Surfactant protein A is degraded by alveolar macrophages.
The metabolism of iodinated lung surfactant protein A (SP-A) by alveolar macrophages in primary culture was examined to determine the role these cells play in the degradation of this surfactant protein. SP-A was isolated from lung lavage obtained from normal bovines, patients with alveolar proteinosis, and silica-treated rats. SP-A (0.5 microgram/ml) was incubated for 3 h with rat alveolar macrophages obtained by lung lavage. Cell association and degradation of human and rat SP-A was three times greater than that of bovine SP-A. During the 3-h period, 50% of total macrophage-associated SP-A was degraded. Degradation was time-, temperature-, and concentration-dependent after a 1-h lag period. SP-A degradation was intracellular, since NH4Cl inhibited degradation > 50%, and macrophage-conditioned medium was ineffective. Tenfold more SP-A was degraded by macrophages than by type II cells isolated after elastase digestion of rat lungs. There was little degradation of SP-A by HeLa cells. We conclude that alveolar macrophages take up and degrade SP-A and thus could contribute to the catabolism of SP-A in the lung.
Bates
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SR
Institute for Environmental Medicine, University of Pennsylvania, School of Medicine, Philadelphia 19104-6068, USA.
Fisher
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AB
D000818:Animals; D002417:Cattle; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D016676:Macrophages, Alveolar / Q000378:metabolism*; D008297:Male; D011510:Proteolipids / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014407:Tumor Cells, Cultured
D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants