NK-cell activation is independent of contact with pDCs, but depends upon type I IFN production by activated pDCs.

<p>A—Analysis of NK-cell cytotoxicity following NK-cell activation with TLR9-stimulated pDCs in contact or in trans-wells. Graphs are representative of three independent experiments. B—Blocking of type I IFN signaling was performed using specific blocking mAbs against IFN-α and type I IFN receptor in NK/pDC co-cultures, followed by cytotoxicity assays performed against SK-N-DZ cells. The graph represents the means of three independent experiments, with error bars representing the standard error of the mean. C—Analysis of NK-cell cytotoxicity following NK-cell activation with TLR9-stimulated pDCs (a-pDC) or IFN-α (1000 IU/mL). The IFN-α concentration was comparable to that estimated under both conditions. Specific lysis of SK-N-DZ, SK-N-AS, and SJNB-7 cells are presented for an E:T ratio of 5:1. Statistical analyses were performed using one-way analysis of variance. *<i>p</i> < 0.05, **<i>p</i> < 0.01, ***<i>p</i> < 0.001. E:T, effector against target; IFN, interferon; IL, interleukin; mAb, monoclonal antibody; NK, natural killer; pDC, plasmacytoid dendritic cell; TLR, toll-like receptor.