Mast cells in mucosal defenses and pathogenesis

This chapter focuses on mast cell ontogeny, heterogeneity, and functions in allergy and immunity. Mature mast cells reside in tissues and are round, oval, spindle, or spiderlike in shape. They contain numerous cytoplasmic granules that may be homogeneously electron-dense or exhibit membrane or complex scroll-like patterns, highly organized crystalline structures, or combinations of these. Numerous biologically active products are synthesized and stored in these granules. Apoptosis is an important homeostatic mechanism that regulates mast cell numbers and functions. Normally, mast cells are considered long-lived (up to months) and maintain relatively constant numbers in tissues. However, this can be altered. The bcl-2 family of proteins is a major class of intracellular regulators that include death agonists and antagonists. Human and rodent mast cells express members of the bcl-2 family. Through a balance between death agonists and antagonists, cytokines and growth factors modulate mast cell survival or death. Mast cells can be activated by the ligation of surface receptors such as Fce{open}RI, CD117, and many others or by activation of specific intracellular signaling molecules such as calcium ionophore, compound 48/80, or phorbol esters.