Lung Histopathology Scoring Protocol

The fresh left lobes of the lungs were fixed in 4% formaldehyde for 48 h and embedded in paraffin. Each paraffin-embedded lung block was cut into 4 μm thin slices and stained with hematoxylin–eosin (Beyotime Biotechnology, Shanghai, China). The hematoxylin–eosin staining was used to assess peribronchial inflammation. The inflammatory changes were assessed by the following score: 0, normal; 1, few cells; 2, a ring of inflammatory cells with 1 cell layer deep; 3, a ring of inflammatory cells with two to 4 cells deep; 4, a ring of inflammatory cells with more than 4 cells deep (Xue et al., 2021 (link)).