Ultrastructural distribution of fibronectin in normal and fibrotic human lung.

We studied the distribution of fibronectin in normal and fibrotic adult human lung and normal hamster lung using affinity-purified antifibronectin Fab'-horseradish peroxidase conjugates. In normal lung, fibronectin staining was present in alveolar capillary and epithelial basal lamina and associated with interstitial collagen fibers. In airway and larger vessels, fibronectin staining was associated with the basal lamina of smooth muscles. In contrast to the relative paucity of staining in normal lung, the alveolar basal lamina of fibrotic lung stained intensely for fibronectin. In addition, there was strong, periodic (approximately 600 A) staining of native collagen fibers for fibronectin. We conclude that fibronectin antigenicity is present in the alveolar epithelial and capillary endothelial basal lamina of normal human and hamster lung. The marked alterations in the apparent amounts and distribution of fibronectin in fibrotic human lung suggest its involvement in the cellular events accompanying human lung fibrosis.