1230 Synthesis and Secretion of Lysozyme

In 1922 Alexander Fleming described the remarkable bacteriolytic activity of an enzyme, lysozyme, which was widely distributed in tissues and secretions (1). Lysozyme (muramidase) is a cationic enzyme, tool wt 14,307, which hydrolyses N-acetyl muramic /3-1, 4 N-acetyl glucosamine linkages in the bacterial cell wall (2). Although a great deal is known about its structure and enzymology its function other than in host defence is still poorly understood. High concentrations of lysozyme are found in leukocytes, especially the polymorphonuclear leukocyte (PMN) 1 and rabbit alveolar macrophage (3). Fractionation studies of the rabbit P M N show that 70 % of its intracellular lysozyme is sedimentable and, unlike other hydrolases, it is found in both the azurophil and specific granules of the cell (4). The BCG-induced rabbit alveolar macrophage is able to release a large fraction of its intracellular lysozyme into the medium during phagocytosis (5) and may secrete lysozyme during cultivation in vitro (6). Large amounts of lysozyme accumulate in the serum and urine of patients (7) and animals (8) bearing monocytic leukemia. In this paper we report that mouse peritoneal macrophages and human monocytes synthesize and secrete substantial amounts of lysozyme in culture. We also study factors which influence the rate of lysozyme production and examine the effect of phagocytosis on its secretion.