Interstitial associations of cells lining air spaces in human pulmonary fibrosis.

An ultrastructural study of the cells that line air spaces in human pulmonary fibrosis is reported. Intimate associations between these cells and cellular elements in the interstitium were consistently found in biopsies from 25 cases. Cytoplasmic extensions of cuboidal pneumocytes protruded through discontinuities in the subjacent basement membrane. Attenuated cells having structural properties of fibroblasts were situated on connective tissue that formed the walls of numerous air spaces. In this situation, a basement membrane was not demonstrable. These heretofore undescribed features suggest a dynamic interaction between certain mesenchymal and epithelial elements in the fibrotic lung.