Microbial-gut interactions in health and disease. Epithelial cell responses.

Pathogenic bacteria use many strategies to secure their survival within the host. Enteropathogens exploit intestinal epithelial cells in many ways, including the manipulation of normal cellular functioning, or of cellular structural components, or by the induction of signalling pathways, such as the production of pro-inflammatory cytokines. However, the enterocyte warns the host of impending danger and, in turn, elicits a protective response. Pathogens are detected by epithelial cells owing to their vast array of surface antigens and secreted products. Epithelial cells have developed both extracellular and intracellular sensing proteins that function as a first line of defence against pathogens; this is followed by acquired immunity, namely IgA, which is used as reinforcement. Thus, in a game of constant attack and defence, the pathogen and the enterocyte aim to outsmart each other in an effort to survive.