IRF3 and viral infectious disease: In the experiments shown in Fig. 1 and below, we used naive A549, A549/Npro, and A549/shIFIT1 cells; naive A549 cells can produce and respond to IFN in response to virus infection, and A549/Npro cells respond to exogenous IFN but cannot produce IFN as they constitutively express Npro from bovine viral diarrhea virus (BVDV), which targets IRF-3 for degradation (43).