FIG. 4.

Vaccine and wild-type STAT1^blind viruses do not block STAT1 nuclear translocation. (A, B, C, and D) Confocal microscopy analysis of STAT1 translocation. HeLa.hSLAM cells were infected with either MVvac2 (A), MVvac2.STAT1^blind (B), MVwt (C), or MVwt.STAT1^blind (D). After stimulation with IFN-α cells were fixed, permeabilized, and stained with antibody to N protein (green), STAT1 (red) and counterstained with DAPI (blue). A merge of the three staining is shown. The overlaps of red and green staining yield yellow, and the overlaps of red and blue staining yield pink. Scale bars, 20 μm. We note that MVvac2 and derivated strains form only small syncytia. (E and F) Characteristics of the STAT1-blind virus in IFN-producing or deficient cells infected with the vaccine (E) or wild-type (F) viruses. HeLa and Vero cells expressing hSLAM were infected with recombinant viruses MVvac2 (black symbols) or MVvac.STAT1blind (empty symbols). Virus titers in IFN-deficient cells (Vero, squares) or IFN-producing (HeLa, circles) cells were determined at the time indicated by TCID₅₀ titration. The data are averages of three experiments.