David E. Elliott

Helminths and the IBD hygiene hypothesis

&NA; Helminths are parasitic animals that have evolved over 100,000,000 years to live in the intestinal track or other locations of their hosts. Colonization of humans with these organisms was nearly universal until the early 20th century. More than 1,000,000,000 people in less developed countries carry helminths even today. Helminths must quell their hosts immune system to successfully colonize. It is likely that helminths sense hostile changes in the local host environment and take action to control such responses. Inflammatory bowel disease (IBD) probably results from an inappropriately vigorous immune response to contents of the intestinal lumen. Environmental factors strongly affect the risk for IBD. People living in less developed countries are protected from IBD. The “IBD hygiene hypothesis” states that raising children in extremely hygienic environments negatively affects immune development, which predisposes them to immunological diseases like IBD later in life. Modern day absence of exposure to intestinal helminths appears to be an important environmental factor contributing to development of these illnesses. Helminths interact with both host innate and adoptive immunity to stimulate immune regulatory circuitry and to dampen effector pathways that drive aberrant inflammation. The first prototype worm therapies directed against immunological diseases are now under study in the United States and various countries around the world. Additional studies are in the advanced planning stage.

Intestinal helminths protect in a murine model of asthma.

Underdeveloped nations are relatively protected from the worldwide asthma epidemic; the hygiene hypothesis suggests this is due to suppression of Th2-mediated inflammation by increased exposure to pathogens and their products. Although microbial exposures can promote Th2-suppressing Th1 responses, even Th2-skewing infections, such as helminths, appear to suppress atopy, suggesting an alternate explanation for these observations. To investigate whether induction of regulatory responses by helminths may counter allergic inflammation, we examined the effects of helminth infection in a murine model of atopic asthma. We chose Heligosomoides polygyrus, a gastrointestinal nematode, as the experimental helminth; this worm does not enter the lung in its life cycle. We found that H. polygyrus infection suppressed allergen-induced airway eosinophilia, bronchial hyperreactivity, and in vitro allergen-recall Th2 responses in an IL-10-dependent manner; total and OVA-specific IgE, however, were increased by worm infection. Finally, helminth-infected mice were protected against eosinophilic inflammation induced by adoptive transfer of OVA-stimulated CD4+ cells, and transfer of cells from helminth-infected/OVA-exposed mice suppressed OVA-induced eosinophilic inflammation, suggesting a role for regulatory cells. Increased CD4+CD25+Foxp3+ cells were found in thoracic lymph nodes of helminth-infected/OVA-exposed mice. Helminthic colonization appears to protect against asthma and atopic disorders; the regulatory cytokine, IL-10, may be a critical player.

Randomised clinical trial: the safety and tolerability of Trichuris suis ova in patients with Crohn's disease

Recent evidence suggests that embryonated eggs of the porcine whipworm Trichuris suis ova (TSO) may be an effective treatment for inflammatory bowel disease (IBD).

Advances in the pathogenesis and treatment of IBD

Crohns disease and ulcerative colitis are chronic remitting and relapsing inflammatory bowel diseases. We present a typical case of Crohns disease in a young woman and discuss potential treatment options. Crohns disease and ulcerative colitis likely result from interaction of multiple genetic and environmental risk and protective factors. Both are diseases ultimately caused by immune dysregulation. Medical therapy is with mesalamine compounds, corticosteroids, immunomodulators and/or biologics that target TNFalpha signaling or alpha4-integrin-mediated trafficking. Investigational agents include those targeted against other cytokines and costimulatory molecules or designed to promote immune regulation such as exposure to helminths which is a focus of this review.

Role of T cell TGF-β signaling in intestinal cytokine responses and helminthic immune modulation.

Colonization with helminthic parasites induces mucosal regulatory cytokines, like IL‐10 or TGF‐β, that are important in suppressing colitis. Helminths induce mucosal T cell IL‐10 secretion and regulate lamina propria mononuclear cell (LPMC) Th1 cytokine generation in an IL‐10‐dependent manner in WT mice. Helminths also stimulate mucosal TGF‐β release. As TGF‐β exerts major regulatory effects on T lymphocytes, we investigated the role of T lymphocyte TGF‐β signaling in helminthic modulation of intestinal immunity. T cell TGF‐β signaling is interrupted in TGF‐β receptor II dominant negative (TGF‐βRII DN) mice by T‐cell‐specific over‐expression of a TGF‐βRII DN. We studied LPMC responses in WT and TGF‐βRII DN mice that were uninfected or colonized with the nematode, Heligmosomoides polygyrus. Our results indicate an essential role of T cell TGF‐β signaling in limiting mucosal Th1 and Th2 responses. Furthermore, we demonstrate that helminthic induction of intestinal T cell IL‐10 secretion requires intact T cell TGF‐β‐signaling pathway. Helminths fail to curtail robust, dysregulated intestinal Th1 cytokine production and chronic colitis in TGF‐βRII DN mice. Thus, T cell TGF‐β signaling is essential for helminthic stimulation of mucosal IL‐10 production, helminthic modulation of intestinal IFN‐γ generation and H. polygyrus‐mediated suppression of chronic colitis.

Cutting Edge: Heligmosomoides polygyrus Induces TLR4 on Murine Mucosal T Cells That Produce TGFβ after Lipopolysaccharide Stimulation

Helminths are immune modulators that down-regulate colitis in inflammatory bowel disease. In animal models, intestinal bacteria drive colitis and in humans certain alleles of the LPS receptor protein TLR4 increase inflammatory bowel disease susceptibility. To understand helminthic immune modulation in the gut, we studied the influence of intestinal Heligmosomoides polygyrus colonization on LPS-induced lamina propria mononuclear cell (LPMC) cytokine responses in mice. LPS did not stimulate TGFβ production from LPMC of uninfected mice. LPS strongly induced LPMC from worm-infected animals to secrete TGFβ, but not TNF-α or IL-12. The TGFβ derived from mucosal T cells. Helminth infection up-regulated TLR4 expression only in lamina propria T cells. LPMC from worm-infected TLR4 mutant animals did not respond to LPS, suggesting that LPS required TLR4 to stimulate TGFβ secretion. Thus, during helminth infection, LPS challenge induces mucosal T cells to make TGFβ through a TLR4-dependent process without promoting synthesis of proinflammatory cytokines.

Helminthic Therapy: Using Worms to Treat Immune-Mediated Disease

There is an epidemic of immune-mediated disease in highly-developed industrialized countries. Such diseases, like inflammatory bowel disease, multiple sclerosis and asthma increase in prevalence as populations adopt modern hygienic practices. These practices prevent exposure to parasitic worms (helminths). Epidemiologic studies suggest that people who carry helminths have less immune-mediated disease. Mice colonized with helminths are protected from disease in models of colitis, encephalitis, Type 1 diabetes and asthma. Clinical trials show that exposure to helminths reduce disease activity in patients with ulcerative colitis or Crohns disease. This chapter reviews some of the work showing that colonization with helminths alters immune responses, against dysregulated inflammation. These helminth-host immune interactions have potentially important implications for the treatment of immune-mediated diseases.

Trichuris suis might be effective in treating allergic rhinitis

generalizability are not uncommon concerns. Study findings can be influenced by self-selection (ie, the healthy worker effect), especially in cross-sectional occupational studies. Studies of farming populations, however, have provided a unique opportunity to study the role of environmental factors in the development of atopic disorders. In the study by Mandhane et al, the longitudinal data were derived from a large, unselected, population-based cohort, which is one of the major strengths of the work. Indeed, the authors found no signs of selection bias in their study. We acknowledge that pet ownership is not a very good surrogate for pet allergen exposures. In particular, personal allergen exposure can be highly variable, both spatially and temporally, because exposure levels are influenced by several factors, including the proximity of the source, reservoir concentration of allergen, nature of the source, and behavioral factors (eg, activity levels). Although homes may be the primary sites of exposure, exposure to cat and dog allergens is not limited to residential environments; both allergens are passively transported from one environment to another. However, the presence of indoor pets, cats and/or dogs, has been shown to be the strongest predictor of high pet allergen levels in homes. The hygiene hypothesis that was proposed as a potential explanation for time trends in allergic disease has remained a subject of intense debate over recent decades. Although the hypothesis has stimulated a substantial amount of research, the underlying etiologic mechanisms that confer protection against developing atopy are not completely understood. Nonetheless, there is increasing evidence to support that exposure to microbial infections in early life, as well as exposure to noninfectious microorganisms and microbial components, can influence innate and adaptive immune responses. Not only are cats and dogs sources of allergens, but also their presence has also been associated with other potential immunomodulatory agents, including endotoxin and other bacterial products. It is therefore not surprising that exposure to cats and dogs in the home might modify immune system development. Exposure to pet allergens and microbial stimuli may have independent effects, or they may operate in an interactive manner. For example, studies have shown that catinduced tolerance (modified TH2 response) is allergen-specific and cannot be explained by increased exposure to endotoxin. It is likely that gene-environment interactions also play an important role in the pathogenesis of allergic disorders. Emerging research suggests that an individual’s response to microbial or other environmental exposures depends on genetic polymorphisms that alter immune responses to environmental stimuli. Although the findings reported by Mandhane et al are intriguing, further research is needed to elucidate the complex relationships between atopy and environmental exposures, including exposures to cats and dogs. Päivi M. Salo, PhD Darryl C. Zeldin, MD

Nematode Asparaginyl-tRNA Synthetase Resolves Intestinal Inflammation in Mice with T-Cell Transfer Colitis

ABSTRACT The therapeutic effects of a controlled parasitic nematode infection on the course of inflammatory bowel disease (IBD) have been demonstrated in both animal and human models. However, the inability of individual well-characterized nematode proteins to recreate these beneficial effects has limited the application of component immunotherapy to human disease. The nematodes that cause chronic human lymphatic filariasis, Brugia malayi and Wuchereria bancrofti, are among the parasites that induce immune suppression. Filarial lymphatic pathology has been shown to involve NF-κB pathway-dependent production of vascular endothelial growth factor (VEGF), and stimulation of VEGF expression has also been reported by interleukin 8 (IL-8) via NF-κB pathways. Previously, we have shown that the filarial asparaginyl-tRNA synthetase (rBmAsnRS) interacts with IL-8 receptors using a combination of extracellular loops that differ from those bound by IL-8. To test the hypothesis that rBmAsnRS might induce an anti-inflammatory effect in vivo, we studied the effects of rBmAsnRS in an established murine colitis model using T-cell transfer mice. T-cell transfer colitis mice treated intraperitoneally with 100 μg of rBmAsnRS four times over 2 weeks showed resolution of cellular infiltration in the colonic mucosa, along with induction of a CD8+ cellular response. In addition, rBmAsnRS induced a rise in IL-10 production from CD3+ and lipopolysaccharide (LPS)- and cytosine phosphate guanosine (CPG)-stimulated splenic cells. In summary, this work demonstrates a novel anti-inflammatory nematode protein, supports the hygiene hypothesis, and supports continued refinement of alternative immunotherapies for treatment of IBD.

Substance P receptor antagonist inhibits murine IgM expression in developing schistosome granulomas by blocking the terminal differentiation of intragranuloma B cells

Schistosome granulomas make substance P (SP). CP96,345 is a nonpeptide SP receptor antagonist active in vivo. Granulomas that form in the presence of SP receptor blockade produce little IgM as compared to normal lesions. The objective of this study was to determine how CP96,345 modulates granuloma IgM production. Schistosome ova were embolized to the lungs of infected mice to induce granulomas of synchronous age. Animals received CP96,345 (50 mg/kg/day) for 4 days following egg embolization. Then granulomas were isolated from tissue and dispersed into single-cell preparations. The dispersed granuloma cells were cultured in vitro to measure IgM and cytokine secretion. Also, granuloma B cells were studied using an IgM ELISPOT assay and flow cytometry. As expected, mice treated with CP96,345 formed granulomas that secreted little IgM. Granulomas from CP96,345-treated mice, as compared to buffer-treated animals, contained few IgM-secreting B lymphocytes, but had appropriate numbers of B cells expressing surface IgM. Also decreased was the capacity of the granulomas to make IFN-gamma, IL-4, IL-5 and IL-6. CP96,345 treatment did not affect splenocyte IgM or cytokine synthesis. These data suggest that CP96,345 inhibits granuloma IgM secretion by blocking intragranuloma B cell maturation at a terminal stage of B cell differentiation. Moreover, SP receptor antagonist affects a variety of cytokine circuits that could influence IgM B cell maturation in vivo.