Rôle of lipids in airway function.

The lipid composition of airway secretion is described. Major differences in the literature may depend on methods. Bronchoalveolar lavage includes a major contribution of alveolar surfactant. Sputum may be contaminated by secretions from the upper airways and saliva, and shows great variations in total lipids and free fatty acids. Diseases affect its composition. Tracheobronchial aspirates and washings are more direct methods and show much cholesterol, DPPC, and other phospholipids. Secretions by explants and cell cultures also show very mixed lipid composition including neutral, phospho- and other lipids. Although much airway lipid may travel up from the alveoli, there is evidence that the larger airways can secrete their own lipids. They may also arise from breakdown of cells. Their functions may include a modification of mucus rheology, an effect on ciliary beat and mucociliary clearance, a modification of mucus adhesiveness, an action on bacterial invasion, and a lessening of the tendency to collapse of small airways due to the surface activity of the lipids.