Evidence for in vivo internalization of human leukocyte elastase by alveolar macrophages

Cell lysates from cultured human alveolar macrophages contain detectable amounts of an elastinolytic enzyme. Although particulate elastin was solubilized only after prolonged incubations, lysates readily hydrolyzed T-OC-alanyl-p-nitrophenol-ester. Hydrolysis of the latter substrate was inhibited by the leukocyte elastase site-specific inhibitor, N-ac-(ala)4-chloromethyl ketone. In addition, radioimmunoelectrophoresis of concentrated alveolar macrophage lysates, previously incubated with 3H diisopropyl-phosphofluoridate (DFP), revealed the presence of DFP binding material that comigrated with inactivated human leukocyte elastase. Human leukocyte elastase can cause lung lesions resembling pulmonary emphysema in experimental animals; therefore, the clearance of this enzyme by alveolar macrophages may represent a significant route for the removal of this potentially pathogenic enzyme from the lung.