Fig. 5: Subpleural fibrosis in SARS-CoV-2 infected hamsters.

a–d Representative images showing sub-pleural fibrotic foci in a lung lobe of a SARS-CoV-2 infected hamster at 14 days post infection (dpi). The left panel shows an overview of one right lung lobe displaying multifocal, extensive, well-demarcated areas of sub-pleural fibrosis. The right panel shows at higher magnification of the area delineated by the rectangle. On hematoxylin-eosin (HE) stained sections, this lesion is characterized by sub-pleural aggregates of spindle cells and abundant, pale eosinophilic, fibrillary, extracellular matrix (a). Azan stain demonstrates the presence of mature collagen fibers in the matrix (blue signal, b). Immunohistochemistry shows abundant α-smooth muscle actin (α-SMA)⁺ myofibroblasts (brown signal in c) as well as infiltration with CD204⁺ M2 macrophages (brown signal, d). e Quantification of sub-pleural fibrosis in lungs of mock and SARS-CoV-2 infected hamsters at 14 dpi. The percentage of affected area relative to total lung area is given. f Quantification of CD204⁺ M2 macrophages in total lung area. Data are shown as box and whisker plots. The bounds of the box plot indicate the 25th and 75th percentiles, the bar indicates medians, and the whiskers indicate minima and maxima. Dots indicate individual values. Data from CD204 quantification was tested by two-tailed Mann–Whitney U test. A p value of ≤0.05 was chosen as the cutoff for statistical significance. N = 10 animals/group for mock and SARS-CoV-2 respectively. Source data are provided as a Source Data file. Scale bars (a–d): 500 µm (overview in a–d), 100 µm (high magnification in a–d).