Type A IgG antibodies recognize plasma-purified β2-GPI in solution only in the presence of cardiolipin. Affinity-purified type A IgG antibodies (20 μg/mL) of patient 1 and patient 2 were coated onto hydrophobic ELISA plates and incubated with plasma-purified β2-GPI, plasma-purified β2-GPI in the presence of cardiolipin vesicles, or plasma β2-GPI in the presence of PS/PC vesicles (20%/80%). Then, the plates were incubated with a polyclonal goat anti-human anti-β2-GPI antibody. Subsequently, the plates were incubated with a rabbit anti-goat peroxidase-labeled antibody. Coloring was performed by using OPD. The obtained optical density was corrected for the optical density obtained with total IgG isolated from pooled plasma from 40 healthy volunteers (incubation with plasma β2-GPI: OD, 0.086; incubation with PS/PC: OD, 0.087; incubation with CL: OD, 0.088).CL indicates cardiolipin vesicles. Error bars represent mean ± SEM of triplicate points.
