After Bone Marrow Transplantation, the Cell-Intrinsic Th2 Pathway Promotes Recipient T Lymphocyte Survival and Regulates Graft-versus-Host Disease.

Recipient T cells can aggravate or regulate lethal and devastating graft-versus-host disease (GVHD) after bone marrow transplantation (BMT). In this context, we have shown before that intestinal immune conditioning with helminths is associated with survival of recipient T cells and Th2 pathway-dependent regulation of GVHD. We investigated the mechanism of survival of recipient T cells and their contribution to GVHD pathogenesis in this helminth infection and BMT model after myeloablative preparation with total body irradiation in mice. Our results indicate that the helminth-induced Th2 pathway directly promotes the survival of recipient T cells after total body irradiation. Th2 cells also directly stimulate recipient T cells to produce TGF-ß, which is required to regulate donor T cell-mediated immune attack of GVHD and can thereby contribute to recipient T cell survival after BMT. Moreover, we show that recipient T cells, conditioned to produce Th2 cytokines and TGF-ß after helminth infection, are fundamentally necessary for GVHD regulation. Taken together, reprogrammed or immune-conditioned recipient T cells after helminth infection are crucial elements of Th2- and TGF-ß-dependent regulation of GVHD after BMT, and their survival is dependent on cell-intrinsic Th2 signaling.

Helminth Lessons in Inflammatory Bowel Diseases (IBD).

Helminths are multicellular invertebrates that colonize the gut of many vertebrate animals including humans. This colonization can result in pathology, which requires treatment. It can also lead to a commensal and possibly even a symbiotic relationship where the helminth and the host benefit from each other's presence. Epidemiological data have linked helminth exposure to protection from immune disorders that include a wide range of diseases, such as allergies, autoimmune illnesses, and idiopathic inflammatory disorders of the gut, which are grouped as inflammatory bowel diseases (IBD). Treatment of moderate to severe IBD involves the use of immune modulators and biologics, which can cause life-threatening complications. In this setting, their safety profile makes helminths or helminth products attractive as novel therapeutic approaches to treat IBD or other immune disorders. Helminths stimulate T helper-2 (Th2) and immune regulatory pathways, which are targeted in IBD treatment. Epidemiological explorations, basic science studies, and clinical research on helminths can lead to the development of safe, potent, and novel therapeutic approaches to prevent or treat IBD in addition to other immune disorders.

Parasitic Infections of the Gastrointestinal Track and Liver.

Parasites have coevolved with humans. Several of them colonize the human body and establish a symbiotic relationship. Other parasites cause severe and lethal diseases. Prevalence of parasitic infections is decreased in highly industrialized countries, largely due to enforced hygienic practices. In contrast, parasites cause significant morbidity and mortality in parts of the world with barriers to effective public hygiene. Some parasites have emerged as potent pathogens in specific patient populations, such as immune suppressed individuals, regardless of sanitation. This article reviews common parasites encountered in clinical practice and, in the setting of host-parasite symbiosis, discusses their immune regulatory role.

Helminth-induced regulation of T-cell transfer colitis requires intact and regulated T cell Stat6 signaling in mice.

Infection with parasitic worms (helminths) alters host immune responses and can inhibit pathogenic inflammation. Helminth infection promotes a strong Th2 and T regulatory response while suppressing Th1 and Th17 function. Th2 responses are largely dependent on transcriptional programs directed by Stat6-signaling. We examined the importance of intact T cell Stat6 signaling on helminth-induced suppression of murine colitis that results from T cell transfer into immune-deficient mice. Colonization with the intestinal nematode Heligmosomoides polygyrus bakeri resolves WT T cell transfer colitis. However, if the transferred T cells lack intact Stat6 then helminth exposure failed to attenuate colitis or suppress MLN T cell IFN-γ or IL17 production. Loss of Stat6 signaling resulted in decreased IL10 and increased IFN-γ co-expression by IL-17+ T cells. We also transferred T cells from mice with constitutive T cell expression of activated Stat6 (Stat6VT). These mice developed a severe eosinophilic colitis that also was not attenuated by helminth infection. These results show that T cell expression of intact but regulated Stat6 signaling is required for helminth infection-associated regulation of pathogenic intestinal inflammation.

Effective Use of the Laboratory in the Management of Patients with Inflammatory Bowel Diseases.

Inflammatory bowel disease (IBD) comprises a group of chronic, intestinal inflammatory disorders, including ulcerative colitis and Crohn's disease. IBD is characterized by periods of relapse and remission. Long-term progressive intestinal inflammation can result in severe and devastating complications, such as intestinal strictures and/or fistulae. Immune suppressive medications with potent side effects are often used to control inflammation and limit disease activity. Laboratory tests guide various decisions in clinical management of IBD. We discuss tests used to diagnose IBD, assess for relapse or remission, monitor the effectiveness of therapeutic regimen, screen for the maintenance of health, and diagnose or prevent complications.

Helminth-Induced Production of TGF-ß and Suppression of Graft-versus-Host Disease Is Dependent on IL-4 Production by Host Cells.

Helminths stimulate the secretion of Th2 cytokines, like IL-4, and suppress lethal graft-versus-host disease (GVHD) after bone marrow transplantation. This suppression depends on the production of immune-modulatory TGF-ß and is associated with TGF-ß-dependent in vivo expansion of Foxp3+ regulatory T cells (Treg). In vivo expansion of Tregs is under investigation for its potential as a therapy for GVHD. Nonetheless, the mechanism of induced and TGF-ß-dependent in vivo expansion of Tregs, in a Th2 polarized environment after helminth infection, is unknown. In this study, we show that helminth-induced IL-4 production by host cells is critical to the induction and maintenance of TGF-ß secretion, TGF-ß-dependent expansion of Foxp3+ Tregs, and the suppression of GVHD. In mice with GVHD, the expanding donor Tregs express the Th2-driving transcription factor, GATA3, which is required for helminth-induced production of IL-4 and TGF-ß. In contrast, TGF-ß is not necessary for GATA3 expression by Foxp3+ Tregs or by Foxp3- CD4 T cells. Various cell types of innate or adaptive immune compartments produce high quantities of IL-4 after helminth infection. As a result, IL-4-mediated suppression of GVHD does not require invariant NKT cells of the host, a cell type known to produce IL-4 and suppress GVHD in other models. Thus, TGF-ß generation, in a manner dependent on IL-4 secretion by host cells and GATA3 expression, constitutes a critical effector arm of helminthic immune modulation that promotes the in vivo expansion of Tregs and suppresses GVHD.

STAT6 and Furin Are Successive Triggers for the Production of TGF-ß by T Cells.

Production of TGF-ß by T cells is key to various aspects of immune homeostasis, with defects in this process causing or aggravating immune-mediated disorders. The molecular mechanisms that lead to TGF-ß generation by T cells remain largely unknown. To address this issue, we take advantage of the fact that intestinal helminths stimulate Th2 cells besides triggering TGF-ß generation by T lymphocytes and regulate immune-mediated disorders. We show that the Th2 cell-inducing transcription factor STAT6 is necessary and sufficient for the expression of TGF-ß propeptide in T cells. STAT6 is also necessary for several helminth-triggered events in mice, such as TGF-ß-dependent suppression of alloreactive inflammation in graft-versus-host disease. Besides STAT6, helminth-induced secretion of active TGF-ß requires cleavage of propeptide by the endopeptidase furin. Thus, for the immune regulatory pathway necessary for TGF-ß production by T cells, our results support a two-step model, composed of STAT6 and furin.

Recirculating Immunocompetent Cells in Colitic Mice Intensify Their Lung Response to Bacterial Endotoxin.

BACKGROUND: Patients with inflammatory bowel disease have higher incidence of airway hyperresponsiveness compared to the general population. Lung inflammation leading to airway hyperresponsiveness causes illnesses for more than ten percent of the population in USA. AIMS: We investigated the lung response to bacterial endotoxin in colitic mice. METHODS: Rag-1 mice were transplanted with negatively selected splenic T cells. Some mice groups were treated with NSAID to develop colitis. All mice were treated with bacterial endotoxin and necropsied 3 weeks later. RESULTS: Colitic mice developed intensified lung inflammation on day 21 of treatment with bacterial endotoxin. Pulmonary lymphocytes from colitic mice displayed a proinflammatory cytokine profile, expressed high ICAM1 and low FoxP3. CD11c+, CD8+ cells bound and responded to non-systemic antigens from gut-localized microbiota and had higher expression of TLR4. CONCLUSIONS: Colitic mice developed exacerbated lung inflammation in response to bacterial endotoxin compared to non-colitic mice. Proinflammatory cytokines from pulmonary lymphocytes induced high expression of ICAM1 and suppressed FoxP3 on CD4+ cells. CD11c+, CD8+ cells binding and responding to gut-localized antigens as well as high expression of TLR4 indicate innate and adaptive lung response to bacterial endotoxin. Inflammatory cells from colons of colitic mice homed in the lungs as well as the intestine suggesting recirculation of sensitized immunocompetent cells. These data support our hypothesis that colitis intensifies lung inflammation.

Intestinal helminths regulate lethal acute graft-versus-host disease and preserve the graft-versus-tumor effect in mice.

Donor T lymphocyte transfer with hematopoietic stem cells suppresses residual tumor growth (graft-versus-tumor [GVT]) in cancer patients undergoing bone marrow transplantation (BMT). However, donor T cell reactivity to host organs causes severe and potentially lethal inflammation called graft-versus-host disease (GVHD). High-dose steroids or other immunosuppressive drugs are used to treat GVHD that have limited ability to control the inflammation while incurring long-term toxicity. Novel strategies are needed to modulate GVHD, preserve GVT, and improve the outcome of BMT. Regulatory T cells (Tregs) control alloantigen-sensitized inflammation of GVHD, sustain GVT, and prevent mortality in BMT. Helminths colonizing the alimentary tract dramatically increase the Treg activity, thereby modulating intestinal or systemic inflammatory responses. These observations led us to hypothesize that helminths can regulate GVHD and maintain GVT in mice. Acute GVHD was induced in helminth (Heligmosomoides polygyrus)-infected or uninfected BALB/c recipients of C57BL/6 donor grafts. Helminth infection suppressed donor T cell inflammatory cytokine generation and reduced GVHD-related mortality, but maintained GVT. H. polygyrus colonization promoted the survival of TGF-ß-generating recipient Tregs after a conditioning regimen with total body irradiation and led to a TGF-ß-dependent in vivo expansion/maturation of donor Tregs after BMT. Helminths did not control GVHD when T cells unresponsive to TGF-ß-mediated immune regulation were used as donor T lymphocytes. These results suggest that helminths suppress acute GVHD using Tregs and TGF-ß-dependent pathways in mice. Helminthic regulation of GVHD and GVT through intestinal immune conditioning may improve the outcome of BMT.

Helminth infections decrease host susceptibility to immune-mediated diseases.

Helminthic infection has become rare in highly industrialized nations. Concurrent with the decline in helminthic infection has been an increase in the prevalence of inflammatory disease. Removal of helminths from our environment and their powerful effects on host immunity may have contributed to this increase. Several helminth species can abrogate disease in murine models of inflammatory bowel disease, type 1 diabetes, multiple sclerosis, and other conditions. Helminths evoke immune regulatory pathways often involving dendritic cells, regulatory T cells, and macrophages that help to control disease. Cytokines, such as IL-4, IL-10, and TGF-ß, have a role. Notable is the helminthic modulatory effect on innate immunity, which impedes development of aberrant adaptive immunity. Investigators are identifying key helminth-derived immune modulatory molecules that may have therapeutic usefulness in the control of inflammatory disease.

Innate immunity in disease.

Cells can innately recognize generic products of viruses, bacteria, fungi, or injured tissue by engagement of pattern recognition receptors. Innate immune cells rapidly respond to this engagement to control commensals, thwart pathogens, and/or prompt repair. Insufficient or excessive activation of the innate immune response results in disease. This review focuses on pattern recognition receptors and cells of the innate immune system that are important for intestinal function. Our improving knowledge pertaining to this important aspect of our immune response is opening potential important new therapeutic opportunities for the treatment of disease.

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.

Where are we on worms?

PURPOSE OF REVIEW: There is something about living in an industrialized country that dramatically increases the risk of acquiring inflammatory bowel disease (IBD). Loss of routine exposure to parasitic worms (helminths), due to modern highly hygienic life styles, likely contributes to this risk. This article reviews current understanding on how helminths influence intestinal inflammation and mucosal immune responses. RECENT FINDINGS: IBD emerges in populations as regions develop socioeconomically and lose exposure to previously ubiquitous helminthic infections. Helminthic infections provided strong selective pressure for the dissemination of gene variants, many of which predispose to development of IBD. In animal models of IBD, helminth colonization suppresses intestinal inflammation through multiple mechanisms including induction of innate and adaptive regulatory circuits. Trials using helminths like hookworm (Necator americanus) or porcine whipworm (Trichuris suis) show that they are safe and may be effective therapies for the control of the aberrant intestinal inflammation seen in Crohn's disease and ulcerative colitis. SUMMARY: Evidence is accumulating that highly hygienic living conditions create risk for developing immune-mediated disease such as IBD. To live in their host, helminths have developed the ability to activate cells of innate and adaptive immunity that suppress inflammation. Therapeutic trials using helminths are in progress.

Helminth-host immunological interactions: prevention and control of immune-mediated diseases.

Exposure to commensal and pathogenic organisms strongly influences our immune system. Exposure to helminths was frequent before humans constructed their current highly hygienic environment. Today, in highly industrialized countries, contact between humans and helminths is rare. Congruent with the decline in helminth infections is an increase in the prevalence of autoimmune and inflammatory disease. It is possible that exclusion of helminths from the environment has permitted the emergence of immune-mediated disease. We review the protective effects of helminths on expression of inflammatory bowel disease, multiple sclerosis, and animal models of these and other inflammatory diseases. We also review the immune pathways altered by helminths that may afford protection from these illnesses. Helminth exposure tends to inhibit IFN-γ and IL-17 production, promote IL-4, IL-10, and TGF-ß release, induce CD4(+) T cell Foxp3 expression, and generate regulatory macrophages, dendritic cells, and B cells. Helminths enable protective pathways that may vary by specific species and disease model. Helminths or their products likely have therapeutic potential to control or prevent immune-mediated illness.

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

Colonization with helminthic parasites induces mucosal regulatory cytokines, like IL-10 or TGF-beta, 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-beta release. As TGF-beta exerts major regulatory effects on T lymphocytes, we investigated the role of T lymphocyte TGF-beta signaling in helminthic modulation of intestinal immunity. T cell TGF-beta signaling is interrupted in TGF-beta receptor II dominant negative (TGF-betaRII DN) mice by T-cell-specific over-expression of a TGF-betaRII DN. We studied LPMC responses in WT and TGF-betaRII DN mice that were uninfected or colonized with the nematode, Heligmosomoides polygyrus. Our results indicate an essential role of T cell TGF-beta 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-beta-signaling pathway. Helminths fail to curtail robust, dysregulated intestinal Th1 cytokine production and chronic colitis in TGF-betaRII DN mice. Thus, T cell TGF-beta signaling is essential for helminthic stimulation of mucosal IL-10 production, helminthic modulation of intestinal IFN-gamma generation and H. polygyrus-mediated suppression of chronic colitis.

Advances in the pathogenesis and treatment of IBD.

Crohn's disease and ulcerative colitis are chronic remitting and relapsing inflammatory bowel diseases. We present a typical case of Crohn's disease in a young woman and discuss potential treatment options. Crohn's 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.

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 Crohn's 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.

Helminths and the IBD hygiene hypothesis.

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 host's 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.