ULTRASTRUCTURE OF PULMONARY MAST-CELLS IN PATIENTS WITH FIBROTIC LUNG DISORDERS

Abstract

The topographic distribution, population density and ultrastructural features of metachromatic cells (mast cells and basophilic leukocytes) were studied in lung biopsies from 5 control patients and 17 fibrotic lung disorder patients. The great majority of metachromatic cells were mast cells. The average number of metachromatic cells per square mm of tissue section was much larger in fibrotic lung disorder patients (45.8 .+-. 6.5) than in control patients (2.6 .+-. 1.6). In control patients, mast cells were most frequently seen in subpleural and perivascular connective tissue. The vast majority of mast cells in fibrotic lung disorder patients was present in thickened, fibrous alveolar septa; mast cells also were found within the alveolar epithelial layer and alveolar lumina. The quantitative distribution of different types of mast cell granules differed in the 2 patient groups: granules composed of scrolls were more frequent in control patients, and combined type granules (containing mixtures of different components within the same granule) were more frequent in fibrotic lung disorder patients. Mast cells in the latter patients appeared to migrate through defects in the basement membrane into the epithelial layer and alveolar lumina; mast cells in these areas often showed reduced numbers of granules and disorganized granule content. Pulmonary parenchymal mast cells in fibrotic lung disorders may undergo a chronic process of partial degranulation which differs from that found in anaphylaxis; this chronic release of mast cell products may contribute to the continuing alveolar injury and to the ventilation-perfusion inequalities observed in the fibrotic lung disorders.