Actin-containing cells in human pulmonary fibrosis.

Lung tissue from five patients with varying degrees of diffuse pulmonary fibrosis was examined for the presence of nonmuscle cells containing the contractile protein actin. Histochemical studies using light- and electron-microscopic techniques suggested that the fibrotic tissue, in areas lacking smooth muscle, had within it numerous cells with cytoplasmic microfilaments composed of actin. Similar cells rarely were observed in control lung tissue. The orientation of these cells within the parenchyma, as well as the arrangement and density of the filaments in the cell, suggests a contractile function. Cells with contractile properties might play a role in the altered dynamics of the lung in diffuse fibrotic pulmonary disease.