Ellipsometry studies of the effect of HCQ on binding of aPL IgG and β2GPI complexes to phospholipid bilayers (30% PS/70% PC). (A) Effects of various concentrations of HCQ on the protein binding. A mixture of aPL IgG (0.5 mg/mL) and β2GPI (5 μg/mL) in HBSA was added to phospholipid bilayer. After the adsorption of the protein had reached equilibrium, increasing doses of HCQ (0.001, 0.01, 0.1, 0.2, 0.5, and 1 mg/mL) were serially added. There was a progressive dose-related dissociation of the complexes from the phospholipid bilayers. Each point shows the mean of duplicate experiments. (B) Ellipsometry tracing of aPL IgG (0.5 mg/mL) premixed with β2GPI (5 μg/mL) and incubated with HCQ (1μg/mL) or control buffer overnight at 4°C before addition to the bilayers. The HCQ-treated immune complexes showed reduced binding compared with the buffer-treated complexes. HCQ had no effect on the adsorption of control IgG and β2GPI. (C) Immediate dissociation of phospholipid-bound aPL IgG–β2GPI complexes by HCQ (1 mg/mL). The drug had no significant effect on the adsorption of control IgG and β2GPI. (D) Similar ellipsometry study with the aPL IgG mAb (IS4) and β2GPI. The phospholipid-bound proteins were rapidly dissociated from the phospholipid bilayer by HCQ (1 mg/mL). There was no significant effect of the drug on the adsorption of control mAb and β2GPI.