FIG 4.

Kinetics of ChinaGD01 replication and sensitivity to type I interferon in vitro. (A) Vero 81 cells were infected with different MERS-CoV strains at an MOI of 0.1 or 0.01, supernatant was harvested at the indicated time points, and viral titers were determined by plaque assay. Student’s t test was used to analyze differences in mean values between groups. All results are expressed as means ± standard errors of the means (SEM). A P value of <0.05 was considered to be statistically significant (*, P ≤ 0.05; **, P ≤ 0.01). (B) Plaque morphology in Vero 81 cells at day 3 p.i. (C) Plaque size comparison and plaque diameter. NS, not significant. (D) Comparison of infectious viral particle per plaque. Plaques were picked from MERS-CoV-infected Vero 81 cells. Viral titers were determined. (E) Vero 81 and Huh 7 cells in triplicate were treated with the indicated concentrations of human IFN-β 24 h prior to being infected with MERS-CoV ChinaGD01 or EMC/2012 at an MOI of 0.1. Cells were then incubated for another 24 h in the presence of the same concentration of IFN-β, supernatants were harvested, and virus titers were determined by plaque assay in Vero 81 cells. Data are representative of those from two independent experiments.