Biochemical Contents of Granules and Lipid Bodies—Two Distinctive Organelles Found in Basophils and Mast Cells

Abstract

Granules and lipid bodies (Figure 1), although in large part the most distinctive cytoplasmic organelles of basophils and mast cells, are by no means unique to these cells. For example, all secretory cells capable of regulated secretion store their unique secretory products in membrane-bound secretory granules (Palade, 1975), and non-membranebound lipid bodies are present in a large variety of mammalian cells including adipocytes (Galli et al., 1985). Although secretory granules have been known for years to function as storage organelles for the unique secretory products of the cells, much less is known regarding the potential role(s) of lipid bodies or of their contents in cell biology (Fawcett, 1981). Since secretory granules and/or their contents diminish in the course of secretion, their role in the storage and secretion of preformed mediators is certain. We have noted an increase in the number of cytoplasmic lipid bodies in a wide variety of nondamaged, activated cells participating in a variety of pathobiologic processes in numerous organ sites for years (A. M. Dvorak and Monahan-Earley, 1986; Galli et al., 1985). Because lipid bodies were particularly prominent in isolated, purified human lung mast cells (A. M. Dvorak et al., 1984a), we initiated studies that led to the recognition that these structures served as a significant storage site for arachidonic acid, an important precursor for the newly synthesized mediators derived from the cyclooxygenase and lipoxygenase metabolic pathways for the production of various eicosanoids (Brocklehurst, 1962; A. M. Dvorak et al., 1983b, 1984a; Hammarström 1983; MacGlashan et al., 1982b; Needleman et al., 1986; Orange and Austen, 1969; Peters et al., 1984; Samuelsson, 1983; Samuelsson et al., 1975; Von Euler, 1936). Human mast cell cytoplasmic secretory granules, by contrast, did not serve this purpose, thereby establishing the biochemical distinctiveness as well as morphologic distinctiveness of these two cytoplasmic organelles in human mast cells.