Cathepsin B activity in stimulated mouse peritoneal macrophages

The activity of cathepsin B was assayed in murine resident peritoneal macrophages, and after stimulation of the cells in vivo and in vitro. The resident cells showed a very low activity of the enzyme, compared to the activities of three other lysosomal enzymes: cathepsin D, acid phosphatase, and beta-glucuronidase which were tested simultaneously. Endocytosis of carrageenan, latex, or carbon particles in vitro induced a prominent rise in intracellular cathepsin B activity. Addition of endotoxin from Escherichia coli in vivo or in vitro, or cell wall products from streptococci in vitro caused no change in cathepsin B activity. There was a release of enzyme activity to the medium after a 72-hour culture of macrophages. However, the release, calculated as a percentage of total activity, was not influenced by any treatments mentioned. All significant rises in enzyme activity could be inhibited by the addition of cycloheximide, and it was concluded that increased enzyme activity was dependent on new protein synthesis.