Histology following chronic gastric fluid aspiration. Evaluation of Masson trichrome-stained tissue demonstrated an increase in peribronchiolar and interstitial fibrosis in (a) left lung specimens after 8 weeks of gastric fluid aspiration compared to (b) lung specimens from untreated rats or rats receiving normal saline. Scattered cellular infiltrates were most apparent in left lungs following chronic aspiration of gastric fluid after 8 weeks and consisted primarily of (c) giant cells (GC), apparent in specimens stained with trichrome and (d) perivascular lymphocytes (arrows) as noted in specimens stained with H&E. In many trichrome-stained left lung specimens from rats receiving gastric fluid, (e) complete airway occlusion was observed reminiscent of lesions observed in lung transplant recipients exhibiting obliterative bronchiolitis (OB). Neither fibrosis nor cellular infiltrates were apparent in right lung specimens from rats undergoing gastric fluid aspiration for (f) 8 weeks or at other time points.