Murine monoclonal anti-DNA antibodies penetrate cells, bind to nuclei, and induce glomerular proliferation and proteinuria in vivo

An Emerging Role for Anti-DNA Antibodies in Systemic Lupus Erythematosus

Anti-DNA antibodies are hallmark autoantibodies produced in systemic lupus erythematosus (SLE), but their pathogenetic role is not fully understood. Accumulating evidence suggests that some anti-DNA antibodies enter different types of live cells and affect the pathophysiology of SLE by stimulating or impairing these cells. Circulating neutrophils in SLE are activated by a type I interferon or other stimuli and are primed to release neutrophil extracellular traps (NETs) on additional stimulation. Anti-DNA antibodies are also involved in this process and may induce NET release. Thereafter, they bind and protect extracellular DNA in the NETs from digestion by nucleases, resulting in increased NET immunogenicity. This review discusses the pathogenetic role of anti-DNA antibodies in SLE, mainly focusing on recent progress in the two research fields concerning antibody penetration into live cells and NETosis.

SB431542 alleviates lupus nephritis by regulating B cells and inhibiting the TLR9/TGFβ1/PDGFB signaling

Lupus nephritis (LN) is the most common cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Currently, immunosuppressive treatments for LN are suboptimal and can induce significant side effects. SB431542 is a selective and potent inhibitor of the TGFβ/Activin/NODAL pathway. Here, we study the effects of SB431542 treatment on LN and discuss the potential mechanisms. SB431542 ameliorated clinical outcomes with a consequent histological improvement in NZB/W mice. A comparative transcriptional profiling analysis revealed 586 differentially expressed genes (247 downregulated genes) in the SB431542 group compared to the control group. We found that the downregulated genes were mainly enriched in the biological processes of B cell activation, B cell proliferation, B cell differentiation, and B cell receptor signaling. Kyoto encyclopedia of genes and genomes pathway analysis revealed that the hematopoietic cell linage pathway was significantly downregulated in the SB431542 group. In addition, we observed that SB431542 reduced the splenic or renal levels of CD20 and the serum levels of anti-dsDNA antibody (IgG) in NZB/W mice. Furthermore, qRT-PCR and immunohistochemistry confirmed that SB431542 inhibits the production of TLR9, TGFβ1, and PDGFB. Thus, due to its immunomodulatory activities, SB431542 could be considered for clinical therapy development for LN.

Can Antinuclear Antibodies Have a Pathogenic Role in Systemic Sclerosis?

Systemic sclerosis (SSc) is a connective tissue disease characterized by extensive fibrosis of the skin and internal organs, associated with vasculopathy and autoimmune features. Antinuclear antibodies (ANA) are found in almost all SSc patients and constitute strong diagnosis and prognosis biomarkers. However, it remains unclear whether ANA are simple bystanders or if they can have a role in the pathophysiology of the disease. One might think that the nuclear nature of their targets prevents any accessibility to autoantibodies. Nevertheless, recent data suggest that ANA could be pathogenic or at least contribute to the perennation of the disease. We review here first the indirect clues of the contribution of ANA to SSc: they are associated to the disease subtypes, they may precede disease onset, their titer correlates with disease activity and severity, there is an association between molecular subsets, and some patients can respond to B-cell targeting therapy. Then, we describe in a second part the mechanisms of ANA production in SSc from individual genetic background to post-transcriptional modifications of neoantigens. Finally, we elaborate on the potential mechanisms of pathogenicity: ANA could be pathogenic through immune-complex-mediated mechanisms; other processes potentially involve molecular mimicry and ANA penetration into the target cell, with a focus on anti-topoisomerase-I antibodies, which are the most probable candidate to play a role in the pathophysiology of SSc. Finally, we outline some technical and conceptual ways to improve our understanding in this field.

Pathophysiological Mechanisms and Treatment of Dermatomyositis and Immune Mediated Necrotizing Myopathies: A Focused Review

Idiopathic inflammatory myopathies (IIM), collectively known as myositis, are a composite group of rare autoimmune diseases affecting mostly skeletal muscle, although other organs or tissues may also be involved. The main clinical feature of myositis is subacute, progressive, symmetrical muscle weakness in the proximal arms and legs, whereas subtypes of myositis may also present with extramuscular features, such as skin involvement, arthritis or interstitial lung disease (ILD). Established subgroups of IIM include dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASyS), overlap myositis (OM) and inclusion body myositis (IBM). Although these subgroups have overlapping clinical features, the widespread variation in the clinical manifestations of IIM suggests different pathophysiological mechanisms. Various components of the immune system are known to be important immunopathogenic pathways in IIM, although the exact pathophysiological mechanisms causing the muscle damage remain unknown. Current treatment, which consists of glucocorticoids and other immunosuppressive or immunomodulating agents, often fails to achieve a sustained beneficial response and is associated with various adverse effects. New therapeutic targets have been identified that may improve outcomes in patients with IIM. A better understanding of the overlapping and diverging pathophysiological mechanisms of the major subgroups of myositis is needed to optimize treatment. The aim of this review is to report on recent advancements regarding DM and IMNM.

Nanobodies as molecular imaging probes

Camelidae derived single-domain antibodies (sdAbs), commonly known as nanobodies (Nbs), are the smallest antibody fragments with full antigen-binding capacity. Owing to their desirable properties such as small size, high specificity, strong affinity, excellent stability, and modularity, nanobodies are on their way to overtake conventional antibodies in terms of popularity. To date, a broad range of nanobodies have been generated against different molecular targets with applications spanning basic research, diagnostics, and therapeutics. In the field of molecular imaging, nanobody-based probes have emerged as a powerful tool. Radioactive or fluorescently labeled nanobodies are now used to detect and track many targets in different biological systems using imaging techniques. In this review, we provide an overview of the use of nanobodies as molecular probes. Additionally, we discuss current techniques for the generation, conjugation, and intracellular delivery of nanobodies.

Rituximab in the Treatment of Interstitial Lung Diseases Related to Anti-Melanoma Differentiation-Associated Gene 5 Dermatomyositis: A Systematic Review

Objective

The effectiveness of rituximab in anti-melanoma differentiation-associated gene 5 (MDA5) dermatomyositis (DM) with interstitial lung disease (ILD) has been explored only in isolated case reports and small series. This paper aims to review the current evidence regarding rituximab (RTX) use in the treatment of ILD related to anti-MDA5 DM (anti-MDA5 DM-ILD).

Methods

We conducted a review by searching PubMed, Web of Science, Embase, and Cochrane for articles with information on patients with anti-MDA5 DM and RTX treatment, published until August 2021, in English language. The selected studies listed variation in chest high-resolution computed tomography (HRCT) and/or pulmonary function test (PFT) as a primary outcome, in patients with anti-MDA5 DM-related ILD after using RTX.

Results

Of the 145 potentially eligible articles, 17 were selected. The information gathered from a total of 35 patients with anti-MDA5 DM-ILD was reviewed, including 13 men and 22 women. Patient age at onset was 47.60 ± 13.72 years old. A total of 11.43% (4/35) of the patients were found to have chronic ILD (C-ILD) and 88.57% (31/30) exhibited rapidly progressive ILD (RP-ILD). Most patients (29/30) had typical DM rashes. Prior to RTX administration, the majority of patients (27/35) were treated with medium- or high-dose glucocorticoids and at least one additional immunotherapeutic agent. With regard to RTX efficacy for ILD in anti-MDA5 DM, 71.43% (25/35) of the patients responded to treatment. Skin rash also improved in more than half of the patients after RTX treatment. The most common side effects were infections, reported by 37.14% (13/35) of the patients after using RTX.

Conclusion

As a CD20 targeting drug, RTX is a promising therapeutic tool for anti-MDA5 DM-ILD, although the risk of infections should be considered before treatment. Further prospective controlled studies are required to evaluate the optimal RTX treatment regimen.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021289714, identifier CRD42021289714.

Dermatomyositis With Anti-MDA5 Antibodies: Bioclinical Features, Pathogenesis and Emerging Therapies

Anti-MDA5 dermatomyositis is a rare systemic autoimmune disease, historically described in Japanese patients with clinically amyopathic dermatomyositis and life-threatening rapidly progressive interstitial lung disease. Subsequently, the complete clinical spectrum of the disease was enriched by skin, articular and vascular manifestations. Depending on the predominance of these symptoms, three distinct clinical phenotypes with different prognosis are now defined. To date, the only known molecular component shared by the three entities are specific antibodies targeting MDA5, a cytosolic protein essential for antiviral host immune responses. Several biological tools have emerged to detect these antibodies, with drawbacks and limitations for each of them. However, the identification of this highly specific serological marker of the disease raises the question of its role in the pathogenesis. Although current knowledge on the pathogenic mechanisms that take place in the disease are still in their enfancy, several lines of evidence support a central role of interferon-mediated vasculopathy in the development of skin and lung lesions, as well as a possible pathogenic involvement of anti-MDA5 antibodies. Here, we review the clinical and biological evidences in favor of these hypothesis, and we discuss the contribution of emerging therapies that shed some light on the pathogenesis of the disease.

Systemic lupus erythematosus (SLE): emerging therapeutic targets

INTRODUCTION

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with a heterogeneous clinical presentation whose etiologies are multifactorial. A myriad of genetic, hormonal, immunologic, and environmental factors contribute to its pathogenesis, and its diverse biological basis and phenotypic presentations make development of therapeutics difficult. In the past decade, tens of therapeutic targets with hundreds of individual candidate therapeutics have been investigated.

AREAS COVERED

We used a PUBMED database search through April 2020 to review the relevant literature. This review discusses therapeutic targets in the adaptive and innate immune systems, specifically: B cell surface antigens, B cell survival factors, Bruton's tyrosine kinase, costimulators, IL-12/IL-23, the calcineurin pathway, the JAK/STAT pathway, and interferons.

EXPERT OPINION

Our ever-improving understanding of SLE pathophysiology in the past decade has allowed us to identify new therapeutic targets. Multiple new drugs are on the horizon that target different elements of the adaptive and innate immune systems. SLE research remains challenging due to the heterogenous clinical presentation of SLE, confounding from background immunosuppressives being taken by SLE patients, animal models that inadequately recapitulate human disease, and imperfect and complicated outcome measures. Despite these limitations, research is promising and ongoing. The search for new therapies that target specific elements of SLE pathophysiology are discussed as well as key findings, pitfalls, and questions surrounding these targets.

Engineering Cell-Permeable Proteins through Insertion of Cell-Penetrating Motifs into Surface Loops

Effective delivery of proteins into the cytosol of mammalian cells would open the door to a wide range of applications. However, despite great efforts from numerous investigators, effective protein delivery in a clinical setting is yet to be accomplished. Herein we report a potentially general approach to engineering cell-permeable proteins by genetically grafting a short cell-penetrating peptide (CPP) to an exposed loop of a protein of interest. The grafted peptide is conformationally constrained, exhibiting enhanced proteolytic stability and cellular entry efficiency. Applying this technique to enhanced green fluorescent protein (EGFP), protein-tyrosine phosphatase 1B (PTP1B), and purine nucleoside phosphorylase (PNP) rendered all three proteins cell-permeable and biologically active in cellular assays. When added into growth medium at 0.5-5 μM concentrations, the engineered PTP1B dose-dependently reduced the phosphotyrosine levels of intracellular proteins, while the modified PNP corrected the metabolic deficiency of PNP-deficient mouse T lymphocytes, providing a potential enzyme replacement therapy for a rare genetic disease.

B-cell therapy in lupus nephritis: an overview

Systemic lupus erythematosus (SLE) is an autoimmune multisystem disease that commonly affects the kidneys. It is characterized by persistent autoantibody production that targets a multitude of self-antigens. B-cells, plasmablasts and plasma cells, as the source of these autoantibodies, play a major role in the development of lupus nephritis (LN), and are therefore promising therapeutic targets. To date, however, randomized clinical trials of B-cell therapies in LN have not lived up to expectations, whereas uncontrolled cohort and observational studies of B-cell antagonists have been more promising. In this article, we will review the current experience with B-cell therapy in LN and highlight the pitfalls that may have limited their success. We will conclude by suggesting B-cell-centric approaches to the management of LN based on what has been learned from the overall B-cell experience in SLE.

Dendritic cell-associated B7-H3 suppresses the production of autoantibodies and renal inflammation in a mouse model of systemic lupus erythematosus

B7-H3 immune modulatory molecule has been implicated in the generation and pathogenesis of autoimmune diseases, the mechanism of action is less known. We explored the role of B7-H3 in the induction of autoantibodies and organ-directed inflammation in a murine systemic lupus erythematosus (SLE) model in which the immunization with DNA extracted from activated T cells induced the production of anti-DNA autoantibodies and subsequent glomerulonephritis, two hallmarks of human SLE. Mice deficient of B7-H3 or treated with a B7-H3 specific antibody produced significantly higher levels of anti-DNA autoantibodies and more severe glomerulonephritis than wild-type mice, indicating an inhibitory function of B7-H3 in this model. Interestingly, immunization of mice with DNA-pulsed dendritic cells induced severe SLE symptoms while B7-H3 on dendritic cells is required in this process. Importantly, treatment of mice with recombinant B7-H3Ig fusion protein effectively ameliorated progression of murine SLE, accompanied with decreased level of anti-DNA autoantibodies and alleviated glomerulonephritis, decreased autoantibody deposition and complement deposition in kidney. Our findings implicate a potential role of B7-H3 on dendritic cells in the induction of SLE and as a potential target for the treatment of autoimmune diseases.

Delayed onset of autoreactive antibody production and M2-skewed macrophages contribute to improved survival of TACI deficient MRL-Fas/Lpr mouse

Anti-B cell activating factor belonging to TNF-family (BAFF) antibody therapy is indicated for the treatment of patients with active systemic lupus erythematosus (SLE). We hypothesized that the BAFF receptor, transmembrane activator and calcium-modulator and cyclophilin interactor (TACI) may be responsible for the generation of antibody secreting plasma cells in SLE. To test this hypothesis, we generated TACI deficient MRL-Fas/Lpr (LPR-TACI−/−) mouse. TACI deficiency resulted in improved survival of MRL-Fas/Lpr mice and delayed production of anti-dsDNA and anti-SAM/RNP antibodies. There was also a delay in the onset of proteinuria and the accumulation of IgG and inflammatory macrophages (Mϕs) in the glomeruli of young LPR-TACI−/− mice compared to wild-type mice. Underscoring the role of TACI in influencing Mϕ phenotype, the transfer of Mϕs from 12-week-old LPR-TACI−/− mice to age-matched sick wild-type animals led to a decrease in proteinuria and improvement in kidney pathology. The fact that, in LPR-TACI−/− mouse a more pronounced delay was in IgM and IgG3 autoreactive antibody isotypes and the kinetics of follicular helper T (Tfh) cell-development was comparable between the littermates suggest a role for TACI in T cell-independent autoantibody production in MRL-Fas/Lpr mouse prior to the onset of T cell-dependent antibody production.

Anti‑IL‑39 (IL‑23p19/Ebi3) polyclonal antibodies ameliorate autoimmune symptoms in lupus‑like mice

The interleukin (IL)-12 family cytokines have been examined as therapeutic targets in the treatment of several autoimmune diseases. Our previous study showed that a novel IL-12 family cytokine, IL-39 (IL-23p19/Ebi3) mediates inflammation in lupus-like mice. In the present study, the effect of anti-mouse IL-39 polyclonal antibodies on autoimmune symptoms in lupus-like mice was investigated. Rabbit anti-mouse IL-39 polyclonal antibodies were produced by immunization with recombinant mouse IL-39, and purified using protein A chromatography. These antibodies were subsequently used to treat lupus-like mice. Flow cytometry, captured images, ELISA and H&E staining were used to determine the effect of anti-IL-39 polyclonal antibodies on inflammatory cells, autoantibody titers, proteinuria, infiltrating inflammatory cells and the structure of the glomerular region. The anti-IL-39 polyclonal antibodies effectively reduced the numbers of inflammatory cells, splenomegaly, autoantibody titers, proteinuria, infiltrating inflammatory cells, and restored the structure of the glomerular region in MRL/lpr mice. Taken together, these results suggested that anti-IL-39 polyclonal antibodies ameliorated autoimmune symptoms in lupus-like mice. Therefore, IL-39 may be used as a possible target for the treatment of systemic lupus erythematosus.

TRIM21 and the Function of Antibodies inside Cells

Therapeutic antibodies targeting disease-associated antigens are key tools in the treatment of cancer and autoimmunity. So far, therapeutic antibodies have targeted antigens that are, or are presumed to be, extracellular. A largely overlooked property of antibodies is their functional activity inside cells. The diverse literature dealing with intracellular antibodies emerged historically from studies of the properties of some autoantibodies. The identification of tripartite motif (TRIM) 21 as an intracellular Fc receptor linking cytosolic antibody recognition to the ubiquitin proteasome system brings this research into sharper focus. We review critically the research related to intracellular antibodies, link this to the TRIM21 effector mechanism, and highlight how this work is exposing the previously restricted intracellular space to the potential of therapeutic antibodies.

IgG4 deposits in pure and combined membranous lupus nephritis

The aim of this study is to determine the frequency and prognosis of IgG4 deposits in renal biopsy of patients with membranous lupus nephritis (MLN). This is a retrospective cohort study in which we included patients with class V alone or combined (III/V or IV/V) of lupus nephritis according to the 2004 ISN/RPS. All the patients included must have availability of renal tissue for immunohistochemistry analyses. We excluded other classes of lupus nephritis. The renal tissue was examined by a nephro-pathologist. We included 65 patients with MLN; of these, 24 (37 %) were class V, and the other had proliferative concomitant with membranous patterns. Seven renal specimens had IgG4 deposits (10 %). Patients with IgG4 deposits had higher levels of eosinophils in serum. All of the patients with IgG4 had renal involvement as first manifestations of systemic lupus erythematosus. The rate of renal failure was 42 and 43 % in IgG4 positive and negative, respectively, 28 % of IgG4 required renal replacement therapy. From a histological view, 42 % of IgG4 had evidence of arteriolar vasculitis in renal biopsies. Lupus patients with IgG4 deposits were more likely to have renal involvement as a first manifestation of systemic lupus erythematosus, and they course with a worse prognosis since they required more dialysis. Also, they have more probability of vascular inflammation on the renal biopsy.

DNA-damaging autoantibodies and cancer: the lupus butterfly theory

Autoantibodies reactive against host DNA are detectable in the circulation of most people with systemic lupus erythematosus (SLE). The long-held view that antibodies cannot penetrate live cells has been disproved. A subset of lupus autoantibodies penetrate cells, translocate to nuclei, and inhibit DNA repair or directly damages DNA. The result of these effects depends on the microenvironment and genetic traits of the cell. Some DNA-damaging antibodies alone have little impact on normal cells, but in the presence of other conditions, such as pre-existing DNA-repair defects, can become highly toxic. These findings raise new questions about autoimmunity and DNA damage, and reveal opportunities for new targeted therapies against malignancies particularly vulnerable to DNA damage. In this Perspectives article, we review the known associations between SLE, DNA damage and cancer, and propose a theory for the effects of DNA-damaging autoantibodies on SLE pathophysiology and cancer risk.

DNA-histone complexes as ligands amplify cell penetration and nuclear targeting of anti-DNA antibodies via energy-independent mechanisms

We have generated three monoclonal cell-penetrating antibodies (CPAbs) from a non-immunized lupus-prone (NZB × NZW)F1 mouse that exhibited high anti-DNA serum titres. These CPAbs are polyreactive because they bind to DNA and other cellular components, and localize mainly in the nucleus of HeLa cells, albeit with a distinct nuclear labelling profile. Herein, we have examined whether DNA-histone complexes (DHC) binding to CPAbs, before cell entry, could modify the cell penetration of CPAbs or their nuclear staining properties. By applying confocal microscopy and image analysis, we found that extracellular binding of purified CPAbs to DHC significantly enhanced their subsequent cell-entry, both in terms of percentages of positively labelled cells and fluorescence intensity (internalized CPAb amount), whereas there was a variable effect on their nuclear staining profile. Internalization of CPAbs, either alone or bound to DHC, remained unaltered after the addition of endocytosis-specific inhibitors at 37° or assay performance at 4°, suggesting the involvement of energy-independent mechanisms in the internalization process. These findings assign to CPAbs a more complex pathogenetic role in systemic lupus erythematosus where both CPAbs and nuclear components are abundant.

Immunological evidence and regulatory potential for cell-penetrating antibodies in intravenous immunoglobulin

Anti-DNA cell-penetrating autoantibodies have been extensively studied in autoimmune but not in normal sera. We investigated herein the presence and properties of cell-penetrating antibodies (CPAbs) in intravenous immunoglobulin (IVIg), a blood product of pooled normal human IgG. IVIg cell penetration was observed into various cell lines, as well as cells from several organs of mice injected intravenously with IVIg therapeutic dose. In all cell types examined in vitro and in vivo, intracellular IgG localized in the cytoplasm, in contrast to the nuclear accumulation of disease-related CPAbs. IVIg was found to rapidly enter cells via an energy-independent mode. The CPAb-fraction was isolated and found to be polyreactive to nuclear and cytoplasmic components; although it corresponded to ~2% of IVIg, it accounted for its inhibitory effect on splenocyte activation. Investigation of IVIg cell penetration capacity provides insight into its mechanisms of action and may account for some of its beneficial effects in numerous diseases.

Lipopolysaccharide induces inducible nitric oxide synthase-dependent podocyte dysfunction via a hypoxia-inducible factor 1α and cell division control protein 42 and Ras-related C3 botulinum toxin substrate 1 pathway

Urine protein loss in immune complex-mediated diseases such as lupus nephritis is associated with podocyte foot process effacement (podocytopathy) but is not always dependent on glomerular immune complex deposition. Several murine and human studies have associated lupus nephritis with inducible nitric oxide synthase (iNOS) expression in what appear to be podocytes. This study was conducted to determine mechanisms of immune-complex-independent and iNOS-dependent podocyte dysfunction. Conditionally immortalized podocytes were cultured with lipopolysaccharide (LPS) and nitric oxide (NO), superoxide (SO), or peroxynitrite donors in the presence or absence of inhibitors of iNOS, reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase or monocyte chemotactic protein 1 (MCP-1), or with sepiapterin to increase coupling of iNOS homodimers. Podocyte NO, SO, and MCP-1 production and nitrotyrosine modifications were determined. The podocytopathy phenotype was determined by measuring cell motility and membrane permeability to albumin. This study determined that NO produced by iNOS is sufficient and necessary to induce podocytopathy. NO probably induces this phenotype via hypoxia-inducible factor 1α and cell division control protein 42 and Ras-related C3 botulinum toxin substrate 1 pathways. With LPS stimulation, neither SO nor peroxynitrite produced by uncoupled iNOS or NADPH oxidase nor MCP-1 was sufficient to induce the full phenotype. This study supports the notion that iNOS may induce autocrine podocyte dysfunction. Thus, targeting iNOS or the pathways of its induction may have therapeutic benefit.

Passive transfer of antibodies to the linear epitope 60 kD Ro 273-289 induces features of Sjögren's syndrome in naive mice

Sjögren's syndrome (SS) is an autoimmune inflammatory disease that primarily affects the lacrimal and salivary glands causing dry eyes and mouth. Antibodies to Ro60 are observed frequently in patients with SS; however, the role of these antibodies in SS initiation and progression remains unclear. The sequence Ro60 273-289 (Ro274) is a known B cell epitope of Ro60 and antibodies to this epitope have been observed in a subset of SS patients and in animals immunized with Ro60 protein. Animals immunized with Ro274 linear peptide develop a Sjögren's-like illness. We hypothesized that passive transfer of anti-Ro274-specific immunoglobulin (Ig)G would induce a Sjögren's-like phenotype. To evaluate this hypothesis, we adoptively transferred affinity-purified Ro274 antibodies into naive BALB/c animals, then evaluated salivary gland histology, function and IgG localization 4 days post-transfer. At this time-point, there was no demonstrable mononuclear cell infiltration and salivary glands were histologically normal, but we observed a functional deficit in stimulated salivary flow of animals receiving Ro274 antibodies compared to animals receiving control IgG. Cellular fractionation and enzyme-linked immunosorbent assay revealed Ro274-specific antibodies in the nucleus and cytoplasmic fractions of isolated parotid salivary gland cells that was confirmed by immunohistochemistry. These data support the hypothesis that antibodies to Ro274 deposit in salivary glands can enter intact salivary gland cells and are involved in the dysregulation of salivary flow in SS.

Multi-antibody composition in lupus nephritis: isotype and antigen specificity make the difference

Research on autoimmune processes involved in glomerulonephritis has been for years based on experimental models. Recent progress in proteomics has radically modified perspectives: laser microdissection and proteomics were crucial for an in vivo analysis of autoantibodies eluted from human biopsies. Lupus nephritis has been the subject of recent independent researches. Main topics have been the definition of renal autoimmune components in human lupus biopsies; methods were laser capture of glomeruli and/or of single cells (CD38+ or Ki-67+) from tubulointerstitial areas as starting step followed by elution and characterization of renal antibodies by proteomics. The innovative approach highlighted different panels of autoantibodies deposited in glomeruli and in tubulo-interstitial areas that actually represented the unique autoimmune components in these patients. IgG2 was the major isotype; new podocyte proteins (αenolase, annexin AI) and already known implanted molecules (DNA, histone 3, C1q) were their target antigens in glomeruli. Vimentin was the antigen in tubulo-interstitial areas. Matching renal autoantibodies with serum allowed the definition of a typical autoantibody serum map that included the same anti-αenolase, anti-annexin AI, anti-DNA, and anti-histone 3 IgG2 already detected in renal tissue. Serum levels of specific autoantibodies were tenfold increased in patients with lupus nephritis allowing a clear differentiation from both rheumatoid arthritis and other glomerulonephritis. In all cases, targeted antigens were characterized as components of lupus NETosis. Matching renal/serum autoantibody composition in vivo furnishes new insights on human lupus nephritis and allows to refine composition of circulating antibodies in patients with lupus. A thoughtful passage from bench to bedside of new knowledge would expand our clinical and therapeutic opportunities.

Serum autoantibodies in pristane induced lupus are regulated by neutrophil gelatinase associated lipocalin

The onset of autoantibodies in systemic autoimmunity can be the result of a breakdown in tolerance at multiple checkpoints. Genetic, hormonal, and immunological factors can combine with environmental influences to accelerate the onset of disease and aggravate disease outcome. Here, we describe a novel mechanism relating to the regulatory role of Neutrophil Gelatinase Associated Lipocalin (NGAL) in modulating the levels of autoantibodies in pristane induced lupus. Following a single injection of pristane intraperitoneally, NGAL expression was induced in both the serum and spleen. Furthermore, NGAL deficient mice were more susceptible to the induction of pristane stimulated autoimmunity, and displayed higher numbers of autoantibody secreting cells and increased expression of activation induced cytidine deaminase (AID) and other inflammatory mediators in the spleen. In contrast, kidney damage was milder in NGAL deficient mice, indicating that NGAL was detrimental in autoantibody mediated kidney disease. These studies indicate that NGAL plays differential roles in different tissues in the context of lupus, and suggest a previously unrecognized role for NGAL in adaptive immunity.

The efficacy of novel B cell biologics as the future of SLE treatment: a review

Systemic lupus erythematosus (SLE) is a chronic autoimmune inflammatory disease with wide ranging multi-systemic effects. Current understanding centralises B cells in SLE pathogenesis with clinical features resulting from autoantibody formation, immune complex deposition, antigen presentation and cytokine activation. Existing standard of care therapies generates adverse side effects; secondary to corticosteroid use and untargeted immunosuppression. The inability to uphold remission and abolish the disease process, in addition to the increasing numbers of patients seen with refractory disease with these therapies, has provoked the development of novel B cell biologics targeting specific pathogenic pathways fundamental to the SLE disease process. Current evidence highlighting the efficacy of Rituximab, Ocrelizumab and Epratuzumab in inducing B cell depletion and achieving disease amelioration through specific B cell surface receptor antagonism is discussed. We review the efficacy of Atacicept, Briobacept and Belimumab in antagonising B lymphocyte stimulator (BLyS) and A proliferation inducing ligand (APRIL), two stimulatory cytokines crucial to B cell survival, growth and function. Two large multicentre randomised controlled trials, BLISS-52 and BLISS-76, have led to FDA approval of Belimumab. Following this breakthrough, other anti-BLyS therapies, Blisibimod and Tabalumab, are currently under Phase III evaluation. Similarly, murine models and Phase I/II trials have demonstrated significant efficacy of Rituximab, Epratuzumab, Briobacept and Atacicept as potential future therapies and we now eagerly await results from Phase III trials. Future research must compare the efficacy of different biologics amongst different patient subpopulations and SLE manifestations, in order to develop clinically and cost effective therapies.

Glomerular autoimmune multicomponents of human lupus nephritis in vivo: α-enolase and annexin AI

Renal targets of autoimmunity in human lupus nephritis (LN) are unknown. We sought to identify autoantibodies and glomerular target antigens in renal biopsy samples from patients with LN and determine whether the same autoantibodies can be detected in circulation. Glomeruli were microdissected from biopsy samples of 20 patients with LN and characterized by proteomic techniques. Serum samples from large cohorts of patients with systemic lupus erythematosus (SLE) with and without LN and other glomerulonephritides were tested. Glomerular IgGs recognized 11 podocyte antigens, with reactivity varying by LN pathology. Notably, IgG2 autoantibodies against α-enolase and annexin AI were detected in 11 and 10 of the biopsy samples, respectively, and predominated over other autoantibodies. Immunohistochemistry revealed colocalization of α-enolase or annexin AI with IgG2 in glomeruli. High levels of serum anti-α-enolase (>15 mg/L) IgG2 and/or anti-annexin AI (>2.7 mg/L) IgG2 were detected in most patients with LN but not patients with other glomerulonephritides, and they identified two cohorts: patients with high anti-α-enolase/low anti-annexin AI IgG2 and patients with low anti-α-enolase/high anti-annexin AI IgG2. Serum levels of both autoantibodies decreased significantly after 12 months of therapy for LN. Anti-α-enolase IgG2 recognized specific epitopes of α-enolase and did not cross-react with dsDNA. Furthermore, nephritogenic monoclonal IgG2 (clone H147) derived from lupus-prone MRL-lpr/lpr mice recognized human α-enolase, suggesting homology between animal models and human LN. These data show a multiantibody composition in LN, where IgG2 autoantibodies against α-enolase and annexin AI predominate in the glomerulus and can be detected in serum.

Dosage of X-linked Toll-like receptor 8 determines gender differences in the development of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease with a high incidence in females and a complex phenotype. Using 564Igi mice, a model of SLE with knock-in genes encoding an autoreactive anti-RNA Ab, we investigated how expression of Toll-like receptors (TLRs) in B cells and neutrophils affects pathogenesis. We established that TLR signaling through MyD88 is necessary for disease. Autoantibody was produced in mice with single deletions of Tlr7, Tlr8, or Tlr9 or combined deletions of Tlr7 and Tlr9. Autoantibody was not produced in the combined absence of Tlr7 and Tlr8, indicating that TLR8 contributes to the break in tolerance. Furthermore, TLR8 was sufficient for the loss of B-cell tolerance, the production of class-switched autoantibody, heightened granulopoiesis, and increased production of type I IFN by neutrophils as well as glomerulonephritis and death. We show that dosage of X-linked Tlr8 plays a major role in the high incidence of disease in females. In addition, we show that the negative regulation of disease by TLR9 is exerted primarily on granulopoiesis and type I IFN production by neutrophils. Collectively, we suggest that individual TLRs play unique roles in the pathogenesis of systemic lupus erythematosus, suggesting new targets for treatment.

Tapping the treasure of intracellular oncotargets with immunotherapy

It is commonly believed that antibodies are too large (∼150 kDa) to access the intracellular compartment. Therefore, therapeutic antibodies have been traditionally used to target cell surface receptors or soluble proteins in the circulation, leaving a large intracellular treasure of potential cancer-specific targets untapped. This review offers new perspectives on our recently proposed concept that antibodies can be used to target intracellular tumor antigens for anti-cancer therapy. We propose to vastly expand the repertoire of potential targets for cancer immunotherapy since many excellent cancer targets are inside cells.

Mediators of inflammation and their effect on resident renal cells: implications in lupus nephritis

Lupus nephritis affects up to 70% of patients with systemic lupus erythematosus and is a major cause of morbidity and mortality. It is characterized by a breakdown of immune tolerance, production of autoantibodies, and deposition of immune complexes within the kidney parenchyma, resulting in local inflammation and subsequent organ damage. To date, numerous mediators of inflammation have been implicated in the development and progression of lupus nephritis, and these include cytokines, chemokines, and glycosaminoglycans. Of these, type I interferons (IFNs) can increase both gene and protein expression of cytokines and chemokines associated with lupus susceptibility, and interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and hyaluronan have been shown to elicit both pro- and anti-inflammatory effects on infiltrating and resident renal cells depending on the status of their microenvironment. Expression of IL-6, TNF-α, type I IFNs, and hyaluronan are increased in the kidneys of patients and mice with active lupus nephritis and have been shown to contribute to disease pathogenesis. There is also evidence that despite clinical remission, ongoing inflammatory processes may occur within the glomerular and tubulointerstitial compartments of the kidney, which further promote kidney injury. In this review, we provide an overview of the synthesis and putative roles of IL-6, TNF-α, IFN-α, and hyaluronan in the pathogenesis of lupus nephritis focusing on their effects on human mesangial cells and proximal renal tubular epithelial cells.

Linking complement and anti-dsDNA antibodies in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus is a severe autoimmune disease that affects multiple organ systems resulting in diverse symptoms and outcomes. It is characterized by antibody production to a variety of self-antigens, but it is specifically associated with those against anti-dsDNA. Anti-dsDNA antibodies are present before the onset of clinical disease and are associated with severe manifestations of lupus such as glomerulonephritis. Their levels fluctuate with changes in disease activity and, in combination with the levels of complement proteins C3 and C4, are strong indicators of disease flare and treatment response in patients with lupus. The decreased complement levels that are noted during flares of lupus activity are believed to be secondary to increased autoantibody production and immune complex formation that results in tissue damage; however, recent data suggest that complement activation can also drive development of these pathogenic autoantibodies. This review will explore the various roles of complement in the development and pathogenesis of anti-dsDNA antibodies.

B-cell-targeted therapies in systemic lupus erythematosus

Autoreactive B cells are one of the key immune cells that have been implicated in the pathogenesis of systemic lupus erythematosus (SLE). In addition to the production of harmful auto-antibodies (auto-Abs), B cells prime autoreactive T cells as antigen-presenting cells and secrete a wide range of pro-inflammatory cytokines that have both autocrine and paracrine effects. Agents that modulate B cells may therefore be of potential therapeutic value. Current strategies include targeting B-cell surface antigens, cytokines that promote B-cell growth and functions, and B- and T-cell interactions. In this article, we review the role of B cells in SLE in animal and human studies, and we examine previous reports that support B-cell modulation as a promising strategy for the treatment of this condition. In addition, we present an update on the clinical trials that have evaluated the therapeutic efficacy and safety of agents that antagonize CD20, CD22 and B-lymphocyte stimulator (BLyS) in human SLE. While the results of many of these studies remain inconclusive, belimumab, a human monoclonal antibody against BLyS, has shown promise and has recently been approved by the US Food and Drug Administration as an indicated therapy for patients with mild to moderate SLE. Undoubtedly, advances in B-cell immunology will continue to lead us to a better understanding of SLE pathogenesis and the development of novel specific therapies that target B cells.

Prostaglandin E2 promotes cellular recovery from established nephrotoxic serum nephritis in mice, prosurvival, and regenerative effects on glomerular cells

We postulated that prostaglandin E2 (PGE2), which exhibits regulatory functions to control immune-mediated inflammation, fibrosis, oxidative stress, and tissue/cellular regeneration, has the potential to improve the course of nephritis. Therefore, the therapeutic potential of prostanoid on established nephritis in mice was evaluated focusing on its role on renal cellular recovery, with emphasis on its cytoprotecting and growth-promoting effects. Acute nephritis was induced in mice by single injection of nephrotoxic serum (NTS), followed by PGE2 administration with severity of nephritis evaluated over time. Mice injected with PGE2 recovered promptly with normalization of blood urea nitrogen and urine protein levels and histology. Recovery was observed with dosing of prostanoid at day 1, as well as day 4. With the use of selective EP1-4 receptor agonists, EP3 receptor has been identified as important in mediating beneficial effects of PGE2 in our system. PGE2 normalized glomerular cell losses during nephrotoxic serum-induced nephritis, restored synaptopodin distribution and F-actin filaments arrangement in glomeruli. In cell culture, PGE2 reduced nephrotoxim serum (NTS)-induced apoptosis of glomerular cells and promoted cell reproliferation after NTS-mediated injury. In conclusion, PGE2 treatment promotes resolution of glomerular inflammation. Consistent with this observation, the regenerative and cytoprotective effects of prostanoid on glomerular cells in culture were observed, suggesting that PGE2 may be beneficial in the treatment of glomerulonephritis.

Role of Structure-Based Changes due to Somatic Mutation in Highly Homologous DNA-Binding and DNA-Hydrolyzing Autoantibodies Exemplified by A23P Substitution in the VH Domain

Anti-DNA autoantibodies are responsible for tissue injury in lupus. A subset of DNA-specific antibodies capable of DNA cleavage can be even more harmful after entering the living cells by destroying nuclear DNA. Origins of anti-DNA autoantibodies are not fully understood, and the mechanism of induction of DNA-cleaving activity remains speculative. The autoantibody BV04-01 derived from lupus-prone mouse is the only DNA-hydrolyzing immunoglobulin with known 3D structure. Identification and analysis of antibodies homologous to BV04-01 may help to understand molecular bases and origins of DNA-cleaving activity of autoantibodies. BLAST search identified murine anti-DNA autoantibody MRL-4 with sequences of variable region genes highly homologous to those of autoantibody BV04-01. Despite significant homology to BV04-01, not only MRL-4 had no DNA-cleaving activity, but also reversion of its unusual P23 mutation to the germline alanine resulted in a dramatic loss of affinity to DNA. Contrary to this effect, transfer of the P23 mutation to the BV04-01 has resulted in a significant drop in DNA binding and almost complete loss of catalytic activity. In the present paper we analyzed the properties of two homologous autoantibodies and mutants thereof and discussed the implications of unusual somatic mutations for the development of autoantibodies with DNA-binding and DNA-hydrolyzing activity.

Awaiting a new era of cancer immunotherapy

A major challenge in cancer therapy is the lack of specificity for cancer cells. Antibody-based therapies have better specificity and, thus, improved efficacy over standard chemotherapy regimens. Monoclonal antibodies (mAb) constitute the most rapidly growing class of human therapeutics and are proven agents for recognizing and destroying malignant cells. However, the development of antibody therapies has focused only on targeting extracellular (cell-surface or secreted) proteins rather than intracellular targets (within cells, such as phosphatases and/or kinases and transcription factors), because antibodies are generally believed to be too large to enter cells, resulting in a large untapped source of intracellular therapeutic targets. Recently, we presented evidence that suggests that intracellular proteins with high expression in cancer cells are useful targets for mAb-based or vaccination immunotherapies, thus challenging current understanding. Here, we further discuss the concept and future uses of these immunotherapies against a large pool of intracellular oncoproteins for cancer therapy. This line of research has the potential to vastly expand the field of antibody therapy and usher in a new era of cancer vaccines.

Autoantibodies and resident renal cells in the pathogenesis of lupus nephritis: getting to know the unknown

Systemic lupus erythematosus is characterized by a breakdown of self-tolerance and production of autoantibodies. Kidney involvement (i.e., lupus nephritis) is both common and severe and can result in permanent damage within the glomerular, vascular, and tubulo-interstitial compartments of the kidney, leading to acute or chronic renal failure. Accumulating evidence shows that anti-dsDNA antibodies play a critical role in the pathogenesis of lupus nephritis through their binding to cell surface proteins of resident kidney cells, thereby triggering the downstream activation of signaling pathways and the release of mediators of inflammation and fibrosis. This paper describes the mechanisms through which autoantibodies interact with resident renal cells and how this interaction plays a part in disease pathogenesis that ultimately leads to structural and functional alterations in lupus nephritis.

IL-21 receptor is required for the systemic accumulation of activated B and T lymphocytes in MRL/MpJ-Fas(lpr/lpr)/J mice

MRL/MpJ-Fas(lpr/lpr)/J (MRL(lpr)) mice develop lupus-like disease manifestations in an IL-21-dependent manner. IL-21 is a pleiotropic cytokine that can influence the activation, differentiation, and expansion of B and T cell effector subsets. Notably, autoreactive CD4(+) T and B cells spontaneously accumulate in MRL(lpr) mice and mediate disease pathogenesis. We sought to identify the particular lymphocyte effector subsets regulated by IL-21 in the context of systemic autoimmunity and, thus, generated MRL(lpr) mice deficient in IL-21R (MRL(lpr).IL-21R(-/-)). Lymphadenopathy and splenomegaly, which are characteristic traits of the MRL(lpr) model were significantly reduced in the absence of IL-21R, suggesting that immune activation was likewise decreased. Indeed, spontaneous germinal center formation and plasma cell accumulation were absent in IL-21R-deficient MRL(lpr) mice. Correspondingly, we observed a significant reduction in autoantibody titers. Activated CD4(+) CD44(+) CD62L(lo) T cells also failed to accumulate, and CD4(+) Th cell differentiation was impaired, as evidenced by a significant reduction in CD4(+) T cells that produced the pronephritogenic cytokine IFN-γ. T extrafollicular helper cells are a recently described subset of activated CD4(+) T cells that function as the primary inducers of autoantibody production in MRL(lpr) mice. Importantly, we demonstrated that T extrafollicular helper cells are dependent on IL-21R for their generation. Together, our data highlighted the novel observation that IL-21 is a critical regulator of multiple pathogenic B and T cell effector subsets in MRL(lpr) mice.

Autoantibodies: Focus on anti-DNA antibodies

Ever since the days of Ehrlich and the birth of humoral immunity, self-reactivity or 'horror autotoxicus' as referred to by Paul Ehrlich, has been of great concern. For instance, in patients with the autoimmune disease systemic lupus erythematosus (SLE), anti-nuclear and anti-DNA antibodies have been recognized for many years. Despite this, the exact mechanism as to how the immune system fails to protect the individual and allows these autoantibodies to develop in this and other systemic autoimmune diseases remains uncertain. So how can we explain their presence? Evidence suggests that B cells expressing autoreactive antibodies do not normally arise but rather undergo negative selection as they develop. In light of this, it might seem contradictory that not all autoreactive B cell clones are eliminated, although this may not even be the intention since autoantibodies are also found in healthy individuals and may even protect from autoimmunity. Here, we will discuss autoantibodies, in particular those recognizing DNA, with regard to their reactivity and their potentially pathogenic or protective properties.

Inefficient clearance of dying cells in patients with SLE: anti-dsDNA autoantibodies, MFG-E8, HMGB-1 and other players

Systemic lupus erythematosus (SLE) is a complex disease resulting from inflammatory responses of the immune system against several autoantigens. Inflammation is conditioned by the continuous presence of autoantibodies and leaked autoantigens, e.g. from not properly cleared dying and dead cells. Various soluble molecules and biophysical properties of the surface of apoptotic cells play significant roles in the appropriate recognition and further processing of dying and dead cells. We exemplarily discuss how Milk fat globule epidermal growth factor 8 (MFG-E8), biophysical membrane alterations, High mobility group box 1 (HMGB1), C-reactive protein (CRP), and anti-nuclear autoantibodies may contribute to the etiopathogenesis of the disease. Up to date knowledge about these key elements may provide new insights that lead to the development of new treatment strategies of the disease.

Anti-DNA antibody induction of protein kinase C phosphorylation and fibronectin synthesis in human and murine lupus and the effect of mycophenolic acid

OBJECTIVE

To examine fibronectin (FN) expression in human lupus nephritis and the effect of anti-DNA antibodies on transforming growth factor beta1 (TGFbeta1) and FN synthesis in cultured human mesangial cells. The effects of mycophenolic acid (MPA) on this pathway, and the effects of mycophenolate mofetil (MMF) treatment in (NZB x NZW)F(1)/J mice were also studied.

METHODS

Immunohistochemical analyses of renal biopsy samples from patients with active diffuse proliferative lupus nephritis were performed. Cultured human mesangial cells were incubated with human polyclonal anti-DNA antibodies, with or without MPA. (NZB x NZW)F(1)/J mice with active nephritis were randomized to receive either MMF (100 mg/kg/day) or vehicle treatment for 12 weeks.

RESULTS

Glomerular FN expression was increased in patients with lupus nephritis, and it colocalized with IgG deposition. Anti-DNA antibodies induced protein kinase Calpha (PKCalpha), PKCbetaI, and PKCbetaII activation, increased levels of bioactive TGFbeta1, and increased FN synthesis in human mesangial cells (P < 0.001 for each comparison versus control conditions). Pretreatment of anti-DNA antibodies with exogenous DNA reduced their cellular binding and abrogated their induction of TGFbeta1 and FN synthesis. Inhibition of PKC activation in human mesangial cells prior to anti-DNA antibody stimulation had no effect on cell proliferation, but resulted in significantly reduced antibody-mediated TGFbeta1 secretion and FN synthesis. MPA treatment down-regulated PKCalpha, PKCbetaI, and PKCbetaII phosphorylation, reduced levels of TGFbeta1 bioactivation, and decreased FN synthesis and deposition into the extracellular matrix. MMF treatment in (NZB x NZW)F(1)/J mice resulted in a reduction in glomerular IgG deposition, PKC activation, and FN expression, as well as an amelioration of proteinuria.

CONCLUSION

Human polyclonal anti-DNA antibodies induce TGFbeta1 and FN synthesis in human mesangial cells through PKC activation, which is inhibited by MPA.

Regulators of B-cell activity in SLE: a better target for treatment than B-cell depletion?

B cells, being a source of characteristic antinuclear autoantibodies, play a crucial role in the pathogenesis of systemic lupus erythematosus (SLE). Evidences indicate that alterations in B-cell regulation are responsible for B-cell hyperactivity as seen in SLE. T cells, soluble factors, and even B cells themselves regulate effector B-cell functions. The latter, so-called regulatory B cells possess regulatory function through production of the cytokine interleukin-10 (IL-10) that can damp down the humoral immune responses. This review will focus on B-cell regulation in the pathogenesis of SLE as a target for intervention. In particular, the regulatory impact of T cells through costimulation, soluble factors such as B lymphocyte stimulator, and the characteristics of IL 10–producing regulatory B cells will be discussed. Therapies targeting B cells as well as B-cell regulation seem promising, but the precise mechanisms involved in these interventions are not completely understood. More insight into B-cell regulation in SLE, and particularly in regulatory B cells, could lead to novel therapeutic strategies.

A common repertoire of autoantibodies is shared by cancer and autoimmune disease patients: Inflammation in their induction and impact on tumor growth

The repertoire of autoantibodies found in cancer patients partly overlaps with that typical of patients with autoimmune diseases. Beside the biochemical and immunological properties of the target antigens and their altered expression in tumor tissues, the intratumoral inflammatory context can play a key role in the induction of autoimmune disease-associated autoantibodies in cancer patients. Furthermore, the impact of such antibodies on cancer growth and progression can be deeply influenced by the interplay with inflammation. The characterization of the spontaneous humoral responses occurring in cancer patients, of the mechanisms that trigger and sustain the autoantibody response and of the biological effects of such autoantibodies may help the rational design of anti-cancer immunotherapeutic protocols.

Pathogenic autoantibodies in systemic lupus erythematosus are derived from both self-reactive and non-self-reactive B cells

Previous studies have shown that both murine and human anti-double-stranded DNA (anti-dsDNA) antibodies can develop from non-DNA-reactive B cells and suggest a crucial role for somatic mutation in dsDNA binding. However, since only a limited number of human anti-dsDNA antibodies have been analyzed previously, we could not exclude other mechanisms for the generation of anti-dsDNA antibodies in patients with systemic lupus erythematosus (SLE). Therefore, we isolated IgM anti-dsDNA antibodies from peripheral blood B cells of a patient with SLE. Three somatically mutated IgM anti-DNA antibodies with pathogenic potential (glomerular binding) were reverted to their germline configuration. Although all three IgM anti-dsDNA antibodies came from the same lupus patient, they displayed different profiles. Reversion to the germline sequence of autoantibodies A9 and B5 resulted in decreased dsDNA binding. In contrast, the germline form of G3-recognized dsDNA as well as the mutated counterpart. These results suggest that mutated IgM anti-dsDNA antibodies may develop from both DNA- and non-DNA-reactive B cells. The implications are that B cell activation occurs in response to self and non-self antigens, while selection after activation may be mediated by self antigen in SLE. Moreover, ineffective tolerance checkpoints may exist before and after antigen activation in SLE.

Autoantibodies from Sjögren's syndrome trigger apoptosis in salivary gland cell line

The presence of serum autoantibodies has been associated with Sjögren's syndrome (SS), an autoimmune rheumatic disease that targets salivary and lachrymal glands. The association of apoptosis with autoantibodies production seems to play a role in the pathogenesis of glandular damage. The best-defined antibodies in SS are those reacting with the ribonucleoprotein antigens SS-A (Ro) and SS-B (La). Anti-Ro antibodies are found in about 70-90%, and anti-La in approximately the same frequency, of patients with primary SS. The objective of this work was to explore whether anti-Ro and anti-La autoantibodies purified from Sjögren IgG fractions are able to trigger apoptotic process in the human salivary gland cell line A-253. Anti-Ro and anti-La autoantibodies were purified on protein G Sepharose affinity column and used for the A-253 cell treatment. Apoptosis induced by autoantibodies was revealed by FACS analysis, and the active caspase-3 and the cleaved caspase-3 substrate poly (ADP-ribose) polymerase (PARP) was demonstrated by colorimetric assay and Western blot. This report shows that anti-Ro and anti-La autoantibodies, but not healthy IgG, activate the caspase-3 and determine the cleavage of PARP in A-253 cells. Apoptosis triggered by Sjögren autoantibodies could be responsible for the impairment of the secretory function in the salivary glands.