FIG 2.

NSs functions as an antagonist of type I IFN signaling. (A and B) The kinetics of NSs expression during SFTSV infection. HEK293 cells were infected with SFTSV at an MOI of 10. At the indicated times p.i., they were either fixed for immunofluorescence assays (IFA) with the rabbit anti-NSs antiserum (A) or harvested for Western blot (WB) analysis using antibodies against the indicated proteins. β-Actin was detected as the sample loading control. (C) NSs expression inhibits IFN-α-induced activation of the ISRE promoter. HEK293 cells were cotransfected with the reporter plasmids, along with plasmids expressing the indicated viral proteins, or the control plasmid (vector). At 36 h posttransfection, cells were treated with IFN-α (200 U/ml) or left untreated for 18 h and then were harvested for measuring luciferase activities or monitoring protein expression through WB analysis. (D) NSs expression suppresses IFN-α-induced expression of ISGs. HEK293 cells cultured in 24-well plates were transfected with the control plasmid (vector) or the NSs expression plasmid (800 ng per well) and treated with IFN-α (200 u/ml) or left untreated for 10 h. Expression of ISGs was measured by real-time PCR. Graphs show means ± SD (n = 3). IFN-elicited transcriptional induction of all four ISGs was inhibited in cells transfected with the NSs expression plasmid compared with those transfected with the control plasmid (*, P < 0.05; Student's t test).