Microscopic characterization of rabbit lung damage produced by Pseudomonas aeruginosa proteases

The intratracheal administration of highly purified Pseudomonas aeruginosa proteases (ca. 10 to 100 microgram) elicited extensive, grossly observable rabbit lung damage by 3 h postinjection. Light and electron microscopic characterization of the lesions revealed: (i) progressive injury and necrosis of type I epithelial cells and capillary endothelial cells from 3 h to 1 day postinjection, and progressively increasing accumulations of erythrocytes, plasma proteins, fibrin, and released type II epithelial cell lamellar bodies in alveolar lumina during that time period; (ii) progressively increasing accumulations of macrophages, but not of polymorphonuclear leukocytes, in alveolar lumina from 3 h to 6 days postinjection; (iii) progressive hyperplasia of type II epithelial cells from 12 h to 4 days postinjection; (iv) progressive infiltration of alveolar septa by mononuclear inflammatory cells (interstitial pneumonitis) from 2 to 6 days postinjection; (v) no loss of alveolar septal connective tissue and no damage to pulmonary arterioles and venules; and (vi) almost normal alveolar structure by ca. 8 days postinjection. The study revealed that the intra-alveolar hemorrhage, the injury and necrosis of alveolar septal cells, and the infiltration by mononuclear cells that have been reported to occur during human pseudomonas pneumonia can also be elicited by the experimental administration of pseudomonas proteases. Thus, the results support the idea that in vivo production and activity of P. aeruginosa proteases is important, at least in part, in eliciting the lung damage characteristic of pseudomonas pneumonia.