FIG 4.

RRV 2548 type I IFN induction and sensitivity in vitro. L929 cells infected with either RRV-T48 or RRV 2548 at an MOI of 0.1 or transfected with poly(I·C) were sampled at 12 h and 24 h p.i. (A) Type I IFN levels in cell culture medium were determined by IFN bioassay. (B) Type I IFN sensitivities of RRV-T48 and 2548 were assessed by growth inhibition and are presented as described for Fig. 2 except that human IFN-β was used at 0.05, 0.1, or 0.25 ng/ml. Error bars represent ± SEMs from three independent experiments. *, P < 0.05; ***, P < 0.001 using two-way ANOVA with Bonferroni’s post hoc test (A); **, P < 0.01; ***, P < 0.001 using Student’s unpaired t test (B).