Specificity of viral induction of ISGs. (A) HFFs were incubated with recombinant Type I IFNs (100 units/ml), recombinant HCMV gB (13 μg/ml), or HCMV [Ad169 strain, at a multiplicity of infection (MOI) of 2], and RNA samples were harvested at 2, 8, and 24 h posttreatment. The samples were analyzed by RNase protection with radiolabeled probes to oligo adenylate synthetase (OAS), ISG of 54 kDa (ISG-54), and actin. The protected samples were separated by denaturing gel electrophoresis and detected by using a phosphor imager (GS-525; Bio-Rad). (B) HFF cells were incubated with purified recombinant forms of HSV glycoproteins (gD, gC, and gB, at 13 μg/ml), recombinant Type I IFNs (100 units/ml), HCMV gB (13 μg/ml), and HCMV (MOI = 2) for 8 h. RNase protection analysis using probes to ISG-54 and actin was performed on RNA from treated samples, as described above. The apparent increase in actin signal seen after both HCMV and gB treatments was because of degradation of protected ISG-54 probes, which are more abundant in those samples with elevated ISG-54 message.