Antiprothrombin Antibodies Research Articles

Which Antiphospholipid Antibodies Should Be Measured in the Antiphospholipid Syndrome?

The results of an analysis of studies published over a 10-year period that addressed the association between antiphospholipid antibodies (aPLs) and thromboembolic events in patients with the antiphospholipid syndrome (APS) are reported. It would appear that lupus anticoagulants are the strongest risk factor for thromboembolic events in aPL-positive patients. Consequently, it is suggested that all patients with clinical manifestations of APS should be tested for these antibodies. On the other hand, the results do not unequivocally show that measurement of anticardiolipin antibodies is of help in defining the thrombotic risk of patients. Furthermore, they only partially support the notion that anti-β2-glycoprotein I and antiprothrombin antibodies may be independent risk factors for thrombosis.

Antiprothrombin autoantibodies in severe preeclampsia and abortion

PURPOSE: We examined the levels of autoantibodies against prethrombin-1 and fragment-1 in pregnant women to determine the type of autoantibodies that were associated with severe preeclampsia or spontaneous abortion. SUBJECTS AND METHODS: We measured autoantibodies bound to prothrombin, prethrombin-1, and fragment-1 by using an enzyme-linked immunosorbent assay (ELISA) in 12 healthy nonpregnant women, 36 women with normal pregnancies, 28 pregnant women with severe preeclampsia, and 19 pregnant women who subsequently had spontaneous abortion. RESULTS: Plasma samples in 10 (36%) of the 28 women with severe preeclampsia and 11 (58%) of the 19 women with spontaneous abortion were positive for antiprothrombin antibodies as compared with 3 (9%) of the 36 women with normal pregancies. All 11 of the positive samples from women who had spontaneous abortions were positive for antiprethrombin-1 antibody, but only 1 was positive for antifragment-1 antibody. The mean ( ± SD) titer of antiprethrombin-1 antibodies in patients with spontaneous abortion (36 ± 9 U) was higher than that in women with normal pregnancies (10 ± 4 U; P <0.01). Antiprethrombin-1 antibody was detected in only 2 women with severe preeclampsia, whereas all 10 women with antiprethrombin antibodies were positive for antifragment-1 antibody. The antifragment-1 antibody titer in patients with severe preeclampsia (49 ± 15 U) was higher than in women with normal pregnancies (13 ± 6 U, P <0.01). CONCLUSIONS: There is a strong and specific association between various types of antiprothrombin antibodies with severe preeclampsia and spontaneous abortion.

A Cross Sectional Study of Antiphospholipid-protein Antibodies in Patients with Venous Thromboembolism

To look for an association between venous thromboembolism (VTE) and antiphospholipid antibodies (aPL) in patients without Systemic Lupus Erythematosus (SLE) when implementing, beside conventional assays, new tests for aPL screening directed towards purified proteic targets. We conducted a cross-sectional, hospital-based study of consecutive unselected outpatients. We compared VTE+ patients to VTE- among 398 consecutive unselected outpatients referred for clinical suspicion of VTE. To detect aPL, the following ELISAs were performed: 1) a conventional standardized ELISA 2) an improved APA assay, 3) an anti-Beta2GPI ELISA, 4) an anti-Annexin V ELISA, 5) an anti-Prothrombin ELISA. We sought an association between VTE and aPL through a quantitative (t-test) and a qualitative comparison (chi-square test, according to the cut-off values set as the 95th percentile of aPL distribution). First we conducted an analysis of all patients. Then we stratified them into 2 subgroups, with or without a wellknown risk factor for VTE (prolonged immobilization >72h, surgery or trauma within the past three months, current malignancy). 61% of patients were classified as VTE-positive. Before stratification, we did not find any significant association between the VTE status and aPL. However, after stratification, in the subgroup without risk factors for VTE, the frequency of positive values as regards the anti Prothrombin antibodies detection was significantly higher in VTE+ patients (p = 0,04). The presence of anti Prothrombin antibodies might be an independent risk factor of VTE. However systematic screening for aPL in non SLE patients referred for VTE suspicion at the time of the thrombo-embolic event has little clinical relevance.

High prevalence of antiphospholipid antibodies in leprosy: evaluation of antigen reactivity.

Antiphospholipid antibodies (aPL) have been reported not only in autoimmune disorders but also in various infectious diseases. Accumulating evidence indicates that beta2 glycoprotein I (beta2GPI) and prothrombin are the main proteins to which autoimmune aPL bind. The aim of this study was to evaluate the prevalence of different aPL in patients with leprosy. We included 51 outpatients (42 lepromatous and 9 borderline leprosy) without any clinical feature of the antiphospholipid syndrome (APS). 35 had lupus anticoagulant and 31 had anticardiolipin antibodies (aCL). Anti-beta2GPI antibodies were highly positive in 29/51 and anti- prothrombin antibodies (anti-II) were detected in 23/51. Almost all aCL and anti-beta2GPI were of IgM isotype, while IgG isotype was more frequent among anti-II. No statistical difference was found when aPL were evaluated in patients grouped according to their bacteriological status. Furthermore, patients under treatment (n=33) had a similar frequency of positive aPL compared to patients in vigilance (n=14). Assessing the specificity of antibody binding to CL and beta2GPI in ELISA by means of inhibition studies with cardiolipin-beta2GPI liposomes, leprosy and APS sera showed a similar behaviour. Comparable results were also found in both groups of patients when inhibition experiments with lysate of Mycobacterium leprae were carried out. In summary, leprosy-related aPL resemble those found in patients with APS but the immunoglobulin isotype is different, with IgM much more prevalent in leprosy patients.

Should we Include Anti-prothrombin Antibodies in the Screening for the Antiphospholipid Syndrome?

Anti-prothrombin antibodies belong to the family of the antiphospholipid antibodies. Their prevalence ranges from 50 to 90% of antiphospholipid-positive patients, depending on the laboratory methodology employed for their detection. ELISA techniques are the most commonly used methods for their measurements, which allow a quick determination of their titer and isotype(s). Unfortunately, no well standardized assays are yet commercially available. The clinical relevance of anti-prothrombin antibodies as risk factors for thromboembolic events has been investigated by a number of retrospective and case-control studies. We reviewed 11 studies: data on 1,440 patients and 371 sex- and age-matched controls were available. Seven studies reported a significant association between anti-prothrombin antibodies and thrombosis by univariate analysis. Multivariate analysis was performed in five studies: only two of them confirmed the association. The sensitivity and specificity of anti-prothrombin antibodies for thrombosis were analysed according to the antibody isotype and to the arterial and/or venous site of thrombosis. The sensitivities are disappointingly low, particularly when the M isotype and arterial thrombosis are considered, whereas the specificities are somewhat better, even though they range widely. These data do not allow to recommend the measurement of anti-prothrombin antibodies in the routine laboratory workout of antiphospholipid-positive patients in order to define their thrombotic risk.

Association of autoantibodies against the phosphatidylserine-prothrombin complex with manifestations of the antiphospholipid syndrome and with the presence of lupus anticoagulant.

To clarify the association of autoantibodies against prothrombin with the clinical manifestations of the antiphospholipid syndrome (APS) and with the presence of lupus anticoagulant (LAC). We examined 265 patients who visited our autoimmune disease clinic. IgG and IgM antiprothrombin antibodies were tested by enzyme-linked immunosorbent assay (ELISA) as either antiphosphatidylserine-prothrombin complex (aPS/PT) antibodies or as antibodies against prothrombin coated on irradiated ELISA plates (as antigen) (aPT). IgG, IgM, and IgA anticardiolipin (aCL) antibodies and their beta2-glycoprotein I (beta2GPI) dependency were also evaluated by ELISA. LAC was tested by 3 different methods. The presence of aPS/PT, but not of aPT, significantly correlated with the clinical manifestations of APS (odds ratio [OR] 4.39, 95% confidence interval [95% CI] 2.06-9.38), and aPS/PT antibodies were as specific as beta2GPI-dependent aCL for APS (93.1% for both). IgG aPS/PT strongly correlated with the presence of LAC as detected using the dilute Russell viper venom time test (OR 38.2, 95% CI 13.4-109.1). Antiprothrombin antibodies are heterogeneous and their clinical relevance depends on the method of detection applied. Positive results on the aPS/PT test can serve as a marker of thrombotic events in patients with autoimmune diseases.

Lupus Anticoagulants Form Immune Complexes With Prothrombin and Phospholipid That Can Augment Thrombin Production in Flow

Lupus anticoagulants (LA) are a family of autoantibodies that are associated with in vitro anticoagulant activity but a strong predisposition to in vivo thrombosis. They are directed against plasma phospholipid binding proteins, including prothrombin. We found that a murine monoclonal antiprothrombin antibody and 7 of 7 LA IgGs tested enhanced binding of prothrombin to 25:75 phosphatidyl serine:phosphatidyl choline vesicles in a concentration-dependent manner. We hypothesized that enhanced binding of prothrombin to phospholipid in the presence of LA IgG might result in increased thrombin production when reactions are performed in flow. Thrombin production by purified prothrombinase components was measured in a phospholipid-coated flow reactor. The flow reactor was incubated with prothrombin, calcium ions, and the IgGs and then perfused with prothrombin, calcium ions, the IgGs, factor Va, and factor Xa. A murine monoclonal antiprothrombin antibody and 4 of 6 LA IgGs from patients with a history of thrombosis increased thrombin production up to 100% over control in the first 15 minutes. In summary, LA IgGs concentrate prothrombin on a phospholipid surface that can augment thrombin production by prothrombinase in flow. These observations suggest that LA might propagate coagulation in flowing blood by facilitating prothrombin interaction with the damaged blood vessel wall.

Different Types of Antiphospholipid Antibodies in AIDS: A Comparison with Syphilis and the Antiphospholipid Syndrome

Alloimmune antiphospholipid antibodies react with phospholipids and are an epiphenomenon of an infectious disease. Most autoimmune antiphospholipid antibodies recognise phospholipid-protein complexes or proteins, such as β 2 glycoprotein I or prothrombin and are related to the clinical features of the antiphospholipid syndrome. Lupus anticoagulant, anticardiolipin antibodies, antiprothrombin, and anti-β 2 glycoprotein I antibodies were studied in 61 human immunodeficiency virus (HIV) patients, 55 syphilis patients, and 45 selected patients with antiphospholipid syndrome. Lupus anticoagulant was present in 72% of HIV and 81% of antiphospholipid syndrome patients. None of the syphilis patients had lupus anticoagulant. Anticardiolipin antibodies were found at comparable prevalence in the three groups (HIV 67%, syphilis 67%, antiphospholipid syndrome 84%). HIV had more frequently anti-β 2 glycoprotein I (13%) and anti-prothrombin (12%) antibodies than syphilis (0 and 4%, respectively), but significantly less than antiphospholipid syndrome (61 and 40%, respectively). Autoimmune antiphospholipid antibodies in HIV without clinical features of antiphospholipid syndrome might be a reflex of the immunological chaos and/or the constant antigenic virus stimulus.

Antiplatelet Factor 4—Heparin Antibodies in Patients with Antiphospholipid Antibodies

Antibodies directed against platelet factor 4-heparin are present in patients with heparin-induced thrombocytopenia (HIT). Additionally, it has been suggested that heparin can be an antigenic target of antiphospholipid antibodies (aPL). We investigated the presence of heparin-platelet factor 4-induced antibodies (HPIA) in 33 patients with aPL. There were 30 patients with lupus anticoagulant, 25 with anticardiolipin antibodies, 21 with anti-β 2 glycoprotein I, and 18 with antiprothrombin antibodies. 20 patients had a history of thrombosis and 19 had received heparin during the last 60 months. We found 7 (21.2%) who had HPIA; 5 of them also had anti-β 2 glycoprotein I antibodies. Four patients had severe thrombocytopenia and suspicion of HIT. Among them, two presented high positive HPIA results, one of them with positive platelet aggregation test. The third patient showed grey zone HPIA and borderline aggregation test and the fourth one had negative results. Among patients without a history of HIT, 2 who had never received heparin presented high positive, one a moderate positive, and one a grey zone HPIA result; all of them with negative aggregation tests. Five positive sera samples were incubated with cardiolipin liposomes in the presence of β 2 glycoprotein I, and whereas an inhibition greater than 50% was achieved in anticardiolipin and anti-β 2 glycoprotein I activities, HPIA results did not change. We demonstrate that HPIA could be frequently found in patients with aPL. They are responsible for HIT in some cases but can also be found in patients who have not received heparin. Whether they predispose patients with aPL to HIT is not known; nevertheless, a close follow-up of heparin treatment in these patients seems to be mandatory.

Antibodies to prothrombin in patients with Sneddon's syndrome.

Antiprothrombin antibodies (aPT), a new serologic marker of antiphospholipid syndrome, were studied in 46 patients randomly selected from 73 with Sneddon's syndrome and 20 matched normal controls. aPT were elevated in 26 patients (57%) and were not found in any of the controls. The addition of aPT data increased the proportion of Sneddon's syndrome patients with at least one type of antiphospholipid syndrome marker from 65 to 78%. The finding that aPT are common in Sneddon's syndrome supports the hypothesis that Sneddon's syndrome is a form of antiphospholipid syndrome.

Prevalence of hepatitis C virus infection in patients with antiphospholipid syndrome

Background/Aims: The aim of this study was to determine the prevalence and clinical significance of hepatitis C virus (HCV) infection in patients with the antiphospholipid syndrome (APS). Methods: A series of 88 consecutive patients (78 female and 10 male), with a mean age of 39 years (range 15–79), was prospectively studied. All patients had been diagnosed with APS: 54 (61%) primary APS and 34 (39%) APS associated with systemic lupus erythematosus. A group of 200 apparently healthly blood donors was included in the study. Anti-HCV antibodies were investigated in the serum of all patients using a third-generation ELISA and confirmed by recombinant immunoblot assay. RNA-HCV was investigated in anti-HCV positive samples by polymerase chain reaction. Anticardiolipin, anti-β2-glycoprotein I and antiprothrombin antibodies were evaluated by ELISA. Lupus anticoagulant was studied by coagulometric assays. Results: Only 2 (2.2%) patients showed positivity for anti-HCV antibodies, but none of them had clinical or biochemical signs of liver disease. Furthermore, RNA-HCV was not detected in serum of any of these patients. Lupus anticoagulant was positive in 57% of patients. Anticardiolipin antibodies were positive in 60% of patients, anti-β2-glycoprotein I antibodies in 43% of patients, and antiprothrombin antibodies in 56% of patients. The prevalence of anti-HCV in blood donors was 1%. Conclusions: The prevalence of anti-HCV in patients with APS is low and similar to that in healthy people in our area. HCV infection does not seem to be involved in the etiopathogenesis of this syndrome.

Antiprothrombin Antibodies: Detection and Clinical Significance in the Antiphospholipid Syndrome

A NTIPHOSPHOLIPID antibodies have been associated with a variety of clinical phenomena, including arterial and venous thrombosis, thrombocytopenia, and obstetric complications. The term “antiphospholipid syndrome”[1][1]is used to link a variety of thromboembolic events to antibodies against

Anti-beta2-glycoprotein I, anti-prothrombin and anticardiolipin antibodies in a longitudinal study of patients with systemic lupus erythematosus and the antiphospholipid syndrome

To determine anti-beta2 glycoprotein-I (anti-beta2GPI) and anti-prothrombin (anti-ProT) antibody levels, and the IgG subclass distribution of anti-beta2GPI antibodies, in serial samples from patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) having initial or recurrent thrombotic/neurological (T/N) events during the study period. To investigate the correlations between these antibodies and beta2GPI antigen, anticardiolipin antibody (aCL), anti-double-stranded (ds) DNA, C3 levels and disease activity. Fifty serum samples were identified from seven patients with SLE who had had T/N events during the follow-up from a cohort under long-term follow-up. IgG anti-beta2GPI, anti-ProT, aCL, IgG subclasses of anti-beta2GPI and beta2GPI antigen levels were determined by ELISA. Corresponding disease activity [British Isles Lupus Assessment Group (BILAG)], anti-dsDNA and C3 levels were compared. IgG anti-beta2GPI antibody levels were elevated in six of the patients before and after the T/N events with less marked fluctuations than aCL antibody levels. The predominant subclass of anti-beta2GPI antibodies was IgG2 before and after the T/N events. IgG anti-ProT antibodies were negative in all cases. There was a significant but weak correlation between anti-beta2GPI and aCL antibodies. No correlation was found between disease activity and IgG anti-beta2GPI antibody and beta2GPI antigen levels. There were fluctuations in beta2GPI antigen levels and a trend to increase after T/N events was observed in some patients. Most of the patients with a T/N event during the study period had IgG anti-beta2GPI, but not IgG anti-ProT antibodies. Many IgG aCL-negative samples were found to have IgG anti-beta2GPI activity during the follow-up period. The predominant subclass of IgG anti-beta2GPI was IgG2, which may have importance in the pathogenesis of APS. beta2GPI antigen levels were found to be increased in some patients with SLE after T/N events. IgG anti-beta2GPI antibodies may be used as an adjunctive marker of future T/N events in patients with SLE and APS with aCL antibodies and lupus anticoagulant.

Anti-beta2-glycoprotein I and anti-prothrombin antibodies in patients with the 'antiphospholipid' syndrome: immunological specificity and clotting profiles.

Lupus anticoagulant (LA) antibodies have been shown to be directed to protein-phospholipid complexes. In this study, we report on LA antibodies from patients with the 'antiphospholipid' syndrome (APS), that are directed to prothrombin and beta2-glycoprotein I, but not to the complexes of these plasma proteins to anionic phospholipids. The anti-prothrombin antibodies studied had different reactivities in two clotting assays: the dilute Russell's viper venom time (dRVVT) and the dilute kaolin clotting time (dKCT). Anti-prothrombin and anti-beta2-glycoprotein I (anti-beta2GPI) antibodies, affinity-purified from one patient with APS were not cross-reactive and had different effects in the dRVVT and dKCT clotting tests. Polyclonal anti-prothrombin antibodies, affinity-purified on a prothrombin column, from two patients with prothrombin reactivity in their plasma, have affinity constants to prothrombin of 104 and 192 nM. The patient with affinity-purified antibodies to prothrombin and beta2GPI, had affinity constants to prothrombin and beta2GPI, respectively, of 192 nM and 3030 nM, respectively. LA antibodies are a heterogeneous population of antibodies that have different immunological specificities and clotting test reactivities in different patients.

Prevalence and significance of anticardiolipin, anti-beta2 glycoprotein I and anti-prothrombin antibodies in chronic hepatitis C.

Antiphospholipid antibodies have been demonstrated in chronic hepatitis C, but their clinical and pathogenetic significance remains elusive. We prospectively studied 115 patients (85 men, mean age 36.9 years) with chronic hepatitis C without cirrhosis and treated by alpha-interferon (alpha-IFN). Antiphospholipid determinations comprised anticardiolipin (ACA), anti-beta2-glycoprotein I and anti-prothrombin antibodies of the IgG and IgM classes. At entry, 24 patients (21%) were found to possess low to moderate ACA levels (18 IgG, two IgM and four both isotypes) compared with only 4/115 age- and sex-matched control subjects (3.5% P=0.001). ACA positivity rate increased to 31% (P=0.01) after a 6-month course of alpha-IFN treatment. In contrast, the prevalence of anti-beta2-glycoprotein I and anti-prothrombin antibodies was not significantly different from controls at either time point. The presence of ACA correlated with that of antinuclear antibodies (P=0.0002), but was not associated with parameters such as histological activity, viral burden and response to alpha-IFN, nor with a history of thrombosis or pregnancy loss. However, a non-significant trend of higher incidence of mild thrombocytopenia among ACA-positive patients was observed. We conclude that low-titre ACA positivity is a common finding in patients with chronic hepatitis C, especially following alpha-IFN treatment, but does not select a category with different clinical features. These data are in keeping with the absence of associated anti-beta2GPI and anti-prothrombin antibodies, and do not support a role for HCV infection in the pathogenesis of the antiphospholipid syndrome.

Differential Effects of Anti–β2-Glycoprotein I and Antiprothrombin Antibodies on the Anticoagulant Activity of Activated Protein C

AbstractAntiprothrombin and anti–β2-glycoprotein I (β2-GPI) antibodies belong to the family of antiphospholipid (APL) antibodies and represent the phospholipid-dependent inhibitors of coagulation. They may be distinguished by analyzing the coagulation profiles generated by the comparison of the ratios of two coagulation tests, the Kaolin Clotting Time (KCT) and the dilute Russell's Viper Venom Time (dRVVT), commonly adopted for their diagnosis. The KCT profile is caused by antiprothrombin antibodies, whereas anti–β2-GPI antibodies are responsible for the dRVVT coagulation profile. The presence of aPL antibodies is frequently associated with acquired resistance to activated Protein C (APC-R), but limited information is available regarding the role of the different antibodies in its development. We studied the time-course of activated Factor V (FVa) generation and inactivation in the plasma of 42 patients with well-defined phospholipid-dependent inhibitors of coagulation: 24 displayed the dRVVT coagulation profile, whereas the other 18 cases showed the KCT profile. In normal pooled plasma, the peak values of FVa (mean ± standard deviation, [SD]: 16.307 ± 4.372 U/mL) were reached in 4 to 5 minutes and an almost complete inactivation (0.088 ± 0.123 U/mL) was obtained within 20 minutes. At this time point, values of residual FVa exceeding 2 SD the mean of controls (0.344 U/mL) were considered abnormal. Patients belonging to the KCT coagulation profile group reached the maximal amount of FVa in plasma (22.740 ± 7.693 U/mL, P = not significant v controls) within 4 to 5 minutes; at 20 minutes, the residual amount of FVa in plasma ranged from 0 to 1.09 U/mL (0.293 ± 0.298; P = .027), but it was found abnormal in only six of the 18 cases. The time-course of FVa in plasma of patients belonging to the dRVVT coagulation profile group differed from that of normal controls in that the peak values (10.955 ± 5.092 U/mL) were reached at 10 minutes and the amount of residual FVa at 20 minutes ranged from 0.320 to 14.450 U/ml (2.544 ± 3.580 U/mL;P = .0191 v normal controls and P = .0114v KCT group patients). Twenty of the 24 patients belonging to the dRVVT profile group had an abnormal inactivation of FVa (χ2 = 0.001 v KCT group patients). History of venous thrombosis was experienced by 15 patients: an abnormal rate of FVa inactivation was found in 11 of them (73%) versus 15 of the 27 cases without thrombosis (56%) (x2= 0.2556). The effect of affinity-purified IgG phospholipid-dependent inhibitors of coagulation on the time-course of FVa generation and inactivation in normal plasma was also investigated. Anti–β2-GPI, but not antiprothrombin antibodies, hampered the inactivation of FVa by endogenous APC, thus reproducing the behavior of the original plasmas. This effect was strictly β2-GPI–dependent. In conclusion, our findings confirm that anti–β2-GPI antibodies identify patients with phospholipid-dependent inhibitors of coagulation at increased risk of thrombosis and suggest acquired APC-R as a possible explanation of the pathogenesis of the thromboembolic events.

Differential Effects of Anti–β2-Glycoprotein I and Antiprothrombin Antibodies on the Anticoagulant Activity of Activated Protein C

Antiprothrombin and anti–β2-glycoprotein I (β2-GPI) antibodies belong to the family of antiphospholipid (APL) antibodies and represent the phospholipid-dependent inhibitors of coagulation. They may be distinguished by analyzing the coagulation profiles generated by the comparison of the ratios of two coagulation tests, the Kaolin Clotting Time (KCT) and the dilute Russell's Viper Venom Time (dRVVT), commonly adopted for their diagnosis. The KCT profile is caused by antiprothrombin antibodies, whereas anti–β2-GPI antibodies are responsible for the dRVVT coagulation profile. The presence of aPL antibodies is frequently associated with acquired resistance to activated Protein C (APC-R), but limited information is available regarding the role of the different antibodies in its development. We studied the time-course of activated Factor V (FVa) generation and inactivation in the plasma of 42 patients with well-defined phospholipid-dependent inhibitors of coagulation: 24 displayed the dRVVT coagulation profile, whereas the other 18 cases showed the KCT profile. In normal pooled plasma, the peak values of FVa (mean ± standard deviation, [SD]: 16.307 ± 4.372 U/mL) were reached in 4 to 5 minutes and an almost complete inactivation (0.088 ± 0.123 U/mL) was obtained within 20 minutes. At this time point, values of residual FVa exceeding 2 SD the mean of controls (0.344 U/mL) were considered abnormal. Patients belonging to the KCT coagulation profile group reached the maximal amount of FVa in plasma (22.740 ± 7.693 U/mL, P = not significant v controls) within 4 to 5 minutes; at 20 minutes, the residual amount of FVa in plasma ranged from 0 to 1.09 U/mL (0.293 ± 0.298; P = .027), but it was found abnormal in only six of the 18 cases. The time-course of FVa in plasma of patients belonging to the dRVVT coagulation profile group differed from that of normal controls in that the peak values (10.955 ± 5.092 U/mL) were reached at 10 minutes and the amount of residual FVa at 20 minutes ranged from 0.320 to 14.450 U/ml (2.544 ± 3.580 U/mL;P = .0191 v normal controls and P = .0114v KCT group patients). Twenty of the 24 patients belonging to the dRVVT profile group had an abnormal inactivation of FVa (χ2 = 0.001 v KCT group patients). History of venous thrombosis was experienced by 15 patients: an abnormal rate of FVa inactivation was found in 11 of them (73%) versus 15 of the 27 cases without thrombosis (56%) (x2= 0.2556). The effect of affinity-purified IgG phospholipid-dependent inhibitors of coagulation on the time-course of FVa generation and inactivation in normal plasma was also investigated. Anti–β2-GPI, but not antiprothrombin antibodies, hampered the inactivation of FVa by endogenous APC, thus reproducing the behavior of the original plasmas. This effect was strictly β2-GPI–dependent. In conclusion, our findings confirm that anti–β2-GPI antibodies identify patients with phospholipid-dependent inhibitors of coagulation at increased risk of thrombosis and suggest acquired APC-R as a possible explanation of the pathogenesis of the thromboembolic events.

Prothrombin as cofactor for antiphospholipids.

Prothrombin is a common antigenic target of antiphospholipid antibodies, since anti-prothrombin antibodies are detected in about 50-90% of the patients. To allow proper immune recognition, prothrombin must be adsorbed on suitable anionic surfaces. The epitope(s) have not yet been identified: the majority of anti-prothrombin antibodies appear to be of poly- or oligoclonal nature. Anti-prothrombin antibodies, either alone or in combination with anti-beta2-glycoprotein I antibodies, are responsible for the lupus anticoagulant activity of about 75% of the cases of phospholipid-dependent inhibitors of coagulation. The two antibodies may be discriminated by means of specific coagulation profiles generated by the comparison of the ratio of the Kaolin Clotting Time (KCT) and the dilute Russell's Viper Venom Time (dRVVT): the KCT profile, which mainly reflects the presence of anti-prothrombin antibodies and the dRVVT profile, which is mostly associated with anti-beta2-glycoprotein I antibodies. This distinction, although somewhat artificial, may be clinically useful, since the KCT profile identifies patients at low risk to develop thrombosis. Similarly, most of the studies that measured anti-prothrombin antibodies by ELISA failed to find a significant association with thrombosis. In conclusion, the clinical relevance of these antibodies has not yet been established.

Anti-prothrombin antibodies and their relation with thrombosis and lupus anticoagulant

Antiphospholipid antibodies are a heterogeneous group of antibodies, comprising antibodies with different antigen specificity. Prothrombin is one of the antigens which can be detected by antiphospholipid antibodies and therefore anti-prothrombin antibodies belong to the antiphospholipid antibody family. The presence of antiphospholipid antibodies correlates strongly with thromboembolic complications; however a mechanism by which these autoantibodies induce a thrombotic complication in vivo is not understood. The classic assays for the detection of antiphospholipid antibodies (LAC and anticardiolipin ELISAs) aim to measure all the antiphospholipid antibodies present in the samples without making a distinction between the different subspecificities of the antibodies present in one single sample. Moreover, most of the in-vitro studies performed were carried out with total IgGs, which contain a mixture of antibodies. The absence of an accurate characterization of the plasma samples and the lack of specificity of the IgGs used in in-vitro tests makes it difficult to determine the contribution of antiprothrombin antibodies to the thrombotic complications. Here we review and critically analyse the literature regarding the clinical relevance of the presence of antiprothrombin antibodies and the possible participation of these antibodies in the pathogenesis of the thrombotic complications.

Towards improved criteria for the antiphospholipid syndrome.

A workshop to be held in Sapporo will attempt to upgrade criteria for the antiphospholipid syndrome (APS). These criteria should probably be based on a scoring system using both clinical and biological items. Clinical criteria could be categorized between 'major', that is thrombosis or obstetrical criteria, and 'minor', to be selected among livedo, heart valve lesions, chorea, adrenal hemorrhage, thrombocytopenia, and others. A similar approach could be proposed for biological criteria, with persistent strong LA, high IgG aCL or antibodies to beta2GPI as major criteria if the workshop accepts antibodies directed to co-factors as APS criteria. Minor criteria could include IgM aCL, low/medium IgG aCL, and VDRL. Whether anti-prothrombin, anti-oxidised LDL, and M5 anti-mitochondrial antibodies should be added to the minor criteria, is open to discussion. In our mind, other parameters should be taken into account such as: young age--a method to avoid the questionable exclusion of arteriosclerosis in cases of arterial thrombosis--and the presence of personal and/or first-degree familial features of auto-immunity. Lastly, a differential diagnosis section is probably needed.