Endothelium as a target for antiphospholipid antibodies

Antiphospholipid Antibodies as Key Players in Systemic Lupus Erythematosus: The Relationship with Cytokines and Immune Dysregulation

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by an overproduction of cytokines, such as interleukins and interferons, contributing to systemic inflammation and tissue damage. Antiphospholipid syndrome is a thrombo-inflammatory autoimmune disease affecting a third of SLE patients. We performed an in-depth analysis of the available literature, and we highlighted the complex interplay between immunity, inflammation, and thrombosis, the three major pathogenic pathways that are trapped in a mutually reinforcing destructive loop.

Should we be targeting type 1 interferons in antiphospholipid syndrome?

Systemic autoimmune diseases are characterized by increased production of type I interferon (IFN-1) and upregulation of IFN-1-inducible genes, suggesting an important role of the IFN-1 pathway in their pathogenesis. Recent studies have demonstrated increased IFN-1 expression in both primary and secondary antiphospholipid syndrome (APS), along with increased toll-like receptor type 9 activity and plasmacytoid dendritic cell function. The increasing knowledge of the association between IFN-1 and APS pathology may provide a rationale for conducting clinical trials to assess the efficacy of IFN-1-targeting drugs in reducing APS-related complications. In this narrative review, we summarize the current knowledge on the role of IFN-1 in APS pathogenesis, explore its clinical implications, and examine the existing evidence regarding therapeutic options that have been investigated to date.

Deficiency of Axl aggravates pulmonary arterial hypertension via BMPR2

Pulmonary arterial hypertension (PAH), is a fatal disease characterized by a pseudo-malignant phenotype. We investigated the expression and the role of the receptor tyrosine kinase Axl in experimental (i.e., monocrotaline and Su5416/hypoxia treated rats) and clinical PAH. In vitro Axl inhibition by R428 and Axl knock-down inhibited growth factor-driven proliferation and migration of non-PAH and PAH PASMCs. Conversely, Axl overexpression conferred a growth advantage. Axl declined in PAECs of PAH patients. Axl blockage inhibited BMP9 signaling and increased PAEC apoptosis, while BMP9 induced Axl phosphorylation. Gas6 induced SMAD1/5/8 phosphorylation and ID1/ID2 increase were blunted by BMP signaling obstruction. Axl association with BMPR2 was facilitated by Gas6/BMP9 stimulation and diminished by R428. In vivo R428 aggravated right ventricular hypertrophy and dysfunction, abrogated BMPR2 signaling, elevated pulmonary endothelial cell apoptosis and loss. Together, Axl is a key regulator of endothelial BMPR2 signaling and potential determinant of PAH.

Abdominal arterial lesions associated with antiphospholipid antibodies: A comparative cross sectional magnetic resonance angiography study

INTRODUCTION

Case reports and small case series suggest that stenotic lesions of the renal, coeliac and mesenteric arteries may occur in the antiphospholipid syndrome (APS) resulting in clinical consequences such as hypertension and abdominal angina.

OBJECTIVE

To determine the prevalence of stenotic lesions in arteries arising from the middle aorta in patients with antiphospholipid antibodies (aPL) compared with healthy, hypertensive and atherosclerotic controls.

PATIENTS AND METHODS

In a cross-sectional comparative radiological study using magnetic resonance angiography (MRA) we assessed 5 groups of subjects for the prevalence of stenotic lesions in arteries arising from the middle aorta: APS/aPL positive, healthy renal donors, patients with hypertension, patients with atherosclerosis defined radiologically and patients with systemic lupus erythematosus and vasculitis who were negative for aPL. All subjects underwent MRA in suspended respiration and images were assessed by 2 senior radiologists blinded to the clinical details.

RESULTS

In the atherosclerosis group, vascular stenotic lesions were more prevalent (71%) than in any other group (p≤ 0.000002). The prevalence of all stenotic lesions in aPL positive patients (33%) was significantly higher than in the renal donors (18%) and hypertensive patients (19%) (p≤ 0.009). Renal artery stenosis was significantly more prevalent in aPL positive patients than in renal donors (p≤ 0.0006) but similar to the prevalence in hypertensive patients. Coeliac and/or mesenteric lesions were significantly more common in aPL positive patients vs hypertensive patients (p≤ 0.001). Stenoses did not correlate with traditional risk factors.

CONCLUSION

Arterial stenotic lesions in arteries arising from the middle aorta were highly prevalent in atherosclerotic subjects and were more common in aPL positive patients than hypertensive patients and healthy renal donors.

Bullous Pemphigoid: Trigger and Predisposing Factors

Bullous pemphigoid (BP) is the most frequent autoimmune subepidermal blistering disease provoked by autoantibodies directed against two hemidesmosomal proteins: BP180 and BP230. Its pathogenesis depends on the interaction between predisposing factors, such as human leukocyte antigen (HLA) genes, comorbidities, aging, and trigger factors. Several trigger factors, such as drugs, thermal or electrical burns, surgical procedures, trauma, ultraviolet irradiation, radiotherapy, chemical preparations, transplants, and infections may induce or exacerbate BP disease. Identification of predisposing and trigger factors can increase the understanding of BP pathogenesis. Furthermore, an accurate anamnesis focused on the recognition of a possible trigger factor can improve prognosis by promptly removing it.

Antiphospholipid antibodies in patients with lupus nephritis: clinical correlations and associations with long-term outcomes

Whether the presence or absence of antiphospholipid antibodies (aPL) in patients with lupus nephritis (LN) is associated with differences in clinical outcomes remains unclear. We reviewed LN patients at a single centre during 2000-2017, and compared the clinical features and long-term outcomes between patients who were seropositive or seronegative for aPL. aPL was detected in 53/149 (35.6%) patients with biopsy-proven LN, and anticardiolipin IgM, anticardiolipin IgG, anti-β2 glycoprotein I and lupus anticoagulant was detected in 18.8%, 18.1%, 10.7% and 8.1%, respectively. Follow-up was 155.8 ± 61.0 months, and was similar between aPL-seropositive and -seronegative patients. aPL seropositivity persisted in 94.3% of patients during remission. aPL-seropositive patients showed inferior patient survival (91% and 85% at 10 and 15 years, respectively, compared to 99% and 95% in aPL-seronegative patients; p = 0.043). Nine (6.0%) patients died during follow-up, including six aPL-seropositive (four thrombotic events and two bleeding complications related to anticoagulation) and three aPL-seronegative patients. aPL seropositivity was associated with more rapid decline in estimated glomerular filtration rate (-1.44 mL/min/year compared to -0.38 mL/min/year in aPL-seronegative patients; p = 0.027) and inferior long-term renal survival (82% and 74% at 10 and 15 years, respectively, compared to 91% and 87% in aPL-seronegative patients; p = 0.034). aPL-seropositive patients also had a higher incidence of thrombotic events and miscarriage (32.1% and 13.2%, respectively, compared to 16.7% and 2.1% in the aPL-seronegative group; p = 0.030 and 0.006). We concluded that aPL seropositivity was associated with inferior long-term patient and renal survival and more frequent thrombotic events and miscarriage in LN patients.

Hypertensive disorders of pregnancy associated with adverse pregnant outcomes in patients with systemic lupus erythematosus: a multicenter retrospective study

BACKGROUND

Hypertension disorders in pregnancy (HDP) were common complications in women with systemic lupus erythematosus (SLE). However, the impact of HDP and the measures to prevent HDP-related fetal adverse pregnancy outcomes (APOs) remained to be explored.

METHODS

A multicenter retrospective study of 342 pregnant women with SLE was performed. Variables related to SLE and APOs were recorded. Fetal development was evaluated by umbilical artery Doppler ultrasonography.

RESULTS

HDP was diagnosed in 45 (13.2%) patients, including pre-eclampsia in 42 and gestational hypertension in 3. Patients with HDP had higher incidence of preterm birth (71.1% vs 20.9%, P < 0.001), intrauterine growth retardation (IUGR) (37.8% vs 11.8%, P < 0.001), low-birth-weight infants (62.2% vs 17.2%, P < 0.001), and very-low-birth-weight infants (37.8% vs 2.7%, P < 0.001), compared with lupus patients without HDP. A total of 35 (77.8%) HDP patients had disease activation during pregnancy. All the events occurred during the second and third trimesters, mainly presenting as moderate-to-high activity (65.7%). Active disease [odds ratios (OR) = 3.9, 95% confidential interval (CI) 1.5-9.7, P = 0.004] and positive anticardiolipin (aCL) antibody (OR = 7.6, 95% CI 2.7-18.6, P < 0.001) were independent risk factors for HDP in lupus patients. Doppler RI and S/D ratio predicted APOs in patients with HDP. The optimal cut-off values for RI and S/D ratio were 0.7 (sensitivity 48.1%, specificity 53.3%) and 3.4 (sensitivity 66.7%, specificity 100%), respectively.

CONCLUSIONS

HDP was a common pregnant complication and caused various fetal and maternal adverse outcomes in patients with SLE. Umbilical artery Doppler ultrasonography was effective in predicting fetal APOs in lupus patients with HDP.Key Points• HDP induced preterm birth, IUGR, low-birth-weight infants, and very-low-birth-weight infants in patients with SLE.• HDP led to lupus activation during the second and third trimesters.• Disease activation and aCL positivity were predictors for HDP.• RI and S/D ratio from umbilical artery Doppler predicted APOs in patients with HDP.

Autonomic neuropathy-in its many guises-as the initial manifestation of the antiphospholipid syndrome

Autonomic disorders have previously been described in association with the antiphospholipid syndrome. The present study aimed to determine the clinical phenotype of patients in whom autonomic dysfunction was the initial manifestation of the antiphospholipid syndrome and to evaluate for autonomic neuropathy in these patients. This was a retrospective study of 22 patients evaluated at the University of Colorado who were found to have a disorder of the autonomic nervous system as the initial manifestation of antiphospholipid syndrome. All patients had persistent antiphospholipid antibody positivity and all patients who underwent skin biopsy were found to have reduced sweat gland nerve fiber density suggestive of an autonomic neuropathy. All patients underwent an extensive evaluation to rule out other causes for their autonomic dysfunction. Patients presented with multiple different autonomic disorders, including postural tachycardia syndrome, gastrointestinal dysmotility, and complex regional pain syndrome. Despite most having low-titer IgM antiphospholipid antibodies, 13 of the 22 patients (59%) suffered one or more thrombotic event, but pregnancy morbidity was minimal. Prothrombin-associated antibodies were helpful in confirming the diagnosis of antiphospholipid syndrome. We conclude that autonomic neuropathy may occur in association with antiphospholipid antibodies and may be the initial manifestation of the syndrome. Increased awareness of this association is important, because it is associated with a significant thrombotic risk and a high degree of disability. In addition, anecdotal experience has suggested that antithrombotic therapy and intravenous immunoglobulin therapy may result in significant clinical improvement in these patients.

Arterial stenosis in antiphospholipid syndrome: Update on the unrevealed mechanisms of an endothelial disease

First described in 1983, antiphospholipid syndrome (APS) is an autoimmune condition characterized by the occurrence of recurrent arterial and/or venous thrombosis, and/or pregnancy morbidity, in the setting of persistent presence of antiphospholipid antibodies (aPL). While thrombosis is the most well-known pathogenic mechanism in this disorder, the relevance of some other mechanisms such as arterial stenosis is being increasingly recognized. Arterial stenosis has been first described in the renal arteries in patients with APS, however intracranial and coeliac arteries can also be involved with various and treatable clinical manifestations. The underlying pathophysiology of this stenotic arterial vasculopathy is not fully understood but some recent studies revealed new insights into the molecular mechanism behind this endothelial cell activation in APS. In this review, we discuss these newly discovered mechanisms and highlight the diagnostic and therapeutic modalities of the APS related arterial stenosis.

A peptide that mimics the Vth region of β2glycoprotein I reverses antiphospholipid-mediated thrombosis in mice

Antiphospholipid (aPL) antibodies bind to 2glycoprotein I (2GPI) and cause endothelial cell (EC) activation and thrombosis in mice. 2GPI binds to EC through its Vth domain and induces their activation. TIFI is a 20 amino acid synthetic peptide that shares similarity with the Vth domain of 2GPI. Our objectives were to examine the ability of TIFI to affect aPL-mediated thrombosis in mice and the interactions of TIFI, 2GPI with phospholipid surfaces and target cells. CD1 mice were injected with IgG from a patient with antiphospholipid syndrome (IgG-APS) or with control IgGNHS and with either TIFI or with control peptide (VITT). Size of induced thrombi was determined. Inhibition and competition studies were done using aPL antibodies, cardiolipin (CL) liposomes in the presence of varying amounts of TIFI and 2GPI. Binding of fluorescinated 2GPI to human ECs and to murine macrophages in the presence or absence of TIFI, was also examined. TIFI significantly decreased thrombus size in mice injected with IgG-APS. TIFI reverted the 2GPI-dependent binding of aPL antibodies to CL liposomes in a dose-dependent fashion. This effect was abrogated by addition of 2GPI, suggesting that TIFI displaces the binding of 2GPI to phospholipids. TIFI inhibited the binding of fluorescinated 2GPI to human EC and to murine macrophages. The data indicate that TIFI abrogates thrombogenic properties of aPL in mice by competing with 2GPI and preventing its binding to target cells. This may be important in designing new modalities for the treatment of thrombosis in APS.

Impaired endothelial function and increased carotid intima-media thickness in association with elevated von Willebrand antigen level in primary antiphospholipid syndrome

Primary antiphospholipid syndrome (APS) is characterized by venous or arterial thrombotic events and/or recurrent abortions, fetal death, preeclasmpsia, eclampsia in the presence of anticardiolipin antibodies or lupus anticoagulant, in the absence of accompanying diseases. Antiphospholipid antibodies can activate endothelial cells, and were recently implicated in atherosclerosis. To assess potential endothelial impairment and early signs of atherosclerosis, flow-mediated (endothelium-dependent) and nitrate-mediated (endothelium independent) vasodilation, as well as von Willebrand factor antigen level and carotid artery intima-media thickness (IMT) were measured in patients with primary antiphospholipid syndrome and in healthy controls. Flow-mediated vasodilation in patients with primary APS was significantly lower than that of controls (3.43 ± 2.86% versus 7.96 ± 3.57%; P < 0.0001). We also found significantly higher von Willebrand antigen levels in patients with primary APS than in the control group (157.91 ± 52.45% versus 125.87 ± 32.8%; P = 0.012). Moreover, carotid artery IMT was significantly larger in the primary APS group compared to controls (0.714 ± 0.2 mm versus 0.58 ± 0.085 mm; P = 0.0037). Our results reflect ongoing endothelial damage and accelerated atherosclerosis in patients with primary APS, and suggest that vasoprotective therapy may be beneficial in the treatment of these patients. Lupus (2007) 16, 497—503.

[Pulmonary arterial hypertension: a flavor of autoimmunity]

It is admitted that autoimmunity results from a combination of risks such as genetic background, environmental triggers, and stochastic events. Pulmonary arterial hypertension (PAH) shares with the so-called prototypic autoimmune diseases, genetic risk factors, female predominance and sex hormone influence, association with other chronic inflammatory and autoimmune diseases, defects in regulatory T cells function, and presence of autoantibodies. Case reports have been published indicating the beneficial effect of some immunosuppressive and anti-inflammatory therapies in PAH, supporting the potential role of immune mechanisms in the pathophysiology of the disease. In this review, we discuss the current knowledge on autoimmune mechanisms operating in PAH, especially mounting a local autoimmune response inside the pulmonary tissue, namely pulmonary lymphoid neogenesis. A better understanding of the role of autoimmunity in pulmonary vascular remodelling may help develop targeted immunomodulatory strategies in PAH.

[Novel immunopathological approaches to pulmonary arterial hypertension]

Inflammation is important for the initiation and the maintenance of vascular remodeling in the most commun animal models of pulmonary hypertension (PH), and its therapeutical targeting blocks PH development in these models. In human, pulmonary vascular lesions of PH are also the source of an intense chemokine production, linked to inflammatory cell recruitment. However, arteritis is uncommon in PH patients. Of note, current PH treatments have immunomodulatory properties. In addition, some studies have shown a correlation between levels of circulating inflammatory mediators and patients' survival. The study of autoimmunity in the pathophysiology of pulmonary arterial hypertension is becoming an area of intense investigation. New immunopathological approaches to PH should allow the development of innovative treatments for this very severe condition.

Increased risk of stroke in patients with bullous pemphigoid: a population-based follow-up study

BACKGROUND AND PURPOSE

Although previous research reveals that cardiovascular events and thromboembolic diseases are important causes of death in patients with bullous pemphigoid (BP), the risk of stroke after the diagnosis of BP relative to the general population remains unknown. Using a randomly selected nationwide population-based sample, this study investigates the risk of stroke in patients with BP compared with unaffected individuals of a similar age.

METHODS

This study analyzes data from Taiwan's National Health Insurance Research Database. This sample included 390 patients with BP and 1950 matched subjects as a comparison group. Stratified Cox proportional hazard regressions were used to calculate the 3-year stroke risk for these 2 groups after adjusting for patient's age, sex, and comorbid medical disorders at baseline.

RESULTS

Of the 2340 patients in the sample, 312 patients (13.3%) had strokes during the 3-year follow-up period, 89 (22.8% of the patients with BP) in the study group and 223 (11.4% of patients without BP) in the comparison group (P<0.001). The hazard ratio for stroke for patients with BP was 2.37 (95% CI, 1.78 to 3.15; P<0.001) times as high that for patients without BP within the 3-year follow-up period after adjusting for hypertension, diabetes, hyperlipidemia, heart failure, atrial fibrillation, and coronary heart disease.

CONCLUSIONS

Patients with BP have an increased risk of stroke and particularly ischemic stroke.

Annexin A2: biology and relevance to the antiphospholipid syndrome

Antiphospholipid antibodies (aPL), the majority of which are directed against beta(2)-glycoprotein I (beta(2)GPI), are associated with an increased incidence of venous and arterial thrombosis. The pathogenesis of antiphospholipid/anti-beta(2)GPI-associated thrombosis has not been defined, and is likely multifactorial. However, accumulating evidence suggests an important role for endothelial cell activation with the acquisition of a procoagulant phenotype by the activated endothelial cell. Previous work demonstrated that endothelial activation by antiphospholipid/anti-beta(2)GPI antibodies is beta(2)GPI-dependent. We extended these observations by defining annexin A2 as an endothelial beta(2)GPI binding site. We also observed that annexin A2 plays a critical role in endothelial cell activation induced by anti-beta(2)GPI antibodies, and others have described direct endothelial activation by anti-annexin A2 antibodies in patients with aPL . Similar findings have been reported using human monocytes, which also express annexin A2. Because annexin A2 is not a transmembrane protein, how binding of beta(2)GPI/anti-beta(2)GPI antibodies, or anti-annexin A2 antibodies, to endothelial annexin A2 causes cellular activation is unknown. Recent studies, however, suggest an important role for the Toll-like receptor family, particularly TLR4. In this article, we review the role of these interactions in the activation of endothelial cells by aPL . The influence of these antibodies on the ability of annexin A2 to enhance t-PA-mediated plasminogen activation is also discussed.

[Acute Q fever, antiphopholipid antibodies and renal artery thrombosis: case report and literature review]

INTRODUCTION

Antiphospholipid antibodies (aPL) can be associated with numerous infectious and particularly Q fever. Data on the pathogenicity of aPL in the course of acute Q fever are scarce.

CASE REPORT

We report the case an acute Coxiella burnetii infection associated with clinical and biological manifestations of the aPL syndrome, including a renal infarction. Along with antibiotic treatment, anticoagulation and intravenous immunoglobulins, the clinical outcome was favourable. Antiphospholipid antibodies and Q fever antibody titers had a closely related evolution.

CONCLUSION

Arterial thrombosis associated with Q fever and aPL is exceptional. The nosology and potential mechanisms are discussed.

[Acquired idiopathic thrombotic thrombocytopenic purpura: arguments for an autoimmune disease]

Thrombotic thrombocytopenic purpura (TTP) is a severe form of thrombotic microangiopathy (TMA) characterized by systemic platelet clumping, hemolytic anemia, and multiorgan failure. TTP results from a defect in ADAMTS13, a plasma enzyme specifically involved in the cleavage of highly hemostatic unusually large (UL) von Willebrand factor (vWF) multimers into smaller and less adhesive vWF forms. Failure to degrade these UL-vWF multimers leads to excessive platelet aggregation and capillary occlusion. ADAMTS13 deficiency is related to mutations of the encoding gene in hereditary TTP, whereas in acquired forms it results from autoantibodies that may alter the protein function. This latter finding strongly suggests that acquired idiopathic TTP corresponds to an autoimmune disease. Acquired idiopathic TTP appears to be associated with clinical features suggestive of autoimmunity in one third of cases. In two thirds, autoantibodies such as antinuclear antibodies may be observed. This review, based on an analysis of the literature and on French experience with TMA, focuses on the different autoimmune manifestations that may be observed in TTP, as well as the putative pathophysiological link between autoimmune manifestations and TTP.

The antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an autoimmune thrombophilic condition that is marked by the presence of antibodies that recognize phospholipid-binding proteins. The clinical manifestations of APS include vascular thrombosis and pregnancy complications, especially recurrent spontaneous miscarriages. This article provides an update on diagnostic and therapeutic approaches to this disorder.

Annexin A5 in cardiovascular disease and systemic lupus erythematosus

Atherosclerosis, a major cause of disease and death from cardiovascular disease (CVD), is an inflammatory disease characterized by T cell and monocyte/macrophage infiltration in the intima of large arteries. During recent years and with improved treatment of acute disease manifestations, it has become clear that the risk of CVD is very high in systemic lupus erythematosus (SLE), often considered a prototypic autoimmune disease. A combination of traditional and non-traditional risk factors, including dyslipidemia, inflammation, antiphospholipid antibodies (aPL) and lipid oxidation are related to CVD in SLE. aPL are highly thrombogenic, and possible mechanisms include direct effects of aPL on endothelial and other cells, and interference with coagulation reactions. More than a thousand proteins of the annexin-superfamily are expressed in eukaryotes. Annexins are ubiquitous, highly conserved, predominantly intracellular proteins, widely distributed in tissues. Annexin A5 (ANXA5) is an important member of the annexin family due to its antithrombotic properties. These are believed to be caused by it forming a two-dimensional protective shield, covering exposed potentially thrombogenic cell surfaces. Recently, ANXA5 has been implicated in SLE since aPL interfere with ANXA5 binding to placental trophoblasts, causing microthrombosis and miscarriage, a rather common complication in SLE. We recently demonstrated that ANXA5 may play a role in CVD and is abundant in late-stage atherosclerotic lesions. Sera from SLE-patients with a history of CVD inhibited ANXA5 binding to endothelium, caused by IgG antibodies, to a significant degree aPL. This review will focus on potential involvement of ANXA5 in pathogenesis of CVD, particularly caused by underlying atherosclerosis and atherothrombosis.

Endothelial function is impaired in patients with primary antiphospholipid syndrome

INTRODUCTION

The aim of this study was to evaluate endothelial function in patients with primary antiphospholipid syndrome (PAPS).

PATIENTS AND METHODS

Flow mediated (FMD) and glyceryl trinitrate (GTN) induced dilation of the right brachial artery were studied in 25 patients with PAPS and 25 controls matched by age, sex and conventional risk factors for atherosclerosis. Fibrinogen, D-dimer, adhesion molecules, tissue plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) antigens and activities were measured.

RESULTS

Mean (SD) FMD was significantly lower in PAPS than in controls (8+/-5% vs. 15+/-6%, P<0.001); GTN-induced dilation did not differ between the groups. There was a correlation between the baseline diameter of the brachial artery and duration of the disease (-0.56, P<0.05) and between GTN induced dilation and duration of the disease (0.51, P<0.05). Concentrations of vascular cell adhesion molecule-1 (P<0.001), intracellular adhesion molecule-1 (P<0.001) and fibrinogen (P<0.05) were higher in patients than in controls but no differences were observed for D-dimer, t-PA and PAI-1 antigens and activities. There was correlation between concentration of vascular cell adhesion molecule-1 and FMD (-0.35, P<0.05) and between intracellular adhesion molecule-1 and FMD (-0.41, P<0.05).

CONCLUSIONS

This study shows that endothelial function is impaired in patients with primary APS, possibly contributing to accelerated atherosclerosis and thromboembolic complications in these patients.

The role of endothelial cell apoptosis in inflammatory and immune diseases

The integrity of the endothelial lining of the vasculature is essential for vascular homeostasis and normal organ function. Endothelial injury or dysfunction has been implicated in the pathogenesis of diverse vascular diseases. Studies in vitro have demonstrated that a wide variety of stimuli can induce programmed cell death (apoptosis) of endothelial cells, and have suggested that apoptosis could be an important mechanism of vascular injury, resulting in vascular leak, inflammation, and coagulation. In this review, we focus on the potential role of endothelial apoptosis in the initiation and progression of inflammatory and immune disorders, reviewing human diseases and in vivo models in which endothelial cell apoptosis has been demonstrated. Although endothelial cell apoptosis is observed in many inflammatory and immune disorders, we find that there is, as yet, only limited experimental evidence demonstrating that it is critical to the pathogenesis of disease.

Annexin A2 mediates endothelial cell activation by antiphospholipid/anti-β2 glycoprotein I antibodies

Patients with antiphospholipid antibodies (APLAs) are at increased risk for arterial and venous thrombosis. Many APLAs associated with these events react with β2 glycoprotein I (β2GPI), and endothelial cell reactive antibodies that activate endothelial cells in a β2GPI-dependent manner occur commonly in these patients. We previously reported that β2GPI binds with high affinity to annexin A2 on the endothelial surface, though the relevance of this interaction to APLA/anti-β2GPI antibody–induced endothelial activation has not been determined. In this report, we confirm that anti-β2GPI antibodies activate endothelial cells in the presence of β2GPI, and demonstrate that anti–annexin A2 antibodies directly cause endothelial cell activation of a similar magnitude and with a similar time course. Moreover, bivalent anti–annexin A2 F(ab′)2 fragments also caused endothelial cell activation, whereas monomeric Fab fragments not only did not cause activation, but blocked activation induced by anti–annexin A2 antibodies and F(ab′)2 fragments, as well as that caused by anti-β2GPI antibodies in the presence of β2GPI. These observations suggest a novel pathway for endothelial activation induced by APLA/anti-β2GPI antibodies that is initiated by cross-linking or clustering of annexin A2 on the endothelial surface.

Endothelial dysfunction and activation as an expression of disease: role of prostacyclin analogs

The endothelium is now considered a real endocrine-paracrine organ, important not only as a structural barrier between the circulation and surrounding tissue, but also because it plays an essential role for local hemodynamics, releasing substances that modulate the vascular calibre and blood cell activation. Here, after a brief but detailed analysis of the importance of the endothelium in vascular homeostasis, in the control of coagulation and in the relations with the different blood cells, we will explain the concept of endothelial dysfunction (altered NO release) and activation (amplified adhesion molecule expression) in inflammatory, connective tissue and post-trasplantation diseases. Furthermore, this review will focus on the activity of prostacyclin and synthetic analogs, especially their ability to interact with the vasodilatation system and their role in modulating cell interaction by surface adhesion molecule expression, cytokines and growth factors release as well as gene transcription factors. Finally, we will consider the therapeutic role of prostacyclin analogs in the prevention and treatment of connective tissue diseases.

Beta-2 glycoprotein I and its role in antiphospholipid syndrome—lessons from knockout mice

The antiphospholipid syndrome is characterized by the presence in serum of autoantibodies against beta2GPI. Although the role of beta2GPI in the pathogenesis of antiphospholipid antibody syndrome (APS) is well recognized, its exact physiological functions still remain undisclosed. Several interactions of beta2GPI with components of the coagulation cascade have been proposed, resulting in both procoagulant and anticoagulant effects. Additionally, beta2GPI has been implicated in the mechanism of recurrent fetal loss entailed in APS. Recently, using a homologous recombination approach, reproduction of mice homozygous for deletion of the beta2GPI gene has been feasible. beta2GPI knockout mice offer a valuable tool for revealing the physiological role of the protein. These mice show decreased in vitro ability for thrombin generation. Furthermore, although mice lacking beta2GPI are fertile, the success of early pregnancy is moderately compromised and functional beta2GPI is believed necessary for optimal implantation and placental morphogenesis.

Antiphospholipid antibodies: update on detection, pathophysiology, and treatment

PURPOSE OF REVIEW

The antiphospholipid syndrome is a noninflammatory disease characterized by the presence of antiphospholipid antibodies in the plasma of patients with venous or arterial thrombosis or obstetric complications. Understanding of the pathology of the syndrome is only rudimentary and no physician can pretend that treatment is adequate. It is not possible to identify patients with the syndrome for certain. This paper reviews the substantial and promising headway made in the past year.

RECENT FINDINGS

It has become clear that lupus anticoagulant is the assay of choice to detect the syndrome and that antibodies directed towards beta2Glycoprotein 1 are the clinical relevant autoantibodies. These antibodies are able to activate a number of cells involved in the regulation of hemostasis.

SUMMARY

The latest developments will make it soon possible to define patient with the syndrome unambiguously. This is absolutely necessary to understand why the presence of antiphospholipid antibodies cause an increased thrombotic risk.

The role of endothelial cell reactive antibodies in peripheral vascular disease

The mechanism by which a small but significant proportion of patients with peripheral vascular disease (PVD) rapidly progress to critical ischaemia is unclear. Both experimental and clinical data suggest a role for autoantibodies in the pathogenesis of atherosclerotic disease, particularly in the accelerated atherosclerosis seen in patients with systemic lupus erythematosus and the anti-phospholipid syndrome. This review examines the evidence for a role for endothelial cell reactive autoantibodies in PVD and the potential mechanisms by which these autoantibodies could contribute to the acceleration of atherosclerosis in a proportion of patients. The identification of such markers could lead to the identification of patients with PVD who are at risk of developing critical ischaemia and may warrant early and aggressive intervention.

Beta 2 glycoprotein I-function in health and disease

Beta-2 glycoprotein I (beta2GPI) is the principal target of autoantibodies in the antiphospholipid syndrome (APS). It is abundant in human plasma and shares high homology between different mammalian species. Although the exact physiological function of beta2GPI has not been fully elucidated, several interactions have been described with other proteins and with negatively charged surfaces, such as anionic phospholipids, dextran and heparin. beta2GPI is involved in the coagulation pathway, exerting both procoagulant and anticoagulant activities. Plasma from beta2GPI-deficient mice exhibits impaired thrombin generation in vitro. Recently, it has been demonstrated that beta2GPI binds factor (F) XI in vitro at concentrations lower than those of the protein in human plasma, and this binding inhibits FXI activation to FXIa by thrombin and FXIIa. Proteolytic cleavage of the fifth domain of beta2GPI abolishes its inhibition of FXI activation and results in reduced ability of the cleaved beta2GPI to bind phospholipids. It retains its ability to bind FXI. In vivo activation of FXI by thrombin is thought to be an important mechanism by which coagulation is accelerated via components of the contact activation pathway. Thus beta2GPI may attenuate the contact activation pathway by inhibiting activation of FXI by thrombin. Moreover, because beta2GPI is the dominant autoantigen in patients with APS, dysregulation of this pathway by autoantibodies may be an important mechanism for thrombosis in patients with APS.

Antibodies to tissue-type plasminogen activator (tPA) in patients with antiphospholipid syndrome: evidence of interaction between the antibodies and the catalytic domain of tPA in 2 patients

The causes of thrombosis and pregnancy loss in antiphospholipid syndrome (APS) are still unknown, although several hypotheses have been proposed and hypofibrinolysis has been implicated. Anti-tissue-type plasminogen activator (tPA) antibodies may induce fibrinolytic defects and preliminary data indicate an association with thrombosis in APS. We measured plasma anti-tPA antibody levels in 91 consecutive patients with APS, 91 healthy controls, 40 patients with antiphospholipid antibodies without APS symptoms, and 23 patients with systemic lupus erythematosus (SLE) without antiphospholipid antibodies and APS symptoms. Patients with APS had anti-tPA antibody levels higher than controls (P = .0001), patients with SLE (P = .0001), and asymptomatic antiphospholipid patients (P = .05). A subgroup of 53 patients had plasma levels of tPA antigen higher (P = .0001) and tPA activity lower (P = .05) than controls, with an inverse correlation (r = -0.454; P = .003) between anti-tPA antibody levels and tPA activity and no correlation with tPA antigen. The 2 patients with the highest antibody levels had tPA activity below the normal range. Their antibodies were, respectively, IgG1 and IgG3; both recognized human tPA, recombinant tPA, and the catalytic domain of tPA, but not beta 2-glycoprotein I, prothrombin, or plasminogen. Our data indicate that anti-tPA antibodies specifically interacting with the catalytic domain of tPA can be found in patients with APS, representing a possible cause of hypofibrinolysis.

Human monoclonal antiphospholipid antibodies disrupt the annexin A5 anticoagulant crystal shield on phospholipid bilayers: evidence from atomic force microscopy and functional assay

The antiphospholipid (aPL) syndrome is an autoimmune condition that is marked by recurrent pregnancy losses and/or systemic vascular thrombosis in patients who have antibodies against phospholipid/co-factor complexes. The mechanism(s) for pregnancy losses and thrombosis in this condition is (are) not known. Annexin A5 is a potent anticoagulant protein, expressed by placental trophoblasts and endothelial cells, that crystallizes over anionic phospholipids, shielding them from availability for coagulation reactions. We previously presented data supporting the hypothesis that aPL antibody-mediated disruption of the anticoagulant annexin A5 shield could be a thrombogenic mechanism in the aPL syndrome. However, this has remained a subject of controversy. We therefore used atomic force microscopy, a method previously used to study the crystallization of annexin A5, to image the effects of monoclonal human aPL antibodies on the crystal structure of the protein over phospholipid bilayers. In the presence of the aPL monoclonal antibodies (mAbs) and beta(2)-GPI, the major aPL co-factor, structures presumed to be aPL mAb-antigen complexes were associated with varying degrees of disruption to the annexin A5 crystallization pattern over the bilayer. In addition, measurements of prothrombinase activity on the phospholipid bilayers showed that the aPL mAbs reduced the anti-coagulant effect of annexin A5 and promoted thrombin generation. These data provide morphological evidence that support the hypothesis that aPL antibodies can disrupt annexin A5 binding to phospholipid membranes and permit increased generation of thrombin. The aPL antibody-mediated disruption of the annexin A5 anticoagulant shield may be an important prothrombotic mechanism in the aPL syndrome.