Acute immunologic pulmonary alveolitis.

Acute immunologic injury of rat lung has been induced by the intrabronchial injection of heterologous antibody and the intravenous injection of radiolabeled antigen. Within 4 h an acute hemorrhagic neutrophil-rich exudate develops in alveolar and interstitial areas and then gradually fades. Lung injury in this model can be quantitated by measurements of increased vascular permeability and extractable hemoglobin. By the use of immunofluorescent techniques, alveolar and interstitial deposits of antigen and antibody have been demonstrated, but not the third component of complement (C3). Although not found in relation to immune complexes, C3 is nevertheless present in damaged lung as measured by accumulation of radiolabeled C3 from the circulation. Ablation experiments indicate the requirement for both circulating neutrophils and C3 for the development of lung injury. These studies provide definition for the development of lung damage induced by immune complexes.