The nonstructural (NS) proteins of RSV, NS1, and NS2 have been shown to inhibit IFN-a and IFN-b production by decreasing proinflammatory transcription factors interferon regulatory factor (IRF)-3, NF-kB, and signal transducers and activators of transcription protein (STAT)-2 (4, 44, 45) . hMPV does not contain NS proteins and has detectable levels of IFN-a in BAL fluid from 6 hours to 5 days after infection, whereas RSV does not have detectable levels at 3 days after infection (46) .