Antibodies to vimentin intermediate filaments in sera from patients with systemic lupus erythematosus

Vimentin takes a hike - Emerging roles of extracellular vimentin in cancer and wound healing

Vimentin is a cytoskeletal protein important for many cellular processes, including proliferation, migration, invasion, stress resistance, signaling, and many more. The vimentin-deficient mouse has revealed many of these functions as it has numerous severe phenotypes, many of which are found only following a suitable challenge or stress. While these functions are usually related to vimentin as a major intracellular protein, vimentin is also emerging as an extracellular protein, exposed at the cell surface in an oligomeric form or secreted to the extracellular environment in soluble and vesicle-bound forms. Thus, this review explores the roles of the extracellular pool of vimentin (eVIM), identified in both normal and pathological states. It focuses specifically on the recent advances regarding the role of eVIM in wound healing and cancer. Finally, it discusses new technologies and future perspectives for the clinical application of eVIM.

Corroboration of cross-reactivity between Mycobacterium leprae and hosts' salivary and cutaneous proteins: A hope for prognostic biomarkers for the pathogenesis of reactions in leprosy

Introduction

Immunological reactions are frequent complications that may occur either before, during, or after treatment and affect 30-50% of leprosy patients. The presence of autoantibodies like rheumatoid factor, antinuclear factor, and antibodies to host collagen, keratin, actin, myosin, endothelial cells, and myelin basic protein (MBP) has been earlier reported in leprosy patients. The purpose of this study was to identify cross-reactive proteins in clinical samples such as saliva and slit skin scrapings (SSS) of leprosy patients which could be utilised as prognostic biomarkers for Type 1 Reaction (T1R) in leprosy.

Method

A total of 10 leprosy patients in T1R and 5 healthy volunteers were recruited. The protein was extracted from their SSS and saliva samples, thereafter, isoelectric focusing (IEF) and two-dimensional PAGE were performed to analyse the proteins. Furthermore, the cross-reactivity was identified by western blotting host proteins in gel against purified IgG from Mycobacterium leprae soluble antigen (MLSA)- hyperimmunized rabbit sera, thereafter, cross-reactive proteins were identified by MS/MS. The cross-reactive host proteins were analysed for homologous bacterial proteins and B cell epitopes (BCEs) were predicted by using bioinformatic tools.

Results

A total of five spots of salivary proteins namely S100-A9, 35.3 kDa, and 41.5 kDa proteins, Serpin peptidase inhibitor (clade A), Cystatin SA-III, and four spots of SSS namely 41.4 kDa protein, Alpha-1 antitrypsin, vimentin, and keratin 1, were identified as cross-reactive. Further, a total of 22 BCEs of cross-reactive host proteins were predicted and visualised.

Discussion

This data provides strong evidence of cross-reactivity/molecular mimicry between host and pathogen in leprosy patients with reaction. These BCEs of cross-reactive proteins could be further studied to predict reactions and may be utilised as an early diagnostic biomarker for T1R in leprosy.

Protein citrullination as a source of cancer neoantigens

BACKGROUND

Citrulline post-translational modification of proteins is mediated by protein arginine deiminase (PADI) family members and has been associated with autoimmune diseases. The role of PADI-citrullinome in immune response in cancer has not been evaluated. We hypothesized that PADI-mediated citrullinome is a source of neoantigens in cancer that induces immune response.

METHODS

Protein expression of PADI family members was evaluated in 196 cancer cell lines by means of indepth proteomic profiling. Gene expression was assessed using messenger RNA data sets from The Cancer Genome Atlas. Immunohistochemical analysis of PADI2 and peptidyl-citrulline was performed using breast cancer tissue sections. Citrullinated 12-34-mer peptides in the putative Major Histocompatibility Complex-II (MHC-II) binding range were profiled in breast cancer cell lines to investigate the relationship between protein citrullination and antigen presentation. We further evaluated immunoglobulin-bound citrullinome by mass spectrometry using 156 patients with breast cancer and 113 cancer-free controls.

RESULTS

Proteomic and gene expression analyses revealed PADI2 to be highly expressed in several cancer types including breast cancer. Immunohistochemical analysis of 422 breast tumor tissues revealed increased expression of PADI2 in ER- tumors (p<0.0001); PADI2 protein expression was positively correlated (p<0.0001) with peptidyl-citrulline staining. PADI2 expression exhibited strong positive correlations with a B cell immune signature and with MHC-II-bound citrullinated peptides. Increased circulating citrullinated antigen-antibody complexes occurred among newly diagnosed breast cancer cases relative to controls (p=0.0012).

CONCLUSIONS

An immune response associated with citrullinome is a rich source of neoantigens in breast cancer with a potential for diagnostic and therapeutic applications.

Post-translational modifications of vimentin reflect different pathological processes associated with non-small cell lung cancer and chronic obstructive pulmonary disease

INTRODUCTION

Vimentin has shown to be highly implicated in cancer initiation and progression. Vimentin is often a target of post-translational modifications (PTMs) which can be disease specific, thus targeting these specific modifications can be of high biomarker potential. In this study we set out to evaluate the biological relevance and serum biomarker potential of citrullinated vimentin (VICM) and non-citrullinated vimentin (VIM) in non-small cell lung cancer (NSCLC) and chronic obstructive pulmonary disease (COPD).

METHODS

A competitive ELISA targeting VIM was developed and quantified in serum from patients with NSCLC and COPD. VIM was compared with levels of VICM in the same indications.

RESULTS

VIM was significantly increased in NSCLC (n = 100) compared to healthy controls (n = 67) in two independent cohorts (p = 0.0003 and p < 0.0001). Furthermore, VIM was highly increased in late stages of NSCLC (p = 0.001), however VIM was not increased in COPD patients (n = 10). Contrarily, serum levels of VICM was not increased in late stages of NSCLC, but highly elevated in patients with COPD (p < 0.0001).

CONCLUSIONS

These findings suggest a biomarker potential of VIM in NSCLC. Our findings also indicate that PTMs of vimentin are highly relevant and that targeting these modifications can have differential biomarker potential.

Extracellular vimentin modulates human dendritic cell activation

Vimentin is an intermediate filament protein traditionally considered to be an intracellular protein with a structural role. However, recent evidence suggests that vimentin can also be found outside the cell in disease conditions such as cancer, traumatic tissue injury, and inflammation. Extracellular vimentin was previously found to stimulate innate immunity by increasing monocyte and macrophage ability to kill bacteria. However, vimentin has also been previously found to decrease neutrophil infiltration into inflamed tissue. How extracellular vimentin affects the initiation of adaptive immune responses is unknown. Initiation of adaptive immunity involves priming of naïve T cells by antigen-presenting cells, the most effective of which are dendritic cells (DCs). In this study, we demonstrate how extracellular vimentin modulates lipopolysaccharide (LPS) - induced activation of human DCs. Using cytometric bead arrays, we show that extracellular vimentin decreases LPS-activated DC secretion of pro-inflammatory cytokines IL-6 and IL-12 while increasing secretion of the anti-inflammatory cytokine IL-10. Using flow cytometry, we show that extracellular vimentin does not significantly affect LPS-induced DC surface expression of MHC I (HLA-ABC) or MHC II (HLA-DR) presentation molecules, costimulatory factors (CD80, CD86), or the DC maturation marker (CD83). Further, LPS-stimulated DCs co-cultured with allogeneic naïve CD4 + T cells (Th0) induced less secretion of the pro-inflammatory Th1 effector cytokine IFN-γ in the presence of vimentin than in the presence of LPS alone. This result suggests that vimentin reduces Th1 differentiation. Taken together, our data suggest that extracellular vimentin may inhibit pro-inflammatory adaptive immune responses, by blocking DC secretion of pro-inflammatory cytokines. Thus, extracellular vimentin may play an important role in cancer or trauma-complications by inducing suppression of the adaptive immune response. In a positive sense, the presence of extracellular vimentin may prevent tissue-damage from contributing to the development of autoimmunity. Consequently, extracellular vimentin may become a novel drug target for treatment of a variety of pro- and anti-inflammatory disease conditions.

Identification of a Specific Vimentin isoform that Induces an Antibody Response in Pancreatic Cancer

Pancreatic cancer has a poor prognosis, in part due to lack of early detection. The identification of circulating tumor antigens or their related autoantibodies provides a means for early cancer diagnosis. We have used a proteomic approach to identify proteins that commonly induce a humoral response in pancreatic cancer. Proteins from a pancreatic adenocarcinoma cell line (Panc-1) were subjected to two-dimensional PAGE, followed by Western blot analysis in which individual sera were tested for autoantibodies. Sera from 36 newly diagnosed patients with pancreatic cancer, 18 patients with chronic pancreatitis and 15 healthy subjects were analyzed. Autoantibodies were detected against a protein identified by mass spectrometry as vimentin, in sera from 16/36 patients with pancreatic cancer (44.4%). Only one of 18 chronic pancreatitis patients and none of the healthy controls exhibited reactivity against this vimentin isoform. Interestingly, none of several other isoforms of vimentin detectable in 2-D gels exhibited reactivity with patient sera. Vimentin protein expression levels were investigated by comparing the integrated intensity of spots visualized in 2-D PAGE gels of various cancers. Pancreatic tumor tissues showed greater than a 3-fold higher expression of total vimentin protein than did the lung, colon, and ovarian tumors that were analyzed. The specific antigenic isoform was found at 5–10 fold higher levels. The detection of autoantibodies to this specific isoform of vimentin may have utility for the early diagnosis of pancreatic cancer.

Incidental CD8 T cell reactivity against caspase-cleaved apoptotic self-antigens from ubiquitously expressed proteins in islets from prediabetic human leucocyte antigen-A2 transgenic non-obese diabetic mice

Apoptosis is known as a major mechanism which contributes to beta cell decay in type 1 diabetes. Commitment to this pathway generally involves caspase-mediated protein cleavage and was found to induce cross-presentation of a specific antigen repertoire under certain inflammatory conditions. We aimed to assess the significance of the CD8 T cell population reactive against such caspase-cleaved apoptotic self-antigens in pancreatic islets of prediabetic human leucocyte antigen (HLA)-A2 transgenic non-obese diabetic chimeric monochain transgene construct (NOD.HHD) mice. We have reproduced a unique peptide library consisting of human CD8 T cell-derived apoptosis-specific antigens, all of which belong to structural proteins expressed ubiquitously in human islets. Pancreatic islets from prediabetic NOD.HHD mice, harbouring humanized major histocompatibilty complex (MHC) class I, were isolated and handpicked at various ages, and islet-infiltrating CD8 T cells were expanded in vitro and used as responders in an interferon (IFN)-γ enzyme-linked immunospot (ELISPOT) assay. Human T2 cells were used as antigen-presenting cells (APC) to avoid endogenous antigen presentation. Analogous to the interindividual variability found with peptides from known islet autoantigens such as islet-specific glucose-6-phosphatase catalytic subunit related protein (IGRP) and insulin, some mice showed variable, low-degree CD8 T cell reactivity against caspase-cleaved self-antigens. Because reactivity was predominantly minor and often undetectable, we conclude that beta cell apoptosis does not routinely provoke the development of dominant cytotoxic T lymphocyte (CTL) reactive against caspase-cleaved self-antigens in the NOD.HHD model.

Autoimmune T cell responses to antigenic peptides presented by bronchoalveolar lavage cell HLA-DR molecules in sarcoidosis

The etiology of sarcoidosis remains unknown. Recently, by mass spectrometric sequencing of peptides eluted from HLA-DR molecules of bronchoalveolar lavage (BAL) cells from DRB10301(pos) patients, we identified potential self-antigens in sarcoidosis. The aim of the present study was to investigate the capacity of selected peptides to stimulate lung and blood T cells of sarcoidosis patients using an interferon-gamma ELISPOT assay. In peripheral blood, there were strong T cell responses to a peptide derived from the cytoskeletal protein vimentin in 6 out of 11 DRB10301(pos) patients with active disease but not in patients with other HLA types. BAL T cell responses against peptides derived from ATP synthase or from lysyl-tRNA synthetase were detected in DRB10301(pos) as well as DRB10301(neg) patients. By using antigenic peptides presented in vivo in the lungs of sarcoidosis patients, we have identified blood and lung T cell autoimmune responses that may help sustain the inflammation in this disease.

Identification of HLA-DR-bound peptides presented by human bronchoalveolar lavage cells in sarcoidosis

Sarcoidosis is an inflammatory disease of unknown etiology, most commonly affecting the lungs. Activated CD4+ T cells accumulate in the lungs of individuals with sarcoidosis and are considered to be of central importance for inflammation. We have previously shown that Scandinavian sarcoidosis patients expressing the HLA-DR allele DRB1*0301 are characterized by large accumulations in the lungs of CD4+ T cells expressing the TCR AV2S3 gene segment. This association afforded us a unique opportunity to identify a sarcoidosis-specific antigen recognized by AV2S3+ T cells. To identify candidates for the postulated sarcoidosis-specific antigen, lung cells from 16 HLA-DRB1*0301pos patients were obtained by bronchoalveolar lavage. HLA-DR molecules were affinity purified and bound peptides acid eluted. Subsequently, peptides were separated by reversed-phase HPLC and analyzed by liquid chromatography-mass spectrometry. We identified 78 amino acid sequences from self proteins presented in the lungs of sarcoidosis patients, some of which were well-known autoantigens such as vimentin and ATP synthase. For the first time, to our knowledge, we have identified HLA-bound peptides presented in vivo during an inflammatory condition. This approach can be extended to characterize HLA-bound peptides in various autoimmune settings.

Relationship of Anti-vimentin antibodies to anti-endothelial antibodies

The intermediate filament protein vimentin is a potential target antigen for autoantibodies in some infectious and autoimmune diseases. Because endothelial cells contain an extensive interconnecting cytoplasmic network of vimentin, we examined the relationship between anti-vimentin and anti-endothelial cell antibodies (AECAs). We measured the level of anti-vimentin antibodies in patients with systemic autoimmune diseases (n=42), healthy blood donors (n=58), and patients with acute inflammation and showing anti-vimentin immunofluorescence (n=50). AECAs were detected by indirect immunofluorescence in human umbilical vein endothelial cells. Anti-vimentin antibodies were detected by indirect immunofluorescence in HEp-2 cells, and levels of anti-vimentin antibodies were measured using an enzyme-linked immunosorbent assay. We did not find significant differences in anti-vimentin levels between AECA-positive and-negative samples for any of the groups; however, serum anti-vimentin antibody levels were significantly higher in patients with acute non-autoimmune inflammatory diseases than in patients with systemic autoimmune diseases or healthy controls. There were no differences between the levels of anti-vimentin antibodies between patients with systemic autoimmune diseases and healthy individuals. The anti-vimentin antibodies levels also did not correlate with the AECA positivity.

Autoantibody explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients

OBJECTIVE

Description of the various autoantibodies that can be detected in patients with systemic lupus erythematosus (SLE).

METHODS

A literature review, using the terms "autoantibody" and "systemic lupus erythematosus", was conducted to search for articles on autoantibodies in SLE, their target antigens, association with disease activity, or other clinical associations.

RESULTS

One hundred sixteen autoantibodies were described in SLE patients. These include autoantibodies that target nuclear antigens, cytoplasmic antigens, cell membrane antigens, phospholipid-associated antigens, blood cells, endothelial cells, and nervous system antigens, plasma proteins, matrix proteins, and miscellaneous antigens. The target of autoantibody, the autoantigen properties, autoantibody frequencies in SLE, as well as clinical associations, and correlation with disease activity are described for all 116 autoantibodies.

CONCLUSIONS

SLE is the autoimmune disease with the largest number of detectable autoantibodies. Their production could be antigen-driven, the result of polyclonal B cell activation, impaired apoptotic pathways, or the outcome of idiotypic network dysregulation.

High molecular weight vimentin complex is formed after proteolytic digestion of vimentin by caspase-3: detection by sera of patients with interstitial pneumonia

In a previous study, we demonstrated anti-vimentin antibodies in sera of patients with interstitial pneumonia. We hypothesized that antibodies in sera might detect vimentin fragments formed during the process of apoptosis. To prove this, recombinant human vimentin was digested by recombinant human caspase-3 or caspase-8. Then, Western blotting using several commercially available antibodies against human vimentin or patients' sera which had anti-vimentin autoantibodies, was performed. As a result, after recombinant human vimentin was digested by caspase-3 or caspase-8, several vimentin fragments were formed and detected by 2 kinds of monoclonal anti-vimentin antibodies (clone 3B4 and clone V9) as well as by polyclonal sheep anti-human vimentin antibody. It was demonstrated that high molecular weight vimentin was formed after the digestion of vimentin by caspase-3, which was only detected by patients' sera. The high molecular weight vimentin was not formed after digestion of vimentin by caspase-8. Our present results show that high molecular weight vimentin was formed after the digestion of vimentin by caspase-3. In addition, it is suggested that this high molecular weight vimentin acted as an autoantigen to form anti-vimentin autoantibody in vivo.

Identification of an autoantigen on the surface of apoptotic human T cells as a new protein interacting with inflammatory group IIA phospholipase A2

One of the most studied secreted phospholipases A2 (sPLA2), the group IIA sPLA2, is found at high levels in inflammatory fluids of patients with autoimmune diseases. A characteristic of group IIA sPLA2 is its preference for negatively charged phospholipids, which become exposed on the extracellular leaflet of apoptotic cell membranes. We recently showed that low molecular weight heparan sulfate proteoglycans (HSPGs) and uncharacterized detergent-insoluble binding site(s) contribute to the enhanced binding of human group IIA PLA2 (hGIIA) to apoptotic human T cells. Using matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry we now identify vimentin as the major HSPG-independent binding protein of hGIIA on apoptotic primary T lymphocytes. Vimentin is partially exposed on the surface of apoptotic T cells and binds hGIIA via its rod domain in a calcium-independent manner. Studies with hGIIA mutants showed that specific motifs in the interfacial binding surface are involved in the interaction with vimentin. The sPLA2 inhibitor LY311727, but not heparin, inhibited this interaction. In contrast, heparin but not LY311727 abrogated the binding of hGIIA to cellular HSPGs. Importantly, vimentin does not inhibit the catalytic activity of hGIIA. Altogether, the results show that vimentin, in conjunction with HSPGs, contributes to the enhanced binding of hGIIA to apoptotic T cells.

Detection of antivimentin antibody in sera of patients with idiopathic pulmonary fibrosis and non-specific interstitial pneumonia

It has been suggested that the humoral immune system plays a role in the pathogenesis of non-specific interstitial pneumonia (NSIP). Although some circulating autoantibodies to cytoskeletal protein(s) have been suggested, the antimyofibroblast antibody has not been investigated in patients with idiopathic pulmonary fibrosis (IPF) and NSIP. The purpose of this study is to evaluate the existence of antimyofibroblast antibody in the sera of patients with IPF and NSIP. The MRC5 cell line was used as a model of myofibroblast. The anti-MRC5 cell antibody was characterized in a patient with NSIP using Western blotting. Since we found that one of the anti-MRC5 antibodies was an antivimentin antibody, we established an enzyme-linked immunosorbent assay (ELISA) to measure the levels of antivimentin antibody in the sera of patients with IPF (n = 12) and NSIP (n = 23). Initially, two anti-MRC5 cell antibodies were detected in the sera of patients with NSIP, one of which was characterized as the antivimentin antibody by Western blotting. The other was characterized as an antivimentin fragment antibody. We established an ELISA to measure the antivimentin antibody and found significantly higher levels in patients with IPF and NSIP than in normal volunteers. One of the anti-MRC5 cell antibodies in the serum of a patient with NSIP was against vimentin. The serum levels of antivimentin antibody were increased in patients with IPF and NSIP compared with that of normal volunteers. These results suggest that the antivimentin antibody may be involved in the process of lung injury in IPF and NSIP.

Monoclonal antibodies derived from BALB/c mice immunized with apoptotic Jurkat T cells recognize known autoantigens

It has been postulated that post-translational modifications and relocalization of proteins during apoptosis may lead to presentation of these molecules to the immune system in such a way that normal mechanisms of tolerance are bypassed. In the present study, Jurkat cells were induced to undergo apoptosis by treatment with the chemotherapeutic agent Ara-C. BALB/c mice were then immunized with the apoptotic cells and hybridomas were generated. Using an indirect immunofluorescence assay, the monoclonal antibodies produced were screened by flow cytometry for those monoclonal antibodies demonstrating reactivity with permeabilized apoptotic Jurkat cells but not with non-permeabilized normal or apoptotic Jurkat cells. Of 281 monoclonal antibodies, 20 monoclonal antibodies with these properties were selected for further analysis. Using 32P- or 35S-metabolically labelled Jurkat cells, these selected monoclonal antibodies were screened for their ability to recognize autoantigens by immunoprecipitation and Western blotting. Well characterized autoimmune sera were then used to confirm the identity of autoantigens by immunoblotting. We demonstrate that immunization of normal mice with apoptotic Jurkat cells results in the formation of antibodies targeting multiple autoantigens or autoantigen complexes, including Ku, rRNPs, snRNPs and vimentin. These findings are consistent with the hypothesis that apoptosis can contribute to the development of autoimmunity.

Death, autoantigen modifications, and tolerance

Autoantibodies present in the serum of patients with a variety of inflammatory diseases have proven useful as diagnostic markers and as probes with which to elucidate biochemical and signaling pathways. The mechanisms governing the generation of autoantibodies remain elusive, constituting a critical missing link in our understanding of rheumatologic illnesses. Several lines of experimentation in recent years have strongly implicated events surrounding cell death in this process. This review will address the potential role played by death-specific modifications of autoantigens in bypassing tolerance to highly conserved autoantigens, including nucleic acids, lipids, and proteins.

Non-muscle myosin as target antigen for human autoantibodies in patients with hepatitis C virus-associated chronic liver diseases

Three patients with hepatitis C virus (HCV)-related chronic liver disease were shown to have autoantibodies strongly reacting with cytoskeletal fibres of non-muscle cells. The heavy chain of non-muscle myosin microfilament was the main target for those autoantibodies, as determined by (i) cell and tissue immunofluorescence studies showing colocalization with an anti-myosin antibody prototype; (ii) primary reactivity in immunoblotting with a 200-kD protein, using either MOLT-4 cells, human platelets, or affinity-purified non-muscle myosin as antigen extract; and (iii) immunoblotting of similar immunoreactive fragments in papain-digested MOLT-4 cell extracts, by using those human sera and antibody prototype. Autoantibodies to non-muscle myosin heavy chain were not previously reported in patients with chronic liver diseases, especially in those associated with HCV infection.

Autoantibodies in the diagnosis of systemic rheumatic diseases

Distinct profiles of autoantibodies directed to intracellular antigens can be detected in the systemic connective tissue diseases. They aid in establishing the correct diagnosis and are included in many sets of diagnostic criteria, such as the ones developed for systemic lupus erythematosus (anti-Smith antigen and anti-double-strand DNA antibodies), mixed connective tissue disease (anti-U1-nuclear ribonucleoprotein antibodies), and Sjögren's syndrome (SS) (anti-SS-A/Ro and anti-SS-B/La antibodies). They are useful prognostic markers in some situations and facilitate clinical and treatment follow-up. Autoantibodies have also been used as probes to gain insights into cell biology, helping to isolate and purify intracellular proteins involved in key cellular functions. We give detailed information on two of the most useful techniques for the detection of autoantibodies in the clinical and research laboratory settings, indirect immunofluorescence and immunoblotting. We also discuss several of the antigen-autoantibody systems found in systemic lupus erythematosus (Smith antigen, U1-nuclear ribonucleoprotein, SS-A/Ro, SS-B/La, proliferating cell nuclear antigen ribosomal ribonucleoprotein, double-strand DNA, histones, antiphospholipids, Ku, Ki/SL), systemic sclerosis (centromere, topo I, RNA polymerases, fibrillarin, polymyositis-Scl, Th/To), polymyositis/dermatomyositis (transferRNA synthetases, signal recognition particle, and others), and SS (SS-A/Ro, SS-B/La, nucleolar organizing region-90, p80-coilin), addressing their clinical significance, common detection methods, immunogenetic associations, and the molecular and cellular biology of the cognate antigens.

Antibodies to T- and L-isoforms of the cytoskeletal protein, fimbrin, in patients with systemic lupus erythematosus

The cytoskeleton is a complex network of proteins that maintain cell shape, mobility, and organelle function. Its components can be divided into three distinct classes: microfilaments, microtubules, and intermediate filaments. Fimbrins are microfilament proteins, a family of cytoplasmic phosphoproteins. Expression of the L-fimbrin isoform is restricted to replicating blood cells and expression of the T-fimbrin isoform to replicating cells of solid tissues. Sera from normals and from patients with systemic lupus erythematosus (SLE), juvenile arthritis, rheumatoid arthritis, Sjögren's syndrome, osteoarthritis, vasculitis, scleroderma, and mixed connective tissue disease were tested for the presence of antibodies to T- and L-fimbrin by ELISA, using purified recombinant fimbrin. The mean OD of sera from SLE patients was significantly higher than in normals (T-fimbrin, P less than 0.0001; L-fimbrin, P less than 0.001). 48 of 98 SLE sera had antibodies to T-fimbrin; 32 had antibodies to L-fimbrin; 20 had antibodies to both; 28 had only anti-T, and 12 had only anti-L-fimbrin. The mean OD for sera of the other rheumatic diseases was not significantly different from normals. The presence of either L- or T-fimbrin antibody was associated with pleuropericarditis (P = 0.015), photosensitivity (P = 0.011), and anti-Sm antibody (P = 0.010). Central nervous system SLE was associated with the presence of the L-fimbrin antibody alone (P = 0.016). There was a strong association between DR7 (but not other MHC alleles) and anti-L-fimbrin antibodies in SLE patients (chi square = 18; P less than 0.00002). No MHC association was observed with anti-T-fimbrin antibodies.

The structure of two IgMs showing different activity from a patient with Waldenstrom's macroglobulinaemia

The two monoclonal IgMs (IgM1 and IgM2) were characterized from a patient Waldenström's macroglobulinaemia that resulted in a gammapathy. Heavy and light chains were isolated from the IgM. The complete primary structure of the two light chains and the NH2-terminal region of the two heavy chain molecules were determined. The sequence data indicated that the heavy and light chains from both IgMs belong to the same (III and II) lambda subgroups. By testing their antibody activity it was found by immunofluorescence and immunoblotting that only IgM2 reacts with an intermediate filament protein.

Inhibiting effect of charged polymers on interaction of human lupus autoantibodies with certain intracellular proteins

The influence of charged polymers on the reaction of immunoglobulins from human lupus sera with cellular proteins was investigated in this study. Through immunoblotting it was shown that polyanions (dextran sulfate, heparin, polyinosinic acid) and polylysine inhibited autoantibody binding to several polypeptides of different molecular mass. Using immunofluorescent staining with affinity isolated monospecific autoantibodies it was demonstrated that the immunoreactivity of two nuclear antigens (p30 and p85) and one cytoplasmic antigen (p40) was sensitive to the presence of charged polymers. The inhibiting effect correlated with the concentration of the polymers. The data obtained suggested the competitive mechanism of inhibition of autoantibody-protein reaction by the charged polymers.

Antiperinuclear factor, a marker autoantibody for rheumatoid arthritis: colocalisation of the perinuclear factor and profilaggrin

The antiperinuclear factor, an autoantibody specific for rheumatoid arthritis, was found in 51/63 (81%) patients with rheumatoid arthritis by indirect immunofluorescence on human buccal mucosa cells. The sensitivity of the antiperinuclear factor test was increased by pretreating the buccal mucosa cells with 0.5% Triton-X100. The specificity of the test for rheumatoid arthritis as compared with control serum samples was maintained. The localisation of the perinuclear factor in the keratohyalin granules of the buccal mucosa cells was verified by immunoelectron microscopy. The perinuclear factor was found to be an insoluble protein whose antigenicity was sensitive to various fixation procedures. In serum samples from patients with rheumatoid arthritis there was a positive correlation between the presence of antiperinuclear factor and the presence of the so called antikeratin antibodies as detected by immunofluorescence on unfixed rat oesophagus cryostat sections. No relation was found between the presence of the perinuclear factor and either the rheumatoid factor, Epstein-Barr virus components, or any cytokeratin. By double immunofluorescence an exact colocalisation of the perinuclear factor and profilaggrin was found. Although the precise biochemical identity of the perinuclear factor remains unclear, our results suggest that it is a protein only present in the fully differentiated squamous epithelial cell layer.

Natural IgG to epidermal cytokeratins vs IgG to the stratum corneum of the rat oesophagus epithelium, so-called 'antikeratin antibodies', in rheumatoid arthritis and other rheumatic diseases

In order to study the relationships between the circulating IgG autoantibodies to epidermal cytokeratins (AECK), which were described in normal human sera as well as in sera from patients with various diseases, and the so-called 'antikeratin' IgG antibodies ('AKA'), which are highly specific for rheumatoid arthritis (RA), we simultaneously investigated AECK by a specific ELISA using cytokeratins from human stratum corneum (SC) and 'AKA' by semiquantitative indirect immunofluorescence assay on rat oesophagus epithelium, in a large series of 595 rheumatic sera including 229 RA. AECK were found to be present in all the 595 sera, with large inter-individual variations in titre. Whatever the titre chosen as threshold, the autoantibodies (auto-Ab) were never found to be specific for any rheumatic disease. Moreover, in RA, they were found to vary independently of IgM rheumatoid factor (IgM-RF), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), while they were found to vary in parallel with the total serum IgG concentration. In contrast, although 568 of the 595 rheumatic sera contained antibodies that labelled the rat oesophagus SC, the highest titre-like values were obtained with RA sera. At a convenient threshold, 95 (41.5%) of the 229 RA were detected while only three false positives (0.08%) remained among the 366 non-RA sera. Moreover, in RA, 'AKA' were found to be related to IgM-RF, ESR and CRP, while their titre was found to be independent of the total serum IgG concentration. Lastly, no statistical correlation was found between the antibodies, either in the whole sample of 595 sera or in any diagnostic group. In conclusion, the simultaneous investigation of AECK and 'AKA' showed that they differ from each other in all the aspects explored. AECK belong to the widely explored family of natural auto-Ab against cytoskeleton components and do not constitute a diagnostic marker while, on the other hand, 'AKA' confirmed their high diagnostic specificity for RA. It can also be asserted that, in spite of their name, 'AKA' do not recognize human epidermal cytokeratins, at least in the denatured form they present in ELISA. Therefore, they recognize either conformational epitope(s) appearing on cytokeratins during the late stages of the cornification process, or epitope(s) borne by rat cytokeratins but absent on human cytokeratins, or lastly a non-cytokeratin SC antigen.

Antibodies to cytoskeletal proteins in patients with Crohn's disease

The immunologic basis of inflammatory bowel disease has been the focus of interest of a series of studies on Crohn's disease and the process of immune sensitization at the gastrointestinal mucosal level is functionally poorly understood. To date only few contradictory reports concerning the incidence of autoantibodies in patients with this disease exist. The aim of this study was to investigate the sera drawn from 60 patients suffering from biopsy-proven Crohn's disease to evaluate the prevalence of autoantibodies against nuclear antigens and cytoskeletal proteins. Using standard methods, no anti-nuclear antibodies or antibodies to extractable nuclear antigens could be detected. All sera were also negative for antibodies to double-stranded DNA, anti-mitochondrial antibodies, and antibodies to gastric parietal cells. Using sensitive enzyme-linke immunosorbent assays with purified antigens and Western blotting with cytoskeletal proteins of human intestinal cells, the following antibodies could be demonstrated: cytokeratin 18 autoantibodies (IgG 20.0%; IgM 6.7%; IgA 13.3%), actin antibodies (IgG 36.7%; IgM 48.3%, IgA 26.7%), desmin antibodies (IgG 6.7%; IgM 15.08%; IgA 5.0%), vimentin antibodies (IgG 3.3%; IgM 16.7%; IgA 10.0%) and tropomyosin antibodies (IgG 3.3%; IgM 3.3%, IgA 5.0%). Statistically significant correlations could be found for levels of cytokeratin 18 antibodies (IgM-type) and the BEST index of activity, and for levels of desmin antibodies (IgM-type) and the van HEES index of activity. Highest levels could be measured for actin antibodies (IgG-type) in patients with isolated disease manifestation in the colon. The mechanism of induction of autoantibodies against cytoskeletal components in Crohn's disease still remains obscure. Unmasking of hidden antigens after cell injury during the inflammatory process of disease might lead to sensitization and antibody production. The pattern of antibodies in patients with Crohn's disease seems to be different compared with that of connective tissue diseases.

Relation of antivimentin antibodies to anticardiolipin antibodies in systemic lupus erythematosus

Tests for antivimentin antibodies (AVA) were performed on 50 systemic lupus erythematosus (SLE) and 63 control sera by indirect immunofluorescence and enzyme linked immunosorbent assay (ELISA). The prevalence was significantly raised in SLE (38% and 50% of sera positive for IgM-AVA and IgG-AVA, respectively, by immunofluorescence; 36% and 64% of sera positive for IgM-AVA and IgG-AVA, respectively, by ELISA) in comparison with the control sera. A significant correlation existed between IgM-AVA, on the one hand, and anticardiolipin antibodies (ACA) and anti-single-stranded DNA (ssDNA), on the other. A stepwise principal component analysis demonstrated that IgM-AVA and IgG-AVA accounted for 71% of the total variance in SLE (50 patients x 5 parameters = total variance). Twenty ACA positive serum samples from patients with syphilis were therefore tested for the presence of AVA, but hardly any were found to be positive. IgM-AVA from patients with SLE were inhibited by cardiolipin and absorbed with ssDNA. An association between AVA positivity and arthralgia was also shown in SLE.

Hybridoma lupus autoantibodies can bind major cytoskeletal filaments in the absence of DNA-binding activity

A panel of 65 systemic lupus erythematosus (SLE) and 61 normal-derived human hybridoma auto-antibodies was studied for cytoskeletal reactivity, using an indirect immunofluorescence method. Reactivity with the cytoskeleton was expressed 3 times more frequently in the SLE-derived antibody group and included intermediate filaments, microfilaments, microtubules, and centrioles. By immunoblot analysis, the antigenic specificity of intermediate filament-reactive SLE hybridoma antibodies was not restricted to vimentin, but included cytokeratins and desmin. The antibodies were also studied for their DNA-binding, lupus anticoagulant, and rheumatoid factor activities. These autoantibody activities were expressed 3-5 times more frequently in the SLE-derived group. The ability to bind DNA was not a prerequisite for reactivity with intermediate filament proteins. Our findings suggest that there are at least 2 subsets of cytoskeletal-reactive hybridoma antibodies: those that recognize epitopes found only on cytoskeletal proteins, and those that recognize epitopes common to both DNA and certain cytoskeletal proteins. In addition, we hypothesize that there may be a third subset of antibodies that recognize a phosphate-containing moiety (phospholipid or phosphoprotein) associated with cytoskeletal filaments.

A patient with lepromatous leprosy and anticytoskeletal antibodies

Sera from 34 patients with lepromatous leprosy were screened for the presence of autoantibodies by indirect immunofluorescence using two epithelial cell lines, PTK2 and HEp2, as substrates. Indirect immunofluorescence staining of both substrates with the serum of a patient with lepromatous leprosy revealed a cytoplasmic intermediate filament staining pattern. After exposure of PTK2 cells to colchicine, the filaments collapsed into thick perinuclear coils, confirming the presence of intermediate filament reactivity. Immunofluorescence of rat fibroblasts with the same serum also revealed an intermediate filamentous staining pattern. Human keratinocytes exposed to the patient's serum revealed a diffuse cytoplasmic staining pattern. Our study suggests the presence of autoantibodies to cytoskeletal intermediate filaments or to molecules associated with vimentin and possibly keratin subunit proteins in the serum of a patient with lepromatous leprosy.

Phagocytosis of keratin filament aggregates following opsonization with IgG-anti-keratin filament autoantibodies

IgG-anti-keratin intermediate filament autoantibodies occur in low titers in all normal human sera. These same antibodies are present in high titers in the sera of patients who have diseases in which cells containing keratin intermediate filaments (KIF) have been damaged, such as systemic lupus erythematosus, graft-versus-host disease, and cutaneous tumors. Since some human autoantibodies are thought to function in part as opsonins promoting the removal of insoluble cellular proteins after tissue injury, we investigated the influence of IgG-anti-KIF autoantibodies on the phagocytosis of insoluble KIF aggregates by human monocytes and polymorphonuclear neutrophils (PMN). Keratin intermediate filaments assembled in vitro were reconstituted into dense spherical KIF aggregates 0.3-2.5 microns in diameter by dialysis against phosphate-buffered saline. Immunoelectron microscopy revealed that, as expected, human IgG-anti-KIF autoantibodies bound to the KIF aggregates. Human monocytes or PMN were incubated either with nonopsonized KIF aggregates or with KIF aggregates that had been reacted with IgG-anti-KIF autoantibodies. The uptake of KIF aggregates was visualized by indirect immunofluorescence, immunoperoxidase staining, and immunoelectron microscopy. Monocytes rapidly and efficiently bound and phagocytosed KIF aggregates that had been coated with IgG-anti-KIF autoantibodies. Nonopsonized KIF aggregates, in contrast, were taken up much less efficiently. Differences were most marked at 4 degrees C for 60 min with phagocytosis of opsonized KIF aggregates by 23 +/- 8% of monocytes in contrast to phagocytosis by only 0.2 +/- 3% monocytes when nonopsonized KIF aggregates were used. Similar results occurred at 37 degrees C for 5 min with phagocytosis by 38 +/- 28% vs 1.8 +/- 0.4% of monocytes of opsonized and nonopsonized KIF aggregates, respectively. A high percentage of PMN also phagocytosed opsonized KIF aggregates, whereas nonopsonized KIF aggregates were ingested less avidly. These data indicate that the opsonization of extracellular KIF aggregates by IgG-anti-KIF autoantibodies plays an important role in promoting the phagocytosis of KIF aggregates. The subsequent phagocytosis represents a rapid and very effective mechanism for the removal of insoluble KIF following keratinocyte cell death.

Anticytoskeletal autoantibodies in the connective tissue diseases

The sera of 103 patients with connective tissue diseases were studied for the presence of anticytoskeletal antibodies by using an indirect immunofluorescence method. PTK2 cells fixed with paraformaldehyde and digitonin were used as substrate. Antibodies to intermediate filaments were detected in sera of 85.7% of polymyositis/dermatomyositis (PM/DM), 62.8% of systemic sclerosis, 54.5% of rheumatoid arthritis, and 37.5% of systemic lupus erythematosus patients, and in 42.5% of normal sera. High titers of these antibodies, which were IgM, were present in 30% of patients' and 5% of normal sera. Antibodies to microfilaments were present in 11.6% of patients' sera and absent in all control sera. These antibodies were IgM or IgG. The switch from an IgM to an IgG antibody was observed in 1 patient. An IgG antibody to the spindle poles and midbody of mitotic cells was present in the serum of 1 patient with the CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasias). Antibodies to intermediate filaments and to microfilaments occur commonly in the connective tissue diseases, particularly in PM/DM, and are not detected with substrates or fixation methods used in routine antinuclear antibody testing.

Autoantibody to the C3b/C4b receptor and absence of this receptor from erythrocytes of a patient with systemic lupus erythematosus

A 29-yr-old woman with systemic lupus erythematosus (SLE) was found to have no detectable C3b/C4b receptors (CR1) on her erythrocytes (E) when they were assayed by the binding of rabbit polyclonal and murine monoclonal (Yz-1) anti-CR1. Analysis by two-color fluorescent flow cytometry of CR1 expression on the patient's B lymphocytes that had been stained indirectly with monoclonal anti-B1 and rabbit F(ab')2 anti-CR1 also revealed a marked deficiency of CR1. Total cellular CR1 of neutrophils, assessed by a sandwich radioimmunoassay, was about half that of neutrophils from normal individuals. Because her E had expressed 173 sites/cell 2 yr before, the CR1 deficiency was considered to be acquired and a possible mechanism was sought. Autoantibody to CR1 was measured by a radioimmunoassay in which serum or its fractions were incubated in microtiter wells that had been coated with purified CR1, and binding of immunoglobulin to the wells was quantitated with 125I-labeled goat IgG antihuman F(ab')2. The CR1-specific binding of immunoglobulin from the patient's serum was 19.1 ng/well of the detecting antibody when her E had eight CR1 sites per cell; that of 28 healthy donors was 1.3 +/- 0.5 ng/well (mean +/- SEM), and that of 34 additional patients with SLE was 0.5 +/- 0.3 ng/well. The activity was present also in purified IgG and its F(ab')2 fragment, indicating that the binding of serum immunoglobulin to CR1 was not mediated by C3 fragments. The specificity of the patient's IgG for CR1 was confirmed when pretreatment of the CR1-coated wells with affinity-purified rabbit F(ab')2 anti-CR1 was shown to inhibit by 68% the binding of the IgG. The autoantibody also interacted with CR1 in cell membranes, as assessed by its capacity to inhibit the binding of indirectly fluoresceinated Yz-1 to neutrophils, and, when combined with goat IgG antihuman F(ab')2, to diminish the binding of dimeric C3b to normal E. During the period of the marked deficiency of CR1 the patient experienced an exacerbation of disease activity which was treated with prednisone. Clinical improvement was accompanied by a decrease in the serum concentration of anti-CR1 to levels present 2 yr earlier, and an increase of CR1 to 170 sites/E. The temporal association between high titers of an autoantibody to CR1, absence of CR1 from E, and heightened activity of SLE suggest that the former may have had a role in the other manifestations of the patient's disease.