Ultrastructure of lymphoid interstitial pneumonia: virus-like particles in bronchiolar epithelium of a patient with Sjögren's syndrome.

Ultrastructural studies of an open lung biopsy of a patient who had lymphoid interstitial pneumonia, Sjögren's syndrome, and a highly elevated level of immunoglobulin M in the serum disclosed the presence in bronchiolar epithelium of numerous round electron-dense particles 70-120 nm in diameter. These were closely reminiscent of the oncogenic type-A viral particles associated with tumors of laboratory and wild mice. In the inflammatory infiltrate the morphology of some small lymphocytes was suggestive of germinative activity, although no germinal centers were found. Plasma cells, which were numerous in the vicinity of the bronchiolar epithelium, contained varying amounts of electron-dense material, probably immunoglobulin, which was also deposited in the irregulary thickened epithelial basal lamina. The observations support the theory that viral infection may be the stimulus to the immunologic abnormalities observed in patients with lymphoid interstitial pneumonia and Sjögren's syndrome.