Specifically, C57BL/6 mice, prone to a Th1-type immune response, and TMPRSS2 KO mice were used for SARS-CoV infection, while transgenic mice expressing the human DPP4 receptor for MERS-CoV (hDPP4-Tg) and hDPP4-Tg KO mice for TMPRSS2 were employed for MERS-CoV infection. The gene discussed is TMPRSS2; the disease is severe acute respiratory syndrome.