We have demonstrated that both live and inactivated rhesus rotavirus efficiently stimulate secretion of type I IFN, in addition to many other cytokines, suggesting that transcription of viral nucleic acid is not required for either viral recognition or subsequent cytokine production by primary human pDCs. Conversely, viral replication is required for activation of the IFN response in fibroblasts [62] . Indeed, further analysis of the viral requirements for IFNa induction suggests that pDCs recognize and respond to input rotavirus dsRNA or some degradation product of the rotavirus genome. This is supported by the inability of genome-free TLPs to effect IFNa secretion, indicating that the lack of IFNa induction following VLP-5) stimulus (n = 3-30). *: p = 0.0313; ***: p#0.0002; Wilcoxon signed rank test. (C) IFNa induction and NSP2 production in pDCs exposed to RRV in the presence or absence of neutralizing VP4 (2G4) or VP7 (159) mAb. doi:10.1371/journal.ppat.1000931.g003 stimulus is due to the absence of a nucleic acid ligand and not to the lack of a minor structural protein, such as VP1 or VP3. To our knowledge, this is the first direct demonstration of the requirement for native viral dsRNA in the initiation of an IFNa response from primary human pDCs.