FIG 3.

Function of NSs as an IFN antagonist in human and murine cells. (A) HEK293T or NIH 3T3 cells transfected with the reporter plasmids were mock infected or infected with SFTSV. Two days after infection, cells were lysed to measure luciferase activity and to examine protein expression using immunoblotting. Relative light units (RLU) in mock-infected cells were set as 1. Fold activation by SFTSV infection is indicated. (B) The reporter plasmids were transfected into HEK293T or NIH 3T3 cells with or without the expression plasmid for NSs. Twenty-four h after transfection, cells were treated with IFN-αA/D (500 U/ml) or left untreated for 18 h and then were lysed to measure luciferase activity and detect protein expression using immunoblotting. RLU in cells transfected with the empty vector or the indicated amount of NSs expression plasmid in the absence of IFN-αA/D were set as 1. Fold activation by IFN-αA/D is indicated. (C) The experiment depicted in panel B was repeated using the expression plasmid for mMARV VP40 in NIH 3T3 cells. (D) NSs expression plasmid (1 μg or 1.5 μg) or control plasmid was transfected into HEK293T or NIH 3T3 cells, respectively. Twenty-four h after transfection, the cells were treated with IFN-αA/D (200 U/ml) for 10 h or left untreated. Expression levels of Isg56 and Oas1 mRNAs in each cell line were measured by real-time qPCR. The mRNA expression levels of ISG56 and OAS1 in untreated cells were set as 1. Fold activation by IFN-αA/D is indicated. These assays were independently performed in triplicate. The data represent averages with SDs. **, P < 0.05 versus no NSs.