Host Response to Pathogenic Bacteria at Mucosal Sites

Abstract

Epithelial cells at mucosal surfaces constitute the first line of defense against pathogens. Intestinal epithelial cells (IECs) form a single layer of cells that isolate the host’ s internal milieu from gut luminal environment. IECs from the distal ileum and colon are in constant contact with a rich micro-bial flora, and yet, under normal conditions, no pathological inflammation is present. However, IECs possess the ability to discriminate between pathogenic and nonpathogenic bacteria because infection of these cells by pathogenic bacteria induces an inflammatory response. Because of the repertoire of proinflammatory molecules they produce when activated by microbial agents or proinflammatory cytokines, IECs can function as sensors of mucosal injury and actively participate in the innate immune mucosal response. Therefore, these cells play an essential role in the maintenance of a deli-cate balance between the defensive immune response and tolerance to local microflora. This chapter outlines some of the mechanisms by which IEC acts as sensor for microbial pathogens and how the proinflammatory response mediated by IEC plays a role in the pathogenesis of inflammatory bowel disease (IBD).