Inhibition of uptake of fVIII by dendritic cells by anti-C1 mAbs. (A) Flow cytometric histograms of 10 nM DyLight 650-conjugated recombinant full-length fVIII uptake by human MDDCs in the absence and presence of 80 nM group A anti-C1 mAbs 2A9, F156, and I84, group AB KM33, and group B B136. Anti–factor IX antibody GMA-138 is shown as a control. Representative histograms of untreated (gray) and treated (white) MDDCs displaying the percentage of internalized fVIII in the absence or presence of the anti-C1 mAbs tested are shown. Percentages of fVIII uptake shown in the insets were estimated by the integrated fluorescence beyond the control histogram. (B) Median fluorescence intensities of human MDDCs incubated with increasing concentrations of DyLight 650-conjugated fVIII alone (control) and in the presence of mAbs 2A9, F156, I84, KM33, and B136.