Ultrastructural changes in the alveolar epithelium in response to Freund's adjuvant.

Serial examination of the lungs of neonatal and adult rabbits treated with Freund's adjuvant demonstrated in addition to the rapid development of interstitial granulomata, marked alterations in the alveolar epithelial cells. Granular pneumonocytes became numerous and were often found adjacent to one another within a single alveolus. Their characteristic lamellar inclusions were increased in size and number, and there was often partial loss of the luminal microvilli. The membranous pneumonocytes were locally thickened, had an irregular luminal border, and on occasion, contained lamellar-like inclusions. These observations indicate that both types of epithelial cell participate in the pulmonary reaction to adjuvant, and that adjuvant-induced changes may be a useful model for studying the dynamics of the response of pulmonary epithelial cells to injury.