Contractile Cells in Normal and Fibrotic Lung

Interstitial pulmonary fibrosis represents a group of fibrosing lung diseases, often of unknown etiology, characterized by hypercellularity and deposition of connective tissue within the interstitium of the alveolar wall (32, 65). Increased “stiffness” of the lung leads to reduced lung volumes and lowered dynamic compliance (80). In interstitial fibrosis, as well as several other forms of lung injury, there is an apparent increase in smooth muscle (SM) cells organized into bundles within areas of the lung where these cells normally are present but difficult to detect, such as the alveolar duct (69, 89, 119). This increase in acinar SM can be quite prominent, and, in some cases, the degree of parenchymal SM hyperplasia is sufficiently excessive to be referred to as “muscular cirrhosis of the lung” (2, 7, 33, 110, 152).