IFN pre-treatment protects against DENV infection.

(A) IFN-competent A549 cells were treated with 100 IU/ml IFN-α prior to (-4 h, -2 h) or after (2 h, 4 h, 6 h, 8 h) or at the time point of infection (0 h) with the DENV2 strain 16681 at a MOI of 10 TCID50/cell. Cells were fixed 24 h post infection and analyzed by immunofluorescence using a NS5-specific antiserum. Mock-treated and DENV-infected cells without IFN treatment served as reference. (B) Quantification of infection efficiency of cells shown in panel (A). For each time point, 500–1,000 cells detected in 3 view fields were analyzed for DENV infection. Mean values and SDs are shown for each time point (** p-value <0.005). (C) IFN-competent A549 cells were infected with the DENV2 strain 16681 at a MOI of 10 TCID50/cell. Cells were harvested at given time points after infection (h p.i.) and lysates were analyzed by Western blot using STAT2-, E- (DENV envelope protein) and β-actin-specific antisera. A representative immunoblot from 3 independent experiments is shown. Numbers in the left refer to the positions of molecular weight standards in kiloDalton (kDa).