Induction of antiphospholipid autoantibodies by immunization with beta 2 glycoprotein I (apolipoprotein H)

Artemisinin analogue SM934 protects against lupus-associated antiphospholipid syndrome via activation of Nrf2 and its targets

Kidney is a major target organ in both antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE). The etiology of antiphospholipid syndrome nephropathy associated lupus nephritis (APSN-LN) is intricate and remains largely unrevealed. We proposed in present work, that generation of antiphospholipid antibodies (aPLs), especially those directed towards the oxidized neoepitopes, are largely linked with the redox status along with disease progression. Moreover, we observed that compromised antioxidative capacity coincided with turbulence of inflammatory cytokine profile in the kidney of male NZW×BXSB F1 mice suffered from APSN-LN. SM934 is an artemisinin derivative that has been proved to have potent immunosuppressive properties. In current study, we elaborated the therapeutic benefits of SM934 in male NZW×BXSB F1 mice, a murine model develops syndrome resembled human APS associated with SLE, for the first time. SM934 treatment comprehensively impeded autoantibodies production, inflammatory cytokine accumulation and excessive oxidative stress in kidney. Among others, we interpreted in present work that both anti-inflammatory and antioxidative effects of SM934 is closely correlated with the enhancement of Nrf2 signaling and expression of its targets. Collectively, our finding confirmed that therapeutic strategy simultaneously exerting antioxidant and anti-inflammatory efficacy provide a novel feasible remedy for treating APSN-LN.

Antiphospholipid syndrome, "the best prophet of the future"

The antiphospholipid syndrome (APS) is an autoimmune disorder characterized by the occurrence of venous and arterial thromboses, often multiple, and obstetric-related adverse events in the presence of antiphospholipid antibodies (aPL). APS, first described in 1983, as thrombosis, abortion and cerebral disease, is nowadays recognised as a systemic disease with a wide constellation of clinical manifestations related to acute and chronic vascular lesions. The presence of aPL is the serological hallmark of APS representing a heterogeneous population of autoantibodies with many antigenic specificities directed to phospholipid-binding proteins, either alone or in combination with phospholipids. Many assays have been developed for aPL detection. Particularly, anticardiolipin antibodies, anti-β2-glycoprotein I antibodies and lupus anticoagulant are essential tools for APS diagnosis. The cumulative evidence indicates that aPL are pathogenic autoantibodies binding to target cells and promoting thrombosis and pregnancy complications through a wide range of pathological mechanisms not yet fully understood. Finally, the recognition of the important role of aPL to assess the individual risk of thrombosis or pregnancy complications has expanded the concept of aPL, and currently aPL profile is regarded as a major risk factor for clinical thrombotic events.

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 β₂ -glycoprotein I (β₂ 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 β₂ GPI induced significant production of aCL and anti-β₂ GPI in WT mice compared with control mice immunized with OVA (P < 0.001) but diminished aCL (P < 0.001) and anti-β₂ GPI (P = 0.016) production in MHCII^-/- mice. Anti-β₂ GPI production was fully restored in DQ6 and DQ8 mice, while levels of anti-β₂ 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.

Autoantibodies to the Atheroma Component Beta2-Glycoprotein I and Risk of Symptomatic Peripheral Artery Disease

Peripheral artery disease (PAD) is mostly related to atherosclerosis. Autoimmunity and, in particular, antibodies to cardiolipin (aCL) and phospholipid cofactors such as beta2-glycoprotein I (beta2-gpI) might influence the development of atheroma. Beta2-glycoprotein I (beta2-gpI) has been found in atheroma. It has previously been shown that immunoglobulin A (IgA) anti-beta2-gpI antibodies are associated with a risk of cerebral ischemia and myocardial infarction. This case control study aimed to determine whether elevated levels of aCL/anti-beta2-gpI antibodies are associated with a risk of symptomatic PAD (sPAD). Cases comprised a nonselected population of patients with sPAD (intermittent claudication or critical ischemia). Patient recruitment was based on arteriography changes. Controls were selected from patients admitted to orthopedic wards as a result of fractures or muscle-ligamentous disorders. Age, sex, race, hypertension, smoking, diabetes mellitus, and hypercholesterolemia were evaluated as risk factors in both groups. IgG/IgM/IgA aCL and anti-beta2-gpI were detected by enzyme-linked immunoabsorbant assays (ELISA). To estimate the grade of association of antibodies with sPAD, odds ratios (OR) were calculated. Logistic regression was utilized for adjustment of confounding factors. Seventy-seven cases and 93 controls were studied. The mean age was 61.5 years for cases and 47.5 years for controls (p <0.001). Among the risk factors evaluated, the presence of hypertension showed the strongest association with sPAD (OR 12.1; 95%CI 5.8—30). The presence of IgA anti-beta2-gpI was independently associated with sPAD (OR 5.4; 95%CI 1.8—15.8; p = 0.01). IgA aCL was strongly associated with the outcome (nonadjusted OR 11.5 after Agresti correction). IgA aCL and IgA anti-beta2-gpI antibodies were not associated with any known risk factors for sPAD or with arteriography changes. The occurrence of these autoantibodies might represent one of the links between autoimmunity and atherosclerosis in patients with sPAD.

Antibodies to age-β2 glycoprotein I in patients with anti-phospholipid antibody syndrome

Anti-phospholipid antibody syndrome (APS) is a systemic autoimmune disease characterized clinically by arterial and/or venous thromboses, recurrent abortions or fetal loss and serologically by the presence of 'anti-phospholipid antibodies' (aPL). The main target antigen of the antibodies is β2 glycoprotein I (β2 GPI). Post-translational oxidative modifications of the protein have been widely described. In this study we aimed to analyse sera reactivity to glucose-modified β2 GPI (G-β2 GPI). Sera collected from 43 patients with APS [15 primary APS (PAPS) and 28 APS associated with systemic lupus erythematosus (SLE) (SAPS)], 30 with SLE, 30 with rheumatoid arthritis (RA) and 40 healthy subjects were analysed by an enzyme-linked immunosorbent assay (ELISA) using a G-β2 GPI. Nine of 15 consecutive PAPS out-patients (60%) and 16 of 28 SAPS (57.1%) showed serum antibodies [immunoglobulin (Ig)G class] against G-β2 GPI (anti-G-β2 GPI) by ELISA. The occurrence of anti-G-β2 GPI was significantly higher in APS patients compared to patients suffering from SLE. No RA patients or control healthy subjects resulted positive for anti-G-β2 GPI. Of note, aG-β2 GPI prompted to identify some APS patients (four PAPS and seven SAPS), who were negative in the classical anti-β2 GPI test. Moreover, in APS patients, anti-G-β2 GPI titre was associated significantly with venous thrombosis and seizure in APS patients. This study demonstrates that G-β2 GPI is a target antigen of humoral immune response in patients with APS, suggesting that β2 GPI glycation products may contain additional epitopes for anti-β2 GPI reactivity. Searching for these antibodies may be useful for evaluating the risk of clinical manifestations.

Pathogenetic mechanisms of antiphospholipid antibody production in antiphospholipid syndrome

Antiphospholiipid syndrome (APS) is an autoimmune disease characterized by the pathological action of antiphospholipid antibodies (aPL), that leads to recurrent pregnancy loss and thrombosis. Despite limited evidence, it is clear that there are both inherited and acquired components of the ontogeny of these antibodies. Animal genetic studies and human familial and population studies highlight the influence of genetic factors in APS, particularly human leukocyte antigen associations. Similarly, both animal and human studies have reported the importance of acquired factors in APS development and infectious agents in particular have a great impact on aPL production. Bacterial and viral agents have been implicated in the induction of autoimmune responses by various mechanisms including molecular mimicry, cryptic autoantigens exposure and apoptosis. In this review we highlight the latest updates with regards to inherited and acquired factors leading to the manufacturing of pathogenic antibodies and APS.

Subclinical atherosclerosis in systemic lupus erythematosus and antiphospholipid syndrome: focus on β2GPI-specific T cell response

OBJECTIVE

Systemic Lupus Erythematosus (SLE) and antiphospholipid syndrome (APS) are associated with a high prevalence of atherosclerosis. β2 glycoprotein I (β2GPI) represents a link between autoimmunity and endothelial dysfunction. Recently, β2GPI reactive T cells have been identified; however, their role in atherosclerosis is still under investigation. We evaluated early atherosclerosis in patients with SLE and APS and investigated T cell reactivity to β2GPI and its relationship with atherosclerotic process.

APPROACH AND RESULTS

Fifty SLE, 18 patients with primary APS (PAPS), and 25 healthy controls were enrolled. Demographic and clinical data, including traditional cardiovascular risk factors, were recorded. Monocyte β2GPI and Tissue Factor (TF) expression and peripheral blood mononuclear cell response to β2GPI stimulation were evaluated. Doppler ultrasound was performed to investigate flow-mediated dilatation (FMD) and carotid intima-media thickness (IMT). We detected an increase in mean IMT and a decrease in FMD in patients with SLE versus controls (P<0.05 and P=0.0001, respectively) and a decrease in FMD in patients with PAPS versus controls (P<0.05). Monocyte β2GPI and TF expression was higher in patients with SLE and PAPS than in controls (P=0.006 and P=0.001, respectively); no correlation of monocyte β2GPI and TF with IMT or FMD was detected. β2GPI induced peripheral blood mononuclear cell proliferation in 32% of patients with SLE, 25% of patients with PAPS yet in none of the controls. Proliferative response to β2GPI correlated with a history of arterial thrombosis, thrombocytopenia, and IMT >0.9 mm.

CONCLUSIONS

A significant percentage of patients with SLE and PAPS show a β2GPI-specific T cell reactivity, which is associated with subclinical atherosclerosis.

Anti-β2-glycoprotein I antibodies

Anti-β(2)-glycoprotein I (anti-β(2)GPI) antibodies are the main antiphospholipid antibodies, along with anticardiolipin and lupus anticoagulant, that characterize the autoimmune disease antiphospholipid syndrome (APS). While the exact physiological functions of β(2)GPI are unknown, there is overwhelming evidence that anti-β(2)GPI antibodies are pathogenic, contributing to thrombosis, pregnancy morbidity, and accelerated atherosclerosis in APS and systemic lupus erythematosus patients. The revelation that these antibodies play a central role in the pathogenesis and pathophysiology of APS has driven research to characterize the physiology and structure of β(2)GPI as well as the pathogenic effects of anti-β(2)GPI antibodies. It has also resulted in the development of improved testing methodologies for detecting these antibodies. In this review we discuss the characteristics of β(2)GPI; the generation, pathogenic effects, and standardized testing of anti-β(2)GPI antibodies; and the potential use of therapies that target the β(2)GPI/anti-β(2)GPI interaction in the treatment of APS.

Significant changes in the levels of secreted cytokines in brains of experimental antiphospholipid syndrome mice

Antiphospholipid syndrome (APS) is characterized by thromboses and neuropsychiatric manifestations possibly linked to brain inflammation. In order to examine the levels of proinflammatory and anti-inflammatory cytokines in experimental APS (eAPS) mice brains, we measured the levels of TNF-α, IFN-γ, and IL-10 in brain homogenates (cytosolic fractions) and in brain slices (secreted level) at 6, 15, and 24 weeks after immunization. We induced eAPS by immunization of Balb/c mice with β(2)-glycoprotein I (β(2)GPI), the major autoantigen in the disease and controls with adjuvant alone. We found increased levels of secreted TNF-α in eAPS mice for the entire experiment period. Cytosolic and secreted IL-10 and IFN-γ levels in eAPS mice were lower at 6 and 15 weeks and higher at 24 weeks after immunization. The results suggest that brain disease in APS is associated with significant and complex changes in proinflammatory and anti-inflammatory cytokines.

Advanced glycation end products of human β₂ glycoprotein I modulate the maturation and function of DCs

In chronic disorders related to endothelial cell dysfunction, plasma β₂ glycoprotein I (β₂GPI) plays a role as a target antigen of pathogenetic autoimmune responses. However, information is still lacking to clarify why β₂GPI triggers autoimmunity. It is possible that posttranslational modification of the protein, such as nonenzymatic glycosylation, leads to the formation of advanced glycation end products (AGEs). The aim of our study was to explore whether glucose-modified β₂GPI is able to interact and activate monocyte-derived immature dendritic cells (iDCs) from healthy human donors. SDS-PAGE and spectrofluorometric analyses indicated that β₂GPI incubated with glucose was sugar modified, and that this modification likely consisted of AGE formation, resulting in AGE-β₂GPI. AGE-β₂GPI caused phenotypical and functional maturation of iDCs involving the activation of p38 MAPK, ERK, and NF-κB. It also induced on DCs a significant up-regulation of RAGE, the receptor for AGEs. Evidence for RAGE involvement comes from blocking experiments with an anti-RAGE mAb, confocal analysis, and coimmunoprecipitation experiments. AGE-β₂GPI-stimulated DCs had increased allostimulatory ability and primed naive T lymphocytes toward a Th2 polarization. These findings might explain in part the interactive role of β₂GPI, AGEs, and DCs in chronic disorders related to endothelial cell dysfunction.

Pathophysiology of the antiphospholipid antibody syndrome

Antiphospholipid antibodies (aPL) are associated with the recurrent pregnancy loss and thrombosis that characterizes the antiphospholipid antibody syndrome (APS). Although the ontogeny of these pathogenic antibodies has not been fully elucidated, there is evidence that indicates the involvement of both genetic and environmental factors. The ability of aPL to induce a procoagulant phenotype in APS patients plays a central role in the development of arterial and venous thrombotic manifestations typical of the disease. Inflammation serves as a necessary link between this procoagulant phenotype and actual thrombus development and is an important mediator of the placental injury seen in APS patients with obstetric complications. Recent evidence has indicated a role for abnormal cellular proliferation and differentiation in the pathophysiology of APS, especially in those patients with pregnancy morbidity and other more atypical manifestations that have no identifiable thrombotic cause. The interplay of genetic and environmental factors responsible for aPL development and the mechanisms by which these antibodies produce disease in APS patients is the focus of this review.

Pathogenetic potential of antiphospholipid antibodies

Antiphospholipid antibodies are autoantibodies that recognize phospholipid-binding proteins such as beta2 glycoprotein (beta2GP)-I, prothrombin or annexins. These antibodies have been associated with arterial or venous thrombotic events and pregnancy morbidity. The molecular mechanisms responsible for the pathogenetic potential of these antibodies include: resistance to activated protein C, acquired Factor XII deficiency resulting in suppression of intrinsic fibrinolytic activity, activation of endothelial cells through the nuclear factor kappaB pathway leading to tissue factor upregulation, adhesion molecule and cytokine expression and activation of platelets. Opposite effects, such as the potentiation of the inhibitory action of beta2GPI on the activation of Factor XI, make the dynamics of the interaction of these antibodies with the coagulation system rather complex. Many of the above functions can be mediated by signaling through molecules of the tumor necrosis factor receptor family, such as CD40, which is recognized by purified anti-beta2GPI antibodies.

Cognitive dysfunction and white matter abnormalities in antiphospholipid syndrome

Diagnosis of the antiphospholipid syndrome (APS) requires that a patient have both a clinical event (thrombosis or pregnancy loss) and persistently positive antiphospholipid antibodies (aPL). Although stroke and transient ischemic attack are the most common neurologic manifestations of APS, both cognitive dysfunction and magnetic resonance imaging (MRI) white matter hyperintensities can occur in aPL-positive patients (with or without APS). Relatively little is known about the cognitive pattern in aPL-positive patients; MRI white matter hyperintensities may be related to underlying attentional and executive cognitive impairment. Studies with sophisticated neuroimaging techniques aimed to better understand MRI white matter hyperintensities may eventually facilitate our understanding of cognitive dysfunction in aPL-positive patients.

Antiphospholipid antibodies: laboratory and pathogenetic aspects

Antiphospholipid antibodies (aPL) constitute a heterogeneous group of autoantibodies that share the ability to bind phospholipids (PL) alone, protein-PL complexes, or PL-binding proteins. They have been detected in isolation, in association with autoimmune diseases such as systemic lupus erythematosus (SLE), and during the course of different infections. aPL have been associated with an array of clinical manifestations in virtually every organ, although deep vein and arterial thrombosis as well as pregnancy morbidity are predominant. The co-occurrence of these clinical findings with aPL constitutes the so-called antiphospholipid syndrome (APS). aPL can be detected by immunological methods [e.g., anticardiolipin antibodies (aCL)] or by functional methods that exploit the effect of aPL on blood coagulation [lupus anticoagulant (LA)]. Since aPL are heterogeneous, numerous immunological and coagulation assays have been developed. These assays have not been fully standardized, and, therefore, problems such as high interlaboratory variation are relatively frequent. Recently, recommendations have been published regarding LA and aCL testing. Not all aPL are pathogenic. However, when they are not associated with infections, they have a role in the pathogenesis of APS. Clinical and experimental data have shown that aPL exert their pathogenic activity by interfering with the function of coagulation factors, such as thrombin and factors X, XI and XII, and with the function of anticoagulant proteins of the protein C system. In addition, aPL interaction with platelets and endothelial cells induces a pro-adhesive activated phenotype.

Are antiphospholipid antibodies an essential requirement for an effective immune response to infections?

Antiphospholipid antibodies show a close association to a variety of infections. Recent data implicate that parvovirus B19 may be used as a model-system for studying the interaction of viral infection and the development of these autoantibodies. B19-related diseases commonly associated with the acute infection show flu-like symptoms, transient arthralgias, leukopenia and thrombocytopenia, and, in pregnant women, spontaneous abortion and hydrops fetalis. Hepatitis, myocarditis, meningitis, encephalitis, as well as pure red cell anemia may occur occasionally. In addition, parvovirus B19 infections have been frequently described as the cause or trigger of various forms of autoimmune diseases affecting all blood cell lines, joints, connective tissue, uvea, and large and small vessels. Molecular mimicry may be one major contribution to the appearance of autoimmune antibodies, for example, antiphospholipid and antineutrophil cytoplasmic antibodies as well as antinuclear antigens. These mechanisms implicated in the pathogenesis of parvovirus B19-triggered autoimmune diseases, especially focused on the development of antiphospholipid antibodies, will be discussed in this mini review.

Overlapping humoral autoimmunity links rheumatic fever and the antiphospholipid syndrome

OBJECTIVE

Rheumatic fever (RF) and the antiphospholipid syndrome (APS) are autoimmune diseases that share similar cardiac and neurological pathologies. We assessed the presence of shared epitopes between M protein, N-acetyl-beta-D-glucosamine (GlcNAc) and beta2 glycoprotein-I (beta2GPI), the pathogenic molecules engaged in these autoimmune conditions.

METHODS

Sera from the APS patients were affinity-purified on beta2GPI and beta2GPI-related peptide columns. Sera from RF patients were affinity-purified on protein G column. The beta2GPI and M protein-related peptides were prepared by conventional solid-phase peptide synthesis. The enzyme-linked immunosorbent assay direct binding and inhibition studies were performed on the RF and APS sera for the presence, and cross-reactivity, of antibodies against beta2GPI, beta2GPI-related peptides, streptococcal M protein, M-derived peptides and GlcNAc.

RESULTS

Antibodies (Abs) to beta2GPI were found in 24.4% of 90 RF patients. Antibodies against various beta2GPI-related peptides were found in 1.1-36.7% of the patients. The immunoglobulin G sera from RF patients possessed significant anti-beta2GPI activity, while sera from APS patients contained a considerable anti-streptococcal M protein as well as anti-GlcNAc activity. Furthermore, affinity-purified anti-beta2GPI and anti-beta2GPI-related peptide Abs from APS patients cross-reacted with streptococcal M protein and M5 peptide, while beta2GPI and beta2GPI-related peptides inhibited anti-streptococcal M protein activity from RF patients. The results were confirmed by immunoblot analyses. The beta2GPI also inhibited anti-GlcNAc activity from APS patients with chorea.

CONCLUSIONS

The results of our study, showing a considerable overlap of humoral immunity in RF and APS, support a hypothesis that common pathogenic mechanisms underlie the development of cardiac valve lesions and Central Nervous System abnormalities in both diseases.

Genetic and immunological factors interact in a mouse model of CNS antiphospholipid syndrome

The antiphospholipid syndrome (APS) includes systemic and central nervous system (CNS) pathology associated with antibodies to a complex of phospholipids and beta(2)-glycoprotein I (beta(2)-GPI). We have recently reported the induction of APS associated with behavioral and cognitive deficits in BALB/c female mice that developed 4-5 months after immunization with beta(2)-GPI. In the present study, we examined the influence of genetic factors on the ability to induce experimental APS with CNS involvement by testing several mouse strains immunized with beta(2)-GPI. Female mice from five strains were immunized once with beta(2)-GPI in complete Freund's adjuvant (CFA) or with CFA alone (controls). Autoantibody levels were examined at 1 and 5 months after immunization. Neurological assessment in a staircase test was performed 4-5 months following the immunization. Induction of APS resulted in elevated levels of antibodies against negatively charged phospholipids and beta(2)-GPI in all five mouse strains. Autoantibody levels were significantly higher in Balb/c, ICR, and C57BL/6 mouse strains compared to AKR and C3H. aPL levels dropped significantly more in the C57BL/6 compared to Balb/c mice over a period of 4 months. Hyperactivity reflected by higher number of stairs climbed in 3 min, was induced by APS in the Balb/c and ICR, mouse strains. Exploratory behavior reflected by more frequent rears, was seen in the APS-Balb/c and AKR mice. Hypoactivity and less exploration were seen in the APS-C57BL/6 and C3H mice. The study supports a link between high levels of aPL and behavioral changes in a mouse APS model. Qualitative differences in behavioral patterns may be due to nervous system as well as immune genetic factors. The minimal effect of APS in C57BL/6 mice may provide a suitable background for the study of transgenes in these mice.

Oxidized β2-glycoprotein I induces human dendritic cell maturation and promotes a T helper type 1 response

The human plasma protein β2-glycoprotein I (β2-GPI) is the most common target for antiphospholipid antibodies associated with thrombotic events in chronic disorders related to endothelial cell dysfunction. Crucial information is needed to clarify why this self-abundant protein is targeted by autoimmune responses. In this study, we investigated whether oxidative modification of β2-GPI, either spontaneous in culture wells or induced by treatment with H2O2, renders this self-protein able to activate immature monocyte-derived dendritic cells (DCs) from healthy human donors. Oxidized β2-GPI caused DCs to mature so that CD83 appeared and CD80, CD86, human leukocyte antigen-D region related (HLA-DR), and CD40 increased. The interaction between oxidized β2-GPI and DCs specifically stimulated these cells to secrete interleukin 12 (IL-12), IL-1β, IL-6, IL-8, tumor necrosis factor α (TNF-α), and IL-10. Oxidized β2-GPI-stimulated DCs had increased allostimulatory ability and primed naive T lymphocytes, thus inducing T helper 1 (Th1) polarization. The interaction between oxidized β2-GPI and DCs involved interleukin-1 receptor associated kinase (IRAK) phosphorylation and nuclear factor κB (NFκB) activation. Pretreatment of β2-GPI with the antioxidant α-tocopherol prevented DC maturation. These findings show that human oxidized β2-GPI, probably by interacting with a member of the Toll-like receptor (TLR) family, causes DCs to mature. Because this key β2-GPI function requires oxidative modification, in several chronic disorders related to endothelial cell dysfunction oxidative stress might trigger the “autoimmune spiral.”

Antiphospholipid antibodies in pediatric patients with prolonged activated partial thromboplastin time during infection

OBJECTIVE

To investigate the close association between different antiphospholipid antibodies (aPL) caused by infection and their appearance together with a prolonged activated partial thromboplastin time (aPTT).

METHODS

Sera from 122 children were evaluated in this study. Thirty-seven children with mild to medium prolonged aPTT (>37.2s) and elevated C-reactive protein (CRP) levels during various forms of infections (group 2), 18 children without infections (group 3) but with mild to medium prolonged aPTT and 13 children with infections (group 4) and with elevated CRP-level as well as a control group (group 1) of 54 patients without any infection and normal aPTT and negative CRP levels were investigated with commercially available ELISA tests (AESKU.Diagnostics, Wendelsheim, Germany) for the presence of antibodies directed against cardiolipin (CL), phosphatidylserine (PS) and beta2-glycoprotein I (beta 2GPI). The cutoff for positive results was defined with the healthy, aged matched control group (group 1) using the mean OD values plus 2 standard deviations. The lupus anticoagulant (dilute Russell's Viper Venom time, dRVVT) and coagulation Factor XII were determined with routine tests (Dade Behring).

RESULTS

Detection of at least one antibody to phospholipids was possible in 89.2% of group 2. It could be shown that IgM anti-beta 2GPI antibodies were found in 27 (59.5%) of group 2, but only in 1 (5.6%) of group 3 (p=0.024) and only in 4 (7.4%) of the controls (p=0.014). The presence of IgG-anti-beta 2GPI antibodies showed no significant difference in the different groups. Furthermore, children of groups 2, 3 and 4 had statistically significant higher levels of antibodies against PS IgG and PS IgM than controls. Also, antibodies to CL of the IgG-type were more frequently detected in children of group 2 than in controls (p=0.038). Detection of CL-IgM antibodies did not reach a significant level in the comparison of the different groups.

CONCLUSION

During commonly acquired infections elevation of aPL of nearly all types seems to be a common process. Mild prolongation of aPTT might reflect this presence of aPL in the course of the infectious disease. Our data suggest that there exists no differences in specificity in comparison to the "pathogenic" aPL but the presence over time might be the trigger for the autoimmune activity to begin.

The molecular basis of antiphospholipid syndrome

We herein review evidence that the phospholipid-binding protein beta2 glycoprotein-1 (beta2GPI) is a causative autoantigen in APS. Recent work suggests that the molecular regions in beta2GPI that facilitate autoimmunization are those that promote binding to negatively charged phospholipids by means of strong positive (anionic) charge and hydrophobicity. Although many common infections can cause antiphospholipid antibodies to be produced in humans, such postinfectious aPL are rarely associated with thromboses or pregnancy morbidity, the central features of antiphospholipid syndrome (APS). We propose that the causes of APS include those infectious agents that mimic the above molecular domains in beta2GPI. In people who are susceptible to APS, tolerance to self-beta2GPI and phospholipids is likely to be broken by foreign bacterial or viral proteins that contain such beta2GPI-like epitopes.

Current debates in antiphospholipid syndrome: the acquired antibody-mediated thrombophilia

Antiphospholipid (APL) syndrome is the most common form of acquired thrombophilia. It can cause significant morbidity and even mortality. The term "APL antibodies" represents a heterogeneous group of antibodies associated with this disorder. Currently no single assay can identify every APL antibody. Clinically relevant APL antibodies are mainly anticardiolipin antibodies (ACA) detected by solid phase enzyme-linked immunosorbent assay (ELISA) and lupus anticoagulants (LA) demonstrated by in vitro coagulation assay. However, there are some other antibodies associated with the APL syndrome (i.e., subgroup APL antibodies). ACAs, LAs, and subgroup APL antibodies represent intersecting, but non-identical, subsets of autoantibodies. Thus, those autoantibodies may coexist or may occur independently. Any organ system and any size of vessel can be affected during the clinical course of the disease. Therefore, the APL syndrome can manifest itself in a wide variety of clinical thrombotic features. Fetal loss and pregnancy morbidity represent a specific challenge. Despite tremendous advances in the understanding of the pathogenesis of APL syndrome during the past decade, the mainstay of management is still anticoagulation. However, there is no general agreement regarding the duration and intensity of anti-coagulant therapy. In this review, we focused on the current dilemmas and their present clarifications in the wide clinicopathologic spectrum of APL syndrome and APL antibody-related distinct pathologic conditions.

Beta-2-glycoprotein-I, infections, antiphospholipid syndrome and therapeutic considerations

Evidence supports the association between infectious agents, antiphospholipid syndrome (APS), and the presence of antiphospholipid antibodies and anti-beta2-glycoprotein-I (beta2GPI) antibodies. Several mechanisms have been proposed to explain the role of bacteria/viruses in induction of an autoimmune condition, such as molecular mimicry between structures of a pathogen and self antigen and bystander activation or bacterial/viral superantigens. Protein databases reveal high homologies between the beta2GPI-related synthetic peptides and infectious agents. Studies employing experimental APS models proved molecular mimicry between beta2GPI-related synthetic peptides, which serve as target epitopes for anti-beta2GPI Abs, and structures within bacteria, viruses (e.g., CMV), and tetanus toxoid. Any explanation of how microbial infections might induce APS must take into account the genetic predisposition. In this paper, we discuss the association of antiphospholipid antibodies, infectious states, and molecular mimicry as a proposed mechanism for development of APS.

Masking of phosphatidylserine inhibits apoptotic cell engulfment and induces autoantibody production in mice

Apoptotic cells are rapidly phagocytosed by professional phagocytes, such as macrophages and dendritic cells. This process prevents the release of potentially noxious or immunogenic intracellular materials from dying cells, and is thought to play a critical role for the maintenance of normal functions in surrounding tissues. Milk fat globule-EGF-factor 8 (MFG-E8), secreted by activated macrophages and immature dendritic cells, links apoptotic cells and phagocytes, and promotes phagocytosis of apoptotic cells. Here, we report that an MFG-E8 mutant, designated as D89E, carrying a point mutation in an RGD motif, inhibited not only the phagocytosis of apoptotic cells by a wide variety of phagocytes, but also inhibited the enhanced production of IL-10 by thioglycollate-elicited peritoneal macrophages phagocytosing apoptotic cells. When intravenously injected into mice, the D89E protein induced the production of autoantibodies including antiphospholipids antibodies and antinuclear antibodies. The production of autoantibodies was enhanced by the coinjection of syngeneic apoptotic thymocytes. After the induction of autoantibody production by D89E, the treated mice showed a long-term elevation of the titer for autoantibodies, and developed IgG deposition in the glomeruli. These results indicated that the impairment of apoptotic cell phagocytosis led to autoantibody production.

Beta-2 glycoprotein I and its role in antiphospholipid syndrome—lessons from knockout mice

The antiphospholipid syndrome is characterized by the presence in serum of autoantibodies against beta2GPI. Although the role of beta2GPI in the pathogenesis of antiphospholipid antibody syndrome (APS) is well recognized, its exact physiological functions still remain undisclosed. Several interactions of beta2GPI with components of the coagulation cascade have been proposed, resulting in both procoagulant and anticoagulant effects. Additionally, beta2GPI has been implicated in the mechanism of recurrent fetal loss entailed in APS. Recently, using a homologous recombination approach, reproduction of mice homozygous for deletion of the beta2GPI gene has been feasible. beta2GPI knockout mice offer a valuable tool for revealing the physiological role of the protein. These mice show decreased in vitro ability for thrombin generation. Furthermore, although mice lacking beta2GPI are fertile, the success of early pregnancy is moderately compromised and functional beta2GPI is believed necessary for optimal implantation and placental morphogenesis.

Prevalence and clinical correlations of antibodies against six beta2-glycoprotein-I-related peptides in the antiphospholipid syndrome

Two-hundred ninety five patients with the antiphospholipid syndrome (APS) were studied for the presence of antibodies against six anti-beta2GPI-related peptides Abs. The prevalence of a wide spectrum of clinical and laboratory parameters of APS was evaluated in all patients, and correlated with the presence of each anti-beta2GPI peptide antibody. The rates of the various antipeptides Abs ranged from 18.0 to 63.7%. Altogether, 87.1% of the patients had antibody reactivity against at least one of the six beta2GPI-related peptides. A high degree of simultaneous reactivity against several beta2GPI-peptides was found. Positive and negative correlations were found between several antipeptides Abs and the rates of thrombosis and fetal loss. Our results point to a heterogeneous activity of antiphospholipid Abs in APS patients, directed, often concurrently, against various epitopes of the beta2GPI molecule. Evaluation of APS patients for the presence of specific antipeptides Abs may be of a value in predicting the risk for future thrombotic and obstetrical complication, as well as for specific therapeutic purposes.

Intrauterine fetal death in mice caused by cytomegalovirus-derived peptide induced aPL antibodies

Immunization of mice with beta2 glycoprotein I (beta2GPI) and also with GDKV, a synthetic peptide representing the phospholipid (PL)-binding site of beta2GPI, induced pathogenic aPL antibodies that bind and activate endothelial cells, enhanced thrombus formation and caused fetal death in pregnant mice. TIFI is a PL-binding peptide spanning the Thr101-Thr120 of ulb0-hcmva from human cytomegalovirus (CMV), which shares structural similarity with the PL-binding site of beta2GPI. Immunization with this peptide induced pathogenic aPL and anti-beta2GPI antibodies in mice. These antibodies activated endothelial cells and enhanced thrombus formation in vivo, but whether these antibodies cause fetal death in mice is not known. The objective of this study was to examine the effects of these antibodies on pregnancy outcome in mice. Two groups of pregnant BALB/c mice were injected with either hybridoma supernatant containing D3/AC10, a CMV-peptide-induced monoclonal aPL, at days four, eight and 12 of the pregnancy, 100 microg per mouse (study group) or with culture media alone (control group). The litter size was significantly smaller in the study group (4.80 +/- 1.15 versus 7.28 +/- 0.18, t = - 2.526, P < 0.03). In conclusion, aPL induced by CMV peptides may have pathogenic properties similar to human autoimmune aPL. These findings further support the hypothesis that at least in some patients with APS, pathogenic aPL antibodies may be generated by immunization with CMV products during incidental exposure to the virus via a molecular mimicry mechanism.

Peripheral vascular disease in antiphospholipid syndrome

Atherosclerosis has been considered an inflammatory disease based on the finding that atherosclerotic lesion contains activated T lymphocytes reacting with oxidized low-density lipoproteins (oxLDL) and heat shock proteins (HSP); it also contains autoantigens like beta2GPI, a target of antibodies occurring in an immune-mediated thrombophilia called antiphospholipid syndrome (APS). Further support to this hypothesis comes from the cross-reactivity, which occurs between antiphospholipid antibodies (aPL) and antibodies to oxLDL. Animal experiments have shown that aPL are associated with atheroma. In addition, accelerated atherosclerosis has been detected in patients with a prototype systemic autoimmune disease, such as systemic lupus erythematosus (SLE). However, the association of APS or aPL with atherosclerosis is a matter of debate due to the small numbers of patients studied, and the fact that traditional risk factors for atherosclerosis coexist. The prevalence of APS ranges from 1.7% to 6%, and that of aPL reaches to 14% among patients with peripheral vascular disease defined on the basis of clinical outcomes. On the other hand, the prevalence of asymptomatic atherosclerosis, defined in terms of plaques in ultrasonography, reaches to 15% of patients with APS compared to 9% of SLE patients and 3% of normal controls. Among SLE patients with aPL, the prevalence of plaques ranges from 6% in premenopausal women to 31% in unselected patients. Less than 10% of APS patients express premature atherosclerosis in the absence of other risk factors. Which APS patient will develop atherosclerosis is unpredictable.

B cell biology, apoptosis, and autoantibodies to phospholipids

Systemic autoimmune diseases are characterised by the development of a relatively narrow spectrum of autoantibodies. These are of considerable diagnostic value. In addition, in some diseases, including anti-phospholipid syndrome, these autoantibodies can be directly pathogenic. Understanding how these autoantibodies are formed represents an important avenue towards understanding the pathogenesis of systemic autoimmune disease itself. The minimum requirements for production of autoantibodies are self-reactive B cells and the availability of autoantigen. In other words, their formation is determined by factors that shape the B cell repertoire and the distribution and immunogenicity of the relevant autoantigens. On the B cell side, the propensity to produce autoantibodies depends on the fidelity of B cell self-tolerance mechanisms, B cell differentiation and selection into different peripheral compartments. These processes are interdependent, because both selection into different peripheral and mechanisms of B cell self-tolerance are influenced by signalling through the B cell receptor (BCR). On the antigen supply side, apoptotic cells appear to be a crucial source of antigenic targets of systemic autoimmunity, and elaborate mechanisms exist to ensure that apoptotic corpses undergo efficient disposal and do not become immunogenic. Several defects have been described where the disposal of apoptotic cells is compromised leading to their accumulation in parenchymal organs. These may become immunogenic resulting in autoantibody formation. The mechanisms that lead to progression from accumulation of autoantigen, in the form of apoptotic corpses, to the production of autoantibodies by self-reactive B cells within different parts of the peripheral repertoire are discussed.

β2-glycoprotein I: antiphospholipid syndrome and T-cell reactivity

There is increasing evidence showing that recurrent thrombosis and intrauterine fetal loss in antiphospholipid syndrome (APS) are attributable to antiphospholipid (aPL) antibodies. We have recently identified autoreactive CD4+ T cells to beta2-glycoprotein I (beta2GPI) that promote production of pathogenic antiphospholipid antibodies. beta2GPI-specific CD4+ T cells preferentially recognize the antigenic peptide containing the major phospholipid (PL)-binding site in the context of DR53. T-cell helper activity that stimulates B cells to produce IgG anti-beta2GPI antibodies is mediated through IL-6 and CD40-CD154 interaction. beta2GPI-specific T cells respond to reduced beta2GPI and recombinant beta2GPI fragments produced in a bacterial expression system but not to native beta2GPI, indicating that the epitopes recognized by beta2GPI-specific T cells are 'cryptic' determinants, which are generated at a subthreshold level by the processing of native beta2GPI under normal circumstances. Although beta2GPI-specific T cells are detected in both APS patients and healthy individuals, these autoreactive T cells are activated in vivo in APS patients but not in healthy individuals. These findings indicate activation of beta2GPI-specific T cells and subsequent production of pathogenic anti-beta2GPI antibodies can be induced by the exposure of such T cells to cryptic peptides of beta2GPI efficiently presented by functional antigen-presenting cells (APC). Delineating the mechanisms that induce the efficient processing and presentation of cryptic determinants of beta2GPI as a consequence of antigen processing would clarify the etiology that initiates the autoantibody response in APS.

Relative purity of thrombin-based hemostatic agents used in surgery

BACKGROUND

Hemostatic agents used in surgery contain thrombin isolated from either a bovine or human source. The use of thrombin derived from a bovine source has been associated with the development of an abnormal immune response, but a study of the immunoreactivity of the various commercially available thrombin preparations has not been conducted. This study determined the relative purity of commercially available thrombin preparations, if humans have natural antibodies that recognize these preparations, and if elicited antibodies against bovine thrombin cross-react with other bovine or human hemostatic agents.

STUDY DESIGN

The purity of hemostatic agents was determined by protein and substrate assays, electrophoresis, and immunoblotting. The natural antigenicity and cross-reactivity of elicited antibodies were measured by ELISA using serum samples from 82 donors from the Red Cross and serum collected from patients exposed to bovine thrombin, respectively.

RESULTS

All of the bovine thrombin preparations were found to contain the xenogeneic carbohydrate galactosealpha1-3galactose. The natural antigenicity of the bovine thrombin preparations was greater than that of a human thrombin preparation and similar to that of porcine aortic endothelial cells. Antibodies elicited against bovine thrombin were found to cross-react with other bovine preparations and other xenoantigens but not with human hemostatic preparations.

CONCLUSIONS

All patients have antibovine thrombin antibodies, even before exposure to bovine thrombin-containing hemostatic agents. The cross-reactivity of elicited antibovine thrombin antibodies indicates that if a patient has been sensitized to a bovine product, it is likely safer to use a human-derived product in lieu of a bovine product.

Viral origin of antiphospholipid antibodies: endothelial cell activation and thrombus enhancement by CMV peptide-induced APL antibodies

Our observations and those from others, give further support to our hypothesis that "autoimmune aPL" may be generated by immunization with products from bacteria or viruses after incidental exposure or infection. We also were able to generate APS-like syndrome in a strain of mice susceptible to autoimmunity, indicating that other factors such as genetics are likely to be involved in the development of APS. Furthermore, not all aPL antibodies generated by immunization with bacterial or viral products are pathogenic. Based on the clinical experience and on the numerous reports indicating presence of aPL in a large number of infectious diseases, it may be expected that not all aPL antibodies produced during infection will be pathogenic. We hypothesize that a limited number aPL antibodies induced by certain viral/bacterial products would be pathogenic in certain groups of predisposed individuals. Identification of these bacterial and/ or viral agents may help to find strategies for the prevention of production of aPL "pathogenic" antibodies. Alternatively, free peptides may be used to induce tolerance against aPL production.

Antibodies to the atherosclerotic plaque components beta2-glycoprotein I and heat-shock proteins as risk factors for acute cerebral ischemia

One third of cases of cerebral ischemia have no clear etiology. A humoral response to the atherosclerotic plaques components beta2-glycoprotein l (beta2-gpl) and heat-shock proteins (Hsp) might be involved in the pathogenesis of stroke. This case-control study includes a complete profile of anti-beta2-gpl antibodies and testing of IgG antibodies to the 60/65 kilodaltons (kDa) Hsp in stroke patients. Ninety-three patients with acute ischemic stroke and 93 controls were evaluated for age, sex, race, hypertension, smoking, previous cardiopathy, diabetes mellitus, hypercholesterolemia and previous history of cerebral ischemia. lgG/lgM/lgA anticardiolipin (aCL) and anti-beta2-gpl antibodies, as well as lgG antibodies to human 60 kDa Hsp and to Mycobacterium bovis 65 kDa Hsp, were detected by immunoassay. Adjusted odds ratios (OR) were calculated by logistic regression. The adjusted OR for IgA anti-beta2-gpl antibodies was 4.6 (90%Cl 1.5 to 14.3; p = 0.025). The non-adjusted OR for IgG antibodies to Hsp 60 was 26.1. The adjusted OR for IgG antibodies to Hsp 65 was 3.2 (90%Cl 1.2 to 8.3; p = 0.044). The adjusted OR for lgG to any Hsp (60 or 65) was 4.8 (90%Cl 1.9 to 12.1; p = 0.006). This study demonstrates that elevated IgA anti-beta2-gpl and lgG anti-Hsp 60/65 antibodies are associated with increased risk of ischemic stroke. The association occurred independently of other risk factors. This humoral response might link autoimmunity, thrombophilia and atherosclerosis in stroke patients.

Antiphospholipid antibodies in pediatric and adult patients with rheumatic disease are associated with parvovirus B19 infection

OBJECTIVE

To show a possible association between parvovirus B19 infection and the presence of antiphospholipid antibodies (aPL) in patients with rheumatic diseases.

METHODS

Serum samples obtained from 88 children with various forms of juvenile rheumatic disease and from 40 adults with systemic lupus erythematosus, the antiphospholipid syndrome, or other rheumatic disease, who had previously been tested and shown to be positive for IgG aPL, were analyzed for the presence of B19 DNA, for antibodies against the B19 viral proteins VP1, VP2, and NS1, and for IgG aPL (anticardiolipin, anti-beta(2)-glycoprotein I, and antiphosphatidylserine). As controls, serum samples obtained from 135 children with noninflammatory bone diseases or growth retardation were also analyzed.

RESULTS

Twenty-four (27%) of the 88 children with rheumatic diseases had detectable amounts of IgG aPL. Fourteen (58%) of these 24 IgG aPL-positive patients showed IgG against VP1/VP2 and viral genomes, indicating the presence of acute (2 patients) or persistent (12 patients) infection. Past parvovirus B19 infection was identified in 7 (29%) of 24 IgG aPL-positive children, as indicated by VP1/VP2-specific IgG in the absence of viral DNA. Three (12%) of 24 IgG aPL-positive children had not been infected with B19. Sixty-nine (51%) of 135 control children displayed VP1/VP2-specific IgG. Three (2%) of these 135 children were IgG aPL positive (2 children had past parvovirus B19 infection, and 1 was negative for parvovirus B19). Analysis of the parvovirus B19 status of 40 adult IgG aPL-positive patients showed that 33 (83%) were anti-IgG VP1/VP2-positive, and viral DNA was detected in 11 patients (28%). Ten of these 11 viremic patients were in the subgroup of 28 IgG aPL-positive SLE patients.

CONCLUSION

Antiphospholipid antibodies are preferentially found in serum of children with juvenile idiopathic arthritis who have been previously infected with parvovirus B19 and have established, persistent infection. Adult patients with IgG aPL positivity have a high incidence of persistent parvovirus B19 infection. We conclude that parvovirus B19 might be directly involved in the elicitation of autoimmune reactions partly mediated by aPL.

Autoreactive CD4(+) T cells to beta(2)-glycoprotein I in patients with antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by recurrent thrombosis and intrauterine fetal loss in association with antiphospholipid antibodies (aPL). We have recently identified autoreactive CD4(+) T cells to beta(2)-glycoprotein I (beta(2)GPI) that promote aPL production in APS patients. beta(2)GPI-specific CD4(+) T cells preferentially recognize the antigenic peptide containing the major phospholipid-binding site in the context of DRB4*0103 (DR53). T-cell receptor beta chains of beta(2)GPI-specific T cells are highly restricted and mainly utilize rearranged Vbeta7 or Vbeta8 gene segments. T-cell helper activity that stimulates B cells to produce anti-beta(2)GPI antibodies is mediated through IL-6 and CD40-CD40 ligand engagement. beta(2)GPI-specific T cells respond to reduced beta(2)GPI and recombinant beta(2)GPI fragments produced in bacteria, but not to native beta(2)GPI, indicating that the epitopes recognized by beta(2)GPI-specific T cells are apparently cryptic. Activation of beta(2)GPI-specific T cells resulting in production of pathogenic anti-beta(2)GPI antibodies can be induced by the exposure to cryptic peptides of beta(2)GPI. Finally, beta(2)GPI-specific T cell is a reasonable target of potential therapeutic strategies that selectively suppress pathogenic aPL production in APS patients.

Behavioral and cognitive deficits occur only after prolonged exposure of mice to antiphospholipid antibodies

The antiphospholipid (Hughes) syndrome (APS) includes systemic and central nervous system (CNS) pathology associated with antibodies to a complex of phospholipids and beta2-glycoprotein I (beta2-GPI). Beta2-GPI immunized mice develop systemic manifestations of APS and we presently examined CNS manifestations in this APS model. Female BALB/c mice were immunized once with beta2-GPI in complete Freund's adjuvant (CFA) or with CFA alone (controls). A staircase test and a T-maze alternation test were performed to test behavior and cognition in independent groups of mice 6, 12 and 18 weeks following the immunization. The APS mice developed elevated levels of antibodies against negatively charged phospholipids and beta2-GPI. Neurological impairment was detected only 18 weeks after the induction of the APS and consisted of both cognitive (53 +/- 4 vs 71 +/- 3% correct choices in the T-maze alternation for APS vs control mice, P < 0.001) and behavioral changes (higher number of rears (18 +/- 2 vs 11 +/- 1, P < 0.006) and higher number of stairs climbed (12 +/- 2 vs 7 +/- 1, P < 0.02). This is the first report of cognitive deficits in this APS model and demonstrates the time course for the development of previously described behavioral changes. The mechanism involved in these CNS manifestations remains to be elucidated.

Antiphospholipid Antibody Syndrome

Antiphospholipid antibody syndrome (APS) is a recently defined autoimmune disorder characterized by recurrent vascular thromboses or recurrent pregnancy morbidity; these features are linked to the presence in blood of autoantibodies against negatively charged phospholipids or phospholipid-binding proteins. Thrombosis can occur in any tissue, in veins, arteries, or the microvasculature. Pregnancy morbidity in APS includes miscarriages or premature birth. Criteria that define the major clinical and laboratory features of APS were published in 1999. In patients with antiphospholipid antibodies and prior thrombosis or pregnancy morbidity, there is a high risk of recurrence that persists as long as antiphospholipid antibodies occur in blood. This risk for recurrence of thrombosis or pregnancy morbidity is greatly reduced by preventive anticoagulant therapy. Patients presenting with thrombosis in APS are initially managed in much the same way as are patients with vascular thrombosis owing to other causes. However, in patients with APS, high-intensity anticoagulation is usually needed to prevent recurrences of thrombosis. Thrombosis in APS is often multifactorial, as with non-APS thrombosis. Therefore, in all patients with APS, other reversible risk factors for thrombosis should be sought. The pregnancy outcome of women with APS who have had prior miscarriages is greatly improved by treatment during pregnancy with a combination of heparin and low-dose aspirin.

Immunization of naive BALB/c mice with human beta2-glycoprotein I breaks tolerance to the murine molecule

OBJECTIVE

Immunization of naive mice with beta2-glycoprotein I (beta2GPI) leads to the generation of pathogenic anticardiolipin antibodies associated with clinical manifestations of the antiphospholipid syndrome (APS). The aim of this study was to determine whether immunization of naive mice with human beta2GPI, which shares homology with mouse beta2GPI molecules, breaks tolerance to murine beta2GPI and leads to the generation of anti-mouse beta2GPI.

METHODS

Twenty-four female BALB/c mice were immunized in the footpads with 10 microg of human beta2GPI. Twelve age- and sex-matched BALB/c mice were immunized in the same manner with Freund's complete adjuvant and served as controls. The reactivity of whole sera, polyclonal IgG, and affinity-purified anti-beta2GPI IgG antibodies against human, bovine, and mouse beta2GPI was evaluated by enzyme-linked immunosorbent assay.

RESULTS

High titers of anti-human beta2GPI IgG antibodies were detected 1 month after immunization. Progressively increasing titers against murine and bovine beta2GPI were recorded 1-4 months after injection.

CONCLUSION

Immunization of mice with human beta2GPI resulted in the generation of antibodies reacting with human, bovine, and murine beta2GPI. The loss of tolerance to mouse beta2GPI is attributable to the high interspecies homology of beta2GPI. These results may point to molecular mimicry as a possible cause of APS.

Bacterial induction of autoantibodies to beta2-glycoprotein-I accounts for the infectious etiology of antiphospholipid syndrome

The antiphospholipid syndrome (APS) is characterized by the presence of pathogenic autoantibodies against beta2-glycoprotein-I (beta2GPI). The factors causing production of anti-beta2GPI remain unidentified, but an association with infectious agents has been reported. Recently, we identified a hexapeptide (TLRVYK) that is recognized specifically by a pathogenic anti-beta2GPI mAb. In the present study we evaluated the APS-related pathogenic potential of microbial pathogens carrying sequences related to this hexapeptide. Mice immunized with a panel of microbial preparations were studied for the development of anti-beta2GPI autoantibodies. IgG specific to the TLRVYK peptide were affinity purified from the immunized mice and passively infused intravenously into naive mice at day 0 of pregnancy. APS parameters were evaluated in the infused mice on day 15 of pregnancy. Following immunization, high titers of antipeptide [TLRVYK] anti-beta2GPI Ab's were observed in mice immunized with Haemophilus influenzae, Neisseria gonorrhoeae, or tetanus toxoid. The specificity of binding to the corresponding target molecules was confirmed by competition and immunoblot assays. Naive mice infused with the affinity-purified antipeptide Ab's had significant thrombocytopenia, prolonged activated partial thromboplastin time and elevated percentage of fetal loss, similar to a control group of mice immunized with a pathogenic anti-beta2GPI mAb. Our study establishes a mechanism of molecular mimicry in experimental APS, demonstrating that bacterial peptides homologous with beta2GPI induce pathogenic anti-beta2GPI Ab's along with APS manifestations.

Bacterial induction of autoantibodies to beta2-glycoprotein-I accounts for the infectious etiology of antiphospholipid syndrome

The antiphospholipid syndrome (APS) is characterized by the presence of pathogenic autoantibodies against beta2-glycoprotein-I (beta2GPI). The factors causing production of anti-beta2GPI remain unidentified, but an association with infectious agents has been reported. Recently, we identified a hexapeptide (TLRVYK) that is recognized specifically by a pathogenic anti-beta2GPI mAb. In the present study we evaluated the APS-related pathogenic potential of microbial pathogens carrying sequences related to this hexapeptide. Mice immunized with a panel of microbial preparations were studied for the development of anti-beta2GPI autoantibodies. IgG specific to the TLRVYK peptide were affinity purified from the immunized mice and passively infused intravenously into naive mice at day 0 of pregnancy. APS parameters were evaluated in the infused mice on day 15 of pregnancy. Following immunization, high titers of antipeptide [TLRVYK] anti-beta2GPI Ab's were observed in mice immunized with Haemophilus influenzae, Neisseria gonorrhoeae, or tetanus toxoid. The specificity of binding to the corresponding target molecules was confirmed by competition and immunoblot assays. Naive mice infused with the affinity-purified antipeptide Ab's had significant thrombocytopenia, prolonged activated partial thromboplastin time and elevated percentage of fetal loss, similar to a control group of mice immunized with a pathogenic anti-beta2GPI mAb. Our study establishes a mechanism of molecular mimicry in experimental APS, demonstrating that bacterial peptides homologous with beta2GPI induce pathogenic anti-beta2GPI Ab's along with APS manifestations.