Ultrastructure of extrinsic allergic bronchiolo-alveolitis.

Electron microscopic findings in open lung biopsies of 13 patients with extrinsic allergic bronchiolo-alveolitis (EABA) were studied. Eleven of the patients had farmer's lung and two had been exposed to other mouldy dust. Numerous lymphocytes, macrophages and giant cells were found both in the alveolar and bronchiolar lumina. Bronchiolar changes included loss of microvilli on the ciliated cells, granulomas, detachment of basal cells from each other, as well as disintegration of the basement membrane. In the alveoles hyperplasia and hypertrophy of type II (granular) pneumocytes often loosely connected with the basement membrane, were frequently demonstrated. Disintegration of the basement membrane accompanied by detachment of the pneumocytes occurred occasionally. In the interstitium lymphocytes, mast cells and plasma cells predominated. The size and shape of lymphocytes were variable. In addition, some lymphocytes with pseudopods were detected both in alveolar lumen and in the interstitium. Mast cells were found in close connection with plasma cells occasionally. Granulomas consisting of these cells and giant cells were usually present. Foreign material resembling hyphal fragments was found in the giant cells of two patients. The present series emphasizes the role of lymphocytes, macrophages, giant cells and mast cells, in the pathogenesis of EABA. The presence of numerous plasma cells in the lung parenchyma suggests the possibility of local antibody response caused by exposure to inhaled antigens.