Gastroenterology

Gastroenterology

Volume 129, Issue 2, August 2005, Pages 550-564
Gastroenterology

Basic-alimentary tract
Interleukin-13 Is the Key Effector Th2 Cytokine in Ulcerative Colitis That Affects Epithelial Tight Junctions, Apoptosis, and Cell Restitution

https://doi.org/10.1053/j.gastro.2005.05.002Get rights and content

Background & Aims: Ulcerative colitis (UC) is characterized by a Th2 immune response with inflammation and epithelial barrier dysfunction. So far, Th2 cytokines have not been shown to directly influence epithelial barrier function. Methods: Lamina propria mononuclear cells (LPMCs) were stimulated and interleukin (IL)-13 was measured by enzyme-linked immunosorbent assay. Functional IL-13 and IL-4 effects were studied on HT-29/B6 colonic epithelial cells in Ussing chambers and by conductance scanning. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays. IL-13/IL-4 receptors were analyzed by reverse-transcription polymerase chain reaction and immunofluorescence. Western blotting combined with immunofluorescence was used to detect tight junction proteins. Furthermore, restitution velocity was measured. Finally, mucosal biopsy specimens from patients with UC were compared with cultured cells for these features. Results: LPMCs from patients with UC produced large amounts of IL-13 (985 ± 73 pg/mL), much more than from controls or patients with Crohn’s disease. IL-13Rα1 and IL-4Rα receptors were present in HT-29/B6 cells and colonic epithelial cells of control patients and patients with UC. IL-13 had a dose-dependent effect on transepithelial resistance of HT-29/B6 monolayers (reduction to 60% ± 4%), whereas IL-4 had no effect. This was due to an increased number of apoptotic cells (5.6-fold ± 0.9-fold) and an increased expression of the pore-forming tight junction protein claudin-2 to 295% ± 37%, both of which contributed equally. Finally, epithelial restitution velocity decreased from 15.1 ± 0.6 to 10.6 ± 0.5 μm/h after treatment with IL-13. Parallel changes were observed in human samples, with an increase in claudin-2 expression to 956% ± 252%. Conclusions: IL-13 was identified as an important effector cytokine in UC that impairs epithelial barrier function by affecting epithelial apoptosis, tight junctions, and restitution velocity.

Section snippets

Lamina Propria Mononuclear Cell Cytokine Production

Lamina propria mononuclear cells (LPMCs) were isolated from surgical specimens of patients undergoing colectomy as described previously.2 Six patients had chronic active UC, and 5 patients had CD; 4 patients without intestinal inflammation with colonic adenocarcinoma served as noninflammatory controls. The institutional review boards approved the collection of surgical specimens. Because repetitive culture of cells from the same surgical specimen showed almost identical cytokine production, we

LPMCs From Patients With UC Produce IL-13

To quantify cytokine production from inflammatory T cells, LPMCs were isolated from intestinal specimens of patients with UC and respective controls (obtained at surgery) and stimulated in culture with antibodies to CD2 and CD28. After 3 days of stimulation, cytokine release in the supernatant was measured by enzyme-linked immunosorbent assay. Cells from patients with UC produced significantly higher levels of IL-13 (985 ± 273 pg/mL) than cells from patients with CD or noninflammatory controls

Discussion

UC is associated with an epithelial barrier defect characterized by reduced active absorption and increased mucosal leakiness13, 14; these abnormalities, rather than active secretion, are responsible for the diarrhea seen in patients with UC. However, the pathologic mechanisms leading to this barrier defect are still far from clear.

One potential factor leading to the observed changes in barrier function is cytokines secreted from lymphocytes infiltrating the lamia propria. In patients with CD,

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    Supported by grants from Deutsche Forschungsgemeinschaft (DFG Schu 559/7-3 and Fr 652/4-2) and the Else Kröner-Fresenius-Stiftung.

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