A18 DEVELOPMENT OF CHRONIC ILEITIS IN THE TNFΔARE MOUSE IS ASSOCIATED WITH A LOSS OF MESENTERIC LYVE1+ MACROPHAGES. (21st February 2022) - Keane, K P
Abstract: Background: Crohn's disease (CD) is a form of inflammatory bowel disease that causes transmural inflammation of any part of the gastrointestinal (GI) tract but preferentially the terminal ileum and/or the colon. This chronic inflammation is not limited to the GI tract but also affects the mesentery of inflamed regions where it induces the formation of tertiary lymphoid organs (TLOs). The homeostatic LYVE1 + macrophages (LYmΦ) have been identified in many different organs including the mesentery. They have been shown to typically align along blood vessels where they participate in the control of collagen deposition and during inflammation, regulate vascular permeability and immune cell recruitment. Here we investigate the role of the mesenteric LYmΦ in a transgenic model of CD, the TNFΔARE mouse which develops terminal ileitis over time and expresses similar mesenteric alterations (TLOs) as seen in CD. Aims: To determine whether the mesenteric LYmΦ population is altered during the development of chronic inflammation in the TNFΔARE mouse and whether they participate in the development of TLOs. Methods: Confocal immunofluorescent imaging of the terminal ileal mesentery of TNFΔARE mice and littermate controls were preformed to identify changes to the populations of LYmΦ during the development of chronic inflammation. Myeloperoxidase activity was used to assess terminal ileitis. Results: During the initial stage of ileitis (8 weeks) LYmΦs are present across the terminal ileal mesentery in both TNFΔARE and age-matched WT littermate controls with a subpopulation aligning along the collecting lymphatic vessels of the mesentery (n=6). At 20 weeks, while the ileitis progresses, aggregates of CD45 + cells have formed within the TNFΔARE mice where LYmΦs also accumulate (n=5). At 28 weeks when the ileitis worsens, the LYmΦs are greatly reduced from the terminal ileal mesentery as well as from the CD45 + cell aggregates (n=5). WT littermate controls never develop large CD45 + cell aggregates (n=5 for each time point). Antibodies to the LYVE1 cytosolic and extracellular domains confirmed the loss of the LYVE1 receptor over receptor cleavage, however, there was no correlation of altered collagen-1 deposition within the mesentery at 28 weeks. Conclusions: Here we show a spatial relationship between LYmΦs and collecting lymphatic vessels as well as a decrease in LYmΦs during the development of chronic ileitis in the TNFΔARE mouse. Whether they contribute to TLO formation, or their loss exacerbates terminal ileitis is still unknown and under current investigation. Funding Agencies: CCC