FIG. 3.

Expression levels of IFN-α (a) and -β (b) protein in A549 cells infected with wt rA2, ΔNS1, ΔNS2, ΔNS1/2, or HPIV3. Expression levels of IFN-α and -β were measured by using, respectively, the Human Interferon-α Multi-Species ELISA kit (PBL Biomedical Laboratories) or the Human Interferon-β ELISA kit (Biosource International) and were calibrated by using standard curves generated from international standards for IFN-α or -β, as designated by the National Institutes of Health (PBL Biomedical Laboratories).