TLR4‐driven Lymphatic Alterations during IBD are driven in PAMP/DAMP Specific Manners

Abstract

BackgroundInflammatory bowel disease (IBD) is characterised by both acute and chronic phase inflammation of the gastro‐intestinal (GI) tract that affect a large and growing number of people worldwide with little to no effective treatments. This is in part due to the lack of understanding of the disease pathogenesis and also the currently poorly described involvement of other systems such as the lymphatics. During DSS induced colitis, mice also develop a severe inflammation of both the colon and terminal ileum with many features similar to IBD. As well as inflammation within the intestinal tract we have previously demonstrated lymphatic remodelling within the mesentery and mesenteric lymph nodes of DSS‐treated mice. The lymphatic remodelling includes lymphangiogenesis, lymphatic vessel dilation and leakiness, as well as cellular infiltration into the surrounding tissue and peripheral draining lymph nodes. The aim of the investigation was to delineate the contribution of PAMP‐ and/or DAMP‐driven lymphatic remodelling and inflammation during disease, in respect to Toll‐like receptor 4 (TLR4) activity.MethodsIntestinal inflammation was induced in C57BL/6 mice by administration of 2.5% DSS in drinking water for 7 days. Mice were treated with TLR4 blocker C34 or Polymyxin‐B (PMXB) daily from days 3–7 of DSS treatment via I.P. injection, and their effects on disease activity and lymphatic function were examined. TLR4 activity and subsequent effect on lymphangiogenesis, lymphadenopathy, and mesenteric lymph node (MLN) cellular composition were assessed.ResultsDSS Mice treated with TLR4 inhibitor, C34, had a significantly improved disease phenotype characterised by reduced ileal and colonic insult. The change correlated with significant reduction in colonic and mesenteric inflammation, resolved mesenteric lymphangiectasia, and CD103+ DC accumulation similar to that of healthy control. PMXB treatment did not resolve inflammation within the colon, or associated mesenteric lymphatic dysfunction, but did however prevent lymphadenopathy within the MLN through alteration of CCL21 gradients and CD103+DC migration.ConclusionsTLR4 appears to mediate several changes within the mesenteric lymphatics, more specifically it is shown to have different outcomes whether stimulation occurs through pathogen derived factors such as LPS or tissue derived DAMPs, a novel phenomenon.Support or Funding InformationThis study was supported by the Lymphedema Research and Education Program, Snyder Institute for Chronic Diseases, Cumming School of Medicine, University of Calgary to P.‐Y.v.d.W.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.