aPL antibodies and a murine monoclonal anti-β₂GPI antibody (E7) increase carotid artery and peritoneal macrophages TF activity in mice through an interaction with ApoER2. ApoER2^+/+ (filled bars) or ApoER2^−/− (open bars) mice were injected with either IgG-NHS, IgG-APS, IgG MoAbC, or E7. Carotid arteries (A) or peritoneal macrophages (B) were harvested from ApoER2^+/+ or ApoER2^−/− mice, and TF activity in homogenates was determined with a commercial chromogenic assay for Xa formation. At least 3 animals were used per condition. Results are expressed as pM · mg⁻¹ · mL⁻¹ ± SEM. An unpaired t test was applied to examine statistical significance. ¶Statistically different from apoER2^+/+ treated with control; (A) NHS (P = .014) or MuMoAb (P = .003) and (B) NHS (P = .004) or MuMoAb (P = .003). *Statistically different from apoER2^+/+ treated with IgG-APS (A, P = .009 and B, P < .0001) or E7 (A, P < .0001 and B, P = .018). **Statistically different from apoER2^−/− treated with IgG-APS (A, P = < .0001 and B, P = .040) or E7 (A, P = .030 and B, P = .0004).