APL antibodies exert complement-mediated cytotoxicity against cells expressing β2GPI/HLA-DR7 complexes. Complement-mediated cytotoxicity by (A) aPL antibody (EY2C9 mAb) or (B) control mAb against cells transfected with β2GPI and HLA-DR7 or HLA-DR8. Percentage specific cytotoxicity is shown as mean ± SD of triplicates. Data are representative of 3 independent experiments.