Autoantibodies associated with lupus induced by diverse drugs target a similar epitope in the (H2A-H2B)-DNA complex

An Autoantigen Atlas From Human Lung HFL1 Cells Offers Clues to Neurological and Diverse Autoimmune Manifestations of COVID-19

COVID-19 is accompanied by a myriad of both transient and long-lasting autoimmune responses. Dermatan sulfate (DS), a glycosaminoglycan crucial for wound healing, has unique affinity for autoantigens (autoAgs) from apoptotic cells. DS-autoAg complexes are capable of stimulating autoreactive B cells and autoantibody production. We used DS-affinity proteomics to define the autoantigen-ome of lung fibroblasts and bioinformatics analyses to study the relationship between autoantigenic proteins and COVID-induced alterations. Using DS-affinity, we identified an autoantigen-ome of 408 proteins from human HFL1 cells, at least 231 of which are known autoAgs. Comparing with available COVID data, 352 proteins of the autoantigen-ome have thus far been found to be altered at protein or RNA levels in SARS-CoV-2 infection, 210 of which are known autoAgs. The COVID-altered proteins are significantly associated with RNA metabolism, translation, vesicles and vesicle transport, cell death, supramolecular fibrils, cytoskeleton, extracellular matrix, and interleukin signaling. They offer clues to neurological problems, fibrosis, smooth muscle dysfunction, and thrombosis. In particular, 150 altered proteins are related to the nervous system, including axon, myelin sheath, neuron projection, neuronal cell body, and olfactory bulb. An association with the melanosome is also identified. The findings from our study illustrate a connection between COVID infection and autoimmunity. The vast number of COVID-altered proteins with high intrinsic propensity to become autoAgs offers an explanation for the diverse autoimmune complications in COVID patients. The variety of autoAgs related to mRNA metabolism, translation, and vesicles suggests a need for long-term monitoring of autoimmunity in COVID. The COVID autoantigen atlas we are establishing provides a detailed molecular map for further investigation of autoimmune sequelae of the pandemic, such as “long COVID” syndrome.

A Master Autoantigen-ome Links Alternative Splicing, Female Predilection, and COVID-19 to Autoimmune Diseases

Chronic and debilitating autoimmune sequelae pose a grave concern for the post-COVID-19 pandemic era. Based on our discovery that the glycosaminoglycan dermatan sulfate (DS) displays peculiar affinity to apoptotic cells and autoantigens (autoAgs) and that DS-autoAg complexes cooperatively stimulate autoreactive B1 cell responses, we compiled a database of 751 candidate autoAgs from six human cell types. At least 657 of these have been found to be affected by SARS-CoV-2 infection based on currently available multi-omic COVID data, and at least 400 are confirmed targets of autoantibodies in a wide array of autoimmune diseases and cancer. The autoantigen-ome is significantly associated with various processes in viral infections, such as translation, protein processing, and vesicle transport. Interestingly, the coding genes of autoAgs predominantly contain multiple exons with many possible alternative splicing variants, short transcripts, and short UTR lengths. These observations and the finding that numerous autoAgs involved in RNA-splicing showed altered expression in viral infections suggest that viruses exploit alternative splicing to reprogram host cell machinery to ensure viral replication and survival. While each cell type gives rise to a unique pool of autoAgs, 39 common autoAgs associated with cell stress and apoptosis were identified from all six cell types, with several being known markers of systemic autoimmune diseases. In particular, the common autoAg UBA1 that catalyzes the first step in ubiquitination is encoded by an X-chromosome escape gene. Given its essential function in apoptotic cell clearance and that X-inactivation escape tends to increase with aging, UBA1 dysfunction can therefore predispose aging women to autoimmune disorders. In summary, we propose a model of how viral infections lead to extensive molecular alterations and host cell death, autoimmune responses facilitated by autoAg-DS complexes, and ultimately autoimmune diseases. Overall, this master autoantigen-ome provides a molecular guide for investigating the myriad of autoimmune sequalae to COVID-19 and clues to the rare but reported adverse effects of the currently available COVID vaccines.

An autoantigen profile of human A549 lung cells reveals viral and host etiologic molecular attributes of autoimmunity in COVID-19

We aim to establish a comprehensive COVID-19 autoantigen atlas in order to understand autoimmune diseases caused by SARS-CoV-2 infection. Based on the unique affinity between dermatan sulfate and autoantigens, we identified 348 proteins from human lung A549 cells, of which 198 are known targets of autoantibodies. Comparison with current COVID data identified 291 proteins that are altered at protein or transcript level in SARS-CoV-2 infection, with 191 being known autoantigens. These known and putative autoantigens are significantly associated with viral replication and trafficking processes, including gene expression, ribonucleoprotein biogenesis, mRNA metabolism, translation, vesicle and vesicle-mediated transport, and apoptosis. They are also associated with cytoskeleton, platelet degranulation, IL-12 signaling, and smooth muscle contraction. Host proteins that interact with and that are perturbed by viral proteins are a major source of autoantigens. Orf3 induces the largest number of protein alterations, Orf9 affects the mitochondrial ribosome, and they and E, M, N, and Nsp proteins affect protein localization to membrane, immune responses, and apoptosis. Phosphorylation and ubiquitination alterations by viral infection define major molecular changes in autoantigen origination. This study provides a large list of autoantigens as well as new targets for future investigation, e.g., UBA1, UCHL1, USP7, CDK11A, PRKDC, PLD3, PSAT1, RAB1A, SLC2A1, platelet activating factor acetylhydrolase, and mitochondrial ribosomal proteins. This study illustrates how viral infection can modify host cellular proteins extensively, yield diverse autoantigens, and trigger a myriad of autoimmune sequelae. Our work provides a rich resource for studies into “long COVID” and related autoimmune sequelae.

An Autoantigen-ome from HS-Sultan B-Lymphoblasts Offers a Molecular Map for Investigating Autoimmune Sequelae of COVID-19

To understand how COVID-19 may induce autoimmune diseases, we have been compiling an atlas of COVID-autoantigens (autoAgs). Using dermatan sulfate (DS) affinity enrichment of autoantigenic proteins extracted from HS-Sultan lymphoblasts, we identified 362 DS-affinity proteins, of which at least 201 (56%) are confirmed autoAgs. Comparison with available multi-omic COVID data shows that 315 (87%) of the 362 proteins are affected in SARS-CoV-2 infection via altered expression, interaction with viral components, or modification by phosphorylation or ubiquitination, at least 186 (59%) of which are known autoAgs. These proteins are associated with gene expression, mRNA processing, mRNA splicing, translation, protein folding, vesicles, and chromosome organization. Numerous nuclear autoAgs were identified, including both classical ANAs and ENAs of systemic autoimmune diseases and unique autoAgs involved in the DNA replication fork, mitotic cell cycle, or telomerase maintenance. We also identified many uncommon autoAgs involved in nucleic acid and peptide biosynthesis and nucleocytoplasmic transport, such as aminoacyl-tRNA synthetases. In addition, this study found autoAgs that potentially interact with multiple SARS-CoV-2 Nsp and Orf components, including CCT/TriC chaperonin, insulin degrading enzyme, platelet-activating factor acetylhydrolase, and the ezrin-moesin-radixin family. Furthermore, B-cell-specific IgM-associated ER complex (including MBZ1, BiP, heat shock proteins, and protein disulfide-isomerases) is enriched by DS-affinity and up-regulated in B-cells of COVID-19 patients, and a similar IgH-associated ER complex was also identified in autoreactive pre-B1 cells in our previous study, which suggests a role of autoreactive B1 cells in COVID-19 that merits further investigation. In summary, this study demonstrates that virally infected cells are characterized by alterations of proteins with propensity to become autoAgs, thereby providing a possible explanation for infection-induced autoimmunity. The COVID autoantigen-ome provides a valuable molecular resource and map for investigation of COVID-related autoimmune sequelae and considerations for vaccine design.

An Autoantigen Profile of Human A549 Lung Cells Reveals Viral and Host Etiologic Molecular Attributes of Autoimmunity in COVID-19

We aim to establish a comprehensive COVID-19 autoantigen atlas in order to understand autoimmune diseases caused by SARS-CoV-2 infection. Based on the unique affinity between dermatan sulfate and autoantigens, we identified 348 proteins from human lung A549 cells, of which 198 are known targets of autoantibodies. Comparison with current COVID data identified 291 proteins that are altered at protein or transcript level in SARS-CoV-2 infection, with 191 being known autoantigens. These known and putative autoantigens are significantly associated with viral replication and trafficking processes, including gene expression, ribonucleoprotein biogenesis, mRNA metabolism, translation, vesicle and vesicle-mediated transport, and apoptosis. They are also associated with cytoskeleton, platelet degranulation, IL-12 signaling, and smooth muscle contraction. Host proteins that interact with and that are perturbed by viral proteins are a major source of autoantigens. Orf3 induces the largest number of protein alterations, Orf9 affects the mitochondrial ribosome, and they and E, M, N, and Nsp proteins affect protein localization to membrane, immune responses, and apoptosis. Phosphorylation and ubiquitination alterations by viral infection define major molecular changes in autoantigen origination. This study provides a large list of autoantigens as well as new targets for future investigation, e.g., UBA1, UCHL1, USP7, CDK11A, PRKDC, PLD3, PSAT1, RAB1A, SLC2A1, platelet activating factor acetylhydrolase, and mitochondrial ribosomal proteins. This study illustrates how viral infection can modify host cellular proteins extensively, yield diverse autoantigens, and trigger a myriad of autoimmune sequelae.

An Autoantigen Atlas from Human Lung HFL1 Cells Offers Clues to Neurological and Diverse Autoimmune Manifestations of COVID-19

COVID-19 is accompanied by a myriad of both transient and long-lasting autoimmune responses. Dermatan sulfate (DS), a glycosaminoglycan crucial for wound healing, has unique affinity for autoantigens (autoAgs) from apoptotic cells. DS-autoAg complexes are capable of stimulating autoreactive B cells and autoantibody production. Using DS affinity, we identified an autoantigenome of 408 proteins from human fetal lung fibroblast HFL11 cells, at least 231 of which are known autoAgs. Comparing with available COVID data, 352 proteins of the autoantigenome have thus far been found to be altered at protein or RNA levels in SARS-Cov-2 infection, 210 of which are known autoAgs. The COVID-altered proteins are significantly associated with RNA metabolism, translation, vesicles and vesicle transport, cell death, supramolecular fibrils, cytoskeleton, extracellular matrix, and interleukin signaling. They offer clues to neurological problems, fibrosis, smooth muscle dysfunction, and thrombosis. In particular, 150 altered proteins are related to the nervous system, including axon, myelin sheath, neuron projection, neuronal cell body, and olfactory bulb. An association with the melanosome is also identified. The findings from our study illustrate a strong connection between viral infection and autoimmunity. The vast number of COVID-altered proteins with propensity to become autoAgs offers an explanation for the diverse autoimmune complications in COVID patients. The variety of autoAgs related to mRNA metabolism, translation, and vesicles raises concerns about potential adverse effects of mRNA vaccines. The COVID autoantigen atlas we are establishing provides a detailed molecular map for further investigation of autoimmune sequelae of the pandemic.

Complication of Mycobacterium tuberculosis treatment: Isoniazid-induced pneumonitis

Prolonged therapy with isoniazid is used for the treatment of pulmonary tuberculosis. Drug-induced lupus erythematosus is a rare, adverse event associated with isoniazid use and can complicate treatment, especially if it is associated with pneumonitis. The diagnosis is made by clinical suspicion, elevated serum titers of anti-nuclear antibody and anti-histone antibody, and new ground-glass opacities on chest tomography. Bronchoscopy with bronchoalveolar lavage and transbronchial biopsy of affected areas of the lung is useful to increase diagnostic accuracy and differentiate between drug-induced pneumonitis, concomitant infection, or other inflammatory processes. Treatment includes systemic corticosteroids and cessation of isoniazid therapy.

A proteomic repertoire of autoantigens identified from the classic autoantibody clinical test substrate HEp-2 cells

BACKGROUND

Autoantibodies are a hallmark of autoimmune diseases. Autoantibody screening by indirect immunofluorescence staining of HEp-2 cells with patient sera is a current standard in clinical practice. Differential diagnosis of autoimmune disorders is based on commonly recognizable nuclear and cytoplasmic staining patterns. In this study, we attempted to identify as many autoantigens as possible from HEp-2 cells using a unique proteomic DS-affinity enrichment strategy.

METHODS

HEp-2 cells were cultured and lysed. Total proteins were extracted from cell lysate and fractionated with DS-Sepharose resins. Proteins were eluted with salt gradients, and fractions with low to high affinity were collected and sequenced by mass spectrometry. Literature text mining was conducted to verify the autoantigenicity of each protein. Protein interaction network and pathway analyses were performed on all identified proteins.

RESULTS

This study identified 107 proteins from fractions with low to high DS-affinity. Of these, 78 are verified autoantigens with previous reports as targets of autoantibodies, whereas 29 might be potential autoantigens yet to be verified. Among the 107 proteins, 82 can be located to nucleus and 15 to the mitotic cell cycle, which may correspond to the dominance of nuclear and mitotic staining patterns in HEp-2 test. There are 55 vesicle-associated proteins and 12 ribonucleoprotein granule proteins, which may contribute to the diverse speckled patterns in HEp-2 stains. There are also 32 proteins related to the cytoskeleton. Protein network analysis indicates that these proteins have significantly more interactions among themselves than would be expected of a random set, with the top 3 networks being mRNA metabolic process regulation, apoptosis, and DNA conformation change.

CONCLUSIONS

This study provides a proteomic repertoire of confirmed and potential autoantigens for future studies, and the findings are consistent with a mechanism for autoantigenicity: how self-molecules may form molecular complexes with DS to elicit autoimmunity. Our data contribute to the molecular etiology of autoimmunity and may deepen our understanding of autoimmune diseases.

When Chest Pain Reveals More: A Case of Hydrochlorothiazide-Induced Systemic Lupus Erythematosus

BACKGROUND Drug induced lupus erythematosus is considered an autoimmune entity which is precipitated by medications. Hydrochlorothiazide has been recognized to cause subacute cutaneous lupus erythematosus, but very few cases of systemic drug induced lupus systemic erythematosus have been reported. CASE REPORT A 57-year-old Caucasian male with a past medical history of hypertension and hyperlipidemia presented with recurrent fevers, chest pain, and dyspnea. Initial evaluation revealed diffuse ST elevations, small pericardial effusion, anemia, and leukopenia. He was initially treated with nonsteroidal anti-inflammatory drugs and prednisone for pericarditis. Six months later, he reported fatigue, arthralgias, morning stiffness, weight loss, fevers, and night sweats. Laboratory tests revealed persistent anemia and leukopenia. Extensive workup, including bone marrow biopsy and infectious evaluations, was negative. Autoimmune workup, however, revealed positive antihistone and antichromatin antibodies despite negative antinuclear antibody. A diagnosis of drug induced lupus secondary to hydrochlorothiazide was made. The medication was stopped, and prednisone was initiated resulting in marked improvement in his symptoms and hematologic abnormalities. CONCLUSIONS This report is one of the few known cases of systemic lupus erythematosus most likely induced by hydrochlorothiazide. Based on our finding, hydrochlorothiazide should be considered a possible offending agent when a patient presents with symptoms suspicious of drug induced lupus.

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.

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.

4-Hydroxy-2-nonenal modified histone-H2A: a possible antigenic stimulus for systemic lupus erythematosus autoantibodies

Protein modifications by 4-hydroxy-2-nonenals (HNE) are involved in various diseases. Histones are DNA protective nucleoprotein, which adopt different structures under oxidative stress. This study was undertaken to test the role of HNE-modified-histone-H2A (HNE-H2A) in systemic lupus erythematosus (SLE). Our data revealed that HNE-mediated-lipid peroxidation in histone-H2A caused alteration in histidine, lysine and cystein residues. In addition, protein carbonyl contents were also high in HNE-H2A. HNE-specific quencher, L-carnosine further reiterates HNE-modifications. Specificity of autoantibodies from SLE patients (n=48) were analyzed towards HNE-H2A and their results were compared with sex- and age-matched controls (n=36). SLE autoantibodies show preferential binding to HNE-H2A in comparison with histone-H2A (p<0.0001). Furthermore, HNE-H2A was also detected in SLE peripheral blood mononuclear cells. In conclusion, this is the first study to demonstrate the role of HNE-modified-histone in SLE. Preferential binding of HNE-H2A by affinity purified SLE-IgG pointed out the likely role of HNE-H2A in the initiation/progression of SLE.

Specific post-translational histone modifications of neutrophil extracellular traps as immunogens and potential targets of lupus autoantibodies

Introduction

Autoreactivity to histones is a pervasive feature of several human autoimmune disorders, including systemic lupus erythematosus (SLE). Specific post-translational modifications (PTMs) of histones within neutrophil extracellular traps (NETs) may potentially drive the process by which tolerance to these chromatin-associated proteins is broken. We hypothesized that NETs and their unique histone PTMs might be capable of inducing autoantibodies that target histones.

Methods

We developed a novel and efficient method for the in vitro production, visualization, and broad profiling of histone-PTMs of human and murine NETs. We also immunized Balb/c mice with murine NETs and profiled their sera on autoantigen and histone peptide microarrays for evidence of autoantibody production to their immunogen.

Results

We confirmed specificity toward acetyl-modified histone H2B as well as to other histone PTMs in sera from patients with SLE known to have autoreactivity against histones. We observed enrichment for distinctive histone marks of transcriptionally silent DNA during NETosis triggered by diverse stimuli. However, NETs derived from human and murine sources did not harbor many of the PTMs toward which autoreactivity was observed in patients with SLE or in MRL/lpr mice. Further, while murine NETs were weak autoantigens in vivo, there was only partial overlap in the immunoglobulin G (IgG) and IgM autoantibody profiles induced by vaccination of mice with NETs and those seen in patients with SLE.

Conclusions

Isolated in vivo exposure to NETs is insufficient to break tolerance and may involve additional factors that have yet to be identified.

Drug-induced lupus erythematosus: incidence, management and prevention

The generation of autoantibodies and autoimmune diseases such as systemic lupus erythematosus has been associated with the use of certain drugs in humans. Early reports suggested that procainamide and hydralazine were associated with the highest risk of developing lupus, quinidine with a moderate risk and all other drugs were considered low or very low risk. More recently, drug-induced lupus has been associated with the use of the newer biological modulators such as tumour necrosis factor (TNF)-α inhibitors and interferons. The clinical features and laboratory findings of TNFα inhibitor-induced lupus are different from that of traditional drug-induced lupus or idiopathic lupus, and standardized criteria for the diagnosis of drug-induced lupus have not been established. The mechanism(s) responsible for the development of drug-induced lupus may vary depending on the drug or even on the patient. Besides lupus, other autoimmune diseases have been associated with drugs or toxins. Diagnosis of drug-induced lupus requires identification of a temporal relationship between drug administration and symptom development, and in traditional drug-induced lupus there must be no pre-existing lupus. Resolution of symptoms generally occurs after cessation of the drug. In this review, we will discuss those drugs that are more commonly associated with drug-induced lupus, with an emphasis on the new biologicals and the difficulty of making the diagnosis of drug-induced lupus against a backdrop of the autoimmune diseases that these drugs are used to treat. Stimulation of the immune system by these drugs to cause autoimmunity may in fact be associated with an increased effectiveness in treating the pathology for which they are prescribed, leading to the dilemma of deciding which is worse, the original disease or the adverse effect of the drug. Optimistically, one must hope that ongoing research in drug development and in pharmacogenetics will help to treat patients with the maximum effectiveness while minimizing side effects. Vigilance and early diagnosis are critical. The purpose of this review is to summarize the most recent developments in our understanding of the incidence, pathogenesis, diagnosis and treatment of drug-induced lupus.

Toxicology of autoimmune diseases

Susceptibility to most autoimmune diseases is dependent on polygenic inheritance, environmental factors, and poorly defined stochastic events. One of the significant challenges facing autoimmune disease research is in identifying the specific events that trigger loss of tolerance and autoimmunity. Although many intrinsic factors, including age, sex, and genetics, contribute to autoimmunity, extrinsic factors such as drugs, chemicals, microbes, or other environmental factors can also act as important initiators. This review explores how certain extrinsic factors, namely, drugs and chemicals, can promote the development of autoimmunity, focusing on a few better characterized agents that, in most instances, have been shown to produce autoimmune manifestations in human populations. Mechanisms of autoimmune disease induction are discussed in terms of research obtained using specific animal models. Although a number of different pathways have been delineated for drug/chemical-induced autoimmunity, some similarities do exist, and a working model is proposed.

The use of laboratory methods in differential diagnosis and treatment of SLE and antiphospholipid syndrome

The detection of autoantibodies has become an important component in the diagnosis and management of systemic lupus erythematosus (SLE) and antiphospholipid syndrome. Their importance lies in the fact that they are not only markers of the disease and used as part of a diagnostic panel, but many of them also show correlation with disease activity. All antibody testing should be interpreted in the context of the clinical features. The antinuclear antibodies test is an effective screening assay in patients with clinical features of SLE. The combination of antinuclear antibodies test, dsDNA and ENA (Ro, La, Sm, RNP) antibodies help to establish the diagnosis of most patients with SLE. New antibodies, such as antinucleosomes and anti-C1q, appear to be useful for SLE diagnosis, monitoring disease activity and predicting renal flares, particularly in dsDNA-negative patients. Anticardiolipin antibodies and lupus anticoagulant are the tests most commonly used in the diagnosis of antiphospholipid syndrome. However, the use of anti-beta(2)-glycoprotein I as a routine diagnostic test remains controversial.

Anti-nuscleosome antibody, a reliable indicator for lupus nephritis

Systemic lupus erythematosus (SLE) is characterized by the presence of antinuclear antibodies (ANA). ANAs are aimed against native DNA, as well as histone proteins and small nuclear ribonucleoproteins, also could be targeted against the entire chromatin, consisted of nucleosomes. Herein, we assessed the frequency and the concentration of anti-nucleosome antibodies (aNS) in a group of 107 Hungarian patients with SLE. Moreover, correlations between these autoantibody concentrations and disease activity, as well as organ manifestations, mainly renal symptoms were evaluated. The occurrence of positive aNS, anti-dsDNA and anti-histone (aH) antibodies were 39.2, 28.0 and 47.6%, respectively. All the three autoantibodies were represented with significantly higher titers in patients with lupus nephritis. A positive correlation was found between the concentration of these autoantibodies and disease activity. The long disease duration (mean 8.5 years) and consequent low disease activity (mean disease activity index: 3.28) could be the reason for the relatively low occurrence of ANAs amongst patients. Besides anti-dsDNA, the assessment of aNS and aH antibodies could be useful in the diagnosis and follow-up of SLE. The authors discuss the possible role of aNS autoantibodies in the pathogenesis of lupus nephritis.

Nucleic acid-associated autoantigens: pathogenic involvement and therapeutic potential

Autoimmunity to ubiquitously expressed macromolecular nucleic acid-protein complexes such as the nucleosome or the spliceosome is a characteristic feature of systemic autoimmune diseases. Disease-specificity and/or association with clinical features of some of these autoimmune responses suggest pathogenic involvement which, however, has been proven in only a few cases so far. Although the mechanisms leading to autoimmunity against nucleic acid-containing complexes are still far from being fully understood, there is increasing experimental evidence that the nucleic acid component may act as a co-stimulator or adjuvans via activation of nucleic acid-binding receptor systems such as Toll-like receptors in antigen-presenting cells. Dysregulated apoptosis and inappropriate stimulation of nucleic acid-sensing receptors may lead to loss of tolerance against the protein components of such complexes, activation of autoreactive T cells and formation of autoantibodies. This has been demonstrated to occur in systemic lupus erythematosus and seems to represent a general mechanism that may be crucial for the development of systemic autoimmune diseases. This review provides a comprehensive overview of the most thoroughly-characterized nucleic acid-associated autoantigens, describing their structure and biological function, as well as the nature and pathogenic importance of the reactivities directed against them. Furthermore, recent advances in immunotherapy such as antigen-specific approaches targeted at nucleic acid-binding antigens are discussed.

[Drug-induced lupus]

Drug-induced lupus (DIL) is syndrome characterised by the occurrence of lupus-like symptoms and serological findings, following exposure to certain drugs. A substantial number of drugs can induce the positivity of antinuclear antibodies (ANA) but the diagnosis of DIL cannot be done in the absence of clinical features. Most patients with DIL have constitutional symptoms, arthralgia or occasionally arthritis, myalgias, fever and weight loss. These features may take weeks or months to develop and use to be mild with renal and central nervous system happening very rarely. ANA are always positive. They are mainly anti-histone proteins. Antibodies to ds-DNA are a rare finding and would tend to favour a diagnosis of idiopathic SLE. They have been associated with the use of tumour necrosis factor inhibitors (ant-TNF) and minocycline. Some drugs can induce particular symptoms o serological abnormalities and the diagnosis may be more difficult. It is the case of minocycline-induced lupus, which uses to affect young women with anti-ds-DNA and p-ANCA antibodies positive and negative anti-histone antibodies. Treatment with anti-TNF alpha is frequently associated with the development of ANA and anti-DNA. The incidence of ANA positive varies between 23-57% and anti-DNA between 9-33%. However, only a small number of patients will develop DIL or vasculitis. Resolution or marked improvement of the symptoms generally occurs within 2-5 weeks of the drugs withdrawal although some patients may require non-steroid anti-inflammatory drug or low dose steroid. Immunosuppressive drugs may be needed in severe cases with renal or neurological involvement. Some patients remain ANA positive for long periods of time. No treatment is necessary for ANA positive in the absence of clinical features.

Drug insight: autoimmune effects of medications-what's new?

Autoantibodies and lupus-like syndromes can develop following the use of certain medications; however, although many patients develop autoantibodies, only a minority develop clinical features. Although these autoantibodies primarily consist of antinuclear and antihistone antibodies, additional types of antibody, such as antineutrophil cytoplasmic antibodies and anti-double-stranded DNA antibodies, have been reported in association with minocycline and tumor necrosis factor inhibitor therapy. Clinical features of drug-related lupus usually consist of constitutional symptoms, arthralgias, arthritis, myalgias and serositis, although cutaneous manifestations have been reported in association with the use of tumor necrosis factor inhibitors. Typically, clinical features resolve with discontinuation of the medication, although antibodies can persist for months or years. Arthralgias and inflammatory arthritis have also been reported in association with the use of aromatase inhibitors and other biologic agents such as interleukins and interferons.

Pathogenic profiles and molecular signatures of antinuclear autoantibodies rescued from NZM2410 lupus mice

Two outstanding questions concerning antinuclear antibodies (ANAs) in lupus involve their pathogenic potential and their molecular signatures. To address these questions, a panel of 56 antinuclear and 47 nonnuclear binding monoclonal antibodies was rescued from four seropositive NZM2410 lupus mice. The monoclonals varied in their reactivity to nucleosomes, ssDNA, dsDNA, and glomerular substrate. A large fraction of the antibodies demonstrated apparent polyreactivity (to DNA, histones, and glomerular antigens) due to bound, DNase-1 sensitive nuclear antigenic bridges. Although nephrophilic immunoglobulin (Ig) M and IgG antibodies were the most pathogenic, the dsDNA-binding antibodies were modestly so; in contrast, antinucleosome antibodies were clearly not pathogenic. Compared with the nonnuclear antigen-binding monoclonal antibodies rescued from the same mice, ANAs exhibited increased utilization of VH5/7183 genes and highly cationic heavy chain (HC) CDR3 regions. Most intriguingly, the CDR3 regions of the ANAs exhibited alternating arginine/lysine peaks at H96, H98, and H100, with neutral troughs at H95, H97, and H99. To summarize, glomerular-binding anti-dsDNA antibodies appear to be the most pathogenic variety of lupus autoantibodies. The presence of an alternating charge pattern in their HC CDR3 regions appears to be a prominent hallmark of ANAs.

Nucleosomes in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by the development of a large array of autoantibodies that primarily are directed against the whole chromatin (antinucleosome) and its individual components, dsDNA and histones. Apoptotic defects and impaired removal of apoptotic cells could contribute to an overload of autoantigens (and in particular of nucleosomes) in circulation or in target tissues that could become available to initiate an autoimmune response. In susceptible individuals, this can lead to autoantibody-mediated tissue damage. In addition to intrinsic or secondary apoptosis/apoptotic cell removal defects, certain apoptotic stimuli (eg, UV, viruses) could lead to posttranscriptional modifications that generate autoantigen cryptic fragments for which cells of the immune system have not been tolerized. Besides their role as a major immunogen in lupus, nucleosomes participate in antibody-mediated renal pathogenicity and act as a bridging molecule that recognizes heparin sulfate/collagen V components of the glomerular basement membrane. New tools that were developed to detect antinucleosome antibodies in the serum of patients (by ELISA) have shown the specificity and the high sensitivity of antinucleosome antibody reactivity in SLE. In particular, antinucleosome could be a useful marker of patients who have SLE and lack anti-dsDNA antibodies, a prognosis marker for imminent relapse, and a diagnosis marker of lupus nephritis.

Concomitant early appearance of anti-ribonucleoprotein and anti-nucleosome antibodies in lupus prone mice

OBJECTIVE

To gain insights on initial stages of the autoimmune response in lupus prone mice taking advantage of new sensitive and quantitative techniques for the detection of autoantibodies specific for RNA- (ribonucleoproteins) and DNA-protein (chromatin) complexes.

METHODS

DNA and nucleosome antibodies were detected by ELISA, antibodies to SmB, U1A-RNP, Ro52, Ro60 and La by a new radioligand assay, using de novo synthesized radio-labeled antigens.

RESULTS

Analysis of anti-chromatin (including anti-nucleosome, anti-dsDNA and anti-histone antibodies) and of anti-snRNP antibodies (including anti-U1A-RNP, anti-SmB, anti-Ro52, anti-Ro60, anti-La antibodies) was performed in sequential sera from B/W, MRL+/+, MRL Yaa and MRL lpr/lpr mice. In a cohort of 105 MRL+/+ mice of different ages, 59, 51, and 57 mice were positive for anti-nucleosome, anti-SmB and anti-U1A-RNP, respectively. None of them was positive for anti-dsDNA. Importantly, antibody positivities were not randomly distributed but were significantly clustered in individual mice. Appearance of DNA- and RNA-protein complex antibodies started at approximately 18-20 weeks of age, preceding that of the anti-dsDNA (or anti-histone) antibodies that only started at 30-32 weeks. Anti-nucleosome, anti-SmB and anti-U1A-RNP antibody responses did not display any cross-reactivity as demonstrated by inhibition and adsorption experiments.

CONCLUSION

These data indicate that anti-nucleosome and anti-snRNP antibodies appear early and concomitantly in lupus prone mice even though they do not share any cross-reactivity. These results fit with the assumption that their production is triggered by tightly physically associated nucleosomes and snRNP autoantigens contained in the same apoptotic bodies.

The major murine systemic lupus erythematosus susceptibility locus Sle1 results in abnormal functions of both B and T cells

Sle1 is a major susceptibility locus in the NZM2410 murine model of systemic lupus erythematosus. When isolated on a C57BL/6 background in the B6.Sle1 congenic strain, Sle1 results in the production of high levels of anti-chromatin IgG Abs, histone-specific T cells, and increased B and T cell activation. We have shown by mixed bone marrow chimeras with allotypic markers that Sle1 is expressed in B cells. Using the same technique, we now show that it is also expressed in T cells. To assess whether Sle1 results in intrinsic defects in B or T cells, we have bred the muMT and Tcralpha(-/-) mutations onto B6.Sle1 resulting in the absence of circulating B cells and alphabeta T cells in B6.Sle1.muMT and B6.Sle1.Tcralpha(-/-), respectively. The immune phenotypes in these two strains were compared with that of B6.Sle1 and B6.muMT or B6.Tcralpha(-/-). Sle1-expressing B cells broke tolerance to chromatin in the absence of T cells, as shown by high levels of anti-ssDNA IgM Abs in B6.Sle1.Tcralpha(-/-) mice, and had an increased expression of activation markers. Conversely, increased expression of activation markers and increased cytokine production were observed in Sle1-expressing T cells in the absence of B cells in B6.Sle1.muMT mice. However, the production of IgG antinuclear Abs required the presence of both T and B cells. These experiments showed that Sle1 expression results in both B and T cells intrinsic defects and demonstrate that the documented involvement of each cell compartment in the production of anti-chromatin Abs corresponds to genetic defects rather than bystander effects.

Genetic dissection of SLE: SLE1 and FAS impact alternate pathways leading to lymphoproliferative autoimmunity

Genetic dissection of lupus pathogenesis in the NZM2410 strain has recently revealed that Sle1 is a potent locus that triggers the formation of IgG anti-histone/DNA antibodies, when expressed on the B6 background as a congenic interval. B6.lpr mice, in contrast, exhibit distinctly different cellular and serological phenotypes. Both strains, however, do not usually exhibit pathogenic autoantibodies, or succumb to lupus nephritis. In this study, we show that the epistatic interaction of Sle1 (in particular, Sle1/Sle1) with FAS(lpr) leads to massive lymphosplenomegaly (with elevated numbers of activated CD4 T cells, CD4(-)CD8(-) double negative (DN) T cells, and B1a cells), high levels of IgG and IgM antinuclear (including anti-ssDNA, anti-dsDNA, and anti-histone/DNA), and antiglomerular autoantibodies, histological, and clinical evidence of glomerulonephritis, and >80% mortality by 5-6 mo of age. Whereas FAS(lpr) functions as a recessive gene, Sle1 exhibits a gene dosage effect. These studies indicate that Sle1 and FAS(lpr) must be impacting alternate pathways leading to lymphoproliferative autoimmunity.

Development of a CENP-A/CENP-B-specific immune response in a patient with systemic sclerosis

Antibodies directed against an epitope motif on CENP-A have been shown to cross-react with mimotopes on other autoantigens and on Epstein-Barr nuclear antigen 1 (EBNA-1), suggesting a molecular mimicry. We describe here the gradual development of an anticentromere immune response in a patient with systemic sclerosis, which started from an antihistone response and was not mediated by molecular mimicry. Via an epitope on histone H3, the antibody response spread to a homologous epitope in the H3 homology domain of CENP-A. This was followed by an intramolecular epitope spreading to N-terminal peptides of CENP-A containing the known epitope motif G-P-X(1)-R-X(2). From there it spread to corresponding epitopes on CENP-B and to mimotopes of the major CENP-A epitope motif on other autoantigens including EBNA-1. Whether the D-penicillamine treatment received by this patient was involved in the triggering of this cascade remains a matter of speculation.

High mass clearance of autoantibodies from a murine model of lupus nephritis by immunoadsorption using star-configured polyethylene glycols

The extracorporeal immunoadsorption of antibodies as part of the therapy for human autoimmune diseases has been limited by technology with inadequate and nonselective mass clearance or problems with bioincompatibility. To overcome these shortcomings, we designed a method utilizing star-configured polyethylene glycols (star-PEGs) having up to 63 free arms with immunoreactive (tresylate ester) end-groups for each arm immobilized to a polymer support substrate. The flexibility and length of the arms are thought to allow optimization of epitope presentation and to permit interaction with immunoligands on adjacent arms. To demonstrate efficacy we used an in vitro murine antibody model of human lupus nephritis, wherein we could study the kinetics and mass clearance of hybridoma derived antihistone antibodies from human plasma. Histones were covalently bound to the star-PEG end-groups and the kinetics of antibody adsorption were assessed using a surface plasmon resonance technique. The equilibrium constants of antihistone antibody binding to histone-star-PEGs that were linked to a support grid demonstrated high affinity with a KA of 3.56E + 07 and a KD of 2.81E - 08. The optimum reaction conditions were determined to accomplish the hydrophilization of polysulfone (PS; by an aqueous nitration method) and polymethylmethacrylate substrates (PMMA; by hydrazine), using sheet casts of both polymer substances. Hollow fiber devices of these polymers (commercial hemodialyzers) were modified so that histone-bound star-PEGs were linked to their intracapillary luminal surfaces, using a process which we have shown retains their immunoadsorption properties for antihistone antibodies. A closed loop recirculating model was constructed to measure mass clearance of antibodies from a reservoir. After optimizing conditions using extraction from saline solutions, the removal of antibody from human plasma by control and surface-modified devices was assessed over 4 h. There was no measurable antibody clearance by the control fibers over this time interval. The 2.1 m2 luminal surface area PMMA devices removed 5.0 +/- 1.1 mg, with a maximum of 7.0 mg. The 1.8 m2 PS device cleared 11.3 +/- 6.2 mg with a maximum of 17.5 mg. In summary, star-PEG immunoadsorption is a promising technique for the treatment of human autoimmune disease because it can achieve very high-mass clearance of autoantibodies using modified biocompatible hollow-fiber polymer devices.

Lessons from the NZM2410 model and related strains

SLE susceptibility requires the interplay of an unknown number of genes and equally unidentified triggering events. The past few years have seen significant advances in our understanding of SLE susceptibility through the genetic analysis of murine models. The NZM2410 strain, which is derived from the NZB/WF1 model has played a significant role in these advances. The main advantages presented by this strain over other models are the genetic homozygozity at all loci and an highly penetrant early onset lupus nephritis in both males and females, indicating that the strongest BWF1 susceptibility loci were retained in NZM2410. After identification of NZM2410 susceptibility loci via linkage analyses, congenic strains have been derived in order to convert a polygenic system into a series of monogenic traits. These congenic strains have been analyzed in an integrated process which has provided simultaneously 1) novel functional characterization of the Sle susceptibility loci, 2) high resolution genetic maps that will lead to the identification of the corresponding susceptibility genes by either candidate locus or positional cloning, and 3) insights into the mechanisms by which these loci interact to produce systemic autoimmunity with fatal end-organ damage.

The major murine systemic lupus erythematosus susceptibility locus, Sle1, is a cluster of functionally related genes

The major murine systemic lupus erythematosus (SLE) susceptibility locus Sle1 is syntenic to a chromosomal region linked with SLE susceptibility in multiple human studies. Congenic analyses have shown that Sle1 breaks tolerance to chromatin, a necessary step for full disease induction that can be suppressed by specific modifier loci. In the present study, our fine mapping analysis of the location of Sle1 has determined that three loci within this congenic interval, termed Sle1a, Sle1b, and Sle1c, can independently cause a loss of tolerance to chromatin. Each displays a distinctive profile of serological and cellular characteristics, with T and B cell functions being more affected by Sle1a and Sle1b, respectively. The epistatic interactions of Sle1 with other susceptibility loci to cause severe nephritis cannot be accounted, however, by these three loci alone, suggesting the existence of an additional locus, termed Sle1d. These findings indicate that the potent autoimmune phenotype caused by the Sle1 genomic interval reflects the combined impact of four, separate, susceptibility genes. This level of genetic complexity, combined with similar findings in other systems, supports the possibility that many complex trait loci reflect the impact of polymorphisms in linked clusters of genes with related functions.

The major murine systemic lupus erythematosus susceptibility locus, Sle1, is a cluster of functionally related genes

The major murine systemic lupus erythematosus (SLE) susceptibility locus Sle1 is syntenic to a chromosomal region linked with SLE susceptibility in multiple human studies. Congenic analyses have shown that Sle1 breaks tolerance to chromatin, a necessary step for full disease induction that can be suppressed by specific modifier loci. In the present study, our fine mapping analysis of the location of Sle1 has determined that three loci within this congenic interval, termed Sle1a, Sle1b, and Sle1c, can independently cause a loss of tolerance to chromatin. Each displays a distinctive profile of serological and cellular characteristics, with T and B cell functions being more affected by Sle1a and Sle1b, respectively. The epistatic interactions of Sle1 with other susceptibility loci to cause severe nephritis cannot be accounted, however, by these three loci alone, suggesting the existence of an additional locus, termed Sle1d. These findings indicate that the potent autoimmune phenotype caused by the Sle1 genomic interval reflects the combined impact of four, separate, susceptibility genes. This level of genetic complexity, combined with similar findings in other systems, supports the possibility that many complex trait loci reflect the impact of polymorphisms in linked clusters of genes with related functions.

Anti-subnucleosome reactivities in systemic lupus erythematosus (SLE) patients and their first-degree relatives

Antibodies specific for dsDNA appear to have different genetic origins and pathogenic consequences, compared with histone/dsDNA-specific antibodies, in a recently described murine model. The purpose of this study was to examine if this is also true in human lupus. Sera from 40 SLE families (comprising 40 probands and 153 first-degree relatives), and 45 normal adult controls were assayed for the levels of anti-dsDNA, anti-H1/dsDNA, anti-H2A/H2B/dsDNA, and anti-H3/H4/dsDNA autoantibodies by ELISA. Both the probands and the first-degree relatives exhibited significantly increased levels of antinuclear antibodies (ANA) targeting the different subnucleosomal epitopes. Importantly, probands with anti-dsDNA antibodies had a significantly higher incidence of renal disease compared with those with just anti-H2A/H2B/dsDNA antibodies, in resonance with murine studies. The frequency of anti-dsDNA and anti-H2A/H2B/DNA ANA among the first-degree relatives was 11.8% and 18.3%, respectively. Surprisingly, whereas probands with anti-dsDNA ANA had families with several seropositive members, first-degree relatives of patients with anti-H2A/H2B/DNA ANA (but not anti-dsDNA ANA) were uniformly ANA-free. These findings suggest that anti-dsDNA ANA in lupus may not only have worse disease associations, they may also have very different genetic origins, compared with anti-H2A/H2B/DNA (or anti-nucleosome) ANA.

Drug-induced rheumatic disorders: incidence, prevention and management

The purpose of this article is to review the causes, the clinical manifestations and the management of the more frequent drug-induced rheumatic disorders. These include: (i) articular and periarticular manifestations induced by fluoroquinolones, nonsteroidal anti-inflammatory drugs, injections of corticosteroids, and retinoids; (ii) multisystemic manifestations such as drug-induced lupus and arthritis induced by vaccination, Bacillus Calmette-Guerin therapy and cytokines; (iii) drug-induced disorders of bone metabolism (corticosteroid-induced osteoporosis, drug-induced osteomalacia and osteonecrosis); and (iv) iatrogenic complex regional pain syndromes. Disorders caused by nonpharmacological and rarely used treatments have been deliberately excluded. Knowledge of these drug-induced clinical symptoms or syndromes allows an earlier diagnosis and treatment, and earlier drug withdrawal if necessary. With the introduction of new medications such as the recombinant cytokines and antiretroviral treatments, the number of drug-induced rheumatic disorders is likely to increase.

Optimization of ligand presentation for immunoadsorption using star-configured polyethylene glycols

Medical, pharmaceutical, and industrial applications of immunoadsorption are frequently limited by the technologic problems of low affinity, inadequate capacity, hydrophobicity, and bioincompatibility. To overcome these difficulties we studied the use of star-burst configured polyethylene glycols (star-PEGs) with immunoreactive molecules covalently bound to the end of each of the multiple flexible arms. The optimum pH ranges were determined to maintain stability of the tresyl chloride modified star reagents, and the chemistry was designed for their subsequent linkage to the immunoadsorbent moiety. We then devised the chemical reactions using nitration or hydrazine activation to tether these 64-arm structures to polymer supports made of polysulfone or polymethylmethacrylate, respectively. Transmission, scanning, and atomic force microscopy confirmed the preservation of the star configuration, even after linkage to the luminal surface of hollow fiber devices. To establish that these modified devices also maintained immunoadsorption reactivity, we used a model having relevance for human autoimmune disease and demonstrated the clearance of antihistone antibodies by tethered histones. This novel approach to increasing the capacity of immunoadsorption benefits from the star configuration which provides a high density of ligand, improved hydrophilicity of the surface, spacing of reactive molecules away from the support structure, and possible optimization of epitope immunoreactivity by arm-to-arm interaction of the bound molecules.

Presence of antinucleosome autoantibodies in a restricted set of connective tissue diseases: antinucleosome antibodies of the IgG3 subclass are markers of renal pathogenicity in systemic lupus erythematosus

OBJECTIVE

To study the frequency and disease specificity of antinucleosome antibody reactivity in diverse connective tissue diseases (CTD), and to determine factors, such as antibody subclass, that may influence the pathogenicity of these antibodies in relation to disease activity.

METHODS

IgG and IgM antinucleosome activities on nucleosome core particles from 496 patients with 13 different CTD and 100 patients with hepatitis C were measured by enzyme-linked immunosorbent assay (ELISA). Of the patients with CTD, 120 had systemic lupus erythematosus (SLE), 37 had scleroderma (systemic sclerosis; SSc), 20 had mixed connective tissue disease (MCTD), and 319 had other CTD, including Sjögren's syndrome, inflammatory myopathy, rheumatoid arthritis, primary antiphospholipid syndrome, Wegener's granulomatosis, Takayasu arteritis, giant cell arteritis, relapsing polychondritis, Behçet's syndrome, and sarcoidosis. Antinucleosome-positive sera were further analyzed, by isotype-specific ELISA, for antinucleosome and anti-double-stranded DNA (anti-dsDNA) IgG subclasses.

RESULTS

SLE, SSc, and MCTD were the only 3 CTD in which antinucleosome IgG were detected (71.7%, 45.9%, and 45.0% of patients, respectively). Antinucleosomes of the IgG3 subclass were present at high levels in patients with active SLE and were virtually absent in those with SSc, MCTD, or inactive SLE, and their levels showed a positive correlation with SLE disease activity. Of note, an increase in levels of antinucleosome of the IgG3 isotype was observed during SLE flares, and this increase was found to be closely associated with active nephritis. Levels of antinucleosome of the IgG1 subclass showed a trend toward an inverse correlation with SLE disease activity. No significant fluctuation in the anti-dsDNA isotype profile was observed in relation to SLE severity or clinical signs.

CONCLUSION

Our data suggest that IgG antinucleosome is a new marker that may help in the differential diagnosis of CTD; antinucleosome of the IgG3 isotype might constitute a selective biologic marker of active SLE, in particular, of lupus nephritis.

Immunopathogenesis of environmentally induced lupus in mice

Systemic lupus erythematosus (SLE) is a systemic autoimmune syndrome defined by clinical and serologic features, including arthritis, glomerulonephritis, and certain autoantibodies such as anti-nuclear ribonucleoprotein (nRNP)/Smith antigen (Sm), DNA, and ribosomal P. Although lupus is considered primarily a genetic disorder, we recently demonstrated the induction of a syndrome strikingly similar to spontaneous lupus in many nonautoimmune strains of mice exposed to the isoprenoid alkane pristane (2,6,10,14-tetramethylpentadecane), a component of mineral oil. Intraperitoneal injection of pristane leads to the formation of lipogranulomas consisting of phagocytic cells that have engulfed the oil and collections of lymphocytes. Subsequently, pristane-treated BALB/c and SJL mice develop autoantibodies characteristic of SLE, including anti-nRNP/Sm, antiribosomal P, anti-Su, antichromatin, anti-single-stranded DNA, and anti-double-stranded DNA. This is accompanied by a severe glomerulonephritis with immune complex deposition, mesangial or mesangiocapillary proliferation, and proteinuria. All inbred mice examined appear to be susceptible to this novel form of chemically induced lupus. Pristane-induced lupus is the only inducible model of autoimmunity associated with the clinical syndrome as well as with the characteristic serologic abnormalities of SLE. Defining the immunopathogenesis of pristane-induced lupus in mice may provide insight into the causes of spontaneous (idiopathic) lupus and also may lead to information concerning possible risks associated with the ingestion or inhalation of mineral oil and exposure to hydrocarbons in the environment.

Lupus-prone mice as models to study xenobiotic-induced acceleration of systemic autoimmunity

The linkage between xenobiotic exposures and autoimmune diseases remains to be clearly defined. However, recent studies have raised the possibility that both genetic and environmental factors act synergistically at several stages or checkpoints to influence disease pathogenesis in susceptible populations. These observations predict that individuals susceptible to spontaneous autoimmunity should be more susceptible following xenobiotic exposure by virtue of the presence of predisposing background genes. To test this possibility, mouse strains with differing genetic susceptibility to murine lupus were examined for acceleration of autoimmune features characteristic of spontaneous systemic autoimmune disease following exposure to the immunostimulatory metals nickel and mercury. Although NiCl(2) exposure did not exacerbate autoimmunity, HgCl(2) significantly accelerated systemic disease in a strain-dependent manner. Mercury-exposed (NZB X NZW)F1 mice had accelerated lymphoid hyperplasia, hypergammaglobulinemia, autoantibodies, and immune complex deposits. Mercury also exacerbated immunopathologic manifestations in MRL+/+ and MR -lpr mice. However, there was less disease acceleration in lpr mice compared with MRL+/+ mice, likely due to the fact that environmental factors are less critical for disease induction when there is strong genetic susceptibility. Non-major histocompatibility complex genes also contributed to mercury-exacerbated disease, as the nonautoimmune AKR mice, which are H-2 identical with the MRL, showed less immunopathology than either the MRL/lpr or MRL+/+ strains. This study demonstrates that genetic susceptibility to spontaneous systemic autoimmunity can be a predisposing factor for HgCl(2)-induced exacerbation of autoimmunity. Such genetic predisposition may have to be considered when assessing the immunotoxicity of xenobiotics. Additional comparative studies using autoimmune-prone and nonautoimmune mice strains with different genetic backgrounds will help determine the contribution that xenobiotic exposure makes in rendering sensitive populations susceptible to autoimmune diseases.

Genetic dissection of lupus pathogenesis: a recipe for nephrophilic autoantibodies

Sle1 and Sle3 are 2 loci that confer susceptibility to lupus nephritis in the NZM2410 strain of mice. Our previous work has shown that B6.NZMc1 mice, congenic for Sle1, exhibit loss of tolerance to chromatin but do not develop any pathogenic autoantibodies or disease. B6.NZMc7 mice, congenic for Sle3, exhibit low-grade polyclonal B- and T-cell activation, elevated CD4/CD8 ratios, and mildly penetrant glomerulonephritis. In contrast to these monocongenics, the present study reveals that B6.NZMc1|c7 mice, bicongenic for Sle1 and Sle3, exhibit splenomegaly, significantly expanded populations of activated B and CD4(+) T cells, and a robust, variegated IgG autoantibody response targeting multiple components of chromatin (including double-stranded DNA), intact glomeruli, and basement membrane matrix antigens. As one might predict, these mice, particularly the females, exhibit highly penetrant glomerulonephritis. These findings lend strong support to a two-step epistatic model for the formation of pathogenic, nephrophilic autoantibodies in lupus. Whereas loci such as Sle1 may serve to breach tolerance to chromatin, full-blown pathogenic maturation of the autoantibody response appears to require additional input from other loci (such as Sle3) and gender-based factors.

Nuclear antigen histone H1 is primarily involved in lupus erythematosus cell formation

OBJECTIVE

To elucidate the nature of the antigen reactive with the "lupus erythematosus (LE) cell factor," the autoantibody involved in the LE cell phenomenon.

METHODS

Serum samples from systemic lupus erythematosus (SLE) patients who were positive for the LE cell phenomenon (LEc+) and SLE patients who were negative for the LE cell phenomenon (LEc-) were used to characterize the nuclear antigen bound by the LE cell factor, by immunoblotting and immunoprecipitation techniques.

RESULTS

All LEc+ sera, but none of the LEc- sera, uniformly reacted with a double band of MW approximately 30 kd in nuclear extracts. Depletion of nuclear protein extracts of antigens bound by pooled LEc- serum allowed precipitation of a low molecular weight protein by pooled LEc+ serum. This protein was able to block LE cell formation by LEc+ serum. Based on its reactivity with antihistone antibody and an electrophoretic mobility identical with that of precipitated and purified histone H1, this protein was identified as histone H1. Moreover, all LEc+ sera, but none of the LEc- sera, reacted with purified histone H1 by immunoblotting, whereas other histones were reactive with both types of sera. In addition, purified histone H1, but none of the other histones, strongly inhibited the induction of LE cells by LEc+ serum.

CONCLUSION

Histone H1 represents the major antigenic component recognized by the LE cell factor. Thus, the LE cell phenomenon appears to be due primarily to anti-histone H1 reactivity.

Antigen specificity of antihistone antibodies in systemic sclerosis

OBJECTIVES

The aim of the study was to determine the prevalence and clinical significance of antibodies to individual histone components in systemic sclerosis (SSc).

METHODS

Serum samples from patients with limited cutaneous SSc (lSSc; n = 42) and diffuse cutaneous SSc (dSSc; n = 28) were examined for IgG and/or IgM antibodies to individual histone components and complexes by enzyme linked immunosorbent assay (ELISA).

RESULTS

The level of IgG antibody to total histones was significantly higher in lSSc and dSSc than in normal controls. The level of IgM antibody to total histones was significantly higher in lSSc, but not in dSSc, than in normal controls. IgG antibody to total histones tended to be increased in dSSc when compared with that in lSSc. On the other hand, IgM antibody to total histones tended to be increased in lSSc when compared with that in dSSc. Although SSc showed various antihistone specificities, H2B, H2A-H2B, (H2A-H2B)-dsDNA were main antigens recognised by IgG antibodies in both lSSc and dSSc. Although IgM antibodies to H2B and H2A-H2B were also detected in both lSSc and dSSc, serum samples from lSSc patients exhibited highest IgM reactivity with H1.

CONCLUSION

SSc may be included among conditions in which heterogeneous antihistone antibodies are produced. IgM antibodies to the most accessible histone H1 may be related to mild clinical features (lSSc) and IgG antibodies to the inner core molecules of native histone such as H2B or complexes including H2B may be associated with severe clinical features (dSSc) in Ssc.

Genetic dissection of SLE pathogenesis. Sle1 on murine chromosome 1 leads to a selective loss of tolerance to H2A/H2B/DNA subnucleosomes

One of the hallmarks of SLE is the loss of tolerance to chromatin. The genes and mechanisms that trigger this loss of tolerance remain unknown. Our genetic studies in the NZM2410 lupus strain have implicated genomic intervals on chromosomes 1 (Sle1), 4 (Sle2), and 7 (Sle3) as conferring strong lupus susceptibility. Interestingly, B6 mice that are congenic for Sle1 (B6.NZMc1) have elevated IgG antichromatin Abs. This study explores the antinuclear antibody fine specificities and underlying cellular defects in these mice. On the B6 background, Sle1 by itself is sufficient to generate a robust, spontaneous antichromatin Ab response, staining Hep-2 nuclei homogeneously, and reacting primarily with H2A/H2B/DNA subnucleosomes. This targeted immune response peaks at 7-9 mo of age, affects both sexes with equally high penetrance (> 75%), and interestingly, does not "spread" to other subnucleosomal chromatin components. Sle1 also leads to an expanded pool of histone-reactive T cells, which may have a role in driving the anti-H2A/H2B/DNA B cells. However, these mice do not exhibit any generalized immunological defects or quantitative aberrations in lymphocyte apoptosis. We hypothesize that Sle1 may lead to the presentation of chromatin in an immunogenic fashion, or directly impact tolerance of chromatin-specific B cells.