ABSTRACT
The microenvironment of the intestinal mucosa is complex. Luminal contents are rich in bacteria, as well as in food antigens and other noxious material that has been ingested, and the defence systems of the intestinal mucosa fight a constant battle to avoid a state of ongoing immune activation. The single-cell layer of the epithelium lining the gastrointestinal tract forms a critical first-line barrier between the external environment and the body proper. Passage of phlogistic products across a transiently or intrinsically leaky intestinal barrier stimulates resident lamina propria macrophages, mast cells, eosinophils and lymphocytes to secrete inflammatory mediators. A normal host can down-regulate this response when the triggering event has resolved, whereas in a susceptible host ongoing enhanced permeability may result in chronic inflammation. In recent years, it has become clear that modulation of innate gut mucosal defence systems by neuroimmune signalling is important in the regulation of the mucosal inflammatory response, and that disturbances at various levels of this regulation can result in intestinal dysfunction and/or diseases. In this chapter we will focus on physiological effects and pathophysiological changes in epithelial secretion and barrier function induced by neuroimmune interactions.
