Regardless of the mechanism, activation of mast cells results in 1) degranulation with resulting release of preformed mediators stored in granules including histamine, heparin, proteases and cytokines such as TNF-??, 2) de novo synthesis of arachidonic acid metabolites (most notably PGD2 and LTC4) from membrane lipids, and 3) synthesis and secretion of cytokines and chemokines (16).Classification