FIG. 5.
A soluble, catalytically inactive form of ACE2 potently inhibits S-protein-mediated infection. (A) HEK293T cells stably expressing ACE2 were infected with 2 × 105 cpm of [32P] reverse transcriptase activity of SH-2-pseudotyped SIV-GFP (diamonds and circles) or of virus lacking any fusion protein (squares) in the presence of the indicated concentrations of ACE2-NN-Ig (circles and squares) or S1(12-327)-Ig (diamonds). Forty-eight hours postinfection, GFP fluorescence was measured by flow cytometry. (B) SARS-CoV (circles and triangles) or medium alone (squares) was preincubated with the indicated concentrations of ACE2-NN-Ig (circles and squares) or BSA (triangles) before infection of Vero E6 cells. Cell viability was determined by staining with a dye (CellTiter96) active in living cells and measuring optical density at 492 nm. Zero points for BSA and ACE2-NN-Ig are included for clarity and extrapolated from the average of BSA values. The experiment is representative of two with quantitatively similar results.