MX1 and infection: To study the cytokine response in pangolin-CoV-HKU4-P251T infection, the mRNA expression levels of major antiviral cytokines (IFN-β, IFN-γ, and Mx1), proinflammatory cytokines (IL-2, IL-12p40, and TNF-α), and chemokines (CXCL-1 and G-CSF) in lung samples of infected hDPP4-mice were measured using qRT-PCR assays (Supplementary Table 1) as described previously16.