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P034. Disruption of the intestinal barrier through M1 macrophages – relevance for IBD?

D. Lissner1, M. Schumann1, T. Stroh1, L.‑I. Kredel1, A. Batra1, A. Kühl1, M. Zeitz1, B. Siegmund1

1Charité – Universitätsmedizin Berlin, Gastroenterologie/Infektiologie/Rheumatologie, Berlin, Germany

Background: Recent studies suggest a beneficial role for regulatory macrophages in inflammatory bowel disease (IBD). Our aim was to characterize the effect of macrophage subtypes on the epithelial barrier.

Methods: Intestinal resection specimens of patients with Crohn's disease (CD) and ulcerative colitis (UC) were analyzed by immunhistochemistry and compared to healthy controls. Peripheral blood monocytes were isolated and polarized into M1- and M2-macrophages. The influence of these cells on epithelial integrity was analyzed using resistance measurements on different epithelial cell lines (Caco‑2, T‑84, HT-29/B6). Cytokine concentrations were determined by cytometric bead array.

Results: In both, IBD patients and healthy controls, CD163+ and stabilin1+ cells were found within the lamina propria, suggesting a permanent presence of M2-macrophages in this compartment. Exlusively in inflamed gut, and here predominantly in CD patients, iNOS+ cells were found subepithelially, suggesting an accumulation of M1-macrophages and thus shifting the balance to a pro-inflammatory state. In-vitro polarized M1-macrophages caused a profound decrease in resistance of epithelial cell layers compared to non-polarized or M2-macrophages, which was further aggravated through stimulation with LPS. Paracellular leakage was revealed by filter staining through deregulation of various tight junction proteins as well as induction of apoptosis in epithelial cells. High concentrations of TNF α were found in the supernatants of M1-macrophages, whereas the predominant cytokine for M2-macrophages was IL‑10. Consequently, the effect of M1-macrophages on epithelial cells was partly abrogated by inhibition of TNF α through infliximab.

Conclusions: The pro-inflammatory milieu in the lamina propria of Crohn's disease patients is shaped by the presence of M1 macrophages. This milieu plays a critical role in mediating an increased leakiness of the epithelial barrier, a prerequisite for the maintenance of intestinal inflammation.