Endotoxin inhalation induces neutrophil chemotaxis by alveolar macrophages

Guinea-pigs were exposed to an aerosol of bacterial endotoxin (lipopolysaccharide, LPS). The free lung cell response and alveolar macrophage (AM) chemotaxis were studied. Neutrophils from guinea-pig blood gave larger migration responses than those obtained by intraperitoneal glycogen stimulation or human neutrophils. An increase in the number of neutrophils in the airways was found with a peak at 12-24 hours after exposure. In animals pre-treated with LPS inhalation for 4 months, the reaction was of shorter duration and smaller magnitude. AM showed in vitro chemotactic activity up to 4 hours after exposure; no difference was found in pre-treated animals. The results suggest that the neutrophil invasion in the airways after LPS is dependent on two mechanisms, the initial being AM chemotaxis, which is not modified by pre-exposure to LPS, and another unknown factor, which is modified by pre-exposure to LPS.