Cathepsin B and prolyl endopeptidase activity in rat peritoneal and alveolar macrophages. Stimulation of peritoneal macrophages by saline lavage.

Cathepsin B and prolyl endopeptidase activity was determined in purified rat pulmonary and peritoneal macrophages and cathepsin B was determined in blood monocytes. The activity of cathepsin B in pulmonary macrophages was more than two times higher than in resident peritoneal macrophages and about eight times higher than in circulating monocytes. The simple process of peritoneal lavage with PBS induced an increase in cathepsin B activity in peritoneal macrophages that by 96 and 144 hr reached those levels observed in pulmonary macrophages. Both pulmonary and peritoneal macrophages contain prolyl endopeptidase activity. Repeated peritoneal lavage induced a significant increase in the activity of the enzyme, but not of the magnitude observed for cathepsin B. The data suggest that the transformation of monocytes into macrophages is associated with a significant increase in cathepsin B activity and that this increase is much greater in pulmonary than in peritoneal macrophages.