Nicked β2GPI suppresses the antiangiogenesis effect of AS4.5 in in vivo angiogenesis assay. Directed in vivo angiogenesis assay was performed. Semiclosed surgical silicone tubings (angioreactors) were prefilled with extracellular matrices containing VEGF and FGF alone, VEGF, FGF, and AS4.5, or VEGF, FGF, AS4.5, plus various concentrations of nicked β2GPI, then implanted subcutaneously into the dorsal flank of athymic nude mice. Blood vessels generated in the angioreactors were quantified by staining of the recovered cell pellets with fluorescein isothiocyanate-lectin. Error bars represent SE. *Fluorescence values in the presence of AS4.5 (0.2 μM) alone were compared with those in the presence of both AS4.5 and nicked β2GPI (0.4 μM) by Student t test (P = .01).