icSARS-CoV and icSARS-ORF7abΔ-CoV infection of cells with and without BST-2 expression. (A and B) HEK293T/ACE2 cells were transfected with pCAGGS carrying BST-2–Flag or a control plasmid. At 24 h posttransfection, HEK293T/ACE2 cells were infected with icSARS-CoV (A) or icSARS-ORF7abΔ-CoV (B) at an MOI of 0.1. Supernatant and cell lysate were taken at 12, 24, and 36 h postinfection. The virus titer in supernatants taken at 12, 24, and 36 h was determined. (C and D) RNA extracted from icSARS-CoV- and icSARS-ORF7abΔ-CoV-infected HEK293T/ACE2 cells was analyzed by real-time PCR for genomic RNA (C) or leader-containing N mRNA (D) levels as a signature of replicating virus. *, significant at a P value of <0.05; **, significant at a P value of <0.01; ***, significant at a P value of <0.001. The data shown are representative of those from two independent experiments.