A single layer of epithelial cells lines the gastrointestinal tract, forming a critical barrier between the luminal contents, which includes antigens and other noxious substances, and the body proper. It has become clear in recent years that the role of mast cells in the gastrointestinal mucosa is not only to react to antigens, but also to actively regulate the barrier and transport properties of the intestinal epithelium. Mucosal mast cells respond to both IgE/antigen‐dependent and non‐IgE‐dependent stimulation, releasing bioactive mediators into adjacent tissues where they induce physiological responses. Studies in models of hypersensitivity and stress have provided evidence that changes in mucosal function are due to either direct action of mast cell mediators on epithelial receptors and/or indirect action via nerves/neurotransmitters.

Studies conducted in the authors' laboratories were funded by grants from the Canadian Institutes of Health Research and the Crohn's and Colitis Foundation of Canada.