2.1. Virus Strain and Cell Line
The SARS CoV strain used in this study is HKU39849. Foetal monkey kidney cells (FRhK-4) were cultured in minimal essential medium (MEM, Gibco, USA) with 10% foetal calf serum and penicillin streptomycin (Gibco, USA) at 37°C in 5% CO2 and were used for growing stock virus and for titration of viral infectivity [1, 2].