Mechanisms of lysosomal enzyme secretion by human U-937 monocytes

Lysosomal enzyme secretion was studied in U-937, a mononuclear phagocyte cell line. The secretion of the marker enzyme, β-N-acetyl-D-glucosaminidase, was low when the cells were challenged with phagocytosable stimuli (asbestos, zymosan, opsonised zymosan). Ammonium cloride and cytochalasin B induced secretion over 24 h of incubation. Phorbol myristate acetate and F-methyl-leucyl-phenylalanine, did not have any effect on secretion. It is suggested that U-937 cells may provide a useful model for the study of mononuclear phagocyte secretory pathways.