FIG. 4.

(A) IFN activity in supernatants of infected MDBK and HEp-2 cells. Cells were mock infected or infected at an MOI of 0.2 with BRSV wt or BRSV ΔNS1/2. Supernatants were harvested 24, 48, and 72 h postinfection and transferred onto RV-infected MDBK cells. RV titers were determined 2 days postinfection. Error bars indicate standard deviations. (B) IFN-β is expressed in BRSV ΔNS1/2-infected but not in wt BRSV-infected HEp-2 cells. Supernatant proteins were precipitated with TCA, and IFN-β was identified in a Western blot made with a polyclonal anti-human IFN-β serum. RSV N protein in cell extracts and NS2 mRNA in total RNA were demonstrated by Western blotting with an anti-RSV serum and an NS2-specific cDNA hybridization probe, respectively, at 37 h postinfection.