In the present study, we demonstrate that primary human pDCs are largely resistant to rotavirus replication, as intracellular Representative histograms showing pDC activation (C) or maturation (D) following exposure to MA104 supernatant alone (dotted line), CpG 2395 (4 mg/ml; shaded) or RRV (moi 5; bold line). (E-H) To determine whether viral replication affected the pDC response, cells exposed to live RRV were gated based on NSP2 expression. The expression of CD86 (E, G) and CD83 (F, H) by NSP2 + and bystander (NSP2 -) pDCs was subsequently assessed. (E, F) Summary of percent CD86 + (E) or CD83 + (F) pDCs in NSP2 + or bystander pDC populations from multiple donors 12hpi (n = 8-9); p#0.0078; Wilcoxon signed rank test. (G, H) Representative histograms showing pDC activation (G) or maturation (H) of NSP2 + (bold) or NSP2bystander (thin line) pDCs in cultures exposed to RRV (moi 5) or mock stimulus (dotted line). doi:10.1371/journal.ppat.1000931.g002 Figure 3 . Intracellular production of IFNa by pDCs after exposure to live or inactivated RRV. (A) Representative FACS plots of IFNa vs. CD123 expression by pDCs exposed to mock, iRRV or RRV stimulus 2-6hpi (moi 5). (B) Time course of IFNa induction in pDCs after mock or RRV (moi staining for NSP2 was observed in only a small percentage (#5%) of cells following RRV exposure, even at a non-physiologically relevant moi of 100. While productive infection was observed in a subset of donors, this was significantly less than that observed in cells highly permissive for rotavirus infection [53] . As rotavirus is generally a lytic virus [31, 54, 55] , the observed lack of significant death in pDC preparations exposed to live RRV, compared to those receiving mock stimulus or inactivated virus, further indicates that few pDCs are permissive to viral replication. These findings are in agreement with previous reports of low frequencies of pDC infection in virus models such as herpes simplex virus 2 [56] , Dengue [57] , human cytomegalovirus [17] , influenza [58] , HCV [24] and HIV [59] . The inability of the primary human peripheral pDC population to be uniformly infected by rotaviruses may be attributable to multiple factors, including age of the individual pDC, stage of the cell cycle, or cell-surface marker expression. Additionally, functionally-distinct pDC subsets have been recently identified on the basis of CD2 expression [60] ; studies are currently underway to elucidate the role of these subsets in the pDC response to rotavirus.