Autoantibody-mediated atherosclerosis

Beta2-glycoprotein I (beta2-GPI) is a major antigen for antiphospholipid antibodies (aPL) present in patients with antiphospholipid syndrome (APS). Oxidized low-density lipoprotein (oxLDL) is subsequently targeted by beta2-GPI and anti-beta2-GPI autoantibodies. Ligands specific for beta2-GPI derived from oxLDL have been characterized as oxidized forms of cholesteryl linoleate, such as 7-ketocholesterol-9-carboxynonanoate, i.e. 9-oxo-9-(7-ketocholest-5-en-3beta-yloxy) nonanoic acid, (namely oxLig-1). The in vitro phenomenon that it is significantly increased in binding of oxLig-1 containing liposomes to macrophages via an interaction with beta2-GPI and an anti-beta2-GPI autoantibody (via the Fcgamma receptor) may propose a novel mechanism on 'autoantibody-mediated atherosclerosis'. Furthermore, autoantibodies against a complex of beta2-GPI and oxLig-1 are detected in sera of APS patients and appearance of the antibodies is associated with episodes of thrombosis, especially, arterial thrombosis. Thus, autoimmune atherogenesis linked to beta2-GPI interaction with oxLDL and autoantibodies may be present in APS.     

Anti-beta 2-glycoprotein I autoantibodies and atherosclerosis

beta 2-Glycoprotein I (beta 2-GPI) is a major antigen for antiphospholipid antibodies (aPL) present in patients with antiphospholipid syndrome (APS). We previously reported that beta 2-GPI specifically binds to oxidized low-density lipoprotein (oxLDL). Further, a ligand specific for beta 2-GPI, oxLig-1, purified from the extracted lipids of oxLDL was identified as 7-ketocholesterol-9-carboxynonanoate (i.e., 9-oxo-9-(7-ketocholest-5-en-3 beta-yloxy) nonanoic acid) OxLig-1 was recognized by beta 2-GPI and subsequently by anti-beta 2-GPI autoantibodies. Binding of liposomes containing oxLig-1 to macrophages were significantly enhanced in the presence of both beta 2-GPI and an anti-beta 2-GPI autoantibody derived from (NZW x BXSB) F1 mouse, an animal APS model, or from APS patients. Anti-beta 2-GPI autoantibodies derived from APS patients with episodes of arterial thrombosis were detected in ELISA, using a solid phase beta 2-GPI complex with oxLig-1. It was also reported that LDL-receptor-deficient mice that were fed a chow diet and immunized with beta 2-GPI had an accelerated atherosclerosis and that beta 2-GPI was abundantly expressed within subendothelial regions and intimal-medial borders of human atherosclerotic plaques. All of these observations strongly suggest that autoimmune atherogenesis linked to beta 2-GPI interaction with oxLDL and autoantibodies may be present in APS.     

IgG autoantibodies against beta2-glycoprotein I complexed with a lipid ligand derived from oxidized low-density lipoprotein are associated with arterial thrombosis in antiphospholipid syndrome

We recently reported [J. Lipid Res. 42 (2001), 697; 43 (2002), 1486; 44 (2003), 716] that [beta2-glycoprotein I (beta2GPI) forms complexes with oxidized LDL (oxLDL) and autoantibodies against these complexes are present in patients with SLE and antiphospholipid syndrome (APS). The relationship of beta2GPI/oxLDL complexes and IgG autoantibodies against beta2GPI complexed with oxLig-1 (an oxLDL-derived ligand) with clinical manifestations of APS was studied in 150 APS and SLE patients. The beta2GPI/oxLDL levels of APS patients were similar to those of SLE patients without APS, but they were significantly higher than healthy individuals. There was no difference in the complex levels among the patients with arterial, venous thrombosis, or pregnancy morbidity. IgG anti-beta2GPI/oxLig-1 levels of APS were significantly higher than those of SLE without APS and healthy individuals. Further, antibody levels of APS patients with arterial thrombosis were significantly higher than those patients with venous thrombosis and pregnancy morbidity. Thus, oxidation of LDL leads the complex formation with beta2GPI in SLE and APS patients. In contrast, anti-beta2GPI/oxLig-1 autoantibodies were generated only in APS and were strongly associated with arterial thrombosis. These results suggest that autoantibodies against beta2GPI/oxLDL complexes are etiologically important in the development of atherosclerosis in APS.     

Oxidized low-density lipoprotein/beta2-glycoprotein I complexes and autoantibodies to oxLig-1/beta2-glycoprotein I in patients with systemic lupus erythematosus and antiphospholipid syndrome

Oxidized low-density lipoprotein (oxLDL) interacts with beta2-glycoprotein I (beta2-GPI) via oxLDL-derived specific ligands (oxLig-1) forming complexes. The prevalence and significance of oxLDL/alpha2-GPI complexes and antibodies to oxLig-1/alpha2-GPI were evaluated in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). The oxLDL/beta2-GPI complex was 69% positive (above mean + 3 SD of control subjects) in 97 consecutive patients with SLE, 62% in 40 patients with SLE with secondary APS, and 60% in 50 control patients with SLE without APS. IgG anti-oxLig-1/beta2-GPI antibody was positive in 31 (32%) of 97 consecutive patients with SLE, in 26 (65%) of 40 patients with SLE with secondary APS, and in 6 (19%) of 32 control patients with SLE. Anti-oxLig-1/beta2-GPI antibodies were 93.7% specific with a positive predictive value of 90.0% for APS, better than anticardiolipin antibodies (80.0% specific, 71.4% predictive value). These results confirm that oxLDL/beta2-GPI complexes are common in SLE and suggest a possible immunogenic role in APS. In contrast, IgG anti-oxLig-1/beta2-GPI antibodies not only are associated with but also are clinically useful risk factors for APS.     

Anti-β 2 -Glycoprotein I Autoantibodies and Atherosclerosis

β-Glycoprotein I (β 2 -GPI) is a major antigen for antiphospholipid antibodies (aPL) present in patients with antiphospholipid syndrome (APS). We previously reported that β 2 -GPI specifically binds to oxidized low-density lipoprotein (oxLDL). Further, a ligand specific for β 2 -GPI, oxLig-1, purified from the extracted lipids of oxLDL was identified as 7-ketocholesterol-9-carboxynonanoate (i.e., 9-oxo-9-(7-ketocholest-5-en-3β-yloxy) nonanoic acid) OxLig-1 was recognized by β 2 -GPI and subsequently by anti-&beta 2 -GPI autoantibodies. Binding of liposomes containing oxLig-1 to macrophages were significantly enhanced in the presence of both β 2 -GPI and an anti-β 2 -GPI autoantibody derived from (NZW×BXSB) F1 mouse, an animal APS model, or from APS patients. Anti-β 2 -GPI autoantibodies derived from APS patients with episodes of arterial thrombosis were detected in ELISA, using a solid phase &beta 2 -GPI complex with oxLig-1. It was also reported that LDL-receptor-deficient mice that were fed a chow diet and immunized with β 2 -GPI had an accelerated atherosclerosis and that β 2 -GPI was abundantly expressed within subendothelial regions and intimal-medial borders of human atherosclerotic plaques. All of these observations strongly suggest that autoimmune atherogenesis linked to β 2 -GPI interaction with oxLDL and autoantibodies may be present in APS.     

Antibodies against beta2-glycoprotein I complexed with an oxidised lipoprotein relate to intima thickening of carotid arteries in primary antiphospholipid syndrome

To explore whether antibodies against beta2-glycoprotein I (beta2GPI) complexed to 7-ketocholesteryl-9-carboxynonanoate (oxLig-1) and to oxidised low-density lipoproteins (oxLDL) relate to paraoxonase activity (PONa) and/or intima media thickness (IMT) of carotid arteries in primary antiphospholipid syndrome (PAPS). As many as 29 thrombotic patients with PAPS, 10 subjects with idiopathic antiphospholipid antibodies (aPL) without thrombosis, 17 thrombotic patients with inherited thrombophilia and 23 healthy controls were investigated. The following were measured in all participants: beta2GPI-oxLDL complexes, IgG anti-beta2GPI-oxLig-1, IgG anti-beta2GPI-oxLDL antibodies (ELISA), PONa, (para-nitrophenol method), IMT of common carotid (CC) artery, carotid bifurcation (B), internal carotid (IC) by high resolution sonography. Beta2GPI-oxLDL complex was highest in the control group (p < 0.01), whereas, IgG anti-beta2GPI-oxLig1 and IgG anti-beta2GPI-oxLDL were highest in PAPS (p < 0.0001). In healthy controls, beta2GPI-oxLDL complexes positively correlated to IMT of the IC (p = 0.007) and negatively to PONa after correction for age (p < 0.03). PONa inversely correlated with age (p = 0.008). In PAPS, IgG anti-beta2GPI-oxLig-1 independently predicted PONa (p = 0.02) and IMT of B (p = 0.003), CC, (p = 0.03) and of IC (p = 0.04). In PAPS, PONa inversely correlated to the IMT of B, CC and IC (p = 0.01, 0.02 and 0.003, respectively). IgG anti-beta2GPI-oxLig-1 may be involved in PAPS related atherogenesis via decreased PON activity.     

Recombinant Domain V of β2-Glycoprotein I Inhibits the Formation of Atherogenic oxLDL/β2-Glycoprotein I Complexes

β2-glycoprotein I (β2-GPI) is a plasma protein that interacts with oxidized low-density lipoproteins (oxLDL) via β2-GPI domain V to form oxLDL/β2-GPI complexes, potential autoantigens promoting atherogenesis in patients with antiphospholipid syndrome (APS). Such a interaction would expose β2-GPI domain I or/and IV, structures recognized by anti-β2-GPI autoantibodies. IgG immune complexes with oxLDL/β2-GPI complexes can interact with macrophages via Fcγ receptor, causing oxLDL/β2-GPI endocytosis and foam cell formation, contributing to atherosclerosis. Here, we use recombinant domain V to study the interaction between oxLDL and β2-GPI and hypothesized that domain V would interfere with this interaction thereby reducing oxLDL macrophage uptake and foam cell formation. The β2-GPI domain V sequence was expressed by using the Pichia pastoris expression system to obtain recombinant domain V of β2-GPI (P.rβ2-GPI DV). ELISA tests demonstrated that P.rβ2-GPI DV interacted with oxLDL via 7-ketocholesteryl-9-carboxynonanoate (oxLig-1), a negatively charged lipid moiety of oxLDL. The ω-carboxyl residue of oxLig-1 is required for the interaction. Serologic tests showed a significant increase in oxLDL and oxLDL/β2-GPI levels in patients with APS (p?P.rβ2-GPI DV was able to bind oxLDL in high affinity and competitively inhibited native β2-GPI (nβ2-GPI) binding to free oxLDL as well as to oxLDL from the oxLDL/β2-GPI complexes. These observations suggest that P.rβ2-GPI DV may be used to inhibit the formation of the oxLDL/β2-GPI complexes, a potential approach for reducing foam cell development and mitigating atherogenesis in patients with APS. The present work provides a new effective strategy to prevent the progression of atherothrombotic vascular complications in APS patients.     

Pathogenic roles of anti-beta2-GPI antibody in patients with antiphospholipid syndrome]

Antiphospholipid syndrome (APS) is characterized by arterial and/or venous thrombosis and pregnancy morbidity in the presence of antiphospholipid antibodies (aPL). Beta2-glycoprotein I (beta2-GPI) and prothrombin are representative autoantigens, the former more extensively investigated. Anti-beta2-GPI antibodies are not only markers of APS, but also are considered to be pathogenic. Possible roles of anti-beta2-GPI antibodies are, 1) enhancement the binding of beta2-GPI to anionic phospholipid and inhibition of protein C activation/activated protein C, 2) to form anti-beta2-GPI antibody-beta2-GPI-oxidized LDL complex and to promote uptake by sub-endothelial macrophage, resulting in atherosclerosis, 3) to dimerize beta2-GPI on the surface of platelets and to activate platelets via apoE receptor 2 and subsequent signal transduction, 4) stimulation of monocytes via p38 MAP kinase pathway and induction of tissue factor production. In pregnancy morbidity, activation of complement cascade plays an important role. These findings may provide a novel target in the management of APS.     

Avidity of anti-beta-2-glycoprotein I antibodies

The terms affinity and avidity are often used indiscriminately, despite clearly differing. Since affinity refers to monovalent binding of antibodies to a monovalent epitope, the majority of data on the binding of anti-beta2-glycoprotein I antibodies (anti-beta2-GPI) characterized their avidity rather than affinity. Anti-beta2-GPI were generally believed to be of low avidity, but heterogeneous avidity of patients' IgG anti-beta2-GPI has been demonstrated. High avidity anti-beta2-GPI monoclonals were reported to possess higher pathogenicity than low avidity anti-beta2-GPI. Polyclonal high avidity anti-beta2-GPI were found to be more common in patients with antiphospholipid syndrome (APS) and associated with thrombosis. Some conformational changes of beta2-GPI are required for the binding of polyclonal anti-beta2-GPI to the antigen: neither high density of the antigen nor high avidity of the anti-beta2-GPI alone is sufficient for the recognition. Avidity of anti-beta2-GPI should be considered in any attempt of inter-laboratory standardisation and/or evaluation of anti-beta2-GPI enzyme-linked immunosorbent assay (ELISA).     

Patients with atherosclerotic syndrome, negative in anti-cardiolipin assays, make IgA autoantibodies that preferentially target domain 4 of beta2-GPI

Autoantibodies targeting beta2-glycoprotein l (beta2-GPI), a component of the atherosclerotic plaque, are commonly found in patients with acute ischemic syndromes. Serum samples from APS (antiphospholipid syndrome) patients and from cardiovascular patients exhibiting acute atherosclerotic syndromes were analyzed for IgG and IgA antibodies in both anti-beta2-GPI and anticardiolipin (aCL) ELISA assays. All of the APS samples used here were positive in both assays. Serum samples from 382 atherosclerosis patients were also analyzed for IgG and IgA antibodies in the same assays. In sharp contrast to the APS samples, we found that only 1% of the samples from atherosclerosis patients were positive for IgA aCL, and 1.6% positive for IgG aCL, whereas 35.6% were positive for IgA anti-beta2-GPI and only 1.6% for IgG anti-beta2-GPI. The antigenic specificity of 29 serum samples from atherosclerosis patients was evaluated. Six different recombinant domain-deleted mutants (DM) of human beta2-GPI and full-length human beta2-GPI (wild-type) were used in competitive inhibition assays to inhibit the autoantibodies from binding in the anti-beta2-GPI ELISA assays. Domain-deleted mutants D--345 and D--45 inhibited the binding in the IgA anti-beta2-GPI assay, suggesting that these autoantibodies recognize domain 4 of the beta2-GPI molecule. These results clearly show that IgA anti-beta2-GPI autoantibodies from atherosclerotic patients are distinct from IgA autoantibodies found in APS samples.     

Which are the best biological markers of the antiphospholipid syndrome?

The diagnosis of antiphospholipid syndrome (APS) requires the presence of both clinical and biological features. Due to the heterogeneity of anti-phospholipid antibodies (aPL) the laboratory approach for their detection includes clotting-based tests for lupus anticoagulant (LA) as well as solid-phase assays for anticardiolipin antibodies (aCL). In addition, as it has been shown that autoimmune aPL recognize epitopes on phospholipid (PL)-binding plasma proteins, assays detecting antibodies to beta 2-glycoprotein I (beta 2-GPI) or prothrombin have been developed. The association between venous or arterial thrombosis and recurrent fetal loss with the presence of conventional aPL (LA and/or aCL) has been confirmed by many studies. The LA and IgG aCL at moderate/high titre seem to exhibit the strongest association with clinical manifestations of the APS. Several reports indicate that LA is less sensitive but more specific than aCL for the APS. Assays against PLs other than CL as well as the use of mixtures of PLs have been proposed to improve the detection of APS-related aPL. Concerning antibodies to PL-binding proteins (detected in the absence of PLs), there is evidence that anti-beta 2-GPI are closely associated with thrombosis and other clinical features of the APS. Moreover, these antibodies may be more specific in the recognition of the APS and in some cases may be present in the absence of aPL detected by standard tests. Many issues are still under debate and are discussed in this review, such as the problems of standardization of anti-beta 2-GPI assays, detection of the IgA isotype of aCL and anti-beta 2-GPI, the coagulation profiles of LA in the recognition of the thrombotic risk and the association of particular markers with subsets of patients with APS.     

Anti-Beta 2-glycoprotein I antibody isotype and IgG subclass in antiphospholipid syndrome patients

Beta 2-glycoprotein I (beta2-GPI) is an antigenic target recognised by antiphospholipid antibodies found in association with the antiphospholipid syndrome (APS). In this study, the prevalence of Immunoglobulin M (IgM) and IgA anti-beta2-GPI antibodies was examined in APS patients and compared with IgG antibodies. In addition the value of measuring antibody isotypes and IgG subclass was investigated in the laboratory diagnosis of APS. A solid phase enzyme linked immunosorbent assay was established to measure IgG, IgM and IgA and IgG subclass antibodies to beta2-GPI in patients with APS and a variety of other thrombotic and non-thrombotic disorders. Raised levels of IgM anti-beta2-GPI antibodies were observed in 65% of patients with APS, 21% with systemic lupus erythematosus (SLE), 23% with rheumatoid factor, 4% with stroke, 5% carotid artery stenosis (CAS), 17% with a biological false positive serology for syphilis, 43% with infectious mononucleosis (IM) and 27% with human immunodeficiency virus (HIV). The median value for IgM antibodies to beta2-GPI for all these groups ranged from 2 to 7 arbitrary units (AU). Elevated levels of IgA antibodies to beta2-GPI were found in patients with APS (47%), SLE (13%), rheumatoid factor (26%), CAS (48%), stroke (25%), VDRL false positive serology for syphilis (33%), IM (47%) and HIV (7%). The median value of IgA antibodies to beta2-GPI in all of these groups ranged from 2 to 4 AU. Conversely the median value for IgG anti-beta2-GPI in APS patients was 112 AU compared to 1-4 AU in the other conditions examined. The presence of IgM and IgA antibodies to beta2-GPI was much less specific and sensitive for APS than IgG, with raised levels of these isotypes seen in a variety of thrombotic and non-thrombotic disorders. Elevated levels of IgG1, IgG2, IgG3 and IgG4 antibodies to beta2-GPI were detected in APS patients. While all four IgG anti-beta2-GPI antibody subclasses were represented in APS patients there appeared to be a significant overall skewing towards to the IgG2 subclass.     

Proteolytic cleavage of beta(2)-glycoprotein I: reduction of antigenicity and the structural relationship

Binding of beta(2)-glycoprotein I (beta(2)-GPI)-dependent anticardiolipin antibodies (aCL) derived from antiphospholipid syndrome (APS) is significantly reduced in aCL ELISA due to loss of the phospholipid (PL) binding property of beta(2)-GPI by plasmin treatment. In the present study, the treatment generated a nicked form of beta(2)-GPI and resulted in loss of antigenicity for the autoantibodies detected in ELISA, using an beta(2)-GPI directly adsorbed polyoxygenated carboxylated plate, the assay system of which was not related to PL binding. The nicked form bound to neither Cu(2+)-oxidized low-density lipoprotein (oxLDL) nor to beta(2)-GPI-specific lipid ligands isolated from oxLDL, the result being a complete loss of subsequent binding of anti-beta(2)-GPI autoantibodies. The conformational change in the nicked domain V was predicted from its intact structure determined by an X-ray analysis (implemented in Protein Data Bank: 1C1Z), molecular modeling and epitope mapping of a monoclonal anti-beta(2)-GPI antibody, i.e. Cof-18, which recognizes the related structure. The analysis revealed that novel hydrophobic and electrostatic interactions appeared in domain V after the cleavage, thereby affecting the PL binding of beta(2)-GPI. Such a conformational change may have important implications for exposure of cryptic epitopes located in the domains such as domain IV.     

Are Oxidized LDL/β2-glycoprotein I Complexes Pathogenic Antigens in Autoimmune-mediated Atherosclerosis?

The oxidative modification of low-density lipoprotein (LDL) in the intima of arteries contributes to the initiation and progression of atherosclerotic lesions. We have previously reported that oxidized LDL (oxLDL) interacts with an endogenous plasma protein, beta2-glycoprotein I (beta2GPI), to form complexes and that the interaction is mediated by oxLDL specific ligands. We have also demonstrated the presence of oxLDL/beta2GPI complexes in the blood stream of patients with systemic inflammatory and autoimmune diseases. These findings implicate that oxLDL/beta2GPI complexes are possible atherogenic autoantigens. Autoantibodies to oxLDL/beta2GPI complexes have been associated with arterial thrombosis. Further, circulating IgG immune complexes containing oxLDL and beta2GPI were also detected in patients with systemic lupus erythematosus (SLE) and/or antiphospholipid syndrome (APS). Although many unanswered questions remain about the exact pathogenic mechanism(s) involved, oxLDL/beta2GPI complexes may be described as metabolic products relevant in atherogenesis and as significant participants in autoimmune-mediated atherosclerosis.     

Isotype distribution and clinical relevance of anti-beta2-glycoprotein I (beta2-GPI) antibodies: importance of IgA isotype.

The aim of this study was to evaluate the prevalence of IgG, IgA and IgM anti-beta2-GPI antibodies in anti-phospholipid syndrome (APS), and to establish the clinical significance of IgA type antibodies compared with the other isotypes. Anti-beta2-GPI antibodies were measured in the sera of 70 patients by solid-phase enzyme immunoassay in gamma-irradiated polystyrene plates coated with human purified beta2-GPI. Thirty-three out of the 70 patients were classified as having APS: three of them had primary, and 30 had secondary APS related to systemic lupus erythematosus (SLE). The remaining 37 patients had SLE without APS. Anti-beta2-GPI antibodies of IgG, IgA and IgM isotypes were present in 84.8%, 59.3% and 51.5% of patients with APS. Both the frequency and the level of each isotype were significantly higher in patients with APS. This association was very strong for IgA (P = 0.0004 for the antibody frequency and P < 0.0001 for the antibody level), as well as for IgG type antibodies (P < 0.0001 and P < 0.0001), whereas it was weaker for IgM (P = 0.01 and P = 0.04). A strong relationship was demonstrated between increased IgA anti-beta2-GPI antibody levels and a history of venous thrombosis, thrombocytopenia, heart valve disease, livedo reticularis and epilepsy. IgG anti-beta2-GPI antibodies were associated with the presence of lupus anticoagulant (LA) in addition to the main features of APS. However, antibodies of IgM isotype were related only to thrombocytopenia and heart valve disease. We recommend the evaluation of anti-beta2-GPI antibodies of IgA isotype in addition to IgG in patients with clinical suspicion of APS.     

beta2-glycoprotein I, the playmaker of the antiphospholipid syndrome

From its discovery in the early 60s till the beginning of the 90s, there was not much interest in plasma protein beta2-glycoprotein I (beta2-GPI). The finding that beta2-GPI acts as an essential cofactor for the detection of antiphospholipid antibodies (aPL) tremendously increased the interest in beta2-GPI [Lancet 335 (1990) 1544; Lancet 336 (1990) 177; Proc. Natl. Acad. Sci. U. S. A. 87 (1990) 4120]. It is now generally accepted that autoantibodies directed towards beta2-GPI are not only a serological marker but that they are involved in the pathology of the antiphospholipid syndrome (APS). In this review, we will first discuss the biochemistry of the protein beta2-GPI and the influence that the antibodies have on the function of beta2-GPI. Next, we will discuss the problems that are faced when assays to detect the presence of the autoantibodies are performed, emphasizing the urgent need for standardization of the anti-beta2-GPI-ELISA. Finally, we will discuss our latest insights into beta2-GPI and its role in the pathology of APS. Thereby, we will focus on the role of dimerized beta2-GPI on platelet and endothelial cell function.     

Inhibition of ras by farnesylthiosalicylate significantly reduces the levels of autoantibodies in two animal models of the antiphospholipid syndrome

BACKGROUND: Stimulation and proliferation of lymphocytes require activation of Ras. S-farnesylthiosalicylic acid (FTS) is a synthetic substance that detaches Ras from the inner cell membrane and induces its rapid degradation. Antiphospholipid antibodies (aPL) are a heterogeneous group of antibodies detected in patients with antiphospholipid syndrome (APS), which is associated with thrombosis, pregnancy losses, and thrombocytopenia. OBJECTIVE: To examine the effect of FTS treatment on aPL levels in a genetic autoimmune model (the MRL/lpr mice) and in an induced model of APS. METHODS: Female Balb/C mice immunized once with beta2-glycoprotein I (beta2-GPI) in complete Freund's adjuvant (CFA) and female MRL/lpr mice were treated intraperitoneally with either FTS (5 mg/Kg/day) or saline 3-5 times a week. aPL and anti-beta2-GPI antibodies were measured by ELISA. RESULTS: FTS treatment 3 times a week resulted in significant decreases of aPL and anti-beta2-GPI antibodies in both animal models. In contrast, more frequent treatment (5 times a week) had no significant effect on autantibody levels in both animal models. We further compared 2 protocols in the induced APS model, one for alternate day treatment and the other for daily treatment on the first 3 days each week, and found a decrease in autoantibody levels only in the alternate day protocol. CONCLUSIONS: Inhibition of Ras activation by FTS is effective in decreasing autoantibody levels in models of APS. The differential modulation of immune function by alternate day compared to daily treatment may provide better understanding of the role of Ras activation in this system.     

Pathogenic role of anti-beta2-glycoprotein I antibodies on human placenta: functional effects related to implantation and roles of heparin

Most of the clinical manifestations of the antiphospholipid syndrome (APS) can be related to thrombotic events; however, placental thrombosis cannot explain all of the pregnancy complications that occur in women with this syndrome. In this regard, it has been hypothesized that antiphospholipid (aPL) antibodies can directly attack trophoblasts, but it is still unclear what pathogenetic mechanisms play a role and which aPL antibodies subpopulations are involved. Although it has been assumed that aPL antibodies are directed against anionic phospholipids (PLs), current advances in the field suggest that antibodies to PL-binding plasma protein such as beta2-glycoprotein-I (beta2-GPI) are the clinically relevant aPL antibodies. It appears that following the attachment of beta2-GPI to PLs, both molecules undergo conformational changes that result in the exposure of cryptic epitopes within the structure of beta2-GPI allowing the subsequent binding of antibodies. aPL antibodies detected by anti-beta2-GPI assays are associated with fetal loss. However, there is still debate on how the antibodies might induce the obstetrical manifestations. The significantly improved outcome of pregnancies treated with heparin has stimulated interest in the drug's mechanisms of action. Several mechanisms could explain its beneficial effects, because in addition to a direct effect of heparin on the coagulation cascade, it might protect pregnancies by reducing the binding of aPL antibodies, reducing inflammation, facilitating implantation and/or inhibiting complement activation. Further investigations are needed to better understand how aPL antibodies induce obstetric complications and to better clarify the functional role of heparin in the human placenta leading to more successful therapeutic options.     

Antiphospholipid antibodies: effects on trophoblast and endothelial cells

PROBLEM: Antiphospholipid syndrome (APS) may affect placental functions through several possible mechanisms. Interaction of antiphospholipid antibodies (aPL) with cells involved in the coagulation cascade is thought to produce a procoagulant state. Thrombotic placental pathology is however not specific for the APS. METHOD OF STUDY: An analysis of published data. RESULTS: It is now generally accepted that the clinically relevant aPL bind to proteins with affinity for phospholipids (PL), such as beta2-glycoprotein I (beta2-GPI). Following the attachment of beta2-GPI to trophoblast anionic PL, both molecules undergo conformational changes resulting in the exposure of cryptic epitopes within the structure of beta2-GPI. This may allow the subsequent binding of antibodies hence affecting trophoblast functions directly. Moreover anti-beta2-GPI antibodies induce the activation of endothelial cells (ECs), resulting in a proinflammatory state which favours the prothrombotic diathesis of the syndrome. CONCLUSION: Numerous ameliorations in the APS knowledge have been introduced in the last few years. To have clarified the mechanism of antibody mediated damage on trophoblast and ECs represents an important step to explain the cellular events leading to pregnancy complications.