Biochemical evidence for an increased and progressive deposition of collagen in lungs of patients with pulmonary fibrosis.

To assess the role of changes in lung collagen in pulmonary fibrosis, the content of this protein was measured in biopsy and autopsy lung from patients with cryptogenic fibrosing alveolitis (CFA), a fibrotic lung disorder of unknown cause. The collagen concentration was measured in lung samples from 21 patients with CFA (14 autopsy and seven open-lung biopsy) and 17 normal subjects; total lung collagen was determined in the right lung of 10 patients who died from CFA and the results were compared with those from 10 normal lungs. There was a wide variation in the collagen concentrations but the mean value (+/- SEM) for patients with CFA (217 +/- 13 mg/g dry weight) was significantly higher (P less than 0.02) than that of the controls (155 +/- 15 mg/g dry weight). The mean collagen concentration of the autopsy samples (243 +/- 20 mg/g dry weight) was significantly higher (P less than 0.05) than that of the biopsy samples (165 +/- 24 mg/g dry weight). The mean total collagen was markedly raised (P less than 0.001) in right lungs of patients with CFA (32.5 +/- 4.3 g) compared with normal lungs (14.0 +/- 1.1 g). When corrected for the predicted lung volume this difference in total lung collagen remained statistically significant (P less than 0.01, mean for patients 4.7 +/- 0.7 mg/ml, controls 2.3 +/- 0.2 mg/ml). These results demonstrate an increased deposition of lung collagen in this form of pulmonary fibrosis. They also suggest that there is a greater collagen concentration in lungs of patients with later disease, indicating a progressive deposition of collagen during the course of the disease.