β2GPI complexed with HLA class II molecules shares aPL antibody epitopes with β2GPI complexed with CL. EY2C9 mAb was incubated with β2GPI in the presence or absence of CL at the concentrations indicated and was used for staining cells transfected with β2GPI and HLA-DR7. (A) MFI of the stained cells and (B) relative MFI compared with staining with EY2C9 mAb alone is shown as mean ± standard deviation (SD) of triplicates. Data are representative of at least 3 independent experiments.