Immune activation in irritable bowel syndrome: can neuroimmune interactions explain symptoms?

Irritable bowel syndrome (IBS) is a functional disorder of the gastrointestinal (GI) tract characterized by pain or discomfort from the lower abdominal region, which is associated with altered bowel habit. Despite its prevalence, there is currently a lack of effective treatment options for patients. IBS has long been considered as a neurological condition resulting from alterations in the brain gut axis, but immunological alterations are increasingly reported in IBS patients, consistent with the hypothesis that there is a chronic, but low-grade, immune activation. Mediators released by immune cells act to either dampen or amplify the activity of GI nerves. Release of a number of these mediators correlates with symptoms of IBS, highlighting the importance of interactions between the immune and the nervous systems. Investigation of the role of microbiota in these interactions is in its early stages, but may provide many answers regarding the mechanisms underlying activation of the immune system in IBS. Identifying what the key changes in the GI immune system are in IBS and how these changes modulate viscerosensory nervous function is essential for the development of novel therapies for the underlying disorder.Patrick A. Hughes, Heddy Zola, Irmeli A. Penttila, L. Ashley Blackshaw, Jane M. Andrews, and Doreen Krumbiege

MMP19 Is Essential for T Cell Development and T Cell-Mediated Cutaneous Immune Responses

Matrix metalloproteinase-19 (MMP19) affects cell proliferation, adhesion, and migration in vitro but its physiological role in vivo is poorly understood. To determine the function of MMP19, we generated mice deficient for MMP19 by disrupting the catalytic domain of mmp19 gene. Although MMP19-deficient mice do not show overt developmental and morphological abnormalities they display a distinct physiological phenotype. In a model of contact hypersensitivity (CHS) MMP19-deficient mice showed impaired T cell-mediated immune reaction that was characterized by limited influx of inflammatory cells, low proliferation of keratinocytes, and reduced number of activated CD8+ T cells in draining lymph nodes. In the inflamed tissue, the low number of CD8+ T cells in MMP19-deficient mice correlated with low amounts of proinflammatory cytokines, especially lymphotactin and interferon-inducible T cell α chemoattractant (I-TAC). Further analyses showed that T cell populations in the blood of immature, unsensitized mice were diminished and that this alteration originated from an altered maturation of thymocytes. In the thymus, thymocytes exhibited low proliferation rates and the number of CD4+CD8+ double-positive cells was remarkably augmented. Based on the phenotype of MMP19-deficient mice we propose that MMP19 is an important factor in cutaneous immune responses and influences the development of T cells

Laminin 5 in the human thymus: control of T cell proliferation via alpha6beta4 integrins.

International audienceLaminin 5 (alpha3beta3gamma2) distribution in the human thymus was investigated by immunofluorescence on frozen sections with anti-alpha3, -beta3, and -gamma2 mAbs. In addition to a linear staining of subcapsular basal laminae, the three mAbs give a disperse staining in the parenchyma restricted to the medullary area on a subset of stellate epithelial cells and vessel structures. We also found that laminin 5 may influence mature human thymocyte expansion; while bulk laminin and laminin 2, when cross-linked, are comitogenic with a TCR signal, cross-linked laminin 5 has no effect. By contrast, soluble laminin 5 inhibits thymocyte proliferation induced by a TCR signal. This is accompanied by a particular pattern of inhibition of early tyrosine kinases, including Zap 70 and p59(fyn) inhibition, but not overall inhibition of p56(lck). Using a mAb specific for alpha6beta4 integrins, we observed that while alpha3beta1 are known to be uniformly present on all thymocytes, alpha6beta4 expression parallels thymocyte maturation; thus a correspondence exists between laminin 5 in the thymic medulla and alpha6beta4 on mature thymocytes. Moreover, the soluble Ab against alpha6beta4 inhibits thymocyte proliferation and reproduces the same pattern of tyrosine kinase phosphorylation suggesting that alpha6beta4 is involved in laminin 5-induced modulation of T cell activation.Laminin 5 (alpha3beta3gamma2) distribution in the human thymus was investigated by immunofluorescence on frozen sections with anti-alpha3, -beta3, and -gamma2 mAbs. In addition to a linear staining of subcapsular basal laminae, the three mAbs give a disperse staining in the parenchyma restricted to the medullary area on a subset of stellate epithelial cells and vessel structures. We also found that laminin 5 may influence mature human thymocyte expansion; while bulk laminin and laminin 2, when cross-linked, are comitogenic with a TCR signal, cross-linked laminin 5 has no effect. By contrast, soluble laminin 5 inhibits thymocyte proliferation induced by a TCR signal. This is accompanied by a particular pattern of inhibition of early tyrosine kinases, including Zap 70 and p59(fyn) inhibition, but not overall inhibition of p56(lck). Using a mAb specific for alpha6beta4 integrins, we observed that while alpha3beta1 are known to be uniformly present on all thymocytes, alpha6beta4 expression parallels thymocyte maturation; thus a correspondence exists between laminin 5 in the thymic medulla and alpha6beta4 on mature thymocytes. Moreover, the soluble Ab against alpha6beta4 inhibits thymocyte proliferation and reproduces the same pattern of tyrosine kinase phosphorylation suggesting that alpha6beta4 is involved in laminin 5-induced modulation of T cell activation

Mature Human Thymocytes Migrate on Laminin-5 with Activation of Metalloproteinase-14 and Cleavage of CD44

International audienceWe have previously shown that laminin-5 is expressed in the human thymic medulla, in which mature thymocytes are located. We now report that laminin-5 promotes migration of mature medullary thymocytes, whereas it has no effect on cortical immature thymocytes. Migration was inhibited by blocking mAbs directed against laminin-5 integrin receptors and by inhibitors of metalloproteinases. Interactions of thymocytes with laminin-5 induced a strong up-regulation of active metalloproteinase-14. However, we found that thymocytes did not cleave the laminin-5 gamma(2) chain, suggesting that they do not use the same pathway as epithelial cells to migrate on laminin-5. Interactions of thymocytes with laminin-5 also induced the release of a soluble fragment of CD44 cell surface molecule. Moreover, CD44-rich supernatants induced thymocyte migration in contrast with supernatants depleted in CD44 by immunoadsorption. CD44 cleavage was recently reported to be due to metalloproteinase-14 activation and led to increased migration in cancer cells. Thus, in this study, we show that laminin-5 promotes human mature thymocyte migration in vitro via a multimolecular mechanism involving laminin-5 integrin receptors, metalloproteinase-14 and CD44. These data suggest that, in vivo, laminin-5 may function in the migration of mature thymocytes within the medulla and be part of the thymic emigration process.We have previously shown that laminin-5 is expressed in the human thymic medulla, in which mature thymocytes are located. We now report that laminin-5 promotes migration of mature medullary thymocytes, whereas it has no effect on cortical immature thymocytes. Migration was inhibited by blocking mAbs directed against laminin-5 integrin receptors and by inhibitors of metalloproteinases. Interactions of thymocytes with laminin-5 induced a strong up-regulation of active metalloproteinase-14. However, we found that thymocytes did not cleave the laminin-5 gamma(2) chain, suggesting that they do not use the same pathway as epithelial cells to migrate on laminin-5. Interactions of thymocytes with laminin-5 also induced the release of a soluble fragment of CD44 cell surface molecule. Moreover, CD44-rich supernatants induced thymocyte migration in contrast with supernatants depleted in CD44 by immunoadsorption. CD44 cleavage was recently reported to be due to metalloproteinase-14 activation and led to increased migration in cancer cells. Thus, in this study, we show that laminin-5 promotes human mature thymocyte migration in vitro via a multimolecular mechanism involving laminin-5 integrin receptors, metalloproteinase-14 and CD44. These data suggest that, in vivo, laminin-5 may function in the migration of mature thymocytes within the medulla and be part of the thymic emigration process

Combination of Allergic Factors Can Worsen Diarrheic Irritable Bowel Syndrome: Role of Barrier Defects and Mast Cells

International audienceOBJECTIVES: Recent evidence suggests a role for increased colonic permeability and mucosal mast cell (MC) mediators on symptoms related to the irritable bowel syndrome (IBS). Whether allergic factors (AFs) are involved in the pathophysiology of IBS is unclear. We addressed the question of the possible influence of an allergic background on IBS symptoms. METHODS: We assessed paracellular permeability, mucosal MCs counts, and spontaneous release of tryptase of colonic biopsy specimens in 34 IBS patients and 15 healthy subjects. The severity of IBS was assessed through self-reported questionnaires. All individuals were tested for the presence of AF, including self-perception of adverse reaction to food, personal and familial history of atopic disease, elevated total or specific immunoglobulin E against food/inhalant antigens, blood eosinophilia, and skin tests. RESULTS: IBS patients had significant enhanced colonic permeability, higher number of MCs, and spontaneous release of tryptase than healthy subjects. The severity of IBS was significantly correlated with colonic permeability (r=0.48, P=0.004), MCs counts (r=0.36, P=0.03), and tryptase (r=0.48, P=0.01). In 13 IBS patients (38.2%) having at least three AFs, symptoms scores, colonic permeability, MCs counts, and tryptase release by colonic biopsies were significantly higher than in those with less than three AFs. IBS patients with at least three AFs were more prone to diarrhea or alternating symptoms. None AF was found to be predictive of IBS severity. CONCLUSIONS: In IBS patients, the presence of an allergic background correlates with a more severe disease and diarrhea predominance, possibly by enhancing mucosal MC activation and paracellular permeability

Combination of Allergic Factors Can Worsen Diarrheic Irritable Bowel Syndrome: Role of Barrier Defects and Mast Cells

International audienceOBJECTIVES: Recent evidence suggests a role for increased colonic permeability and mucosal mast cell (MC) mediators on symptoms related to the irritable bowel syndrome (IBS). Whether allergic factors (AFs) are involved in the pathophysiology of IBS is unclear. We addressed the question of the possible influence of an allergic background on IBS symptoms. METHODS: We assessed paracellular permeability, mucosal MCs counts, and spontaneous release of tryptase of colonic biopsy specimens in 34 IBS patients and 15 healthy subjects. The severity of IBS was assessed through self-reported questionnaires. All individuals were tested for the presence of AF, including self-perception of adverse reaction to food, personal and familial history of atopic disease, elevated total or specific immunoglobulin E against food/inhalant antigens, blood eosinophilia, and skin tests. RESULTS: IBS patients had significant enhanced colonic permeability, higher number of MCs, and spontaneous release of tryptase than healthy subjects. The severity of IBS was significantly correlated with colonic permeability (r=0.48, P=0.004), MCs counts (r=0.36, P=0.03), and tryptase (r=0.48, P=0.01). In 13 IBS patients (38.2%) having at least three AFs, symptoms scores, colonic permeability, MCs counts, and tryptase release by colonic biopsies were significantly higher than in those with less than three AFs. IBS patients with at least three AFs were more prone to diarrhea or alternating symptoms. None AF was found to be predictive of IBS severity. CONCLUSIONS: In IBS patients, the presence of an allergic background correlates with a more severe disease and diarrhea predominance, possibly by enhancing mucosal MC activation and paracellular permeability

Negative Effects on Psychological Health and Quality of Life of Genuine Irritable Bowel Syndrome-type Symptoms in Patients With Inflammatory Bowel Disease

Background & Aims: Symptoms compatible with irritable bowel syndrome (IBS) are common in patients with inflammatory bowel disease (IBD), but it is unclear whether this relates to occult IBD activity. We attempted to resolve this issue in a secondary care population using a cross-sectional study design. Methods: We analyzed Rome III IBS symptoms; disease activity indices; and psychological, somatization, and quality of life data from 378 consecutive, unselected adult patients with IBD seen in clinics at St. James's University Hospital in Leeds, United Kingdom, from November 2012 through June 2015. Participants provided a stool sample for fecal calprotectin (FC) analysis; levels of ≥250 μg/g were used to define mucosal inflammation. Using symptom data and FC levels we identified 4 distinct groups of patients: those with true IBS-type symptoms (IBS-type symptoms with FC levels <250 μg/g, regardless of disease activity indices), quiescent IBD (no IBS-type symptoms with FC levels <250 μg/g, regardless of disease activity indices), occult inflammation (normal disease activity indices and FC levels ≥250 μg/g, regardless of IBS symptom status), or active IBD (abnormal disease activity indices with FC levels ≥250 μg/g, regardless of IBS symptom status). We compared characteristics between these groups. Results: Fifty-seven of 206 patients with Crohn’s disease (27.7%), and 34 of 172 patients with ulcerative colitis (19.8%) had true IBS-type symptoms. Levels of psychological co-morbidity and somatization were significantly higher among patients with true IBS-type symptoms than patients with quiescent IBD or occult inflammation. Quality of life levels were also significantly reduced compared with patients with quiescent disease or occult inflammation, and were similar to those of patients with active IBD. Using FC levels of ≥100 μg/g to define mucosal inflammation, we found a similar effect of IBS-type symptoms on psychological health and quality of life. Conclusions: In a cross-sectional study, we identified a distinct group of patients with IBD and genuine IBS-type symptoms in the absence mucosal inflammation. These symptoms had negative effects on psychological wellbeing and quality of life—to the same degree as active IBD. New management strategies are required for this patient group