Effects of HCQ on aPL IgGs binding to THP-1 monocytes. Incubation of THP-1 monocytes with aPL IgGs resulted in significantly greater IgG binding than incubation with control IgGs. HCQ at both 1 μg/mL and 1 mg/mL significantly reduced the binding of aPL IgGs to levels similar to cells incubated with control IgG. The drug had no effect on the binding of control IgGs to the cells. Error bars represent SD.