MoDCs, but not LCs, activate NK cells directly, whereas DDC-IDCs are intermediate in activity. Size (forward scatter [FSC]), granularity (side scatter [SSC]), and surface expression of the CD56 and CD16 epitopes were quantified by flow cytometry. FSC and SSC were measured on purified NK cells stimulated for 7 days by Langerhans cells (LC), dermal-interstitial DCs (DDC-IDC), and monocyte-derived DCs (moDC), all at an NK-cell-DC ratio of 10:1. CD56 and CD16 expression was quantified on gated CD3^- lymphocytes, which lacked autofluorescence in channel FL-3 and were located in the FSC/SSC lymphocyte gate (dotted line). Percentages indicate NK blasts, CD16^-CD56^bright, CD16⁺CD56^bright, and CD16⁺CD56^dim cells. The phenotype of NK cells directly isolated from blood before DC stimulation is shown at the far left. This could not be shown at 7 days without DC stimulation, because NK cells die when cultured at high purity without stimulation or cytokines. Note that most peripheral blood NK cells are CD56^dim but not CD56^- directly after isolation from PBMCs. LCs remained more viable (high FSC/SSC; top right corner of dot plot) in these cocultures with NK cells than did either DDC-IDCs or moDCs. The data are representative of 7 independent experiments.