For instance, when 293T cells expressing human ACE2 but not TMPRSS2 were infected with SARS-CoV in the presence of 25 mM NH4Cl, which prevents endosomal acidification and hence blocks Cathepsin B/L, the extent of infection reduced ~40-fold over that in the absence of NH4Cl [29]. The gene discussed is CTSB; the disease is infection.