(A) IFN-β production in SV-40–transformed dermal fibroblasts (SV-40 fibroblasts) left nonstimulated (NS), treated with poly(I:C), or infected with VSV-WT (WT) or VSV-M51R mutant at various MOIs (0.01, 0.1, 1) for 24 hours, as measured by ELISA. C1 is a healthy control. (B) IFN-β mRNA levels in fibroblasts left NS or infected for 24 hours with VSV-WT or -M51R at a MOI of 1. β-glucuronidase mRNA levels were used for normalization. The error bars indicate SD of biological triplicates from 3 independent experiments. P values were obtained for 1-way ANOVA and subsequent Tukey’s multiple comparison tests. (C) dsRNA from VSV-WT– and VSV-M51R–infected fibroblasts, visualized by electrophoresis in 1.5% agar gels, blotting onto nylon membranes and incubation with a monoclonal antibody against dsRNA. Ethidium bromide (EtBr) staining of the agar gel is shown as a loading control. Data from 3 independent experiments are shown. **P < 0.01, ***P < 0.001, ****P < 0.0001.