Kinetics of MHC II and dextran endocytosis in pDCs. Fresh pDCs were exposed to flu for 0, 3, or 24 hours. Cells were then collected and allowed to bind at 0°C with either (A) the Ii chain–specific mAb BU45 or (B) the peptide-bound MHC II specific mAb L243. Cells were then shifted to 37°C for the length of time indicated. Ligands remaining on the cell surface were detected using PE-labeled secondary antibodies. Estimation of the percentages of antibody present at the cell surface was made by flow cytometric analysis of the samples and using the following formula (MFI of each time point/MFI at t = 0) × 100. Data from 3 independent experiments were used to calculate means and SD. (C) Uptake of FITC-dextran. Flow cytometry profiles of the indicated populations of DCs are presented. Cells were activated for 0, 24, or 48 hours and then exposed to FITC-dextran at 37°C for 60 minutes (black lines). As a control, cells were incubated at 0°C during the same time (gray lines). Numbers indicate MFI values. Results presented are representative of 4 independent experiments.