Ellipsometry studies of effects of aPL IgG and cofactor on displacement of annexin-V from PS/PC phospholipid bilayers. (A) Shows the rapid adsorption of annexin-V to the PS/PC (30%/70%) phospholipid bilayer. Treatment with EDTA and measurement of the desorption of this protein can be used to measure the amount of annexin-V on the phospholipid surface. As shown, this calcium-dependent binding protein is completely desorbed from the phospholipid surface by addition of 6 mmol/L EDTA. (B) Shows that incubation of the annexin-V–coated phospholipid bilayer with a polyclonal human aPL IgG in the absence of β₂-GPI does not displace the annexin-V, ie, the quantity of annexin-V desorbed after treatment with EDTA matches the quantity of annexin-V, which had originally adsorbed. (C) Incubation of the annexin-V–coated phospholipid bilayer with β₂-GPI followed by polyclonal aPL IgG results in a significant reduction of the quantity of annexin-V on the bilayer. This is reflected by the marked reduction of the amount of annexin-V, which desorbs after treatment with EDTA. (D) In contrast, treatment of the phospholipid bilayer with the β₂-GPI cofactor followed by a control (non-aPL) IgG fraction does not change the quantity of annexin-V on the phospholipid surface at all, ie, the quantity of annexin-V that is desorbed by treatment with EDTA is the same as the quantity that had been adsorbed in the first place.