Characterization of the endothelial surface proteins recognized by anti-endothelial antibodies in primary and secondary autoimmune vasculitis

Endothelial cells and endothelial progenitor cells in the pathogenesis of systemic sclerosis

Systemic sclerosis (SSc) is a connective tissue disease characterized by excessive fibrosis, microvasculopathy, and autoimmunity. Endothelial cell (EC) injury and subsequent endothelial cell dysfunction is believed to be an initial event that eventually leads to a vicious pathogenic cycle. This process is further enhanced by defective angiogenesis and vasculogenesis, as the vascular repair machinery does not work properly. Endothelial progenitor cells (EPCs) are functionally and quantitatively insufficient to recover the endothelium in SSc patients. The dysfunctional ECs and EPCs not only trigger the formation of typical vascular lesions, such as progressive intimal fibrosis in small arteries and the loss of capillaries, but also promote a series of inflammatory and profibrotic processes, such as endothelial-mesenchymal transition and recruitment and accumulation of monocytic EPCs with profibrotic properties. These processes together contribute to the accumulation of extracellular matrix in the affected tissue. This review features current insights into the roles of ECs and EPCs in the pathogenesis of SSc.

Asbestos-associated mesothelial cell autoantibodies promote collagen deposition in vitro

Fibrosis, characterized by excessive collagen protein deposition, is a progressive disease that can fatally inhibit organ function. Prolonged exposure to pathogens or environmental toxicants such as asbestos can lead to chronic inflammatory responses associated with fibrosis. Significant exposure to amphibole asbestos has been reported in and around Libby, Montana due to local mining of asbestos-contaminated vermiculite. These exposures have been implicated in a unique disease etiology characterized predominantly by pleural disorders, including fibrosis. We recently reported the discovery of mesothelial cell autoantibodies (MCAAs) in the sera of Libby residents and demonstrated a positive and significant correlation with pleural disease; however, a mechanistic link was not determined. Here we demonstrate that MCAAs induce pleural mesothelial cells to produce a collagen matrix but do not affect production of the pro-inflammatory cytokine tumor growth factor-β. While autoantibodies commonly induce a pro-fibrotic state by inducing epithelial-mesenchymal transition (EMT) of target cells, we found no evidence supporting EMT in cells exposed to MCAA positive human sera. Although implicated in other models of pulmonary fibrosis, activity of the protein SPARC (secreted protein, acidic and rich in cysteine) did not affect MCAA-induced collagen deposition. However, matrix formation was dependent on matrix metalloproteinase (MMP) activity, and we noted increased expression of MMP-8 and -9 in supernatants of mesothelial cells incubated with MCAA positive sera compared to control. These data suggest a mechanism by which MCAA binding leads to increased collagen deposition through altering MMP expression and provides an important mechanistic link between MCAAs and asbestos-related, autoimmune-induced pleural fibrosis.

Alteration of fibroblast phenotype by asbestos-induced autoantibodies

Pulmonary fibrosis is a relentlessly progressive disease for which the etiology can be idiopathic or associated with environmental or occupational exposures. There is not a clear explanation for the chronic and progressive nature of the disease, leaving treatment and prevention options limited. However, there is increasing evidence of an autoimmune component, since fibrotic diseases are often accompanied by production of autoantibodies. Because exposure to silicates such as silica and asbestos can lead to both autoantibodies and pulmonary/pleural fibrosis, these exposures provide an excellent tool for examining the relationship between these outcomes. This study explored the possibility that autoantibodies induced by asbestos exposure in mice would affect fibroblast phenotype. L929 fibroblasts and primary lung fibroblasts were treated with serum IgG from asbestos- or saline-treated mice, and tested for binding using cell-based ELISA, and for phenotypic changes using immunofluorescence, laser scanning cytometry and Sirius Red collagen assay. Autoantibodies in the serum of C57Bl/6 mice exposed to asbestos (but not sera from untreated mice) bound to mouse fibroblasts. The autoantibodies induced differentiation to a myofibroblast phenotype, as demonstrated by increased expression of smooth muscle α-actin (SMA), which was lost when the serum was cleared of IgG. Cells treated with purified IgG of exposed mice produced excess collagen. Using ELISA, we tested serum antibody binding to DNA topoisomerase (Topo) I, vimentin, TGFβ-R, and PDGF-Rα. Antibodies to DNA Topo I and to PDGF-Rα were detected, both of which have been shown by others to be able to affect fibroblast phenotype. The anti-fibroblast antibodies (AFA) also induced STAT-1 activation, implicating the PDGF-R pathway as part of the response to AFA binding. These data support the hypothesis that asbestos induces AFA that modify fibroblast phenotype, and suggest a mechanism whereby autoantibodies may mediate some of the fibrotic manifestations of asbestos exposure.

Peroxiredoxin 2 is a novel autoantigen for anti-endothelial cell antibodies in systemic vasculitis

Anti-endothelial cell antibodies (AECA) have been frequently detected in systemic vasculitis, which affects blood vessels of various sizes. To understand the pathogenic roles of AECA in systemic vasculitis, we attempted to identify target antigens for AECA comprehensively by a proteomic approach. Proteins extracted from human umbilical vein endothelial cells (HUVEC) were separated by two-dimensional electrophoresis, and Western blotting was subsequently conducted using sera from patients with systemic vasculitis. As a result, 53 autoantigenic protein spots for AECA were detected, nine of which were identified by mass spectrometry. One of the identified proteins was peroxiredoxin 2 (Prx2), an anti-oxidant enzyme. Frequency of anti-Prx2 autoantibodies, measured by enzyme-linked immunosorbent assay (ELISA), was significantly higher in systemic vasculitis (60%) compared to those in collagen diseases without clinical vasculitis (7%, P < 0·01) and healthy individuals (0%, P < 0·01). Further, the titres changed in parallel with the disease activity during time-courses. The presence of anti-Prx2 autoantibodies correlated significantly with elevation of serum d-dimers and thrombin-antithrombin complex (P < 0·05). Immunocytochemical analysis revealed that live endothelial cells expressed Prx2 on their surface. Interestingly, stimulation of HUVEC with rabbit anti-Prx2 antibodies increased secretion of interleukin (IL)-6, IL-1β, IL-1ra, growth regulated oncogene (GRO)-α, granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF), IL-8 and monocyte chemoattractant protein (MCP)-1 more than twofold compared to that of with rabbit immunoglobulin (Ig)G. Taken together, our data suggest that anti-Prx2 autoantibodies would be a useful marker for systemic vasculitis and would be involved in the inflammatory processes of systemic vasculitis.

Antiendothelial cell antibodies induce apoptosis of bone marrow endothelial progenitors in systemic sclerosis

OBJECTIVE

Patients with systemic sclerosis (SSc) have significantly fewer and functionally impaired endothelial progenitor cells (EPC) in peripheral blood and bone marrow; further, endothelial apoptosis seems to play a primary role in the pathogenesis of vascular damage. We investigated whether the failure of bone marrow EPC is related to their apoptotic phenotype and analyzed the possible mechanisms inducing apoptosis.

METHODS

The presence of apoptotic cells was investigated in bone marrow aspirates taken from patients with SSc; microvessel density (MVD) and the immunohistochemical expression of vascular endothelial growth factor (VEGF) were also measured in bone marrow biopsies. A correlation between EPC apoptosis and the presence of antiendothelial cell antibodies (AECA) was also investigated.

RESULTS

We confirmed the presence of bone marrow EPC dysfunction in SSc, while hematopoiesis was not impaired. Bone marrow studies showed a high percentage of apoptotic progenitors, no signs of fibrosis or an altered MVD, and an increased VEGF index. The patients' bone marrow plasma showed significant titers of AECA, and their presence correlated with that of apoptotic progenitors. These findings were further confirmed by an in vitro assay in which the apoptosis of normal progenitors was induced by the addition of AECA+ purified IgG.

CONCLUSION

Our results showed that apoptosis in patients with SSc involves the source compartment of endothelial progenitors and correlates with AECA activity. These findings support the hypothesis that AECA may play a pathogenetic role by affecting the bone marrow EPC machinery that should repair the peripheral vascular lesions.

Pathogenesis of ANCA-associated vasculitis

Antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) comprises a group of systemic inflammatory vasculitides associated with circulating autoantibodies directed against the neutrophil granule components proteinase 3 and myeloperoxidase. ANCA interact with their target antigens on cytokine primed neutrophils, causing neutrophil activation via several signaling pathways that culminates in endothelial interaction, degranulation, cytokine production, and endothelial and tissue damage. The presence of autoantibodies implies the assistance of autoreactive T-helper cells and B cells, and a failure of regulatory mechanisms. This article reviews the current evidence for the pathogenic mechanisms culminating in autoantibody production, the effects of ANCA-neutrophil and neutrophil-endothelial interactions, and the mechanisms of tissue damage.

Enhanced reactivity to malondialdehyde-modified proteins by systemic lupus erythematosus autoantibodies

OBJECTIVE

Evaluation of the reactivity of autoantibodies of systemic lupus erythematosus (SLE) patients directed against malondialdehyde (MDA)-modified catalase, superoxide dismutase (SOD), and different Hep2 protein fractions (hydrophobic, hydrophilic, and nuclear).

METHOD

Thiol groups and MDA-protein adducts were first assessed among 65 SLE patients and 60 healthy controls. Then, the reactivities of SLE immunoglobulin (Ig)G autoantibodies towards MDA-modified and unmodified proteins were compared using a standard enzyme-linked immunosorbent assay (ELISA).

RESULTS

An increase in the levels of MDA-modified proteins and a decrease in the concentration of thiol groups among SLE patients (p < 0.05) were observed. IgG circulating autoantibodies in the sera of SLE patients exhibited a significant enhanced reactivity (p < 0.05) against catalase and SOD-modified proteins. The same data were observed in the different protein fractions extracted from cultured cells (p < 0.05).

CONCLUSION

These data reinforce the role of oxidative stress and especially lipid peroxidation products in the progression of SLE disease.

Evidence for a novel human-specific xeno-auto-antibody response against vascular endothelium

Humans are genetically unable to synthesize the common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc). However, Neu5Gc can be metabolically incorporated and covalently expressed on cultured human cell surfaces. Meanwhile, humans express varying and sometimes high titers of polyclonal anti-Neu5Gc antibodies. Here, a survey of human tissues by immunohistochemistry with both a monospecific chicken anti-Neu5Gc antibody and with affinity-purified human anti-Neu5Gc antibodies demonstrates endothelial expression of Neu5Gc, likely originating from Neu5Gc-rich foods like red meats. We hypothesized that the combination of Neu5Gc incorporation and anti-Neu5Gc antibodies can induce endothelial activation. Indeed, the incubation of high-titer human sera with Neu5Gc-fed endothelial cells led to Neu5Gc-dependent antibody binding, complement deposition, endothelial activation, selectin expression, increased cytokine secretion, and monocyte binding. The proinflammatory cytokine tumor necrosis factor-alpha also selectively enhanced human anti-Neu5Gc antibody reactivity. Anti-Neu5Gc antibodies affinity-purified from human serum also directed Neu5Gc-dependent complement deposition onto cultured endothelial cells. These data indicate a novel human-specific mechanism in which Neu5Gc-rich foods deliver immunogenic Neu5Gc to the endothelium, giving anti-Neu5Gc antibody- and complement-dependent activation, and potentially contributing to human vascular pathologies. In the case of atherosclerosis, Neu5Gc is present both in endothelium overlying plaques and in subendothelial regions, providing multiple pathways for accelerating inflammation in this disease.

Antiendothelial cells autoantibodies in vasculitis-associated systemic diseases

Antiendothelial cell antibodies (AECA) have been detected in healthy individuals, as well as in autoimmune and systemic inflammatory diseases, including systemic vasculitides. AECA have been reported in large vessel vasculitides such as giant cell arteritis and Takayasu arteritis; medium-sized vessel vasculitides, such as polyarteritis nodosa related to hepatitis B virus infection and Kawasaki disease; and small-sized vessel vasculitides, such as Wegener's granulomatosis, microscopic polyangiitis, and Henoch-Schonlein purpura. In Takayasu arteritis and antineutrophil cytoplasm antibody-positive vasculitides, AECA have been reported to correlate with disease activity. A cell-based enzyme-linked immunosorbent assay (ELISA) using cultured human umbilical vein endothelial cells (HUVEC) represent one of the reference techniques for AECA detection, although flow cytometry and immunobloting have also been proposed. AECA might contribute to the pathogenesis of systemic vasculitides and vasculitis-associated diseases through (1) activation of endothelial cells (EC), (2) direct cytotoxic effect due to complement-dependent cytotoxicity or indirect cytotoxic effect secondary to antibody-dependent cytotoxicity, (3) induction of coagulation, (4) induction of apoptosis through the binding of phospholipids or heat-shock protein 60, and (5) induction of EC activation. None of the identified target antigens of AECA is specific for EC, and EC-specific target antigens of AECA remain to be identified in systemic vasculitides.

Using proteomics to identify targets of antiendothelial cell antibodies

Antiendothelial cell antibodies represent a heterogeneous group of antibodies directed against a variety of antigen determinants of endothelial cells. Antibodies reacting with endothelial structures have been detected in sera from patients with autoimmune vasculitis, both primary and secondary to systemic connective tissue diseases. It may interfere with several functions and, therefore, may be a pathophysiological relevance. The analysis of the antigens recognized by antiendothelial cell antibodies showed that the antibodies are directed against a heterogeneous family of both constitutive and nonconstitutive surface endothelial proteins. Proteomics is a field of science that evaluates a large number of proteins expressed from a given cell line or organism. The technology of proteomics has been used as a method for discovering the target protein specific to a particular disease by searching for the expression or modification of the protein. Recently, progress has been made in defining the target antigens of these antibodies and proteomic technologies is one of them. This review will focus on the proteomic technologies in searching autoantigens/autoantibodies associated with disease of the endothelium.

Anti–Endothelial Cell Autoantibodies Selectively Activate SAPK/JNK Signalling in Wegener’s Granulomatosis

The pathogenic role of anti-endothelial cell antibodies (AECA) in vascular injury is debated. It was previously shown that many patients with Wegener's granulomatosis (WG) have AECA that react with human kidney microvascular endothelial cells (EC). In addition, during active disease, renal endothelium strongly expresses the inflammatory molecules vascular adhesion protein-1 (VAP-1) and MHC class I-related antigen A (MICA). This study sought to determine whether AECA mediates this upregulation of VAP-1 and MICA and to define better the signaling pathways that are activated by these autoantibodies upon binding to EC in the kidney. Stimulation of human kidney microvascular EC with AECA IgG upregulated surface expression of MICA and VAP-1, elicited a rapid Ca2+ flux, induced high levels of the chemokines monocyte chemoattractant protein-1 and granulocyte chemotactic protein-2, induced specific phosphorylation of stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK) and the transcription factors c-Jun and activating transcription factor-2, and activated NF-kappaB. Specific inhibitors of SAPK/JNK significantly reduced AECA-induced chemokine production and phosphorylation of c-Jun and activating transcription factor-2 and abrogated protein expression of MICA but not VAP-1. In kidney sections from patients with WG, infiltrating cells that expressed the ligand for MICA (NKG2D+) were identified, as were CD8+ and 32 gamma delta+ T cells. In conclusion, AECA may be involved in the pathogenesis of WG, and the SAPK/JNK pathway and the endothelial inflammatory protein VAP-1 may be novel therapeutic targets for vasculitis.

Pathogenic mechanisms of anti-endothelial cell antibodies (AECA): their prevalence and clinical relevance

Anti‐endothelial cell antibodies (AECA) represent a heterogeneous family of autoantibodies directed against structural endothelial proteins, as well as antigens adhering to endothelial cells. Although AECA immunoassays still show a high‐interlaboratory variability, several findings suggest a pathogenic role of these autoantibodies in diseases characterized by endothelial damage. In this chapter, we analyze the knowledge about AECA prevalence, clinical relevance, and their pathogenic role in autoimmune diseases focusing in particular on systemic lupus erythematosus, antiphospholipid syndrome, systemic sclerosis (SSc), and systemic vasculitis.

Antiendothelial cell antibodies in vasculitis and connective tissue disease

Antiendothelial cell antibodies (AECA) are a heterogeneous family of antibodies reacting with endothelial cell antigens. These antibodies are found in various diseases and recognise several antigen determinants. Different pathophysiological effects have been observed in in vitro experiments, which include direct or indirect cytotoxicity and endothelial cell apoptosis. Furthermore, some AECA activate endothelial cells, resulting in increased leucocyte adhesiveness, activation of coagulation and vascular thrombosis. In animal models, it has been shown that AECA could promote vascular damage. Neither the endothelial cell antigens nor their precise role in the pathogenecity of different diseases in which AECA are found is well characterised. Nowadays, it is not known whether AECA are an epiphenomenon accompanying vascular injury or whether they are pathogenic. It is controversial whether fluctuations in AECA titres are associated with disease activity during follow-up studies. This review summarises the present knowledge about AECA, AECA antigens and their potential role in the pathogenecity of vasculitis and connective tissue diseases.

Anti-endothelial antibodies and neuropsychiatric systemic lupus erythematosus

The pathogenesis of neuropsychiatric systemic lupus erythematosus (NPSLE) has been attributed to autoantibody-mediated neural dysfunction, vasculopathy, and coagulopathy. Several autoantibodies specificities have been reported in serum and cerebrospinal fluid of NPSLE patients (i.e., antineuronal, antiribosomal P proteins, antiglial fibrillary acidic proteins, antiphospholipid, and anti-endothelial antibodies). We have recently demonstrated an association between serum anti-endothelial antibodies and psychosis or depression in patients with SLE. Subsequently, by screening a cDNA library from human umbilical artery endothelial cells with serum from a SLE patient with psychosis, one positive strongly reactive clone was identified encoding the C-terminal region (C-ter) of Nedd5, an intracytoplasmatic protein of the septin family. Anti-Nedd5 antibodies have been found significantly associated with psychiatric manifestations in SLE patients, strengthening the view of a possible implication of autoantibodies in the development of psychiatric disorders.

Anti-endothelial cell antibodies from patients with limited cutaneous systemic sclerosis bind to centromeric protein B (CENP-B)

By using a quantitative immunoblotting technique on protein extracts of human macrovascular and microvascular endothelial cells, we have analyzed the self-reactive repertoires of IgG from 20 patients with limited cutaneous SSc, 40 patients with diffuse SSc and 60 age- and sex-matched healthy controls. Serum IgG from 15/20 patients with limited cutaneous SSc and anti-centromere antibodies bound to at least one of the two 75- and 85-kDa protein bands in the different endothelial cell extracts, whereas IgG from healthy controls or patients with diffuse SSc did not. N-terminal sequencing of the 75- and 85-kDa bands identified CENP-B as the sole antigen in both bands. Moreover, IgG from all of the SSc patients who recognized the 75- and/or 85-kDa bands bound to a full-length recombinant CENP-B protein as assessed by ELISA, whereas IgG from other SSc patients did not. The main target of anti-endothelial cell antibodies in patients with limited cutaneous SSc is the nuclear and ubiquitous protein CENP-B.

Endothelium, a target for immune-mediated assault in connective tissue disease

Evidence is lacking that antibodies (Ab) to endothelial cells (AECA) are pathogenic. They are frequently associated with antiphospholipid Ab (aPL), binding to complexes of phosphatidylserine (PS) with beta2GPI. Recent studies have, however, kindled a new debate on their pathogenicity of AECA. A group is responsible for PS reaching the surface of a cell, a feature of commitment to apoptosis. Defective clearance by macrophages of AECA-induced apoptotic cells might display beta2GPI on their surface, and challenge T cell tolerance, until aPL production. Some AECA are thus induced by cell membrane structures, while others recognize "planted" antigens and possibly ligand-receptor complexes. A second group promotes procoagulant factor, and a third has the capacity to trigger apoptosis. Clearly, the most direct demonstration of the pathogenicity of AECA is the autoAb-induced murine model of vasculiltis.

Precocious intima-media thickening in patients with primary Sjögren's syndrome

OBJECTIVE

Systemic lupus erythematosus and rheumatoid arthritis represent independent risk factors for atherosclerosis (ATS), although this may be confounded by continuous pharmacologic treatment. Primary Sjögren's syndrome (SS) shares several features of these diseases and may therefore represent an interesting model for verifying the presence of accelerated ATS in the absence of pharmacologic interference. The present study therefore used this model to describe the presence of accelerated ATS in a group of young women.

METHODS

Thirty-seven untreated white women with primary SS were evaluated clinically and serologically. Carotid and femoral artery intima-media thickness (IMT) was evaluated in the patients and in 35 age-matched healthy women who served as controls.

RESULTS

The patients had a higher IMT than did the controls at both the carotid (mean +/- SD 0.82 +/- 0.24 mm versus 0.63 +/- 0.20 mm; P < or = 0.001) and the femoral (0.81 +/- 0.26 mm versus 0.67 +/- 0.23 mm; P < or = 0.019) levels, and had a higher prevalence of carotid intima-media thickening (49% versus 11% of controls; P < or = 0.001). The patient subset with high carotid IMT showed an increased prevalence of leukopenia and circulating anti-SSA antibodies; interestingly, the number of leukocytes was inversely correlated with the level of arterial IMT in patients with SS. Multivariate analysis demonstrated that anti-SSA antibodies were independent predictors of carotid artery thickening, while leukopenia was a predictor of both carotid and femoral artery thickening.

CONCLUSION

Subclinical ATS was evident in about one-half of the patients with SS. Its association with some features typical of connective tissue diseases, such as the presence of anti-SSA and leukopenia, suggests that the immune dysregulation characterizing this autoimmune disorder may play a key role in inducing early ATS.

New target antigens for antiendothelial cell antibodies

Numerous connective tissue diseases, such as systemic lupus erythematosus (SLE), and infectious states, such as leprosy, are characterized by early vascular endothelial cell (EC) damage. There is substantial interest in the role of anti-EC antibodies (AECA) in such an injury. Due to the diversity of AECA-associated conditions, these autoantibodies are likely to be heterogeneous, and, therefore, identification of their antigens (Ag) to be difficult. They may be classified into three groups: membrane components, ligand-receptor complexes and Ag derived from the blood and attached to the cell surface. New technologies have been developed to sort it out, such as expression libraries and two-dimensional electrophoresis. A handful of Ag have hitherto been recognized viz. heat-shock protein 60 in SLE and leprosy, or plasminogen activator inhibitor-1 in SLE and Wegener granulomatosis. In reality, most of the target Ag for AECA remain to be identified.

Increased levels of circulating endothelial cells in chronic periaortitis as a marker of active disease

BACKGROUND

The pathogenesis of chronic periaortitis (CP) has not been clarified. The histologic features and the association with autoimmune diseases suggest an immune-mediated disorder with marked inflammatory vascular and perivascular lesions. To clarify the role of vascular damage we looked for the presence and the surface phenotype of circulating endothelial cells (CECs) in the peripheral blood of patients with chronic periaortitis.

METHODS

Eleven patients with CP were evaluated for the presence of CECs; 9 patients had active and 2 inactive disease. Three patients with active disease were also evaluated 3 months after therapy. Ten atherosclerotic patients, 10 patients with renal insufficiency of variable degree and etiology, and 40 healthy subjects were evaluated as controls. Five-parameter, 3-color flow cytometry was performed with a FACScan. CECs were defined as CD45 negative, CD31, P1H12, and CD36 positive, and activated CECs as CD45 negative and P1H12, CD62 positive.

RESULTS

The median number of CECs in patients with CP (10(6) cells/mL) was significantly higher than in healthy controls (16 cells/mL, P= 0.0004) and atherosclerotic patients (25 cells/mL, P= 0.0005) Two patients with inactive disease had a CEC count comparable to that of normal subjects. In 2 of the 3 patients reevaluated, 3 months after therapy CEC numbers normalized. Almost all CECs were microvascular in origin and showed an activated phenotype.

CONCLUSION

The presence of a high number of CECs in the active phase of chronic periaortitis and their normalization during inactive disease suggest that endothelial damage may play a role in the pathogenesis of the disease.

Premature atherosclerosis in systemic lupus erythematosus

Significant advances have been made in defining the spectrum of clinical manifestations and the prognosis of systemic lupus erythematosus (SLE). With the use of corticosteroids and other immunosuppressive agents as well as better management of complications such as infection, there has been a dramatic improvement in the short-term prognosis of patients who have SLE from less than 50% survival at 5 years to 93% at 5 years and 85% and 10 years. However, many patients who survive early complications of organ failure and sepsis later develop premature coronary artery disease (CAD). In this evidence-based review, the magnitude of the problem of premature atherosclerosis in SLE is defined and evaluation of the strength of association of risk factors determined to date. The authors focus on the emerging role of new modalities for noninvasive assessment of vascular health in patients who have SLE and offer a strategy for screening and management of those at risk of CAD. The article concludes with a discussion on the important questions that remain to be answered and future directions for research.

Inflammatory response and the endothelium

Antiphospholipid-mediated endothelium perturbation plays a role in antiphospholipid syndrome (APS)-associated vasculopathy. Antiphospholipid antibodies activate endothelium both in vitro and in vivo experimental models by inducing a pro-inflammatory/-coagulant phenotype; the antibodies recognize beta2 glycoprotein I (beta2GPI) on human endothelial cells (EC) from different parts of the vasculature. In spite of such large in vitro evidence, few studies have addressed the issue whether or not a comparable endothelial perturbation might be detectable in vivo. We investigated several indirect ex vivo parameters of endothelial dysfunction: plasma levels of soluble adhesion molecules (sADM), soluble thrombomodulin (sTM), von Willebrand factor (vWF) and tissue plasminogen activator (t-PA) by solid-phase assays. The study included: patients with primary antiphospholipid syndrome (n=32), with the syndrome secondary to non-active systemic lupus erythematosus (SLE, n=10), six patients with persistent antiphospholipid positivity at medium/high titre without any clinical manifestation of the syndrome. Fifty-two age and sex matched healthy subjects have been enrolled as controls. In addition, circulating endothelial cells identified by flow cytometry and the brachial artery flow-mediated vasodilation (FMV) were evaluated in 26 patients (20 primary and 6 lupus syndromes) and 30 healthy controls. Plasma levels of soluble adhesion molecules did not differ from controls, while a significant increase in von Willebrand factor titres (P<0.05) was found. No significant difference was found regarding the number of circulating endothelial cells and flow-mediated vasodilation. As a whole, these findings do suggest that antiphospholipid antibodies per se are not able to support a full-blown endothelial perturbation in vivo. As shown in antiphospholipid syndrome experimental animal models, a two-hit hypothesis is suggested.

Anti-endothelial cell antibodies (AECA) in patients with propylthiouracil (PTU)-induced ANCA positive vasculitis are associated with disease activity

Increasing evidence has demonstrated that propylthiouracil (PTU) could induce ANCA positive vasculitis. However, our previous work has suggested that only one-fifth of the PTU-induced ANCA positive patients had clinical vasculitis and so the mechanism is not clear. Anti-endothelial cell antibodies (AECA) have been implicated in the pathogenesis of various vasculitides, including primary ANCA positive systemic vasculitis. The purpose of this study is to investigate the prevalence of AECA and their possible role in the pathogenesis of patients with PTU-induced ANCA positive vasculitis. Sera from 11 patients with PTU-induced ANCA positive vasculitis at both active and quiescent phases, and sera from 10 patients with PTU-induced ANCA but without clinical vasculitis, were studied. Sera from 30 healthy blood donors were collected as normal controls. Soluble proteins from 1% Triton-100 extracted in vitro cultured human umbilical vein endothelial cells were used as antigens and an immunoblotting technique was performed to determine the presence of AECA, and their specific target antigens were identified. In patients with PTU-induced ANCA positive vasculitis, 10 of the 11 patients in an active phase of disease were serum IgG-AECA positive and six protein bands of endothelial antigens could be blotted (61 kD, 69 kD, 77 kD, 85 kD, 91 kD and 97 kD). However, in the quiescent phase, seven of the 10 positive sera turned negative. None of the ANCA positive but vasculitis negative patients or normal controls were AECA positive. In conclusion, AECA could be found in sera from patients with PTU-induced ANCA positive vasculitis and were associated more closely with vasculitic disease activity.

Wegener's granulomatosis is associated with organ-specific antiendothelial cell antibodies

BACKGROUND

Antiendothelial cell antibodies (AECA), usually detected using human umbilical vein endothelial cells (HUVEC), are frequently observed in systemic vasculitis, but their pathogenic role is unclear. Heterogeneity of endothelial cells necessitates use of clinically relevant endothelial cells for elucidation of the role of AECA in systemic vasculitis involving small blood vessels of specific organs.

METHODS

Human endothelial cells were isolated from normal tissue specimens from the nose, kidney, lung, liver, and umbilical vein. Using flow cytometry, AECA were detected against both unstimulated and cytokine-stimulated [tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma)] endothelial cells. Functional capacity of AECA was determined by complement fixation assay. Sera from patients with Wegener's granulomatosis (16), limited Wegener's granulomatosis (8), renal limited disease (4), microscopic polyangiitis (MPA) (5), rheumatoid arthritis (10), and systemic lupus erythematosus (SLE) (9), and from healthy controls (20) were analyzed.

RESULTS

Compared with controls (1) Wegener's granulomatosis is significantly associated with noncytotoxic AECA that selectively bind surface antigens on unstimulated nasal, kidney, and lung endothelial cells; (2) binding of Wegener's granulomatosis AECA to kidney and nasal endothelial cells in particular was lost upon treatment with IFN-gamma and TNF-alpha; (3) the two cytokines per se were cytotoxic (30%) to nasal and lung endothelial cells and lysis was further increased (60%) by addition of systemic vasculitis serum; and (4) Wegener's granulomatosis serum caused agglutination of cytokine-stimulated nasal endothelial cells.

CONCLUSION

Based on these findings we suggest that AECA may be one factor involved in the initiation of Wegener's granulomatosis. Antigen identification and elucidation of the pathogenic roles of AECA and inflammatory cytokines in systemic vasculitis using these cells will be particularly important.

Autoimmune Mouse Antibodies Recognize Multiple Antigens Proposed in Human Immune-Mediated Hearing Loss

HYPOTHESIS

Autoimmune diseased mice with hearing loss will have autoantibodies against the various cochlear antigens proposed in clinical autoimmune inner ear disease.

BACKGROUND

Serum antibodies of patients with hearing loss recognize several proteins that are proposed as possible antigenic targets in the ear. This often leads to a clinical diagnosis of autoimmune inner ear disease, although it is not clear how these antibodies cause inner ear disease. Therefore, to better understand the relationship of autoantibodies and ear disease, an examination was made of serum autoantibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse with hearing loss. Similar antibody patterns in the mouse would provide an animal model in which to investigate potential autoimmune mechanisms of this clinical ear disorder.

METHODS

Sera from MRL/MpJ-Fas(lpr) autoimmune mice and normal C3H mice were tested by the enzyme-linked immunosorbent assay technique for reactivity against various reported cochlear antigens: heat shock protein 70 (bovine, human, bacterial), laminin, heparan sulfate proteoglycan, cardiolipin, and collagen types II and IV.

RESULTS

The autoimmune mouse sera showed significantly greater antibody reactivity against all of the antigens when compared with normal mouse sera.

CONCLUSIONS

Serum antibodies from autoimmune mice recognized several putative autoantigens reported for patients with hearing loss, suggesting that comparable antigen-antibody mechanisms might be operating. However, the recognition of multiple antigens did not identify any one as being the specific target in autoimmune hearing loss. The correlation of antibodies in the MRL/MpJ-Fas(lpr) autoimmune mouse and human studies indicates this animal model should aid further investigations into potential cochlear antigens in autoimmune hearing loss.

IgM and IgG autoantibodies from microscopic polyangiitis patients but not those with other small- and medium-sized vessel vasculitides recognize multiple endothelial cell antigens

Using a quantitative immunoblotting technique on extracts of macrovascular and microvascular endothelial cells (EC), we analyzed serum IgM and IgG reactivities of patients with active disease fulfilling the ACR and Chapel Hill criteria for the diagnosis of polyarteritis nodosa (PAN) (n = 8), PAN related to hepatitis B virus (HBV) infection (HBV-PAN) (n = 5), Wegener's granulomatosis (n = 6), microscopic polyangiitis (MPA) (n = 18), Churg-Strauss syndrome (n = 8), and patients with chronic HBV infection without PAN (n = 5) and age- and gender-matched healthy individuals (n = 45). MPA patients' IgM bound to 200-, 105-, 80-, 65-, 45-, 35-, and 33-kDa major bands, whereas IgM from controls and other patients bound predominantly to the 65-kDa band in EC extracts. MPA patients' IgG reacted mainly with 105-, 70-, 55-, and 38-kDa protein bands, whereas IgG from controls and other patients did not. Our results provide evidence that IgM and to a lesser degree IgG from MPA patients specifically recognize multiple EC antigens.

Endothelium as a target for antiphospholipid antibodies

Several, and not necessarily alternative, pathogenic mechanisms have been suggested to sustain the thrombophilic diathesis of the anti-phospholipid syndrome. Among them, interference of anti-phospholipid antibodies with cell acting in the coagulation cascade likely plays a major role. Anti-phospholipid antibodies have been shown to react with endothelial cells mainly by reacting with beta 2 glycoprotein I expressed on the cell membrane surface. Beta 2 glycoprotein I can adhere to endothelial cell surface through the Annexin II receptor and through negatively charged structures (heparin-like molecules) that are bound by the phospholipid-binding site of the molecule. The autoantibody binding involves a yet unknown receptor that activates a signalling pathway able to translocate NFkappaB from the cytoplasm to the nucleus and to activate genes for adhesion molecule, pro-inflammatory cytokine and Tissue Factor up-regulation. The ultimate effect is the induction of a pro-inflammatory and a pro-coagulant endothelial phenotype that has been reproduced both in vitro and in vivo experimental models. Additional effects of anti-phospholipid-mediated endothelial cell activation are the interference with the protein C/S system, with the Annexin V binding, the up-regulation of endothelin I synthesis and the induction of apoptosis. Altogether these effects cooperate in switching endothelium from an anti-coagulant to a pro-coagulant surface.

The pathology and pathogenesis of retinal vasculitis

Retinal vasculitis is a rare, but potentially blinding intraocular inflammatory condition with diverse aetiology. Although commonly idiopathic, it has a strong association with systemic inflammatory diseases known to involve other areas of the central nervous system, most notably Behcet's disease, sarcoidosis, systemic lupus erythematosis and multiple sclerosis. This article describes the clinicopathologic features of retinal vasculitis and its visually damaging sequelae, reviewing available human histopathologic studies and work with experimental models to discuss the pathogenesis and immunopathology. Evidence indicates that noninfective retinal vasculitis is an autoimmune condition that may be induced by antecedent infection with microbes cross-reacting with putative autoantigens, influenced by genetic susceptibility of both HLA associations and cytokine polymorphisms. The growing understanding of the cellular mechanisms involved in the effector immune response is already providing a rationale for more specific therapeutic approaches.

Antiendothelial cell antibodies in systemic lupus erythematosus

Sera from patients with systemic lupus erythematosus have been reported to contain IgM and/or IgG binding to endothelial cells (EC), i.e. anti-EC antibodies (AECA). Similar autoantibodies have been claimed to occur in a number of conditions associated with vasculitis. The original cyto-enzyme-linked immunosorbent assay (ELISA) remains the most widely used method for the detection of AECAs, although numerous pitfalls have been identified since then. These difficulties may explain why a consensus on the prevalence of AECAs has not been reached thus far. It is therefore desirable to confirm a positive result in the cyto-ELISA using other methods, such as flow cytometry, immunoprecipitation or Western blot. Yet, these methods appear to be difficult to use on a routine basis. With regard to the AECA effects, their binding induces activation of ECs, as substantiated by up-regulation of adhesion molecules, and synthesis of cytokines and chemokines, followed by their secretion. Some of these autoantibodies encourage the local production of tissue factor, and thereby favour coagulation. Other AECAs trigger apoptosis of ECs, although the Fas receptor does not seem to be involved in this process. In fact, since the target antigens are not well defined, the current challenge is to identify EC target molecules, and thus to gain further insights into the pathogenesis of diseases with vasculitis.

The role of anti-endothelial cell antibodies in Kawasaki disease - in vitro and in vivo studies

Kawasaki disease (KD) is a systemic vasculitis with cardiac and noncardiac complications. Anti--endothelial cell antibodies (AECA) are found among many patients with KD. The aim of this study was to investigate the pathogenic role of AECA in KD using in vitro and in vivo experimental models. F(ab)2 fragments of IgG-AECA and IgM-AECA were affinity purified from a patient with active KD. Their endothelial binding and ability to induce a pro-adhesive and a pro-inflammatory phenotype were evaluated in vitro. Twenty Balb/C mice were immunized with KD-AECA or with control Ig (N-Ig) to induce AECA in a murine model by the idiotypic manipulation method. Both KD-AECA isotypes bind significantly to human umbilical vein endothelial cell (HUVEC) compared to N-Ig. The in vitro activity was demonstrated by the antibodies ability to activate endothelial cells resulting in increased IL-6 secretion, adhesion molecule expression and monocytic cell line (U937) adherence to HUVEC. Five of the mice that received KD-AECA developed murine AECA after 3 months. None of the mice that received N-Ig produced AECA. The murine AECA increased monocyte adhesion to EC in vitro, similarly to the AECA used for immunization. Furthermore, all the mice that developed AECA had proteinuria and IgG deposition in the renal mesangium. No histological or immunofluorescence evidence of cardiac vasculitis could be detected. AECA might play a role in the emergence of some of KD manifestations.

Vitronectin- and fibronectin-containing immune complexes in primary systemic vasculitis

In primary systemic vasculitis anti endothelial cell autoantibodies (AECA) have been described frequently. They represent a heterogeneous group of autoantibodies whose target antigens are mostly unknown. We tried to find AECA-antigens by a co-operative binding assay with a panel of monoclonal antibodies (mAb) directed to human umbilical vein endothelial cells (HUVEC) and extracellular matrix proteins. The mAb were used to bind antigens from lysate of endothelial cells, and binding of human antibodies to these antigens was measured. mAb directed to Vitronectin (VN) and Fibronectin (FN) resulted in enhanced binding of antibodies in sera from patients with Churg Strauss Syndrome (CSS) and Wegener's Granulomatosis (WG) compared to normal sera. Neither free autoantibodies against VN or FN could be detected nor did the addition of endothelial cell lysate influence the binding activity from the patients' sera. This suggests that preformed VN and FN-containing immune complexes (IC) are present in the patient sera. The amount of IC was decreased by incubation with HUVEC, demonstrating that these IC can bind to endothelial cells. However, their involvement in the pathogenesis of the disease is not clearly defined. Our data suggest that there are preformed IC present in sera of patients with CSS and WG that contain VN and FN and bind to endothelial cells.

Are antineutrophil cytoplasmic antibody-associated vasculitides pauci-immune?

The role of ICs in ANCA-associated vasculitides remains controversial. The ANCA-associated vasculitides are described as being pauci-immune. We hypothesize that the absence of ICs is a result of an exaggerated inflammatory response caused by the presence of ANCAs. We present evidence indicating that ICs may play a role in the initiation or relapses of the disease. The nature of the involved antigen(s) is not yet known. Possible candidates are reviewed and include ANCA antigens, AECA antigens, and staphylococcal antigens.

Antiphospholipid antibodies and the endothelium

The interaction between aPL (particularly anti-beta 2GPI antibodies) and endothelium does represent a potential pathogenetic mechanism for the thrombotic manifestations of the syndrome. The autoantibody-mediated EC activation probably plays a role in sustaining the appearance of a proadhesive, proinflammatory, and procoagulant phenotype. The heterogeneity of the APS clinical manifestations is likely linked to the varied effects that aPL can induce on ECs and to the different functions that ECs display depending on the anatomic localization.

Human monoclonal anti-endothelial cell IgG-derived from a systemic lupus erythematosus patient binds and activates human endothelium in vitro

Our objectives were to obtain monoclonal anti-endothelial cell antibodies (AECA) from systemic lupus erythematosus (SLE) patients, to characterize their antigen specificity, and their capability to induce a pro-inflammatory and pro-adhesive endothelial phenotype, and to investigate the mechanism of endothelial cell (EC) activation in vitro. Monoclonal IgG AECA were generated by hybridoma formation with human SLE B cells. Antigen specificity was characterized by immunoblotting with enriched cell membrane fractions, by cytofluorimetry and by cell solid-phase ELISA. Endothelial activation was evaluated by measuring increases in U937 cell adhesiveness, adhesion molecule (E-selectin and ICAM-1) expression and IL-6 production. In addition, mechanisms of endothelial activation were investigated by assessment of NF-kappaB by measuring the loss of its inhibitor I-kappaB. mAb E-3 bound live EC and recognized a 42 kDa EC membrane protein, it enhanced U937 adhesiveness, E-selectin and ICAM-1 expression and IL-6 production, and caused the loss of I-kappaB. We conclude this is the first in vitro demonstration that a human monoclonal AECA from a SLE patient reacts with a constitutive endothelial membrane antigen and induces a pro-inflammatory endothelial phenotype through NF-kappaB activation.

Endothelial cell apoptosis in systemic sclerosis is induced by antibody-dependent cell-mediated cytotoxicity via CD95

OBJECTIVE

Apoptosis of endothelial cells is a key event in the pathogenesis of systemic sclerosis (SSc). The aim of the present study was to analyze in vitro the mechanism causing endothelial cell apoptosis in SSc.

METHODS

Human dermal microvascular endothelial cells (HDMEC) or human umbilical vein endothelial cells (HUVEC) were cultured with native or heat-inactivated serum from SSc patients or controls with or without interleukin-2-activated natural killer (NK) cells or peripheral blood mononuclear cells. SSc and control sera were tested for the presence or absence, respectively, of anti-endothelial cell antibodies (AECA) by indirect immunofluorescence. Apoptosis was detected by the TUNEL technique.

RESULTS

Native sera alone had no effect. Apoptosis induction was observed on HDMEC, but not on HUVEC, in the presence of AECA-positive SSc sera and activated NK cells, and could be inhibited by an anti-Fas ligand antibody. Inhibition of the perforin/granzyme pathway with concanamycin A had no effect on apoptosis induction in this in vitro model. Immunofluorescence analysis of cryosections from SSc skin showed Fas (CD95) expression by endothelial cells, supporting the in vitro findings.

CONCLUSION

The results suggest that endothelial cell apoptosis in SSc is induced by antibody-dependent cell-mediated cytotoxicity via the Fas pathway. These data not only provide insight into the pathogenesis of SSc, but also may open new ways to rational therapy for this disease.

The identification of endothelial cell autoantigens

The identity of many endothelial cell autoantigens remains unclear. This study has used human monoclonal anti-endothelial cell autoantibodies isolated from patients with SLE to identify endothelial autoantigens. Thirteen antibodies reactive with endothelial cell membrane preparations were isolated and cloned, one of which has previously been demonstrated to be pro-inflammatory. Western blotting demonstrates that these antibodies recognize a variety of proteins in endothelial cell membrane preparations. Further characterization of five antibodies by cDNA library screening, immunofluorescence and Western blotting proves that two of these antibodies recognized the cytoskeletal proteins tubulin and vimentin. A further antibody identified a clone derived from human collagenase, an identification supported by Western blotting. The multiple clones selected by other antibodies are not compatible with the molecular weight of the antigen recognized in Western blotting studies. This study has clearly identified two endothelial cell autoantigens present in membrane preparations and provides strong evidence as to the identity of a third.

Anti-endothelial cell antibodies in patients with coronary atherosclerosis

Anti-endothelial cell antibodies (AECA) have been shown to possess endothelial cell activation properties and to harbor pathogenic potential in experimental animal models of autoimmune systemic disorders. Atherosclerosis is a form of an inflammatory condition in which the immune system has been shown to be involved. The aim of the present study was to assess the presence of AECA in patients with coronary atherosclerosis. A total of 134 patients admitted for chest pain of suspected anginal origin were evaluated for coronary artery atherosclerosis by angiography. Sera were drawn prior to the procedure for the determination of AECA employing cyto-ELISA. AECA positive sera were further evaluated for its ability to promote in vitro E-selectin expression by HUVEC using a cell-based ELISA. Patients with no coronary artery involvement had levels of AECA that did not differ from those obtained for patients with confirmed coronary atherosclerosis (one, two or three vessel disease). Furthermore, AECA positive sera from patients, with or without coronary atherosclerosis displayed similar capacity of inducing E-selectin expression by endothelial cells. AECA may not stand as an optimal mean of discriminating atherosclerotic from non-atherosclerotic patients. The ability of AECA to activate endothelial cells is also not unique to patients with atherosclerosis and is evident also in age-matched control subjects.

The vascular perspective of systemic sclerosis: of chickens, mice and men

Systemic sclerosis (SSc), or scleroderma, is an autoimmune connective tissue disease characterized by structural and functional vascular abnormalities, perivascular mononuclear cell infiltration, and increased deposition of extracellular matrix in skin and internal organs. The initial stages of SSc are generally not accessible for analysis in man, therefore, the availability of appropriate animal models is of great importance for the elucidation of the pathogenesis of this disease. UCD-200 chickens show the entire clinical, histopathological and serological spectrum of SSc, whereas tight skin (Tsk)1/+ and Tsk2/+ mice, other animal models of scleroderma, lack the vascular injury. A parallel comparative study of skin biopsies of UCD-200 chickens and human SSc patients revealed that endothelial cell apoptosis, induced by anti-endothelial cell antibody (AECA)- dependent cellular cytotoxicity, is a primary event in the pathogenesis of SSc. This review focuses on recently established data on endothelial cell injury in animals with spontaneous disease and humans, AECA, adhesion molecules and cytokine profiles that support a vascular pathogenesis in scleroderma.

Anti-endothelial cell IgG fractions from systemic lupus erythematosus patients bind to human endothelial cells and induce a pro-adhesive and a pro-inflammatory phenotype in vitro

Affinity purified immunoglobulin G (IgG) fractions from systemic lupus erythematosus (SLE) patients positive for anti-endothelial cell antibodies (AECA) bind human umbilical vein endothelial cell (HUVEC) monolayers. In vitro incubation of serial protein concentrations of SLE AECA IgG induces a dose-dependent endothelial activation: i) increase of functional adhesion of the monocytic cell line U937; ii) upregulation of E-Selectin, ICAM-1, VCAM-1 expression evaluated by a cell solid-phase enzyme linked immunoassay; and iii) increased secretion of interleukin (IL)-6 in the culture supernatants. Control experiments carried out with HUVEC monolayers incubated with IgG fractions from normal healthy controls or from AECA negative SLE sera do not affect at all endothelial adhesion molecule expression or pro-inflammatory cytokine secretion. The AECA IgG effects are not related to both anti-phospholipid or anti-DNA activities. Taken together the findings suggest that these autoantibodies might be important in recruiting and in activating mononuclear leukocytes responsible for vessel wall infiltration and raise the possibility that AECA might display a pathogenic role in SLE vessel damage.

Monoclonal anti-endothelial cell antibodies from a patient with Takayasu arteritis activate endothelial cells from large vessels

OBJECTIVE

To create monoclonal anti-endothelial cell antibodies (mAECA) from a patient with Takayasu arteritis to evaluate their ability to activate human umbilical vein endothelial cells (HUVEC), and to characterize the mechanism of EC activation.

METHODS

A panel of mAECA was generated from peripheral blood lymphocytes of a patient with Takayasu arteritis, using Epstein-Barr virus transformation. Activity against macrovascular EC (HUVEC) and microvascular EC (human bone marrow EC immortalized by SV40) antigens was detected by enzyme-linked immunosorbent assay. Inhibition studies were used to select the monoclonal antibodies (mAECA) which share the same EC epitope binding specificity as the total IgG-AECA from the Takayasu arteritis patient. The binding of the mAECA to human aortic EC was studied by immunohistochemistry. The secretion levels of interleukin-6 (IL-6) and von Willebrand factor (vWF) were determined, to serve as markers for EC activation. The activated EC were examined for the adherence of a monocytic cell line (U937), as well as for expression of vascular cell adhesion molecule 1, intercellular adhesion molecule 1, and E-selectin. In addition, nuclear extracts of the mAECA-treated EC were analyzed for the induction of translocation of nuclear factor kappaB (NF-kappaB), using a specific NF-kappaB oligoprobe in an electrophoretic mobility shift assay.

RESULTS

Six mAECA were selected, the mixture of which produced 100% inhibition of binding of the original IgG (from the patient with Takayasu arteritis) to HUVEC. All mAECA possessed high activity against macrovascular EC, but none had significant antimicrovascular EC activity. The mAECA, but not normal human IgG, had anti-human aortic EC activity. Four of the 6 mAECA activated EC, manifested by increased IL-6 and vWF secretion. The 4 mAECA induced EC expression of adhesion molecules and increased adhesion of U937 monocytic cells to EC. In addition, these mAECA stimulated the nuclear translocation of the NF-kappaB transcription factor.

CONCLUSION

Our findings suggest that AECA may directly stimulate EC in Takayasu arteritis through elevation of adhesion molecule expression associated with NF-kappaB activation and adhesion of monocytes, and may therefore play a pathogenic role in the development of the vasculopathy in Takayasu arteritis.

IgG anti-endothelial cell autoantibodies from patients with systemic lupus erythematosus or systemic vasculitis stimulate the release of two endothelial cell-derived mediators, which enhance adhesion molecule expression and leukocyte adhesion in an autocrine manner

OBJECTIVE

To investigate the ability of anti-endothelial cell antibodies (AECA) to modulate endothelial cell function.

METHODS

The effects of purified IgG from 11 patients with systemic lupus erythematosus (SLE) and 4 patients with systemic vasculitis on the expression of adhesion molecules (intercellular adhesion molecule 1, vascular cell adhesion molecule 1, E-selectin) by human umbilical vein endothelial cells and on the adhesion of the human promyelocytic cell line U937 were examined in vitro.

RESULTS

IgG from 6 of 8 AECA-positive SLE patients and 3 of 3 AECA-positive systemic vasculitis patients up-regulated adhesion molecule expression and leukocyte adhesion to endothelial cells. The 4 AECA-negative samples had no effect. Transfer experiments demonstrated that at later time points (2-8 hours) after AECA addition, endothelium-derived interleukin-1 (IL-1) accounted for the ability of AECA to increase leukocyte adhesion. However, even within very short times after addition of AECA (<30 minutes), endothelial cells released a distinct transferable mediator with similar effects.

CONCLUSION

AECA in patients with SLE or systemic vasculitis may contribute to pathogenesis by increasing leukocyte adhesion to endothelial cells. AECA act by inducing the release of at least two endothelium-derived mediators, one (as-yet-unidentified) rapidly and another (IL-1) more slowly, both of which stimulate endothelial cells in an autocrine manner.

Intestinal reperfusion injury is mediated by IgM and complement

Intestinal ischemia-reperfusion injury is dependent on complement. This study examines the role of the alternative and classic pathways of complement and IgM in a murine model of intestinal ischemia-reperfusion. Wild-type animals, mice deficient in complement factor 4 (C4), C3, or Ig, or wild-type mice treated with soluble complement receptor 1 were subjected to 40 min of jejunal ischemia and 3 h of reperfusion. Compared with wild types, knockout and treated mice had significantly reduced intestinal injury, indicated by lowered permeability to radiolabeled albumin. When animals deficient in Ig were reconstituted with IgM, the degree of injury was restored to wild-type levels. Immunohistological staining of intestine for C3 and IgM showed colocalization in the mucosa of wild-type controls and minimal staining for both in the intestine of Ig-deficient and C4-deficient mice. We conclude that intestinal ischemia-reperfusion injury is dependent on the classic complement pathway and IgM.