SLR14-mediated disease prevention and antiviral control rely on IFN-I signaling. (A and B) Experimental scheme. K18-hACE2 mice were i.v. administered with 15 µg SLR14 or vehicle. 3 h after injection, BALF and lung tissues were collected for IFN-I ELISA (A) and RT-qPCR (B), respectively. (C–M) Experimental scheme. K18-hACE2 mice were intranasally infected with 10³ PFU SARS-CoV-2 (2019n-CoV/USA_WA1/2020). 2 h before infection, 15 µg SLR14 or vehicle was i.v. administered. 24 h before SLR14 injection, half of the SLR14-treated mice were additionally given 2 mg anti-IFNAR antibodies. Weight loss and survival were monitored daily up to 14 DPI. In a separate cohort, lung and trachea tissues were collected for virological analysis 3, 6, and 8 DPI. Nasal washes and brain tissues were collected for virological analysis at 8 DPI. (C–E) Weight loss and survival of K18-hACE2 mice treated with vehicle + PBS, SLR14 + PBS, or SLR14 + αIFNAR from 1 to 14 DPI. (F–H) Measurement of vRNA in the lung parenchyma 3, 6, and 8 DPI by RT-qPCR using the CDCN2 primer-probe set. (I–K) Measurement of vRNA in the trachea 3, 6, and 8 DPI by RT-qPCR using the CDCN2 primer-probe set. (L and M) Measurement of vRNA in the nasal wash (L) or the brain (M) 8 DPI by RT-qPCR using the CDCN2 primer-probe set. (N) The experimental scheme was similar to that of Fig. 2, C–M, with the exception that mice were infected with a sublethal dose of SARS-CoV-2. Sera were then collected from survivor mice 14 DPI and used for anti–SARS-CoV-2 S1 IgG measurement by ELISA. Mean ± SEM; statistical significance was calculated by two-way ANOVA followed by Bonferroni correction (A and B), log-rank Mantel–Cox test (E), or one-way ANOVA followed by Tukey correction (F–M); *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001. Data are pooled from or representative of two independent experiments.