Inhibition of pulmonary macrophage function by airway mucus

As a model for the interaction between macrophages and mucus in the tracheobronchial tree, we incubated sheep alveolar macrophages in vitro with and without airway mucus from the same animal and tested their phagocytic function and rates of general protein synthesis. Airway mucus was obtained by tracheal suction after previous subcutaneous injection of the sheep with pilocarpine (0.5 mg/kg) and subsequently diluted. Pulmonary macrophages were obtained by saline lavage through a balloon-tipped fiber-optic bronchoscope. In incubated attached macrophages, phenylalanine incorporation into protein was inhibited 51% by mucus (P less than 0.001). Phagocytosis of 1.09-microns latex particles was inhibited 75% by mucus at nonsaturating levels of particles (P less than 0.001) and by 47% at saturating levels of particles (P less than 0.001). Inhibitory activity for protein synthesis and phagocytosis was retained in the 104,000 g supernatant fraction of whole mucus (sol), while the gel fraction inhibited phagocytosis only. This difference did not appear to be related to physical factors. We conclude that diluted airway mucus interferes with pulmonary macrophage function as assessed by rates of general protein synthesis and phagocytosis.