Bronchial changes in rat lung allografts in the process of acute rejection

We examined histologically the bronchial changes in rat lung allografts during the process of acute rejection. The lungs of BN donor rats were orthotopically transplanted to the left hemithoraxes of LEW recipient rats (n=15). LEW to LEW isografts were used as controls (n=12). Recipient rats were sacrificed daily from 1 to 6 days after transplantation. Left lungs were fixed with 2.5% phosphate-buffered glutarlaldehyde, embedded in paraffin and stained with hematoxylin-eosin, methylgreen-pyronin and PAS. In the bronchial epithelium of allografted lungs, an increased percentage of goblet cells, sawtooth-like changes and mitosis were observed. Disturbed basal cell alignment and vacuole degeneration of epithelial cells appeared in the alveolar phase. The ratio of goblet cells to epithelial cells was significantly increased in middle sized bronchi with a diameter of 500 to 999 μm on day 3 (mainly during the vascular phase). As a result of progressive bronchial damage, the ratio decreased rapidly from day 5 on. In conclusion, the bronchial epithelium of allografted lungs changes through the following three steps in the process of acute rejection. In the first step, the bronchial epithelium reacts with hyperplasia against submucosal inflammation. In the second step, the epithelium shows atypism and pleomorphism. In the final step, the epithelium goes on to cell death and necrosis.