It is well understood that pDCs activate natural killer cells [15] , macrophages [15, 16] and T and B cells [17, 18] , presumably, in part, through IFNa stimulus. Recent evidence suggests that pDCs may have additional antiviral effects, including the direct inhibition of viral replication in target cells secondary to the secretion of type I IFN [19, 20, 21] . pDCs are also implicated in restricting viral replication in vivo, as there is an inverse correlation between circulating pDC numbers and human immunodeficiency virus (HIV) or hepatitis C virus (HCV) viral load [22, 23, 24, 25] .