TLR9 and viral infectious disease: These data highlight the significance of pDCs and TLR9 signaling in IFN-α secretion during viral infections, as suggested by previous reports (Gurney et al., 2004; Krug et al., 2004; Smit et al., 2006; Wang et al., 2006; Kader et al., 2013; Schijf et al., 2013).