Identification of an Fcγ receptor–independent mechanism by which intravenous immunoglobulin ameliorates antiphospholipid antibody–induced thrombogenic phenotype

Objective

Patients with the antiphospholipid antibody syndrome (APS) often experience recurrent arterial and venous thrombosis and pregnancy losses. Intravenous immunoglobulin (IVIG) therapy has prevented pregnancy loss in some women with APS and has reversed fetal resorption rates in murine models of pregnancy loss. Although the basis for these effects is unknown, effector mechanisms of pathogenic antibodies often involve receptors for IgG (Fcγ receptors [FcγR]). We examined the potential mechanisms of action of IVIG in an in vivo murine model of antiphospholipid antibody (aPL)–induced thrombosis and endothelial cell activation.

Methods

Mice infused with IgG containing human anticardiolipin antibodies (aCL) were treated with IVIG (36 μg IV), saline, or ovalbumin. Surgically induced thrombus formation and in vivo leukocyte adhesion to endothelial cells were measured. Circulating levels of aCL were measured by enzyme‐linked immunosorbent assay. To determine whether FcγR are required for the effects of IVIG, we treated mice deficient in stimulatory FcγR. To examine the effects of IVIG on endogenously generated antibody, we treated mice immunized with β₂‐glycoprotein I (β₂GPI).

Results

IVIG treatment inhibited aPL‐induced endothelial cell activation and enhancement of thrombosis in mice passively infused with human aPL–containing IgG, and this was associated with a decrease in aPL levels. Similarly, IVIG lowered aPL levels and inhibited thrombogenesis in mice immunized with β₂GPI. The thrombophilic effects of aPL were evident in FcγR‐deficient mice.

Conclusion

Treatment with IVIG inhibits the thrombogenic effects of aPL in vivo and reduces the levels of aCL in the circulation. Blockade of stimulatory FcγR on inflammatory cells is not necessary for this effect. The mechanism of action of IVIG is more likely saturation of the IgG transport receptor, leading to accelerated catabolism of pathogenic aPL. These results have implications in the management of thrombosis in APS and may have applications for pregnant patients with a history of APS.

     

Antiphospholipid antibodies (aPL) in systemic lupus erythematosus. Are they specific tools for the diagnosis of aPL syndrome?

OBJECTIVE--Antiphospholipid antibody (aPL) specificity for aPL-related events was evaluated in systemic lupus erythematosus (SLE). METHODS--A study was carried out on 105 patients affected with SLE comparing the prevalence of lupus anticoagulant (LA) and IgG and IgM anticardiolipin antibodies (aCL) between patients with and without features of antiphospholipid syndrome (APS). Antiphospholipid antibody profile was subsequently evaluated in the aPL positive patients with and without aPL-related events, thus excluding the patients with complications of APS possibly due to factors other than aPL. RESULTS--LA showed a strong association with thrombosis and livedo reticularis, and IgG aCL with thrombosis and neurological disorders, while no clinical features were associated with IgM aCL. A considerable number of aPL positive patients with no aPL-related manifestations was also observed, suggesting the low specificity of aPL assays (54.4%). When studying the 60 aPL positive patients, LA was specific (91.3%) for the diagnosis of aPL-related thrombosis, whereas aCL were not specific, although IgG aCL mean levels were higher in patients with arterial thrombosis than in those without APS features. CONCLUSIONS--LA but not aCL positivity is a specific tool for the diagnosis of thrombotic complications due to aPL in SLE.     

Heterogeneity of antibodies to beta2-glycoprotein 1 from patients with systemic lupus erythematosus

We studied antibodies to beta2-glycoprotein 1 (anti-beta2GP1) from 72 patients with systemic lupus erythematosus (SLE) with or without antiphospholipid syndrome (APS) or with or without anticardiolipin antibodies (aCL). Fifteen patients had APS and positive antiphospholipid antibodies [clinical APS(+)/aPL(+)], 12 patients had APS, negative serum IgG and IgM aCL, antiphosphatidylethanolamine, anti-phosphatidylserine and no lupus anticoagulant [clinical APS(+)/ aPL(-)]. A third group included 16 patients without APS but high aCL levels [clinical APS(-)/ aPL(+)]. In a fourth group we studied 29 patients without clinical manifestations of APS or aCL [clinical APS(-)/aPL(-)]. One hundred anticardiolipin and VDRL-negative normal sera were studied as controls. IgG antibodies to cardiolipin proper in a bovine beta2GP-free system, to human beta2GP1 immobilized on cardiolipin or to human beta2GP1 alone were detected in all sera by ELISA using irradiated and nonirradiated plates from two manufacturers. Sera from APS(+)/aPL(+) patients showed IgG binding to CL, CL + beta2GP1 and beta2GP1 in irradiated and nonirradiated plates. APS(+)/ aPL(-) sera had more significant IgG binding to beta2GP1 than normal controls when studied in both irradiated or nonirradiated plates (P = 0.001). This binding was inhibited by solid-phase cardiolipin in a dose-dependent manner. Sera from the APS(-)/aPL(+) subgroup had comparable IgG activity in both the CL and CL + beta2GP1 assays, while no anti-beta2GP1 activity was detected in these sera. Sera from the clinical APS(-)/aPL(-) patients were negative in the three ELISA systems. Antibodies to human beta2GP1 from SLE patients recognize various epitopes. Those from APS(+)/ aPL(+) patients appear to react with an epitope boosted by cardiolipin in addition to another one present in the native protein. In contrast, anti-beta2GP1 from patients with APS(+)/aPL(-) are blocked by cardiolipin, suggesting that their epitope is the phospholipid-binding site.     

Interpretation and recommended testing for antiphospholipid antibodies

The antiphospholipid syndrome (APS) is defined by the association of arterial and/or venous thrombosis and/or pregnancy complications with the presence of at least one of the main laboratory-detected antiphospholipid antibodies (aPL) (i.e., lupus anticoagulants [LA], IgG and/or IgM anticardiolipin antibodies [aCL], and IgG and/or IgM anti-β2-glycoprotein I antibodies [aβ2GPI]). During the last decade efforts have been made to improve the harmonization and reproducibility of laboratory detection of aPL and guidelines have been published. The prognostic significance of aPL is being clarified through the fine elucidation of their antigenic targets and pathogenic mechanisms. Several clinical studies have consistently reported that LA is a stronger risk factor for both arterial and venous thrombosis compared with aCL and aβ2GPI. In particular, LA activity dependent on the first domain of β2-glycoprotein I and triple aPL positivity are prognosticators of the thrombotic and obstetric risks. Hopefully, this increasing knowledge will help improve diagnostic and treatment strategies for APS.     

Antiphospholipid-mediated thrombosis: interplay between anticardiolipin antibodies and vascular cells.

The antiphospholipid syndrome (APS) is characterized by thrombosis or pregnancy morbidity in the presence of antiphospholipid autoantibodies (aPL). aPL are a heterogeneous family of autoantibodies with diverse cross-reactivities whose origin and role have not been fully elucidated. Many of the autoantibodies associated with APS are directed against phospholipid-binding plasma proteins, such as beta2-GPI and prothrombin, or phospholipid-protein complexes. The mechanisms by which aPL cause thrombosis are not completely understood. There is no unique mechanism able to explain all symptoms associated with the presence of aPL. Different theories have been proposed, including the effect of aPL on endothelial cells, monocytes, and platelets. aPL are able to recognize, injure, or activate cultured vascular endothelial cells. Cultured endothelial cells incubated with aPL express increased levels of cell adhesion molecules and tissue factor (TF), an effect mediated by beta2-GPI, and may promote inflammation and thrombosis. Overexpression of TF has been also shown in monocytes in vitro and ex vivo. TF is the major initiator of coagulation in vivo; thus, its dysregulation may be one of the most important contributors to thrombosis. Effects of aPL upon platelets are not completely elucidated. aPL bind anionic phospholipid but they are normally in the inner side of cell membranes. When platelets are activated by different agonists, anionic phospholipids are exposed. There is some evidence showing that activated platelets are present in aPL-positive patients. Increased levels of beta-thrombomodulin, and microvesicle formation seem to support this hypothesis. Activated platelets may contribute to thrombosis by persistent exposure of a procoagulant surface.     

Anticardiolipin IgG subclasses association of IgG2 with arterial and/or venous thrombosis

Objective. To determine whether the presence of anticardiolipin antibodies (aCL) of a specific IgG subclass is associated with clinical complications of the antiphospholipid antibody syndrome (APS) and whether polymorphisms of Fc receptors for IgG (FcγR) with differential binding preferences contribute to an increased risk of thrombotic complications. Methods. In 60 patients with IgG aCL, we assessed clinical complications of the APS, measured the level of antibody activity, and determined the IgG subclass distribution of aCL by a modified enzymelinked immunosorbent assay (ELISA) with murine antihuman IgG subclass monoclonal antibodies. Selective IgG subclass adsorption studies were performed to determine the relative contribution of specific IgG subclasses to overall aCL activity. Fcγ receptor IIA (FcγRIIA) genotypes of aCL patients with thrombosis and of non-systemic lupus erythematosus controls were determined by polymerase chain reaction amplification of genomic DNA and allele-specific probes. Results. IgG2 aCL, detected in 75% of the patients, was the major subclass of aCL. Selective adsorption studies demonstrated that IgG2, in contrast to IgG1, was the predominant subclass responsible for aCL reactivity. IgG2 aCL was the only subclass associated with clinical complications, specifically, arterial and/or venous thrombosis (P < 0.04). The presence of FcγRIIA-H131, a receptor expressed on platelets, monocytes, and endothelial cells and the only human FcγR which efficiently recognizes IgG2, was associated with thrombosis in aCL patients. Among 45 high-titer (>40 GPL [IgG phospholipid] units) aCL patients with thrombosis, 40% were homozygous for FcγRIIA-H131, compared with 25% of disease-free controls (P = 0.042). Conclusion. While all 4 IgG subclasses are found in autoimmune aCL, only the presence of IgG2 is significantly associated with thrombotic complications. Reactivity in aCL ELISA is largely due to the presence of IgG2 in high-titer patients. The presence of IgG2 aCL, particularly in association with FcγRIIA-H131, may be a useful clinical predictor of increased thrombotic risk in patients with autoimmune IgG aCL. Allelic variants of FcγRIIA with distinct capacities to interact with IgG subclasses provide a mechanism for genetic susceptibility to an autoantibody-induced prothrombotic state.     

Characterization of IgG monoclonal anti-cardiolipin/anti-beta2GP1 antibodies from two patients with antiphospholipid syndrome reveals three species of antibodies

Antiphospholipid antibodies (aPL), including antibodies detected in anti-cardiolipin (aCL) enzyme-linked immunosorbent assays and in lupus anticoagulant (LA) tests, are strongly associated with recurrent thrombosis and recurrent fetal loss, i.e. the antiphospholipid syndrome (APS). Although recent studies suggest that most APS-associated aCL are directed against the phospholipid (PL)-binding plasma protein beta2-glycoprotein 1 (beta2GP1), the precise nature of aCL binding specificities remains controversial. To address the issue of aCL specificity we generated five new monoclonal IgG aCL from two patients with APS. Characterization of these five aCL, as well as two previously published IgG aCL, revealed three patterns of reactivity: (1) four antibodies reacted strongly with human beta2GP1-cardiolipin (CL) complexes and weakly with human beta2GP1 alone; (2) two antibodies recognized bovine beta2GP1, but not human beta2GP1; (3) one antibody reacted with complexes of human beta2GP1 and CL, but not with human beta2GP1 alone. Only one monoclonal displayed weak LA activity. These patient-derived IgG monoclonal antibodies, and additional ones to be generated, may help define varying species of antibodies detected in aCL assays and identify the specific antibodies that may be pathogenic.     

Antiphospholipid antibody-associated chorea

OBJECTIVE: To describe the clinical features, treatment, and outcomes of patients with antiphospholipid antibody (aPL)-associated chorea. METHODS: The study cohort consisted of consecutive patients with chorea evaluated between 1990 and 2005 with documented aPL at time of their neurologic diagnosis. RESULTS: Eighteen patients were identified, 4 with systemic lupus erythematosus (SLE). The 14 non-SLE patients experienced 1.6 vascular thromboses/pregnancy losses per person, while patients with SLE experienced 0.5 events/person. Four non-SLE patients (29%) and no SLE patients met criteria for antiphospholipid antibody syndrome (APS). None of these 4 tested positive for IgM anticardiolipin antibody (aCL). In contrast, 10 (71%) non-APS patients tested positive for IgM aCL. Chorea was most often bilateral, mild to moderate, and occurred once with a median age at onset of 44 and 33 years in non-SLE and SLE patients, respectively. Therapy included immunosuppression in 3 (21%) non-SLE patients and in all SLE patients. Antidopaminergic agents were used in 7 (39%). All patients responded to treatment. Five patients received anticoagulation for thrombosis and 2 died of bleeding complications, both non-SLE patients. CONCLUSION: aPL-associated chorea occurs most often in women and severity is mild to moderate. Clinical expression of chorea does not differ between those with and without SLE. Anticoagulation should be reserved for thrombosis treatment and not simply for chorea in the presence of aPL, as 2 patients died of bleeding. The absence of IgM aCL in patients with APS supports prior evidence that IgG aCL and lupus anticoagulant may be the more clinically relevant antibodies for thrombosis. However, IgM aCL may be important in patients with chorea.     

Anti-beta2-glycoprotein I autoantibodies, in vitro thrombin generation, and the antiphospholipid syndrome

OBJECTIVE: Thrombin plays a pivotal role in the regulation of hemostasis. We examined the effect of antiphospholipid (aPL) antibodies, in particular those with specificity for beta2-glycoprotein I (beta2-GPI), on in vitro thrombin generation, and examined the association with clinical manifestations of the antiphospholipid syndrome (APS). METHODS: We studied plasma samples from 59 patients with aPL antibodies determined by the presence of either elevated anticardiolipin (aCL) antibodies or lupus anticoagulant (LAC). Direct antibody binding of IgG, IgM, and IgA to beta2-GPI and prothrombin (PT) was determined by ELISA. Affinity purification of total IgG and IgG anti-B2-GPI antibodies was performed using staphylococcal protein A and phospholipid liposomes. A chromogenic assay was used to determine the effect of plasma samples and purified autoantibodies on in vitro thrombin generation. RESULTS: Thirty-three of 59 (56%) plasma samples inhibited in vitro generation of thrombin and 7/59 (12%) accelerated thrombin formation. There was a strong negative correlation between thrombin generation and IgG aCL (r = -0.72, p < 0.001) and IgG anti-beta2-GPI (r = -0.71, p < 0.001) antibody levels, and a weaker correlation with LAC (r = -0.46, p = 0.001). This association was not found with anti-PT antibodies and could not be attributed to concurrent therapy with warfarin. Additional experiments with affinity purified IgG antibodies indicated a dose dependent inhibition of thrombin generation, which was restricted to anti-beta2-GPI antibodies. Patients with a history of core clinical manifestations of the APS [venous and arterial thrombosis, recurrent (> or = 2) fetal loss] had significantly greater inhibition of in vitro thrombin generation (mean +/- SEM Z score: -3.38 +/- 0.51 vs -1.42 +/- 0.56; p = 0.01) and higher levels of IgG aCL (mean +/- SEM Z score: 8.39 +/- 1.12 vs 5.39 +/- 0.88; p = 0.04) and IgG anti-beta2-GPI antibodies (mean +/- SEM Z score: 4.49 +/- 0.69 vs 2.26 +/- 0.54; p = 0.01). Odds ratios for these variables and clinical manifestations of the APS were 5.43, 4.17, and 3.28, respectively. CONCLUSION: aPL antibodies may accelerate or inhibit the rate of in vitro thrombin formation. The predominant effect is inhibition that is restricted to IgG anti-beta2-GPI antibodies and it is strongly associated with clinical manifestations of the APS.     

Antiphospholipid syndrome induced by HIV

A 24-y-old male who developed necrotic lesions on the lower extremities together with testicular thrombosis necessitating orchiectomy, demonstrated high level IgG anticardiolipin (aCL) associated with acute HIV infection. This is one of the first cases describing a close relationship between viral infection and the classic antiphospholipid syndrome (APS). It is well documented that HIV patients may produce antiphospholipid antibodies (aPL), but the full-blown picture of the APS is distinctly uncommon with HIV or any other viral infection, possibly due to the overproduction of the IgM isotype rather than IgG aCL as in this case. The induction of thrombosis following infections has been well described in patients with catastrophic antiphospholipid syndrome (CAPS) but not in patients with the 'classic or simple' APS.     

Some antiphospholipid antibodies recognize conformational epitopes shared by beta2-glycoprotein I and the homologous catalytic domains of several serine proteases

OBJECTIVE: To test the hypothesis that some antiphospholipid antibodies (aPL) in patients with the antiphospholipid syndrome (APS) recognize a conformational epitope shared by beta2-glycoprotein I (beta2GPI; the major autoantigen for the antiphospholipid antibodies) and the homologous catalytic domains of several serine proteases (such as thrombin, activated protein C [APC], and plasmin) involved in hemostasis. METHODS: We generated 4 new IgG monoclonal aPL (2 screened against beta2GPI, 1 against thrombin, and 1 against protein C) from 2 APS patients. The monoclonal antibodies (mAb) were analyzed for binding to beta2GPI, thrombin, APC, and plasmin, as well as for anticardiolipin antibody (aCL) activity. To demonstrate a shared epitope between beta2GPI and a serine protease, 1 mAb was studied by cross-inhibition analysis. RESULTS: Both of the IgG anti-beta2GPI mAb bound to thrombin, APC, and plasmin. On the other hand, the 1 anti-thrombin mAb and the 1 anti-protein C mAb also bound to beta2GPI. Moreover, the binding of 1 cross-reactive mAb to beta2GPI was inhibited by alpha-thrombin (which contains only the catalytic domain of thrombin). All 4 mAb displayed aCL activity. CONCLUSION: Taken together with the findings that some aCL bind to several serine proteases that participate in hemostasis and share homologous catalytic domains, these data demonstrate that some aCL in APS patients recognize one or more conformational epitopes shared by beta2GPI and the catalytic domains of disease-relevant serine proteases.     

Clinical features and pregnancy outcome in antiphospholipid syndrome patients with history of severe pregnancy complications

Abstract

Objective. To clarify the clinical significance of antiphospholipid antibody (aPL) profile in patients with obstetric antiphospholipid syndrome (APS).

Methods. Clinical records of 13 pregnant patients (15 pregnancies) with obstetrical APS were reviewed over 10 years. Patients who met the Sapporo Criteria fully were studied, whereas those with only early pregnancy loss were excluded. In addition to classical aPL: lupus anticoagulant (LA), anticardiolipin antibody (aCL), and anti-β2-glycoprotein I (aβ2GPI); phosphatidylserine-dependent anti-prothrombin antibody (aPS/PT) and kininogen-dependent anti-phosphatidylethanolamine antibody (aPE) were also examined in each case.

Results. Cases were divided into two groups according to patient response to standard treatment: good and poor outcome groups. All cases with poor outcome presented LA, with IgG aβ2GPI and IgG aPS/PT were also frequently observed. IgG aPE did not correlate with pregnancy outcome.

Conclusion. aPL profile may predict pregnancy outcome in patients with this subset of obstetric APS.     

Anti-cardiolipin and anti-beta2 glycoprotein I antibodies in Indian patients with systemic lupus erythematosus: association with the presence of seizures

The aim of this study was to examine whether the clinical features of antiphospholipid antibody syndrome are associated with anti-cardiolipin and anti-beta2 glycoprotein I antibodies in Indian patients with SLE. Seventy-six patients (71 females), who fulfilled 1982 ACR criteria for SLE, were prospectively studied for the clinical features of antiphospholipid antibody syndrome (APS), and their sera were analysed for the presence of IgG/IgM/IgA anti-cardiolipin antibodies (aCL) by an in-house ELISA and, in 65 of them, for the presence of IgG anti-beta2 glycoprotein I antibodies (anti-beta2 GPI) by a commercial kit. Thirty-nine (51%) patients were positive for aCL, all of which were positive for IgG aCL, either alone (79.6%) or along with IgM and/or IgA. Twenty-seven (69.3%) out of 39 aCL-positive and seven (26.9%) out of 26 aCL-negative sera were positive for IgG antibodies to beta2 GPI. There was a significant correlation (r = 0.66, P < 0.05) between the levels of aCL and anti-beta2 GPI antibodies. Forty-one patients had features of definite or suggestive APS. Thrombocytopenia, recurrent pregnancy loss and CNS manifestations (seizures eight, infarct one) were seen in 20, 13 and nine patients, respectively. Thrombosis of the peripheral vessels was seen in only one patient. Only the presence of seizures was significantly associated with the presence of aCL and anti-beta2 GPI antibodies (P < 0.05). The characteristic association of definite APS (recurrent pregnancy loss and arterial/venous thrombosis) was lacking.     

Novel considerations in the pathogenesis of the antiphospholipid syndrome: involvement of the tissue factor pathway of blood coagulation

The antiphospholipid syndrome (APS) is characterized by clinical manifestations such as venous and arterial thrombosis, thrombocytopenia and/or recurrent pregnancy loss, as well as the persistent presence of laboratory markers of antiphospholipid (aPL) antibodies detected in laboratory assays. Though it is generally accepted that aPL antibodies, such as anticardiolipin (aCL), anti-beta2 glycoprotein I (anti-beta2GPI), and lupus anticoagulants (LA) contribute to the pathogenesis of APS, precise mechanism(s) are yet to be fully described. It is probable that aPL antibodies bind to a range of cellular targets (e.g., platelets, endothelial cells, and monocytes), leading to thrombosis and obstetric complications. There is now increasing evidence that alterations to the tissue factor (TF) pathway of blood coagulation contribute toward hypercoagulability in patients with aPL antibodies. This article reviews current evidence that suggests changes and/or interference to the major pathway of blood coagulation may represent a novel mechanism that contributes to the development of APS.     

Laboratory diagnosis and management challenges in the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is characterized by recurrent arterial and/or venous thrombosis and pregnancy morbidity manifested by early or late losses. Laboratory diagnosis ofAPS relies on the demonstration of a positive test for antiphospholipid antibodies (aPL). In clinical practice, the gold standard tests are those that detect anticardiolipin antibodies (aCL) and/or the lupus anticoagulant (LA). Although other specificities for aPL have been described their clinical utility and standardization has still to be established. Persistence of aPL positive tests must be demonstrated, and other causes and underlying factors considered. Although it is universally recognized that the routine screening tests (aCL and/or LA) might miss some cases, careful differential diagnosis and repeat testing are mandatory before the diagnosis of 'seronegative APS' can be made. Correct identification of patients with APS is important, because prophylactic anticoagulant therapy can prevent thrombosis from recurring, and treatment of affected women during pregnancy can improve fetal and maternal outcome.     

Testing for antiphospholipid antibodies: Advances and best practices

The diagnosis of antiphospholipid syndrome (APS) relies on the detection of circulating antiphospholipid antibodies (aPL). Currently, lupus anticoagulant (LAC), anticardiolipin (aCL), and antibeta2‐glycoprotein I antibodies (aβ2GPI) IgG or IgM are included as laboratory criteria if persistently present. Progress has been made on the standardization of tests as guidelines on LAC testing and immunological assays for aCL and aβ2GPI are published. However, LAC measurement remains a complicated procedure with many pitfalls and interfered by anticoagulant therapy. Solid‐phase assays for aCL and aβ2GPI still show interassay differences. These methodological issues make the laboratory diagnosis of APS challenging. In the interpretation of aPL results, antibody profiles help in identifying patients at risk. Noncriteria aPL, such as antibodies against the domain I of beta2‐glycoprotein (aDI) and antiphosphatidylserine‐prothrombin (aPS/PT) antibodies have been studied in the last years and may be useful in risk stratification of APS patients. But, aDI and aPS/PT are not included in the current diagnostic criteria and testing in daily practice is not recommended as these antibodies have no added value in the diagnosis of APS. This review will focus on the technical aspects of the laboratory methods, the clinical relevance of assays and interpretation of aPL results in the diagnosis of APS.     

Influence of hypergammaglobulinemia on antiphospholipid antibodies titres

PURPOSE: Antiphospholipid antibodies (aPL), anticardiolipin antibodies (aCL) or lupus anticoagulant (LA), are indispensable for the diagnosis of antiphospholipid syndrome (APS). However, antiphospholipid assays can generate false positive results. MATERIALS: We have studied the influence of hypergammaglobulinemia (HG) on aPL antibodies titers in 232 patients twice as positive for aPL antibodies. RESULTS: Out of 232 patients, 93 have an APS (76 primary APS, 17 secondary APS). Thrombosis occurred 138 times in APS patients. Of 139 patients without APS, 95 have an auto-immune disease, 28 have an isolated prolonged KCT and 16 an evolutive neoplasia. LA seems to be the best marker of APS. On the other hand aCL IgG and M, anti-beta2-GP1 IgM titers are significantly higher in patients without APS but with HG. CONCLUSION: Those results suggest that biological APS diagnosis should be carefully performed in patients with HG. In this case, other additional risk factors must be considered for the etiological diagnosis of thrombosis.     

Pathogenic role of antiphospholipid antibodies

The antiphospholipid antibody syndrome (APS) is characterized by recurrent arterial and venous thrombosis and/or pregnancy in association with antiphospholipid (aPL) antibodies. The pathogenic mechanisms in APS that lead to in vivo injury are incompletely understood. Recent evidence suggests that APL antibodies alter regulation of haemostasis and induce activation of complement. We will discuss the current knowledge on how aPL antibodies trigger increased inflammation and enhanced thrombotic tendency, and thereby lead to tissue damage.     

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.     

Infant perinatal thrombosis and antiphospholipid antibodies: a review

Perinatal thrombosis in infants born to mothers with antiphospholipid antibodies (aPL) is a rare event, but with risk of death or severe sequelae. We analysed 16 infants with such perinatal thrombosis reported in the literature in the last 20 years. Thromboses were arterial (13/16), mostly strokes (8/16). Hydrops fetalis with left renal vein thrombosis was associated to a lupus anticoagulant (LA) present only in the child. Risk factors additional to aPL: either prenatal (preeclampsia and/or intra-uterine growth retardation) or perinatal (asphyxia, sepsis, arterial or venous catheter and congenital thrombophilia) were present (one to four of them) in nine out of the 14 evaluable babies. aPL were the only risk factor found in five full term babies who suffered from stroke in four cases and from renal thrombosis in another. Eleven of these infants with aPL in their serum presented a neonatal APS with the same antibody (LA or aCL IgG) found in neonates and their mothers, while the other infants had thrombosis with aPL only in their mother's blood. aCL IgM was only found in one neonate who suffered from sepsis. Thrombosis treatments were diverse. This analysis suggests that women with aPL should be investigated for other thrombophilic risk factors and that aPL should be detected systematically at birth in the offspring of mothers with APS.