IRF3 and viral infectious disease: Based on results obtained with viral infections of cell lines, IFN-β and IFN-α4 (and presumably also IFN-α5) act as immediate-early IFNs that are elicited by activation of the transcription factor interferon-regulatory factor (IRF)-3 and IRF-7 and account for the subsequent amplification of the type I IFN response via crosslinking of IFNAR (41).