The presence of multiple prothrombotic risk factors is associated with a higher risk of thrombosis in individuals with anticardiolipin antibodies

OBJECTIVE: To explore the effect of multiple prothrombotic risk factors in individuals with anticardiolipin antibodies (aCL), we evaluated immunologic, coagulation, and genetic prothrombotic abnormalities in a cohort of individuals with different aCL titers. METHODS: We recruited 87 individuals into 4 categories (normal, low, intermediate, or high) based on their baseline IgG aCL (aCL-IgG) titers. We measured at followup: repeat aCL-IgG, IgM aCL (aCL-IgM), antibodies to beta2-glycoprotein I (anti-beta2-GPI), lupus anticoagulant (LAC) antibodies, protein C, protein S, activated protein C resistance, factor V506 Leiden mutation, methyl tetrahydrofolate reductase (MTHFR) C677T genotype, and prothrombin 20210A gene mutation. Thrombotic events were confirmed. RESULTS: At recruitment, 20 individuals were negative for aCL-IgG and 67 were positive (22 low, 20 intermediate, and 25 high titer). Twenty of the 87 participants had experienced a previous thrombotic event: 4 in the aCL-IgG negative group and 16 in the aCL-IgG positive group. Among the 87 individuals, the number of those with concomitant prothrombotic risk factors was as follows: 5 had no other prothrombotic risk factors, 32 had 1 risk factor, 24 had 2 risk factors, 10 had 3 risk factors, 10 had 4 risk factors, and 6 had 5 risk factors. Thrombotic events were observed in 20%, 13%, 33%, 10%, 30%, and 50% of these groups, respectively, and the odds ratio associated with a previous thrombotic event was 1.46 per each additional prothrombotic risk factor (95% confidence interval: 1.003-2.134). CONCLUSION: In individuals with positive aCL-IgG, we observed an association between the number of prothrombotic risk factors and history of thrombotic events.     

Evaluation of Cerebrospinal Fluid for the Presence of Anticardiolipin Antibodies (aCL) in NP-SLE Patients

Many neurological or psychiatric manifestations of SLE (NP-SLE) are related to the presence of anticardiolipin antibodies (aCL) in the patient’s sera. The aim of this study was to evaluate the presence of aCL in cerebrospinal fluid (CSF) in SLE patients with NP features. Fifteen SLE patients were studied, all with NP features. CSF was evaluated for intrathecal IgG synthesis, oligoclonal IgG, and blood–brain barrier impairment. Sera and CSF were tested by ELISA for the presence of aCL-IgG and aCL-IgM with and without β₂ glycoprotein (β₂ GPI) cofactor. CSF and sera of 50 low back pain patients served as controls. Six patients were aCL(+) and nine aCL(–). In all patients the general CSF examination was normal. In all patients the value of indices of intrathecal IgG synthesis were normal but oligoclonal protein was present in the CSF of three patients. In none of the patients was the blood–brain barrier impaired. Neither aCL-IgG nor aCL-IgM was detected in the CSF of any NP-SLE patient. Mean levels of aCL in patients without cofactor β₂ GPI and with cofactor were as follows: for IgG class 0.005 and 0.057 OD (negative); for IgM class 0.004 and 0.024 OD (negative). We could not detect aCL in the CSF of patients with NP-SLE, even if sera were positive for aCL. Received: 6 July 1999 / Accepted: 18 January 2000     

Anti β2 glycoprotein I antibodies: detection and association with thrombosis

Summary. It has been demonstrated that antiphospholipid antibodies (aPL) recognize epitopes formed by anionic phospholipids and protein cofactors. β₂ glycoprotein I (β₂GPI) is accepted as the cofactor of anticardiolipin antibodies (aCL). In the present study we explored the presence and clinical associations of anti β₂GPI antibodies of IgG isotype (aβ₂GPI-IgG), measured by ELISA. We studied sera from 169 patients with aCL and/or lupus anticoagulant (LA), including 52 patients with systemic lupus erythematosus and 49 with primary antiphospholipid syndrome (PAPS). We found 31.9% positive sera for aβGPI-IgG in the whole population and 48.6% in the aCL-IgG(+) group. There was a good correlation between the titre of aCL-IgG and the optical density for aβGPI-IgG ( r = 0.69, P <0.01). The presence of aβ₂GPI-IgG was associated with the presence of aCL-IgG ( P <0.0001) and LA ( P <0.0005). However, none of 23 LA (+) patients without aCL had aβ₂GPI-IgG.
We found a statistically significant association between the presence of aβ₂GPI-IgG and a history of venous thromboembolism (VTE) in our patients ( P <0.005). This association was observed in PAPS ( P <0.05) but not in secondary antiphospholipid syndrome (SAPS).
Our study confirms that some aPL(+) sera react with β₂GPI in special experimental conditions. In addition, the presence of these antibodies is associated with a history of VTE.     

Anticardiolipin antibodies, free protein S levels and thrombosis: a survey in a selected population of rheumatoid arthritis patients.

OBJECTIVE: To investigate plasma levels of natural anticoagulant proteins such as protein S, protein C and antithrombin III in a selected population of patients with rheumatoid arthritis (RA) with and without anticardiolipin antibody (aCL) positivity, and to evaluate the possible relationships with an increased risk of thrombotic events in RA. METHODS: A total of 184 female RA patients attending our Extra-Articular Involvement RA Clinic were evaluated for aCL levels, total and free protein S, protein C and antithrombin III concentrations, and for the occurrence of thrombotic events. Patients were grouped as aCL positive (n = 35) and aCL negative (n = 149). RESULTS: Higher rates of venous and/or arterial thromboses were diagnosed in patients with RA compared to controls (P = 0.01). In particular, lower free protein S levels were found in aCL-positive patients with RA compared to both aCL-negative patients and controls (P = 0.001). Functional assays for protein C, antithrombin III as well as total protein S levels were found to be in the normal range in all patients and controls. CONCLUSION: The association observed between aCL positivity and decreased levels of free protein S in RA patients may represent one of the risk factors for thrombotic events.     

Resistance to activated protein C activity of an anti-/2 -glycoprotein I antibody in the presence of β-glycoprotein I

Some researchers claim that lupus anticoagulant-positive plasma may cause a false-positive reaction in the test for activated protein C (APC) resistance, a hereditary thrombophilic state characterized by abnormal factor V, which frequently causes venous thrombosis, We investigated whether anti-/3₂ -glycoprotein I antibody (aGPI), which has recently come to be regarded as an anti-cardiolipin antibody (aCL) itself, might have an effect on the APC resistance test.     

Value of autoantibodies to beta(2)-glycoprotein 1 in the diagnosis of antiphospholipid syndrome

OBJECTIVES: To define the specificity and positive predictive value of anti-beta(2)-glycoprotein 1 (anti-beta(2)GP1) antibodies for the diagnosis of antiphospholipid syndrome (APS). METHODS: We determined the presence of anticardiolipin (aCL) antibodies and anti-beta(2)-glycoprotein 1 (anti-beta(2)GP1) immunoglobulin (Ig) G and IgM in 191 consecutive sera from 191 patients and reviewed clinical data separately. aCL IgG and IgM were detected separately using commercial ELISA kits. Anti-beta(2)GP1 antibodies were detected with an in-house ELISA using beta(2)GP1. RESULTS: Seven patients were diagnosed as having APS and 184 as having other diseases. Thirty-six patients were aCL-positive and 12 were anti-beta(2)GP1-positive, seven of these 12 were APS patients. The specificity for anti-beta(2)GP1 in our population was 97%, with a positive predictive value (PPV) of 58%. Among the aCL-positive patients, specificity was 90% and PPV 70-87%. CONCLUSIONS: This study shows that anti-beta(2)GP1 antibodies have a higher specificity and PPV than aCL for APS. The PPV of anti-beta(2)GP1 was greater in aCL-positive than in all patients. We conclude that screening for anti-beta(2)GP1 antibodies in aCL-positive patients increases the specificity and the PPV of aCL testing. In addition, we show that there is no need to screen for anti-beta(2)GP1 antibodies in the absence of aCL antibodies and in the absence of strong clinical suspicion of APS.     

Anti-cardiolipin and anti-beta2 glycoprotein I antibodies in Indian patients with systemic lupus erythematosus: association with the presence of seizures

The aim of this study was to examine whether the clinical features of antiphospholipid antibody syndrome are associated with anti-cardiolipin and anti-beta2 glycoprotein I antibodies in Indian patients with SLE. Seventy-six patients (71 females), who fulfilled 1982 ACR criteria for SLE, were prospectively studied for the clinical features of antiphospholipid antibody syndrome (APS), and their sera were analysed for the presence of IgG/IgM/IgA anti-cardiolipin antibodies (aCL) by an in-house ELISA and, in 65 of them, for the presence of IgG anti-beta2 glycoprotein I antibodies (anti-beta2 GPI) by a commercial kit. Thirty-nine (51%) patients were positive for aCL, all of which were positive for IgG aCL, either alone (79.6%) or along with IgM and/or IgA. Twenty-seven (69.3%) out of 39 aCL-positive and seven (26.9%) out of 26 aCL-negative sera were positive for IgG antibodies to beta2 GPI. There was a significant correlation (r = 0.66, P < 0.05) between the levels of aCL and anti-beta2 GPI antibodies. Forty-one patients had features of definite or suggestive APS. Thrombocytopenia, recurrent pregnancy loss and CNS manifestations (seizures eight, infarct one) were seen in 20, 13 and nine patients, respectively. Thrombosis of the peripheral vessels was seen in only one patient. Only the presence of seizures was significantly associated with the presence of aCL and anti-beta2 GPI antibodies (P < 0.05). The characteristic association of definite APS (recurrent pregnancy loss and arterial/venous thrombosis) was lacking.     

The increase of blood anticardiolipin antibody depends on the underlying etiology in cerebral ischemia.

Although anticardiolipin antibody (aCL) has been suggested to be a potent risk factor for thrombosis and atherosclerosis in multiple arterial beds, conflicting results still exist between aCL and cerebral ischemia in the general stroke population. To elucidate if this discrepancy relates to the heterogeneity of underlying etiologies, blood beta(2)-glycoprotein I dependent-aCL was evaluated in 432 Taiwanese adults associated with cerebral ischemia who were classified into five subtypes according to their causes of cerebral ischemia. The results were compared with those in 100 healthy controls. A definite increase of aCL-IgG isotype was found in 41 patients (9.35%) and four controls (4.0%). The relative risk was 2.52. The frequency of increased aCL-IgG was 12.2%, 12.8%, 8.8%, 3.9%, and 3.5% in patients with large-artery atherosclerotic disease, stroke of unknown etiology, small-artery occlusive disease, cardioembolism, and stroke of other known etiology, respectively. Only patient with large-artery atherosclerotic disease (p<0.025) and stroke of unknown etiology (p<0.05) had a higher frequency of increased aCL than control. The frequencies of abnormal result of activated partial thromboplastin time, antinuclear factor, Coombs' test, and venereal disease research laboratory were 2.84%, 1.22%, 1.02%, and 1.34% in these 41 patients, respectively. Accordingly, aCL-IgG selectively increases in patients with large-artery atherosclerosis and stroke of unknown etiology, reflecting selective activation of humoral immunity for aCL in the pathogenesis of cerebral ischemia.     

A thrombin-cross-reactive anticardiolipin antibody binds to and inhibits the anticoagulant function of activated protein C

OBJECTIVE: To test the hypotheses that some thrombin-reactive anticardiolipin antibodies (aCL) may bind to protein C (PC) and/or activated PC (APC), and that some of the PC- and APC-reactive aCL may inhibit PC activation and/or the function of APC. METHODS: We studied the reactivity of patient-derived monoclonal aCL with PC and APC. We examined the effects of the reactive antibodies on PC activation and on the activity of APC in plasma coagulation. RESULTS: Five of 5 patient-derived, thrombin-reactive monoclonal aCL bound to PC and APC. In addition, 1 patient-derived monoclonal antiprothrombin antibody (APT) that displayed aCL activity and reacted with thrombin also bound to PC and APC. Of these 6 PC- and APC-reactive aCL/APT, all failed to inhibit PC activation, but 1 (CL15) shortened the plasma coagulation time in the presence of exogenous APC and thus inhibited the anticoagulant function of APC. CONCLUSION: Most of the thrombin-reactive aCL in patients with antiphospholipid syndrome may bind to PC and APC. Of the APC-reactive aCL, some (like CL15) may inhibit the anticoagulant function of APC and are thus likely to be prothrombotic in the host.     

The increase of blood anticardiolipin antibody depends on the underlying etiology in cerebral ischemia.

Although anticardiolipin antibody (aCL) has been suggested to be a potent risk factor for thrombosis and atherosclerosis in multiple arterial beds, conflicting results exist between aCL and cerebral ischemia in the general stroke population. To elucidate if this discrepancy relates to the heterogeneity of underlying etiologies, the blood beta(2)-glycoprotein I dependent-aCL in 432 Taiwanese adults was examined. The associated cerebral ischemia in these patients was classified into five subtypes according to the cause of cerebral ischemia. The results were compared with those in 100 healthy controls. A definite increase of aCL-IgG isotype was found in 41 patients (9.35%) and four controls (4.0%). The relative risk was 2.52. The frequency of increased aCL-IgG was 12.2%, 12.8%, 8.8%, 3.9%, and 3.5% in patients with large-artery atherosclerotic disease, stroke of unknown etiology, small-artery occlusive disease, cardioembolism, and stroke of other known etiology, respectively. Only patients with large-artery atherosclerotic disease (p<0.025) and stroke of unknown etiology (p<0.05) had higher frequencies of increased aCL than those in control subjects. The frequencies of abnormal results of activated partial thromboplastin time, antinuclear factor, Coombs' test, and venereal disease research laboratory were 2.84%, 1.22%, 1.02%, and 1.34% in these 41 patients, respectively. Accordingly, aCL-IgG selectively increases in patients with large-artery atherosclerosis and stroke of unknown etiology, reflecting selective activation of humoral immunity for aCL in the pathogenesis of cerebral ischemia.     

Detection of acquired resistance to activated protein C associated with antiphospholipid antibodies using a novel clotting assay.

Antiphospholipid antibodies (aPA) frequently interfere with the protein C pathway. This manifests as acquired activated protein C (APC) resistance in the absence of factor V Leiden and has been proposed as a putative mechanism for the pathogenesis of the antiphospholipid syndrome (APS). We have developed a Russell's viper venom test, performed with and without activation of endogenous protein C, which is sensitive to aPA-associated APC resistance. Results were reported as the endogenous APC ratio (EAPCr); the ratio of the two clotting times normalized against pooled normal plasma. Forty-four patients with aPA, anticardiolipin and/or lupus anticoagulant, including 34 with a history of thrombosis or pregnancy morbidity; a control group of aPA-negative patients; and 26 healthy normals were studied. EAPCr (mean, SD) was significantly higher in APS patients (1.94, 0.58) than normals (0.98, 0.12) or controls (1.14, 0.19; P < 0.00001). Elevated EAPCr (> 1.22) occurred in 91% of aPA-positive patients, predominantly due to resistance to APC (87%) rather than prolonged basal clotting times alone (15%). Significant correlation was observed between the EAPCr value and dilute Russell's viper venom time (rs = 0.44, P = 0.003), IgG anticardiolipin (rs = 0.54, P = 0.002), protein S (r = -0.46, P = 0.01) and activated partial thromboplastin time-based APC resistance (r = -0.61, P = 0.001). There was no significant relationship between EAPCr and protein C concentration, anti-beta2-glycoprotein-I (anti-beta2GPI) or IgM anticardiolipin. Purified aPA IgG caused a dose-dependent increase in APC resistance when added to normal plasma. We conclude that aPA-associated acquired APC resistance is a common feature of APS and may be independent of anti-beta2GPI.     

A thrombin–cross‐reactive anticardiolipin antibody binds to and inhibits the anticoagulant function of activated protein C

Objective

To test the hypotheses that some thrombin‐reactive anticardiolipin antibodies (aCL) may bind to protein C (PC) and/or activated PC (APC), and that some of the PC‐ and APC‐reactive aCL may inhibit PC activation and/or the function of APC.

Methods

We studied the reactivity of patient‐derived monoclonal aCL with PC and APC. We examined the effects of the reactive antibodies on PC activation and on the activity of APC in plasma coagulation.

Results

Five of 5 patient‐derived, thrombin‐reactive monoclonal aCL bound to PC and APC. In addition, 1 patient‐derived monoclonal antiprothrombin antibody (APT) that displayed aCL activity and reacted with thrombin also bound to PC and APC. Of these 6 PC‐ and APC‐reactive aCL/APT, all failed to inhibit PC activation, but 1 (CL15) shortened the plasma coagulation time in the presence of exogenous APC and thus inhibited the anticoagulant function of APC.

Conclusion

Most of the thrombin‐reactive aCL in patients with antiphospholipid syndrome may bind to PC and APC. Of the APC‐reactive aCL, some (like CL15) may inhibit the anticoagulant function of APC and are thus likely to be prothrombotic in the host.

     

Blood coagulation factor Va abnormality associated with resistance to activated protein C in venous thrombophilia

A coagulation test abnormality, termed activated protein C (APC) resistance, involving poor anticoagulant response to APC is currently the most common laboratory finding among venous thrombophilic patients. Because the anticoagulant activity of APC involves inactivation of factors Va and VIIIa, studies were made to assess the presence of abnormal factors V or VIII. Diluted aliquots of plasma from two unrelated patients with APC resistance and thrombosis were added to either factor VIII-deficient or factor V-deficient plasma and APC resistance assays were performed. The results suggested that patients' factor V but not factor VIII rendered the substrate plasma APC resistant. When factor V that had been partially purified from normal or APC resistant patients' plasmas using immunoaffinity chromatography was added to factor V-deficient plasma, APC resistance assays showed that patients' factor V or factor Va, but not normal factor V, rendered the substrate plasma resistant to APC. Studies of the inactivation of each partially purified thrombin-activated factor Va by APC suggested that half of the patients' factor Va was resistant to APC. These results support the hypothesis that the APC resistance of some venous thrombophilic plasmas is caused by abnormal factor Va.     

Inhibitory activity of anti-β2-glycoprotein I antibody on factor va degradation by activated-protein C and its cofactor protein S

We investigated the influence of anti-β₂-glycoprotein I (aGPI), which recently has come to be regarded as anti-cardiolipin antibody (aCL) itself, on factor Va (FVa) degradation by activated protein C/protein S system. We found that aGPI had an inhibitory effect on FVa degradation with β₂-glycoprotein I-dependency, thus suggesting aGPI/aCL is a highly possible factor as the pathogenesis of thrombosis observed in aGPI/aCL-positive patients. © 1995 Wiley-Liss, Inc.     

Anticardiolipin and anti-beta2glycoprotein-I antibodies in patients with systemic lupus erythematosus: comparison between Colombians and Spaniards

We studied the prevalence, isotype distribution, and clinical significance of anticardiolipin (aCL) and anti-beta2glycoprotein I (anti-beta2GPI) antibodies in two populations of patients with systemic lupus erythematosus (SLE), 160 Colombians and 160 Spaniards. All sera were tested in our laboratory by enzyme-linked immunosorbent assay (ELISA) for IgG, IgM, and IgA aCL, as well as IgG and IgM anti-beta2GPI. Positive results for at least 1 of the 3 aCL isotypes were found in 40 Colombians (25%) and 55 Spaniards (34%). IgG aCL was the predominant isotype in both populations. Positive results for at least 1 of the anti-beta2GPI isotypes were found in 34 Colombians (21%) and 29 Spaniards (18%). IgG anti-beta2GPI was the dominant isotype in Colombians, while IgM was predominant in Spaniards. Positivity for anti-beta2GPI in aCL-positive patients was present in 77% in the Colombian group and 50% in the Spaniard group. Among Colombians, IgG aCL and anti-beta2GPI correlated with thrombosis, fetal loss, and thrombocytopenia. Among Spaniards, IgG aCL and IgG anti-beta2GPI correlated with thrombosis, fetal loss, and livedo reticularis. For detecting thrombosis and fetal loss, aCL ELISA was more sensitive than anti-beta2GPI in Spaniards, and anti-beta2GPI ELISA was more specific than aCL in both populations.     

Ischemic colitis and acquired resistance to activated protein C in a woman using oral contraceptives

We present the case history of a 22-yr-old woman diagnosed with ischemic colitis associated with the use of oral contraceptives (OC). At the time of her presenting symptoms activated protein C (APC) resistance, a risk factor for thrombosis, was demonstrated. There was no laboratory evidence of inherited thrombophilia; that is, antithrombin III, protein C and protein S levels were normal and the factor V Leiden mutation was not present. The OC were discontinued and the patient's symptoms improved. Subsequent evaluation revealed that the activated protein C resistance had resolved. This case illustrates APC resistance as a potential link between OC use and its known association with ischemic colitis.     

Budd-Chiari syndrome in a patient with factor V Leiden--successful treatment by TIPSS placement followed by liver transplantation.

The causes of Budd-Chiari syndrome (BCS) comprise several diseases leading to thrombophilia. One of the most common thrombophilic disorders is resistance against activated protein C, caused by a single point mutation of the factor V gene. In December 1993, a 22-year-old patient was given a diagnosis of subacute BCS with occlusion of all major hepatic veins. Placement of a transjugular intrahepatic portosystemic stent shunt led to rapid disappearance of ascites and hepatic encephalopathy. During the following two years, recurrent partial occlusions of the shunt were treated by balloon angioplasty. The cause of the BCS still being unknown, in October 1996 we performed extensive laboratory investigations concerning states of thrombophilia and found moderately elevated IgG anticardiolipin antibodies (19.7 U/ml) and a resistance against activated protein C caused by heterozygosity for a point mutation of the factor V gene (1691G-->A; factor V Leiden). As a consequence, oral anticoagulation with coumarin was initiated. In October 1997, elective liver transplantation was performed which led to disappearance of APC resistance. Moreover, IgG anticardiolipin antibodies have been negative since then. If BCS is caused by APC resistance, liver transplantation not only treats the chronic liver disease but also cures the state of thrombophilia since factor V is mainly synthesized in the liver.     

Relations beetwen severity of anemia and certain antiphospholipid antibodies presence in systemic lupus erythematosus patients

Anaemia is a common hematological abnormality in systemic lupus erythematosus (SLE). Autoimmune hemolytic anaemia (AHA) is one of the types of anaemia in SLE. Other reasons of anaemia in SLE are: chronic inflammatory diseases, insufficient level of elements necessary for erythropoiesis and chronic renal disease. The aim of the study was to examine the relations between severity of anemia and presence of certain antiphospholipid antibodies (aPL) in SLE. The study group consisted of 24 patients (one man and 23 women) with active lupus. Anticardiolipin antibodies (aCL), anti-02 glycoprotein I antibodies (anti-beta2 GPI IgM and IgG) and red cell parameters: haemoglobin level (Hb), erythrocytes (RBC), mean corpuscular volume (MCV), mean corpuscular haemoglobin mass (MCH), mean corpuscular haemoglobin concentration (MCHC) and ferritin level were measured before beginning or intensification of treatment. The activity of SLE was measured by SLEDAI and C3 complements. The patients were divided into two subgroups: subgroup with aCL-IgG above 20 u/ml and below 20 u/ml. In patients with aCL-IgG above 20 u/ml the mean Hb level was lower, and the mean ferritin level was significantly higher than in patients with aCL-IgG level below 20 u/ml. We observed a negative, significant correlations between Hb and aCL-IgG (p = 0.01; R = -0.47) and between Hb and anti-32 GPI IgG (p = 0,0003; R = -0,67) and a negative correlation between Hb and activity of SLE estimated by SLEDAI (p = 0.02; R = -0.45) and positive between Hb and C3 complement (p = 0.02; R = +0.5). In conclusion: antiphospholipid antibodies presence in patients with SLE can influence the severity of anaemia.     

Thrombotic microangiopathy in patients with phosphatidylserine dependent antiprothrombin antibodies and antiphospholipid syndrome

Thrombotic microangiopathy (TMA) is a rare disorder characterized by microvascular thrombosis. TMA has been reported in patients with antiphospholipid antibodies and/or antiphospholipid syndrome but its pathogenesis is not clarified. We present two patients with TMA associated with IgG phosphatidylserine dependent antiprothrombin antibodies (aPS/PT). CASE 1: A 44-year-old Japanese female with systemic lupus erythematosus (SLE) and positive lupus anticoagulant (LA) was started on ticlopidine after having stroke. Four weeks later she developed TMA. IgG/M/A anticardiolipin antibodies (aCL) were negative, but strong positive IgG aPS/PT were detected. CASE 2: A 32-year-old Russian female with SLE was admitted because of hypertension, renal insufficiency and proteinuria at 14 weeks of pregnancy. She developed TMA after surgical abortion. IgG aPS/PT and LA were strongly positive but IgG/M/A aCL were negative. Neither case had von Willebrand factor cleaving protease (ADAMTS-13), suggesting that TMA in those patients was associated with thrombophilia rather than insufficient ADAMTS-13. Both patients were successfully treated with a series of plasma exchange.     

Anti-beta2-glycoprotein I autoantibodies, in vitro thrombin generation, and the antiphospholipid syndrome

OBJECTIVE: Thrombin plays a pivotal role in the regulation of hemostasis. We examined the effect of antiphospholipid (aPL) antibodies, in particular those with specificity for beta2-glycoprotein I (beta2-GPI), on in vitro thrombin generation, and examined the association with clinical manifestations of the antiphospholipid syndrome (APS). METHODS: We studied plasma samples from 59 patients with aPL antibodies determined by the presence of either elevated anticardiolipin (aCL) antibodies or lupus anticoagulant (LAC). Direct antibody binding of IgG, IgM, and IgA to beta2-GPI and prothrombin (PT) was determined by ELISA. Affinity purification of total IgG and IgG anti-B2-GPI antibodies was performed using staphylococcal protein A and phospholipid liposomes. A chromogenic assay was used to determine the effect of plasma samples and purified autoantibodies on in vitro thrombin generation. RESULTS: Thirty-three of 59 (56%) plasma samples inhibited in vitro generation of thrombin and 7/59 (12%) accelerated thrombin formation. There was a strong negative correlation between thrombin generation and IgG aCL (r = -0.72, p < 0.001) and IgG anti-beta2-GPI (r = -0.71, p < 0.001) antibody levels, and a weaker correlation with LAC (r = -0.46, p = 0.001). This association was not found with anti-PT antibodies and could not be attributed to concurrent therapy with warfarin. Additional experiments with affinity purified IgG antibodies indicated a dose dependent inhibition of thrombin generation, which was restricted to anti-beta2-GPI antibodies. Patients with a history of core clinical manifestations of the APS [venous and arterial thrombosis, recurrent (> or = 2) fetal loss] had significantly greater inhibition of in vitro thrombin generation (mean +/- SEM Z score: -3.38 +/- 0.51 vs -1.42 +/- 0.56; p = 0.01) and higher levels of IgG aCL (mean +/- SEM Z score: 8.39 +/- 1.12 vs 5.39 +/- 0.88; p = 0.04) and IgG anti-beta2-GPI antibodies (mean +/- SEM Z score: 4.49 +/- 0.69 vs 2.26 +/- 0.54; p = 0.01). Odds ratios for these variables and clinical manifestations of the APS were 5.43, 4.17, and 3.28, respectively. CONCLUSION: aPL antibodies may accelerate or inhibit the rate of in vitro thrombin formation. The predominant effect is inhibition that is restricted to IgG anti-beta2-GPI antibodies and it is strongly associated with clinical manifestations of the APS.