Are autoantibodies triggering endothelial cell apoptosis really pathogenic?

Pathogenesis of large vessel vasculitis: Implications for disease classification and future therapies

Despite being recognised over a century ago, the aetiology and pathogenesis of large vessel vasculitis (LVV) still remains elusive. Takayasu’s arteritis (TA) and giant cell arteritis (GCA) represent the two major categories of LVV, each with distinctive clinical features. Over the last 10 years an increased understanding of the immunopathogenesis of the inflammatory cascade within the aortic wall has revived the view that LVVs may represent subtypes of the same pathological process, with implications in the treatment of this disease. In this review, the histological, genetic and immunopathological features of TA and GCA will be discussed and the evidence for a common underlying disease mechanism examined. Novel markers of disease activity and therapies based on advances in our understanding of the immunopathogenesis of these conditions will also be discussed.

Anti-ribosomal-phosphoprotein autoantibodies penetrate to neuronal cells via neuronal growth associated protein, affecting neuronal cells in vitro

OBJECTIVE

Anti-ribosomal-phosphoprotein antibodies (anti-Ribos.P Abs) are detected in 10-45% of NPSLE patients. Intracerebroventricular administration of anti-ribosomal-P Abs induces depression-like behaviour in mice. We aimed to discern the mechanism by which anti-Ribos.P Abs induce behavioural changes in mice.

METHODS

Anti-Ribos.P Abs were exposed to human and rat neuronal cell cultures, as well as to human umbilical vein endothelial cell cultures for a control. The cellular localization of anti-Ribo.P Abs was found by an immunofluorescent technique using a confocal microscope. Identification of the target molecules was undertaken using a cDNA library. Immunohistochemistry and an inhibition assay were carried out to confirm the identity of the target molecules. Neuronal cell proliferation was measured by bromodeoxyuridine, and Akt and Erk expression by immunoblot.

RESULTS

Human anti-Ribos.P Abs penetrated into human neuronal cells and rat hippocampal cell cultures in vitro, but not to endothelial cells as examined. Screening a high-content human cDNA-library with anti-Ribos.P Abs identified neuronal growth-associated protein (GAP43) as a target for anti-Ribos.P Abs. Ex vivo anti-Ribos.P Abs bind to mouse brain sections of hippocampus, dentate and amygdala. Anti-Ribos.P Abs brain-binding was prevented by GAP43 protein. Interestingly, GAP43 inhibited in a dose-dependent manner the anti-Ribos.P Abs binding to recombinant-ribosomal-P0, indicating mimicry between the ribosomal-P0 protein and GAP43. Furthermore, anti-Ribos.P Abs reduced neuronal cell proliferation activity in vitro (P < 0.001), whereas GAP43 decreased this inhibitory activity by a factor of 7.6. The last was related to Akt and Erk dephosphorylation.

CONCLUSION

Anti-Ribos.P Abs penetrate neuronal cells in vitro by targeting GAP43. Anti -Ribos.P Abs inhibit neuronal-cell proliferation via inhibition of Akt and Erk. Our data contribute to deciphering the mechanism for anti-Ribos.P Abs' pathogenic activity in NPSLE.

Sex differences at cellular level: "cells have a sex"

Different pathways involved in the complex machinery implicated in determining cell fate have been investigated in the recent years. Different forms of cell death have been described: apart from the "classical" form of death known as necrosis, a well characterized traumatic injury of the cell, several additional forms of cell death have been identified. Among these, apoptosis has been characterized in detail. These studies stem from the implication that the apoptotic process plays a key role in a plethora of human pathologies, including cardiovascular diseases. In fact, defects in the mechanisms of cell death, i.e., both an increase or a decrease of apoptosis, have been associated with the pathogenesis of vessel and myocardial diseases. Some new insights also derived from the study of autophagy, a less characterized form of cell damage mainly associated with cell survival strategies but that also leads, as final event, to the death of the cell. Interestingly, very recently, a gender difference has been found in this respect: cells from males and females can behave differently. In fact, they seem to display several different features, including those determining their fate. These gender cytology differences are briefly described here. The study of this gender disparity is of great relevance in cardiovascular disease pathogenesis and pharmacology. The comprehension of the gender-related mechanisms of cell demise can in fact disclose new scenarios in preclinical and clinical management of cardiovascular diseases.

Immunology, autoimmunity, and autoantibodies in Parkinson's disease

Recent revelations of immune alterations in Parkinson's disease have led to the convergence that an autoimmune mechanism may play a role in the etiopathogenesis of this neurodegenerative disease. In the current study, 77 Parkinson's disease patients and 77 matched healthy controls were analyzed for the presence of seven autoantibodies previously found to be associated with central nervous system manifestations namely: antineuronal-cells, anti-brain lysate, anti-dsDNA, anti-phosphatidylserine, anti-cardiolipin, anti-serotonin, and anti-melanocytes antibodies. Patients underwent systematic assessments of demographics, clinical, and biochemical manifestations. Three autoantibodies were found to be more prevalent among Parkinson's disease patients (antineuronal cells10.3% vs. 1.3%, p = 0.017; anti-brain lysate 9.1% vs. 1.3%, p = 0.032; anti-dsDNA 10.3% vs. 2.6%, p = 0.049). Clinical manifestations of Parkinson's disease, particularly dyskinesia and depression, were found to be associated with the presence of these autoantibodies.

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.

Gender disparity in susceptibility to oxidative stress and apoptosis induced by autoantibodies specific to RLIP76 in vascular cells

AIM

Ral-binding protein 1 (RLIP76) is a cell surface protein that catalyzes the extrusion from the cell of reduced glutathione (GSH) conjugates. We recently demonstrated the presence of serum antibodies to RLIP76 (aaRLIP76) in patients with immune-mediated diseases characterized by vascular dysfunction. The aim of this work was to analyze the possible implication of gender in this issue, investigating the effects of aaRLIP76 in rat vascular smooth muscle cells and human endothelial cells from males and females.

RESULTS

We observed that, after aaRLIP76 treatment, vascular cells from females showed a significantly higher susceptibility to the disturbance of intracellular redox balance, in terms of H(2)O(2) and O(2)(*) production, 4-hydroxy-t-2,3-nonenal and GSH levels, C-Jun NH2 kinase signaling activation, and apoptosis in comparison with cells from males. Interestingly, under mild oxidative stress (H(2)O(2) 30 μm for 30 min), these sex-associated differences became significantly more pronounced. Experiments carried out in the presence of sex hormones in the culture medium clearly suggested that estrogens could significantly increase the susceptibility of cells from females to the effects of aaRLIP76, whereas cells from males appeared unaffected.

INNOVATION

These results open a new perspective in the gender-dependent pathogenic mechanisms of autoimmune diseases characterized by vascular dysfunction.

CONCLUSIONS

Altogether these results suggest that the impairment of RLIP76 by aaRLIP76 can play a role in the damage of vascular cells from females, contributing to the gender-associated pathogenesis of immune-mediated vascular diseases.

Pathogenesis of Takayasu's arteritis: a 2011 update

While our knowledge of the pathogenesis of Takayasu's arteritis (TA) has considerably improved during the last decade, the exact pathogenic sequence remains to be elucidated. It is now hypothesised that an unknown stimulus triggers the expression of the 65kDa Heat-shock protein in the aortic tissue which, in turn, induces the Major Histocompatibility Class I Chain-Related A (MICA) on vascular cells. The γδ T cells and NK cells expressing NKG2D receptors recognize MICA on vascular smooth muscle cells and release perforin, resulting in acute vascular inflammation. Pro-inflammatory cytokines are released and increase the recruitment of mononuclear cells within the vascular wall. T cells infiltrate and recognize one or a few antigens presented by a shared epitope, which is associated with specific major Histocompatibility Complex alleles on the dendritic cells, these latter being activated through Toll-like receptors. Th1 lymphocytes drive the formation of giant cells through the production of interferon-γ, and activate macrophages with release of VEGF resulting in increased neovascularisation and PDGF, resulting in smooth muscle migration and intimal proliferation. Th17 cells induced by the IL-23 microenvironnement also contribute to vascular lesions through activation of infiltrating neutrophils. Although still controversial, dendritic cells may cooperate with B lymphocytes and trigger the production of anti-endothelial cell auto-antibodies resulting in complement-dependent cytotoxicity against endothelial cells. In a near future, novel drugs specifically designed to target some of the pathogenic mechanisms described above could be expanding the physician's therapeutic arsenal in Takayasu's arteritis.

Antiendothelial cell antibodies in patients with coronary artery ectasia

BACKGROUND

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.

METHODS AND RESULTS

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).

CONCLUSION

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.

Comparative assessment of vascular function in autoimmune rheumatic diseases: considerations of prevention and treatment

Numerous autoimmune-inflammatory rheumatic diseases have been associated with accelerated atherosclerosis or other types of vasculopathy leading to increased cardio- and cerebrovascular disease risk. Traditional risk factors, as well as the role of systemic inflammation including cytokines, chemokines, proteases, autoantibodies, adhesion receptors and others have been implicated in the development of these vascular pathologies. The characteristics of vasculopathies may significantly differ depending on the underlying disease. While classical accelerated atherosclerosis has been associated with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) or spondyloarthropathies (SpA), obliterative vasculopathy may rather be characteristic for systemic sclerosis (SSc) or mixed connective tissue disease (MCTD). Antiphospholipid antibodies have been implicated in vasculopathies underlying SLE, antiphospholipid syndrome (APS), RA and MCTD. There is also heterogeneity with respect to inflammatory risk factors. Cytokines, such as tumor necrosis factor-α (TNF-α) or interleukin 6 (IL-6) and immune complexes are primarily involved in arthritides, such as RA, SpA, as well as in SLE. On the other hand, autoantibodies including anti-oxLDL anti-cardiolipin and anti-β2GPI are rather involved in SLE- and APS-associated vasculopathies. Regarding the non-invasive assessment of vascular function, endothelial dysfunction, overt atherosclerosis and vascular stiffness may be indicated by brachial artery flow-mediated vasodilation (FMD), common carotid intima-media thickness (ccIMT) and aortic pulse-wave velocity (PWV), respectively. These abnormalities have been described in most inflammatory rheumatic diseases. While ccIMT and stiffness are relatively stable, FMD may be influenced by many confounding factors. In addition to traditional vasculoprotection, immunosuppressive agents including corticosteroids, traditional and biologic DMARDs may have significant vascular and metabolic effects. The official EULAR recommendations on the assessment and management of cardiovascular disease in arthritides have just been published, and similar recommendations in connective tissue diseases are to be developed soon.

Coagulation and autoimmunity in scleroderma interstitial lung disease

OBJECTIVES

Interstitial lung disease in systemic sclerosis (SSc-ILD) is often an irreversible and progressive fibrosing process that now is the leading cause of scleroderma-related deaths. In this review we present our current understanding of the role played by coagulation and particularly by thrombin in autoimmune-mediated tissue injury and fibrosis, mainly as it relates to SSc-ILD.

METHODS

We used PubMed to search for articles published up to October 2010 for keywords referring to autoimmunity, coagulation, pulmonary fibrosis, and scleroderma.

RESULTS

SSc-ILD is an autoimmune disease associated with lymphocyte activation and release of various cytokines and growth factors. The production of autoantibodies is a central feature in SSc. Activation of the coagulation cascade with release of thrombin is 1 of the earliest events following tissue injury. Thrombin contributes to autoimmune responses by activating of pathogenic Th2 lymphocyte profile in SSc. Thrombin also modulates tissue repair responses, stimulates transformation of epithelial cells, endothelial cells, and fibroblasts into myofibroblast phenotype, and induces secretion of several pro-immune and profibrotic factors, which serve as antigens for pathogenic autoantibodies production in SSc-ILD.

CONCLUSIONS

The identification of links between autoimmunity and coagulation would provide new insights into the pathogenesis of pulmonary fibrosis associated with autoimmune diseases and further acknowledge the importance of thrombin in the development of SSc-ILD.

IVIg modulates BCR signaling through CD22 and promotes apoptosis in mature human B lymphocytes

Among various mechanisms for interactions with B cells, intravenous immunoglobulin (IVIg) may operate through the insertion of its Fc part into the Fc-γ receptor, or the binding of its sialic acid (SA)–bearing glycans to the negatively regulating CD22 lectin. It appeared that IVIg reduces B lymphocyte viability in a dose- and time-dependent manner. Furthermore, we show by confocal microscopy that SA-positive IgG, but not SA-negative IgG bind to CD22. This interaction reduces the strength of B-cell receptor–mediated signaling trough down-regulating tyrosine phosphorylation of Lyn and the B-cell linker proteins, and up-regulating phospholipase Cγ2 activation. This cascade resulted in a sustained activation of Erk 1/2 and arrest of the cell cycle at the G1 phase. These changes may be accounted for the efficacy of IVIg in autoimmune diseases.

Anti-endothelial cell antibodies are increased in patients with previous myocardial infarction

OBJECTIVES

Atherosclerosis is an inflammatory disease of multifactorial origin, in which immune cells together with metabolic risk factors may initiate, propagate, and activate lesions in the arterial tree. We investigated the role of auto-antibodies against endothelial cells in patients with previous myocardial infarction.

DESIGN

One hundred and four patients were studied four to five years after acute myocardial infarction (aged 36-84 years) and 83 sex-matched healthy controls (aged 32-70 years). Anti-endothelial cells IgM and IgG auto-antibodies (AECA) were quantified in plasma using flow cytometry.

RESULTS

IgM and IgG AECA were significantly higher (23.08 ± 0.81 and 10.63 ± 0.31 channel shifts, respectively; p < 0.001) in patients as compared to controls (13.40 ± 0.95 and 3.53 ± 0.54 channel shifts, respectively). Further, patients who got an invasive treatment had significantly higher levels of AECA as compared to patients with only medical treatment. Plasma concentration of IgG was positively (p < 0.05) correlated to the levels of high-sensitivity C-reactive protein (hsCRP).

CONCLUSIONS

We report for the first time evidence that AECA are related to signs of inflammation and are increased in patients with atherosclerosis and previous myocardial infarction and with further increase with severity of disease.

Pathogenesis of giant cell arteritis: More than just an inflammatory condition?

Giant cell arteritis (GCA) is characterized by intimal hyperplasia and luminal obstruction leading to ischemic manifestations involving extra-cranial branches of carotid arteries and aorta. Histopathological lesions involve all layers of the arterial wall and are associated with multinucleated giant cells, fragmented internal elastic lamina and polymorphic cellular infiltrates, including T lymphocytes and macrophages. The pathophysiology of GCA is still poorly understood. After dendritic cell activation, CD4(+) T lymphocytes, T helper 1 (Th1) cells, produce interferon gamma and modulate macrophage activation and functions, and Th17 cells produce interleukin 17 (IL-17), which can induce cytokine production by macrophages and fibroblasts. Macrophages in the adventitia produce pro-inflammatory cytokines such as IL-1, IL-6 and tumor necrosis factor alpha. These cytokines promote arterial wall and systemic inflammation. Questions remain regarding the nature of the antigen(s) triggering dendritic cell activation and the mechanisms underlying vascular remodeling. Here we review recent advances in the pathogenesis of GCA, with emphasis on the interactions between cells of the immune system and components of the vessel wall, including vascular smooth muscle cells and endothelial cells, leading to vascular remodeling. Finally, we propose new areas of investigation that could help understand the triggering factors and key pathogenic events in GCA.