Catastrophic antiphospholipid syndrome. Clinical and laboratory features of 50 patients

Antiphospholipid antibody syndrome

Antiphospholipid antibodies are directed against phospholipid-protein complexes and include lupus anticoagulant, anticardiolipin antibodies, and anti-beta-2 glycoprotein I antibodies. Antiphospholipid antibody syndrome is a common cause of acquired thrombophilia and is characterized by venous or arterial thromboembolism or pregnancy morbidity and the presence of antiphospholipid antibodies. Antibodies should be demonstrable on at least 2 occasions separated by 12 weeks. Heterogeneity of the autoantibodies and absence of gold standard assays makes interpretation of laboratory results a challenge for both laboratorians and clinicians. This review discusses the key laboratory and clinical aspects of antiphospholipid antibody syndrome. Particular focus is given to lupus anticoagulant detection, in view of recently updated laboratory guidelines.

Unusual vascular focal high-grade arterial stenoses in a young woman with systemic lupus erythematosus and secondary antiphospholipid syndrome

We report the case of a 28-year old woman with an unusual presentation of peripheral arterial occlusive disease clinically characterized by intermittent claudication and bilateral, focal stenoses of the iliac arteries without signs of atherosclerosis in other vascular beds. The successful percutaneous intervention is described in detail and pathogenetic aspects of the disease are discussed.

Antiphospholipid syndrome; its implication in cardiovascular diseases: a review

Antiphospholipid syndrome (APLS) is a rare syndrome mainly characterized by several hyper-coagulable complications and therefore, implicated in the operated cardiac surgery patient. APLS comprises clinical features such as arterial or venous thromboses, valve disease, coronary artery disease, intracardiac thrombus formation, pulmonary hypertension and dilated cardiomyopathy. The most commonly affected valve is the mitral, followed by the aortic and tricuspid valve. For APLS diagnosis essential is the detection of so-called antiphospholipid antibodies (aPL) as anticardiolipin antibodies (aCL) or lupus anticoagulant (LA). Minor alterations in the anticoagulation, infection, and surgical stress may trigger widespread thrombosis. The incidence of thrombosis is highest during the following perioperative periods: preoperatively during the withdrawal of warfarin, postoperatively during the period of hypercoagulability despite warfarin or heparin therapy, or postoperatively before adequate anticoagulation achievement. Cardiac valvular pathology includes irregular thickening of the valve leaflets due to deposition of immune complexes that may lead to vegetations and valve dysfunction; a significant risk factor for stroke. Patients with APLS are at increased risk for thrombosis and adequate anticoagulation is of vital importance during cardiopulmonary bypass (CPB). A successful outcome requires multidisciplinary management in order to prevent thrombotic or bleeding complications and to manage perioperative anticoagulation. More work and reporting on anticoagulation management and adjuvant therapy in patients with APLS during extracorporeal circulation are necessary.

When You are About to Diagnose Chronic Hemolytic Uremic Syndrome, Please Think More Deep

Antiphospholipid syndrome is one type of immunological diseases which may be primary or secondary characterized by repeated thrombosis that it may be called “sticky blood syndrome”. Although a well-known disease in gynecology, there is no sufficient data in pediatrics field; so we see that it is important to discuss this interesting case.

Guidelines on the use of therapeutic apheresis in clinical practice--evidence-based approach from the Apheresis Applications Committee of the American Society for Apheresis

The American Society for Apheresis (ASFA) Apheresis Applications Committee is charged with a review and categorization of indications for therapeutic apheresis. Beginning with the 2007 ASFA Special Issue (fourth edition), the subcommittee has incorporated systematic review and evidence-based approach in the grading and categorization of indications. This Fifth ASFA Special Issue has further improved the process of using evidence-based medicine in the recommendations by refining the category definitions and by adding a grade of recommendation based on widely accepted GRADE system. The concept of a fact sheet was introduced in the Fourth edition and is only slightly modified in this current edition. The fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis. The article consists of 59 fact sheets devoted to each disease entity currently categorized by the ASFA as category I through III. Category IV indications are also listed.

Severe vascular lesions and poor functional outcome in kidney transplant recipients with lupus anticoagulant antibodies

The impact of antiphospholipid antibodies (APA) on clinical outcome and graft histology following renal transplantation remains poorly known and controversial. We retrospectively explored the functional and histological significance of APA, primarily lupus anticoagulant (LA), in kidney transplant recipients using a systematic evaluation of 3- and 12-month posttransplant screening biopsies and glomerular filtration rate measurements (mGFR). During the study period, 37 patients had APA (2.7%), primarily LA, and 12 fulfilled antiphospholipid syndrome (APS) diagnostic criteria (0.8%) at the time of transplantation. Early after transplantation, 4 of the 12 APS patients died. Early thrombosis of graft vessels and deep venous thrombosis occurred more frequently in APA+ patients than in controls (27% vs. 7%, p < 0.05 and 35% vs. 14%, p < 0.05, respectively). The survival rate was significantly lower in patients with APS. Strikingly, the hallmark lesions of APS-associated nephropathy (APSN) were found in most of screening graft biopsies in APA+ patients but not in the controls. Accordingly, APA+ patients had a dramatic increase in chronic vascular scores and a faster decline in mGFR at 1 year. In conclusion, renal transplantation may be life-threatening in APS patients, and the presence of LA at the time of transplantation is associated with a high rate of allograft APSN and poor transplantation outcomes.

Dermatological manifestations of Hughes’ antiphospholipid antibody syndrome

The dermatological manifestations of antiphospholipid syndrome (APS) may be the presenting features of APS syndrome. They are extremely diverse and heterogeneous, ranging from minor signs to life-threatening conditions such as widespread cutaneous necrosis. Their clinical significance is highly variable. Livedo reticularis is strongly associated with the arterial and microangiopathic subtypes of APS. Scientific data are required to determine the optimum management of these patients, who might benefit from recently developed antithrombotic agents. Lupus (2010) 19, 1071—1077.

Infant with probable catastrophic antiphospholipid syndrome successfully managed with rituximab

The antiphospholipid syndrome (APS) is an acquired thrombophilic disorder characterized by the presence of autoantibodies to a variety of phospholipids and phospholipid-binding proteins. Clinical manifestations range from being asymptomatic to having imminently life-threatening events. Catastrophic antiphospholipid syndrome (CAPS) occurs in <1% of patients with APS and is defined by multiple small-vessel occlusions that lead to multiple-organ failure and is associated with high morbidity and mortality rates. Here we report the case of a 3-month-old boy with probable CAPS who presented to us with digital necrosis and pulmonary hemorrhage. In addition, a skin biopsy demonstrated multiple small-vessel thromboses without signs of vasculitis. Results of testing for autoantibodies were positive for anti-beta(2) glycoprotein I (anti-beta(2)-GPI) only. His treatment consisted of high-dose steroids, immunoglobulin therapy, exchange transfusion, cyclophosphamide, and rituximab as well as iloprost and bosentan as vasodilators for his ischemia; he showed an excellent clinical response. To the best of our knowledge, this is the youngest patient with probable CAPS, the first reported patient to test positive for anti-beta(2)-GPI antibodies and negative for anticardiolipin antibodies and lupus anticoagulant, and the second patient reported to be successfully treated with an immunomodulatory regimen including rituximab.

Management of the antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by recurrent venous or arterial thromboses, fetal losses and thrombocytopenia in the presence of antiphospholipid antibodies, namely lupus anticoagulant, anticardiolipin antibodies or antibodies directed to various proteins, mainly β2 glycoprotein I, or all three. There is consensus in treating patients with APS and first venous thrombosis with oral anticoagulation to a target international normalized ratio (INR) of 2.0-3.0. A recent systematic review recommended a target INR of >3.0 in those patients with APS and arterial thrombosis. The approach in women with obstetric manifestations of APS is based on the use of aspirin plus heparin. The best treatment for patients with the catastrophic variant of the APS is a combination of anticoagulation, corticosteroids, and plasma exchange or intravenous immunoglobulins.

Antiphospholipid syndrome: frequency, main causes and risk factors of mortality

The presence of antiphospholipid antibodies has been shown to be related to an increased risk of thrombotic events. In patients with definite antiphospholipid syndrome (APS), that is, those who have had thrombosis and at least two positive determinations of antiphospholipid antibodies, secondary thromboprophylaxis with long-term anticoagulation therapy results in a low rate of recurrent thrombotic events, ranging from 0.016 to 0.031 events per patient per year. Thrombotic complications are, however, the most common cause of death in APS. The mortality rate in a large European cohort of patients with APS during a 5-year study period was 5.3%, and up to 40% of the deaths in this cohort were attributed to severe thrombotic events such as myocardial infarction, stroke and pulmonary embolism. Catastrophic APS is an unusual form of the disease, being observed in less than 1% of reported cases of APS, which is associated with a much higher mortality rate than classical APS. The combined use of anticoagulation, corticosteroids, plasma exchange and intravenous immunoglobulin therapy could result in a dramatic reduction in mortality, by approximately 20%, in patients with catastrophic APS.

Catastrophic antiphospholipid syndrome (CAPS): update from the ‘CAPS Registry’

Although less than 1% of patients with the antiphospholipid syndrome (APS) develop the catastrophic variant, its potentially lethal outcome emphasizes its importance in clinical medicine today. However, the rarity of this variant makes it extraordinarily difficult to study in any systematic way. In order to put together all of the published case reports as well as the new diagnosed cases from all over the world, an international registry of patients with catastrophic APS (CAPS Registry) was created in 2000 by the European Forum on Antiphospholipid Antibodies (see http://www.med.ub.es/MIMMUN/FORUM/CAPS.HTM). Currently, it documents the entire clinical, laboratory and therapeutic data of more than 300 patients whose data has been fully registered.

Antiphospholipid antibodies in critical illness

The antiphospholipid syndrome is defined by the presence of antiphospholipid antibodies in patients with recurrent venous or arterial thromboembolism or pregnancy morbidity. Antithrombotic therapies are the mainstay of treatment to reduce the risk of recurrent thromboembolism. Among patients with antiphospholipid antibodies, the absolute risk of new thrombosis developing is low in healthy patients without previous thrombotic events. However, the risk of recurrent thrombosis appears to be high in patients with a history of arterial or venous thrombosis. Compared with placebo or untreated control, anticoagulation with warfarin administered to achieve an international normalized ratio of 2.0 to 3.0 probably reduces the risk of recurrence of thrombotic events. Aspirin and moderate-intensity warfarin appear equally effective for preventing recurrent stroke in patients with a single positive antiphospholipid antibody test result and previous stroke. It is unknown how best to prevent first stroke in patients found to be persistently positive for the antiphospholipid syndrome. The catastrophic variant of the antiphospholipid syndrome is a condition characterized by multiple vascular occlusive events, usually affecting small vessels and evolving over a short period of time. This condition has a very high mortality rate. First-line treatment with therapeutic anticoagulation, corticosteroids, plasma exchange, and intravenous immunoglobulin seems to be effective in reducing mortality and risk of catastrophic thrombotic events in these patients. In conclusion, moderate-intensity warfarin is effective for preventing recurrent thrombotic events in patients with venous thrombosis. Aspirin appears to be as effective as moderate-intensity warfarin for preventing recurrent stroke in patients with previous stroke and a single positive test result for antiphospholipid antibody. The optimal treatment of other clinical manifestations of antiphospholipid syndrome needs to be addressed in well-designed prospective studies.

Update on the diagnosis, treatment, and prognosis of the catastrophic antiphospholipid syndrome

The catastrophic antiphospholipid syndrome (APS) is a potentially life-threatening condition, the diagnosis of which requires a high degree of clinical awareness on the part of attending physicians. Patients with APS present with 1) clinical evidence of multiple organ involvement developed over a very short time; 2) histopathologic evidence of multiple small-vessel occlusions; and 3) laboratory confirmation of the presence of antiphospholipid antibodies, usually in high titer. A combination of anticoagulants, corticosteroids, intravenous immunoglobulins, and plasma exchanges is the basic treatment for all patients with this severe condition. Unfortunately, despite current therapies, the mortality rate is still high (around 30%). However, once patients with catastrophic APS have recovered, they usually follow a stable course with continued anticoagulation and few patients present with a relapse of the catastrophic episode.

Catastrophic cerebral antiphospholipid syndrome presenting as cerebral infarction with haemorrhagic transformation after sudden withdrawal of warfarin in a patient with primary antiphospholipid syndrome

Catastrophic antiphospholipid syndrome (APS) is caused by thrombotic vascular occlusions that affect both small and large vessels, producing ischaemia in the affected organs. The "catastrophic" variant of the antiphospholipid syndrome (cAPS) develops over a short period of time. Although patients with cAPS represent <1% of all patients with APS, they are usually life threatening with a 50% mortality rate. A strong association with concomitant infection is thought to act as the main trigger of microthromboses in cAPS. Several theories have been proposed to explain these physiopathological features. Some of them suggest the possibility of molecular mimicry between components of infectious microorganisms and natural anticoagulants, which might be involved in the production of cross-reacting antiphospholipid antibodies. We present a case of catastrophic cerebral APS characterised by massive temporal lobe infarction and subsequent haemorrhagic transformation after sudden withdrawal of warfarin.

The cardiac manifestations of antiphospholipid syndrome and their echocardiographic recognition

Antiphospholipid syndrome is an autoimmune disorder characterized by the presence of antiphospholipid antibodies, hypercoagulability, vascular thrombosis, and recurrent fetal loss. Cardiac involvement occurs frequently. Leaflet thickening and vegetations are detected quite often echocardiographically, but hemodynamically significant stenotic and/or regurgitant valvular disease is uncommon. Antiphospholipid syndrome can also cause left and right ventricular systolic and diastolic dysfunction as well as pulmonary hypertension. Other findings include spontaneous echo contrast and in situ mural thrombosis. In this review, the author discusses the major cardiac manifestations of antiphospholipid syndrome and highlights the role of echocardiography in their detection.

The CAPS Registry: morbidity and mortality of the catastrophic antiphospholipid syndrome

Although less than 1% of patients with the antiphospholipid syndrome (APS) develop the catastrophic variant, its potentially lethal outcome emphasises its importance in clinical medicine today. However, the rarity of this variant makes it extraordinarily difficult to study in any systematic way. To put together all the published case reports as well as the new diagnosed cases from all over the world, an international registry of patients with catastrophic APS (CAPS Registry) was created in 2000 by the European Forum on Antiphospholipid Antibodies. Currently, it documents the entire clinical, laboratory and therapeutic data of more than 300 patients whose data has been fully registered. This registry can be freely consulted at the Internet (http://www.med.ub.es/MIMMUN/FORUM/CAPS.HTM), and it is expected that the periodical analysis of these data will allow us to increase our knowledge of this condition.

Antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an autoimmune systemic disease that is diagnosed when there is vascular thrombosis and/or pregnancy morbidity occurring with persistently positive antiphospholipid antibodies (aPL) (lupus anticoagulant test, anticardiolipin antibodies, and/or anti-beta(2)-glycoprotein I antibodies). Although International APS Classification Criteria have been formulated to provide a uniform approach to APS research, aPL may cause a spectrum of clinical manifestations, some of which are not included in these criteria. The main aPL-related cardiac manifestations include valve abnormalities (vegetations and/or thickening), myocardial infarction (MI), intracardiac thrombi, and myocardial microthrombosis. In this article, we will review the definition, etiopathogenesis, clinical manifestations, diagnosis, and treatment of aPL-related clinical events with emphasis on cardiac manifestations.

Pregnancy and catastrophic antiphospholipid syndrome

Antiphospholipid syndrome (APS) is clearly related to maternal morbidity. The most characteristic feature is pregnancy loss; however, several other serious complications had been reported including fetal growth restriction, uteroplacental insufficiency, fetal distress, pre-eclampsia, and HELLP syndrome. Herein, we review the different aspects of obstetric APS features, with special emphasis on its life-threatening variant known as catastrophic APS (Asherson's syndrome) and its relationship with a thrombotic microangiopathy such as HELLP syndrome.

Catastrophic antiphospholipid syndrome: treatment, prognosis, and the risk of relapse

The "catastrophic" variant of the antiphospholipid syndrome (APS) is characterized by multiple vascular occlusive events, usually affecting small vessels and developing over a short period of time. Although patients with catastrophic APS represent less than 1% of all patients with APS, they are usually in a life-threatening situation with a 50% mortality rate. The purpose of this paper is to review the treatment strategies and prognostic factors in patients with catastrophic APS. A detailed description of the clinical and laboratory features of the syndrome can be found in the other articles of this issue.

[Liver infarcts with early HELLP syndrome and probable catastrophic antiphospholipid syndrome]

INTRODUCTION

Among microangiopathic disorders of pregnancy, catastrophic antiphospholipid syndrome (CAPS) is a maternal and fetal life-threatening disorder. Hepatic involvement of this multi-systemic disorder can be confused with HELLP syndrome, occurring usually later in the course of pregnancy.

CASE REPORT

We report a case of probable CAPS with hepatic disease in a pregnant woman at 13 week's gestation, with antiphospholipid syndrome and biological features of HELLP syndrome. Unspecific hepatic imaging, well-described in our case allowed undelayed therapy.

CONCLUSION

CAPS and HELLP syndrome, both severe microangiopathic disorders, may be associated. Nosological distinction does not modify treatment strategy, which is a maternal and foetal emergency, but their overlapping requires aggressive and early management.

Antiphospholipid antibody syndrome

The antiphospholipid antibody syndrome (APS) is defined by the persistent presence of antiphospholipid antibodies in patients with recurrent venous or arterial thromboembolism or pregnancy morbidity. Anti-thrombotic therapy is the mainstay of treatment given the high risk of recurrent thromboembolism that characterizes this condition. Despite the prothrombotic nature of APS, thrombocytopenia is present in a proportion of patients. which can complicate management and limit the use of antithrombotic therapy. The mechanism of APS-associated thrombocytopenia is multifactorial and its relation to thrombotic risk poorly characterized. However, the presence of thrombocytopenia does not appear to reduce thrombotic risk in patients with APS, who can develop thromboembolic complications necessitating antithrombotic treatment. In these cases, treatment of the thrombocytopenia may be necessary to facilitate administration of antithrombotic agents. Clinical trials have demonstrated that patients with antiphospholipid antibodies and venous thromboembolism should be treated with vitamin K antagonists (warfarin); that ischemic stroke may be treated with aspirin or warfarin; and that women with recurrent pregnancy loss should receive prophylactic-dose heparin and aspirin. However, application of these trial results to patients with APS-associated thrombocytopenia can be challenging since there are limited data on the optimal use of antithrombotic agents in this setting. Issues such as determining the platelet threshold at which antithrombotic agents can be safely used and managing patients with both bleeding and thromboembolic complications remain unresolved. Ultimately the risks and benefits of antithrombotic therapy, balanced against the severity of the thrombocytopenia and its potential bleeding risks, need to be assessed using an individualized patient approach.

The physiopathology of the catastrophic antiphospholipid (Asherson's) syndrome: compelling evidence

Catastrophic antiphospholipid (Asherson's) syndrome (cAPS) was described in the past as a severe variant of the antiphospholipid syndrome (APS). Currently growing evidence suggests it is a unique condition. This statement is based on several clinical and physiopathological features that although not well understood define cAPS by itself. The remarkable features of cAPS are the presence of antiphospholipid antibodies (aPLAs) and microthromboses. Additional physiopathological features are the presence of anemia and thrombocytopenia, which are also often described in similar autoimmune conditions. A strong association with concomitant infection is thought to act as the main trigger of microthromboses in cAPS. Several theories have been proposed to explain these physiopathological features. Some of them suggest the possibility of molecular mimicry between components of infectious microorganisms and natural anticoagulants, which might be involved in the production of cross-reacting aPLAs in cAPS. Some genetic risk factors have also been suggested to be implicated in the onset of cAPS, however they have not been defined yet. Herein, we review the remarkable physiopathological features commonly described in cAPS hitherto. We concluded that although they are not completely understood, it is possible to differentiate them from similar conditions. Nevertheless further studies on these physiopathological mechanisms of the disease are needed.

Catastrophic antiphospholipid (Asherson's) syndrome

Catastrophic antiphospholipid syndrome is characterized by multiple organ involvement developing over a very short period of time, histopathological evidence of multiple small vessel occlusions, and laboratory confirmation of the presence of antiphospholipid antibodies. Knowledge of its treatment is vital as the outcome can be lethal.

[Clinical features and treatments of antiphospholipid syndrome]

Antiphospholipid antibodies are serological markers of antiphospholipid syndrome (APS). Diversity of so-called antiphospholipid antibodies is well-known. These antibodies are directed against phospholipid binding proteins such as beta(2)-glycoprotein I and prothrombin as well as against phospholipids such as cardiolipin. Thrombosis and pregnancy morbidity are clinical features of APS. In addition, cardiovascular manifestations, neurological disorders, skin manifestations, renal involvements and thrombocytopenia are reported to be significant in clinical aspects of APS. Anticoagulation therapy and antiplatelet therapy are effective for the secondary prevention of thrombosis in APS.

Antiphospholipid antibody syndrome and autoimmune diseases

The arbitrary division between antiphospholipid antibody syndrome and secondary antiphospholipid antibody syndrome has not proven useful. Antiphospholipid antibodies in the absence of antiphospholipid antibody syndrome often occur as epiphenomena in many autoimmune diseases. They are very common in systemic lupus erythematosus. Antiphospholipid antibody syndrome is a significant comorbidity in lupus but is uncommon in Sjögren's syndrome, rheumatoid arthritis, scleroderma, and systemic vasculitis. Evidence is growing that antiphospholipid antibodies may have a pathogenic role in pulmonary hypertension and accelerated atherosclerosis of autoimmune diseases.

Treatment options for patients who have antiphospholipid syndromes

The antiphospholipid thrombosis syndrome, associated with anticardiolipin (aCL) or subgroup antibodies, can be divided into one of six subgroups (I-VI). There is little overlap (about 10% or less) between these subtypes, and patients usually conveniently fit into only one of these clinical types. Although there appears to be no correlation with the type, or titer, of aCL antibody and type of syndrome, the subclassification of thrombosis and aCL antibody patients into these groups is important from the therapy standpoint. This article also reviews the clinical presentations associated with each of these six subgroups.

The clinical spectrum of antiphospholipid syndrome

Antiphospholipid syndrome (APS) is a disorder characterized by a wide variety of clinical manifestations. Virtually any organ system or tissue may be affected by the consequences of large- or small-vessel thrombosis. There is a broad spectrum of disease among individuals with antiphospholipid antibodies (aPL). Patients may exhibit clinical features suggesting APS but not fulfill the International Criteria for a "definite" diagnosis. Seronegative APS patients demonstrate typical idiopathic thromboses but aPL are not initially detected. Patients defined with definite APS demonstrate nearly identical sites of venous and arterial thrombosis, regardless of the presence or absence of systemic lupus erythematosus. Microangiopathic APS may present with isolated tissue and organ injury or as the overwhelming "thrombotic storm" observed in catastrophic APS.

The severity of systemic lupus erythematosus negatively correlates with the increasing number of CD4+CD25(high)FoxP3+ regulatory T cells during repeated plasmapheresis treatments of patients

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by increased pathologic autoantibody production. A decrease in the number of CD4+CD25(high)FoxP3+ regulatory T cells can play a key role in the loss of tolerance to self antigens. Our aim was to determine the absolute number of peripheral CD4+CD25(high)FoxP3+ T cells in 44 patients with SLE, furthermore, to measure the changes in the number of CD+CD25(high)FoxP3+ T cells in 5 patients with severe SLE treated with repeated plasmapheresis for 4-6 days in comparison to the changes in the activity of disease (SLEDAI). Percent of CD4+CD25(high)FoxP3+ T cells were measured by flow cytometry. The absolute number of peripheral CD4+CD25(high)FoxP3+ T cells was significantly decreased in the 44 patients with SLE compared to the healthy controls n = 32 (0.012 +/- 0.006 vs. 0.038 +/- 0.017 G/L, p < 0.05). In the 5 patients with severe SLE the repeated plasmapheresis treatments increased the peripheral number of CD4+CD25(high)FoxP3+ T cells. As the number of CD4+CD25(high)FoxP3+ T cells increased during the treatment, the activity of disease (the value of SLE activity index) decreased. In the peripheral blood of SLE patients not only the ratio was decreased (as it was published earlier) but also the absolute number of these regulatory T cells. The repeated plasmapheresis treatments of SLE patients induced a significant increase in the number of peripheral CD4+CD25(high)FoxP3+ T cells in parallel to the decrease in the values of SLEDAI (the activity of disease). This phenomenon is, among others, possibly due to the elimination of interpheron-alpha and lymphocytotoxic antibodies during plasmapheresis.