Conjugate formation capacity by pDCs and cDCs. (A) Expression of MHC class II, costimulatory and adhesion molecules by Flt3-L-derived immature and CpG-matured pDCs and cDCs. The phenotype of immature (gray histogram) or mature (white histogram) pDCs or cDCs was analyzed by 3-color flow cytometry. Dotted lines correspond to the negative control. (B) Immature or CpG-matured pDCs and cDCs were conjugated with OT-II CD4⁺ T cells either in the absence (□) or presence of OVA peptide (10 μg/mL) at 30 minutes (■) or 2 hours (). Cells were allowed to adhere to poly-L-lysine (PLL) and fixed. Results are expressed as the percentage of DCs forming conjugates with T lymphocytes. Data represent the arithmetic mean plus or minus SEM of 5 experiments. ipDC indicates immature pDCs; mpDC, mature pDCs; icDC, immature cDCs; mcDC, mature cDCs. *P < .05 compared with ipDCs.