MX1 and influenza: Plasmacytoid dendritic cells are known to produce much of the initial IFN-α (Ito et al., 2005; Liu, 2005), and it is thought that the autocrine action of IFN-α on the pDCs upregulates antiviral factors such as Mx1 and thus protects against influenza infection (Cella et al., 1999).