Effects of antibodies against PSR and other endothelial adhesion markers on PS-positive erythrocyte adhesion to human lung microendothelial cells. Following incubation of endothelial cells for 6 hours in the presence or absence of IL-1α (10 ng/mL), cell monolayers were pretreated with antibodies against desired adhesion molecule at 40 μg/mL, or an equivalent amount of an isotype-matched negative control immunoglobulin (IgG or IgM) for 45 minutes. The monolayers were then tested for their adhesive potential using PS-positive red cells with 15% PS positivity prepared by treating control erythrocytes with A23187. These adhesion assays were performed using red cells at 10% hematocrit in the absence of plasma and plasma-associated soluble adhesion ligands. Results 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 medium control or the IgM control at P < .01. Please note that to test CD62P or P-selectin–mediated adhesion, endothelial cells were subjected to activation with A23187 for 30 minutes, pretreated with anti-CD62P for 45 minutes, and then assessed for their adhesinogenic potential with PS-positive erythrocytes (see legend to Table 1 and “Results” for additional details).