Two antiprothrombin antibodies against prothrombin and prothrombin-phosphatidyl serine show partial but not total identity

Serum Reactive Antibodies against the N-Methyl-D-Aspartate Receptor NR2 Subunit-Could They Act as Potential Biomarkers?

Synaptic dysfunction and disrupted communication between neuronal and glial cells play an essential role in the underlying mechanisms of multiple sclerosis (MS). Earlier studies have revealed the importance of glutamate receptors, particularly the N-methyl-D-aspartate (NMDA) receptor, in excitotoxicity, leading to abnormal synaptic transmission and damage of neurons. Our study aimed to determine whether antibodies to the NR2 subunit of NMDAR are detected in MS patients and evaluate the correlation between antibody presence and clinical outcome. Furthermore, our focus extended to examine a possible link between NR2 reactivity and anti-coagulant antibody levels as pro-inflammatory molecules associated with MS. A cross-sectional study was carried out, including 95 patients with MS and 61 age- and gender-matched healthy controls (HCs). The enzyme-linked immunosorbent assay was used to detect anti-NR2 antibodies in serum samples of participants along with IgG antibodies against factor (F)VIIa, thrombin, prothrombin, FXa, and plasmin. According to our results, significantly elevated levels of anti-NR2 antibodies were detected in MS patients compared to HCs (p < 0.05), and this holds true when we compared the Relapsing-Remitting MS course with HCs (p < 0.05). A monotonically increasing correlation was found between NR2 seropositivity and advanced disability (rs = 0.30; p < 0.01), anti-NR2 antibodies and disease worsening (rs = 0.24; p < 0.05), as well as between antibody activity against NR2 and thrombin (rs = 0.33; p < 0.01). The presence of anti-NR2 antibodies in MS patients was less associated with anti-plasmin IgG antibodies [OR:0.96 (95%CI: 0.92-0.99); p < 0.05]; however, such an association was not demonstrated when analyzing only RRMS patients. In view of our findings, NR2-reactive antibodies may play, paving the way for further research into their potential as biomarkers and therapeutic targets in MS.

Beyond the classics: The emerging value of anti-phosphatidylserine/prothrombin antibodies in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by the presence of antiphospholipid antibodies (aPLs), which can lead to thrombosis and pregnancy complications. Within the diverse range of aPLs, anti-phosphatidylserine/prothrombin antibodies (aPS/PT) have gained significance in clinical practice. The detection of aPS/PT has proven valuable in identifying APS patients and stratifying their risk, especially when combined with other aPL tests like lupus anticoagulant (LA) and anti-β2-glycoprotein I (aβ2GPI). Multivariate analyses have confirmed aPS/PT as an independent risk factor for vascular thrombosis and obstetric complications, with its inclusion in the aPL score and the Global Anti-Phospholipid Syndrome Score (GAPSS) aiding in risk evaluation. However, challenges remain in the laboratory testing of aPS/PT, including the need for assay standardization and its lower sensitivity in certain patient populations. Further research is necessary to validate the clinical utility of aPS/PT antibodies in APS diagnosis, risk stratification, and management.

Antiphosphatidylserine/prothrombin complex antibodies as a determinant of prothrombotic plasma fibrin clot properties in patients with antiphospholipid syndrome

BACKGROUND

Antiphosphatidylserine/prothrombin complex (aPS/PT) antibodies are recognized as a marker for antiphospholipid syndrome (APS). Dense and poorly lysable fibrin clots occur in thrombotic APS. Compact clots predict thromboembolism, but determinants of the unfavorable clot phenotype remain unknown in APS. We hypothesized that elevated aPS/PT antibodies determine unfavorable clot features.

METHODS

In a cohort study involving 124 consecutive patients with thrombotic APS, we measured at baseline plasma fibrin clot permeability (Ks ), efficiency of fibrinolysis (clot lysis time, CLT), and turbidity (off anticoagulation) along with immunoglobulin (Ig)G/IgM aPS/PT. During follow-up, symptomatic thromboembolic events were recorded.

RESULTS

Elevated IgG and IgM aPS/PT antibodies >30 international enzyme units (UI) were detected in 54.8% and 42.7% of APS patients, including 76.2% and 54% of lupus anticoagulant- (LA, n = 63) positive patients, respectively. Elevated IgG and IgM aPS/PT antibodies predicted low Ks (lower quartile, <6 × 10-9  cm2 ; odds ratio [OR] = 5.93, 95% confidence interval [CI] 2.09-16.82 and OR = 11.79, 95% CI 4.10-33.92) and prolonged CLT (top quartile, ≥116 min; OR = 4.85, 95% CI 2.42-25.07 and OR = 6.04, 95% CI 2.42-15.07). No such associations were observed for anticardiolipin or β2-glycoprotein I antibodies or LA presence. During follow-up (median 72.5, range 66-83 months), thromboembolic events observed in 32 (26.7%, 4.6%/year) patients were independently predicted by IgG aPS/PT antibodies >30 UI (hazard ratio [HR] = 3.04, 95% CI 1.20-8.88) and low Ks (HR = 3.00, 95% CI 1.41-6.50).

CONCLUSIONS

We identified aPS/PT antibodies as a determinant of denser and poorly lysable plasma fibrin clot formation in APS patients. The association of elevated aPS/PT antibodies with thromboembolism in APS could be at least in part mediated by prothrombotic clot properties.

Antibodies to Phosphatidylserine/Prothrombin Complex in Antiphospholipid Syndrome: Analytical and Clinical Perspectives

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by thrombosis and/or pregnancy-related morbidity accompanied by persistently positive antiphospholipid antibodies (aPL). Current laboratory criteria for APS classification recommend testing for lupus anticoagulant as well as IgG and IgM anticardiolipin, and beta-2 glycoprotein I (anti-β2GPI) antibodies. However, there appears to be a subset of patients with classical APS manifestations who test negative for the recommended criteria aPL tests. While acknowledging that such patients may have clinical features that are not of an autoimmune etiology, experts also speculate that these "seronegative" patients may test negative for relevant autoantibodies as a result of a lack of harmonization and/or standardization. Alternatively, they may have aPL that target other antigens involved in the pathogenesis of APS. In the latter, autoantibodies that recognize a phosphatidylserine/prothrombin (PS/PT) complex have been reported to be associated with APS and may have diagnostic relevance. This review highlights analytical and clinical attributes associated with PS/PT antibodies, taking into consideration the performance characteristics of criteria aPL tests in APS with specific recommendations for harmonization and standardization efforts.

Laboratory evaluation of anti-phospholipid syndrome: a preliminary prospective study of phosphatidylserine/prothrombin antibodies in an at-risk patient cohort

Immunoglobulin (Ig)G/IgM autoantibodies to phosphatidylserine/prothrombin (aPS/PT) were evaluated individually and in combination with criteria anti-phospholipid (aPL) tests in a prospectively ascertained cohort of patients at risk for anti-phospholipid syndrome (APS). One hundred and sixty (160) consecutive requests for lupus anti-coagulant (LAC) from the University of Utah Health Sciences Center were identified during 8 weeks. Of these, 104 unique patients had additional requests for cardiolipin (aCL) and/or beta2 glycoprotein I (aβ2 GPI) IgG and/or IgM; samples were retained and analysed for aPS/PT, aCL and/or aβ2 GPI IgG and IgM antibodies. Following testing, a comprehensive chart review was performed and patients categorized according to their clinical diagnosis. Individual and combined sensitivities, specificities, odd ratios (OR), diagnostic accuracy for specific tests or combinations by receiver operating characteristic (ROC), area under the curve (AUC) analyses and correlations between test results were determined. The sensitivities of aPS/PT IgG/IgM (54·6/45·5%) were lower than LAC (81·8%) but higher relative to aCL IgG/IgM (27·3/0%) or aβ2 GPI IgG/IgM (27·3/0%). The best correlation between LAC and any aPL test was observed with aPS/PT (P = 0·002). There was no significant difference in the diagnostic accuracies for any panel with LAC: LAC/aβ2 GPI IgG/aCL IgG [AUC 0·979, OR 475·4, 95% confidence interval (CI) 23·1-9056·5, P = 0·0001 and LAC/aβ2 GPI IgG/aPS/PT IgG or LAC/aPS/PT IgG/aCL IgG (AUC 0·962, OR 265·3, 14·2-4958·2, P = 0·0001). The high correlation between LAC and aPS/PT IgG/IgM in this preliminary study suggest that this marker may be useful in the evaluation of APS. More studies to determine the optimal aPL antibody tests combination are needed.

Anti-factor Xa antibodies in patients with antiphospholipid syndrome and their effects upon coagulation assays

Introduction

The aim of this study was to examine the prevalence and functional effects of antibodies directed against Factor (F)Xa and other serine proteases (SP) in patients with antiphospholipid syndrome (APS).

Methods

Serum from patients with APS (n = 59), systemic lupus erythematosus (SLE; n = 106), other autoimmune rheumatic disease (ARD; n = 63) and 40 healthy controls (HC) were tested for IgG activity against thrombin (Thr), FXa, FVIIa, phosphatidylserine (PS)/FXa and antithrombin (AT)-III by enzyme-linked immunosorbent assay (ELISA). Anti-FXa positive IgG were purified to measure their avidity by chaotropic ELISA and functional effects upon clotting time (FXa-ACT) and FXa enzymatic activity (± AT-III).

Results

Anti-FXa IgG were found in patients with SLE (49.1%) and APS (33.9%) (P <0.05) but not in ARD controls and HC. In contrast, anti-Thr and anti-PS/FXa IgG were identified in other ARD and anti-FVIIa IgG were low in all groups. The avidity of APS-IgG to FXa was significantly higher than SLE-IgG (P <0.05). Greatest prolongation of FXa-ACT was observed with APS-IgG and greatest inhibitory effect upon FXa enzymatic activity was found with APS-IgG followed by SLE-IgG compared to HC-IgG. ATIII inhibition of FXa was significantly reduced by APS-IgG compared with HC and SLE (P <0.05) and did not correlate with binding to AT-III.

Conclusion

APS anti-FXa IgG have higher avidity to FXa and greater effects upon the enzymatic and coagulant activity of FXa compared with SLE anti-FXa IgG. Further studies of anti-FXa antibodies in APS, SLE and other non-autoimmune thrombotic disease cohorts are now required to evaluate whether targeting FXa with selective inhibitors in patients bearing anti-FXa antibodies may be an effective treatment strategy.

Detection of antiphosphatidylserine/prothrombin antibodies and their potential diagnostic value

Antiprothrombin antibodies, measured with phosphatidylserine/prothrombin complex (aPS/PT) ELISA, have been reported to be associated with antiphospholipid syndrome (APS). They are currently being evaluated as a potential classification criterion for this autoimmune disease, characterized by thromboses and obstetric complications. Given the present lack of clinically useful tests for the accurate diagnosis of APS, we aimed to evaluate in-house and commercial assays for determination of aPS/PT as a potential serological marker for APS. We screened 156 patients with systemic autoimmune diseases for antibodies against PS/PT, β₂-glycoprotein I, cardiolipin and for lupus anticoagulant activity. We demonstrated a high degree of concordance between the concentrations of aPS/PT measured with the in-house and commercial assays. Both assays performed comparably relating to the clinical manifestations of APS, such as arterial and venous thromboses and obstetric complications. IgG aPS/PT represented the strongest independent risk factor for the presence of obstetric complications, among all tested aPL. Both IgG and IgM aPS/PT were associated with venous thrombosis, but not with arterial thrombosis. Most importantly, the association between the presence of IgG/IgM aPS/PT and lupus anticoagulant activity was highly significant. Taken together, aPS/PT antibodies detected with the in-house or commercial ELISA represent a promising serological marker for APS and its subsets.

Antiphosphatidylserine/prothrombin antibodies (aPS/PT) as potential markers of antiphospholipid syndrome

The antiphospholipid antibodies present in antiphospholipid syndrome (APS) are directed at a number of phospholipid-binding proteins: β2 glycoprotein I (β2GPI), prothrombin, and so on. Antibodies directed at β2GPI are accepted as a classification criterion for APS, while the presence of antiprothrombin antibodies is not. In the present article, we investigated the possible role of antiphosphatidylserine/prothrombin antibodies (aPS/PT) as marker of APS on a cohort of 295 individuals with APS (95 primary APS and 45 secondary APS) and APS-related diseases. We found aPS/PT to be highly associated with venous thrombosis (immunoglobulin G [IgG] aPS/PT odds ratio [OR], 7.44; 95% confidence interval [CI], 3.97-13.92 and IgM aPS/PT OR, 2.54; 95% CI, 1.35-4.77) and obstetric abnormalities (IgG aPS/PT OR, 2.37; 95% CI, 1.04-5.43), but not with arterial thrombosis. A very high degree of concordance between the concentration of aPS/PT and lupus anticoagulant activity was demonstrated. Therefore, we support the inclusion of aPS/PT determination as second-level assay to confirm APS classification.

Modified phosphatidylserine-dependent antiprothrombin [corrected] ELISA enables identification of patients negative for other antiphospholipid antibodies and also detects low avidity antibodies

BACKGROUND

Two approaches for detecting anti-prothrombin antibodies have been described. The first detects antibodies against prothrombin alone and the second, phos-phatidylserine-dependent antiprothrombin antibodies. The latter more often correlate with clinical manifestations of antiphospholipid syndrome and with lupus anticoagulant activity.

METHODS

In order to increase the capacity of antibody binding, we modified the previously described phosphatidylser-ine-dependent antiprothrombin ELISA and determined their avidity. We examined 203 patients with systemic autoimmune diseases and 222 blood donors.

RESULTS

Our modification resulted in a greater intensity of antibody binding to prothrombin on phosphatidylserine-coated plate surfaces compared to the previously described method. By changing ELISA conditions, we were able to detect with one assay the two, presumably different, populations of antiprothrombin antibodies. Diagnostic specificities of both ELISAs for antiphospholipid syndrome were similar (92.5% vs. 93.1%), while the sensitivity of the modified phosphatidylserine-dependent antiprothrombin ELISA was significantly higher than the anti-prothrombin alone ELISA (59% vs. 25%). Low avidity antiprothrombin antibodies were only detected in the modified phosphatidylserine-dependent antiprothrombin ELISA. Four percent of patients with positive phosphatidylserine-dependent antiprothrombin antibodies, showing clinical manifestations of antiphospholipid syndrome, were negative for all other antiphospholipid antibodies. The risk for antiphospholipid syndrome increased with the number of antiphospholipid antibody positivity.

CONCLUSIONS

We conclude that antibodies detected with a modified phosphatidylserine-dependent antiprothrombin ELISA could improve the diagnosis of antiphospholipid syndrome by offering additional information on the risk for thrombosis, especially in patients negative for other antiphospholipid antibodies.

Does the anti-prothrombin antibodies measurement provide additional information in patients with thrombosis?

The aim of this study is to get new insight into the relevance of IgG anti-prothrombin antibodies in patients with thrombosis and to determine whether human prothrombin alone (aPT) or complexed to phosphatidylserine (aPS/PT) should be preferentially used for measuring these antibodies by enzyme-linked immunosorbent assay (ELISA). To this end, prevalence of anti-prothrombin antibodies, their characteristics in terms of avidity and heterogeneity, and their relationship with anti-beta2 glycoprotein I antibodies (abeta2GPI) were studied in 152 patients with thrombosis. Patients were divided into two groups according to the presence or absence of antiphospholipid antibodies (aPL), called aPL+ or aPL-, respectively. In the aPL- group (n=90), the prevalence of anti-prothrombin antibodies was substantial (10%) but not significantly different from that of control (5%). In the aPL+ group (n=62), lupus anticoagulant (LA) or anticardiolipin antibodies (aCL) positive, 61% were positive for anti-prothrombin antibodies with no statistical difference between aPT and aPS/PT prevalence (42% vs. 55%, respectively). In the whole thrombotic population, 19% were only aPT and 34% only aPS/PT suggesting the presence of different antibodies. Absorption experiments confirmed the heterogeneity of aPT and aPS/PT. No difference in their avidity was demonstrated. From the aPL+ group, 60 were LA positive. Among them, 18% were negative for abeta2GPI and anti-prothrombin antibodies showing that the detection of these antibodies could not substitute for LA determination. In conclusion, our data show that the screening of the different anti-prothrombin antibodies is not warranted in the aPL+ group since these antibodies do not provide additional information compared to aCL, LA and/or abeta2GPI measurement. Nevertheless, the substantial prevalence of anti-prothrombin antibodies in the aPL- group should be further explored in a large prospective study.

Anti-phosphatidylserine-prothorombin antibody in patients with recurrent abortion and preeclampsia

AIM

The aim of the study was to describe the frequency of anti-phosphatidylserine-prothrombin antibody(aPS/PTAb) in patients with recurrent abortion and preeclampsia, and to study the relationship between the presence of aPS/PTAb and clinical finding. Eighty six cases of recurrent abortion and 82 cases of preeclampsia were studied. A aPS/PTAb was measured by an enzyme linked immunosorbent assay (ELISA).

RESULTS

In patients with recurrent abortion, 3 out of 86 cases(3.4%) were positive in IgG antibody measurements and 5 out of 86(5.8%) were positive in IgM antibody measurements. In patients with preeclampsia, 2 out of 82 cases(2.5%) were positive in IgG antibody measurements and 13 out of 82(16%) were positive in IgM antibody measurements. The positive rates of aPS/PTAb in severe hypertension-positive cases is greater than in hypertension-negative cases(p=0.045). The positive rates of aPS/PTAb is higher tendency with in severe type than in mild type(p=0.117). The positive rates of aPS/PTAb is higher tendency with proteinuria and/or hypertension than without proteinuria(p=0.098) or hypertension(p=0.096).

CONCLUSION

We found that aPS/PTAb appears in some cases of patients with recurrent abortion and preeclampsia. Our data suggest that aPS/PTAb might be a risk factor in patients with recurrent abortion, and may relate to clinical finding in preeclampsia.