Endothelial cell αvβ3 integrin is the ligand involved in adhesion of both activated and nonactivated SS RBCs. Adhesion of sham-treated and activated SS RBCs was assayed with and without incubation of nonactivated EC-RF24 cells (A-B) and HUVECs (C) with various mAbs. Panels D-E show adhesion of nontreated SS RBCs to activated EC-RF24 cells. Error bars show SD of 3 different experiments measuring adhesion at a shear stress of 2 dynes/cm² (n = 3 for each of A-E). (A) EC-RF24 cells were incubated without or with 10 μg/mL anti-αvβ3 and αIIbβ3 integrin mAb 7E3, 10 μg/mL anti-αvβ3 integrin mAb LM609, or 10 μg/mL anti-αIIbβ3 integrin mAb 10E5, washed, and then tested for their ability to support adhesion of sham-treated SS RBCs or SS RBCs treated with 0.2 mM IBMX + 176 μM db-cAMP. (B) EC-RF24 cells were incubated without or with 40 μg/mL mAb, 10 μg/mL anti–laminin-10/11 mAb, anti-CD44 mAb, or anti-β1 integrin mAb, and then washed before being tested for their ability to support adhesion of sham-treated SS RBCs or SS RBCs treated with 0.2 mM IBMX + 80 μM forskolin. (C) HUVECs were incubated without mAb or with 10 μg/mL LM609 or 10E5, then washed before being tested for their ability to support adhesion of sham-treated SS RBCs or SS RBCs treated with 20 nM epinephrine for 1 minute. (D) EC-RF24 cells were first activated by exposure to 10 ng/mL TNF-α, incubated with 25 μg/mL recombinant CD44-Fc or LW-Fc protein, and then washed before being tested for their ability to support adhesion of nontreated SS RBCs at a shear stress of 2 dynes/cm². (E) Nontreated SS RBCs were incubated with 10 μg/mL anti-CD44 or anti-LW mAb, washed, and then tested for adhesion to EC-RF24 cells activated with 10 ng/mL TNF-α.