MYOFIBROBLASTS IN DIFFUSE ALVEOLAR DAMAGE OF THE LUNG

The myofibroblast is an ultrastructurally and metabolically distinctiv e connective tissue cell identified as a key participant in tissue rem odeling in human granulation tissue, organ fibrosis, and the fibroblas tic host response to malignant neoplasms. In this study of myofibrobla sts in human lung diffuse alveolar damage (DAD), we identified 36 auto psy cases in which DAD could be histologically documented. DAD is know n to progress from initial injury through an exudative, proliferative, and terminal fibrotic phase. In the exudative phase (16 cases), myofi broblasts expressing alpha-smooth muscle actin (alpha-SMA) are found i n the septa and less frequently in hyaline membranes. In the prolifera tive phase (18 cases), many myofibroblasts in septa, hyaline membranes , and intra-alveolar fibroplasia express alpha-SMA. The alpha-SMA phen otype should be used in additional studies of myofibroblast differenti ation, replication, and apoptosis, A better understanding of the biolo gy of this cell type should offer new therapy for patients with DAD.