Internalization of cell surface CD63 does not accompany FITC-Dx endocytosis. Endocytosis of FITC-Dx (one mg/mL) and CD63 cell-surface expression were assessed as described in “Materials and methods.” Anti-CD63 FC-5.01 and anti-CD81 Mabs binding to control DCs (FL2: phycoerythrin fluorescence) is shown in the left panels. Binding of anti-CD63 Mab and of anti-CD81 Mab (FL2) to DCs incubated with FITC-Dx (FL1: FITC fluorescence) in the absence or presence of α-mannan is shown on center right and center left panels, respectively. Binding of isotype-matched control immunoglobulins are indicated in the upper and lower right panels. Control DCs were not incubated with FITC-Dx. Binding of FITC-Dx at 4°C is indicated in the right panel. In total, 10 000 events were analyzed. FITC-Dx endocytosis was confirmed by confocal microscopy (data not shown). The dot plots shown are representative of at least 5 experiments.