Heligmosomoides polygyrus bakeri induces tolerogenic dendritic cells that block colitis and prevent antigen-specific gut T cell responses

Worm proteins of Schistosoma mansoni reduce the severity of experimental chronic colitis in mice by suppressing colonic proinflammatory immune responses

Although helminthic therapy as a possible new option to treat inflammatory bowel disease is a well-established concept by now, the search for immunomodulatory helminth-derived compounds and their mechanisms of action is still ongoing. We investigated the therapeutic potential and the underlying immunological mechanisms of Schistosoma mansoni soluble worm proteins (SmSWP) in an adoptive T cell transfer mouse model of chronic colitis. Both a curative and a preventive treatment protocol were included in this study. The curative administration of SmSWP (started when colitis was established), resulted in a significant improvement of the clinical disease score, colonoscopy, macroscopic and microscopic inflammation score, colon length and myeloperoxidase activity. The therapeutic potential of the preventive SmSWP treatment (started before colitis was established), was less pronounced compared with the curative SmSWP treatment but still resulted in an improved clinical disease score, body weight loss, colon length and microscopic inflammation score. Both the curative and preventive SmSWP treatment downregulated the mRNA expression of the proinflammatory cytokines IFN-γ and IL-17A and upregulated the mRNA expression of the anti-inflammatory cytokine IL-4 in the colon at the end of the experiment. This colonic immunomodulatory effect of SmSWP could not be confirmed at the protein level. Moreover, the effect of SmSWP appeared to be a local colonic phenomenon, since the flow cytometric T cell characterization of the mesenteric lymph nodes and the cytokine measurements in the serum did not reveal any effect of SmSWP treatment. In conclusion, SmSWP treatment reduced the severity of colitis in the adoptive transfer mouse model via the suppression of proinflammatory cytokines and the induction of an anti-inflammatory response in the colon.

Mucosal immune responses following intestinal nematode infection

In most natural environments, the large majority of mammals harbour parasitic helminths that often live as adults within the intestine for prolonged periods (1-2 years). Although these organisms have been eradicated to a large extent within westernized human populations, those living within rural areas of developing countries continue to suffer from high infection rates. Indeed, recent estimates indicate that approximately 2.5 billion people worldwide, mainly children, currently suffer from infection with intestinal helminths (also known as geohelminths and soil-transmitted helminths) . Paradoxically, the eradication of helminths is thought to contribute to the increased incidence of autoimmune diseases and allergy observed in developed countries. In this review, we will summarize our current understanding of host-helminth interactions at the mucosal surface that result in parasite expulsion or permit the establishment of chronic infections with luminal dwelling adult worms. We will also provide insight into the adaptive immune mechanisms that provide immune protection against re-infection with helminth larvae, a process that is likely to be key to the future development of successful vaccination strategies. Lastly, the contribution of helminths to immune modulation and particularly to the treatment of allergy and inflammatory bowel disease will be discussed.

Blockade of IL-33 release and suppression of type 2 innate lymphoid cell responses by helminth secreted products in airway allergy

Helminth parasites such as the nematode Heligmosomoides polygyrus strongly inhibit T helper type 2 (Th2) allergy, as well as colitis and autoimmunity. Here, we show that the soluble excretory/secretory products of H. polygyrus (HES) potently suppress inflammation induced by allergens from the common fungus Alternaria alternata. Alternaria extract, when administered to mice intranasally with ovalbumin (OVA) protein, induces a rapid (1-48 h) innate response while also priming an OVA-specific Th2 response that can be evoked 14 days later by intranasal administration of OVA alone. In this model, HES coadministration with Alternaria/OVA suppressed early IL-33 release, innate lymphoid cell (ILC) production of IL-4, IL-5, and IL-13, and localized eosinophilia. Upon OVA challenge, type 2 ILC (ILC2)/Th2 cytokine production and eosinophilia were diminished in HES-treated mice. HES administration 6 h before Alternaria blocked the allergic response, and its suppressive activity was abolished by heat treatment. Administration of recombinant IL-33 at sensitization with Alternaria/OVA/HES abrogated HES suppression of OVA-specific responses at challenge, indicating that suppression of early Alternaria-induced IL-33 release could be central to the anti-allergic effects of HES. Thus, this helminth parasite targets IL-33 production as part of its armory of suppressive effects, forestalling the development of the type 2 immune response to infection and allergic sensitization.

Of worms, mice and man: an overview of experimental and clinical helminth-based therapy for inflammatory bowel disease

The incidence of inflammatory and autoimmune disorders is highest in well-developed countries which is directly related to their higher hygienic standards: it is suggested that the lack of exposure to helminths contributes to the susceptibility for immune-related diseases. Epidemiological, experimental and clinical data support the idea that helminths provide protection against immune-mediated diseases such as inflammatory bowel disease (IBD). The most likely mechanism for the suppression of immune responses by helminths is the release of helminth-derived immunomodulatory molecules. This article reviews the experimental and clinical studies investigating the therapeutic potential of helminth-based therapy in IBD and also focuses on the current knowledge of its immunomodulatory mechanisms of action highlighting innate as well as adaptive immune mechanisms. Identifying the mechanisms by which these helminths and helminth-derived molecules modulate the immune system will help in creating novel drugs for the treatment of IBD and other disorders that result from an overactive immune response.

Understanding the role of antibodies in murine infections with Heligmosomoides (polygyrus) bakeri: 35 years ago, now and 35 years ahead

The rodent intestinal nematode H.p.bakeri has played an important role in the exploration of the host-parasite relationship of chronic nematode infections for over six decades, since the parasite was first isolated in the 1950s by Ehrenford. It soon became a popular laboratory model providing a tractable experimental system that is easy to maintain in the laboratory and far more cost-effective than other laboratory nematode-rodent model systems. Immunity to this parasite is complex, dependent on antibodies, but confounded by the parasite's potent immunosuppressive secretions that facilitate chronic survival in murine hosts. In this review, we remind readers of the state of knowledge in the 1970s, when the first volume of Parasite Immunology was published, focusing on the role of antibodies in protective immunity. We show how our understanding of the host-parasite relationship then developed over the following 35 years to date, we propose testable hypotheses for future researchers to tackle, and we speculate on how the new technologies will be applied to enable an increasingly refined understanding of the role of antibodies in host-protective immunity, and its evasion, to be achieved in the longer term.

Increased susceptibility to Trichuris muris infection and exacerbation of colitis in Mdr1a-/- mice

AIM: To investigate the influence of Trichuris muris (T. muris) infection in a mouse model of genetic susceptibility to inflammatory bowel disease, Mdr1a-/-.

METHODS: Mdr1a-/- mice were housed under specific pathogen free conditions to slow the development of colitis and compared to congenic FVB controls. Mice were infected with approximately 200 embryonated ova from T. muris and assessed for worm burden and histological and functional markers of gut inflammation on day 19 post infection.

RESULTS: Mdr1a-/- mice exhibited a marked increase in susceptibility to T. muris infection with a 10-fold increase in colonic worm count by day 19 pi compared to FVB controls. Prior to infection, Mdr1a-/- exhibited low-level mucosal inflammation with evidence of an enhanced Th1 environment. T. muris infection accelerated the progression of colitis in Mdr1a-/- as evidenced by marked increases in several indicators including histological damage score, mucosal CD4⁺ T-cell and DC infiltration and dramatically increased production of pro-inflammatory cytokines.

CONCLUSION: These data provide further evidence of the complex interaction between T. muris and an inflammatory bowel disease (IBD)-susceptible host which may have relevance to the application of helminth therapy in the treatment of human IBD.

Tolerogenic dendritic cell vaccines to treat autoimmune diseases: can the unattainable dream turn into reality?

Autoimmune diseases affect about one in 15 individuals in developed countries and are characterized by a breakdown in immune tolerance. Current therapeutic approaches against destructive immune responses in autoimmune diseases are based on non-specific agents systemically suppressing the function of many immune effector cells. This indiscriminate immunosuppression, however, often causes serious and sometimes life-threatening side effects. Therefore, the need for more specific treatments resulting in lower toxicity and longer-term solutions is high. Because of the established role of dendritic cells (DCs) in maintaining the balance between immunity and tolerance, tolerogenic (tol)DCs might be novel therapeutic targets to prevent undesirable (auto-)immune responses. The idea behind tolDC therapy is that it is a highly targeted, antigen-specific treatment that only affects the auto-reactive inflammatory response. The therapeutic potential of tolDCs has already been proven in experimental animal models of different autoimmune disorders as well as with in vitro experiments using ex vivo generated human tolDCs, thus the challenge remains in bringing tolDC therapy to the clinic, although first clinical trials have been conducted. In this review, we will extensively discuss the use of tolDCs for induction of antigen-specific tolerance in several autoimmune disease settings, from bench to bedside, including currently applied strategies to generate tolDCs as well as technical difficulties and challenges in the field.

Role of macrophages in the altered epithelial function during a type 2 immune response induced by enteric nematode infection

Parasitic enteric nematodes induce a type 2 immune response characterized by increased production of Th2 cytokines, IL-4 and IL-13, and recruitment of alternatively activated macrophages (M2) to the site of infection. Nematode infection is associated with changes in epithelial permeability and inhibition of sodium-linked glucose absorption, but the role of M2 in these effects is unknown. Clodronate-containing liposomes were administered prior to and during nematode infection to deplete macrophages and prevent the development of M2 in response to infection with Nippostrongylus brasiliensis. The inhibition of epithelial glucose absorption that is associated with nematode infection involved a macrophage-dependent reduction in SGLT1 activity, with no change in receptor expression, and a macrophage-independent down-regulation of GLUT2 expression. The reduced transport of glucose into the enterocyte is compensated partially by an up-regulation of the constitutive GLUT1 transporter consistent with stress-induced activation of HIF-1α. Thus, nematode infection results in a “lean” epithelial phenotype that features decreased SGLT1 activity, decreased expression of GLUT2 and an emergent dependence on GLUT1 for glucose uptake into the enterocyte. Macrophages do not play a role in enteric nematode infection-induced changes in epithelial barrier function. There is a greater contribution, however, of paracellular absorption of glucose to supply the energy demands of host resistance. These data provide further evidence of the ability of macrophages to alter glucose metabolism of neighboring cells.

Potential treatment of inflammatory bowel disease: a review of helminths therapy

An inflammatory bowel disease (IBD) is most common in highly industrialized Western countries but uncommon in less developed areas of the world where helminths are frequent. The hygiene hypothesis proposes that the recent increase in allergic and autoimmune diseases is due to modern highly hygienic life styles and medical conditions. Loss of routine exposure to parasitic helminths, as a result of increasing lifestyle-associated factors, may be one factor leading to the increased disease prevalence. In animal models and clinical trials of IBD, gastrointestinal nematodes colonization suppresses intestinal inflammation through multiple mechanisms including induction of innate and adaptive regulatory circuits. Studies using helminths like Trichuris suis or Necator americanus showed that these helminths are safe and may be effective therapeutic approaches for the control of IBD and other immune diseases. The aim of present review was to exploring the therapeutic use of helminths for the control of IBD.

Environmental influences on the onset and clinical course of Crohn's disease-part 2: infections and medication use

The pathogenesis of Crohn's disease (CD) involves host, genetic, and environmental factors. These factors result in disturbances in the innate and adaptive immune systems and composition of the intestinal microbiota. Epidemiologic and migration studies support an environmental component in the development of CD. Environmental risk factors include childhood hygiene, air pollution, breastfeeding, smoking, diet, stress, exercise, seasonal variation, appendectomy, medications, and infections. This 2-part series provides an overview of these external contributors to the development or exacerbation of CD. Part 1, which was published in a previous issue, focused on childhood factors, perinatal influences, and lifestyle choices. Part 2, presented here, details the effects of infections, antibiotics, nonsteroidal anti-inflammatory drugs, and oral contraceptives.

Animal models of ulcerative colitis and their application in drug research

The specific pathogenesis underlying inflammatory bowel disease is complex, and it is even more difficult to decipher the pathophysiology to explain for the similarities and differences between two of its major subtypes, Crohn's disease and ulcerative colitis (UC). Animal models are indispensable to pry into mechanistic details that will facilitate better preclinical drug/therapy design to target specific components involved in the disease pathogenesis. This review focuses on common animal models that are particularly useful for the study of UC and its therapeutic strategy. Recent reports of the latest compounds, therapeutic strategies, and approaches tested on UC animal models are also discussed.

Animal models of ulcerative colitis and their application in drug research

The specific pathogenesis underlying inflammatory bowel disease is complex, and it is even more difficult to decipher the pathophysiology to explain for the similarities and differences between two of its major subtypes, Crohn's disease and ulcerative colitis (UC). Animal models are indispensable to pry into mechanistic details that will facilitate better preclinical drug/therapy design to target specific components involved in the disease pathogenesis. This review focuses on common animal models that are particularly useful for the study of UC and its therapeutic strategy. Recent reports of the latest compounds, therapeutic strategies, and approaches tested on UC animal models are also discussed.

Regulatory cell populations in the intestinal mucosa

PURPOSE OF REVIEW

The purpose of this review is to summarize recent advances in the fields of intestinal T-regulatory cell (Treg) and tolerogenic dendritic cell subsets. Under homeostatic conditions, CD4(+) Tregs and tolerogenic dendritic cells function to maintain mucosal tolerance. Loss of immune homeostasis is the primary cause of intestinal abnormalities, including inflammatory bowel disease. Thus, an improved understanding of cellular mechanisms promoting tolerance will be critical for the development of more efficacious therapies to treat chronic intestinal inflammation.

RECENT FINDINGS

Significant progress has been made in the past year in the study of mucosal Treg and dendritic cell populations. In particular, efforts have focused on the migration and differentiation of these cells in the intestinal mucosa, the functional consequences of cross-talk with the intestinal microbiome, mechanisms by which tolerogenic dendritic cells take up antigen, and regulation of retinoic acid synthesis.

SUMMARY

Recent studies examining tolerogenic cell populations of the intestinal mucosa highlight the progress in understanding the function, regulation, and cross-talk of Treg and dendritic cell populations, and their interactions with the gut microbiota. Scientific advances in these areas will undoubtedly lead to the development of more effective therapeutic strategies for intestinal abnormalities such as inflammatory bowel disease.

Treg inducing adjuvants for therapeutic vaccination against chronic inflammatory diseases

Many existing therapies in autoimmune diseases are based on systemic suppression of inflammation and the observed side effects of these therapies illustrate the pressing need for more specific interventions. Regulatory T-cells (Treg) are pivotal controllers of (auto-aggressive) immune responses and inflammation, and decreased Treg numbers and/or functioning have been associated with autoimmune disease. Therefore, Treg became frequently studied targets for more specific immunotherapy. Especially antigen-specific targeting of Treg would enable local and tailor made interventions, while obviating the negative side effect of general immuno-suppression. Self-antigens that participate in inflammation, irrespective of the etiology of the different autoimmune diseases, are held to be candidate antigens for antigen-specific interventions. Rather than tolerance induction to disease inciting self-antigens, which are frequently unknown, general self-antigens expressed at sites of inflammation would allow targeting of disease independent, but inflammatory-site specific, regulatory mechanisms. Preferably, such self-antigens should be abundantly expressed and up-regulated at the inflammatory-site. In this perspective heat shock proteins (Hsp) have several characteristics that make them highly attractive targets for antigen-specific Treg inducing therapy. The development of an antigen-specific Treg inducing vaccine is a major novel goal in the field of immunotherapy in autoimmune diseases. However, progress is hampered not only by the lack of effective antigens, but also by the fact that other factors such as dose, route, and the presence or absence of an adjuvant, turned out to be critical unknowns, with respect to the effective induction of Treg. In addition, the use of a Treg inducing adjuvant might be required to achieve an effective regulatory response, in the case of ongoing inflammation. Future goals in clinical trials will be the optimization of natural Treg expansion (or the induction of adaptive Treg) without loss of their suppressive function or the concomitant induction of non-regulatory T-cells. Here, we will discuss the potential use of protein/peptide-based vaccines combined with Treg inducing adjuvants for the development of therapeutic vaccines against chronic inflammatory conditions.

Secretion of protective antigens by tissue-stage nematode larvae revealed by proteomic analysis and vaccination-induced sterile immunity

Gastrointestinal nematode parasites infect over 1 billion humans, with little evidence for generation of sterilising immunity. These helminths are highly adapted to their mammalian host, following a developmental program through successive niches, while effectively down-modulating host immune responsiveness. Larvae of Heligmosomoides polygyrus, for example, encyst in the intestinal submucosa, before emerging as adult worms into the duodenal lumen. Adults release immunomodulatory excretory-secretory (ES) products, but mice immunised with adult H. polygyrus ES become fully immune to challenge infection. ES products of the intestinal wall 4th stage (L4) larvae are similarly important in host-parasite interactions, as they readily generate sterile immunity against infection, while released material from the egg stage is ineffective. Proteomic analyses of L4 ES identifies protective antigen targets as well as potential tissue-phase immunomodulatory molecules, using as comparators the adult ES proteome and a profile of H. polygyrus egg-released material. While 135 proteins are shared between L4 and adult ES, 72 are L4 ES-specific; L4-specific proteins correspond to those whose transcription is restricted to larval stages, while shared proteins are generally transcribed by all life cycle forms. Two protein families are more heavily represented in the L4 secretome, the Sushi domain, associated with complement regulation, and the ShK/SXC domain related to a toxin interfering with T cell signalling. Both adult and L4 ES contain extensive but distinct arrays of Venom allergen/Ancylostoma secreted protein-Like (VAL) members, with acetylcholinesterases (ACEs) and apyrase APY-3 particularly abundant in L4 ES. Serum antibodies from mice vaccinated with L4 and adult ES react strongly to the VAL-1 protein and to ACE-1, indicating that these two antigens represent major vaccine targets for this intestinal nematode. We have thus defined an extensive and novel repertoire of H. polygyrus proteins closely implicated in immune modulation and protective immunity.

Intestinal helminth parasites are highly prevalent in humans and animals, and survive for long periods by deviating the host immune system. No vaccines are currently available to control these infections. Many helminths invade through barrier surfaces (such as the skin or the digestive tract) and develop through tissue larval stages before reaching their final niche such as the intestinal lumen. We studied the tissue larval stage of a mouse parasite, Heligmosomoides polygyrus, to test whether proteins released by this stage could elicit protective immunity, and found that they indeed constitute very effective vaccine antigens. Proteomic analysis to identify the individual proteins released by the larvae demonstrated that while many products are shared between tissue-dwelling larvae and adults occupying the intestinal lumen, larvae express higher levels of two gene families linked to immunomodulation, namely the Sushi protein family and the ShK toxin family. Antibody analysis of serum from vaccinated mice identified two major antigens recognised by the protective immune response as VAL-1 and ACE-1, which are respectively members of the venom allergen and acetylcholinesterase families. This work establishes that tissue larvae are the source of protective antigens for future vaccines, and highlights their production of two potentially immunomodulatory gene families.

IL-1β suppresses innate IL-25 and IL-33 production and maintains helminth chronicity

Approximately 2 billion people currently suffer from intestinal helminth infections, which are typically chronic in nature and result in growth retardation, vitamin A deficiency, anemia and poor cognitive function. Such chronicity results from co-evolution between helminths and their mammalian hosts; however, the molecular mechanisms by which these organisms avert immune rejection are not clear. We have found that the natural murine helminth, Heligmosomoides polygyrus bakeri (Hp) elicits the secretion of IL-1β in vivo and in vitro and that this cytokine is critical for shaping a mucosal environment suited to helminth chronicity. Indeed in mice deficient for IL-1β (IL-1β(-/-)), or treated with the soluble IL-1βR antagonist, Anakinra, helminth infection results in enhanced type 2 immunity and accelerated parasite expulsion. IL-1β acts to decrease production of IL-25 and IL-33 at early time points following infection and parasite rejection was determined to require IL-25. Taken together, these data indicate that Hp promotes the release of host-derived IL-1β that suppresses the release of innate cytokines, resulting in suboptimal type 2 immunity and allowing pathogen chronicity.

A clinical review of recent findings in the epidemiology of inflammatory bowel disease

Inflammatory bowel diseases (IBD), including both Crohn's disease and ulcerative colitis, are disorders of chronic inflammation of the gastrointestinal tract marked by episodes of relapse and remission. Over the past several decades, advances have been made in understanding the epidemiology of IBD. The incidence and prevalence of both Crohn's disease and ulcerative colitis have been increasing worldwide across pediatric and adult populations. As IBD is thought to be related to a combination of individual genetic susceptibility, environmental triggers, and alterations in the gut microbiome that stimulate an inflammatory response, understanding the potentially modifiable environmental risk factors associated with the development or the course of IBD could impact disease rates or management in the future. Current hypotheses as to the development of IBD are reviewed, as are a host of environmental cofactors that have been investigated as both protective and inciting factors for IBD onset. Such environmental factors include breast feeding, gastrointestinal infections, urban versus rural lifestyle, medication exposures, stress, smoking, and diet. The role of these factors in disease course is also reviewed. Looking forward, there is still much to be learned about the etiology of IBD and how specific environmental exposures intimately impact the development of disease and also the potential for relapse.

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 therapies: translating the unknown unknowns to known knowns

The use of live helminth infections is currently in clinical trials as a novel approach for the treatment of a range of allergic and autoimmune diseases. This rapid progression from observational studies some 20 years ago to helminth clinical trials can be attributed to huge advances in not just pre-clinical and clinical evidence, pertaining to the efficacy of these parasites in unrelated diseases, but also a greater understanding of the complex immunological mechanisms that underpin these effects. Helminths have exerted significant evolutionary selective pressures on the host immune genome or "immunome". Studies on helminths were pivotal in a paradigm shift in immunology with recent discoveries of a number of novel immune cell populations. Critically, these new discoveries highlight the need to further understand the underlying mechanism behind the desirable therapeutic effects that helminths offer. With these unknown unknowns there is the distinct possibility that a true, fundamental modus operandi for helminth therapy will arrive long after it has been established in the clinic.

Translatability of helminth therapy in inflammatory bowel diseases

Modern hygienic lifestyles are associated with the emergence of inflammatory bowel disease (IBD) which now afflicts millions of people in highly-developed countries. Meticulous hygiene interrupts conduits of transmission required for ubiquitous exposure to parasitic worms (helminths). We proposed that loss of exposure to helminths permits development of IBD. Early clinical trials suggested that exposure to helminths such as Trichuris suis or Necator americanus can improve IBD. Over the last several years, processes to "medicinalize"T. suis have been developed and use of this helminth is now being studied in large multi-center clinical trials. Concurrently, we and others have identified some of the immune regulatory mechanisms elicited by helminth exposure that suppress inappropriate intestinal inflammation. These efforts could soon result in new therapies for patients with IBD.