In Vitro Synthesis and Secretion of Lysozyme by Mononuclear Phagocytes

Abstract

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. Materials and MethodsCell C u l t u r e s . -Mouse peritoneal macrophages: Female mice of the NCS (Rockefeller) strain, weighing 25-30 g were used. Peritoneal macrophages were harvested, without anticoagulants, by standard procedures (9); the cells were obtained either 4 days after stimulation by intraperitoneai injection of 0.75 ml thioglycollate medium (I0) or from control, unstimulated mice. The cell yield from unstimulated mice was 5-8 X 106 cells, of which 30-40% were macrophages and the remainder lymphocytes; thioglycollate-stimulated mice yielded 15-20 X 106 cells, consisting of 75-90% macrophages and 10-25% lymphocytes.

Surface properties of bacillus Calmette-Guérin-activated mouse macrophages. Reduced expression of mannose-specific endocytosis, Fc receptors, and antigen F4/80 accompanies induction of Ia.

“…The defect in mannose-specific endocytosis by BCG-PM persisted after 60 h of cultivation and still represented 25% of uptake by TPM and RPM, which displayed similar activity (Table I). In contrast, all three populations of macrophages secreted a comparable amount of lysozyme, an index of constitutive secretory activity (17). It was noted that these cultures contained few remaining lymphocytes and that the continued depression of endocytosis by BCG-PM was apparently stable and autonomous.…”

Elastase secretion by stimulated macrophages. Characterization and regulation.

“…They are all secreted in parallel over prolonged periods in culture (11,12,25) . As a class, these products can be readily differentiated from other secretory products, such as lysozyme and intracellular acid hydrolases, which are regulated independently (13) .…”

Serum lysozyme as a marker of host resistance. I. Production by macrophages resident in rat sarcomata

“…Increased levels of lysozyme are found in the serum in those diseases characterized by granuloma formation, such as tuberculosis, sarcoidosis and Crohn's disease, and very high levels can also be found in the serum and urine of patients with myelomonocytic and monocytic leukaemia (Osserman and Lawlor, 1966). The major cell types responsible for the synthesis and release of lysozyme are of the monocyte-macrophage series although it can also be found in the lysosomes of granulocytes from which it is released when the cells degranulate (McClelland and van Furth, 1975 (Gordon, Todd and Cohn, 1974). This finding indicates that the levels of lysozyme in tissue fluids may, under well defined conditions, reflect the number of functioning macrophages in an animal.…”