New aspects in the synthesis and secretion of lysozyme by cultured human monocyte cell lines

The main purpose of this study was to investigate lysozyme synthesis and secretion in three human monocyte cell lines: U-937, HL-60, and THP-1, using sensitive fluorescence-based assay of lysozyme activity. PMA and hIFN-γ were evaluated for inducing lysozyme activity. Using well-defined cell lines from the cell culture collection, no lysozyme activity could be detected in the cultured U-937 cells either with or without addition of the inducing factors. These data suggested, contrary to previous reports, that U-937 cell line cannot synthesize or secrete active lysozyme. THP-1 and HL-60 cells were proved to produce enzymatically active lysozyme in increasing amounts with the time course. PMA and hIFN-γ had no significant inducing effect on the production or the release of active lysozyme in THP-1 and HL-60 cells. We showed inhibiting effect of PMA and hIFN-γ on the lysozyme activity, particularly in HL-60 cell line.