Autoantibodies against β2GPI/HLA class II complex are detected in most APS patients. (A-B) Distribution of serum anti-β2GPI/HLA-DR7 complex antibody titers in APS patients and healthy controls. Anti-β2GPI/HLA-DR7 complex antibody titers higher than the normal upper limit for anti-β2GPI/HLA-DR7 complex antibody titers established by using 100 healthy controls (1.8 U) are indicated as red bars. (C-D) Correlations between serum anti-β2GPI/HLA-DR7 complex antibody titers and serum anti-β2GPI antibody or aCL antibody titers in APS patients. The normal upper limits for anti-β2GPI antibody, aCL antibody, and anti-β2GPI/HLA-DR7 complex antibody titers are shown as dashed lines. Patients whose anti-β2GPI/HLA-DR7 complex antibody titers are higher than the normal upper limit are indicated as red circles. Data are representative of at least 3 independent experiments.