Alveolar destruction in experimental Klebsiella pneumonia

Sequential histological changes of the lungs were studied in experimental Klebsiella pneumonia, using untreated control mice, cyclophosphamide-treated mice, and carrageenan-treated mice. Cyclophosphamide was used to deplete polymorphonuclear leukocytes and monocytes, and carrageenan was used to deplete mononuclear phagocytes selectively. At 72 hours, varying degree of alveolar necrosis could be seen in untreated control mice. However, the lung lesions of cyclophosphamide- or carrageenan-treated mice were significantly different from those of the control mice. The lung lesions of cyclophosphamide-treated mice indicated that destruction of the alveolar septa was not induced by K. pneumoniae itself but by inflammatory cells, because the alveolar walls were preserved very well in spite of considerable bacterial multiplication in alveolar lumina until infiltration of inflammatory cells occurred. The lung lesions of carrageenan-treated mice showed that alveolar spaces were packed with polymorphonuclear leukocytes, but the alveolar walls were preserved very well as far as the authors could tell after examining the lung lesions by silver impregnation staining. These results suggest that macrophages rather than polymorphonuclear leukocytes and organisms play an important role in alveolar injury in experimental Klebsiella pneumonia.