Morphological definition of a case of 'usual' interstitial pneumonia.

A 61-year-old Caucasian female complained of shortness of breath, fever, and a period of rapid weight loss. After routine studies, the patient underwent an open lung biopsy in order to define the characteristics of the interstitial lung disease, and initiate appropriate therapeutic intervention. Typical fibrotic and cellular proliferation were evident in the parenchyma, as determined by standard light microscopy. However, in a correlated study using light microscopy of plastic embedded tissue, as well as scanning and transmission electron microscopy, a major proliferating cell type was identified as a type II pneumocyte. These cells were the predominant lining cells of the alveoli and clearly protruded into and limited available respiratory air spaces. The predominance of type II pneumocytes in the pathogenesis of certain respiratory diseases requires that a better explanation be sought for this phenomenon.