Further, infection with the SARS-CoV-2 Beta variant lead to a marked infiltration of lymphocytes, neutrophils and macrophages into the lungs of wt, but not TMPRSS2 KO mice; meanwhile, infection-mediated infiltration, measured for wt and TMPRSS2 KO mice, were within the background range (Figure 4A,C–E). Here, TMPRSS2 is linked to infection.