Effects of endothelial activation and modulators of PS interaction on adhesion of PS-positive erythrocytes to human lung microvascular endothelial cells. (A) Effects of endothelial activation on PS-positive erythrocyte adhesion to HLMECs. Endothelial cells were subjected to activation either with hypoxia for 24 hours, or with IL-1α (10 ng/mL), TNF-α (10 ng/mL), or LPS (100 ng/mL) for 6 hours. Monolayers then were tested for their adhesive potential using either PS-negative or PS-positive red cells prepared by treating control erythrocytes with A23187. Adhesion of red cells to unactivated control endothelium (control) also is shown. Values presented are the mean (± SD) from 3 to 12 experiments. Adhesion of test red cells to test endothelium was presented as fold change compared with adhesion of PS-negative red cells to unactivated endothelial cells. *Values significantly different from the respective controls at P < .05 to P < .001. (B) Effects of liposomes, serine phosphates, and annexin-V on erythrocyte adhesion to HLMECs. Following activation of endothelial cells for 6 hours with IL-1α (10 ng/mL), cell monolayers were preincubated in the presence or the absence of PC liposomes (PCL), or PS liposomes (PSL) containing 30 μM total phospholipid, 100 μM serine-l-phosphate (SLP), or 100 μM serine-d-phosphate (SDP) for 45 minutes. Monolayers then were tested for their adhesive potential in the presence of appropriate modulator using red cells pretreated for 45 minutes with appropriate inhibitor. In experiments assessing the effects of annexin-V (ANV), PS-positive erythrocytes (used at 2.5% hematocrit) were pretreated with 300 μg annexin-V/mL for 45 minutes, and then tested for their adhesive potential. Values presented are the mean (± SD) from 3 to 7 experiments. Adhesion of test red cells to test endothelium was presented as fold change compared with adhesion of PS-negative red cells to unactivated endothelial cells. *Values significantly different from the respective controls at P < .05 to P < .01.