Alveolar macrophagic reactions. V. Ultrastructure of alveolar wall changes (mural alveolitis)

Ultrastructural observations of alveolar walls after intratracheal administration of aluminium silicate and parenteral injection of heparin are reported. The alveolar walls appeared cellularly thickened and shortened, the air spaces reduced, the basement membranes undulated. The number of intermembranary interstitial cells of histiocytary-macrophagic type is increased, the granulous alveolocytes are concentrated mostly at the intersection of alveolar walls, the fibroblast-fibrocytes as well. The flat alveolocytes with their large cytoplasmic expansions covered the reduced surface of air spaces. Macrophages contained amorphous masses of aluminium silicate within giant phagosomes.