FIGURE 3.

Affinity modulation of PECAM-1. A, PECAM-1 nanodiscs were added to HUVECs in the presence of Fab fragments of the indicated antibodies. Fabs from the IgD6-specific mAb, PECAM-1.2 (▴) consistently increased nanodisc binding, while Fabs from the IgD1-specific mAb, PECAM-1.3 (■), inhibited nanodisc binding. Fabs from normal mouse IgG (●) was used as a control. A representative experiment is shown. B, level of nanodisc binding across five independent experiments, performed as in panel A, was normalized to the level of Pnano binding to iHUVECs in the absence of any added mAb. Note that PECAM-1.2 Fabs increased Pnano binding (*, p = 0.03), while PECAM-1.3 Fabs inhibited Pnano binding (**, p = 0.006). Both mAbs were added at a final concentration of 40 μg/ml. Similar augmentation was seen using the IgD6-specific mAb 4G6 (not shown).