IgM Anti-endothelial Cell Antibodies Research Articles

Clinical, paraclinical and serological findings in Susac syndrome: an international multicenter study

BackgroundSusac syndrome (SuS) is a rare disorder thought to be caused by autoimmune-mediated occlusions of microvessels in the brain, retina and inner ear leading to central nervous system (CNS) dysfunction, visual disturbances due to branch retinal artery occlusions (BRAO), and hearing deficits. Recently, a role for anti-endothelial cell antibodies (AECA) in SuS has been proposed.ObjectivesTo report the clinical and paraclinical findings in the largest single series of patients so far and to investigate the frequency, titers, and clinical relevance of AECA in SuS.Patients and methodsA total of 107 serum samples from 20 patients with definite SuS, 5 with abortive forms of SuS (all with BRAO), and 70 controls were tested for AECA by immunohistochemistry employing primate brain tissue sections.ResultsIgG-AECA >1:100 were detected in 25% (5/20) of patients with definite SuS and in 4.3% (3/70) of the controls. Median titers were significantly higher in SuS (1:3200, range 1:100 to 1:17500) than in controls (1:100, range 1:10 to 1:320); IgG-AECA titers >1:320 were exclusively present in patients with SuS; three controls had very low titers (1:10). Follow-up samples (n = 4) from a seropositive SuS patient obtained over a period of 29 months remained positive at high titers. In all seropositive cases, AECA belonged to the complement-activating IgG1 subclass. All but one of the IgG-AECA-positive samples were positive also for IgA-AECA and 45% for IgM-AECA. SuS took a severe and relapsing course in most patients and was associated with bilateral visual and hearing impairment, a broad panel of neurological and neuropsychological symptoms, and brain atrophy in the majority of cases. Seropositive and seronegative patients did not differ with regard to any of the clinical or paraclinical parameters analyzed.ConclusionsSuS took a severe and protracted course in the present cohort, resulting in significant impairment. Our finding of high-titer IgG1 and IgM AECA in some patients suggest that humoral autoimmunity targeting the microvasculature may play a role in the pathogenesis of SuS, at least in a subset of patients. Further studies are warranted to define the exact target structures of AECA in SuS.

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Aim To determine the changes in gene expression in Endothelial Precursor Cells (EPC) exposed to Anti Endothelial Cell Antibodies (AECA) that are Non-HLA-specific. Methods Magnetic-bead column isolation followed by XM-One crossmatch procedure using reagents from Absorber Inc. was employed to identify serum samples with non-HLA AECA. For Gene expression assays, EPCs were obtained from T and B cell depleted PBL using reagents from Absorber Inc. The endothelial cell gene expression was performed on total RNA using Real-Time RT-PCR profiler reagents from QIAGEN Inc. Results EPCs exposed to a combination of IgM and IgG AECAs, affected the expression of more endothelial cell genes than EPCs exposed to IgM or IgG alone. Exposure of EPCs to IgM AECA alone caused changes in a few genes while exposure to IgG AECA alone did not significantly alter expression of any endothelial cell genes. In all, the genes which were up-regulated (ANXA5; APOE; BAX; BCL2L1; CALCA; CFLAR; COL18A1; EDN1; EDN2; EDNRA; FLT1; HIF1A; HMOX1; ICAM1; ITGAV; ITGB1; KDR; OCLN; PF4; SELE; THBS1) were those associated with pro-apoptotic, thrombocytic and or hemolytic events. One of the highly down-regulated genes was the Tissue inhibitor of Matrix Metalloproteinase (TIMP) that inhibit the matrix metalloproteinases which leads to increased extracellular protein deposition resulting in excessive extracellular connective tissue deposition, which is a hallmark of fibrosis which in turn is associated with chronic allograft rejection. Conclusions Human EPCs seem to respond to non-HLA antibodies by altering the gene expressions of endothelial cell biology which might be associated with events leading to allograft injury in a complement independent way. More detailed gene expression studies with organ specific endothelial cells and IgM/IgG specific non-HLA endothelial cell antibodies are needed to assess the full significance of AECA in allograft rejection.

Validation of a New Biomarker in Patients with Kawasaki Disease Identified by Proteomics

Systemic vasculitis is a heterogeneous disorder characterized by chronic or acute inflammation, and is classified into groups by the size of the affected blood vessels: large vessel vasculitis, medium vessel vasculitis, or small vessel vasculitis. The pathogenesis of systemic vasculitis is not yet understood and except for Anti-neutrophil Cytoplasmic Antibodies (ANCA) for a subset of small vessel vasculitis, biomarkers for diagnosis and disease activity in systemic vasculitis have still to be discovered. Kawasaki Disease (KD) is an acute systemic vasculitis of infancy and early childhood. It mainly affects small and medium size blood vessels, and can cause cardiovascular complications like coronary artery aneurysm. Anti-endothelial Cell Antibodies (AECA) have been detected in a variety of diseases associated with vascular injury,and KD is one of them. Further, the presence of AECA has been correlated with disease activity, and/or its clinical manifestations [1,2]. A number of mechanisms for AECA, for example, activation and apoptosis of vascular Endothelial Cells (ECs), have been proposed [3]. In KD patients, IgM AECA mediate complement-dependent cytotoxicity against Human Umbilical Vein Endothelial Cells (HUVEC) and gammaglobulin, a standard therapy for KD, may reduce their effect [4]. Grunebaum et al. [5] demonstrated that AECA increased the secretion of Interleukin-6 (IL-6) from HUVEC, in KD patients. However, a significant role for AECA in systemic vasculitis has yet to be found. To evaluate the roles of AECA in detail, it is essential that their target antigens are identified and that the role of individual target antigens is assessed. Various approaches, such as expression libraries and proteomic, have been developed to identify biomarkers [6-11]. In KD, two target antigens for the AECA, tropomyosin and T-plastin, were identified using serological analysis of a recombinant cDNA expression library [11]. However, target antigens suitable for clinical applications, including Myeloperoxidase (MPO) and proteinase 3 of ANCA, remain to be discovered. Proteomics is a powerful tool for detecting and identifying biomarker proteins, because proteomics techniques allow the global analyses of protein function, modifications, composition and dynamics to be performed. In addition, current proteomic techniques can be used to analyze several samples from, for example, serum, urine, cerebrospinal fluid, and various tissues and cells. These kinds of analyses may lead to clinical applications. To identify the target proteins for AECA in patients with vasculitis, we used a proteomics approach that included 2-dimensional electrophoresis and Western Blotting, followed by mass spectrometry [9]. Briefly, we extracted the proteins from HUVEC and HeLa cells (control), and separated them by 2-dimensional electrophoresis to detect AECA antigens specific for ECs. We then analyzed the antigens by Western Blotting against serum samples from patients with vasculitis. We selected the spots that were detected only in the HUVEC samples, and not in HeLa cell samples. This procedure should identify candidate antigens, specific for ECs. We identified the detected proteins by peptide mass fingerprinting. Currently, we have detected more than 150 candidate antigenic spots, and identified more than 50 protein spots. In our earlier study, we identified Peroxiredoxin-2 (Prx2), a member of the Peroxiredoxin (Prx) family of peroxidases, as a target antigen for AECA [9]. In mammalian cells, the Prx family has at least six members (Table 1), and Prx2 is one of the most rapid and potent responders to oxidative stress. Furthermore, oxidative stress has been implicated as a pathogenic factor, and/or a progression-related factor in various diseases, including vasculitis. For these reasons, Prx2 was selected for further investigation. We investigated the clinical significance of anti-Prx2 antibodies in patients with KD. The titers of IgG antibodies to recombinant Prx2 were evaluated by ELISA (Enzymelinked Immunosorbent Assay), using 30 untreated patients with KD, including three patients with Coronary Artery Lesions (CALs), and 15 age- and sex-matched controls. The optical density value of the average ± 2 Standard Deviations (SDs) in the control individuals was defined as 100 AU, and values more than 100 AU, were regarded as positive. IgG antibodies to recombinant Prx2 were detected in 60% (18 of 30) of the untreated patients with KD, whereas no IgG antibodies were detected in the control individuals (Figure 1). We also evaluated the titers of IgM and IgA antibodies to recombinant Prx2 by ELISA, in patients with KD and in controls. IgM antibodies to recombinant Prx2 were

Induction of elastin expression in vascular endothelial cells relates to hepatoportal sclerosis in idiopathic portal hypertension: possible link to serum anti-endothelial cell antibodies

Hepatoportal sclerosis accompanied by dense elastic fibre deposition is generally regarded as the primary lesion in the development of idiopathic portal hypertension (IPH). This study was performed to clarify the mechanism of elastic fibre deposition in the peripheral portal tracts of IPH liver in relation to serum anti-endothelial cell antibodies (AECA). In-vitro experiments were performed using human dermal microvascular endothelial cells (HMVEC) and patients' sera. The presence of serum AECA was assayed by a cell-based enzyme-linked immunosorbent assay (ELISA) using HMVEC. Immunohistochemical analysis of elastin was performed using liver tissue sections of IPH patients. IPH sera contained one or more AECA that could bind to the vascular endothelial cells of the peripheral portal tracts of the liver. When the value of AECA greater than the mean ± 2 standard deviations of healthy controls was regarded as positive, the positive detection rate of either immunoglobulin (Ig)G, IgA or IgM AECA in IPH sera was 30% (10 of 33 cases). IPH sera induced the expression of elastin in HMVEC, which appeared to be associated with the presence of AECA. Apoptosis was also induced in HMVEC by the stimulation with IPH sera. In vivo, elastin expression was observed in the endothelial cells of the peripheral portal tracts of IPH livers in a proportion of cases. The disease pathogenesis of IPH seems to be heterogeneous, and this study elucidated a possible contribution of the induction of elastin expression in the portal vessels to hepatoportal sclerosis of IPH, which might be linked to serum AECA as a causative factor.

Antiendothelial cell antibodies in patients with coronary artery ectasia

The mechanisms involved in the pathogenesis of coronary artery ectasia (CAE) have not been elucidated. Circulating antiendothelial cell antibodies (AECA) are often detectable in systemic vasculitis and have been implicated in the pathogenesis of endothelial injury. Their prevalence in CAE is not known. Out of 475 consecutive patients subjected to coronary angiography, 27 patients were diagnosed with CAE. Thirty patients matched for age, body mass index, sex, and coronary artery disease prevalence, served as controls. Serum AECA of IgG, IgM, and IgA isotypes were detected using a cell-based enzyme-linked immunosorbent assay (ELISA). Antinuclear antibodies (ANA) and antineutrophil cytoplasmic antibodies (ANCA) were detected using indirect immunofluorescence. IgG and IgM anticardiolipin antibodies (aCL) were detected using commercial ELISA. The prevalence of ANA and ANCA was similar in CAE patients and controls (33.3 vs. 43.3%, and 3.3 vs. 7.4%, respectively). There was no significant difference in IgG or IgM aCL reactivity between patients and controls. Both CAE patients and controls were negative for IgG AECA. The frequency of IgM AECA positivity was similar in CAE patients and controls. The prevalence of AECA of the IgA isotype was significantly higher in CAE patients (37.0 vs. 10%, P<0.05). There is increased prevalence of circulating AECA of the IgA isotype in patients with CAE. This provides evidence for a role of autoimmunity in the pathogenesis of certain cases of CAE.

Prevalence of anti-endothelial cell antibodies in idiopathic pulmonary arterial hypertension: Table 1—

To the Editors: Pulmonary arterial hypertension (PAH) is a rare disease often resulting in right-sided heart failure and premature death 1. PAH is idiopathic (IPAH), heritable, or related to conditions such as connective tissue diseases (CTD) 2. IPAH prognosis remains poor despite improved patient survival with current treatment options. Therefore, elucidating the pathophysiology of IPAH is important for the discovery of novel therapeutic approaches. Inflammation and immune reactivity have been implicated in the pathophysiology of IPAH. In 2005, Tamby et al. 3 described the presence of anti-endothelial cell antibodies (AECA) in IPAH, pointing at the involvement of humoral immunity. AECA are a heterogeneous family of auto-antibodies capable of reacting with different endothelial cell (EC) structures 4. In PAH, pulmonary EC dysfunction is considered a key player in the initiation and progression of the disease 5. Systemic sclerosis (SSc) is a paradigm of autoimmune PAH, as 10–15% of these patients develop PAH 6. Interestingly, in SSc, immunoglobuliln (Ig)G AECA targeting cell-surface antigens have indeed been shown to induce EC dysfunction 7, 8. Thus, IgG AECA-induced endothelial dysfunction may be the initiating event in IPAH. Whereas IgG auto-antibodies are considered pathogenic in various autoimmune diseases, IgM auto-antibodies have been proposed to be protective in these diseases 9. Regarding a pathophysiological role of AECA, it is important to identify whether AECA are reactive with EC-surface antigens. To corroborate and further investigate the role of the humoral immune system in IPAH, we aimed to study the prevalence of IgG, as well as IgM AECA targeting cell-surface EC antigens using a cell-based ELISA with viable human umbilical vein EC (HUVEC). We screened five study cohorts for the presence of AECA. 1) 29 IPAH patients; mean pulmonary artery …

Multicenter Evaluation of a Novel Endothelial Cell Crossmatch Test in Kidney Transplantation

Despite their clinical importance, clinical routine tests to detect anti-endothelial cell antibodies (AECA) in organ transplantation have not been readily available. This multicenter prospective kidney transplantation trial evaluates the efficacy of a novel endothelial cell crossmatch (ECXM) test to detect donor-reactive AECA associated with kidney allograft rejection. Pretransplant serum samples from 147 patients were tested for AECA by a novel flow cytometric crossmatch technique (XM-ONE) using peripheral blood endothelial progenitor cells as targets. Patient enrolment was based on acceptance for transplantation determined by donor lymphocyte crossmatch results. Donor-reactive AECA were found in 35 of 147 (24%) patients. A significantly higher proportion of patients with a positive ECXM had rejections (16 of 35, 46%) during the follow-up of at least 3 months compared with those without AECA (13 of 112, 12%; P<0.00005). Both IgG and IgM AECAs were associated with graft rejections. Mean serum creatinine levels were significantly higher in patients with a positive ECXM test at 3 and 6 months posttransplant. XM-ONE is quick, easy to perform on whole blood samples and identifies patients at risk for rejection and reduced graft function not identified by conventional lymphocyte crossmatches.

Vascular damage in Wegener’s granulomatosis and microscopic polyarteritis: presence of anti-endothelial cell antibodies and their relation to anti-neutrophil cytoplasm antibodies

To define mechanisms of vascular injury in Wegener's granulomatosis and microscopic polyarteritis, anti-endothelial cell antibodies (AECA) were sought in serum from 168 patients, all of whom had anti-neutrophil cytoplasm antibodies (ANCA) detectable by indirect immunofluorescence. Using an ELISA with human umbilical vein endothelial cells (HUVEC), IgG AECA were demonstrated in 59% and IgM AECA in 68% of patients. Pretreatment of HUVEC with tumour necrosis factor (TNF), IL-1 or interferon-gamma (IFN-gamma) led to increased binding. Adsorption of AECA/ANCA-containing serum with HUVEC or neutrophils demonstrated that AECA and ANCA recognized different targets. von Willebrand factor (vWf) antigen levels in the patient samples were markedly elevated, with a mean of 3.10 +/- 1.89 U/ml (control population mean 1.04 +/- 0.36 U/ml), suggesting widespread endothelial cell damage. Studies using an 111In-labelled HUVEC release assay with 29 AECA-containing sera did not demonstrate complement-mediated cytotoxicity, even following activation of HUVEC with TNF. Four out of 16 AECA-containing sera tested showed antibody-dependent cellular cytotoxicity with unfractionated peripheral blood mononuclear cells. These data suggest that patients with Wegener's granulomatosis or microscopic polyarteritis can develop AECA to constitutively expressed but cytokine modulated determinants on HUVEC. These antibodies do not appear to support complement-mediated cytotoxicity, but a proportion can support antibody-dependent cellular cytotoxicity, suggesting that they may contribute to vascular injury.

Antiendothelial cell antibodies can be cytotoxic to endothelial cells without cytokine pre-stimulation and correlate with ELISA antibody measurement in Kawasaki disease.

To confirm the presence of antiendothelial cell antibodies (AECA) and study the clinical value of their measurement in Kawasaki disease (KD), sera from patients with KD were assessed for binding to human umbilical vein endothelial cells (HUVEC) using a cellular based ELISA, and for complement-mediated cytotoxicity using 111In-labelled HUVEC. In the ELISA assay, IgM AECA were detected in 16/22 sera, whereas IgG AECA were only present in one out of 19 sera. There was a significant difference in IgM AECA titres when comparing patients with controls. Eight out of 16 sera showed cytotoxicity against HUVEC, and this was significantly enhanced when HUVEC were pretreated with tumour necrosis factor (TNF). IgM AECA titres measured by ELISA were positively correlated with their cytotoxicity. The findings suggest that IgM class AECA in sera from patients with KD are detectable by ELISA method, and that some of these antibodies, 50% in this study, can mediate complement-dependent cytotoxicity against endothelial cells.

Antibodies to endothelial cells in Kawasaki disease lyse endothelial cells without cytokine pretreatment.

Kawasaki disease (KD) is characterized by diffuse vasculitis and marked immune activation. To confirm the presence of antiendothelial cell antibodies (AECA) and cytotoxicity of AECA, we investigated the presence of AECA using ELISA and cytotoxicity of AECA in KD. Sera from patients with acute KD were assessed for binding to human umbilical vein endothelial cells (HUVEC) using a cell-based ELISA, and for cytotoxicity against HUVEC as indicated by the conversion of a tetrazolium salt (MTT) into a coloured product. IgM AECA were detected in 8/19 KD sera, IgG AECA were detected in 5/19 KD sera. Significant differences in both AECA titres existed between patients and febrile and afebrile controls. Six out of 19 patients showed complement-dependent cytotoxicity against HUVEC. Cytotoxicity was significantly enhanced by pretreating HUVEC with tumour necrosis factor (TNF), and reduced by incubation with gammaglobulin. Serum titres of IgM AECA in the KD patients were positively correlated with cytotoxicity. Findings suggest that IgM AECA mediates complement-dependent cytotoxicity against endothelial cells in patients with KD, and gammaglobulin may reduce complement-dependent cytotoxicity of AECA against endothelial cells.

Anti-endothelial cell antibodies to the endothelial hybridoma cell line (EAhy926) in systemic lupus erythematosus patients with antiphospholipid antibodies.

The endothelial hybridoma (EAhy926) cell line was employed to clarify whether antiphospholipid antibodies (aPA) [lupus anticoagulant (LA), antiprothrombin antibody (aPT) and/or anticardiolipin antibody (aCL)] and anti-endothelial cell antibodies (AECA) are identical, and establish whether beta2-glycoprotein I (beta2-GPI) is needed for reactivity of aPA to endothelial cells. Ig-G AECA was positive in 9/30 SLE patients with aPA (30.0%) and 10/22 SLE patients negative for aPA (45.5%). Ig-M AECA was positive in one SLE patient with aPA and one SLE patient without aPA. AECA-positivity was not significantly different among unfixed, TNF-stimulated and fixed EAhy926. The influence of beta2-GPI on the reactivity of serum to EAhy926 was minimal, and absorption experiments of serum with cardiolipin-liposome/beta2-GPI or phosphatidylserine-liposome/prothrombin gave little evidence of cross-reactivity of aPA and AECA. The results of our study suggest that aPA and AECA may have partially cross-reacted, but were different antibodies. However, further study is needed to clarify the clinico-pathological significance of AECA.

Endothelin-1 release from cultured endothelial cells induced by sera from patients with systemic lupus erythematosus.

To clarify the pathophysiological role of endothelin-1 (ET-1) in the vascular injury associated with systemic lupus erythematosus (SLE) by investigating the effect of sera from patients with SLE on ET-1 release from cultured human umbilical vein endothelial cells. Confluent monolayers of cultured human umbilical vein endothelial cells were incubated with serum samples (diluted 1:10) from 25 patients with SLE and 16 normal controls for two hours at 37 degrees C and ET-1 concentration in the culture supernatant was measured by enzyme immunoassay. The mean release of ET-1 from endothelial cells in the presence of serum from SLE patients was greater than in the presence of serum from normal controls (p < 0.005). ET-1 release from endothelial cells significantly correlated with the titre of IgM anti-endothelial cell antibodies (IgM-AECA) and immune complex concentration in sera from SLE patients (p < 0.05 and p < 0.01, respectively). After gel chromatography of the serum from an SLE patient, those fractions containing IgM-AECA or immune complex were shown to stimulate ET-1 release from endothelial cells. Heat aggregated IgG also stimulated ET-1 release from endothelial cells in a concentration dependent manner. IgM-AECA and immune complexes may stimulate ET-1 release from endothelial cells and ET-1 may play an important role in the initiation and development of vascular injury, such as pulmonary hypertension and lupus nephritis, in SLE.

Antibodies to Endothelial Cells in Patients with Behçet's Disease

Autoantibodies that bind to endothelial cells have been identified in patients with several forms of vasculitis. Behçet's disease—a multisystem inflammatory disorder of unknown etiology—is associated with thrombosis in addition to systemic manifestations resulting from small and large vessel vasculitis. We studied 72 Turkish patients (33 female, 39 male) with Behçet's disease in order to investigate the prevalence of antiendothelial cell antibodies (AECA) and to examine their possible relationship with clinical and laboratory features of the illness. Sera from 30 healthy Turkish people were used as controls. Human umbilical vein endothelial cells were cultured and used unfixed in a cellular ELISA to detect AECA. IgG and/or IgM AECA were found in 13 (18.1%) patients but not in healthy controls. Antiendothelial cell antibodies did not induce complement-mediated cytotoxicity as assessed by 51Cr release assay and the binding was not due to immune complexes. The prevalences of acute thrombotic events and retinal vasculitis at the time of the AECA assay among patients with AECA were significantly higher than those in patients without AECA. Laboratory parameters of active disease were higher in patients with AECA. There was no correlation between other clinical and laboratory features of Behçet's disease and AECA. Anticardiolipin and antineutrophil cytoplasmic antibodies were negative in our series, excluding a possibility of crossreaction with AECA. Our results suggest a possible role of AECA in association with thrombosis and vasculitis in patients with Behçet's disease.

Antiendothelial Cell Antibodies in Patients with the Antiphospholipid Syndrome

Antiendothelial cell antibodies (AECA) have been detected in 20 out of 30 patients (67%) with thrombosis associated with antiphospholipid antibodies. Seven patients had systemic lupus erythematosus and 13 had the "primary" antiphospholipid syndrome. Seven patients had both IgG and IgM AECA, 9 had IgG AECA only, and 4 had only IgM AECA. None of 30 control patients with thrombotic events not related to antiphospholipid antibodies had a positive titre of AECA (P less than 0.001). No correlation between AECA, antinuclear antibodies, anti-dsDNA antibodies, anti-neutrophil cytoplasm antibodies, precipitating antibodies to soluble nuclear and cytoplasmic antigens or complement components was found. The possible role of these AECA in the pathogenesis of thrombotic events is discussed.

IgG and IgM anti-endothelial cell antibodies in patients with collagen-vascular disorders

A cellular enzyme-linked immunosorbent assay (ELISA) was used to detect circulating anti-endothelial cell antibodies (AECA) in sera of patients suffering from rheumatoid arthritis (RA). Felty's syndrome (FS), systemic lupus erythematosus (SLE), progressive systemic sclerosis (PSS) and those with a "lupus anticoagulant" (LA). IgG AECA were detected in RA, FS, SLE and LA sera, while IgM AECA were only detected in RA and FS. AECA were not specific for endothelial cells. However, IgG binding to endothelial cells and dermal fibroblasts was F(ab) mediated while in all other cell types tested, nonspecific binding most likely via the Fc region occurred. In RA and FS rheumatoid factor was shown to augment immunoglobulin binding to endothelial cells. Additional studies revealed that some of these pathological sera also contained cytotoxic IgG autoantibodies which fixed complement and damaged human umbilical vein endothelial cells in vitro. These studies suggest that a group of autoantibodies, present in a variety of collagen vascular disorders, react with endothelial cells and thus may be important aetiopathogenic factors in the vasculopathies associated with these disorders.

Anti-endothelial cell antibodies: detection and characterization using a cellular enzyme-linked immunosorbent assay.

Anti-endothelial cell antibodies (AECA) have been detected in autoimmune diseases such as systemic lupus erythematosus (SLE) and scleroderma (PSS) but their role in pathogenesis is unknown. Immunofluorescence, immunohistochemistry, complement-dependent antibody lysis, and radioimmunoassay have been used in the past to detect AECA. We have developed a rapid, sensitive, and quantitative cellular enzyme-linked immunosorbent assay (ELISA) to detect and characterize AECA. Sera were obtained from 28 normal volunteers, 28 patients with SLE, and 14 patients with PSS. We also performed studies in 47 patients with various monoclonal gammopathies. Endothelial cells (EC) were obtained from human umbilical veins by standard methods and subcultured on 96-well tissue culture plates without fixation. EC were then sequentially incubated with sera, peroxidase-conjugated goat anti-human Ig (IgG, IgM, or IgA), and substrate. Optical density readings were converted to arbitrary units by developing a standard curve. Heavy-chain specific antibodies were used to determine the class of AECA binding to EC. IgG was purified by using protein A columns and digested with pepsin to obtain F(ab')2 fragments. The mean units of AECA from normals were 19.3 for IgG and 12.5 for IgM. SLE sera showed significant levels of IgM AECA (37 units, P less than 0.001) but not IgG (29 units, P less than 0.1). PSS sera showed significant levels of both IgM AECA (38 units, P = 0.001) and IgG AECA (42.7 units, P less than 0.005). IgA AECA were not detected in normal, SLE, or PSS sera. Blocking Fc receptors with rabbit IgG did not affect the titer of IgG or IgM AECA.(ABSTRACT TRUNCATED AT 250 WORDS)