Fig. 2

Histological evaluation of acute lung injury in the first 4 days after a single orotracheal instillation of gastric fluid. a Light microscopy (hematoxylin and eosin stain) of lung from a control animal and from animals studied 4, 12 and 24 h and at day 4, after gastric fluid instillation. Polymorphonuclear neutrophils and red blood cells with abundant intra-alveolar proteinaceous material are seen at 4 h. A more intense reaction is seen at 12 and 24 h. At day 4, markers of ALI, as seen in the first 24 h, are no longer observed. Instead, intra-alveolar buds of granulation tissue, characteristic of OP containing giant-cell granulomas are seen. Arrow: giant-cell granuloma inside a Masson body. Original magnification: 200X. b Light microscopy (alpha-SMA immunostaining) of control lung and lung of animals studied at 24 h and at day 4 after gastric fluid instillation. The control and 24-h samples exhibit alpha-SMA (brown) staining localized to the wall of bronchioles and blood vessels only. Intra-alveolar alpha-SMA-positive structures (myofibroblasts) are observed only at day 4. Original magnification: 200X