Alveolar macrophage procoagulant activity is increased in acute hyperoxic lung injury

Alveolar macrophage accumulation and interstitial fibrin deposition are prominent in adult respiratory distress syndrome and chronic interstitial lung diseases. The role of alveolar macrophages in the initiation of fibrin deposition and lung injury in these diseases is uncertain. Expression of procoagulant activity by these cells may provide evidence of macrophage activation and involvement in the initiation of lung fibrin deposition. An experimental model of hyperoxia-induced lung injury in rats was studied for assessment of the relationship of lung injury, fibrin deposition, and alveolar macrophage procoagulant activity. Lung injury was assessed histologically and functionally, and the accumulation of inflammatory cells was quantified by bronchoalveolar lavage. Pulmonary injury, manifested by increased capillary permeability, developed progressively during exposure to hyperoxia and was associated with significant augmentation of the procoagulant activity of alveolar macrophages early in the disease. This increase preceded the accumulation of polymorphonuclear leukocytes. Alveolar macrophage procoagulant activity had functional characteristics consistent with tissue factor. These studies provide evidence of early alveolar macrophage activation in acute hyperoxic lung injury in rats and suggest a role for procoagulant activity in the development of interstitial fibrin deposition.