Simian (RRV and SA11) tissue-culture adapted rotaviruses were grown in fetal monkey kidney (MA104) cells in the presence of trypsin, except where noted, as previously described [79, 80] . Where indicated, RRV empty and genome-containing TLPs were purified from MA104 cell lysates by cesium chloride density gradient centrifugation following genetron extraction and pelleting through a sucrose cushion, as previously described [81, 82] . DLPs were created by treating TLPs with 20 nM EDTA, thus removing the outer viral proteins VP4 and VP7, as previously described [32] . Purified viral preparations were dialyzed to remove residual cesium chloride prior to pDC stimulus. A portion of the RRV lysate preparation was inactivated by treatment with 40 mg/ml psoralen, followed by exposure to ultraviolet light for 40 minutes, as described [83] . The inactivation of infectivity and transcriptional activity of the RRV in the psoralen preparations was confirmed by cell culture assay and the elimination of endogenous RNA polymerase activity by in vitro assay. Except where noted, viral preparations were trypsin activated (5 mg/ml) at 37uC for 20-30 minutes prior to pDC infection. Preparations were endotoxinfree, as determined by Limulus amebocyte lysate test (Charles River, Wilmington, MA).