Fig. 2.

Impact of SARS S processing by TMPRSS2 on cathepsin dependence and neutralization sensitivity. (A) 293T cells engineered to express large amounts of ACE2 were incubated with the indicated concentrations of the cathepsin B/L inhibitor MDL 28170 and inoculated with pseudotypes in triplicate, and luciferase activities were determined at 72 h postinfection. Activities measured in the absence of inhibitor were set as 100%. A representative experiment out of three is shown; error bars indicate standard deviations. In the absence of inhibitor, the following luciferase counts were measured: VSV-G, 55,642 ± 4877 cps; SARS S plus pcDNA3, 64,751 ± 11,505 cps; SARS S plus TMPRSS2, 59,071 ± 5,087 cps; SARS plus TMPRSS4, 94,684 ± 4,576 cps. (B) Equal volumes of pseudotypes bearing SARS S wt were incubated for 60 min with the indicated dilutions of the sera R1 and R1LI1 in triplicate and then added to ACE2-expressing 293T cells. Luciferase activities in cell lysates were determined after 72 h, and activities measured in the absence of serum were set as 100%. The results ± standard deviations of a representative experiment are shown. Similar results were obtained in two independent experiments. In the absence of serum, the following luciferase counts were measured: VSV-G, 9,037,372 ± 33,0551 cps; SARS-S plus pcDNA3, 5,411,448 ± 304,990 cps; SARS-S plus TMPRSS2, 444,923 ± 27,314 cps.