Abstract
In the recent years, the incidence of inflammatory bowel disease (IBD) has dramatically increased in young subjects, however, the pathogenesis of paediatric IBD is poorly investigated. In this study we aimed to evaluate the cytokine pattern and the phenotype of cytokine producing cells in the intestinal mucosa of paediatric patients affected by Crohn’s disease (CD) or ulcerative colitis (UC) and of non-IBD healthy controls (HC). Cytokine (IL-15, TNF-α, INF-γ) production was analyzed at basal condition and after mitogen stimulation either intracellularly by flow cytometry or in intestinal cell culture supernatants by enzyme-linked immunosorbent assay (ELISA). A higher frequency of enterocytes (EpCam+ cells) was observed in UC patients compared to CD or HC. An expansion of enterocytes producing IL-15 and TNF-α were found in IBD patients compared to HC. A marked expression of IL-15 in the intestinal epithelium of IBD patients was further confirmed by immunohistochemistry. Myeloid dendritic (CD11c+) cells producing TNF-α and INF-γ were increased in IBD biopsies. Unexpectedly, only after a strong mitogen stimulus, as phytohaemagglutinin, the frequency of CD3+ cells producing IFN-γ was increased in IBD compared to control intestinal mucosa. Interestingly, functional studies performed on organ cultures of intestinal biopsies with neutralizing anti-IL-15 monoclonal antibody showed a marked reduction of mononuclear cell activation, proliferation of crypt enterocytes, as well as a reduction of TNF-α release in organ culture supernatants. In conclusion, we found that in the gut mucosa of IBD children both enterocytes and dendritic cells produce proinflammatory cytokines. The over-expression of IL-15 by enterocytes in IBD intestine and the reduced IBD inflammation by IL-15 blockage suggests that this cytokine could be a therapeutic target in IBD.
Highlights
Crohn’s disease (CD) and ulcerative colitis (UC) are chronic inflammatory bowel diseases (IBD) in which an abnormal immune response against the luminal microflora is thought to be the main causative factor [1,2]
By using specific cell markers, we investigated enterocytes identified as epithelial cell adhesion molecule (EpCam) positive cells, myeloid dendritic cells identified as CD11c positive cells, and T lymphocytes identified as CD3 positive cells
We have investigated the proinflammatory cytokine profile, through an ex vivo analysis, in the intestinal mucosa of paediatric subjects with Crohn’s disease and ulcerative colitis, the two main forms of inflammatory bowel diseases
Summary
Crohn’s disease (CD) and ulcerative colitis (UC) are chronic inflammatory bowel diseases (IBD) in which an abnormal immune response against the luminal microflora is thought to be the main causative factor [1,2]. Gut inflammation occurring in patients with IBD is characterized by the infiltration and activation of both adaptive branch, as T and B lymphocytes, and innate system, as macrophages and dendritic cells (DC), which in turn produce massive amounts of proinflammatory cytokines contributing to the typical mucosal lesions [3, 4]. The great majority of the proinflammatory cytokines are produced by lamina propria mononuclear cells both in CD and UC [6], and very little is known regarding the epithelium compartment. DC are the most potent professional antigen presenting cells, and in mucosal immunity they have an important role in maintaining the fragile equilibrium between tolerance and inflammatory response to mucosal antigens [7]. The involvement of mucosal DC in IBD pathogenesis has been documented [8], though very little is known on their functions in paediatric IBD
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