Western blot analysis
Lysates of cells or filtered supernatants containing pseudoviruses were separated by SDS–PAGE, followed by transfer to a nitrocellulose membrane (Millipore,USA). For detection of S protein, the membrane was incubated with anti-HA tag mouse monoclonal antibody (bimake, USA, 1:2000), and the bound antibodies were detected by Horseradish Peroxidase (HRP)-conjugated goat anti-mouse IgG (Abbkine, China, 1:5,000). For detection of HIV-1 p24 in supernatants, monoclonal antibody against HIV p24 (p24 MAb) was used as the primary antibody at a dilution of 1:8,000, followed by incubation with HRP-conjugated goat anti-mouse IgG at the same dilution. To detect the expression of 20 ACE2s in HeLa cells, Mouse anti-His tag monoclonal antibody (Bioworld, USA, 1:5000) was used as the first antibody, followed by incubation with HRP-conjugated goat anti-mouse IgG at the same dilution.