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Release of mediators from mast cells can be induced in a non-cytotoxic way by a number of agents including histamine releasing factors produced by a variety of iriflammatory cells and eosinophil granule-derived cationic proteins. Neuropeptides can cause mast cells to release histamine but they respond differently to the same stimuli among their subtypes. Naturally occurring aliphatic polyamines also induce a histamine release from mast cells.
Two neutral serine proteases, tryptase and chymase, have been shown to be present in human mast cells. Tryptase-positive, chymase-negative mast cells are the predominant type in the lung and intestinal mucosa and the tryptase-positive, chymase-positive cells in skin and intestinal submucosa, whereas rodent mast cell subpopulations are referred to as mucosal mast cells and connective tissue mast cells.
The interactions of mast cells with a variety of stimuli result in the secretion of mediators through intracellular biochemical events. Calcium and cyclic AMP appear to be two major biochemical factors for the control of cellular activities and are known to activate protein kinase C and cyclic AMP-dependent protein kinase, respectively. Another line of evidence indicates that extracellular stimuli induce phospholipid turnover, especially increased metabolisms of inositol phospholipids. GTP-binding protein is not involved in the induction of the antigen-induced triggering signal to phospholipase C which initiates the enhancement of inositol phospholipids turnover.
