MAST-CELL HETEROGENEITY AND HYPERPLASIA IN BLEOMYCIN-INDUCED PULMONARY FIBROSIS OF RATS

Abstract

Mast cell distibution, density and histochemical subtype were studied in rat respiratory tracts with bleomycin-induced pulmonary fibrosis. In normal rats, mast cell densities were highest in the trachea and lowest in the bronchus and parenchyma. Two histochemically distinct mast cell populations were identified in the mucosa adjacent to the tracheal cartilage, but elsewhere only a single typical connective tissue-like mast cell population was found. After intratracheally administered bleomycin, lung histamine levels (.mu.g/g wet wt) increased as much as 14-fold by day 50. Pulmonary mast cell changes were present early in the fibrotic process and by day 14 the mast cell density in the parenchyma was 10 times normal. These parenchymal mast cells were histochemically of the connective tissue type. Pronounced mast cell hyperplasia occurs during experimental pulmonary fibrosis evolution. This model provides a powerful tool to study pulmonary mast cells and to identify their ratio in fibrotic disease.