A New Type of Coagulation Inhibitor

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

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

Antiphospholipid antibodies--we are not quite there yet

The diagnosis of antiphospholipid syndrome is predominantly made in the laboratory and depends on the persistent presence of antiphospholipid antibodies in individuals with thrombosis or pregnancy morbidity. Correct diagnosis of the syndrome is imperative to prevent unnecessary long secondary thromboprophylaxis. Three antiphospholipid antibody subtypes are included in the classification criteria of the antiphospholipid syndrome: lupus anticoagulants, anticardiolipin antibodies and anti-β2-glycoprotein I antibodies. Only lupus anticoagulants are undisputedly associated with thrombosis, which is why the serological criteria of the antiphospholipid syndrome are under debate. All of the assays used to detect antiphospholipid antibodies are in need of better standardization, although progress has been made in the detection of lupus anticoagulants. The inconsistent association between both anticardiolipin and anti-β2-glycoprotein I antibodies and thrombosis is a cause for alarm. We are in need of better assays to detect those individuals at risk for thrombosis and population-based prospective studies to provide us with accurate risk assessments.

Attempts to make sense of the antiphospholipid syndrome

Many investigators have been intrigued by the paradoxical association of a circulating anticoagulant, first called lupus anticoagulant by Feinstein and Rapaport [1], with a tendency to develop thrombosis, as initially described by Walter Bowie [2]. Work in Leuven on this topic started when Luis Carreras, an Argentinian hematologist, joined the laboratory of blood coagulation at this university in 1979. At that time, the head of the laboratory was Marc Verstraete. Luis had a particular interest in antibody-mediated coagulation disorders, and had prepared reviews on thrombosis and thrombocytopenia induced by heparin [3] and on the lupus inhibitor [4]. In Leuven, he joined Jos Vermylen, senior member of the laboratory, and an internist with particular interest in hemostasis, thrombosis and vascular disease. As such, Professor Vermylen was involved in both laboratory research and patient care.

Current status and implications of autoimmune antiphospholipid antibodies in relation to thrombotic disease

This review briefly describes the development of the concepts of antiphospholipid antibody and of antiphospholipid syndrome. It focuses on the two main antigenic targets, beta2 glycoprotein I and prothrombin. An excessive production of natural antibodies rather than an immune response to exogenous antigen is proposed as pathogenetic for the development of these antibodies. The review attempts to explain how some of these antibodies are anticoagulant in vitro yet prothrombotic in vivo. The final section discusses when to test for such antibodies, how to test and how to consider treatment of patients with the antiphospholipid syndrome.

The 'antiphospholipid syndrome' and the 'lupus anticoagulant'

In recent years an association has been described between, on the one hand, an in vitro prolongation of phospholipid-dependent coagulation tests (the 'lupus anticoagulant') or the demonstration of antiphospholipid antibodies and, on the other, clinical events, particularly recurrent thrombosis (usually venous but sometimes arterial), thrombocytopenia, and also recurrent mid-term fetal loss. Other less well-documented associations with haemolytic anaemia, livedo reticularis, strokes and other neurological syndromes have been suggested. The antibodies are present temporarily in many infections, are usually of IgM isotype and thrombosis does not occur. However, they are persistently present and mainly of IgG isotype in a number of auto-immune disorders associated with thrombosis, in particular systemic lupus erythematosus, in which 50% of patients will show antibody of one isotype or another. The strongest association is with antinuclear factor-negative lupus and 'lupus-like' disorders in which a full diagnosis of classical lupus cannot be made. The clotting test abnormality and antiphospholipid antibodies may be found also in otherwise normal individuals suffering thrombosis or fetal loss--the so-called primary antiphospholipid syndrome. These data raise important questions for management, but many details are controversial despite a decade's work; this review examines the present position and outlines some of the difficulties, particularly from the point of view of nephrology and paediatrics.

Comparison of laboratory tests used for identification of the lupus anticoagulant

A comparison of the sensitivities of the ten most commonly used tests for the identification of the lupus anticoagulant (LA) and the lupus cofactor phenomenon was undertaken on 18 patients. All investigations, except the cardiolipin-antibody ELISA assay, were carried out using patient's plasma alone followed by a 1:1 mix with control plasma. Dilution studies (1:3, 1:6, 1:9--patient:control) were also carried out. The kaolin clotting time (KCT) was the only test positive in all patients at all dilutions, while the dilute activated partial thromboplastin time with kaolin (Dil-APTT) registered 17 of 18 positive at all dilutions. Both the dilute Russell viper venom time (Dil-RVVT) and the tissue thromboplastin inhibition time (TTI) (1/500 thromboplastin) identified the LA in 17 of 18 patients on initial testing but were less sensitive in the dilution studies. The KCT is not a suitable test for routine laboratory use, as it requires an individual filtration step. Therefore a combination of either the Dil-APTT or Dil-RVVT together with the TTI (1/500 dilution thromboplastin) is recommended for routine LA screening, as all patients with LA in this study were identified using these easily automated tests. The lupus cofactor phenomenon was most frequently demonstrated using the Dil-APTT.

Lupus anticoagulant in women with multiple spontaneous miscarriage

A link between the presence of the lupus anticoagulant (LA) and recurrent spontaneous miscarriage exists; however, the incidence of the LA in patients with unexplained recurrent miscarriage is unknown. We have therefore investigated the incidence of the LA in women with recurrent miscarriage but without evidence of systemic lupus erythematosus or other syndromes known to predispose towards spontaneous abortion. Plasma from 29 such women was obtained and tested in the activated partial thromboplastin time (APTT), testing for correction with normal plasma if prolonged and in the dilute simplastin time test (DSTT), again mixing with normal plasma if prolonged. Using a prolongation in either/or both tests which was not corrected by mixing with normal plasma as criteria for the presence of the LA, 14 (48%) patients showed evidence for the presence of the LA. Substitution of platelet-rich plasma for phospholipid and plasma in the APTT corrected the prolonged clotting time in every patient (9/29) in which it was prolonged, further substantiating the presence of the LA. We suggest that the presence of the LA should be investigated in any patient with unexplained recurrent miscarriage.

Inhibitors of coagulation in children

Acquired inhibitors of coagulation factor interaction in nonhemophilic children are usually nonspecific, transient, and unassociated with clinical bleeding. They occur with some frequency and are the most common cause for a prolonged APTT found by routine testing. In children, some association with viral infections and treatment with penicillin has been noted, but their interrelationship with the development of antibodies remains unclear. The exact nature of these antibodies, usually directed against coagulant factor phospholipid, is not clear and multiple antibodies both specific as well as nonspecific may occur. No therapy is generally required. Rarely has the acute development of antibodies directed against specific coagulation factors occurred. The laboratory evaluation of the type of inhibitor is, therefore, most important as specific inhibitors may be associated with life-threatening bleeding situations. Their therapy should probably include attempts at eradication of the inhibitor by immunosuppressive agents or other newer modalities. Unfortunately, little information is available regarding the nature and outcome of specific inhibitors in children. Acquired inhibitors in hemophilic patients occur in about 6 to 10% of patients. Newer approaches to their therapy include activated PCC which have generally improved the outlook for such patients. Treatment regimens involve a knowledge of inhibitor response and the concomitant use of plasmapheresis, high-dose or continuous i.v. Factor VIII, and porcine Factor VIII, followed by activated PCC. The role of immunosuppressive agents and other newer modalities appears promising, however, prospective controlled studies are necessary to evaluate their role in the overall management of such patients.

Chlorpromazine-induced lupus anticoagulant and associated immunologic abnormalities

Chronic administration of chlorpromazine is associated with the development of a lupus-like circulating anticoagulant and a variety of immunological abnormalities. The prevalence of these findings was studied in 123 psychiatric patients. The anticoagulant was present in 11 of 30 patients receiving chlorpromazine (CPZ), in none of 17 patients who had been off phenothiazine therapy for over a year and in none of 53 controls. It was also seen in 5 of 13 patients who had been switched from CPZ to another phenothiazine even after several years being off CPZ. The anticoagulant was characterized by prolongation of the partial thromboplastin time, thromboplastin dilution test, and Russell's viper venom time. Washed frozen platelets partially corrected the abnormality induced by the anticoagulant. In all but one case the anticoagulant was associated with positive antinuclear antibody test and/or increased serum IgM. Six of 16 patients also had decreased complement levels, and two had a positive direct Coombs' test. None of these patients manifested bleeding, hemolysis, splenomegaly, or other clinical features of systemic lupus erythematosus.

"Lupus" anticoagulant and inhibition of prostacyclin formation in patients with repeated abortion, intrauterine growth retardation and intrauterine death

We discovered a "lupus' anticoagulant in 2 out of 42 women with a history of repeated abortions, intrauterine growth retardation and intrauterine death of unknown origin. The "lupus' anticoagulant was detected by an abnormal dilute tissue thromboplastin assay(prothrombin time performed with dilute thromboplastin). The production of prostacyclin by fresh or exhausted rings of rat aorta was decreased by the plasma of one of these two patients with a "lupus' anticoagulant. In view of the increasing evidence for a physiological role of prostacyclin in pregnancy and fetal life, we suggest that an inhibition of prostacyclin production could compromise fetal outcome.

Lupus anticoagulant after measles

A 2 2/12 years old boy developed a "lupus anticoagulant" after measles. Fibrinogen concentration and activity of factors II, V, VII, VIII, IX, X, XI and XII were normal, but partial thromboplastin time and thromboplastin time were prolonged. Thrombin time was within the normal range. Mixing normal plasma with the patient's plasma immediately prolonged the partial thromboplastin time, and incubation of the sample did not increase the inhibition. The immunglobulin fraction prepared from the patient's plasma on DEAE-sephacel also prolonged the partial thromboplastin time in cross mixing experiments. The thrombocyte count and thrombocyte functions were normal. In spite of the pathological partial thromboplastin and thromboplastin times, surgery was performed without excessive bleeding during the operation and without delayed wound healing.

A chlorpromazine-induced inhibitor of blood coagulation

An inhibitor of blood coagulation was detected in the plasma of four schizophrenic patients receiving long-term chlorpromazine therapy. The partial thromboplastin time (PTT) was prolonged in all four patients and the prothrombin time (tpt) was prolonged in one. The inhibitor which resembled in many respects that seen in patients with systemic lupus erythematosus (SLE), was shown to be associated with the tigM-rich fractions of the serum. None of the patients manifested a clinical bleeding tendency and in two, discontinuation of the chlorpromazine was followed by a decrease in the activity of the anticoagulant. While three of the patients had a positive antinuclear antibody test (ANA) and the fourth a false positive serology for syphilis, no further evidence for SLE was found.

The lupus anticoagulant

The clinical and laboratory experience with the lupus anticoagulant was reviewed in 37 patients. The anti-coagulant is thought to act by blocking the activation of prothrombin by the prothrombin activator comlex of factors Xa, V, and phospholipid. Although the anticoagulant has been principally associated with diseases of immune origin, 14 of the present patients had disorders not thought to be immune in nature. Eighteen patients underwent twenty-one operative procedures with only a single episode of excessive bleeding. In the author's experience, the lupus anticoagulant is a rare cause of bleeding.