Annexin-V binding to microtiter plates coated with phosphatidyl serine (PS). PS-coated microtiter plate wells treated with aPL plasmas bound significantly less biotin-labeled annexin-V than PS-coated microtiter plate wells, which had been treated with control plasmas. Annexin-V was detected by addition of phosphatase-labeled streptavidin followed by p-nitrophenyl phosphate substrate. The mean OD (±SEM) of the aPL plasma-treated wells was 0.085 ± 0.003 and 0.123 ± 0.005 for the wells treated with control plasmas (n = 10 for each group, P < .0001).