Histological features. (A-D) Transmural and peribronchial infiltration by lymphoctytes and histiocytes was found, with prominent and diffuse involvement of respiratory and terminal bronchioles; most of the histiocytes were foamy macrophages, which formed “nodules”, distributed especially in the wall of respiratory bronchioles, in the surrounding interalveolar septa and around the blood and lymphatic vessels. HE, x25. (E) The inflammatory infiltrate showed a characteristic topography: the bronchiolar lumen contained neutrophils, while the peribronchiolar infiltrate was constituted of an inner layer of lymphocytes and an outer layer of histiocytes. HE, x200. (F) Note the exuberant perivascular distribution of foamy macrophages. HE, x200.