FIG 2.

Recombinant IFN expression from a bicistronic flavivirus. (A) Vero cells grown in 6-well culture trays (5 × 10⁵ cells/well) were infected with MVEV.IFN-β (IFN-β) or the control virus MVEV.C-IRES (C.IRES) at a multiplicity of 5 PFU per cell. At 24 h p.i., the entire culture supernatant (1 ml) was harvested and replaced with 1 ml of fresh medium, a second harvest was taken at 48 h p.i., and the IFN-β protein concentration in both samples was determined by ELISA. Means from 2 samples ± standard deviations (SD) are presented. (B) Wild-type B6 MEFs in 6-well culture trays (5 × 10⁵ cells/well) were treated for 16 h with 1.5 ml of 10²- or 10³-fold dilutions of UV-inactivated culture fluid that was harvested 48 h p.i. from Vero cells infected with MVEV.IFN-β or MVEV.C-IRES. After this pretreatment, MEFs were infected with Semliki Forest virus (multiplicity of infection of ∼1), and 24 h later, virus yields were measured by plaque titration on Vero cells. Means from 3 samples ± SD are presented.