DDX41 was a crucial DNA sensor in THP-1 cells. (A and B) Total RNA was extracted from THP-1 or HFF cells and used for determining the expression of IFI16 and DDX41 by RT-PCR (A) and qRT-PCR (B), respectively. GAPDH was used as an internal control. (C) THP-1 cells were transfected with siRNA (final concentration of 50 nM) for the knockdown of DDX41 and IFI16 or nonspecific control (si-Ctrl), as indicated. After 24 h of transfection, the effects of knockdown of DDX41 and IFI16 were evaluated by immunoblotting, using GAPDH as a loading control. (D) THP-1 cells were treated with nonspecific control siRNA (si-Ctrl) or siRNA against IFI16 or DDX41, as indicated. After 24 h of treatment, THP-1 cells were transfected with HSV-1 60-mer dsDNA (final concentration of 1 µg/mL) for 8 h, and then the IFN-β mRNA level was determined by qRT-PCR. The values were normalized to GAPDH and standardized to 100% in the control groups, as indicated. Data are the means ± SD (n = 3) from one representative experiment. Similar results were obtained from three independent experiments. ** P < 0.01; *** P < 0.001.