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. 2023 Jun 12;120(25):e2207210120. doi: 10.1073/pnas.2207210120

Fig. 2.

Fig. 2.

Pathological changes after specific infection of AT2 cells by SARS-CoV-2. (A and B) Schematic diagrams illustrating the knock-in strategy of R26-hACE2-tdT mouse line by homologous recombination (A) and the strategy for inducing hACE2 and tdT expression (B). (C) Cartoon image showing that the R26-hACE2-tdT model could be combined with different genetic models for inducing expression of hACE2 in target cell type according to the research needs. (D) A schematic diagram illustrating the experimental design. (E) Whole-mount views of the lungs of Sftpc-CreER;R26-hACE2-tdT mice after tam treatment. (F) Immunostaining for tdTomato, hACE2, and Sftpc on lung sections of Sftpc-CreER;R26-hACE2-tdT mice. Yellow arrowheads indicate tdT+hACE2+Sftpc+ AT2 cells. Quantification of the percentage of AT2 cells expressing hACE2. Data are presented as mean ± SD; n = 4 mice per group. (G) A schematic diagram illustrating the virus infection strategy. (H) Immunostaining for tdT and SARS-CoV-2 S protein on lung sections at 4 days post infection (dpi) and uninfected mice. (I) Quantification of the percentage of tdT+ cells infected by SARS-CoV-2 in damaged regions. n = 4 mice per group. (J) RT-qPCR quantification of SARS-CoV-2 ORF gene expression in the lungs in uninfected, 4, 7, and 14 dpi. Data are presented as mean ± SD; n = 3 or 4 mice per group. Unpaired, two-tailed t test. (K) H&E staining of lung tissues in uninfected, 4, 7, and 14 dpi groups. (L) H&E score of the lung injuries in uninfected, 4, 7, and 14 dpi groups. P value was calculated by unpaired two-tailed Student's t test. Data are presented as mean ± SD; n = 3 or 4 mice per group. (M) IHC staining for CD45+ immune cells of lungs in uninfected, 4, 7, and 14 dpi groups. (N) Quantification of the cell number of CD45+ immune cells of infected lung tissues. P value was calculated by unpaired two-tailed Student's t test. Data are presented as mean ± SD; n = 3 or 4 mice per group. (O) Cartoon image showing that the Sftpc-CreER;R26-hACE2-tdT model could be specifically used for inducing the expression of hACE2 and tdT in AT2 cells. After host cell entry, SARS-CoV-2 virus could specifically infect AT2 cells via hACE2, resulting in epithelium-derived lung pneumonia. Tam, tamoxifen. tdT, tdTomato. A-tubulin, Acetylated-tubulin. (Scale bars, yellow, 1 mm; white, 100 μm; black, 200 μm.)