ABSTRACT
Mast cells are distributed throughout normal connective tissues, where they often lie adjacent to blood and lymphatic vessels, near or within nerves, and beneath epithelial surfaces, that are exposed to the external environment, such as those of the respiratory and gastrointestinal systems and the skin. The abundance of mast cells in normal gastrointestinal tissues and the ability of mast cells and basophils to release inflammatory mediators in response to multiple immunologic and nonimmunologic stimuli have fueled speculation that these cells may play an important role in gastrointestinal pathophysiological processes. Basophils and mast cells contain, or elaborate on appropriate stimulation, a diverse array of potent biologically active mediators. Mast cells and basophils form histamine by the decarboxylation of histidine and store histamine as an ionic complex with the highly charged carboxyl and/or sulfate groups of the glycosaminoglycan side chains of the proteoglycans.
