Inhibition and competition of RGD-erythrocytes and lactadherin-erythrocytes for binding and uptake by HUVECs. (A) HUVECs were preincubated with wortmannin (50 nM) and cytochalasin D (10 μM) for 30 minutes followed by 1-hour incubation with PKH-26–labeled RGD-erythrocytes and lactadherin (LA)–erythrocytes. Both RGD-erythrocytes and LA-erythrocytes show the same inhibitor profile, indicating that both are processed by the same internalization route (values mean ± SEM). (B) Lactadherin-erythrocytes were PKH-26 labeled and added to HUVECs in presence of an equal volume (1:1 vol/vol) of unlabeled RAD- or RGD-erythrocytes. After 1-hour incubation at 37°C, samples were removed and wells were washed. Next, cells were detached with trypsin/EDTA and measured by FACS. Percentage of maximum inhibition was calculated and expressed as mean plus or minus SEM.