The mast cell.

The mast cell is the cellular basis for immediate hypersensitivity reactions. The specificity of the immediate hypersensitivity reaction is attributable to IgE molecules fixed to specific membrane receptors which, when stimulated by specific antigen, initiates the process of degranulation of the mast cell. The granules provide three separate sources of biologic activity: performed or primary mediators, newly generated or secondary mediators, and activities associated with the granular matrix. A number of biologic consequences are generated in response to these mediators and these include: increased vascular permeability, vasodilation, smooth muscle spasm, polymorphonuclear leukocyte chemotaxis, stimulation of adenylate and guanylate cyclase, superoxide radical generation, prostaglandin formation, mucous and gastric acid secretion, hypotension, tissue destruction, and mononuclear leukocyte infiltration. This pharmacopia of activities accounts for the clinical aspects of allergic diseases, suggests that the mast cell granule may be involved in the host's defense against parasitic infections, and is compatible with a suggested role of the mast cell as a widely distributed, monocellular endocrine system.