Figure 4.

Antibody‐beta2‐glycoprotein I (β2GPI) complexes bind to factor V (FV) with high affinity and have an indirect effect on lupus anticoagulant. 3B7 was immobilized on a microtiter plate and saturated with β2GPI. A, Plates were incubated with purified FV, factor VIII (FVIII), or activated FV (FVa) at the indicated concentrations and binding was assessed with polyclonal antibodies (n = 2). B, Plates were incubated with several dilutions of pooled normal plasma and binding of FV or FVIII was assessed (n = 3). Data were analyzed with non‐linear regression assuming a 1:1 interaction. C, D, Normalized lupus anticoagulant (nLA) ratios were obtained with dilute Russell's viper venom time (dRVVT) screen and confirm reagents in pooled normal plasma supplemented with increasing concentrations of monoclonal anti‐β2GPI (3B7 or 27G7; C) or anti‐prothrombin (28F4 or 3B1; D) antibodies (25, 50, 100, and 150 µg/mL; n = 3). Antibody concentrations were expressed relative to the concentrations of β2GPI or prothrombin in plasma