Determination of cell surface expression of wild-type and mutant D1128A S proteins by FACS analysis and determination of wild-type and mutant D1128A S protein incorporation in S-pp by ELISA.

<p>(A) FACS analysis was performed with 293 FT cells were transfected with empty vector (full line) or with plasmids expressing full length wild-type S (dotted line) or full length mutant D1128A S (dash line). Cells were harvested 72 hours post-transfection and stained with mouse mAb 7G12, followed by FITC-conjugated goat anti-mouse antibody. Results shown are representative of 3 independent experiments. (B) Pseudoviral particles not expressing S (pNL43-R-E-Luc virus), S-pp expressing wild-type S (S-WT-pp) and mutant D1128A S (S-D1128A-pp) were coated on a 96-well plate at 16 ng/well, as previously quantitated using P24 ELISA, and detected using mAb 7G12 (top) and mAb P24 (bottom) at 4-fold serial dilutions. Optical density (OD) was measured at 450 nm. Bars represent SD of the experiment carried out in triplicates. MAb P24 was used as a control antibody to ensure equal amounts of S-pp were coated onto each well.