Effect of intact/nicked β2GPI on the proliferation of HAECs in the presence or absence of AS4.5. (A) HAECs were subjected to cell-proliferation assay using tetrazolium/formazan-based method. A total of 5000 HAECs were placed onto each wells of 96-well plate and incubated for 72 hours. The effect of serial concentrations of intact or nicked β2GPI was tested in the presence or absence of 50 nM AS4.5. HAEC proliferation in the presence of AS4.5 alone (50 nM)* was compared with that in the presence of both AS4.5 (50 nM) and nicked β2GPI (0.4 μM; **P = .021; Student t test). (B) Proliferations of HUVECs were tested using the same proliferation assay. (C) HUVEC proliferation was tested in the presence of VEGF. HUVEC proliferation in the presence of AS4.5 alone (50 nM)* was compared with that in the presence of both AS4.5 (50 nM) and nicked β2GPI (0.1 μM; **P = .030; Student t test). Error bars represent SE.