ALVEOLAR RESPONSE TO EXPERIMENTAL PNEUMOCYSTIS-CARINII PNEUMONIA IN THE RAT

  • 1 January 1980
    • journal article
    • research article
    • Vol. 99  (3) , 561-588
Abstract
To characterize the alveolar response to P. carinii pneumonia, light microscopy and EM were used to trace the development of experimental infections with P. carinii in rats treated with cortisone acetate and a low-protein diet. The 1st changes were found by the 8th day of treatment and consisted of the selective attachment of Pneumocystis organisms, mostly trophozoites, to alveolar Type 1 pneumocytes; the host cells were undamaged and no inflammatory response was seen. After approximately 1 mo. of treatment, the seemingly innocuous host-parasite interaction was succeeded by focal necrosis of the Type 1 pneumocytes adjacent to organisms; hyperplasia of nearby Type 2 pneumocytes also occurred, to replace the dead Type 1 pneumocytes. Even at this stage, inflammatory reaction was conspicuously absent except for occasional alveolar macrophages in the diseased alveoli; in addition, all cells of the alveolar-capillary membrane other than Type 1 pneumocytes appeared entirely normal. Not only did the present study clarify the nature of alveolar injury caused by P. carinii, but it also provided an experimental animal model in which selective injury of the alveolar lining cells occurs.