Gene Expression in Epithelial Cells Modulated by Bacteria

Epithelial cells have been recognized to play an important role in mucosal immunity and therefore exhibit a number of immunological functions including expression of adhesion molecules, secretion of effector molecules such as defensins, and expression of cytokines and cytokine receptors [6, 7]. Thus, epithelial cells are an integral part of the mucosal immunity network which by secretion of inflammatory cytokines and chemokines may signal the presence of pathogenic bacteria to the mucosal immune system [7-9]. The inflammatory reaction at mucosal sites can assist pathogen control, but it may also be subverted by the pathogen to promote its dissemination in the host. Moreover, epithelial cells constitute a crucial physical barrier between the underlying mucosa and microorganisms residing in the lumen of the human intestinal tract. To overcome this barrier, many enteric pathogens have evolved the ability to invade and pass through the intestinal epithelium as a key initial step to establish mucosal and, subsequently, systemic infection of the host. Microbial entry into the epithelium is an active process that requires signaling from the invading pathogen to the host cell, although the specific signaling pathways involved differ for various microorganisms.

462 | 21 Expression Analysis of Human Genes During Infection 21.4.1

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