Correlation between the potency of a beta2-glycoprotein I-dependent lupus anticoagulant and the level of resistance to activated protein C

Thrombin Generation Assay in Antiphospholipid Antibodies Positive Subjects as a Personalized Thrombotic Risk Assessment: State of the Art and Perspectives

PURPOSE OF THE REVIEW

Thrombotic risk assessment in antiphospholipid positive (aPL +) subjects is a major challenge, and the study of in vitro thrombin generation (thrombin generation assays (TGA)) could provide useful information. Activated protein C (APC) sensitivity is involved in thrombotic events in antiphospholipid syndrome patients. We summarized methods used to assess APC sensitivity with TGA and evaluated the prognostic role of APC resistance through literature search.

RECENT FINDINGS

APC resistance induced by aPL is a complex pathway. Several cross-sectional studies assessed APC sensitivity to understand thrombotic event mechanisms in aPL + subjects. Only one prospective cohort had investigated the prognostic impact of APC resistance in aPL + subjects, with a positive and significant correlation between APC sensitivity and the risk of thrombosis during the follow up (hazard ratio, 6.07 [95% CI, 1.69-21.87]). APC resistance assessed with TGA could be associated with thrombotic events in aPL + subjects.

Anti-β2-glycoprotein I and anti-phosphatidylserine/prothrombin antibodies interfere with cleavage of factor V(a) by activated protein C

BACKGROUND

The acquired thrombotic risk factor known as lupus anticoagulant (LA) interferes with laboratory clotting assays and can be caused by autoantibodies against β2-glycoprotein I (β2GPI) and prothrombin. LA is associated with activated protein C (APC) resistance, which might contribute to thrombotic risk in patients with antiphospholipid syndrome. How antibodies against β2GPI and prothrombin cause APC resistance is currently unclear.

OBJECTIVES

To investigate how anti-β2GPI and antiphosphatidylserine/prothrombin (PS/PT) antibodies induce APC resistance.

METHODS

The effects of anti-β2GPI and anti-PS/PT antibodies on APC resistance were studied in plasma (of patients with antiphospholipid syndrome) and with purified coagulation factors and antibodies.

RESULTS

APC resistance was observed in LA-positive patients with anti-β2GPI or anti-PS/PT antibodies and in normal plasma spiked with monoclonal anti-β2GPI or anti-PS/PT antibodies with LA activity. Analysis of factor (F)V cleavage patterns after APC incubation indicated that anti-β2GPI antibodies attenuated APC-mediated FV cleavage at R506 and R306. APC-mediated cleavage at R506 is required for FV cofactor activity during inactivation of FVIIIa. Assays with purified coagulation factors confirmed that anti-β2GPI antibodies interfered with the cofactor function of FV during FVIIIa inactivation but not with FVa inactivation. Anti-PS/PT antibodies attenuated APC-mediated FVa and FVIIIa inactivation. Analysis of FV(a) cleavage patterns after APC incubation indicated that anti-PS/PT antibodies interfere with APC-mediated cleavage of FV at positions R506 and R306.

CONCLUSION

Anti-β2GPI antibodies with LA activity contribute to a procoagulant state by causing APC resistance via interference with the cofactor function of FV during FVIIIa inactivation. LA-causing anti-PS/PT antibodies interfere with the anticoagulant function of APC by preventing FV(a) cleavage.

Interaction between Antiphospholipid Antibodies and Protein C Anticoagulant Pathway: A Narrative Review

Thrombotic antiphospholipid syndrome (APS) is a condition in which thrombosis in venous, arterial, and/or small vessels is ascribed to the presence of antiphospholipid antibodies (aPL). Among the various proposed pathogenic theories to explain thrombotic APS, those involving the interaction between aPL and the protein C system have gained much consensus. Indeed, robust data show an acquired activated protein C resistance (APC-R) in these patients. The role of aPL in this impairment is clear, but the mechanism of action is uncertain, as the type of aPL and to what extent aPL are involved remains a gray area. Lupus anticoagulant (LA) is often associated with APC-R, but antibodies generating LA comprise those directed to β2-glycoprotein I and antiphosphatidylserine/prothrombin. Moreover, the induction of APC-R by aPL requires the presence of phospholipids and is suppressed by the presence of an excess of phospholipids. How phospholipids exposed on the cell membranes work in the system in vivo is unknown. Interestingly, acquired APC-R due to aPL might explain the clinical phenotypes of thrombotic APS. Indeed, the literature reports cases of both venous and arterial thromboembolism as well as skin necrosis, the latter observed in the severe form of protein C deficiency and in catastrophic APS.

Neuropsychiatric Manifestations of Antiphospholipid Syndrome—A Narrative Review

Antiphospholipid syndrome (APS) is a common autoimmune pro-thrombotic condition characterised by thrombosis and pregnancy morbidity. There are a broad range of neuropsychiatric manifestations associated with APS, from focal symptoms to more global dysfunction. Patients commonly present with transient ischaemic attacks and ischaemic strokes, with identifiable lesions on brain imaging. However, the underlying pathogenesis remains uncertain in other manifestations, such as cognitive dysfunction, seizures, headache and chorea. The aim is to provide a comprehensive review of the various neuropsychiatric manifestations associated with APS. A detailed literature search was applied to PubMed, including citations from 1983 to December 2021.

Microparticles: An Alternative Explanation to the Behavior of Vascular Antiphospholipid Syndrome

Antiphospholipid syndrome is an autoimmune disease characterized by the persistent presence of antiphospholipid antibodies, along with occurrence of vascular thrombosis and pregnancy morbidity. The variety of antiphospholipid antibodies and their related mechanisms, as well as the behavior of disease in wide groups of patients, have led some authors to propose a differentiation of this syndrome into two independent entities: vascular and obstetric antiphospholipid syndrome. Thus, previous studies have discussed whether specific autoantibodies may be responsible for this differentiation or, in contrast, how the same antibodies are able to generate two different clinical presentations. This discussion is yet to be settled. The capability of serum IgG from patients with vascular thrombosis to trigger the biogenesis of endothelial cell-derived microparticles in vitro is one of the previously discussed differences between the clinical entities of antiphospholipid syndrome. These vesicles constitute a prothrombotic mechanism as they can directly lead to clot activation in murine models and recalcified human plasma. Nevertheless, other indirect mechanisms by which microparticles can spread a procoagulant phenotype could be critical to understanding their role in antiphospholipid syndrome. For this reason, questions regarding the cargo of microparticles, and the signaling pathways involved in their biogenesis, are of interest in attempting to explain the behavior of this autoimmune disease.

Clinical Relevance of Isolated Lupus Anticoagulant Positivity in Patients with Thrombotic Antiphospholipid Syndrome

Background Patients positive for all three types of antiphospholipid antibodies (aPLs; triple positivity) have been identified for having a high risk for thrombotic events. However, the clinical significance of isolated lupus anticoagulant (LAC) positivity is debated.

Objectives To investigate the clinical relevance of isolated LAC.

Methods A total of 456 patients were enrolled in this study; 66 antiphospholipid syndrome patients and 390 control patients. The control group consisted of autoimmune patients (n = 91), patients with thrombosis but without aPLs (n = 127), and normal controls (n = 172). LAC, anticardiolipin (anti-CL), and anti-β2 glycoprotein I (anti-β2GPI) immunoglobulin G (IgG) and immunoglobulin M (IgM) were determined according to the International Society on Thrombosis and Haemostasis (ISTH) guidelines. Anti-CL and anti-β2GPI were measured by four different solid-phase platforms to overcome variability between test systems. The noncriteria IgA anti-CL and anti-β2GPI, antidomain I of β2GPI IgG, and antiphosphatidylserine/prothrombin antibodies (anti-PS/PT) IgG and IgM were detected according to the ISTH guidelines for solid-phase assays.

Results In total, 70 patients were positive for LAC, of which 44 were negative for both anti-β2GPI and anti-CL antibodies. We found that isolated LAC proved to be strongly associated with vascular thrombosis (odds ratio [OR]: 7.3; 95% confidence interval [CI]: 3.3–16.1), even better than triple-positive samples (OR: 4.3; 95% CI: 1.6–12.2). The titers of the anti-PS/PT IgG and IgM were significantly higher in triple-positivity samples compared with samples with isolated LAC positivity. The majority of single LAC positives were anti-PS/PT-negative. We observed that LAC positivity was weaker in isolated LAC-positive patients compared with LAC activity in triple-positive patients.

Conclusion Isolated LAC was highly associated with thrombosis. The presence of anti-PS/PT antibodies could not explain LAC positivity in isolated LAC. Isolated LAC showed a weaker LAC activity compared with triple-positive patients.

Anti-β2-glycoprotein I autoantibodies influence thrombin generation parameters via various mechanisms

INTRODUCTION

Antiphospholipid syndrome (APS) is a systemic autoimmune disease characterised by recurrent thrombotic events, pregnancy loss and thrombocytopenia and the presence of antiphospholipid antibodies (APL). The exact pathomechanism of APS is still unknown, thus we investigated the effect of anti-β₂-glycoprotein I (anti-β₂GPI) on thrombin generation in different plasma samples.

METHODS

For the separation of anti-β₂GPI IgG, overall 12 APS patients were selected. The criteria were the existence of lupus anticoagulant, and the presence of anti-CL and anti-β₂GPI, the latter exceeding at least 25 times the upper reference limit. We purified anti-β₂GPI IgG antibodies from APS patients by affinity chromatography and added the antibodies to normal pooled, and heterozygous forms of inherited thrombophilia plasma samples (prothrombin G20210A, factor V Leiden). To further specify the mechanism of the effect, we also used factor deficient plasmas in the thrombin generation assay.

RESULTS

In normal pooled plasma, the anti-β₂GPI significantly prolonged Lag Time according to the lupus anticoagulant effect, in contrast, it also elevated Peak Thrombin significantly, which suggests a procoagulant effect. The antibody was also able to exert this multi-faceted effect both in FV_Leiden heterozygous plasma and prothrombin G20210A heterozygous polymorphism, however, the prolonging effect was more remarkable in the latter. By using factor deficient plasmas, it was found that FVII is required for the prolongation, while intrinsic factors are needed for the elevation of the Peak Thrombin.

CONCLUSION

The anti-β₂GPI autoantibodies exert their effect in both normal and thrombophilic plasmas via various mechanisms.

Thrombin generation in subjects with lupus anticoagulant without prior thrombosis or gestational morbidities

BACKGROUND

Lupus anticoagulant (LA) can be a cause of thrombosis and/or pregnancy morbidities, producing antiphospholipid syndrome (APS). An increase in thrombin generation (TG) is correlated with prothrombotic status. Several changes in TG-derived parameters have been reported in APS patients.

OBJECTIVES

Evaluate whether the TG phenotype of APS can also be described in LA subjects without clinical manifestations of APS, and to investigate the possible influence of both LA potency and antiphospholipid (aPL) profile on it.

RESULTS

TG was analyzed in 153 cases of LA and 41 healthy controls. We have observed prolongation of both lag time (3.7 min vs 2.32 min, p < 0.001) and time to peak (6.48 min vs 5.27 min, p < 0.001), increased peak height (221.7 nM vs 182.7 nM, p < 0.001), slightly higher ETP (221.7 nM·min vs 182.7 nM·min, p = 0.041), and higher velocity index (100.7 nM/min vs 74.53 nM/min, p = 0.001) in LA subjects compared to controls. After adding thrombomodulin (TM), ETP%inh was significantly lower in LA group (37.90% vs 59.90%, p < 0.001) showing resistance to TM/activated protein C (APC). Significant differences were found in lag time, time to peak and ETP%inh according to the potency and aPL profile.

CONCLUSIONS

Previously described differences in TG-derived parameters in APS patients have been confirmed in incidental LA subjects: prolonged lag time and time to peak, slightly higher ETP, higher peak height, and less sensitivity to TM/APC. High LA potency and triple-positive aPL profile enhance differences in lag time, time to peak and, especially, increase APC resistance, but no effect in ETP was observed.

Prothrombin conversion is accelerated in the antiphospholipid syndrome and insensitive to thrombomodulin

Antiphospholipid syndrome (APS) is a condition in which the presence of antibodies against phospholipid-binding proteins is associated with thrombophilia and/or pregnancy morbidity. Although antiphospholipid antibodies have anticoagulant characteristics in vitro, they are associated with thromboembolic complications. Thrombin generation (TG) is a sensitive global test of coagulation, and elevated TG is associated with thrombosis. Increased TG can be caused by increased prothrombin conversion, decreased thrombin inactivation, or a combination of both. In this study, we measured TG in APS patients and healthy controls with and without vitamin K antagonist (VKA) treatment at 1 and 5 pM tissue factor and with thrombomodulin. Prothrombin conversion and thrombin inactivation were determined by thrombin dynamics analysis. The TG peak was increased in nontreated APS patients at 1 pM TF compared with nontreated controls. Prothrombin conversion was significantly increased in nontreated APS patients. In contrast, prothrombin conversion did not differ in controls and patients that were on VKA therapy. Thrombin inactivation was comparable between controls and APS patients in the presence and absence of VKAs. Both TG (peak and ETP) and prothrombin conversion were significantly higher in APS patients with prior thrombosis compared with patients without a history of thrombosis. In this study, we demonstrate that in APS, the hemostatic balance shifts toward a more prothrombotic phenotype due to elevated prothrombin conversion but unchanged thrombin inactivation rates. Within the group of APS patients, increased TG and prothrombin conversion are associated with a history of thrombosis.

Clinical Risk Assessment in the Antiphospholipid Syndrome: Current Landscape and Emerging Biomarkers

PURPOSE OF REVIEW

Laboratory criteria for the classification of antiphospholipid syndrome include the detection of a lupus anticoagulant and/or anticardiolipin and anti-β2-glycoprotein I antibodies. However, the majority of patients who test positive in these assays do not have thrombosis. Current risk-stratification tools are largely limited to the antiphospholipid antibody profile and traditional thrombotic risk factors.

RECENT FINDINGS

Novel biomarkers that correlate with disease activity and potentially provide insight into future clinical events include domain 1 specific anti-β₂GPI antibodies, antibodies to other phospholipids or phospholipid/protein antigens (such as anti-PS/PT), and functional/biological assays such as thrombin generation, complement activation, levels of circulating microparticles, and annexin A5 resistance. Clinical risk scores may also have value in predicting clinical events. Biomarkers that predict thrombosis risk in patients with antiphospholipid antibodies have been long sought, and several biomarkers have been proposed. Ultimately, integration of biomarkers with established assays and clinical characteristics may offer the best chance of identifying patients at highest risk of APS-related complications.

Diagnosis and management of the antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy complications in the presence of persistent antiphospholipid antibodies (APLA). Laboratory diagnosis of APLA depends upon the detection of a lupus anticoagulant, which prolongs phospholipid-dependent anticoagulation tests, and/or anticardiolipin (aCL) and anti-β2-glycoprotein-1 (β2GPI) antibodies. APLA are primarily directed toward phospholipid binding proteins. Pathophysiologic mechanisms underlying thrombosis and pregnancy loss in APS include APLA induced cellular activation, inhibition of natural anticoagulant and fibrinolytic systems, and complement activation, among others. There is a high rate of recurrent thrombosis in APS, especially in triple positive patients (patients with lupus anticoagulant, aCL and anti-β2GPI antibodies), and indefinite anticoagulation with a vitamin K antagonist is the standard of care for thrombotic APS. There is currently insufficient evidence to recommend the routine use of direct oral anticoagulants (DOAC) in thrombotic APS. Aspirin with low molecular weight or unfractionated heparin may reduce the incidence of pregnancy loss in obstetric APS. Recent insights into the pathogenesis of APS have led to the identification of new potential therapeutic interventions, including anti-inflammatory and immunomodulatory therapies. Additional research is needed to better understand the effects of APLA on activation of signaling pathways in vascular cells, to identify more predictive biomarkers that define patients at greatest risk for a first or recurrent APLA-related clinical event, and to determine the safety and efficacy of DOACs and novel anti-inflammatory and immune-modulatory therapies for refractory APS.

Recent advances in understanding antiphospholipid syndrome

Antiphospholipid syndrome (APS), also known as Hughes Syndrome, is a systemic autoimmune disease characterized by thrombosis and/or pregnancy morbidity in the presence of persistently positive antiphospholipid antibodies. A patient with APS must meet at least one of two clinical criteria (vascular thrombosis or complications of pregnancy) and at least one of two laboratory criteria including the persistent presence of lupus anticoagulant (LA), anticardiolipin antibodies (aCL), and/or anti-b2 glycoprotein I (anti-b2GPI) antibodies of IgG or IgM isotype at medium to high titres in patient’s plasma. However, several other autoantibodies targeting other coagulation cascade proteins (i.e. prothrombin) or their complex with phospholipids (i.e. phosphatidylserine/prothrombin complex), or to some domains of β2GPI, have been proposed to be also relevant to APS. In fact, the value of testing for new aPL specificities in the identification of APS in thrombosis and/or pregnancy morbidity patients is currently being investigated.

Circulating microparticles in patients with antiphospholipid antibodies: characterization and associations

The antiphospholipid syndrome is characterized by venous or arterial thrombosis and/or recurrent fetal loss in the presence of circulating antiphospholipid antibodies. These antibodies cause activation of endothelial and other cell types leading to the release of microparticles with procoagulant and pro-inflammatory properties. The aims of this study were to characterize the levels of endothelial cell, monocyte or platelet derived, and tissue factor-bearing microparticles in patients with antiphospholipid antibodies, to determine the association of circulating microparticles with anticardiolipin and anti-β2-glycoprotein antibodies, and to define the cellular origin of microparticles that express tissue factor. Microparticle content within citrated blood from 47 patients with antiphospholipid antibodies and 144 healthy controls was analyzed within 2hours of venipuncture. Levels of Annexin-V, CD105 and CD144 (endothelial derived), CD41 (platelet derived) and tissue factor positive microparticles were significantly higher in patients than controls. Though levels of CD14 (monocyte-derived) microparticles in patient plasma were not significantly increased, increased levels of CD14 and tissue factor positive microparticles were observed in patients. Levels of microparticles that stained for CD105 and CD144 showed a positive correlation with IgG (R=0.60, p=0.006) and IgM anti-beta2-glycoprotein I antibodies (R=0.58, p=0.006). The elevation of endothelial and platelet derived microparticles in patients with antiphospholipid antibodies and their correlation with anti-β2-glycoprotein I antibodies suggests a chronic state of vascular cell activation in these individuals and an important role for β2-glycoprotein I in development of the pro-thrombotic state associated with antiphospholipid antibodies.

Receptors involved in cell activation by antiphospholipid antibodies

The antiphospholipid syndrome (APS) is an autoimmune disease associated with arterial or venous thrombosis and/or recurrent fetal loss and is caused by pathogenic antiphospholipid antibodies (aPLA). The plasma protein β2-glycoprotein 1 (β2GP1) has been identified as a major target of aPLA associated with APS. Cell activation by aPLA appears to be a major pathogenic cause in the pathogenesis of APS. Receptors, co-receptors and accessory molecules are known to assist the pathogenic effects of aPLA. Members of the TLR family and the platelet receptor apolipoprotein E receptor 2' (apoER2'), a receptor belonging to the low-density lipoprotein receptor (LDL-R) family, as well as GPIbα, were identified as putative candidates for aPLA recognition. CD14, a co-receptor for TLR2 and TLR4, and annexin A2, a ubiquitous Ca2+ -binding protein that is essential for actin-dependent vesicle transport, could serve as important accessory molecules in mediating the pathogenic effects of aPLA. Finally, complement activation has been reported in association with the pathogenicity of APS. The relative contribution of these different mechanisms in the pathogenesis of APS is controversial. Here, we review the various in vivo and in vitro models that have been used to investigate the pathogenic mechanisms of aPLA in APS.

Endothelial cell activation by antiphospholipid antibodies is modulated by Kruppel-like transcription factors

Antiphospholipid syndrome is characterized by thrombosis and/or recurrent pregnancy loss in the presence of antiphospholipid antibodies (APLAs). The majority of APLAs are directed against phospholipid-binding proteins, particularly β₂-glycoprotein I (β₂GPI). Anti-β₂GPI antibodies activate endothelial cells in a β₂GPI-dependent manner through a pathway that involves NF-κB. Krüppel-like factors (KLFs) play a critical role in regulating the endothelial response to inflammatory stimuli. We hypothesized that activation of endothelial cells by APLA/anti-β₂GPI antibodies might be associated with decreased expression of KLFs, which in turn might facilitate cellular activation mediated through NF-κB. Our experimental results confirmed this hypothesis, demonstrating markedly decreased expression of KLF2 and KLF4 after incubation of cells with APLA/anti-β₂GPI antibodies. Restoration of KLF2 or KLF4 levels inhibited NF-κB transcriptional activity and blocked APLA/anti-β₂GPI-mediated endothelial activation despite NF-κB p65 phosphorylation. Chromatin immunoprecipitation analysis demonstrated that inhibition of NF-κB transcriptional activity by KLFs reflects sequestration of the cotranscriptional activator CBP/p300, making this cofactor unavailable to NF-κB. These findings suggest that the endothelial response to APLA/anti-β₂GPI antibodies reflects competition between KLFs and NF-κB for their common cofactor, CBP/p300. Taken together, these observations are the first to implicate the KLFs as novel participants in the endothelial proinflammatory response to APLA/anti-β₂GPI antibodies.

Lupus anticoagulant interference in activated protein C resistance testing: in vitro phenomenon or in vivo pathophysiologic effect?

Second-generation activated protein C resistance (APC-R) assay was developed to avert interferences from lupus anticoagulant (LA) and warfarin therapy by prediluting the patient sample with factor V (FV)-depleted plasma. We investigated the effect of LA on the second generation APC-R assay in 121 LA-positive patients. Twenty-five APC-R-positive patients were tested for the mutation in FV (Leiden, Hong Kong, and Cambridge). Eleven had FV Leiden and twelve were negative for any mutation (2 were not tested). Of 12, 8 had APC-R suggestive of heterozygous and 4 had APC-R suggestive of homozygous defects. These patients had strong LA activity, compared to those with concurrent FVL. This was associated with a trend toward increased thrombosis risk compared to those with normal APC-R. These findings suggest that LA causes acquired APC-R, reflecting an in vivo pathophysiologic effect of LA rather than merely an in vitro phenomenon even with the second generation APC-R assay.

An international multicentre-laboratory evaluation of a new assay to detect specifically lupus anticoagulants dependent on the presence of anti-beta2-glycoprotein autoantibodies

BACKGROUND

Antiphospholipid syndrome (APS) is diagnosed by the simultaneous presence of vascular thrombosis and/or pregnancy morbidity and detection of antiphospholipid antibodies in plasma.

OBJECTIVES

We have shown that prolongation of clotting time by anti-beta2-glycoprotein I (beta2GPI) antibodies correlates better with thrombosis than a positive classic lupus anticoagulant (LAC) assay in a single center study. To confirm or falsify this finding we have conducted a multicenter study.

METHODS AND RESULTS

In 325 LAC-positive samples, we found that the beta2GPI-dependent LAC correlated 2.0 times better with thrombosis than the classic LAC assay. Although significant, this was a minimal improvement compared with the 'classic' LAC. It was published that calcium influences the behavior of anti-beta2GPI antibodies in coagulation assays. To investigate whether calcium plays a role in the present study, we divided the patient population into two groups: (i) blood was collected in 0.109 m sodium citrate and (ii) blood was drawn in 0.129 m sodium citrate as anticoagulant. We found that a positive result with the beta2GPI-dependent LAC assay correlated better with thrombosis [odds ratio (OR): 3.3, 95% confidence interval (CI) 1.9-5.8] when 0.109 m sodium citrate was used compared with 0.129 m sodium citrate (OR: 0.4, 95% CI 0.1-1.1).

CONCLUSION

We were able to confirm in an international multicenter study that a positive result in a beta2GPI-dependent LAC assay correlates better with thrombosis than the classic LAC assay, but that the assay needs further study as it is sensitive to external factors such as the sodium citrate concentration used as anticoagulant in the test sample.

Antiphospholipid antibodies and the protein C pathway

Haemostasis is a delicate balance between procoagulant and anticoagulant processes. In the human body usually anticoagulant mechanisms prevail over procoagulant mechanisms, thereby preventing a prothrombotic state. The antiphospholipid syndrome is an example in which this balance is shifted to a more prothrombotic state due to the presence of antiphospholipid antibodies. One of the most extensively proposed pathogenic mechanisms within the antiphospholipid syndrome is the inhibition of protein C by antiphospholipid antibodies. Antiphospholipid antibodies have been described to have different actions on the protein C pathway, for example decreasing protein C and/or S plasma levels, inducing increased resistance against activated protein C and lowering thrombin levels (resulting in an impaired protein C activation). This review briefly discusses the actions of protein C in human body but mainly focuses on the effects of antiphospholipid antibodies on the protein C pathway that have been described in literature.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

Behçet's Disease as a Model of Venous Thrombosis

Behçet's disease (BD) is a chronic inflammatory disease of unknown aetiology characterized by recurrent oral, genital aphthous ulcerations, uveitis, skin lesions and other multisystem affections associated with vasculitis. Different types of vessels, predominantly veins, can be affected in BD. The frequency of vascular lesions in BD, such as superficial and deep venous thromboses, arterial aneurysms and occlusions, ranges between 7-29%. In this review, various factors of thrombogenesis in BD, particularly pro- and antithrombotic endothelial and non-endothelial factors, factors of coagulation, platelet activation and rheological changes are presented and discussed from positions of Virchow's triad of venous thrombosis. Despite advances in understanding of thrombogenesis in BD, still many issues of diagnosis and targeted preventive and therapeutic measures remain unresolved. Further studies are needed to clarify the pathobiology of BD-related thrombosis and to provide the clinicians with recommendations over the utility, safety and effectiveness of the antithrombotic therapy in BD.

Behçet’s Disease as a Model of Venous Thrombosis

Behçet’s disease (BD) is a chronic inflammatory disease of unknown aetiology characterized by recurrent oral, genital aphthous ulcerations, uveitis, skin lesions and other multisystem affections associated with vasculitis. Different types of vessels, predominantly veins, can be affected in BD. The frequency of vascular lesions in BD, such as superficial and deep venous thromboses, arterial aneurysms and occlusions, ranges between 7-29%.

In this review, various factors of thrombogenesis in BD, particularly pro- and antithrombotic endothelial and non-endothelial factors, factors of coagulation, platelet activation and rheological changes are presented and discussed from positions of Virchow’s triad of venous thrombosis.

Despite advances in understanding of thrombogenesis in BD, still many issues of diagnosis and targeted preventive and therapeutic measures remain unresolved. Further studies are needed to clarify the pathobiology of BD-related thrombosis and to provide the clinicians with recommendations over the utility, safety and effectiveness of the antithrombotic therapy in BD.

Antiphospholipid antibodies in critical illness

The antiphospholipid syndrome is defined by the presence of antiphospholipid antibodies in patients with recurrent venous or arterial thromboembolism or pregnancy morbidity. Antithrombotic therapies are the mainstay of treatment to reduce the risk of recurrent thromboembolism. Among patients with antiphospholipid antibodies, the absolute risk of new thrombosis developing is low in healthy patients without previous thrombotic events. However, the risk of recurrent thrombosis appears to be high in patients with a history of arterial or venous thrombosis. Compared with placebo or untreated control, anticoagulation with warfarin administered to achieve an international normalized ratio of 2.0 to 3.0 probably reduces the risk of recurrence of thrombotic events. Aspirin and moderate-intensity warfarin appear equally effective for preventing recurrent stroke in patients with a single positive antiphospholipid antibody test result and previous stroke. It is unknown how best to prevent first stroke in patients found to be persistently positive for the antiphospholipid syndrome. The catastrophic variant of the antiphospholipid syndrome is a condition characterized by multiple vascular occlusive events, usually affecting small vessels and evolving over a short period of time. This condition has a very high mortality rate. First-line treatment with therapeutic anticoagulation, corticosteroids, plasma exchange, and intravenous immunoglobulin seems to be effective in reducing mortality and risk of catastrophic thrombotic events in these patients. In conclusion, moderate-intensity warfarin is effective for preventing recurrent thrombotic events in patients with venous thrombosis. Aspirin appears to be as effective as moderate-intensity warfarin for preventing recurrent stroke in patients with previous stroke and a single positive test result for antiphospholipid antibody. The optimal treatment of other clinical manifestations of antiphospholipid syndrome needs to be addressed in well-designed prospective studies.

Graph-theoretical comparison of protein surfaces reveals potential determinants of cross-reactivity and the molecular mimicry

Different proteins, even without sequence similarity, still can contain similar surface regions involved in protein-protein interactions with common target. These regions can serve as structural determinants of cross-reactivity and molecular mimicry. Molecular mimicry, defined as the process in which structural properties of one molecule are simulated by the dissimilar molecules, is implicated in several biologically important processes, including autoimmune and allergic reactions, binding of some ligands to common receptor, and interactions in cell signaling. The problem of identification of the determinants of molecular mimicry is not completely solved at this time. We hypothesize that identification of structurally and chemically similar surface regions of two protein molecules capable of binding to the same target will allow us to identify sites involved in cross-reactivity including determinants of the molecular mimicry. We used a graph-theoretical approach in order to determine highly similar surface regions of two proteins with known three-dimensional structures. This approach uses a variation of Maximal Common Subgraph (MCS) isomorphism, where an association graph is constructed based on the surface-exposed residues of the two molecules and the matching regions are found based on the maximum cliques in the association graph. Testing the proposed method on the targets of autoantibody involved in antiphopholipid syndrome (APS)--beta2-GPI, PC, thrombin, factor IX, factor X, and plasmin allowed identifying potential epitopes for antibody that can inhibit coagulation proteases. Application of this method to the Activated Protein C and factor VII Gla-domains revealed surface regions involved in EPCR and plasma membrane binding, consistent with known experimental results. Analysis of major pollen allergen that can cause food allergies through cross-reactivity found known epitopes involved in cross-reactivity and also revealed additional surface regions that can complement the list of epitopes. Taken together, our results suggest that the proposed graph-theoretical approach can identify determinants of cross-reactivity and molecular mimicry.

How I treat the antiphospholipid syndrome

This article discusses how we approach medical decision making in the treatment of the various facets of the antiphospholipid syndrome (APS), including secondary prophylaxis in the setting of venous and arterial thrombosis, as well as treatment for the prevention of recurrent miscarriages and fetal death. The role of primary thromboprophylaxis is also discussed in depth. Great emphasis is given to incorporating the most up-to-date and relevant evidence base both from the APS literature, and from large, recent, randomized controlled trials (RCTs) of primary and secondary thrombotic prophylaxis in the general population setting (ie, the population that has not been specifically investigated for APS).

European attempts for the standardisation of the antiphospholipid antibodies

According to the Sydney criteria, antiphospholipid syndrome (APS) diagnosis is closely related to the demonstration of antiphospholipid antibodies (aPL) in patients sera. For this purpose, three different assays are conventionally accepted: lupus anticoagulant (LA), anticardiolipin (aCL) and anti-β2 glycoprotein I (β2GPI) antibodies. LA, described in the 1950s is a coagulation-based functional assay, which indirectly detects the presence of aPL. The aCL ELISA was developed in 1985; the identification of β2GPI as a major target of aPL, allowed the introduction of anti-β2GPI ELISA. Even if the diagnostic criteria for APS have been well defined, the laboratory detection of aPL is not always reproducible for many reasons. To achieve a univocal diagnostic definition of APS, efforts were made to reduce the inter- and/or intra-laboratory variability of the diagnostic tests. In this article, we analyse the studies performed to standardise aPL assays that were developed within the European Forum on Antiphospholipid Antibodies.

Mechanisms of antiphospholipid-induced thrombosis: effects on the protein C system

An acquired resistance to activated protein C (APC) has been demonstrated in patients with antiphospholipid antibodies (aPL). Recent studies report interactions between beta2 glycoprotein I (beta2GPI) and prothrombin-binding antibodies and the protein C system. Some aPL in patients recognize one or more conformational epitopes shared by beta2GPI and catalytic domains of APC. Both beta2GPI and anti-prothrombin antibodies are associated with APC resistance. Several clinical studies have focused on an association between aPL and APC resistance, determined by classic activated partial thromboplastin time-based tests. It has been shown in most studies that APC resistance was associated with lupus anticoagulants. APC resistance is also associated with thrombosis, especially venous thromboembolism. Several recent studies have reported a novel integrated approach of coagulation using calibrated automated thrombography. This technique allows an approach of APC sensitivity without interference with lupus anticoagulants. Clinical associations between APC resistance and thromboembolic events have been demonstrated.