Mast cells are important effector cells in IgE-mediated reactions by secreting histamine, chymase, tryptase, leukotrienes (LTs), prostaglandin D2 (PGD2) and several multifunctional cytokines; they include interleukin-6 (IL-6), IL-8, IL-13, tumor necrosis factor-alpha (TNF-a), stem cell factor (SCF) and many chemotactic factors (Galli, 2000; Mekori & Metcalfe, 2000). These cytokines contribute to the late-phase allergic reactions and to allergic inflammation through the recruitment of immune cells into the site of inflammation (Wedemeyer et al., 2000; Theoharides & Cochrane, 2004). Tryptase, expressed by all subsets of human mast cells and comprising up to 25% of the total intracellular proteins, has emerged as an important mediator in allergic diseases (Shaoheng et al., 1998). Tryptase and other serine proteases are signaling molecules that cleave protease-activated surface receptor-2 (PAR-2) leading to widespread inflammation (Steinhoff et al., 2000; Cottrell et al., 2003). Calcium influx is necessary for mast cell mediator secretion (Kimata et al., 2000b) and PAR-2 activation has also been associated with a brisk increase in intracellular calcium concentration (Dery et al., 1998).
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