(b) Higher magnification of a first alveolar duct bifurcation (B) where numerous fibers (arrows) can be readily observed at their sites of original deposition. epithelial cells of the alveolar duets, endothelial and smooth mus- cle cells of small peribronchiolar blood vessels all exhibited highly significant increases in incorporation of tritiated thymi- dine [3H]Tdr) or bromodeoxyuridine (BrdU). b) A progressive fibrotic lesion developed at the sites where asbestos fibers initial- ly were deposited and lung macrophages accumulated.
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