Cutting edge: in the absence of TGF-β signaling in T cells, fewer CD103+ regulatory T cells develop, but exuberant IFN-γ production renders mice more susceptible to helminth infection

The multi-faceted roles of TGF-β in regulation of immunity to infection

Transforming Growth Factor-β is a potent regulator of the immune system, acting at every stage from thymic differentiation, population of the periphery, control of responsiveness, tissue repair and generation of memory. It is therefore a central player in the immune response to infectious pathogens, but its contribution is often clouded by multiple roles acting on different cells in time and space. Hence, context is all-important in understanding when TGF-β is beneficial or detrimental to the outcome of infection. In this review, a full range of infectious agents from viruses to helminth parasites are explored within this framework, drawing contrasts and general conclusions about the importance of TGF-β in these diseases.

Transgenic expression of a T cell epitope in Strongyloides ratti reveals that helminth-specific CD4+ T cells constitute both Th2 and Treg populations

Helminths are distinct from microbial pathogens in both size and complexity, and are the likely evolutionary driving force for type 2 immunity. CD4+ helper T cells can both coordinate worm clearance and prevent immunopathology, but issues of T cell antigen specificity in the context of helminth-induced Th2 and T regulatory cell (Treg) responses have not been addressed. Herein, we generated a novel transgenic line of the gastrointestinal nematode Strongyloides ratti expressing the immunodominant CD4+ T cell epitope 2W1S as a fusion protein with green fluorescent protein (GFP) and FLAG peptide in order to track and study helminth-specific CD4+ T cells. C57BL/6 mice infected with this stable transgenic line (termed Hulk) underwent a dose-dependent expansion of activated CD44hiCD11ahi 2W1S-specific CD4+ T cells, preferentially in the lung parenchyma. Transcriptional profiling of 2W1S-specific CD4+ T cells isolated from mice infected with either Hulk or the enteric bacterial pathogen Salmonella expressing 2W1S revealed that pathogen context exerted a dominant influence over CD4+ T cell phenotype. Interestingly, Hulk-elicited 2W1S-specific CD4+ T cells exhibited both Th2 and Treg phenotypes and expressed high levels of the EGFR ligand amphiregulin, which differed greatly from the phenotype of 2W1S-specific CD4+ T cells elicited by 2W1S-expressing Salmonella. While immunization with 2W1S peptide did not enhance clearance of Hulk infection, immunization did increase total amphiregulin production as well as the number of amphiregulin-expressing CD3+ cells in the lung following Hulk infection. Altogether, this new model system elucidates effector as well as immunosuppressive and wound reparative roles of helminth-specific CD4+ T cells. This report establishes a new resource for studying the nature and function of helminth-specific T cells.

Polyamines polarized Th2/Th9 cell-fate decision by regulating GATA3 expression

Polyamines produced by both prokaryotes and eukaryotes are bioactive substances with pleiotropic effects. Accumulating evidence has demonstrated that polyamines contribute to anti-inflammatory responses by suppressing the expression of proinflammatory cytokines in mononuclear cells and macrophages. However, the effects of polyamines on CD4⁺ T cell responses remain to be elucidated. Here, we investigated the effect of polyamines on cell fate decisions of naïve CD4⁺ T cells in vitro. We found that endogenously generated polyamines are essential for the development of T helper 2 (Th2) cells. Treatment with DL-2-difluoromethylornithine (DFMO), an inhibitor of polyamine biosynthesis, diminished GATA3 expression in CD4⁺ T cells under Th2-skewed conditions. Supplementation of exogenous polyamines rescued GATA3 downregulation caused by DFMO treatment in CD4⁺ T cells. Transcriptome analysis revealed that deprivation of endogenous polyamines resulted in upregulated Th9-related genes, such as Il9, Irf4, and Batf3, even under the Th2-skewing conditions. Depletion of intracellular polyamines reduced GATA3 expression but increased IL-9-producing CD4⁺ T cells under both Th2 and Th9-skewing conditions. Furthermore, oral administration of DFMO increased IL-9-producing CD4⁺ T cells in small intestine in mice. Thus, our data indicate that polyamines play a critical role in the regulation of the Th2/Th9 balance.

Suppressive mechanisms by Heligmosomoides polygyrus-induced Tregs in C57BL/6 mice change over time and differ to that of naïve mice

Disrupting or harnessing immune suppression is leading to new therapeutic avenues in a number of immune-related diseases. Understanding the suppressive functions of regulatory T cells (Tregs) in different environments is therefore key. Parasitic worms are strong inducers of Tregs and previous research has suggested that parasite-induced Tregs are stronger suppressors than naïve Tregs. In strains susceptible to the intestinal worm Heligmosomoides polygyrus, like C57BL/6 mice, it has been hypothesized that increased Treg suppression downregulates both Th1 and Th2 responses, leading to chronic infections and high worm burden. Here, we show that the suppressive capacity of Tregs is no different between cells from infected and/or naive animals. In vitro suppression induced by CD4⁺ CD25⁺ Tregs (Peyers' Patches or the mesenteric lymph nodes), isolated early (day 7, tissue dwelling phase) or late (day 21, luminal phase) during infection was similar to that induced by cells from naïve animals. Suppression was CTLA-4 dependent in Tregs from acute but not chronic infection or in Tregs from naïve animals. This highlights the versatility of Tregs and the importance of extensive Treg characterization prior to potential in vivo manipulation of this cell type.

IL-4 together with IL-1β induces antitumor Th9 cell differentiation in the absence of TGF-β signaling

IL-9-producing CD4⁺ (Th9) cells are a subset of CD4⁺ T-helper cells that are endowed with powerful antitumor capacity. Both IL-4 and TGF-β have been reported to be indispensable for Th9 cell-priming and differentiation. Here we show, by contrast, that Th9 cell development can occur in the absence of TGF-β signaling. When TGF-β was replaced by IL-1β, the combination of IL-1β and IL-4 efficiently promoted IL-9-producing T cells (Th9^IL-4+IL-1β). Th9^{IL-4+ IL-1β} cells are phenotypically distinct T cells compared to classic Th9 cells (Th9^IL-4+TGF-β) and other Th cells, and are enriched for IL-1 and NF-κB gene signatures. Inhibition of NF-κB but not TGF-β-signaling negates IL-9 production by Th9^IL-4+IL-1β cells. Furthermore, when compared with classic Th9^IL-4+TGF-β cells, Th9^IL-4+IL-1β cells are less exhausted, exhibit cytotoxic T effector gene signature and tumor killing function, and exert a superior antitumor response in a mouse melanoma model. Our study thus describes an alternative pathway for Th9 cell differentiation and provides a potential avenue for antitumor therapies.

CD4⁺ helper T cells producing IL-9 (Th9) have been implicated in anti-tumor immunity, with Th9 differentiation inducible in vitro via IL-4 and TGFβ treatment. Here the authors show that replacing TGFβ with IL-1β induces a distinct IL-9⁺ CD4⁺ population that have strong cytotoxic and anti-tumor activity in preclinical mouse models.

Manipulation of the balance between Th2 and Th2/1 hybrid cells affects parasite nematode fitness in mice

T-helper type 2 (Th2) responses are central to the control of helminth infections, but sensitive to opposing cytokine signals favoring Th1 priming. We previously reported on GATA-3⁺ T-bet⁺ Th2/1 hybrid cell differentiation in helminth mono-infections, resulting in a substantial proportion of cells coproducing IFN-γ next to Th2 cytokines. Here, we demonstrate Th2/1 cells as the major source of parasite-specific IFN-γ production in acute and chronic infections with the enteric nematode Heligmosomoides polygyrus. Th2/1 cells differentiated from naive precursors and accumulated in spleen and intestine of infected mice, resulting in increased systemic and mucosal IFN-γ production. IFN-γ supplementation early during infection supported Th2/1 differentiation, associated with elevated parasite fecundity and the maintenance of high worm burdens in the chronic stage of infection, whereas mice lacking IFN-γ signals generated poor Th2/1 responses and restricted parasite fecundity more efficiently. These findings suggest that Th2/1 hybrid responses take part in immune regulation during helminth infection and restrain effective anti-helminth immunity.

TGF-β mimic proteins form an extended gene family in the murine parasite Heligmosomoides polygyrus

We recently reported the discovery of a new parasite-derived protein that functionally mimics the immunosuppressive cytokine transforming growth factor (TGF)-β. The Heligmosomoides polygyrus TGF-β Mimic (Hp-TGM) shares no homology to any TGF-β family member, however it binds the mammalian TGF-β receptor and induces expression of Foxp3, the canonical transcription factor of both mouse and human regulatory T cells. Hp-TGM consists of five atypical Complement Control Protein (CCP, Pfam 00084) domains, each lacking certain conserved residues and 12-15 amino acids longer than the 60-70 amino acids consensus domain, but with a recognizable 3-cysteine, tryptophan, cysteine motif. We now report on the identification of a family of nine related Hp-TGM homologues represented in the secreted proteome and transcriptome of H. polygyrus. Recombinant proteins from five of the nine new TGM members were tested for TGF-β activity, but only two were functionally active in an MFB-F11 reporter assay, and by the induction of T cell Foxp3 expression. Sequence comparisons reveal that proteins with functional activity are similar or identical to Hp-TGM across the first three CCP domains, but more variable in domains 4 and 5. Inactive proteins diverged in all domains, or lacked some domains entirely. Testing truncated versions of Hp-TGM confirmed that domains 1-3 are essential for full activity in vitro, while domains 4 and 5 are not required. Further studies will elucidate whether these latter domains fulfill other functions in promoting host immune regulation during infection and if the more divergent family members play other roles in immunomodulation.

Immune modulation of Th1, Th2, and T-reg transcriptional factors differing from cytokine levels in Schistosoma japonicum infection

In spite of long-term integrated control programs for Schistosoma japonicum infection in China, the infection is still persistent due to its zoonotic transmission and disease severity which further complicate its control. Th1, Th2, and T-reg cells are involved in S. japonicum immunity; however, their exact roles in immunopathology of this infection are still questionable. Therefore, the monitoring of these T cell subsets' immune responses during a primary infection of S. japonicum at both transcriptional (mRNA) and protein (cytokines) levels would be essential to point out. In experimentally infected white New Zealand rabbits, mRNA expression levels of TBX2, IRF8, GATA3, STAT6, FoxP3, and MAFF were evaluated using qPCR, whereas Th1 (IFN-γ and TNF-α), Th2 (IL4 and IL13), and T-reg (IL10 and TGF-β1) cytokines were measured by ELISA test. Those parameters were estimated at two phases: the first being 4 and 8 weeks post-infection and the second phase at 12 weeks post-infection. The infected rabbits were categorized into group1 which was treated with praziquantel after the 8th week of infection and group 2 which was left untreated. In the first stage of infection, Th1 was superior to the other types at both mRNA (TBX2 and IRF8) and protein (IFN-γ and TNF-α) levels, but at the late stage, Th2 cytokines (IL4 and IL13) were surprisingly dominated without comparable change in Th2 transcriptional level in group 1. Concisely, the evaluation of T cell transcriptional factors provided clearer evidence about T cellular roles which would be a valuable supplement to control this disease in terms of protective and therapeutic vaccinations.

Plastic and micro-evolutionary responses of a nematode to the host immune environment

Parasitic organisms have to cope with the defences deployed by their hosts and this can be achieved adopting immune evasion strategies or optimal life history traits according to the prevailing pattern of immune-mediated mortality. Parasites often encounter variable immune environments both within and between hosts, promoting the evolution of plastic strategies instead of fixed responses. Here, we explored the plasticity and micro-evolutionary responses of immunomodulatory mechanisms and life history traits to the immune environment provided by the host, using the parasitic nematode Heligmosomoides polygyrus. To test if the parasite responds plastically to the immune environment, we stimulated the systemic inflammatory response of mice and we assessed i) the expression of two genes with candidate immunomodulatory functions (Hp-Tgh2 and Hp-CPI); ii) changes in the number of eggs shed in the faeces. To test if the immune environment induces a micro-evolutionary response in the parasite, we maintained the nematode in mice whose inflammatory response was up- or down-regulated during four generations. We found that H. polygyrus plastically responded to a sudden rise of pro-inflammatory cytokines, up-regulating the expression of two candidate genes involved in the process of immune modulation, and enhancing egg output. At the micro-evolutionary level, parasites maintained in hosts experiencing different levels of inflammation did not have differential expression of Hp-Tgh2 and Hp-CPI genes when infecting unmanipulated, control, mice. However, parasites maintained in mice with an up-regulated inflammation shed more eggs compared to the control line. Overall, our study shows that H. polygyrus can plastically adjust the expression of immunomodulatory genes and life history traits, and responds to selection exerted by the host immune system.

TGF-β in tolerance, development and regulation of immunity

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The broader superfamily of TGF-β-like proteins is reviewed, and signaling pathways summarised.

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The role of TGF-β in the immune tolerance and control of infectious disease is discussed.

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The superfamily member AMH is involved in embryonic sexual differentiation.

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Helminth parasites appear to exploit the TGF-β pathway to suppress host immunity.

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TGF-β homologues and mimics from parasites offer a new route for therapeutic tolerance induction.

The TGF-β superfamily is an ancient metazoan protein class which cuts across cell and tissue differentiation, developmental biology and immunology. Its many members are regulated at multiple levels from intricate control of gene transcription, post-translational processing and activation, and signaling through overlapping receptor structures and downstream intracellular messengers. We have been interested in TGF-β homologues firstly as key players in the induction of immunological tolerance, the topic so closely associated with Ray Owen. Secondly, our interests in how parasites may manipulate the immune system of their host has also brought us to study the TGF-β pathway in infections with longlived, essentially tolerogenic, helminth parasites. Finally, within the spectrum of mammalian TGF-β proteins is an exquisitely tightly-regulated gene, anti-Müllerian hormone (AMH), whose role in sex determination underpins the phenotype of freemartin calves that formed the focus of Ray’s seminal work on immunological tolerance.

The Oral Tolerance as a Complex Network Phenomenon

The phenomenon of oral tolerance refers to a local and systemic state of tolerance induced in the gut after its exposure to innocuous antigens. Recent findings have shown the interrelationship between cellular and molecular components of oral tolerance, but its representation through a network of interactions has not been investigated. Our work aims at identifying the causal relationship of each element in an oral tolerance network, and also to propose a phenomenological model that's capable of predicting the stochastic behavior of this network when under manipulation. We compared the changes of a "healthy" network caused by "knock-outs" (KOs) in two approaches: an analytical approach by the Perron Frobenius theory; and a computational approach, which we describe within this work in order to find numerical results for the model. Both approaches have shown the most relevant immunological components for this phenomena, that happens to corroborate the empirical results from animal models. Besides explain in a intelligible fashion how the components interacts in a complex manner, we also managed to describe and quantify the importance of KOs that hasn't been empirically tested.

Cultivation of Heligmosomoides polygyrus: an immunomodulatory nematode parasite and its secreted products

Heligmosomoides polygyrus (formerly known as Nematospiroides dubius, and also referred to by some as H. bakeri) is a gastrointestinal helminth that employs multiple immunomodulatory mechanisms to establish chronic infection in mice and closely resembles prevalent human helminth infections. H. polygyrus has been studied extensively in the field of helminth-derived immune regulation and has been found to potently suppress experimental models of allergy and autoimmunity (both with active infection and isolated secreted products). The protocol described in this paper outlines management of the H. polygyrus life cycle for consistent production of L3 larvae, recovery of adult parasites, and collection of their excretory-secretory products (HES).

Systems biologic analysis of T regulatory cells genetic pathways in murine primary biliary cirrhosis

CD4(+)Foxp3(+) regulatory T cells (Tregs) play a non-redundant role in control of excessive immune responses, and defects in Tregs have been shown both in patients and murine models of primary biliary cirrhosis (PBC), a progressive autoimmune biliary disease. Herein, we took advantage of a murine model of PBC, the dominant negative transforming growth factor β receptor II (dnTGFβRII) mice, to assess Treg genetic defects and their functional effects in PBC. By using high-resolution microarrays with verification by PCR and protein expression, we found profound and wide-ranging differences between dnTGFβRII and normal, wild type Tregs. Critical transcription factors were down-regulated including Eos, Ahr, Klf2, Foxp1 in dnTGFβRII Tregs. Functionally, dnTGFβRII Tregs expressed an activated, pro-inflammatory phenotype with upregulation of Ccl5, Granzyme B and IFN-γ. Genetic pathway analysis suggested that the primary effect of loss of TGFβ pathway signaling was to down regulate immune regulatory processes, with a secondary upregulation of inflammatory processes. These findings provide new insights into T regulatory genetic defects; aberrations of the identified genes or genetic pathways should be investigated in human PBC Tregs. This approach which takes advantage of biologic pathway analysis illustrates the ability to identify genes/pathways that are affected both independently and dependent on abnormalities in TGFβ signaling. Such approaches will become increasingly useful in human autoimmunity.

Successful immunotherapy of autoimmune cholangitis by adoptive transfer of forkhead box protein 3(+) regulatory T cells

Treatment of primary biliary cirrhosis (PBC) has lagged behind that of other autoimmune diseases. In this study we have addressed the potential utility of immunotherapy using regulatory T cells (Treg ) to treat murine autoimmune cholangitis. In particular, we have taken advantage of our ability to produce portal inflammation and bile duct cell loss by transfer of CD8(+) T cells from the dominant negative form of transforming growth factor beta receptor type II (dnTGF-βRII) mice to recombination-activating gene (Rag)1(-/-) recipients. We then used this robust established adoptive transfer system and co-transferred CD8(+) T cells from dnTGF-βRII mice with either C57BL/6 or dnTGF-βRII forkhead box protein 3 (FoxP3(+) ) T cells. Recipient mice were monitored for histology, including portal inflammation and intralobular biliary cell damage, and also included a study of the phenotypical changes in recipient lymphoid populations and local and systemic cytokine production. Importantly, we report herein that adoptive transfer of Treg from C57BL/6 but not dnTGF-βRII mice significantly reduced the pathology of autoimmune cholangitis, including decreased portal inflammation and bile duct damage as well as down-regulation of the secondary inflammatory response. Further, to define the mechanism of action that explains the differential ability of C57BL/6 Treg versus dnTGF-βRII Treg on the ability to down-regulate autoimmune cholangitis, we noted significant differential expression of glycoprotein A repetitions predominant (GARP), CD73, CD101 and CD103 and a functionally significant increase in interleukin (IL)-10 in Treg from C57BL/6 compared to dnTGF-βRII mice. Our data reflect the therapeutic potential of wild-type CD4(+) FoxP3(+) Treg in reducing the excessive T cell responses of autoimmune cholangitis, which has significance for the potential immunotherapy of PBC.

Systemic impact of intestinal helminth infections

In this review, we examine the evidence that intestinal helminths can control harmful inflammatory responses and promote homeostasis by triggering systemic immune responses. Induction of separable components of immunity by helminths, which includes type 2 and immune regulatory responses, can both contribute toward the reduction in harmful type 1 immune responses that drive certain inflammatory diseases. Despite inducing type 2 responses, intestinal helminths may also downregulate harmful type 2 immune responses including allergic responses. We consider the possibility that intestinal helminth infection may indirectly affect inflammation by influencing the composition of the intestinal microbiome. Taken together, the studies reviewed herein suggest that intestinal helminth-induced responses have potent systemic effects on the immune system, raising the possibility that whole parasites or specific molecules produced by these metazoans may be an important resource for the development of future immunotherapies to control inflammatory diseases.

IL-25 exhibits disparate roles during Th2-cell differentiation versus effector function

A keenly sought therapeutic approach for the treatment of allergic disease is the identification and neutralization of the cytokine that regulates the differentiation of T helper 2 (Th2) cells. Th2 cells are exciting targets for asthma therapies. Recently, the cytokine IL-25 has been shown to enhance Th2-type immune activity and play important roles in mediating allergic inflammatory responses. To investigate this further, we crossed IL-25(-/-) C57BL/6 mice with G4 IL-4 C57BL/6 reporter mice and developed an assay for in vitro and in vivo IL-4-independent Th2-cell differentiation. These assays were used to determine whether IL-25 was critical for the formation of Th2 cells. We found there was no physiological role for IL-25 in either the differentiation of Th2 cells or their development to effector or memory Th2-cell subsets. Importantly, this data challenges the newly found and growing status of the cytokine IL-25 and its proposed role in promoting Th2-cell responses.

Expansion of Foxp3(+) T-cell populations by Candida albicans enhances both Th17-cell responses and fungal dissemination after intravenous challenge

Candida albicans remains the fungus most frequently associated with nosocomial bloodstream infection. In disseminated candidiasis, the role of Foxp3(+) regulatory T (Treg) cells remains largely unexplored. Our aims were to characterize Foxp3(+) Treg-cell activation in a murine intravenous challenge model of disseminated C. albicans infection, and determine the contribution to disease. Flow cytometric analyses demonstrated that C. albicans infection drove in vivo expansion of a splenic CD4(+) Foxp3(+) population that correlated positively with fungal burden. Depletion from Foxp3(hCD2) reporter mice in vivo confirmed that Foxp3(+) cells exacerbated fungal burden and inflammatory renal disease. The CD4(+) Foxp3(+) population expanded further after in vitro stimulation with C. albicans antigens (Ags), and included at least three cell types. These arose from proliferation of the natural Treg-cell subset, together with conversion of Foxp3(-) cells to the induced Treg-cell form, and to a cell type sharing effector Th17-cell characteristics, expressing ROR-γt, and secreting IL-17A. The expanded Foxp3(+) T cells inhibited Th1 and Th2 responses, but enhanced Th17-cell responses to C. albicans Ags in vitro, and in vivo depletion confirmed their ability to enhance the Th17-cell response. These data lead to a model for disseminated candidiasis whereby expansion of Foxp3(+) T cells promotes Th17-cell responses that drive pathology.

Innate and adaptive type 2 immune cell responses in genetically controlled resistance to intestinal helminth infection

The nematode Heligmosomoides polygyrus is an excellent model for intestinal helminth parasitism. Infection in mice persists for varying lengths of time in different inbred strains, with CBA and C57BL/6 mice being fully susceptible, BALB/c partially so and SJL able to expel worms within 2–3 weeks of infection. We find that resistance correlates not only with the adaptive Th2 response, including IL-10 but with activation of innate lymphoid cell and macrophage populations. In addition, the titer and specificity range of the serum antibody response is maximal in resistant mice. In susceptible strains, Th2 responses were found to be counterbalanced by IFN-γ-producing CD4⁺ and CD8⁺ cells, but these are not solely responsible for susceptibility as mice deficient in either CD8⁺ T cells or IFN-γ remain unable to expel the parasites. Foxp3⁺ Treg numbers were comparable in all strains, but in the most resistant SJL strain, this population does not upregulate CD103 in infection, and in the lamina propria the frequency of Foxp3⁺CD103⁺ T cells is significantly lower than in susceptible mice. The more resistant SJL and BALB/c mice develop macrophage-rich IL-4Rα-dependent Type 2 granulomas around intestinal sites of larval invasion, and expression of alternative activation markers Arginase-1, Ch3L3 (Ym1) and RELM-α within the intestine and the peritoneal lavage was also strongly correlated with helminth elimination in these strains. Clodronate depletion of phagocytic cells compromises resistance of BALB/c mice and slows expulsion in the SJL strain. Thus, Type 2 immunity involves IL-4Rα-dependent innate cells including but not limited to a phagocyte population, the latter likely involving the action of specific antibodies.

Loss of the TGFβ-activating integrin αvβ8 on dendritic cells protects mice from chronic intestinal parasitic infection via control of type 2 immunity

Chronic intestinal parasite infection is a major global health problem, but mechanisms that promote chronicity are poorly understood. Here we describe a novel cellular and molecular pathway involved in the development of chronic intestinal parasite infection. We show that, early during development of chronic infection with the murine intestinal parasite Trichuris muris, TGFβ signalling in CD4+ T-cells is induced and that antibody-mediated inhibition of TGFβ function results in protection from infection. Mechanistically, we find that enhanced TGFβ signalling in CD4+ T-cells during infection involves expression of the TGFβ-activating integrin αvβ8 by dendritic cells (DCs), which we have previously shown is highly expressed by a subset of DCs in the intestine. Importantly, mice lacking integrin αvβ8 on DCs were completely resistant to chronic infection with T. muris, indicating an important functional role for integrin αvβ8-mediated TGFβ activation in promoting chronic infection. Protection from infection was dependent on CD4+ T-cells, but appeared independent of Foxp3+ Tregs. Instead, mice lacking integrin αvβ8 expression on DCs displayed an early increase in production of the protective type 2 cytokine IL-13 by CD4+ T-cells, and inhibition of this increase by crossing mice to IL-4 knockout mice restored parasite infection. Our results therefore provide novel insights into how type 2 immunity is controlled in the intestine, and may help contribute to development of new therapies aimed at promoting expulsion of gut helminths.

Infection with intestinal parasitic worms is a major global health problem, with billions of people infected world-wide. Often these worms (known as helminths) develop a long-lasting chronic infection, due to failure of the host to mount the correct type of immune response that would normally expel the parasite. However, how the immune system is controlled leading to chronic helminth infection is not well understood. Here we identify a novel pathway of importance in the development of chronic helminth infection. Using a model parasite which infects mice, we find that a protein called transforming growth factor beta (TGFβ signals to T-cells early during the development of chronic infection and that blocking this signal protects mice from infection. We have also uncovered a key pathway and cell type that controls TGFβ function during development of chronic infection. When a protein called integrin αvβ8 is absent from dendritic cells of the immune system, TGFβ is no longer activated to signal to T-cells and mice are able to mount a protective (type 2) immune response resulting in worm expulsion. Our findings therefore provide new insights into how chronic infections develop and identify potential molecular targets for the prevention of chronic helminth infection.

Helminths and their implication in sepsis - a new branch of their immunomodulatory behaviour?

The prevalence of autoimmune and allergic disorders has dramatically increased in developed countries, and it is believed that our ‘cleaner living’ reduces exposure to certain microorganisms and leads to deviated and/or reduced regulation of the immune system. In substantiation of this health hygiene hypothesis, multiple epidemiological studies and animal models have characterized the protective immune responses induced by helminths during auto-inflammatory disorders. The beneficial effects of such helminths, like schistosomes and filariae, are thought to lie in their immunomodulatory capacity, which can be induced by different life-cycle stages or components thereof. In addition to suppressing autoimmunity recent evidence indicates that concurrent helminth infections also counterbalance exacerbated pro-inflammatory immune responses that occur during sepsis, improving survival. As with allergy, epidemiological studies have observed a steady rise in severe sepsis cases and although this may have resulted from several factors (immunosuppressive drugs, chemotherapy, transplantation, increased awareness and increased surgical procedures), it is tempting to hypothesize that the lack of helminth infections in Western countries may have contributed to this phenomenon. This review summarizes how helminths modulate host immunity during sepsis, such as manipulating macrophage activation and provides an overview about the possible implications that may arise during overwhelming bacterial co-infections.

This well written review gives a comprehensive overview on the immunopathology of sepsis and the modulation of immune responses by helminths. It provides evidence that helminths or components thereof may improve the outcome of severe infections. This will allow the development of therapeutic strategies to fight infections and sepsis.

Th9 cells: differentiation and disease

CD4(+) T-helper cells regulate immunity and inflammation through the acquisition of potential to secrete specific cytokines. The acquisition of cytokine-secreting potential, in a process termed T-helper cell differentiation, is a response to multiple environmental signals including the cytokine milieu. The most recently defined subset of T-helper cells are termed Th9 and are identified by the potent production of interleukin-9 (IL-9). Given the pleiotropic functions of IL-9, Th9 cells might be involved in pathogen immunity and immune-mediated disease. In this review, I focus on recent developments in understanding the signals that promote Th9 differentiation, the transcription factors that regulate IL-9 expression, and finally the potential roles for Th9 cells in immunity in vivo.

Regulatory T cells control NK cells in an insulitic lesion by depriving them of IL-2

Pancreatic T reg cells control the availability of CD4⁺ T cell–secreted IL-2 to limit NK cell function.

Regulatory T (T reg) cells control progression to autoimmune diabetes in the BDC2.5/NOD mouse model by reining in natural killer (NK) cells that infiltrate the pancreatic islets, inhibiting both their proliferation and production of diabetogenic interferon-γ. In this study, we have explored the molecular mechanisms underlying this NK–T reg cell axis, following leads from a kinetic exploration of gene expression changes early after punctual perturbation of T reg cells in BDC2.5/NOD mice. Results from gene signature analyses, quantification of STAT5 phosphorylation levels, cytokine neutralization experiments, cytokine supplementation studies, and evaluations of intracellular cytokine levels collectively argue for a scenario in which T reg cells regulate NK cell functions by controlling the bioavailability of limiting amounts of IL-2 in the islets, generated mainly by infiltrating CD4⁺ T cells. This scenario represents a previously unappreciated intertwining of the innate and adaptive immune systems: CD4⁺ T cells priming NK cells to provoke a destructive T effector cell response. Our findings highlight the need to consider potential effects on NK cells when designing therapeutic strategies based on manipulation of IL-2 levels or targets.

Differential control of Helios(+/-) Treg development by monocyte subsets through disparate inflammatory cytokines

Foxp3(+) regulatory T cells (Tregs) play a pivotal role in control of autoimmunity and pathological immune responses. Helios, the Ikarus family transcription factor, binds to the Foxp3 promoter, stabilizing its expression, and is expressed in 70% of peripheral Tregs of healthy individuals. This frequency is altered during malignancy, infection, and autoimmunity, although the mechanisms that control proliferation and relative numbers of Helios(+/-) Tregs remain largely unknown. Using a T-cell-monocyte in vitro stimulation assay, we now show that proliferation of Helios(+) Tregs is inhibited by CD16(+) monocyte subset. Antibody blocking with anti-interleukin (IL)-12 reversed this inhibition, whereas addition of IL-12 suppressed Helios(+) Treg expansion, indicating that CD16(+) monocyte control of Helios(+) Treg numbers is mediated through IL-12. In contrast, proliferation of Helios(-) Tregs, which express higher levels of tumor necrosis factor receptor II (TNFRII), was suppressed by TNF-α, whereas anti-TNF-α and anti-TNFRII reversed the inhibition. CD16(-) monocyte subset was mainly responsible for TNF-α-mediated control of Helios(-) Treg expansion. Altogether, these data suggest a differential role for monocyte subsets in control of Helios(+/-) Treg development that is mediated by distinct inflammatory cytokines. These data may have important implications for understanding the pathogenesis as well as control of chronic inflammatory and autoimmune diseases.

Modification of hemodynamic and immune responses to exposure with a weak antigen by the expression of a hypomorphic BMPR2 gene

Background

Hypomorphic mutations in the bone morphogenic protein receptor (BMPR2) confer a much greater risk for developing pulmonary arterial hypertension (PAH). However, not all carriers of a mutation in the BMPR2 gene suffer from PAH. We have previously shown that prolonged T helper 2 (Th2) responses in the lungs to a mild antigen delivered via the airways induce severe pulmonary arterial remodeling, but no pulmonary hypertension. The current studies were designed to test the idea that Th2 responses to a mild antigen together with the expression of a hypomorphic BMPR2 gene would trigger pulmonary hypertension.

Methodology/Principal Findings

Mice that expressed a hypomorphic BMPR2 transgene (transgene-positive) and transgene-negative mice were either exposed to saline, or primed and exposed to a mild antigen (Ovalbumin) over a prolonged period of time. Only transgene-positive but not transgene-negative mice exposed to antigen developed significantly increased right ventricular systolic pressures, while both groups showed pulmonary artery remodeling with severe muscularization and airway inflammation to a similar degree. Antigen exposure resulted in a smaller increase in the percentage of Interleukin (IL)-13 positive T cells in the lymph nodes, and in a smaller increase in resistin-like-molecule (RELM)α expression and a decreased ratio of expression of IL-33 relative to its receptor (IL-1-receptor-like 1, IL1RL1-ST2) in the right ventricles of transgene-positive mice compared to transgene-negative animals. Furthermore, only antigen-challenged transgene-positive mice showed a significant increase in Interferon (IFN)γ positive T cells over saline-exposed controls.

Conclusions/Significance

Our study suggests that exposure with a mild Th2 antigen can trigger pulmonary hypertension on the background of the expression of a hypomorphic BMPR2 gene and that conversely, the expression of the hypomorphic BMPR2 gene can alter the immune response to a mild, inhaled antigen.

Immunity to the model intestinal helminth parasite Heligmosomoides polygyrus

Heligmosomoides polygyrus is a natural intestinal parasite of mice, which offers an excellent model of the immunology of gastrointestinal helminth infections of humans and livestock. It is able to establish long-term chronic infections in many strains of mice, exerting potent immunomodulatory effects that dampen both protective immunity and bystander reactions to allergens and autoantigens. Immunity to the parasite develops naturally in some mouse strains and can be induced in others through immunization; while the mechanisms of protective immunity are not yet fully defined, both antibodies and a host cellular component are required, with strongest evidence for a role of alternatively activated macrophages. We discuss the balance between resistance and susceptibility in this model system and highlight new themes in innate and adaptive immunity, immunomodulation, and regulation of responsiveness in helminth infection.