PEGylated Domain I of Beta-2-Glycoprotein I Inhibits Thrombosis in a Chronic Mouse Model of the Antiphospholipid Syndrome.

Antiphospholipid syndrome (APS) is an autoimmune disorder in which autoantibodies cause clinical effects of vascular thrombosis and pregnancy morbidity. The only evidence-based treatments are anticoagulant medications such as warfarin and heparin. These medications have a number of disadvantages, notably risk of haemorrhage. Therefore, there is a pressing need to develop new, more focused treatments that target the actual pathogenic disease process in APS. The pathogenic antibodies exert their effects by interacting with phospholipid-binding proteins, of which the most important is beta-2-glycoprotein I. This protein has five domains, of which the N-terminal Domain I (DI) is the main site for binding of pathogenic autoantibodies. We previously demonstrated bacterial expression of human DI and showed that this product could inhibit the ability of IgG from patients with APS (APS-IgG) to promote thrombosis in a mouse model. Since DI is a small 7kDa protein, its serum half-life would be too short to be therapeutically useful. We therefore used site-specific chemical addition of polyethylene glycol (PEG) to produce a larger variant of DI (PEG-DI) and showed that PEG-DI was equally effective as the non-PEGylated DI in inhibiting thrombosis caused by passive transfer of APS-IgG in mice. In this paper, we have used a mouse model that reflects human APS much more closely than the passive transfer of APS-IgG. In this model, the mice are immunized with human beta-2-glycoprotein I and develop endogenous anti-beta-2-glycoprotein I antibodies. When submitted to a pinch stimulus at the femoral vein, these mice develop clots. Our results show that PEG-DI inhibits production of thromboses in this model and also reduces expression of tissue factor in the aortas of the mice. No toxicity was seen in mice that received PEG-DI. Therefore, these results provide further evidence supporting possible efficacy of PEG-DI as a potential treatment for APS.

Comparison of real world and core laboratory lupus anticoagulant results from the Antiphospholipid Syndrome Alliance for Clinical Trials and International Networking (APS ACTION) clinical database and repository.

BACKGROUND: Variability remains a challenge in lupus anticoagulant (LA) testing. OBJECTIVE: To validate LA test performance between Antiphospholipid Syndrome Alliance for Clinical Trials and International Networking (APS ACTION) Core laboratories and examine agreement in LA status between Core and local/hospital laboratories contributing patients to this prospective registry. METHODS: Five Core laboratories used the same reagents, analyzer type, protocols, and characterized samples for LA validation. Non-anticoagulated registry samples were retested at the corresponding regional Core laboratories and anticoagulated samples at a single Core laboratory. Categorical agreement and discrepancies in LA status between Core and local/hospital laboratories were analyzed. RESULTS: Clotting times for the reference/characterized plasmas used for normalized ratios were similar between Core laboratories (CV <4%); precision and agreement for LA positive/negative plasma were similar (all CV ≤5%) in the four laboratories that completed both parts of the validation exercise; 418 registry samples underwent LA testing. Agreement for LA positive/negative status between Core and local/hospital laboratories was observed in 87% (115/132) non-anticoagulated and 77% (183/237) anticoagulated samples. However, 28.7% (120/418) of samples showed discordance between the Core and local/hospital laboratories or equivocal LA results. Some of the results of the local/hospital laboratories might have been unreliable in 24.7% (41/166) and 23% (58/252) of the total non-anticoagulated and anticoagulated samples, respectively. Equivocal results by the Core laboratory might have also contributed to discordance. CONCLUSIONS: Laboratories can achieve good agreement in LA performance by use of the same reagents, analyzer type, and protocols. The standardized Core laboratory results underpin accurate interpretation of APS ACTION clinical data.

Oral administration of Domain-I of beta-2glycoprotein-I induces immunological tolerance in experimental murine antiphospholipid syndrome.

It is well established that the humoral immunity in antiphospholipid syndrome (APS) is presented by circulating pathogenic anti-ß2GPI autoantibodies targeting mainly domain I of the ß2GPI protein, playing a major role in the disease pathogenesis. Previously, we have demonstrated that treatment of experimental APS mice with tolerogenic dendritic cells loaded with domain-I was more efficient in tolerance induction than with the whole molecule or domain-V. In the current study we had orally administered a domain-I derivative of the ß2GPI molecule, as a new therapeutic approach to induce oral tolerance in this mouse model of APS. BALB/c mice immunized with ß2GPI, were fed with either domain-I, domain-V derivative or the complete ß2GPI protein. ß2GPI immunized mice developed experimental APS which were fed with domain-I significantly had decreased fetal loss (p < 0.004), a lower size of thrombi (p < 0.001) and lower circulating anti-ß2GPI Abs in comparison to mice fed with domain-V or PBS (p < 0.002). Likewise, Domain-I fed mice had a lowered inflammatory response, exhibited by decreased expression of inflammatory cytokines (IFNγ, IL-6, IL-17) and elevated production of IL-10 anti-inflammatory cytokine by splenocytes. Moreover, the anti-inflammatory response in the domain-I fed APS mice was associated with increased circulating miRNA variations (155, 146, 182, 98) by RT-PCR, which are associated with immunomodulation of the immune network. We propose that oral tolerance with domain-I can be a novel therapy for patients with APS.

PEGylated Domain I of Beta-2-Glycoprotein I Inhibits the Binding, Coagulopathic, and Thrombogenic Properties of IgG From Patients With the Antiphospholipid Syndrome.

APS is an autoimmune disease in which antiphospholipid antibodies (aPL) cause vascular thrombosis and pregnancy morbidity. In patients with APS, aPL exert pathogenic actions by binding serum beta-2-glycoprotein I (ß2GPI) via its N-terminal domain I (DI). We previously showed that bacterially-expressed recombinant DI inhibits biological actions of IgG derived from serum of patients with APS (APS-IgG). DI is too small (7 kDa) to be a viable therapeutic agent. Addition of polyethylene glycol (PEGylation) to small molecules enhances the serum half-life, reduces proteolytic targeting and can decrease immunogenicity. It is a common method of tailoring pharmacokinetic parameters and has been used in the production of many therapies in the clinic. However, PEGylation of molecules may reduce their biological activity, and the size of the PEG group can alter the balance between activity and half-life extension. Here we achieve production of site-specific PEGylation of recombinant DI (PEG-DI) and describe the activities in vitro and in vivo of three variants with different size PEG groups. All variants were able to inhibit APS-IgG from: binding to whole ß2GPI in ELISA, altering the clotting properties of human plasma and promoting thrombosis and tissue factor expression in mice. These findings provide an important step on the path to developing DI into a first-in-class therapeutic in APS.

Performance Evaluation and Clinical Associations of Immunoassays That Detect Antibodies to Negatively Charged Phospholipids Other Than Cardiolipin.

OBJECTIVES: We evaluate the performance characteristics of antiphosphatidylserine (anti-PS), antiphosphatidylinositol (anti-PI), and antiphospholipid mixture (APhL) enzyme-linked immunosorbent assays (ELISAs) compared with anticardiolipin (aCL) and anti-ß2 glycoprotein I (anti-ß2GPI) in a large group of patients with antiphospholipid (aPL)-related diseases. METHODS: Serum samples from 548 patients from the Hopkins and Jamaican systemic lupus erythematosus cohorts, the PROMISSE cohort, and the Antiphospholipid Standardization Laboratory were examined for immunoglobulin G (IgG)/immunoglobulin M (IgM) positivity in aCL, anti-ß2GPI, anti-PS, anti-PI, and APhL ELISA assays. RESULTS: All IgG assays were associated with one or more thrombotic and/or obstetric manifestations, with an increased risk associated with higher antibody titers. Analytical performance was similar among assays, but IgG assays performed better than IgM counterparts. CONCLUSIONS: Increasing titers of APhL, anti-PS, and anti-PI antibodies could indicate an increased risk of thrombotic and/or obstetric aPL-related manifestations. These assays may be promising biomarkers for particular APS manifestations.

Major Histocompatibility Complex Class II Alleles Influence Induction of Pathogenic Antiphospholipid Antibodies in a Mouse Model of Thrombosis.

OBJECTIVE: Both environmental and genetic factors are important in the development of antiphospholipid antibodies (aPL) in patients with antiphospholipid syndrome (APS). Currently, the only available data on predisposing genetic factors have been obtained from epidemiologic studies, without mechanistic evidence. Therefore, we studied the influence of major histocompatibility complex (MHC) class II alleles on the production of aPL in a mouse model of APS. METHODS: Three groups of mice, MHC class II-deficient (MHCII-/- ) mice, MHCII-/- mice transgenic for human HLA-DQ6 (DQ6), DQ8, or DR4 alleles, and the corresponding wild-type (WT) mouse strains were immunized; half were immunized with human ß2 -glycoprotein I (ß2 GPI), and the other half were immunized with control ovalbumin (OVA) protein. Thrombus formation in vivo, tissue factor activity in carotid and peritoneal macrophages, and serum levels of tumor necrosis factor (TNF), IgG anticardiolipin (aCL), antibodies, and anti-OVA antibodies were determined. RESULTS: Immunization with ß2 GPI induced significant production of aCL and anti-ß2 GPI in WT mice compared with control mice immunized with OVA (P < 0.001) but diminished aCL (P < 0.001) and anti-ß2 GPI (P = 0.016) production in MHCII-/- mice. Anti-ß2 GPI production was fully restored in DQ6 and DQ8 mice, while levels of anti-ß2 GPI in DR4 mice and aCL in all transgenic lines were only partially restored (P < 0.001 to P < 0.046). Thrombus size in WT mice was twice that in MHCII-/- mice (P < 0.001) but similar to that in all transgenic lines. Carotid and peritoneal macrophage tissue factor levels decreased by >50% in MHCII-/- mice compared with wild-type B6 mice and were restored in DQ8 mice but not DR4 mice or DQ6 mice. TNF levels decreased 4-fold in MHCII-/- mice (P < 0.001) and were not restored in transgenic mice. CONCLUSION: Our mechanistic study is the first to show that MHC class II alleles influence not only quantitative aPL production but also the pathogenic capacity of induced aPL.

Proof-of-concept study demonstrating the pathogenicity of affinity-purified IgG antibodies directed to domain I of ß2-glycoprotein I in a mouse model of anti-phospholipid antibody-induced thrombosis.

OBJECTIVE: IgG aPL against domain I of ß2-glycoprotein I (ß2GPI) [anti-DI (aDI)] is associated with the pathogenesis of APS, an autoimmune disease defined by thrombosis and pregnancy morbidity. To date, however, no study has demonstrated direct pathogenicity of IgG aDI in vivo. In this proof-of-concept study, we designed a novel system to affinity purify polyclonal aDI aPL in order to assess its prothrombotic ability in a well-characterized mouse microcirculation model for APS. METHODS: Two polyclonal IgG fractions were isolated from serum of a patient with APS, both with high aPL activity but differing in aDI activity (aDI-rich and aDI-poor). These IgG fractions were tested for their pathogenic ability in an in vivo mouse model of thrombosis. Male CD1 mice were injected intraperitoneally with either aDI-rich or aDI-poor IgG; as a control, IgG isolated from healthy serum was used. A pinch injury was applied to the right femoral vein and thrombus dynamics and tissue factor activity in isolated tissue were evaluated. RESULTS: Both aDI-rich and aDI-poor IgG retained aCL and anti-ß2GPI activity, while only aDI-rich IgG displayed high aDI activity, as defined by our in-house cut-offs for positivity in each assay. aDI-rich IgG induced significantly larger thrombi in vivo compared with aDI-poor IgG (P < 0.0001). Similarly, aDI-rich IgG significantly enhanced the procoagulant activity of carotid artery endothelium and peritoneal macrophages isolated from experimental animals (P < 0.01). CONCLUSION: These data directly demonstrate that the ability to cause thrombosis in vivo is concentrated in the aDI fraction of aPL.

Value of isolated IgA anti-ß2 -glycoprotein I positivity in the diagnosis of the antiphospholipid syndrome.

OBJECTIVE: To examine the prevalence of isolated IgA anti-ß2 -glycoprotein I (anti-ß2 GPI) positivity and the association of these antibodies, and a subgroup that bind specifically to domain IV/V of ß2 GPI, with clinical manifestations of the antiphospholipid syndrome (APS) in 3 patient groups and to evaluate the pathogenicity of IgA anti-ß2 GPI in a mouse model of thrombosis. METHODS: Patients with systemic lupus erythematosus (SLE) from a multiethnic, multicenter cohort (LUpus in MInorities, NAture versus nurture [LUMINA]) (n = 558), patients with SLE from the Hopkins Lupus Cohort (n = 215), and serum samples referred to the Antiphospholipid Standardization Laboratory (APLS) (n = 5,098) were evaluated. IgA anti-ß2 GPI titers and binding to domain IV/V of ß2 GPI were examined by enzyme-linked immunosorbent assay (ELISA). CD1 mice were inoculated with purified IgA anti-ß2 GPI antibodies, and surgical procedures and ELISAs were performed to evaluate thrombus development and tissue factor (TF) activity. RESULTS: A total of 198 patients were found to be positive for IgA anti-ß2 GPI isotype, and 57 patients were positive exclusively for IgA anti-ß2 GPI antibodies. Of these, 13 of 23 patients (56.5%) in the LUMINA cohort, 17 of 17 patients (100%) in the Hopkins cohort, and 10 of 17 patients (58.9%) referred to APLS had at least one APS-related clinical manifestation. Fifty-four percent of all the IgA anti-ß2 GPI-positive serum samples reacted with domain IV/V of anti-ß2 GPI, and 77% of those had clinical features of APS. Isolated IgA anti-ß2 GPI positivity was associated with an increased risk of arterial thrombosis (P < 0.001), venous thrombosis (P = 0.015), and all thrombosis (P < 0.001). The association between isolated IgA anti-ß2 GPI and arterial thrombosis (P = 0.0003) and all thrombosis (P = 0.0003) remained significant after adjusting for other risk factors for thrombosis. In vivo mouse studies demonstrated that IgA anti-ß2 GPI antibodies induced significantly larger thrombi and higher TF levels compared to controls. CONCLUSION: Isolated IgA anti-ß2 GPI-positive titers may identify additional patients with clinical features of APS. Testing for these antibodies when other antiphospholipid tests are negative and APS is suspected is recommended. IgA anti-ß2 GPI antibodies directed to domain IV/V of ß2 GPI represent an important subgroup of clinically relevant antiphospholipids.

Apolipoprotein E receptor 2 is involved in the thrombotic complications in a murine model of the antiphospholipid syndrome.

Antiphospholipid (aPL)/anti-ß(2) glycoprotein I (anti-ß(2)GPI) antibodies stimulates tissue factor (TF) expression within vasculature and in blood cells, thereby leading to increased thrombosis. Several cellular receptors have been proposed to mediate these effects, but no convincing evidence for the involvement of a specific one has been provided. We investigated the role of Apolipoprotein E receptor 2 (ApoER2') on the pathogenic effects of a patient-derived polyclonal aPL IgG preparation (IgG-APS), a murine anti-ß(2)GPI monoclonal antibody (E7) and of a constructed dimeric ß(2)GPI I (dimer), which in vitro mimics ß(2)GPI-antibody immune complexes, using an animal model of thrombosis, and ApoER2-deficient (-/-) mice. In wild type mice, IgG-APS, E7 and the dimer increased thrombus formation, carotid artery TF activity as well as peritoneal macrophage TF activity/expression. Those pathogenic effects were significantly reduced in ApoER2 (-/-) mice. In addition, those effects induced by the IgG-APS, by E7 and by the dimer were inhibited by treatment of wild-type mice with soluble binding domain 1 of ApoER2 (sBD1). Altogether these data show that ApoER2 is involved in pathogenesis of antiphospholipids antibodies.

Statins for the treatment of antiphospholipid syndrome?

Fluvastatin has been shown to revert proinflammatory/prothrombotic effects of antiphospholipid antibodies (aPL) in vitro and in mice. Here, we examined whether fluvastatin affects the levels of proinflammatory/prothrombotic markers in antiphospholipid syndrome (APS) patients. Vascular endothelial growth factor (VEGF), soluble tissue factor (sTF), tumor necrosis factor-alpha (TNF-alpha), soluble intercellular adhesion molecule-1 (sICAM-1), sE-selectin (E-sel), C-reactive protein (CRP), and soluble vascular cell adhesion molecule (sVCAM-1), were measured in the sera of 93 APS patients and 60 controls and in the sera of nine patients with APS before and after 30 days of treatment with fluvastatin. Elevated levels of VEGF, sTF, and TNF-alpha were found in APS patients. Fluvastatin significantly reduced those markers in the majority of treated subjects. The data from this study show that statins may be beneficial in aPL-positive patients and warrant larger clinical trials to confirm the efficacy of the drug for the treatment of APS clinical manifestations.

Annexin A2 is involved in antiphospholipid antibody-mediated pathogenic effects in vitro and in vivo.

Antiphospholipid (aPL) antibodies recognize receptor-bound beta(2) glycoprotein I (beta(2)GPI) on target cells, and induce an intracellular signaling and a procoagulant/proinflammatory phenotype that leads to thrombosis. Evidence indicates that annexin A2 (A2), a receptor for tissue plasminogen activator and plasminogen, binds beta(2)GPI on target cells. However, whether A2 mediates pathogenic effects of aPL antibodies in vivo is unknown. In this work, we studied the effects of human aPL antibodies in A2-deficient (A2(-/-)) mice. A2(-/-) and A2(+/+) mice were injected with immunoglobulin G (IgG) isolated from either a patient with antiphospholipid syndrome (IgG-APS), a healthy control subject (IgG-normal human serum), a monoclonal anti-beta(2)GPI antibody (4C5), an anti-A2 monoclonal antibody, or monoclonal antibody of irrelevant specificity as control. We found that, after IgG-APS or 4C5 injections and vascular injury, mean thrombus size was significantly smaller and tissue factor activity was significantly less in A2(-/-) mice compared with A2(+/+) mice. The expression of vascular cell adhesion molecule-1 induced by IgG-APS or 4C5 in explanted A2(-/-) aorta was also significantly reduced compared with A2(+/+) mice. Interestingly, anti-A2 monoclonal antibody significantly decreased aPL-induced expression of intercellular cell adhesion molecule-1, E-selectin, and tissue factor activity on cultured endothelial cells. Together, these data indicate for the first time that A2 mediates the pathogenic effects of aPL antibodies in vivo and in vitro APS.

The frequency of anticardiolipin antibodies and genetic mutations associated with hypercoagulability among patients with Wegener's granulomatosis with and without history of a thrombotic event.

OBJECTIVE: Venous thrombotic events (VTE), including both deep venous thrombosis and pulmonary emboli, are now recognized as an important complication of Wegener's granulomatosis (WG), but the mechanism(s) of this occurrence is unclear. The frequency of anticardiolipin antibodies (aCL), anti-beta2-glycoprotein antibodies (anti-beta2-GP), and several genetic hypercoagulable factors were examined in a large cohort of patients with WG. METHODS: One hundred eighty patients with active WG had serum and DNA samples collected upon entry into a clinical trial. Of the 180 patients, 29 patients had VTE -- 13 before trial entry, 16 during trial. aCL (IgG, IgM, and IgA) and anti-beta2-GP (IgG and IgM) were evaluated in 176 patients. Factor V Leiden (FVL), the prothrombin gene mutation (G20210A, PGM), and methylenetetrahydrofolate reductase (MTHFR) gene mutation were tested in the 29 patients with thrombotic events, and 36 patients without. RESULTS: aCL occurred with increased frequencies in patients with WG when compared to the general population (1%-5%): 12% had aCL and 3% had anti-beta2-GP. There was no difference in the prevalences of aCL or anti-beta2-GP based on clotting status. The prevalence of the genetic hypercoagulable factors examined in patients with WG was comparable to the reported rates in the general population. CONCLUSION: Although the incidence of clinically significant VTE is increased in patients with WG, this increased risk is not explained by increased prevalences of aCL, anti-beta2-GP, FVL, or mutations in PGM or MTHFR. These observations suggest a need to search for new genetic or acquired prothrombotic abnormalities to account for the increased thrombotic event rate in patients with active WG.

C5a receptor-deficient mice are protected from thrombophilia and endothelial cell activation induced by some antiphospholipid antibodies.

Recent findings indicate that complement activation--involving specifically C3 and C5--contributes to antiphospholipid (aPL)-mediated thrombosis. Two complement effector pathways are initiated by the cleavage of C5, C5a and C5b, which leads to the formation of the C5b-9 membrane attack complex. To delineate and distinguish the role of C5a from the C5b-9 membrane attack complex seeded by C5b, we examined the in vivo effects (thrombosis) of aPL on C5a receptor-deficient (C5aR-/-) mice. C5aR-/- and C5aR+/+ mice were injected with IgM or with IgG from two different patients with APS (IgM-APS or IgG-APS) or with control IgM or IgG (IgM-NHS or IgG-NHS) twice. Complement fixing activity of the Ig fractions and anticardiolipin activity in the sera of the mice were determined by enzyme-linked immunosorbent assay. Surgical procedures to study thrombus dynamics were performed. IgM-APS but not IgG-APS fixed C1q to cardiolipin-coated plates. IgM-APS significantly enhanced thrombus size in C5aR+/+ mice compared to C5aR+/+ mice treated with IgM-NHS (3198 +/- 2361 microm2 versus 585 +/- 460 microm2). C5aR-/- mice treated with IgM-APS showed a significant reduction in thrombi size as compared with C5aR+/+ mice (676 +/- 690 microm2 versus 3198 +/- 2361 microm2; P = 0.001). IgG-APS enhanced thrombus formation significantly in C5aR+/+ when compared to IgG-NHS-treated mice (3507 +/- 965 microm2 versus 1321 +/- 798 microm2), and these effects were not altered in C5aR-/- mice (3400 +/- 1681 microm2). The data indicate that C5aR-/- mice are protected from the thrombogenic effects of some aPL antibodies.

Antiendothelial cell antibodies in patients with Wegener's granulomatosis: prevalence and correlation with disease activity and manifestations.

OBJECTIVE: Previous studies in small cohorts of patients with Wegener's granulomatosis (WG) or antineutrophil cytoplasmic antibody (ANCA) associated vasculitis have yielded conflicting data regarding the prevalence of antiendothelial cell antibodies (AECA), ranging from 8% to 100%, and the use of AECA as a measure of disease activity. We examined a large, well-characterized cohort of patients with WG and active disease for the presence of AECA. METHODS: Serum from subjects with WG who participated in a clinical therapeutic trial was collected at baseline, when all subjects had active disease. Clinical manifestations and disease activity were documented using the Birmingham Vasculitis Activity Score for WG (BVAS/WG). Serum AECA (IgG) was measured by cyto-ELISA using unfixed human umbilical vein endothelial cells (HUVEC). The AECA positivity cutoff was determined using 71 healthy control samples. Statistical analyses utilized Student's t test, chi-square and Fisher's exact tests, and linear regression. RESULTS: AECA were detected in 34 of 173 (20%) evaluated serum samples. Mean BVAS/WG did not differ between patients with (7.3 +/- 3.2) or without AECA (7.0 +/- 3.3) (p = 0.58). Among the 34 patients positive for AECA, the antibody titer did not correlate with disease activity (BVAS/WG; r = 0.09, p = 0.60). There were no statistically significant differences in the frequency of major clinical manifestations between patients with or without AECA. CONCLUSION: AECA, as measured using HUVEC, are not highly prevalent among patients with active WG, are not associated with specific clinical manifestations, and do not correlate with level of disease activity.

Toll-like receptor and antiphospholipid mediated thrombosis: in vivo studies.

OBJECTIVE: A study was undertaken to investigate the in vivo pathogenic role of Toll-like receptor 4 (TLR-4) in the antiphospholipid syndrome (APS) by studying the thrombogenic antiphospholipid (aPL) activity in lipopolysaccharide (LPS) non-responsive (LPS-/-) mice and the association between tlr4 gene polymorphisms and APS in patients. METHODS: IgGs from two patients with APS, one with aPL negative systemic lupus erythematosus (SLE) and one with normal human serum (NHS), were evaluated for thrombosis, tissue factor (TF) activity and endothelial cell activation in LPS-/- mice displaying a tlr4 spontaneous mutation vs LPS responsive (LPS+/+) mice. Human tlr4 Asp299Gly and Thr399Ile polymorphisms were evaluated by allele-specific PCR in 110 patients with APS with arterial/venous thrombosis and in 220 controls of the same ethnic origin. RESULTS: IgG-APS produced significantly larger thrombi and more leucocytes (WBC) adhering to endothelial cells in the cremaster muscle microcirculation of LPS+/+ mice than IgG-NHS or aPL negative SLE-IgG. These effects were abrogated after absorption of the anti-beta(2)glycoprotein I activity by an affinity column. The two IgG-APS induced significantly smaller thrombi and fewer WBC adhering to endothelial cells in LPS-/- mice than in LPS+/+ mice. IgG-APS induced higher TF activity in carotid artery homogenates of LPS+/+ mice than in LPS-/- mice. The prevalence of Asp299Gly and Thr399Ile tlr4 polymorphisms was significantly lower than in controls. CONCLUSIONS: These findings in LPS-/- mice and the reduction in the "protective" polymorphism in patients with APS with thrombosis suggest that TLR-4 is involved in the interaction of aPL with endothelial cells in vivo.