P. Giuffrida

The function of tissue transglutaminase in celiac disease

Celiac disease is a chronic small bowel disorder caused by an abnormal immune response to an array of epitopes of wheat gluten and related proteins of rye and barley in genetically susceptible individuals who express the HLA-DQ2/-DQ8 haplotype. Gluten peptides are efficiently presented by celiac disease-specific HLA-DQ2- and HLA-DQ8-positive antigen presenting cells to CD4(+) T-cells that, once activated, drive a T helper cell type 1 response leading to the development of the typical celiac lesion-villous atrophy, crypt hyperplasia and intraepithelial and lamina propria infiltration of inflammatory cells. Tissue transglutaminase (tTG) is a calcium dependent ubiquitous enzyme which catalyses posttranslational modification of proteins and is released from cells during inflammation. tTG is suggested to exert at least two crucial roles in celiac disease: as a deamidating enzyme, that can enhance the immunostimulatory effect of gluten, and as a target autoantigen in the immune response. Since glutamine-rich gliadin peptides are excellent substrates for tTG, and the resulting deamidated and thus negatively charged peptides have much higher affinity for the HLA-DQ2 and HLA-DQ8 molecules, the action of tTG is believed to be a key step in the pathogenesis of celiac disease. This review is focused on the function of tTG in celiac disease, although it also deals with novel advances in tTG-based therapies.

In Crohn's disease fibrosis-reduced expression of the miR-29 family enhances collagen expression in intestinal fibroblasts

Intestinal fibrosis with stricture formation is a complication of CD (Crohns disease) that may mandate surgical resection. Accurate biomarkers that reflect the relative contribution of fibrosis to an individual stricture are an unmet need in managing patients with CD. The miRNA-29 (miR-29) family has been implicated in cardiac, hepatic and pulmonary fibrosis. In the present study, we investigated the expression of miR-29a, miR-29b and miR-29c in mucosa overlying a stricture in CD patients (SCD) paired with mucosa from non-strictured areas (NSCD). There was significant down-regulation of the miR-29 family in mucosa overlying SCD compared with mucosa overlying NSCD. miR-29b showed the largest fold-decrease and was selected for functional analysis. Overexpression of miR-29b in CD fibroblasts led to a down-regulation of collagen I and III transcripts and collagen III protein, but did not alter MMP (matrix metalloproteinase)-3, MMP-12 and TIMP (tissue inhibitor of metalloproteinase)-1 production. TGF (transforming growth factor)-β1 up-regulated collagen I and III transcripts and collagen III protein as a consequence of the down-regulation of miR-29b, and TGF-β1-induced collagen expression was reversed by exogenous overexpression of miR-29b. Furthermore, serum levels of miR-29 were lower in patients with stricturing disease compared with those without. These findings implicate the miR-29 family in the pathogenesis of intestinal fibrosis in CD and provide impetus for the further evaluation of the miR-29 family as biomarkers.

Absence of a role for interleukin‐13 in inflammatory bowel disease

IL‐13 has been implicated in the pathogenesis of ulcerative colitis (UC), and may have a role in animal models of gut fibrosis. We studied the involvement of IL‐13 in inflammation and fibrosis in UC and Crohns disease (CD). Intestinal biopsies and anti‐CD3/CD28‐ or anti‐CD2/CD28‐stimulated lamina propria mononuclear cells from UC and CD patients and control subjects were cultured, and IL‐13, IL‐4, IL‐5, IL‐17A and IFN‐γ production was measured. Mucosal IL‐13‐producing cells were characterised by flow cytometry. Gut explants from strictured CD, non‐strictured CD and healthy donors were cultured ex vivo, and secreted IL‐13, IL‐1β and collagen were measured. IL‐13 production by mucosal explants and activated lamina propria mononuclear cells did not differ between CD, UC and control subjects, and was at least a log lower than IFN‐γ and IL‐17A. IL‐13‐producing cells, and in particular natural killer T cells, were uniformly low in all groups. IL‐4 and IL‐5 were undetectable in culture supernatants. Explants of CD strictures produced low amounts of IL‐13, whereas IL‐1β and collagen were elevated. We could not confirm that UC or strictured CD are associated with elevated IL‐13 production. These data suggest that an anti‐IL‐13 Ab would not be an appropriate therapeutic strategy in inflammatory bowel disease.

The role of transforming growth factor (TGF)-β in modulating the immune response and fibrogenesis in the gut

Transforming growth factor (TGF)-β, a pleiotropic cytokine released by both immune and non-immune cells in the gut, exerts an important tolerogenic action by promoting regulatory T cell differentiation. TGF-β also enhances enterocyte migration and regulates extracellular matrix turnover, thereby playing a crucial role in tissue remodeling in the gut. In this review we describe the mechanisms by which abnormal TGF-β signaling impairs intestinal immune tolerance and tissue repair, thus predisposing to the onset of immune-mediated bowel disorders, such as inflammatory bowel disease and celiac disease. Additionally, we will discuss potential therapeutic strategies aiming at restoring physiologic TGF-β signaling in chronic intestinal diseases.

New insights into immune mechanisms underlying autoimmune diseases of the gastrointestinal tract.

Recent progresses in the immune mechanisms implicated in chronic inflammatory disorders have led to a more in-depth knowledge of the pathogenesis of autoimmune diseases of the gastrointestinal tract, including autoimmune atrophic gastritis, celiac disease, autoimmune enteropathy and ulcerative colitis. While the pathogenic role of specific circulating autoantibodies, i.e., respectively anti-parietal cell, anti-tissue transglutaminase, anti-enterocyte and anti-neutrophil cytoplasmic, is still controversial, some common T-cell mediated mechanisms for inflammation - increase in T helper cell type 1/type 17 pro-inflammatory cytokines- or losing self-tolerance-abnormal regulatory T cell function - are recognized as crucial mediators of the tissue damage causing atrophy of the stomach mucosa in autoimmune atrophic gastritis, villous flattening of the small bowel in celiac disease and autoimmune enteropathy, and mucosal ulceration of the colon in ulcerative colitis. This review deals with novel advances in the immunological bases of the aforementioned autoimmune gastrointestinal disorders, and it also highlights immune mechanisms of progression from chronic inflammation to cancer and implications for new therapeutic targets.

The role of interleukin 17 in Crohn’s disease-associated intestinal fibrosis

BackgroundInterleukin (IL)-17A and IL-17E (also known as IL-25) have been implicated in fibrosis in various tissues. However, the role of these cytokines in the development of intestinal strictures in Crohn’s disease (CD) has not been explored. We investigated the levels of IL-17A and IL-17E and their receptors in CD strictured and non-strictured gut, and the effects of IL-17A and IL-17E on CD myofibroblasts.ResultsIL-17A was significantly overexpressed in strictured compared with non-strictured CD tissues, whereas no significant difference was found in the expression of IL-17E or IL-17A and IL-17E receptors (IL-17RC and IL-17RB, respectively) in strictured and non-strictured CD areas. Strictured CD explants released significantly higher amounts of IL-17A than non-strictured explants, whereas no difference was found as for IL-17E, IL-6, or tumor necrosis factor-α production. IL-17A, but not IL-17E, significantly inhibited myofibroblast migration, and also significantly upregulated matrix metalloproteinase (MMP)-3, MMP-12, tissue inhibitor of metalloproteinase-1 and collagen production by myofibroblasts from strictured CD tissues.ConclusionsOur results suggest that IL-17A, but not IL-17E, is pro-fibrotic in CD. Further studies are needed to clarify whether the therapeutic blockade of IL-17A through the anti-IL-17A monoclonal antibody secukinumab is able to counteract the fibrogenic process in CD.

Analysis of the cytokine profile in the duodenal mucosa of refractory coeliac disease patients

RCD [refractory CD (coeliac disease)] is characterized by severe symptoms/signs of malabsorption and mucosal damage unresponsive to a GFD (gluten-free diet). The pathogenesis of RCD is not fully understood. In the present paper, we have characterized the mucosal profile of effector cytokines in RCD. Duodenal biopsies were taken from patients with RCD, patients with active CD and normal controls and were analysed for inflammatory cytokines by real-time PCR and ELISA. IFN (interferon)-γ and IL (interleukin)-21 transcripts were increased in active CD patients but not in RCD patients as compared with normal controls, whereas IL-17A RNA was up-regulated in both active CD and RCD. No significant increase in IL-15 transcripts was observed in both active CD and RCD, whereas IL-15 protein was increased in active CD. IL-6 and TNF (tumour necrosis factor)-α were up-regulated only in RCD. As a proof, we present the case of a woman affected by RCD who responded to anti-TNF-α treatment with improvement of malabsorptive symptoms/signs but no healing of mucosal lesions. The findings indicate that the profile of mucosal effector cytokines differs between RCD and active CD and suggest that TNF-α, IL-6 and IL-17A, but not Th1-type cytokines, could drive the detrimental response in this condition.

Is it worth investigating splenic function in patients with celiac disease

Celiac disease, an immune-mediated enteropathy induced in genetically susceptible individuals by the ingestion of gluten, is the most frequent disorder associated with splenic hypofunction or atrophy. Defective splenic function affects more than one-third of adult patients with celiac disease, and it may predispose to a higher risk of infections by encapsulated bacteria and thromboembolic and autoimmune complications, particularly when celiac patients have concomitant pre-malignant and malignant complications (refractory celiac disease, ulcerative jejunoileitis and enteropathy-associated T-cell lymphoma). However, the clinical management of patients with celiac disease does not take into account the evaluation of splenic function, and in patients with high degree of hyposplenism or splenic atrophy the prophylactic immunization with specific vaccines against the polysaccharide antigens of encapsulated bacteria is not currently recommended. We critically re-evaluate clinical and diagnostic aspects of spleen dysfunction in celiac disease, and highlight new perspectives in the prophylactic management of infections in this condition.

Effect of Tumor Necrosis Factor-α Blockade on Mucosal Addressin Cell-adhesion Molecule-1 in Crohn's Disease

Background:Mucosal addressin cell-adhesion molecule (MAdCAM)-1, which is overexpressed on gut endothelium in active Crohns disease (CD), promotes intestinal recruitment of integrin &agr;4&bgr;7+ T cells that sustain chronic inflammation. As tumor necrosis factor alpha (TNF)-&agr;, a cytokine centrally involved in CD, modulates gut endothelial adhesion molecules, we here explored the in vivo and ex vivo effects of TNF-&agr; blockade on MAdCAM-1 expression in CD. Methods:MAdCAM-1 was determined by immunoblotting in colonic biopsies collected before and 10 weeks after either infliximab or adalimumab treatment in CD patients, and in CD biopsies incubated with either infliximab or adalimumab or control IgG1. Integrin &bgr;7+ circulating T cells were analyzed by flow cytometry. Results:MAdCAM-1 significantly decreased after either infliximab or adalimumab treatment in responder but not in nonresponder patients. In parallel, an increase of circulating &bgr;7+ T cells was found in responder patients only. A marked downregulation of MAdCAM-1 was observed in CD biopsies cultured with either infliximab or adalimumab in comparison to IgG1-treated biopsies. Conclusions:Our findings showing that MAdCAM-1 is downregulated by TNF-&agr; blockade point to a novel mechanism of action of anti-TNF-&agr; antibodies in CD.

Increase in neuroendocrine cells in the duodenal mucosa of patients with refractory celiac disease.

OBJECTIVES:Several immune-mediated gastrointestinal disorders, including celiac disease (CD), are associated with neuroendocrine cell hyperplasia. However, neuroendocrine cells have never been explored in refractory CD (RCD).METHODS:Serial duodenal sections from 17 patients with RCD (6 type 1 and 11 type 2), 16 uncomplicated CD patients before and after gluten-free diet, 14 patients with potential CD, 27 patients with non-CD villous atrophy, i.e., common variable immunodeficiency (n=12), Whipples disease (n=10) and giardiasis (n=5), and 16 healthy subjects were processed for the immunohistochemical detection of chromogranin A (CgA), serotonin, and somatostatin. Mucosal tryptophan hydroxylase (TpH)-1 and serotonin-selective reuptake transporter (SERT) transcripts were measured by quantitative reverse transcription-PCR. Serum CgA and 24-h urine 5-hydroxyindoleacetic acid (5-HIAA) were assessed. Biopsies from treated CD patients were cultured with serotonin or peptic tryptic digest of gliadin (PT-gliadin), and interferon (IFN)-γ was detected by ELISA in culture supernatants.RESULTS:Epithelial cells positive for CgA and serotonin, but not somatostatin, were significantly increased in RCD. Raised mucosal transcripts of TpH-1, but not SERT, were found in RCD. On biopsies from treated CD patients, serotonin upregulated IFN-γ production at levels comparable to those induced by PT-gliadin. Serum CgA, but not urine 5-HIAA, was increased in RCD. No significant difference was found between RCD type 1 and type 2 in terms of neuroendocrine cells, mucosal TpH-1 transcripts, and serum CgA.CONCLUSIONS:Serotonin-producing neuroendocrine cells are increased in RCD mucosa. IFN-γ upregulation induced by serotonin suggests that this monoamine may have a role in sustaining the local inflammatory response in CD.