Histopathology and lung injury score

Lung tissues were excised and washed with saline solution. They were then fixed in 4% formalin and embedded in paraffin. They were cut into 5 μm sections, stained with hematoxylin and eosin (H&E), and visualized under an optical microscope (Olympus Optical, Tokyo, Japan) for histological analysis. Tissue sections were then evaluated based on the method described by (Wang L. et al., 2016), which using the following scoring system to grade the degree of lung injury. Features were focal thickening of the alveolar membranes, congestion, pulmonary edema, intra-alveolar hemorrhage, interstitial neutrophil infiltration, and intra-alveolar neutrophil infiltration. Each feature was assigned a score from 0 to 3 based on its absence (0) or presence to a mild (1), moderate (2), or severe (3) degree, and the total cumulative histology score was determined.