Myofibroblasts in diffuse alveolar damage of the lung.

The myofibroblast is an ultrastructurally and metabolically distinctive connective tissue cell identified as a key participant in tissue remodeling in human granulation tissue, organ fibrosis, and the fibroblastic host response to malignant neoplasms. In this study of myofibroblasts in human lung diffuse alveolar damage (DAD), we identified 36 autopsy cases in which DAD could be histologically documented. DAD is known to progress from initial injury through an exudative, proliferative, and terminal fibrotic phase. In the exudative phase (16 cases), myofibroblasts expressing alpha-smooth muscle actin (alpha-SMA) are found in the septa and less frequently in hyaline membranes. In the proliferative phase (18 cases), many myofibroblasts in septa, hyaline membranes, and intra-alveolar fibroplasia express alpha-SMA. The alpha-SMA phenotype should be used in additional studies of myofibroblast differentiation, replication, and apoptosis. A better understanding of the biology of this cell type should offer new therapy for patients with DAD.