Electron Microscopic Investigations on Dust Penetration into the Pulmonary Interstitium in Experimental Pneumoconioses

Abstract

Pneumoconioses produced by intratracheal applications of various dusts (quartz, coal, Cd and lead sulfide) in rats were investigated by EM to follow the pathway of the dust particles from the alveoli into the pulmonary interstitium. As postulated by Spencer in 1977 on the basis of light microscopic investigations, the dust particles produced necroses of the alveolar septae (alveolar ulcers). Two forms of necroses occurred. With a less severe dust exposure, individual pneumocytes and their basement membrane were destroyed by dust particles. Dust-laden macrophages were deposited which were displaced into the stroma after reepithelization of the alveolar defect. With massive dust exposure, most pneumocytes of the affected alveoli became necrotic. The affected alveoli collapsed and were replaced by connective tissue so that the dust was situated in the connective tissue stroma. A transcellular penetration of the dust particles into the pulmonary interstitium or an immigration of dust-laden macrophages into the pulmonary stroma through the intercellular junctions of intact pneumocytes was not observed in any pneumoconiosis models.