenvironment that is required. Although IL-4 and its STAT6-signalling pathway are critical for the expression of Th2 effector immune responses in peripheral tissues such as the skin, lung and gut, IL-4 and STAT6 signalling are not required for the initial generation of IL-4-producing Th2 cells in the lymph node. This finding reveals that we have yet to identify the key cytokine or microenvironment that stimulates the development of this most intriguing CD4(+) T-helper subset and emphasises the tissue specificity and timing of IL-4/STAT6-dependent Th2 effector responses.

Omega-1, a glycoprotein secreted by Schistosoma mansoni eggs, drives Th2 responses

Soluble egg antigens of the parasitic helminth Schistosoma mansoni (S. mansoni egg antigen [SEA]) induce strong Th2 responses both in vitro and in vivo. However, the specific molecules that prime the development of Th2 responses have not been identified. We report that omega-1, a glycoprotein which is secreted from S. mansoni eggs and present in SEA, is capable of conditioning human monocyte-derived dendritic cells in vitro to drive T helper 2 (Th2) polarization with similar characteristics as whole SEA. Furthermore, using IL-4 dual reporter mice, we show that both natural and recombinant omega-1 alone are sufficient to generate Th2 responses in vivo, even in the absence of IL-4R signaling. Finally, omega-1-depleted SEA displays an impaired capacity for Th2 priming in vitro, but not in vivo, suggesting the existence of additional factors within SEA that can compensate for the omega-1-mediated effects. Collectively, we identify omega-1, a single component of SEA, as a potent inducer of Th2 responses.

The major component in schistosome eggs responsible for conditioning dendritic cells for Th2 polarization is a T2 ribonuclease (omega-1)

Schistosoma mansoni eggs contain factors that trigger potent Th2 responses in vivo and condition mouse dendritic cells (DCs) to promote Th2 lymphocyte differentiation. Using an in vitro bystander polarization assay as the readout, we purified and identified the major Th2-inducing component from soluble egg extract (SEA) as the secreted T2 ribonuclease, omega-1. The Th2-promoting activity of omega-1 was found to be sensitive to ribonuclease inhibition and did not require MyD88/TRIF signaling in DCs. In common with unfractioned SEA, the purified native protein suppresses lipopolysaccharide-induced DC activation, but unlike SEA, it fails to trigger interleukin 4 production from basophils. Importantly, omega-1-exposed DCs displayed pronounced cytoskeletal changes and exhibited decreased antigen-dependent conjugate formation with CD4(+) T cells. Based on this evidence, we hypothesize that S. mansoni omega-1 acts by limiting the interaction of DCs with CD4(+) T lymphocytes, thereby lowering the strength of the activation signal delivered.

T-helper 1 and T-helper 2 adjuvants induce distinct differences in the magnitude, quality and kinetics of the early inflammatory response at the site of injection

Vaccine adjuvants activate the innate immune system and thus influence subsequent adaptive T-cell responses. However, little is known about the initial immune mechanisms preceding the adjuvant-induced differentiation of T-helper (Th) cells. The effect of a T-helper 1 (Th1) adjuvant, dimethyldioctadecylammonium liposomes with monophosphoryl lipid-A (DDA/MPL), and a T-helper 2 adjuvant, aluminium hydroxide [Al(OH)(3)], on early, innate chemotactic signals and inflammatory cell influx at the site of injection was therefore investigated. Injection of the adjuvants into the peritoneal cavity of mice demonstrated distinct differences in the magnitude, quality and kinetics of the response. The inflammatory response to DDA/MPL was prominent, inducing high local levels of pro-inflammatory cytokines, chemokines and a pronounced inflammatory exudate consisting of neutrophils, monocytes/macrophages and activated natural killer cells. This was in contrast to the response induced by Al(OH)(3), which, although sharing some of the early chemokine signals, was more moderate and consisted almost exclusively of neutrophils and eosinophils. Notably, Al(OH)(3) specifically induced the release of a significant amount of interleukin (IL)-5, whereas DDA/MPL induced high amounts of tumour necrosis factor-alpha (TNF-alpha), IL-1alpha and IL-6. Finally, a microarray analysis confirmed that the effect of DDA/MPL was broader with more than five times as many genes being specifically up-regulated after injection of DDA/MPL compared with Al(OH)(3). Thus, the adjuvants induced qualitatively distinct local inflammatory signals early after injection.

Selective induction of the Notch ligand Jagged-1 in macrophages by soluble egg antigen from Schistosoma mansoni involves ERK signalling

Soluble egg antigen (SEA) from the helminth Schistosoma mansoni promotes T helper type 2 (Th2) responses by modulating antigen-presenting cell function. The Jagged/Notch pathway has recently been implicated in driving Th2 development. We show here that SEA rapidly up-regulated mRNA and protein expression of the Notch ligand Jagged-1 in both murine bone marrow-derived macrophages (BMMs) and human monocyte-derived macrophages (HMDMs). Another potential Th2-promoting factor, interleukin (IL)-33, was not transcriptionally induced by SEA in BMMs. Up-regulation of Jagged-1 mRNA by SEA was also apparent in conventional dendritic cells (DCs), although the effect was less striking than in BMMs. Conversely, SEA-pulsed DCs, but not BMMs, promoted IL-4 production upon T-cell activation, suggesting that Jagged-1 induction alone is insufficient for instructing Th2 development. A comparison of the responses initiated in BMMs by SEA and the bacterial endotoxin lipopolysaccharide (LPS) revealed common activation of extracellular signal-regulated kinase-1/2 (ERK-1/2) and p38 phosphorylation, as well as induction of Jagged-1 mRNA. However, only LPS triggered IkappaB degradation, phosphorylation of c-Jun N-terminal kinase (Jnk) and signal transducer and activator of transcription 1 (Stat1) Tyr701, and IL-33 and IL-12p40 mRNA up-regulation. Inducible gene expression was modified by the presence of the macrophage growth factor colony-stimulating factor (CSF)-1, which inhibited Jagged-1 induction by SEA and LPS, but enhanced LPS-induced IL-12p40 expression. Unlike LPS, SEA robustly activated signalling in HEK293 cells expressing either Toll-like receptor 2 (TLR2) or TLR4/MD2. Pharmacological inhibition of the ERK-1/2 pathway impaired SEA- and LPS-inducible Jagged-1 expression in BMMs. Taken together, our data suggest that Jagged-1 is an ERK-dependent target of TLR signalling that has a macrophage-specific function in the response to SEA.

Immunomodulatory parasites and toll-like receptor-mediated tumour necrosis factor alpha responsiveness in wild mammals

Background

Immunological analyses of wild populations can increase our understanding of how vertebrate immune systems respond to 'natural' levels of exposure to diverse infections. A major recent advance in immunology has been the recognition of the central role of phylogenetically conserved toll-like receptors in triggering innate immunity and the subsequent recruitment of adaptive response programmes. We studied the cross-sectional associations between individual levels of systemic toll-like receptor-mediated tumour necrosis factor alpha responsiveness and macro- and microparasite infections in a natural wood mouse (Apodemus sylvaticus) population.

Results

Amongst a diverse group of macroparasites, only levels of the nematode Heligmosomoides polygyrus and the louse Polyplax serrata were correlated (negatively) with innate immune responsiveness (measured by splenocyte tumour necrosis factor alpha responses to a panel of toll-like receptor agonists). Polyplax serrata infection explained a strikingly high proportion of the total variation in innate responses. Contrastingly, faecal oocyst count in microparasitic Eimeria spp. was positively associated with innate immune responsiveness, most significantly for the endosomal receptors TLR7 and TLR9.

Conclusion

Analogy with relevant laboratory models suggests the underlying causality for the observed patterns may be parasite-driven immunomodulatory effects on the host. A subset of immunomodulatory parasite species could thus have a key role in structuring other infections in natural vertebrate populations by affecting the 'upstream' innate mediators, like toll-like receptors, that are important in initiating immunity. Furthermore, the magnitude of the present result suggests that populations free from immunosuppressive parasites may exist at 'unnaturally' elevated levels of innate immune activation, perhaps leading to an increased risk of immunopathology.

Review series on helminths, immune modulation and the hygiene hypothesis: immunity against helminths and immunological phenomena in modern human populations: coevolutionary legacies?

Although the molecules and cells involved in triggering immune responses against parasitic worms (helminths) remain enigmatic, research has continued to implicate expansions of T-helper type 2 (Th2) cells and regulatory T-helper (T(reg)) cells as a characteristic response to these organisms. An intimate association has also emerged between Th2 responses and wound-healing functions. As helminth infections in humans are associated with a strong Th2/T(reg) immunoregulatory footprint (often termed a 'modified Th2' response), plausible links have been made to increased susceptibility to microbial pathogens in helminth-infected populations in the tropics and to the breakdowns in immunological control (allergy and autoimmunity) that are increasing in frequency in helminth-free developed countries. Removal of helminths and their anti-inflammatory influence may also have hazards for populations exposed to infectious agents, such as malaria and influenza, whose worst effects are mediated by excessive inflammatory reactions. The patterns seen in the control of helminth immunity are discussed from an evolutionary perspective. Whilst an inability to correctly regulate the immune system in the absence of helminth infection might seem highly counter-adaptive, the very ancient and pervasive relationship between vertebrates and helminths supports a view that immunological control networks have been selected to function within the context of a modified Th2 environment. The absence of immunoregulatory stimuli from helminths may therefore uncover maladaptations that were not previously exposed to selection.

New insights into the roles of dendritic cells in intestinal immunity and tolerance

Dendritic cells (DCs) play a critical key role in the initiation of immune responses to pathogens. Paradoxically, they also prevent potentially damaging immune responses being directed against the multitude of harmless antigens, to which the body is exposed daily. These roles are particularly important in the intestine, where only a single layer of epithelial cells provides a barrier against billions of commensal microorganisms, pathogens, and food antigens, over a huge surface area. In the intestine, therefore, DCs are required to perform their dual roles very efficiently to protect the body from the dual threats of invading pathogens and unwanted inflammatory reactions. In this review, we first describe the biology of DCs and their interactions with other cells types, paying particular attention to intestinal DCs. We, then, examine the ways in which this biology may become misdirected, resulting in inflammatory bowel disease. Finally, we discuss how DCs potentiate immune responses against viral, bacterial, parasitic infections, and their importance in the pathogenesis of prion diseases. We, therefore, provide an overview of the complex cellular interactions that affect intestinal DCs and control the balance between immunity and tolerance.

Review series on helminths, immune modulation and the hygiene hypothesis: mechanisms underlying helminth modulation of dendritic cell function

Dendritic cells (DCs) play a central role in activating CD4 T (T helper, Th) cells. As a component of their response to pathogen-associated stimuli, DCs produce cytokines and express surface molecules that provide important cues to modulate the effector functions of responding Th cells. Much is known of how DCs respond to, and influence immune response outcome to, bacterial and viral pathogens. However, relatively little is understood about how DCs respond to helminth parasites. This is an area of considerable interest since it impacts our understanding of the initiation of Th2 responses, which are stereotypically associated with helminth infections, and the regulation of allergic and autoimmune pathologies which evidence suggests are less severe or absent in individuals infected with helminths. This review attempts to summarize our understanding of the effects of helminth products on dendritic cell biology.