Domain mapping of the anti–β₂-GPI mAbs. Monoclonal antibody (5 nM) was mixed with varying concentrations of inhibitor as indicated and tested for binding to intact β₂-GPI in ELISA as described in “Materials and methods.” The names over the panels indicate the domains of β₂-GPI present in the inhibitor being tested. The percent binding remaining is indicated on the y-axis. □, mAb no. 1529; •, mAb no. 1519; ○, mAb no. 1522; ▴, mAb no. 1527.