Effect of HCQ on aCL and anti-β2GPI IgG ELISAs and the LA test. Serum or plasma samples were incubated with HCQ at 1 μg/mL and 1 mg/mL or buffer control overnight at 4°C before the assays. (A) The results of aCL IgG ELISA for sera with elevated aCL IgG levels. Incubation of sera with HCQ significantly decreased the levels of aCL IgG compared with buffer control. The higher HCQ concentration of 1 mg/mL had a greater effect than the lower concentration of the drug. (B) The results of HCQ on anti-β2GPI IgG ELISA. Incubation of sera with HCQ significantly decreased the binding of anti-β2GPI IgG compared with incubation with buffer control. The higher HCQ concentration of 1 mg/mL had a greater effect than the lower concentration of the drug. (C) The results of lupus anticoagulant test for LA-positive plasmas. Incubation of plasmas with HCQ at 1 mg/mL significantly decreased lupus anticoagulant activity compared with the buffer controls and lower concentration of the drug; incubation of plasmas with HCQ at 1 μg/mL showed no significant effect.