Lymphotoxin-β Rezeptoren Blockade reduziert Leukozyten-Endothelzellen-Interaktion in vivo durch Downregulation von MadCAM-1 bei experimenteller chronischer Kolitis

Background: The lymphotoxin-β receptor (LTβR) pathway is critical for maintenance of organized lymphoid structures and involved in development of colitis as shown in different mouse colitis models. Thus, the mechanisms by which LTβR activation contributes to the pathology the chronic form of DSS-colitis was investigated. Moreover, it was demonstrated that mucosal addressin cell adhesion molecule-1 (MadCAM-1), which is strongly expressed in inflamed intestinal mucosa, plays a significant role in development of chronic DSS-colitis [1, 2]. Material and Methods: Acute colitis was induced in Balb/c mice (20 ± 0.4g; n = 10 per group) by oral administration of 5% dextran sodium sulfate (DSS) dissolved in drinking water for 4 cycles of treatment [3]. Two weeks after completion of 4 cycles of DSS treatment, mice in the therapy group received 100 µg i.p. of a monoclonal antibody against LTβR for 6 days. Mice of the control group received 100µg of an isotyp antibody. To prepare mice for cell injection, a venous and arterial catheter was implanted in anaesthetized animals. The colon was then mobilized and extriorized for in vivo microscopy. Leukocyte-endothelium interaction in collecting and postcapillary venules was visualized and quantified by epiillumination at a 680-fold magnification. For in vivo microscopy of the mucosa the colon was incised and leukocyte extravasation was calculated. Then tissue was taken out for histological and immunohistochemical tests. Results: Treatment of chronic form of DSS-induced colitis with LTβR-Ig significantly attenuated the development and histological manifestation of the disease. The expression of the proinflammatory cytokines TNF, IL-Iβ and IL-6 was clearly reduced by LTβR-Ig treatment in the chronic form of colitis. Moreover LTβR-Ig treatment significantly downregulated MadCAM-1 expression, leading to reduced leucocyte endothelium interaction. Additionally, reduced extravasation of leucocytes to intestinal mucosa was observed. MadCAM expression was semi-quantitatively detected by immunhistochemistry. Conclusions: Our results show, that LTβR pathway inhibition leads to a downregulation of MadCAM-1 expression. This leads to a significant reduction of leucocyte-endothelium interaction, extravasation of lymphocytes and also to a better histological score. This study verifies the pathophyiological role of LTβR pathway inhibition in the rise of inflammatory bowel disease, that is mediated by MadCAM-1.