IN CHYLOPTYSIS, SP-A AFFECTS THE CLEARANCE OF SERUM-LIPOPROTEINS ENTERING THE AIRWAYS

Serum lipoproteins may enter the airways and appear in sputum (chylopt ysis) when the lymphatic circulation is impaired by inflammation, neop lasia, or an abnormal proliferation of smooth muscle cells. While anal yzing the bronchoalveolar lavage fluid of a patient with chyloptysis, we noticed that surfactant could not be separated from contaminating s erum lipoproteins and speculated that lipoproteins might interact with surfactant components. To clarify this point we immobilized surfactan t protein (SP) A on microtiter wells and incubated it with I-125-label ed very low density lipoproteins (VLDLs), low-density lipoproteins, an d high-density lipoproteins. We found that SP-A binds lipoproteins. St udying in greater detail the interaction of SP-A with VLDLs, we found that the binding is time and concentration dependent; is inhibited by unlabeled lipoproteins, phospholipids, and antibodies to SP-A; is incr eased by Ca2+; and is unaffected by methyl alpha-D-mannopyranoside. Wh ole surfactant is a potent inhibitor of binding. Furthermore, we found that SP-A increases the degradation of VLDLs by alveolar macrophages and favors the association of VLDLs with alveolar surfactant. We concl ude that SP-A influences the disposal of serum lipoproteins entering t he airways and speculate that binding to alveolar surfactant might rep resent an important step in the interaction between exogenous substanc es and the lung.