Study of antigenicity of β2GPI–PF4 complex. Coated plates either with β2GPI alone (10 μg/mL) or with β2GPI + PF4 (10 μg/mL and 2 μg/mL, respectively) were incubated with sera from patients with APS (n = 10). After the addition of secondary antibody, OD values were measured at 410 nm.