Concomitant isolation of protein C inhibitor and unnicked beta2-glycoprotein I

The Predictive Value of the aCL and Anti-β2GPI at the Time of Acute Deep Vein Thrombosis-A Two-Year Prospective Study

Antiphospholipid syndrome (APS) is an important cause of deep vein thrombosis (DVT). According to current APS classification criteria, APS cannot be confirmed until 24 weeks after DVT. This time frame results in frequent discontinuation of anticoagulant treatment before APS is diagnosed. Therefore, the aim of our study was to evaluate the potential predictive value of anticardiolipin (aCL) and anti-β2glycoprotein I (anti-β2GPI) before discontinuation of anticoagulation therapy. Patients with newly diagnosed DVT were included into a 24-month prospective study. All patients received anticoagulant therapy. aCL and anti-β2GPI were determined at inclusion and every four weeks for the first 24 weeks and then one and two years after inclusion. APS was confirmed in 24/221 (10.9%) patients. At the time of acute DVT 20/24 (83.3%), APS patients had positive aCL and/or anti-β2GPI. Two patients had low aCL levels and two were negative at the time of acute DVT but later met APS criteria due to lupus anticoagulant (LA). Our data indicate that negative aCL and/or anti-β2GPI at the time of acute DVT make further aPL testing unnecessary; however, LA should be determined after discontinuation of anticoagulant therapy. Positive aCL and/or anti-β2GPI at the time of acute DVT have a strong positive predictive value for APS and may support therapeutic decisions.

The role of thrombospondin-1 in the pathogenesis of antiphospholipid syndrome

OBJECTIVE

Antiphospholipid syndrome (APS) is an acquired thrombophilia characterized by recurrent thrombosis and/or pregnancy morbidity, in the presence of antibodies to β2 glycoprotein-I (β2GPI), prothrombin or Lupus anticoagulant (LA). Anti-β2GPI antibodies recognize complexes of β2GPI dimers with CXCL4 chemokine and activate platelets. Thrombospondin 1 (TSP-1) is secreted by platelets and exhibits prothrombotic and proinflammatory properties. Therefore, we investigated its implication in APS.

METHODS

Plasma from APS patients (n = 100), Systemic Lupus Erythematosus (SLE) (n = 27) and healthy donors (HD) (n = 50) was analyzed for TSP-1, IL-1β, IL-17A and free active TGF-β1 by ELISA. Human Umbilical Vein Endothelial Cells (HUVECs) and HD monocytes were treated with total HD-IgG or anti-β2GPI, β2GPI and CXCL4 and CD4⁺ T-cells were stimulated by monocyte supernatants. TSP-1, IL-1β, IL-17A TGF-β1 levels were quantified by ELISA and Real-Time PCR.

RESULTS

Higher plasma levels of TSP-1 and TGF-β1, which positively correlated each other, were observed in APS but not HDs or SLE patients. Patients with arterial thrombotic events or those undergoing a clinical event had the highest TSP-1 levels. These patients also had detectable IL-1β, IL-17A in their plasma. HD-derived monocytes and HUVECs stimulated with anti-β2GPI-IgG-β2GPI-CXCL4 secreted the highest TSP-1 and IL-1β levels. Supernatants from anti-β2GPI-β2GPI-CXCL4 treated monocytes induced IL-17A expression from CD4⁺ T-cells. Transcript levels followed a similar pattern.

CONCLUSIONS

TSP-1 is probably implicated in the pathogenesis of APS. In vitro cell treatments along with high TSP-1 levels in plasma of APS patients suggest that high TSP-1 levels could mark a prothrombotic state and an underlying inflammatory process.

Added value of non-criteria antiphospholipid antibodies for antiphospholipid syndrome: lessons learned from year-long routine measurements

The international classification criteria for definite antiphospholipid syndrome (APS) include three laboratory measurements: lupus anticoagulant (LA), IgG and IgM isotypes of anti-cardiolipin (aCL) and anti-β2glycoprotein I antibodies (anti-β2GPI). When persistently elevated, they are specific for APS; however, many patients that fulfil clinical criteria may exhibit negative serological results. These "seronegative" APS (SN-APS) are exposed to an increased thrombotic risk. The aims of our cross-sectional, retrospective study of consecutive autoimmune patients' samples were to evaluate the association of non-criteria antiphospholipid antibodies (aPL) with thrombosis and obstetric events, to calculate the risk score for adverse events and to assess the specific contribution of single aPL positivity in SN-APS. LA, aCL, anti-β2GPI and anti-phosphatidylserine/prothrombin antibodies (aPS/PT) of IgG, IgM, and IgA isotypes were determined in sera of 323 patients with autoimmune disorders. Medical records of all patients were carefully analyzed. aCL, anti-β2GPI and aPS/PT of IgG and IgA isotypes were significantly associated with thrombosis while none of the IgM aPL showed such association. aPS/PT of all isotypes, aCL and anti-β2GPI of IgG and IgA isotype showed significant correlation to obstetric events. When considering results of aPS/PT ELISA, we could additionally identify 3% of thrombotic patients and 2% of obstetric patients. Thrombotic and obstetric risk scores were calculated showing significantly higher association to clinical events, as compared to evaluating individual risk factors. aPS/PT could represent an additional biomarker in SN-APS patients. IgA aPL are associated with thrombosis and obstetric complications. Risk scores accounting different aPL and conventional risk factors, better assesses risk for adverse event, as compared to evaluating individual factors alone.

Stroke and antiphospholipid syndrome-antiphospholipid antibodies are a risk factor for an ischemic cerebrovascular event

Testing for antiphospholipid antibodies could be an important part in determining the cause of a cerebrovascular event (CVE). Currently, it is also unknown whether antiphospholipid antibodies represent a risk factor for the development of a CVE and whether the selected therapy options are efficacious. So, this study aimed at (1) determining the frequency of patients experiencing a CVE and fulfilling the laboratory criterion for an antiphospholipid syndrome (APS), (2) investigating whether the persistent presence of antiphospholipid antibodies represented a risk factor for a CVE, and (3) focusing on the efficacy of the selected treatment strategy in the first year after the CVE. Eighty-nine patients with an acute CVE were prospectively followed for 1 year. At least two sera from each were tested for lupus anticoagulants, anticardiolipin, anti-β2-glycoprotein I, anti-phosphatidylserine/prothrombin and anti-annexin V antibodies. Twenty out of eighty-nine (22%) of CVE patients fulfilled the criteria for APS (17/20 for definitive and 3 for probable APS). There was a significant association between persistently present antiphospholipid antibodies and the CVE (OR, 4.62). No statistically significant difference was found in the CVE recurrence rate between APS-CVE and non-APS-CVE patients being treated mainly with acetyl salicylic acid. Antiphospholipid antibodies represent an independent risk factor for a CVE. In the first year after the CVE, antiplatelet therapy seemed to be sufficient in secondary CVE thromboprophylaxis in most APS patients.

Anti-Phosphatidylserine/Prothrombin Antibodies Are Associated with Adverse Pregnancy Outcomes

Objective. To determine the prevalence and clinical association of anti-phosphatidylserine/prothrombin antibodies (aPS/PT) in patients with a history of pregnancy complications relevant to antiphospholipid syndrome (APS). Materials and Methods. Two hundred and eleven patients with a history of (a) three or more consecutive miscarriages before 10th week of gestation (WG) (n = 64), (b) death of a morphologically normal fetus beyond 10th WG (n = 72), (c) premature birth of a morphologically normal neonate before 34th WG due to eclampsia, preeclamsia and placental insufficiency (n = 33), and (d) less than three unexplained consecutive miscarriages before 10th WG (n = 42). Subjects sera were analyzed for lupus anticoagulant (LA), anti-cardiolipin (aCL), anti-β₂-glycoprotein I (anti-β₂GPI), and aPS/PT antibodies. Results. 41/169 (24.3%) of patients were positive for at least one measured aPL. The highest prevalence was found for aPS/PT and aCL (13.0% and 12.4%, resp.) followed by LA (7.7%) and anti-β₂GPI (7.1%). 11/169 with APS-related obstetric manifestations had only aPS/PT. 17.8% of patients were positive for LA or aCL and/or anti-β₂GPI; however when adding the aPS/PT results, an additional 7% of patients could be evaluated for APS. Conclusion. aPS/PT are associated with recurrent early or late abortions and with premature delivery irrespective of other aPL.

Anti-β2-glycoprotein I paratopes and β2-glycoprotein I epitopes characterization using random peptide libraries

Studies concerning interactions between anti-β2-glycoprotein I antibodies (anti-β2GPI) and β2-glycoprotein I (β2GPI) suggest relevance of charge interactions and hydrogen bonds. However, paratope of diagnostically and clinically relevant anti-β2GPI and epitope characteristics of β2GPI, still remain unclear. The aim of our study was to determine paratope characteristics of various anti-β2GPI antibodies and epitope characteristics of β2GPI using phage display. Monoclonal IgG anti-β2GPI, purified polyclonal high avidity and low avidity IgG anti-β2GPI derived from plasma of APS patients were used to screen phage display libraries. The affinity and competition ability of selected clones were evaluated. Various heptapeptides presenting putative paratopes of anti-β2GPI and specific heptapeptides presenting putative epitopes of β2GPI were determined. Epitope presenting peptides bind to the respective anti-β2GPI and consequently interrupt antibody-antigen interaction. The amino acid composition of selected peptides confirmed the importance of hydrogen bonds and charge interactions in the binding of anti-β2GPI to the antigen. Epitopes recognized by high avidity anti-β2GPI predominately contain hydrogen bond forming side chains, while in low avidity anti-β2GPI epitope the charged side chains prevail. The alignment of selected sequences to three-dimensional antigen structure revealed that polyclonal high avidity anti-β2GPI recognize native epitopes that are accessible regardless of β2GPI's conformation whereas the epitope recognized by low avidity anti-β2GPI is cryptic and cannot be accessed when β2GPI takes the closed plasma conformation.

Optimization of unnicked β2-glycoprotein I and high avidity anti-β2-glycoprotein I antibodies isolation

Patient biological material for isolation of β2-glycoprotein I (β2GPI) and high avidity IgG anti-β2-glycoprotein I antibodies (HAv anti-β2GPI) dictates its full utilization. The aim of our study was to evaluate/improve procedures for isolation of unnicked β2GPI and HAv aβ2GPI to gain unmodified proteins in higher yields/purity. Isolation of β2GPI from plasma was a stepwise procedure combining nonspecific and specific methods. For isolation of polyclonal HAv aβ2GPI affinity chromatographies with immobilized protein G and human β2GPI were used. The unknown protein found during isolation was identified by liquid chromatography electrospray ionization mass spectrometry and the nonredundant National Center for Biotechnology Information database. The average mass of the isolated unnicked purified β2GPI increased from 6.56 mg to 9.94 mg. In the optimized isolation procedure the high molecular weight protein (proteoglycan 4) was successfully separated from β2GPI in the 1st peaks with size exclusion chromatography. The average efficiency of the isolation procedure for polyclonal HAv anti-β2GPI from different matrixes was 13.8%, as determined by our in-house anti-β2GPI ELISA. We modified the in-house isolation and purification procedures of unnicked β2GPI and HAv anti-β2GPI, improving the purity of antigen and antibodies as well as increasing the number of tests routinely performed with the in-house ELISA by ~50%.

The use of atomic force microscopy to study the pathologic effects of anti-annexin autoantibodies

Patients with recurrent pregnancy loss and a history of thrombotic events have often been noted to have autoantibodies directed at annexin A5. However, the relationship of these autoantibodies to immunopathology is still unknown, although it has been proposed that they have a direct effect on the function of annexin A5. Annexin A5 may be a significant immunological target with pathologic implications. Essentially, annexin A5 is an anticoagulant protein that crystallizes over negatively charged phospholipid surfaces and thereby blocks them from availability for coagulation reactions. To address this issue, we have taken advantage of our expertise with atomic force microscopy and studied anti-annexin A5 autoantibodies isolated from patients and focused on the ability of these antibodies to influence annexin A5 crystallization on planar mica-supported phospholipid bilayers. We report herein that such antibodies from patients, but not controls, produced a significant disruption of incomplete annexin A5 crystalline shield on phospholipid bilayer. In addition, the IgG fraction isolated from such patients significantly decreased the velocity of annexin A5 crystallization. Atomic force microscopy is a powerful tool to study the pathologic mechanisms of autoantibodies and the data herein reflect the potential of anti-annexin A5 antibodies that produce pathology in a number of varied but overlapping clinical conditions, including autoimmune thrombosis and antiphospholipid syndrome.

Budding of giant unilamellar vesicles induced by an amphitropic protein β2-glycoprotein I

β(2)-glycoprotein I (β(2)GPI) is a plasma protein capable of binding reversibly to membranes, and is classified among the amphitropic proteins. Part of the protein intercalates into the outer membrane leaflet, altering the difference between the preferred areas of the membrane leaflets, which results in membrane shape transformations. Budding, as a specific example of such shape transformations, was studied using giant unilamellar vesicles. Our aim was to identify the vesicle parameters that influence the degree of membrane budding by studying this process qualitatively and quantitatively. A simple theoretical model has been developed and assessed against the experimental observations. The results show that β(2)GPI binds in a concentration dependent manner, causing transitions between vesicle shapes with increasing numbers of buds. Higher numbers of buds are characteristic of larger and/or more flaccid vesicles. When the vesicle membrane is strained, a higher β(2)GPI concentration is needed to produce the same effects as on the unstrained vesicle. Vesicles were found to be highly individual in their behaviour, so each was treated individually. Specific vesicle behaviour was found to be the consequence of the neck between the main vesicle body and the buds, which could be either open, closed for the exchange of solution, or closed for the exchange of both solution and membrane.

Avidity of anti-beta-2-glycoprotein I antibodies

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

High avidity anti-beta 2-glycoprotein I antibodies in patients with antiphospholipid syndrome

OBJECTIVE

To evaluate avidity of IgG anti-beta 2-glycoprotein I antibodies (anti-beta2-GPI) in patients with antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE) in relation to thrombosis, and to demonstrate a possible affinity maturation of IgG anti-beta 2-GPI during the disease course.

METHODS

64 sera from 32 patients (18 with primary or secondary APS, 14 with SLE without APS) and their respective IgG fractions or affinity purified anti-beta 2-GPI were studied by anticardiolipin (aCL) and anti-beta 2-GPI enzyme linked immunosorbent assay and by chaotropic assay.

RESULTS

Six, 12, and 14 patients had high, low, and heterogeneous avidity IgG anti-beta 2-GPI, respectively. In 12 patients an increase in antibody avidity was observed over a period of between four and 12 years. More patients with APS were in the high avidity than in the low avidity anti-beta 2-GPI group, while the opposite was observed for SLE alone (both p<0.05). The most common clinical feature among patients with high avidity anti-beta 2-GPI was thrombosis, mainly venous thrombosis (p<0.05 and p<0.02, respectively, v the low avidity anti-beta 2-GPI group).

CONCLUSIONS

Patients with APS with or without SLE may have anti-beta2-GPI of high, low, or heterogeneous avidity. High avidity anti-beta 2-GPI appear to be associated with thrombosis and APS, while in pure SLE low avidity anti-beta 2-GPI may prevail. Monitoring of avidity may help elucidate the role of anti-beta 2-GPI affinity maturation in the pathogenesis of APS.