Sa1829 Dendritic Cell Characteristics in Pouchitis

Abstract

In inflammatory bowel disease (IBD) models, the body's innate and adaptive immune systems influence differentiation of multipotent gut stem cells. These stem cells differentiate into mucous producing goblet cells, enterocytes, enteroendocrine cells or Paneth cells. Differentiation related to inflammatory stress has been well studied in the lung and liver but gut stem cell differentiation in IBD has only a small body of literature. Hypothesis: Changing environments in the TNBS mouse model of chronic colitis modulate the lineage of colonic mucosal stem cells. Methods: BALB/c mice were given weekly colonic exposure to TNBS, to induce colitis, or saline as a control. Colon, spleen and mesenteric lymph nodes were collected from groups of mice (n=4-5) every other week from 5-17 weeks(W). Sections of tissue were prepared for microscopic, protein and real-time PCR (RT-PCR) analysis. Colonic muscle segments were isolated to assess smooth muscle contractility. BrdU was administered to each mouse 2 hours prior to harvest. Results: Mircoscopic analysis of TNBS-treated colon demonstrates increased submucosal cellularity and collagen deposition at 5W. This cellularity decreases but the collagen deposition is unchanged and is increasingly organized (strands) in the subsequent study intervals. During this time there was a 25% increase in thickness of the colonic mucosa and corresponding increase in the number of BdrU positive cells that peak at 15W. There are prominent goblet cells and significant mucous production associated with elevated levels of IL-13 and MUC2 and low levels of IL-2, IL-17, TGF β1 and TNFα. From 13-17W there was marked disruption of normal mucosal architecture. BrdU positive crypt cells drop precipitously at 17W coincident with a decrease in goblet cells and an increase in lymphocytic and stromal cells in the lamina propria. At this time there is a marked upregulation in IL-17, TNFα and IFNγ. Conclusions: The development of chronic inflammation is a transition phasing response to a changing microenvironment in the chronic mouse model. First, an acute inflammatory response is apparent at 5W. This is followed by a second mucosal proliferative phase characterized by proliferation of goblet cells due to elevated levels of IL-13. There is suppression of fibrosis during this period. The 3rd phase, evolving between 13-17W, is marked by architectural disruption, an increase in proinflammatory cytokines, a dramatic decrease in crypt goblet cell replication and a dramatic increase in stromal cellularity and fibrosis.