Autoimmune causes of recurrent pregnancy loss

Recurrent pregnancy loss (RPL) is the loss of 3 or more spontaneous and consecutive pregnancies. There are many causes, such as genetic, anatomic, hormonal, medical and immunologic causes. Two theories, the alloimmune and the autoimmune theories, explain the immunologic cause. The Antiphospholipid Antibody (APA) Syndrome is considered as the autoimmune cause of RPL. It involves two antibodies, Lupus anticoagulant (LAC) and the anti-cardiolipin antibody (ACA). The rate of LAC is 7% and of ACA is 15%, among pregnant women. These two antibodies are believed to cause thrombosis in the maternal circulation, leading to the events that lead to the fetal losses. Women with these antibodies, along with other factors, are believed to be at high risk for RPL. The diagnostic criteria for the APA syndrome include elevated LAC or ACA serum levels and clinical findings of thrombosis, thrombocytopenia and RPL. Presently, the medical treatment of the APA syndrome includes heparin, low-dose aspirin, and immunoglobulins. There must also be an active attempt to search for other causes of RPL among patients with APA syndrome, such as anatomic, endocrinologic, anatomic and medical problems. Management of RPL should also include extensive counseling for the patient and her family.

Evaluation of bedside prothrombin time and activated partial thromboplastin time measurement by coagulation analyzer CoaguCheck Plus in various clinical settings

In the present study CoaguCheck Plus (CCP), a coagulation test system using whole blood, was evaluated with respect to its comparability with widely distributed conventional routine coagulation assays. A correlation of r = 0.997 (p < 0.0001) was found between INR of CCP-prothrombin time (CCP-PT) and Thrombotest (KC-1 analyzer) in patients on oral anticoagulant therapy. A correlation of r = 0.899 (p < 0.001) between CCP-aPTT and Actin ES aPTT (STA analyzer) was found in heparinized patients. Impaired hepatic hepatic coagulation factor synthesis in liver cirrhosis patients was detected by CCP-PT with a sensitivity of 0.75 and by Normotest (STA analyzer) with a sensitivity of 0.92. Those patients with normal CCP-PT values and liver disease had, only mild reductions (> 30% of normals) in coagulation factors II, V, VII or X. CCP-aPTT was also performed in patients with a deficiency in the so called endogenous coagulation factors VIII, IX, XI and XII. CCP-aPTT showed a sensitivity similar to that of Actin FS aPTT in the detection even of mild deficiencies in factors VIII, IX and XII; factor XI deficiency was however detected only in patients with severe (< 12% of normals) disease; lupus anticoagulants were detected with a high sensitivity.

Monitoring of oral anticoagulant therapy in lupus anticoagulant positive patients with the anti-phospholipid syndrome

Introduction of the International Normalized Ratio (INR) has improved the standardization of laboratory control of oral anticoagulant therapy (OAT). However, it has been reported that misleading INR results can be obtained from OAT patients with lupus anticoagulant (LA). To investigate this claim, we studied 35 OAT patients, 14 of whom had anti-phospholipid syndrome (APS) with a documented LA. Attainment of anticoagulation was confirmed by chromogenic assay of factor VII and factor X. Prothrombin times were performed using eight thromboplastins (five derived from rabbit brain, two recombinant human tissue factor and one made from human placenta) with an International Sensitivity Index (ISI) of <1.40. When using the thromboplastin manufacturers' ISI there was a significant difference (ANOVA, P<0.0001) between INR results obtained with the eight reagents for both APS (average CV = 12.4%) and non-APS (average CV = 12.5%) patient groups. Variation using the eight thromboplastins was assessed by calculating the CV for each sample; these values were then pooled for each patient group to give the average CV for all samples with all reagents for the two patient groups. Results for both patient groups exhibited markedly reduced variation (APS group average CV = 6.5%, non-APS group average CV = 5.8%) when locally assigned ISI values were employed in the calculation of INRs. Our data does not support the suggestion that the INR may not reflect the true level of anticoagulation in the long-term warfarin-treated patient, in whom lupus anticoagulant was detected. However, there was strong evidence that thromboplastin use should be restricted to those clot detection systems for which the reagent's manufacturer has assigned an ISI, or local ISI assignment must be undertaken. The inappropriate use of a generic (i.e. optical or mechanical clot detection system without regard to specific analyser type) ISI value can lead to ambiguous results.

Possible pathogenetic role of activated platelets in the primary antiphospholipid syndrome involving the central nervous system

Neurological disorders occurring in the primary antiphospholipid syndrome (neuro-PAPS) have not yet been completely understood. Platelet activation has been suggested to play a crucial role in the pathogenesis of hemostatic disorders in the antiphospholipid syndrome, but no association with neuro-PAPS has been investigated so far. Therefore, we investigated 16 patients with PAPS by flow cytometry in the presence of circulating activated platelets as defined by the surface expression of activation-dependent glycoprotein CD62. In addition, the relationship among activated platelets and anticardiolipin antibodies (aCL) was evaluated. Compared to normal subjects CD62 was found significantly increased in these patients. Furthermore, a significantly increased percentage of CD62-positive platelets was found in the neuro-PAPS group (nine patients) compared to the non-neuro-PAPS patients (seven subjects). On the contrary, no significant difference was found between the two groups with regard to aCL IgG and platelet number. Furthermore, within the neuro-PAPS group, no difference was evidenced, in the CD62-positive platelet percentage, between the four subjects with thrombocytopenia and the five with the normal blood platelet count. Similarly, neuro-PAPS subjects with previous peripheral arterial and/or venous thrombosis did not show a significantly more elevated level of CD62-positive platelets. Finally, a linear correlation was found between the aCL IgG level and the CD62-positive platelet percentage in all the patients and, more significantly, in the neuro-PAPS group, but not within the non-neuro-PAPS patients. Our data demonstrate that circulating activated platelets are detectable by flow cytometry in the majority of PAPS patients and suggest the existence of a relationship among activated platelets, aCL, and neurological disease that patients affected by PAPS might undergo.

[Use of elimination of plasma phospholipid membranes for detection of "lupus anticoagulant" effects]

The coagulation activity of plasma phospholipid membranes (PM) was measured in plasma depleted for platelets (PDP) in 50 normal subjects and 33 patients with the antiphospholipid syndrome (APS) and the "lupus anticoagulant" in the plasma. The normal value for phospholipid activation of clotting was 99.8 +/- 3.5% (from 75 to 125%), whereas in patients with APS and lupus anticoagulant it was 42.1 +/- 8.2% (p < 0.001). Addition of PM from patients' PDP to normal plasma free from PM did not normalize clotting. Addition of PM from normal plasma to patients' PDP normalized the clotting time. Therapy with discrete plasmapheresis increased the phospholipid activation value in the patients from 42.1 to 73.3% (p < 0.01), which was due to removal of the PM-antiphospholipid antibody complex from PDP. The proposed microfiltration method can be used in the complex of tests for detecting the lupus anticoagulant in patient's plasma.

Antiphospholipid antibodies in primary Sjögren's syndrome: prevalence and clinical significance in a series of 80 patients

OBJECTIVE

To determine the prevalence and clinical significance of antiphospholipid antibodies (aPL) in a cohort of patients with primary Sjögren's syndrome (SS).

METHODS

Eighty patients with primary SS were studied prospectively. The prevalence of aPL and characteristics of the clinical and laboratory features of these patients were compared with those of the following groups of patients: (i) 50 patients with SS associated with systemic lupus erythematosus (SLE); (ii) 100 patients with SLE without SS; and (iii) 100 healthy blood donors from the blood bank of our hospital.

RESULTS

Only 11 (14%) patients with primary SS were found to have aPL (anticardiolipin antibodies or lupus anticoagulant, or both) in their sera, but anti beta 2-glycoprotein I antibodies were not detected in any patient. In contrast, aPL were detected in 12 (24%) patients with SS secondary to SLE and in 21 (21%) patients with SLE without SS. None of the healthy controls presented aPL in their sera. Patients with primary SS presented a lower prevalence of thrombocytopenia (p < 0.05) and livedo reticularis (p < 0.01) compared with the other two groups of patients. No patient with primary SS was diagnosed as having an antiphospholipid syndrome (APS), while 4 (8%) patients with secondary SS and 9 (9%) with SLE without SS were found to have APS (p < 0.05).

CONCLUSION

In patients with primary SS, aPL are present in a lower percentage than in patients with SS secondary to SLE or in patients with SLE without SS. The presence of aPL in these primary SS patients is not associated with the clinical events of APS.

Primary antiphospholipid antibody syndrome and retinal occlusive vasculopathy

PURPOSE

To report a 31-year-old healthy patient with retinal venous occlusion in his left eye attributable to primary antiphospholipid antibody syndrome.

METHODS

The patient was examined clinically. Multiple serologic and clinical investigations were performed to determine the causative disease. He was closely followed up for more than 3 years.

RESULTS

The presence of lupus anticoagulant in our patient was indicated by a kaolin clotting time index of 27 (normal, <17) and confirmed by the demonstration of IgG antibodies against phospholipids. After long-term oral anticoagulant treatment for 2 years, lupus anticoagulant levels returned to normal, and therapy was stopped. No further thrombotic event occurred during follow-up.

CONCLUSIONS

In retinal vascular occlusions of unexplained origin, antiphospholipid antibodies may play an important role in the pathogenesis. Detecting these antibodies in the serum of patients with retinal vascular occlusion helps determine the appropriate treatment with long-term oral anticoagulants.

Widespread cutaneous necrosis and antiphospholipid antibodies: two episodes related to surgical manipulation and urinary tract infection

Widespread cutaneous necrosis (WCN) associated with antiphospholipid antibodies is rare. Its mechanisms have yet to be elucidated, and there are no well-established guidelines for its management. We describe a woman who had two episodes of WCN related to surgical manipulation for urinary tract obstruction and urinary tract infection. Lupus anticoagulant was always positive. In the second episode anticardiolipin antibodies were elevated, and protein C levels were temporarily decreased. We found only ten previously reported cases of WCN associated with antiphospholipid antibodies, none of which were related to surgical manipulation.

Severe bleeding due to acquired hypoprothrombinemia-lupus anticoagulant syndrome. Case report and review of literature

A 17-year-old girl was admitted to our department with a hemorrhagic syndrome due to a serious coagulopathy; prothrombin time (PT) INR was 2.46 and the activated partial thromboplastin time (aPTT) ratio 3.46. Coagulation tests with pooled normal fresh plasma did not correct aPTT because of a coagulation inhibitor, and only partially corrected PT. Factor II activity reached only 5%. Diluted Russell viper venom tests (dRVVT) and kaolin clotting time (KCT) of patient plasma (PP) and of a mixture of PP/normal plasma (NP) detected the lupus anticoagulant (LA). The level of factor II antigen was 10%. We diagnosed systemic lupus erythematosus (SLE) with a rare acquired hypoprothrombinemia-LA syndrome (HLAS). The patient was treated with corticosteroids and high-dose Ig and a normal PT value was re-established.

Causes and outcome of deep-vein thrombosis in otherwise-healthy patients under 50 years

We examined thrombophilic mechanisms and outcome in 54 patients with deep-vein thrombosis (DVT), who were otherwise apparently healthy and aged < or = 50 years. Patients were followed up 6 years (median) after a confirmed first DVT between 1987-1992 with no known predisposing illnesses. Patients were traced through the hospital registry and compared with 25 matched controls. Tested thrombophilic mechanisms were either genetic (activated protein C [APC] resistance; anti-thrombin III deficiency [ATIII]; protein C or protein S deficiency [PC, PS]) or acquired (lupus anti-coagulant [LAC]/anti-cardiolipin antibodies [ACA]; subsequent diagnosis of cancer). Twenty-nine DVT patients attended for full studies. The remaining 25 were interviewed by phone and none had a reported neoplastic disease, confirmed by their hospital records and the National Cancer Registry. These patients' demographics, risk factors and subsequent course were similar in all respects to the studied group. In the control group, APC resistance was the only coagulopathy found (1/25, 4%), and it was also the most common abnormality among DVT patients (8/29, 28%) (p = 0.009). Three DVT patients had LAC/ACA (10%) and one each, ATIII, PC and PS deficiencies (3.3% each). No malignancy was encountered during a follow-up of 7.9 +/- 5.7 years. Circumstantial risk factors were found in 52% of the patients, 21% had a family history of DVT, and 41% had recurrent DVT. These characteristics were not significantly different when DVT patients with and without coagulopathy were compared.

[Clinical significance and predictive value of laboratory tests in thrombosis associated with antiphospolipid antibodies]

Antiphospholipid antibodies are a wide ranging, heterogeneous family of autoantibodies, formerly believed to be directed to anionic phospholipids. Recent research, however, has confirmed that they are directed to plasma proteins bound to suitable (phospholipid) anionic surfaces. The most well-known and best characterized antigens are beta 2-glycoprotein I, recognized by anticardiolipin antibodies, and prothrombin, recognized by most lupus anticoagulants. Lupus anticoagulants are generally identified on the basis of their capacity to prolong the phospholipid-dependent coagulation tests. Two types of lupus anticoagulants, anticardiolipin-type A, and antiprothrombin antibodies, whose presence is associated with different coagulation profiles, have been identified. Anticardiolipin-type A and antiprothrombin antibodies may be detected also by specific immunoassays. The capacity of several methodologies to detect antiphospholipid antibodies reflects chiefly their immunological and functional heterogeneity. Since most of the laboratory methods have not yet been standardized, the results of studies on the clinical relevance of antiphospholipid antibodies must be analyzed with caution. The association between antiphospholipid antibodies with peculiar clinical manifestations such as venous and arterial thrombosis, recurrent miscarriage, and thrombocytopenia, characterizes the so-called "antiphospholipid syndrome". Retrospective and cross-sectional studies have confirmed the role of anticardiolipin antibodies and lupus anticoagulants as risk factors for both venous and arterial thrombosis, the most common clinical manifestations of the antiphospholipid syndrome. Prospective studies performed in different patient populations have confirmed the association between anticardiolipin antibodies and lupus anticoagulants with venous, and possibly, arterial thrombosis, although information on the predictive value of the various laboratory tests with respect to thrombosis is still limited. It is hoped that the development and standardization of assays that selectively identify antiphospholipid antibodies associated with increased risk of thrombosis will lead to therapeutic strategies able to prevent thromboembolic complications of the antiphospholipid syndrome.

Reliability of a modified tissue factor-dependent factor V assay for activated protein C resistant factor Va using a calcium-containing thromboplastin

The original tissue factor-dependent factor V assay for activated protein C resistant factor Va (Blood 1995; 85: 1704-1711) has been modified to use a calcium containing thromboplastin and to express results as an observed to expected ratio (Obs/Exp.). The latter permits establishing a normal range independent of variations due to differences in reagents. Comparing Obs/Exp ratios with DNA analysis in 72 persons revealed that an Obs/Exp ratio of 0.6 distinguished without overlap normals from heterozygotes for FV R506Q. Three homozygotes had a ratio of < 0.1. Application of this Obs/Exp cut-off ratio of 0.6 to a total of 226 plasma samples tested to date discriminated without overlap between normals and heterozygotes. We conclude that this assay-readily adaptable to any dedicated coagulation laboratory and capable of yielding reliable results in all clinical circumstances in which testing is indicated-can distinguish between normals and heterozygotes for the FV R506Q mutation without the need for confirmatory DNA analysis.

Risk of arterial thrombosis in patients with anticardiolipin antibodies and lupus anticoagulant

The relationship between arterial or venous thrombosis and the levels of anticardiolipin antibodies (aCL) and/or existence of lupus anticoagulant (LA) was studied. The 141 patients with systemic lupus erythematosus (SLE) were divided into four groups: aCL single positive (25 cases), LA single positive (11 cases), aCL and LA double positive (25 cases), aCL and LA double negative (80 cases). The prevalence of thrombosis was higher in aCL and LA double positive patients (21/25 cases, 84.0%, P <0.01) than that in aCL single positive patients (4/25 cases, 16.0%), LA single positive patients (1/11 cases, 9.1%) and double negative patients (3/80 cases, 3.8%). Furthermore, in these double positive patients, all patients (10/10 cases) with a high positive level of aCL (> 10 units/ml) had arterial thrombosis, whereas only 2/15 patients (13.3%) with a low positive level of aCL (3-10 units/ml) were affected. Venous thrombosis was frequently found in the low positive group (9/15 cases, 60.0%). On the contrary, none of 105 LA negative patients had arterial thrombosis and only seven (6.7%) had venous thrombosis. These findings indicate that a high aCL activity combined with a LA positive result might be a risk factor for arterial thrombosis.

Evaluation of sensitivity and specificity of a standardized procedure using different reagents for the detection of lupus anticoagulants. The Working Group on Hemostasis of the Société Française de Biologie Clinique and for the Groupe d'Etudes sur I'Hémostase et la Thrombose

This study was designed to test the sensitivity and specificity of a combination of 3 phospholipid-dependent assays performed with various reagents, for the detection of lupus anticoagulant (LA). Plasmas containing an LA (n = 56) or displaying various confounding pathologies [58 intrinsic pathway factor deficiencies, 9 factor VIII inhibitors, 28 plasmas from patients treated with an oral anticoagulant (OAC)] were selected. In a first step, the efficiency of each assay and reagent was assessed using the Receiving Operating Characteristic (ROC) method. Optimal cut-offs providing both sensitivity and specificity > or = 80% were determined. The APTT assay and most of the phospholipid neutralization assays failed to discriminate factor VIII inhibitors from LA. In a second step, using the optimal cut-offs determined above, the results of all the possible combinations of the 3 assays performed with 4 different reagents were analyzed. Thirteen combinations of reagents allowed > or = 80% of plasmas of each category (LA, factor deficiency or OAC) to be correctly classified (3/3 positive test results in LA-containing plasmas and 0/3 positive results in LA-negative samples).

A new method for characterization and epitope determination of a lupus anticoagulant-associated neutralizing antiprothrombin antibody

A patient had both lupus anticoagulant hypoprothrombinemia syndrome and celiac disease. The presence of a neutralizing antiprothrombin antibody in the patient's serum was demonstrated by coagulation tests, immunoadsorption, and Western blot analysis. The probable cause for the severe hypoprothrombinemia was clearance of prothrombin-antibody complexes from the circulation. Studies showed the antiprothrombin antibody binding to human prothrombin was phospholipid- and Ca(++)-independent; the antibody did not bind to human thrombin. The target epitope of the antibody was studied by Western blot analysis of mutated recombinant human prothrombin molecules. The antibody reacted with the fragment 2-A region of prothrombin, spanning the second kringle domain and the thrombin A chain within prothrombin. Based on this new method, the proposed mechanism for the neutralizing action of the antibody is impairment of prothrombin activation by the prothrombinase complex, either by steric hindrance of the hydrolysis of prothrombin by factor Xa or by interference of the interaction of prothrombin with factor Va; both reactions are required for efficient conversion of prothrombin to thrombin.

Nodular regenerative hyperplasia of the liver in systemic lupus erythematosus. The relationship with anticardiolipin antibody and lupus anticoagulant

Recent reports have indicated that nodular regenerative hyperplasia (NRH) associated with systemic lupus erythematosus (SLE) is related to anticardiolipin antibodies (aCL) and/or lupus anticoagulant (LA). We describe a patient with SLE complicated by NRH, who did not show neither aCL nor LA activity. This case suggests that the pathogenesis of NRH in patients with autoimmune diseases is heterogeneous and not confined to aCL and LA.

Flow cytometric detection of circulating activated platelets in primary antiphospholipid syndrome. Correlation with thrombocytopenia and anticardiolipin antibodies

Platelet activation has been suggested to play a crucial role in the pathogenesis of haemostatic disorders in antiphospholipid syndrome (APS). In 16 patients with primary APS (PAPS) we investigated by flow cytometry the presence of circulating activated platelets as defined by the surface expression of activation-dependent glycoproteins CD62 and CD63. In addition, the relationships among activated platelets, thrombocytopenia, antiphospholipid antibodies (aPL) and platelet associated IgG (PalgG) were evaluated. Compared to normal subjects CD62, but not CD63 expression, was found significantly increased in patients. All thrombocytopenic subjects showed a percentage of CD62 expressing platelets above the cut off. In thrombocytopenics a significantly increased percentage of CD62 and higher levels of aCL IgG were found compared to PAPS patients with normal platelet count. No correlation was found between activated platelets and both lupus anticoagulant antibodies and PalgG. Our data demonstrate that circulating activated platelets are detectable by flow cytometry in the majority of PAPS patients and suggest the existence of a relationship among activated platelets, thrombocytopenia and aPL levels.

Pathogenesis and treatment of the antiphospholipid antibody syndrome

Antiphospholipid antibody syndrome (APS) is one of the most important causes of thrombophilia, presenting most often as venous or arterial thrombosis, recurrent pregnancy loss, or thrombocytopenia. Both the lupus anticoagulant and anticardiolipin antibody are associated with APS. The mechanism of the prothrombotic state is not understood, but may involve beta-2 glycoprotein 1 (a naturally occurring anticoagulant), platelet aggregation, the protein C pathway, or endothelial cell function. The current treatment recommendation, after a venous or arterial thrombosis, is high-intensity, long-term warfarin therapy.

Free protein S deficiency may be found in patients with antiphospholipid antibodies who do not have systemic lupus erythematosus

In order to determine if there is a relationship between antiphospholipid antibodies and reduced free protein S levels, we evaluated 21 patients who had an antiphospholipid antibody but had neither a history of venous thromboembolism nor systemic lupus erythematosus (cases) and 55 matched controls, who did not have an antiphospholipid antibody, a history of thrombosis or systemic lupus erythematosus. Cases and controls had similar protein C and antithrombin levels. Six of 21 cases had reduced free protein S antigen levels, compared to 5 of 55 controls (chi 2 = 5.823 p < 0.025). In addition, the mean free protein S level was significantly lower in cases than in controls (0.30 +/- 0.09 units vs 0.39 +/- 0.13 units, p < 0.01, two-tailed Student's t-test). We conclude that antiphospholipid antibodies are associated with a significant decrease in free protein S levels, and that this acquired free protein S deficiency may contribute to the thrombotic diathesis seen in patients with antiphospholipid antibodies.

Antigenic specificities of antiphospholipid autoantibodies: implications for clinical laboratory testing and diagnosis of the antiphospholipid syndrome

Most autoantibodies associated with the antiphospholipid (aPL) syndrome and detected in standard anticardiolipin and/or lupus anticoagulant assays are directed against beta 2-glycoprotein I (beta 2-GPI) or prothrombin. Recent data indicate that these antibodies can also be detected in immunoassays utilizing purified protein antigens, in the absence of phospholipids. Initial clinical studies suggest that positivity in anti-beta 2-GPI immunoassays is more closely associated with the clinical manifestations of the aPL syndrome than is positivity in conventional anticardiolipin ELISAs. Anti-beta 2-GPI immunoassays may detect certain anti-beta 2-GPI antibodies that are not detectable in conventional anticardiolipin assays, but do not detect authentic (beta 2-GPI-independent) anticardiolipin antibodies. It appears that the former, but not the latter, antibodies are associated with the clinical manifestations of the aPL syndrome. The potential advantages and disadvantages of these new immunoassays in the clinical evaluation of the aPL syndrome are discussed.

[A case of medial medullary infarction with prominent deep sensory impairment]

We report a patient with medial medullary infarction who showed deep sensory impairment as his prominent neurological manifestation. A 54-year-old man with a history of hypertension was admitted to our hospital with numbness of the bilateral upper and lower extremities, followed by dysarthria and right hemiparesis. Physical examination revealed no abnormalities except for high blood pressure. He hiccuped continuously. On neurological examination, he exhibited dysarthria, mild dysphagia and right hemiparesis without facial or lingual paresis. Sensitivity to light touch and pinprick was normal, but sensitivity to vibration and joint position was severely decreased in the bilateral upper and lower extremities, predominantly in the lower extremities and on the right side in the upper extremities. He had been treated with antiedema agents and thromboxane synthetase inhibitor. His hiccups stopped within two weeks, and his right hemiparesis gradually improved within one month. However, his deep sensory impairments remained prominent. Blood examinations disclosed positive lupus anticoagulant. MRI showed bilateral infarction at the medial portion of the upper medulla oblongata, extending to both pyramids, especially on the left. Somatosensory evoked potentials (SEP) after median nerve stimulation showed P14 and the later components with prolonged latency. No SEP were recorded after posterior tibial nerve stimulation. The latency of P14 was well correlated with the severity of deep sensory impairments in the upper extremities. Neurological manifestations of our patient are not typical of medial medullary infarction, and are informative about the functional anatomy of the deep sensory tract in the medulla oblongata. We discuss the relation of the intractable hiccups to the bilateral medial medullary lesions, and emphasize the importance of lupus anticoagulant as one of the risk factors in brainstem infarction.

Lupus anticoagulants/antiphospholipid-protein antibodies: the great imposters

Antiphospholipid-protein antibodies (APA) represent a family of immunoglobulins which recognize protein-phospholipid complexes. A variety of proteins have been implicated including: prothrombin, annexin V, beta 2-Glycoprotein I, and protein S. APA are detected utilizing either coagulation-based tests to identify lupus anticoagulants (LA) or solid phase ELISA assays to identify anticardiolipin antibodies (ACA). APA may be seen in a variety of different clinical settings including convalescence from infections, resulting from exposure to certain drugs, or in association with autoimmune diseases. Autoimmune APA have been linked to a variety of thromboembolic complications involving both arterial and venous sites. In addition, recurrent fetal loss has been linked to a APA. The underlying pathophysiology of the thromboembolic events remains controversial. Given the diversity of anatomic sites, more than one thromboembolic mechanism(s) is likely. Abnormalities of the protein C system most likely account for the venous thromboembolic events. Because of the spectrum of clinical complications, virtually any clinician may encounter patients with the APA syndrome (thrombosis, thrombocytopenia, recurrent fetal loss coupled with positive LA or ACA testing).

Different target specificities of phospholipid-dependent antibodies

Phospholipid dependent antibodies are usually measured with assays for antiphospholipid/anticardiolipin antibodies (aPLA) or for lupus anticoagulant (LA) activity. Most of them are targeted to complexes of beta 2-glycoprotein I (beta 2-GPI) and anionic phospholipids (PLP) or to prothrombin for some LA. New understandings allow a better standardisation and optimisation of assays' reactivity. Antigenic targets of phospholipid dependent antibodies were studied on plasmas from 38 patients with the antiphospholipid syndrome (APS) and presenting aPLA and/or LA. Using human beta 2-GPI-PLP complexes as solid phase antigen offers the highest sensitivity for measuring aPLA. Many aPLA, but not all, also react with beta 2-GPI coated on solid phase, however there is no evidence until now that this latter reactivity shows a closest association with the clinical context. Most of the patients with LA present an immunological reactivity to beta 2-GPI alone or to prothrombin, when these proteins are coated on solid phase. In two cases there was a reactivity to only beta 2-GPI-PLP complexes. For the various immunoassays, using NUNC type I plates offers a good binding capacity for coating antigens. They are then present at enough density on solid phase for insuring an efficient binding of autoantibodies. This is an important factor for assay sensitivity and reproducibility. Interestingly, in 1 case with LA, autoantibodies were reactive with coated beta 2-GPI alone but not with its PLP-complexes. In another case reactivity to beta 2-GPI was much higher than that to beta 2-GPI-PLP.