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.

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.

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.

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.