Hyperplasia of type II pneumocytes in pulmonary lymphangioleiomyomatosis -Immunohistochemical and electron microscopic study

Background.-Little is known of the morphology of the pneumocytes lining the parenchymal cysts in lymphangioleiomyomatosis (LAM), Objective.-To evaluate the structural characteristics of the alveolar epith elial cells in LAM. Methods-Immunohistochemical and electron microscopic studies were performed on lung tissue from 22 women with pulmonary LAM. Results.-Epithelial cells that reacted with PE-10 (a mouse monoclonal antib ody that recognizes the surfactant apoprotein A in type II pneumocytes) and TTF-1 tan antibody that identifies nuclear transcription factor found in t ype II pneumocytes) were the predominant cell type lining the surfaces of l esions of LAM and normal areas of lung. Scanning and transmission electron microscopic studies confirmed that these cells were type II pneumocytes as demonstrated by (1) apical microvilli, (2) electron-dense lamellar bodies, and (3) cytoplasmic projections that extended from the basal surfaces into the underlying connective tissue, where they made extensive contact with in terstitial connective tissue cells. A few cells had morphologic characteris tics of type I pneumocytes, including large flat surfaces lacking microvill i. Cells that appeared intermediate between type I and type II pneumocytes were observed occasionally. Conclusions,These observations and the reactivity of these cells with antib ody to proliferating cell nuclear antigen demonstrate that extensive hyperp lasia of type II pneumocytes is a major characteristic of LAM.