Anti s2 antibody

To evaluate S protein expression in the cell lysates, HEK293T cells were transfected with plasmids encoding different S proteins. At 40 h post-transfection, the cells were lysed using RIPA lysis buffer containing protease inhibitors. To determine the incorporation of S proteins into the pseudovirions, the pseudovirus-containing supernatant was pelleted through a 20% sucrose cushion at 25,000 rpm at 4 °C for 2 h. Viral pellets were resuspended in 1 × loading buffer. Cell lysates and pseudovirion pellets were separated using 10% sodium dodecyl–sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and transferred to nitrocellulose membranes. The SARS-CoV-2 S proteins were detected with a rabbit polyclonal anti-S2 antibody (Sinobiological Inc., Beijing, China), and the blot was further stained with horseradish peroxidase-conjugated goat anti-rabbit IgG and visualized with Clarity Western ECL substrate (Bio-Rad, Hercules, CA, USA). β-actin and HIV capsid protein (p24) were detected using a mouse monoclonal anti-β-actin antibody (Sigma, St. Louis, MO, USA) and a rabbit polyclonal anti-p24 antibody (Sinobiological Inc., Beijing, China), respectively.