Pulmonary macrophage: a major source of lipoprotein lipase in the lung.

The lipase released by heparin infusion into perfused rat lungs is shown to be identical with lipoprotein lipase on the basis of the following characteristics: 1) it required plasma for full activity; 2) it was largely inhibited by 1 M NaCl; and 3) it bound to a heparin-Sepharose gel and eluted with buffer containing 1.5 M NaCl. Macrophages prepared from rat lungs released a considerable amount of lipoprotein lipase, with characteristics similar to those of the lipoprotein lipase released from heparin-perfused rat lungs. Pulmonary surfactant-producing type II pneumocytes did not cause a significant release of lipoprotein lipase. No apparent lipoprotein lipase activities were detected in the conditioned medium of other lung cells from which macrophages had been selectively removed.