Occurrence of different types of contractile cells in some lung fibrosis

Two different morphologic patterns of pulmonary fibrosis have been identified by means of anti-actin antisera and electron microscopy. The first type, observed in chronic passive congestion and also in radiation-induced fibrosis, is characterized by hyaline alveolar walls, with scarce cells, mostly normal fibroblasts. The second type, on the contrary, shows a high cellularity of the alveolar walls with actin-rich cell proliferation, i.e. contractile interstitial cells in usual interstitial pneumonia and shock lung, myofibroblasts in organizing pneumonia, and smooth muscle cells in honeycomb lungs.