Acute and Subacute Effects of Injury on the Canine Alveolar Septum: Results (5)

Clustering of type 2 cells in alveolar “corners” or septal junctions in mouse lungs has been described previously by Adamson and Bowden. Brains report on lungs fixed by intravascular perfusion shows alveolar macrophages also clustered at the alveolar septal junction. We have shown in previous studies that in normal human lungs preserved by vascular perfusion-fixation, type 2 cells, alveolar macrophages and septal interstitial gaps all predominate at “corners,” or sites of junctions of alveolar septa. The present report extends these studies to canine lungs and confirms these findings. In addition, the increase in predominance of pores and gaps in the treated animals two and four weeks after papain instillation, and the significantly increased prevalence of all three features (alveolar macrophages, type 2 cells and septal gaps) in the alveoli of the animal sacrificed two weeks after papain instillation suggests both an increase in vulnerability to proteolytic injury and an associated increase in septal repair activities at these sites. birth control pills
The increased prevalence of type 2 cells in septal gaps at junctional sites, combined with changes in the morphology of type 2 cell organelles in the animal two weeks after treatment (dilated cistemae of endoplasmic reticulum) (Fig 3) suggest a more comprehensive role for type 2 cells in septal repair than that of acting merely as precursors of type 1 cells.