To characterize the interaction between pDCs (phenotypically defined as viable lineage -HLA-DR + CD11c -CD123 + cells, Figure  S1 ) and rotavirus, pDCs were purified from human blood by negative selection (mean purity 6 standard error mean [SEM]: 86.48%60.92) and exposed to RRV at a multiplicity of infection (moi) of 5 or 10, or to equivalent quantities of inactivated RRV (iRRV). Expression of NSP2, a viral nonstructural protein expressed only in cells in which rotavirus replicates, was detected by intracellular flow cytometry at 6 and 12 hours post infection (hpi). As illustrated in Figure 1 , NSP2 was not detected in pDCs receiving MA104 supernatant (mock-treated; Figure 1A ) or iRRV (data not shown), but was expressed in a small but significant percentage (mean 6 SEM, moi 5: 1.18%60.23 6hpi, 1.43%60.28 12hpi; moi 10: 1.45%60.25 6hpi, 3.02%60.99 12hpi) of pDCs inoculated with live RRV (Figure 1B and 1D) . Additionally, NSP2 was detected only after pDCs were permeabilized (data not shown). Two populations of NSP2 + cells, NSP2 dim and NSP2 bright , were frequently apparent in pDCs exposed to live RRV ( Figure 1B and 1C) ; approximately 20% of donors had only a single NSP2 dim population. While the total percent of pDCs expressing NSP2 following RRV challenge increased from 6 to 12hpi, this increase was not significant (moi 5: p = 0.77; moi 10: p = 0.30; Mann-Whitney) ( Figure 1D ). The percent of NSP2 + pDCs also increased with moi (6hpi: p = 0.26; 12hpi: p = 0.063; Mann-Whitney), but remained a minor proportion of the total pDC population (median: 2.01%, moi