Fig. 3: Experimental infection of TMPRSS2-knockout mice with SARS-CoV-2 variants.

C57BL/6 (WT) and TMPRSS2-knockout (KO) mice were inoculated intranasally with Beta (TY8-612) (a, b), Gamma (TY-503) (c, d) and Omicron (TY38-873) variants (e–i). (a, c, e left panels) Body weight curve during the observation period a: n = 8 (4 males and 4 females for KO and WT); c n = 8 (KO, 4 males and 4 females), n = 9 (WT, 3 males and 5 females); e n = 8 (4 males and 4 females for KO and WT); a **P = 0.0037 at 2 days post-infection (p.i.) and 0.0019 at 8 days p.i., ***P = 0.0002 at 9 days p.i. and ****P < 0.0001 from 3 to 7 days p.i.; c ****P < 0.0001 at 3 days p.i. and **P = 0.0060 at 4 days p.i., by two-way ANOVA followed by Bonferroni’s multiple comparison test. Data are mean ± SEM. (a, c middle panels and e right panel) Serum neutralisation titres (NT) at 9 days p.i., respectively. The dashed line indicates the limit of detection (<2) a n = 8 (4 males and 4 females for KO and WT); c n = 8 (KO, 4 males and 4 females), n = 9 (WT, 3 males and 5 females); e n = 8 (4 males and 4 females for KO and WT); a ***P = 0.0006; c **P = 0.0028 by two-tailed Mann–Whitney U test. Data with a geometric mean (GMT) ± 95% confidence interval, CI (a, c right panels and f). Viral titres in lung homogenates or nasal cavity at 6 h and 1 to 4 days p.i. (n = 4 per group, 2 males and 2 females). The detection limit was 10^1.5 TCID₅₀/g of tissue. a ***P = 0.0004 at 6 h and P = 0.0002 at 4 days p.i. and ****P < 0.0001; c *P = 0.0226 at 3 days p.i.), **P = 0.0064 at 1 day p.i. and ***P = 0.0002 at 2 days p.i.; f *P = 0.0147 at 3 days p.i. by two-way ANOVA followed by Bonferroni’s multiple comparison test. Data are mean ± SD. (b, d, i) Histopathology of the respiratory tract from WT and TMPRSS2-KO mice infected with Beta, Gamma and Omicron variants. Immunohistochemical analysis (IHC) using an anti-SARS-CoV-2 NP antibody at 1 and/or 3 days p.i (n = 4 per group, 2 males and 2 females). Haematoxylin and eosin staining (HE) at 3, 5, or 9 days p.i. Br, bronchi; V, vein; Al; alveoli; OB, olfactory bulb; OM, olfactory mucosa. Bars, 50 or 100 µm. Red arrows indicate virus antigens (g, h) The levels of viral RNA (g) and subgenomic viral RNA (h) in the lung homogenates or nasal cavity at different time points after inoculation (n = 4 per group, 2 males and 2 females). Each gene was normalised to that of total RNA. Samples were from the same experiment as those in (g). g left panel: *P = 0.0184; g right panel: *P = 0.0272 and **P = 0.0055; h left panel: *P = 0.0165; h right panel: *P = 0.0221 and ***P = 0.0006 by two-way ANOVA followed by Bonferroni’s multiple comparison test. Data are mean ± SD.