BSG and susceptibility to pneumonia measurement: All the results indicate that SARS-CoV-2 infection via CD147 induces stronger innate and adaptive immune responses, which may explain the decreased viral titer in lung tissues of hCD147 mouse at 6 d.p.i. Based on the observed different pneumonia phenotypes between SARS-CoV-2-infected hCD147 and hACE2 mouse models at 2 d.p.i., we assume a different immune response between the two mouse models at the initiation of virus infection.