FIG. 6.

Inhibition of SARS-CoV S-mediated infection by sera from SARS patients. (A) Detection of cell-surface-expressed SARS-CoV S protein by SARS patient serum. The SARS-CoV S protein was transiently expressed in 293T cells as described in the legend to Fig. 1. The cells were stained with serum from a convalescent SARS patient, and staining was analyzed by FACS. Results of a representative experiment are shown; similar results were obtained in an independent experiment. (B) Neutralization of S-bearing pseudotypes by sera from SARS patients. Pseudotypes bearing the VSV G or SARS-CoV S protein, which had been normalized to equal luciferase activity upon infection of target cells in the absence of serum, were preincubated for 30 min with serial dilutions of sera from convalescent SARS patients or control serum from a healthy donor. The virus-antibody mixture was incubated with Huh-7 cells for 7 h followed by complete removal of the culture medium. After 72 h, luciferase activity was determined in cell extracts. Each experiment was performed in triplicate; results of one out of two experiments are shown.