PDCs and CD11c⁺ DCs both induce extensive HCMV-dependent proliferation but different cytokine profiles in CD4⁺ memory T cells. PDCs or CD11c⁺ DCs were cocultured with autologous CFSE-labeled purified CD4⁺ T cells in the presence of HCMV (MOI of 5) or mock, as indicated. On day 6.5, accumulated proliferation was measured by flow cytometry as the percentage of CFSE^low cells, gated on CD3⁺CD123⁻ (PDC cultures) or CD3⁺CD11c⁻ (CD11c⁺ DC cultures) cells. A representative experiment is shown in panel A. Proliferation was HCMV-dependent in cells from HCMV seropositive individuals (A-B) and was lower in cocultures with PDCs than with CD11c⁺ DCs (B; n = 7, *P < .001 relative to mock, **P < .05 relative to CD11c⁺ DC cultures). Only minor responses were observed in seronegative individuals (B; n = 3). Supernatants from the cocultures described in panels A and B were harvested following stimulation with HCMV on day 6.5 (C), or at 12, 24, and 48 hours (D). Cytokines were measured with CBA. (C) The IL-10 levels were 8.8 ± 2.2-fold higher in cultures with PDCs than with CD11c⁺ DCs, whereas the amounts of IFN-γ were 5.7 ± 1.6-fold higher in the cocultures containing CD11c⁺ DCs as opposed to PDCs (n = 12, *P < .05). (D) IL-10 was detected at 24 hours in the PDC cocultures, whereas IFN-γ was detected at 12 hours in the CD11c⁺ DC cocultures. One representative experiment of 2 is shown. (E) Cytokine production was measured by flow cytometry at the single-cell level in CD3⁺ T cells from DC–T-cell cocultures 24 hours subsequent to HCMV stimulation. One representative experiment of 3 is shown. Means and SEM are indicated in panels B and C.