Activation of endothelial cells by rabbit anti-β₂GPI antibodies. Endothelial cells were cultured in 96-well microplates and prepared as described in “Materials and methods.” Cells were then incubated for 4 hours with either medium alone, human β₂GPI (100 nM), rabbit anti–human β₂GPI antibodies (600 nM), β₂GPI (100 nM) and rabbit anti–human β₂GPI antibodies (600 nM), β₂GPI (100 nM) and normal rabbit IgG (NRIgG; 600 nM) or LPS (1 μg/mL). (A) Adhesion of CMFDA-labeled Mono Mac 6 cells, measured in arbitrary fluorescence units (AFUs). (B) Expression of endothelial cell surface E-selectin, measured by ELISA. Error bars represent the mean plus or minus SEM of quadruplicate points. ***P < .0001 versus medium alone. This experiment is representative of 4 so performed.