Alveolar epithelial responses in experimental streptococcal pneumonia.
We describe an experimental model of pneumonia in Wistar rats evoked by Streptococcus sanguis. The lesion developed rapidly as a confluent bronchopneumonia of the single-lobed left lung. Except at the extreme base, where an abscess formed, the pneumonic process thereafter resolved, and most of the lung appeared microscopically and ultrastructurally normal 8 days after infection. Sequential electron microscopic studies revealed that in the areas of lung which subsequently resolved, damage was restricted to type 1 pneumocytes. Within 24 h of infection, the unaffected type 2 pneumocytes were observed to proliferate, transform into elongated pneumocytes of intermediate morphology, and then undermine and strip off the damaged type 1 cells from the subjacent basement membrane. Thereafter, the intermediate type pneumocytes completed their transformation into definitive type 1 cells, thus completing the repair process. We hypothesize that this represents an accelerated form of the normal type 1 replacement mechanism, and that uncomplicated epithelial repair following acute alveolar damage is possible if type 2 pneumocytes escape significant damage, so that they retain their capacity to proliferate and differentiate into type 1 epithelium.
Rhodes
G C
GC
School of Pathology, University of New South Wales, Kensington, Australia.
Tapsall
J W
JW
Lykke
A W
AW
D000818:Animals; D004195:Disease Models, Animal; D004848:Epithelium / Q000473:pathology; D005260:Female; D008854:Microscopy, Electron; D011014:Pneumonia / Q000209:etiology / Q000473:pathology*; D011650:Pulmonary Alveoli / Q000473:pathology*; D051381:Rats; D011919:Rats, Inbred Strains; D013290:Streptococcal Infections / Q000473:pathology*; D013298:Streptococcus sanguis