Mechanisms underlying gut dysfunction in a murine model of chronic parasitic infection

Irritable bowel syndrome (IBS) is common in countries where chronic parasitic infestations are endemic. However, the relationship between parasitic infection and IBS is not clear. The aim of this study was to examine whether chronic parasitic infection is accompanied by gut dysfunction and whether the continued presence of the parasite is required for the maintenance of the dysfunction. We used chronic Trichuris muris infection in Th1-biased susceptible AKR mice to evaluate this relationship. AKR mice were infected with T. muris and were euthanized on various days postinfection (pi) to examine worm burden, muscle function, and immune and inflammatory responses. Mice were treated with the anthelmintic oxantel pamoate to assess the effect of eradication of infection on muscle function. Infection resulted in persistence of the parasite, elevated IFN-γ, and increased MPO activity evident at 45 days pi. This was accompanied by a reduction in muscle contractility and excitatory innervation. Whereas parasite eradication at 7 days pi normalized IFN-γ and muscle contractility, eradication at 28 days pi failed to normalize muscle contractility. Administration of dexamethasone after parasite eradication normalized all parameters. Anthelmintic treatment improved histology except for eosinophils, which were normalized by subsequent dexamethasone therapy. Persistent gut dysfunction is independent of the continued presence of the parasite and is maintained by inflammatory process that includes eosinophils. Thus data in this preclinical model suggest that parasitic infection could be a cause of IBS, and the lack of symptomatic improvement following eradication is insufficient evidence to refute a causal relationship between the infection and IBS.

Serotonin has a key role in pathogenesis of experimental colitis

BACKGROUND & AIMS

Mucosal changes in inflammatory bowel disease are characterized by ulcerative lesions accompanied by a prominent infiltrate of immune cells as well as alteration in serotonin (5-hydroxytryptamine [5-HT])-producing enterochromaffin cells. We investigated the role of 5-HT in colonic inflammation in mice.

METHODS

Colitis was induced with dextran sulfate sodium or dinitrobenzene sulfonic acid in tryptophan hydroxylase 1-deficient (TPH1(-/-)) mice, which have markedly reduced 5-HT in the gastrointestinal tract, and in mice given the 5-HT synthesis inhibitor parachlorophenylalanine.

RESULTS

Delayed onset, decreased severity of clinical disease, and significantly lower macroscopic and histologic damage scores were observed in TPH1(-/-) mice, compared with wild-type mice, and in mice given parachlorophenylalanine after induction of colitis by dextran sulfate sodium. This was associated with down-regulation of macrophage infiltration and production of proinflammatory cytokines. 5-HT stimulated production of proinflammatory cytokines from macrophages collected from the peritoneal cavity of wild-type mice; this process was inhibited by a nuclear factor kappaB inhibitor, indicating a critical role for nuclear factor kappaB signaling in 5-HT-mediated activation of immune cells. Restoration of 5-HT levels in TPH1(-/-) mice by the 5-HT precursor 5-hydroxytryptophan increased the severity of DSS-induced colitis. We also observed significant reduction in severity of colitis in TPH1(-/-) mice after induction of dinitrobenzene sulfonic acid-induced colitis.

CONCLUSIONS

5-HT is involved in the pathogenesis of inflammation in experimental colitis. These findings provide insight into the mechanisms of gastrointestinal inflammation and could lead to new therapeutic strategies for inflammatory disorders.

Helminth antigen-based strategy to ameliorate inflammation in an experimental model of colitis

Inflammatory bowel disease (IBD) is the most common and serious chronic inflammatory condition of the gut. Among the distinct T helper (Th) cell subsets, a Th1 type response is associated predominantly with Crohn's disease (CD) while helminth infections generate a strong Th2 type response. IBD is most prevalent in developed countries but rare in countries where infections with helminths are common. Thus, it has been hypothesized that infection with helminth infection influence the development of CD and recent clinical and experimental studies suggest strongly a beneficial role of helminth infection in IBD. In the present study we examined the effects of rectal submucosal administration of helminth antigens on subsequent experimental colitis. Mice were treated with Trichinella spiralis antigens prior to the induction of dinitrobenzenesulphonic acid (DNBS)-induced colitis and were killed 3 days post-DNBS to assess colonic damage macroscopically, histologically and by myeloperoxidase (MPO) activity, inducible nitric oxide synthase (iNOS) and cytokine levels. Previous treatment with T. spiralis antigens reduced the severity of colitis significantly, as assessed macroscopically and histologically, and reduced the mortality rate. This benefit was correlated with a down-regulation of MPO activity, interleukin (IL)-1beta production and iNOS expression and an up-regulation of IL-13 and transforming growth factor-beta production in colon. These results clearly show a beneficial role of local treatment with helminth antigens for experimental colitis and prompt consideration of helminth antigen-based therapy for IBD instead of infection with live parasites.

Enterochromaffin cell and 5-hydroxytryptamine responses to the same infectious agent differ in Th1 and Th2 dominant environments

BACKGROUND/AIM

5-Hydroxytryptamine (5-HT) released from enterochromaffin cells influences intestinal homeostasis by altering gut physiology and is implicated in the pathophysiology of various gut disorders. The mechanisms regulating 5-HT production in the gut remain unclear. This study investigated the T helper (Th) 1/Th2-based immunoregulation of enterochromaffin cell function and 5-HT production in a model of enteric infection.

METHODS AND RESULTS

Trichuris muris-infected AKR (susceptible to infection and generates Th1 response), BALB/c (resistant to infection and generates Th2 response), Stat4-deficient (impaired in Th1 response) and Stat6-deficient (impaired in Th2 response) mice were investigated to assess enterochromaffin cells, 5-HT and cytokines. In association with the generation of a Th2 response we observed higher enterochromaffin cell numbers and 5-HT content in the colon of BALB/c mice compared with AKR mice. Numbers of enterochromaffin cells and amount of 5-HT were significantly lower in Stat6-deficient mice after infection compared with Stat4-deficient mice. In addition, enterochromaffin cell numbers and 5-HT content were significantly higher after reconstitution of severe combined immunodeficient mice with in-vitro polarised Th2 cells.

CONCLUSION

The study demonstrated that enterochromaffin cell and 5-HT responses to the same infectious agent are influenced by Th1 or Th2 cytokine predominance and suggests that the immunological profile of the inflammatory response is important in the regulation of enterochromaffin cell biology in the gut. In addition to new data on enterochromaffin cell function in enteric infection and inflammation, this study provides important information on the immuno-endocrine axis in the gut, which may ultimately lead to improved strategies against gut disorders.

The protective effect of the vagus nerve in a murine model of chronic relapsing colitis

The vagus nerve inhibits the response to systemic administration of endotoxin, and we have recently extended this observation to show that the vagus attenuates acute experimental colitis in mice. The purpose of the present study was to determine whether there is a tonic counterinflammatory influence of the vagus on colitis maintained over several weeks. We assessed disease activity index, macroscopic and histological damage, myeloperoxidase (MPO) activity, and Th1 and Th2 cytokine profiles in chronic colitis induced by administration of dextran sodium sulfate (DSS) in drinking water for three cycles during 5 days with 11 days of rest between each cycle (DSS 3, 2, 2%) in healthy and vagotomized C57BL/6 mice and in mice deficient in macrophage-colony stimulating factor (M-CSF). A pyloroplasty was performed in vagotomized mice. Vagotomy accelerated the onset and the severity of inflammation during the first and second but not the third cycle. Although macroscopic scores were not significantly changed, histological scores as well as MPO activity and colonic tissue levels of IL-1alpha, TNF-alpha, IFN-gamma, and IL-18 but not IL-4 were significantly increased in vagotomized mice compared with sham-operated mice that received DSS. In control mice (without colitis), vagotomy per se did not affect any inflammatory marker. Vagotomy had no effect on the colitis in M-CSF-derived macrophage-deficient mice. These results indicate that the vagus protects against acute relapses on a background of chronic inflammation. Identification of the molecular mechanisms underlying the protective role of parasympathetic nerves opens a new therapeutic avenue for the treatment of acute relapses of chronic inflammatory bowel disease.

CD4+ T cell-mediated immunological control of enterochromaffin cell hyperplasia and 5-hydroxytryptamine production in enteric infection

BACKGROUND

Enterochromaffin (EC) cells are dispersed throughout the gastrointestinal (GI) mucosa and are the main source of 5-hydroxytryptamine (5-HT) in the gut. 5-HT has been implicated in the pathophysiology of several GI disorders, but the mechanisms regulating 5-HT production in the gut are unknown.

AIM

To investigate the role of CD4(+) T cells in the production of 5-HT using a model of enteric parasitic infection.

METHODS AND RESULTS

Severe combined immunodeficient (SCID) mice and their wild-type controls were infected with the nematode Trichuris muris and killed on various days after infection to study colonic EC cells and 5-HT production. The number of EC cells and the amount of 5-HT produced were significantly higher in infected wild-type mice than in non-infected mice. The number of EC cells and the amount of 5-HT after infection were significantly lower in SCID mice after infection than in wild-type mice. The number of EC cells and the amount of 5-HT was significantly increased after reconstitution of SCID mice with CD4(+) T cells from infected mice and this was accompanied by an upregulation of colonic CD3 T cells and T helper 2 (Th2) cytokines. Laser capture microdissection-based molecular and immunofluorescence techniques revealed the presence of interleukin 13 receptor alpha1-chain on EC cells.

CONCLUSION

These results show an important immunoendocrine axis in the gut, where secretory products from CD4(+) T cells interact with EC cells to enhance the production of 5-HT in the gut via Th2-based mechanisms. These results show new insights into the mechanisms of gut function, which may ultimately lead to improved therapeutic strategies in functional and inflammatory disorders of the GI tract.

Critical role of MCP-1 in the pathogenesis of experimental colitis in the context of immune and enterochromaffin cells

Mucosal changes in inflammatory bowel disease (IBD) are characterized by ulcerative lesions accompanied by a prominent infiltrate of inflammatory cells including lymphocytes, macrophages, and neutrophils and alterations in 5-hydroxytryptamine (5-HT)-producing enterochromaffin (EC) cells. Mechanisms involved in recruiting and activating these cells are thought to involve a complex interplay of inflammatory mediators. Studies in clinical and experimental IBD have shown the upregulation of various chemokines including monocyte chemoattractant protein (MCP)-1 in mucosal tissues. However, precise information on the roles of this chemokine or the mechanisms by which it takes part in the pathogenesis of IBD are not clear. In this study, we investigated the role of MCP-1 in the development of hapten-induced experimental colitis in mice deficient in MCP-1. Our results showed a significant reduction in the severity of colitis both macroscopically and histologically along with a decrease in mortality in MCP-1-deficient mice compared with wild-type control mice. This was correlated with a downregulation of myeloperoxidase activity, IL-1beta, IL-12p40, and IFN-gamma production, and infiltration of CD3+ T cells and macrophages in the colonic mucosa. In addition, we observed significantly lower numbers of 5-HT-expressing EC cells in the colon of MCP-1-deficient mice compared with those in wild-type mice after dinitrobenzenesulfonic acid. These results provide evidence for a critical role of MCP-1 in the development of colonic inflammation in this model in the context of immune and enteric endocrine cells.

CD4+ T-cell modulation of visceral nociception in mice

BACKGROUND & AIMS

Although inflammatory and immune cells are present in the gut in the absence of pathology, their presence does not result in sensitization of sensory nerves, implying the existence of a local antinociceptive influence. We hypothesized that a component of the immune system exerts an antinociceptive influence, thus enabling the gut to function in the absence of undue pain or discomfort.

METHODS

Visceromotor responses to colorectal distention were measured in mice with severe combined immune deficiency (SCID) and their wild-type controls.

RESULTS

SCID mice exhibited significantly lower pain thresholds. Transfer of CD4(+) T, but not B lymphocytes, normalized visceral pain in these mice. The restoration of normal visceral nociception following T-cell reconstitution in SCID mice was blocked by naloxone methiodide. Using an enzyme immunoassay and immunohistochemistry for beta-endorphin, we showed that in vitro stimulation of T lymphocytes induced the synthesis and release of beta-endorphin and that transfer of T cells into SCID mice increased the expression of beta-endorphin in the enteric nervous system.

CONCLUSIONS

These findings indicate that the immune system is a critical determinant of visceral nociception and that T lymphocytes provide an important opioid-mediated antinociceptive influence in the gut.

Induction of a fibrogenic response in mouse colon by overexpression of monocyte chemoattractant protein 1

BACKGROUND AND AIMS

Monocyte chemoattractant protein 1 (MCP-1) is increased transmurally in inflammatory bowel disease (IBD). Although MCP-1 is considered to play an important role in fibrotic disease in other organs, the role of MCP-1 in gut fibrosis is unknown. We investigated the fibrotic potential of MCP-1 in the gut by overexpressing this chemokine in the mouse colorectal wall.

METHODS

Intramural gene transfer by direct injection of adenovector into the mouse rectal wall was established. C57BL/6 and Rag2(-/-) (B and T cell deficient) mice received 2.5 x 10(9) plaque forming units of an adenovector encoding murine MCP-1 (AdMCP-1) or control virus (AdDL70) via intramural injection. Mice were killed at various time points and tissues were obtained for histopathological and biochemical analysis.

RESULTS

AdMCP-1 significantly increased collagen production in the colorectum and this was associated with significant elevation of transforming growth factor beta (TGF-beta) and tissue inhibitor of metalloproteinase (TIMP-1) protein. Transmural collagen deposition was observed after AdMCP-1 administration, and was accompanied by CD3+ T cells, F4/80+ macrophages, and vimentin+ cell infiltrates. Collagen was differentially distributed, with type I deposited in the muscularis mucosa and muscularis propria and type III in the submucosa and myenteric plexus. AdMCP-1 failed to induce collagen overproduction in immunodeficient Rag2(-/-) mice.

CONCLUSION

These findings suggest that MCP-1 can induce fibrosis in the gut and that this process involves interaction between T cells and vimentin positive fibroblasts/myofibroblasts, as well as the subsequent upregulation of TGF-beta and TIMP-1 production. This model provides a basis for considering MCP-1 in the pathogenesis of strictures in IBD.

Disruption of CD40-CD40 ligand pathway inhibits the development of intestinal muscle hypercontractility and protective immunity in nematode infection

In our previous studies, we demonstrated that during Trichinella spiralis infection, T helper (Th) 2 cells contribute to the development of intestinal muscle hypercontractility and worm expulsion from the gut via STAT6. In addition, we have linked the altered muscle contractility to the eviction of the parasite and thereby to the host defense. However, the initial events linking infection to the development of muscle hypercontractility are poorly understood. In this study, we examined the contribution of CD40-CD40 ligand (CD40L) interaction in the development of intestinal muscle hypercontractility, in monocyte chemoattractant protein-1 (MCP-1) production, and in the Th2 response in CD40 ligand-deficient (CD40L -/-) mice infected with T. spiralis. Expulsion of intestinal worms was substantially delayed in CD40L -/- mice compared with the wild-type mice after T. spiralis infection. Consistent with delayed worm expulsion, there was a significant attenuation of intestinal muscle contractility in CD40L -/- mice. Infected CD40L -/- mice also exhibited marked impairment in the production of MCP-1, IL-4, IL-13, IgG1, IgE, and mouse mucosal MCP 1 (MMCP-1), and in goblet cell response. These results demonstrate that CD40-CD40 ligand interaction plays an important role in MCP-1 production, Th2 response, intestinal muscle hypercontractility, and worm expulsion in nematode infection. The present data suggest that the early events leading to the generation of Th2 response include CD40-CD40 ligand interaction, which subsequently influences the production of Th2 cytokines, most likely via upregulation of MCP-1.

Alpha tocopherol protects against immunosuppressive and immunotoxic effects of lead

Chronic exposure to lead (Pb) is associated with multiorgan toxicity. The precise mechanism(s) involved, however, remains incompletely defined. The present study was undertaken to analyze the effect of Pb on the immune system and determine the ability of alpha tocopherol (AT) to reverse Pb-induced immunotoxicity. Groups of TO Mice (6 per group) were treated ip for 2 weeks with saline alone, Pb acetate alone, Pb plus AT, or with AT alone. Spleens were then analyzed for (i) cellular composition by flow cytometry, (ii) cellular response to B and T cell mitogens and (iii) production of nitric oxide (NO). Pb treatment resulted in a significant state of splenomegaly associated mainly with an influx of CD11b+ myeloid cells. Surprisingly, however, these cells exhibited no upregulation in expression of activation markers and did not produce NO. The lymphocyte mitogenic responses were inhibited by > or = 70% in Pb-treated group. Concurrent treatment with Pb and AT resulted in almost a complete reversal of Pb-induced splenic cellular influx. Despite this, however, mitogenic responses in Pb + AT treated group were approximately 50% of those observed in normal (saline-treated) controls. We conclude that (1) chronic treatment with Pb acetate induces a state of splenomegaly and decreased proliferation in response to mitogenic stimuli and (2) co-treatment with AT largely reversed the cellular influx but this was associated with only a partial improvement of the mitogenic responses. These results highlight the role of AT as a potentially effective antioxidant in the immune system.