Fig. 2.

Light microscopy of the surgical biopsy from the left lung's lingula shows lung parenchyma containing large areas where the alveoli are totally filled with a granular proteinaceous material that is strongly eosinophilic on hematoxylin-and eosin staining (HE). The alveolar walls display diffuse moderate infiltration of lympho-histiocytic cells. The intraalveolar material is also positive with the periodic acid-Schiff stain and diastase-resistant (PAS + D), as well as strongly immunohistochemically positive for surfactant-A protein (S–A) and to a less extent for surfactant-B (not shown), consistent with its derivation from surfactant phospholipids and protein components. Accumulation of surfactant-A is also seen in the hyperplastic pneumocytes covering the alveolar walls and in the intraalveolar macrophages. Cytokeratin staining (CK) highlights the hyperplastic type-II pneumocytes on the alveolar walls and the proteinaceous cell debris of exfoliated pneumocytes in the intraalveolar material. (All figures, 100X).