The anti-Sm immune response in autoimmunity and cell biology

Transforming mutations in the development of pathogenic B cell clones and autoantibodies

Autoimmune diseases are characterized by serum autoantibodies, some of which are pathogenic, causing severe manifestations and organ injury. However, autoantibodies of the same antigenic reactivity are also present in the serum of asymptomatic people years before they develop any clinical signs of autoimmunity. Autoantibodies can arise during multiple stages of B cell development, and various genetic and environmental factors drive their production. However, what drives the development of pathogenic autoantibodies is poorly understood. Advances in single-cell technology have enabled the deep analysis of rare B cell clones producing pathogenic autoantibodies responsible for vasculitis in patients with primary Sjögren's syndrome complicated by mixed cryoglobulinaemia. These findings demonstrated a cascade of genetic events involving stereotypic immunoglobulin V(D)J recombination and transforming somatic mutations in lymphoma genes and V(D)J regions that disrupted antibody quality control mechanisms and decreased autoantibody solubility. Most studies consider V(D)J mutations that enhance autoantibody affinity to drive pathology; however, V(D)J mutations that increase autoantibody propensity to form insoluble complexes could be a major contributor to autoantibody pathogenicity. Defining the molecular characteristics of pathogenic autoantibodies and failed tolerance checkpoints driving their formation will improve prognostication, enabling early treatment to prevent escalating organ damage and B cell malignancy.

The role of cyclic GMP-AMP synthase and Interferon-I-inducible protein 16 as candidatebiomarkers of systemic lupus erythematosus

BACKGROUND

Diverse clinical and serological manifestations of systemic lupus erythematosus (SLE) compromise its diagnosis and treatment. A more reliable biomarker for SLE, which can play a critical role in either diagnosis, monitoring the disease progress or evaluating the response to treatment for individualized therapeutic, is necessary. DNA sensor is an important mediator of inflammation in systemic autoimmune diseases. However, the potential role for DNA sensor as disease activity biomarkers for SLE remained obscure. We detected the aberrant activation of DNA sensors and the corresponding IFN-β response in SLE patients, and to evaluate their potential role as disease biomarkers for SLE.

METHODS

We quantified the expressions of IFN-I and DNA sensor, such as cGAS, IFI16, DDX41, DAI and their down-stream adaptor STING in PBMC derived from patients with SLE (n = 100), healthy controls (HCs) (n = 62) by real-time PCR. The relationships between the expression of cGAS or IFI16 and clinical features in SLE patients were investigated. ROC curve analysis was performed to examine the predictive value of cGAS and IFI16 in SLE diagnosis, disease activity monitoring, specific organ manifestation and therapeutic response. RNA interference-mediated depletion of IFI16 or cGAS was conducted to evaluate their impact on IFN-I response.

RESULTS

The expressions of cGAS and IFI16 were significantly higher in PBMC from SLE patients, closely correlated with the SLEDAI scores and high anti-dsDNA antibody titers. While the AUC for cGAS (0.767) was less than that of IFI16 and IFN-β, the AUC for IFI16 (0.856) and IFN-β (0.856) were similar. Expression of cGAS and IFI16 combine with IFN-β in PBMC showed high sensitivity (89.2%) and specificity (89.1%) for discrimination between mild and moderate/severe disease activity in SLE. Higher expression of IFI16 was association with ocular disorder in SLE patients. Neither IFI16 nor cGAS was a reliable indicator of therapeutic response. RNA interference-mediated depletion of IFI16 or cGAS prevented active SLE serum-induced upregulating in both IFN-α and IFN-β.

CONCLUSIONS

High expression levels of cGAS and IFI16 in PBMC from SLE patients correlated strongly with disease activity. Both cGAS and IFI16 mediated signaling pathway were account for the robust production of IFN-β. Expression of cGAS and IFI16 combined with IFN-β in PBMC might serve as potential biomarkers for early diagnosis and monitoring disease activity in SLE.

Anti-Sm antibodies in the classification criteria of systemic lupus erythematosus

Systemic lupus erythematosus is characterized by autoantibodies and immune complex deposition. Several autoantibodies against mainly nuclear autoantigens have been described. One of these nuclear autoantigens is the Smith antigen. In this review, we focus on the position of autoantibodies against the Smith antigen in the classification criteria, the characteristics of the antigen, the production of anti-Smith antibodies in SLE and we discuss the different test methods available, together with their pitfalls, to detect these autoantibodies.

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Patients having anti-Sm antibodies already fulfil sixty percent of the criteria required for SLE classification.

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Correct interpretation of anti-Smith antibody test results is strongly related to the choice of the test used for detection.

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Anti-Sm antibodies are very specific for SLE.

Chinese SLE Treatment and Research Group Registry (CSTAR) XIII: prevalence and risk factors for chronic scarring alopecia in patients with systemic lupus erythematosus

Background

Scarring alopecia in systemic lupus erythematosus (SLE) patients caused reduced life quality and prolonged disease course. This case-control study aims to survey the prevalence of scarring alopecia during the disease course of SLE and evaluate the risk factors for scarring alopecia in Chinese SLE patients.

Methods

SLE patients in Chinese SLE treatment and Research group (CSTAR) were recruited. Scarring alopecia was defined according to SLICC/ACR-DI which was collected during follow-up visits or via self-reported questionnaires. We collected demographic characteristics, common comorbidities, autoantibody profiles, disease activity status, major organ involvements, and treatment strategies of these patients at registry. Univariate and multivariate logistic regression analyses were used to investigate the risk factors for scarring alopecia.

Results

We recruited 4792 SLE patients, and 374 (7.80%) patients had scarring alopecia. Mucocutaneous lesions (OR 2.062, p < 0.001), high SLICC/ACR-DI (OR 1.409, p < 0.001), and positive anti-Sm (OR 1.374, p = 0.029) were risk factors for scarring alopecia, while renal (OR 0.714, p = 0.028) and cardio-respiratory involvements (OR 0.347, p = 0.044), and immunosuppressant treatment (OR 0.675, p < 0.001) were significantly negative associated with it.

Conclusions

The prevalence of scarring alopecia in SLE patients is 7.80%. Active treatment strategies should be adopted to prevent scarring alopecia occurring.

An updated advance of autoantibodies in autoimmune diseases

Autoantibodies are abnormal antibodies which are generated by pathogenic B cells when targeting an individual's own tissue. Autoantibodies have been identified as a symbol of autoimmune disorders and are frequently considered a clinical marker of these disorders. Autoimmune diseases, including system lupus erythematosus and rheumatoid arthritis, consist of a series of disorders that share some similarities and differences. They are characterized by chronic, systemic, excessive immune activation and inflammation and involve in almost all body tissues. Autoimmune diseases occur more frequently in women than men due to hormonal impacts. In this review we systemically introduce and summarize the latest advances of various autoantibodies in multiple autoimmune diseases.

An Update on the Pathogenesis of Skin Damage in Lupus

PURPOSE OF REVIEW

Lupus erythematosus (LE) is characterized by broad and varied clinical forms ranging from a localized skin lesion to a life-threatening form with severe systemic manifestations. The overlapping between cutaneous LE (CLE) and systemic LE (SLE) brings difficulties to physicians for early accurate diagnosis and sometimes may lead to delayed treatment for patients. We comprehensively review recent progress about the similarities and differences of the main three subsets of LE in pathogenesis and immunological mechanisms, with a particular focus on the skin damage.

RECENT FINDINGS

Recent studies on the mechanisms contributing to the skin damage in lupus have shown a close association of abnormal circulating inflammatory cells and abundant production of IgG autoantibodies with the skin damage of SLE, whereas few evidences if serum autoantibodies and circulating inflammatory cells are involved in the pathogenesis of CLE, especially for the discoid LE (DLE). Till now, the pathogenesis and molecular/cellular mechanism for the progress from CLE to SLE are far from clear. But more and more factors correlated with the differences among the subsets of LE and progression from CLE to SLE have been found, such as the mutation of IRF5, IFN regulatory factors and abnormalities of plasmacytoid dendritic cells (PDCs), Th1 cells, and B cells, which could be the potential biomarkers for the interventions in the development of LE. A further understanding in pathogenesis and immunological mechanisms for skin damage in different subsets of LE makes us think more about the differences and cross-links in the pathogenic mechanism of CLE and SLE, which will shed a light in predictive biomarkers and therapies in LE.

Interferon-induced protein 44-like gene promoter is differentially methylated in peripheral blood mononuclear cells of systemic lupus erythematosus patients

Background:

The objectives of this study were to compare the interferon-induced protein 44-like (IFI44L) promoter methylation level between systemic lupus erythematosus (SLE) patients and healthy controls and to evaluate its diagnostic value in SLE.

Materials and Methods:

The IFI44L promoter methylation level was measured in 49 patients with SLE and 50 healthy controls. Quantitative analysis of promoter methylation IFI44L gene in genomic DNA samples extracted from peripheral blood mononuclear cells was examined in SLE patients and healthy controls. The level of DNA methylation was compared between SLE patients and healthy controls as well as within SLE patient groups based on the presence of renal involvement. Moreover, diagnostic values of IFI44L were calculated.

Results:

The IFI44L promoter methylation level in SLE patients was significantly lower than healthy controls (median, 43.8 vs. 57, respectively; P = 0.008). The level of IFI44L promoter methylation was not significantly different between SLE patients with renal involvement and SLE patients without renal involvement (84.6% vs. 92.7%, respectively; P = 0.774). The IFI44L promoter methylation level ≤94.3% was the best cutoff point with a sensitivity of 91.8% and a specificity of 38% to distinguish patients with SLE from healthy individuals.

Conclusion:

The level of IFI44L promoter methylation from whole peripheral blood in Iranian SLE patients was significantly lower than healthy controls. Furthermore, the DNA methylation level of IFI44L promoter was not associated with renal damage in patients with SLE.

Anti-centrosome antibodies: Prevalence and disease association in Chinese population

Anti-centrosome antibodies are rare findings with undefined clinical significance in clinical research. We aimed at investigating the prevalence and clinical significance of anti-centrosome antibodies in Chinese population. Testing results of total of 281,230 ANA-positive sera were retrospectively obtained from West China Hospital Sichuan University in China between 2008 and 2017. We retrospectively collected and analysed the clinical and laboratory data of the patients with positive anti-centrosome antibody. Of the 356 453 patients tested, 281 230 patients had positive antinuclear antibodies (ANAs, 78.9%), but only 78 patients with positive anti-centrosome antibodies (0.022%), of which 74.4% are females. Diagnoses were established in 69 of 78 patients: 37 cases were autoimmune diseases, mainly including undifferentiated connective tissue diseases (UCTD, 9/37), rheumatoid arthritis (RA, 6/37), Sjögren's syndrome (SS, 5/37) and primary biliary cirrhosis (PBC, 5/37), and the remaining were other autoimmune conditions. The most frequent clinical symptoms of the anti-centrosome-positive patients were arthralgia and eyes and mouth drying. Additionally, 86.7% of anti-centrosome antibodies were not associated with other ANA profiles; however, when associated, the most frequent ANA was anti-U1RNP. Anti-centrosome antibodies are featured by a low prevalence and female gender predominance. They are correlated with some specific diseases, both autoimmune diseases, especially UCTD, RA, SS and PBC, and non-autoimmune diseases, such as infection and cancer, which suggests that they might be potential supporting serological markers of these diseases.

A comprehensive autoantigen-ome of autoimmune liver diseases identified from dermatan sulfate affinity enrichment of liver tissue proteins

BACKGROUND

Autoimmune diseases result from aberrant immune attacks by the body itself. It is mysterious how autoantigens, a large cohort of seemingly unconnected molecules expressed in different parts of the body, can induce similar autoimmune responses. We have previously found that dermatan sulfate (DS) can form complexes with molecules of apoptotic cells and stimulate autoreactive CD5+ B cells to produce autoantibodies. Hence, autoantigenic molecules share a unique biochemical property in their affinity to DS. This study sought to further test this uniform principle of autoantigenicity.

RESULTS

Proteomes were extracted from freshly collected mouse livers. They were loaded onto columns packed with DS-Sepharose resins. Proteins were eluted with step gradients of increasing salt strength. Proteins that bound to DS with weak, moderate, or strong affinity were eluted with 0.4, 0.6, and 1.0 M NaCl, respectively. After desalting, trypsin digestion, and gel electrophoresis, proteins were sequenced by mass spectrometry. To validate whether these proteins have been previously identified as autoantigens, an extensive literature search was conducted using the protein name or its alternative names as keywords. Of the 41 proteins identified from the strong DS-affinity fraction, 33 (80%) were verified autoantigens. Of the 46 proteins with moderate DS-affinity, 27 (59%) were verified autoantigens. Of the 125 proteins with weak DS-affinity, 44 (35%) were known autoantigens. Strikingly, these autoantigens fell into the classical autoantibody categories of autoimmune liver diseases: ANA (anti-nuclear autoantibodies), SMA (anti-smooth muscle autoantibodies), AMA (anti-mitochondrial autoantibodies), and LKM (liver-kidney microsomal autoantigens).

CONCLUSIONS

This study of DS-affinity enrichment of liver proteins establishes a comprehensive autoantigen-ome for autoimmune liver diseases, yielding 104 verified and 108 potential autoantigens. The liver autoantigen-ome sheds light on the molecular origins of autoimmune liver diseases and further supports the notion of a unifying biochemical principle of autoantigenicity.

Deoxyribonucleic Acid Methylation in Systemic Lupus Erythematosus: Implications for Future Clinical Practice

Differential deoxyribonucleic acid (DNA) methylation has emerged as a critical feature of systemic lupus erythematosus (SLE). Genome-wide DNA methylation studies have revealed methylation patterns characteristic of SLE—in particular, robust hypomethylation of interferon-regulated genes is a prominent finding in all cells of the immune system studied to date. These patterns reliably distinguish individuals with SLE from healthy controls and from individuals with other autoimmune diseases. For example, hypomethylation within IFI44L is both highly sensitive and highly specific for SLE, superior to currently available biomarkers. Furthermore, methylation status of other genetic loci has been associated with clinically relevant features of SLE including disease severity and organ-specific manifestations. Finally, DNA methylation studies have provided important insights into the pathophysiology of SLE. Most recently, there is a growing body of evidence that the transcription factor enhancer of zeste homolog 2 (EZH2) plays an important role in triggering SLE disease activity via epigenetic mechanisms, and that EZH2 blockade may be a future treatment option in SLE. In this short review, we discuss the DNA methylation patterns associated with SLE, their relationship to clinically significant features of SLE, and their implications in the development of novel diagnostic and therapeutic approaches to this complex disease.

Anti-SmD1 antibodies are associated with renal disorder, seizures, and pulmonary arterial hypertension in Chinese patients with active SLE

Detection of autoantibodies in systemic lupus erythematosus (SLE) plays an important role in timely diagnosis and earlier treatment of SLE. In this study, we used a SmD1 polypeptide-based ELISA to determine anti-SmD1 antibody in 269 SLE, including100 naïve (had not been treated with steroids or immunosuppressants at study inception) SLE patients and 169 non-naive SLE patients; 233 controls with other rheumatic diseases (RDC) (70 RA, 40 AS, 73SSc, and 50 SS), and 110 healthy controls (HC) group. The positive rate of anti-SmD1 among all SLE patients was 60.97%, higher than that in the RDC group (13.30%, P = 0.000) or the HC group (9.09%, P = 0.000). The positive rate of anti-SmD1 in non-naive SLE patients was higher than that for anti-dsDNA antibodies (44.97%, P = 0.03). Positivity for anti-SmD1 only was found in 14.00% of naive SLE patients and 16.00% of non-naive SLE patients. In naive SLE patients, the serum concentration of anti-SmD1 was lower after treatment than before treatment (P = 0.039). Active SLE patients positive for anti-SmD1 were more likely to have malar rash, rash, nonscarring alopecia, PAH and hypocomplementemia. High positivity for anti-SmD1 only in patients with SLE indicated the importance and necessity of detection of anti-SmD1 in patients with SLE.

Translating epigenetics into clinic: focus on lupus

Systemic lupus erythematosus (SLE) is a chronic relapsing–remitting autoimmune disease with highly heterogeneous phenotypes. Biomarkers with high sensitivity and specificity are useful for early diagnosis as well as monitoring disease activity and long-term complications. Epigenetics potentially provide novel biomarkers in autoimmune diseases. These may include DNA methylation changes in relevant lupus-prone genes or histone modifications and microRNAs to upregulate and downregulate relevant gene expression. The timing and nature of epigenetic modification provide such changes. In lupus, DNA methylation alterations in cytokine genes, such as IFN-related gene and retrovirus gene, have been found to offer biomarkers for lupus diagnosis. Histone modifications such as histone methylation and acetylation lead to transcriptional alterations of several genes such as PTPN22, LRP1B, and TNFSF70. There are varieties of microRNAs applied as lupus biomarkers, including DNMT1-related microRNAs, renal function-associated microRNAs, microRNAs involved in the immune system, and microRNAs for phenotype classification. Thus, we conclude a wide range of promising roles of epigenetic biomarkers aiding in the diagnosing and monitoring of lupus diseases and the risk of organ damage.

Novel biomarkers for systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex and highly heterogeneous disease. By now, no novel drug has been approved by the US FDA in the past 50 years, except Belimumab, a monoclonal antibody to inhibit B-cell activating factor. The stagnating drug development of lupus may be due to our limited understanding of disease etiopathogenesis and the extreme heterogeneity of patient population. Thus, the individualized treatment for SLE becomes necessary. Recently, biomarkers have shown potential in individualized treatment. This review comprehensively summarizes novel potential biomarkers, discusses their current status in preclinical studies and clinical use, sensitivity to treatments and correlation with the disease activity, and provides an insight into the possibility of biomarkers in the utilization of individualized treatment for SLE.

Organ-specific biomarkers in lupus

Systemic lupus erythematosus (SLE) is a complex and highly heterogeneous disease, which affects multiple organs, including joints, skin, kidneys, heart, hematopoietic system, and nerve system. While the etiopathogenesis of SLE still remains unclear, genetic susceptibilities and aberrant epigenetic modifications are believed to be involved. For precision therapy, it is necessary to assess accurately and objectively organ involvements and disease activity, which is difficult by current clinical laboratory tests. Biomarkers, which are a biologic, genetic, epigenetic or a chemical characteristic and conveniently detectable, serve as measures of disease diagnosis, activity, prognosis, and manifestation prediction, thereby providing instruction for individualized therapy. In addition, biomarkers differ according to different manifestations, since the disease activity index and treatments vary significantly. For example, unlike other non-renal SLE, lupus nephritis requires significant immunosuppressive drugs. Over the past decades, the research on biomarkers in lupus has been strengthened and numerous promising biomarkers have been identified at levels of genomics, transcriptomics and proteomics. In this review, we summarize the conventional and novel biomarkers in the tissue-specific manner, and discuss their roles in specific organ diagnosis, future manifestation prediction, disease activity assessment and their correlation with histology results. By doing so, it aims to shed a light on individualized treatment.

ADMA metabolism and clearance

The plasma concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is the resultant of many processes at cellular and organ levels. Post-translational methylation of arginine residues of pro teins plays a crucial role in the regulation of their functions, which include processes such as transcription, translation and RNA splicing. Because protein methylation is irreversible, the methylation signal can be turned off only by proteolysis of the entire protein. Consequently, most methylated proteins have high turnover rates. Free ADMA, which is formed during proteolysis, is actively degraded by the intracellular enzyme dimethylarginine dimethylaminohydrolase (DDAH). Some ADMA escapes degradation and leaves the cell via cationic amino acid transporters. These trans porters also mediate uptake of ADMA by neighboring cells or distant organs, thereby facilitating active interorgan transport. Clearance of ADMA from the plasma occurs in small part by urinary excretion, but the bulk of ADMA is degraded by intracellular DDAH, after uptake from the circulation. This review discusses the various processes involved in ADMA metabolism: protein methylation, proteolysis of methylated proteins, metabolism by DDAH, and interorgan transport. In addition, the role of the kidney and the liver in the clearance of ADMA is highlighted.

Advances in the diagnosis and classification of systemic lupus erythematosus

INTRODUCTION

Systemic lupus erythematosus (SLE) is the prototype of systemic autoimmune diseases. Patients with SLE display a wide spectrum of clinical and serological findings that can mislead and delay the diagnosis. Diagnostic criteria have not been developed yet, whereas several sets of classification criteria are available; however, none of them has 100% sensitivity and 100% specificity, i.e. the hallmark of diagnostic criteria. Nevertheless, classification criteria are often misused as diagnostic criteria, which may affect earliness of diagnosis and lead to more misdiagnosed cases. Areas covered: In this review, we compare old and new classification criteria, discussing their application and pinpointing their limitations in the management of patients. Moreover, we will focus on current and novel biomarkers for SLE diagnosis, highlighting their predictive value and applicability in clinical practice. Expert commentary: SLE diagnosis still represents a challenge, remaining largely based on a clinical judgment. Besides SLE diagnosis, even its classification is still challenging to date. Indeed, although classification of SLE seems to be achieved more frequently with the 2012 SLICC criteria than with the previous 1997 ACR criteria, this last-updated 2012 set might be improved. Notably, diagnostic and classification criteria should be applied to any subject in the world, and consequently they should include immunological variables validated in different populations, which is still an unmet need.

The critical role of epigenetics in systemic lupus erythematosus and autoimmunity

One of the major disappointments in human autoimmunity has been the relative failure on genome-wide association studies to provide "smoking genetic guns" that would explain the critical role of genetic susceptibility to loss of tolerance. It is well known that autoimmunity refers to the abnormal state that the dysregulated immune system attacks the healthy cells and tissues due to the loss of immunological tolerance to self-antigens. Its clinical outcomes are generally characterized by the presence of autoreactive immune cells and (or) the development of autoantibodies, leading to various types of autoimmune disorders. The etiology and pathogenesis of autoimmune diseases are highly complex. Both genetic predisposition and environmental factors such as nutrition, infection, and chemicals are implicated in the pathogenic process of autoimmunity, however, how much and by what mechanisms each of these factors contribute to the development of autoimmunity remain unclear. Epigenetics, which refers to potentially heritable changes in gene expression and function that do not involve alterations of the DNA sequence, has provided us with a brand new key to answer these questions. In the recent decades, increasing evidence have demonstrated the roles of epigenetic dysregulation, including DNA methylation, histone modification, and noncoding RNA, in the pathogenesis of autoimmune diseases, especially systemic lupus erythematosus (SLE), which have shed light on a new era for autoimmunity research. Notably, DNA hypomethylation and reactivation of the inactive X chromosome are two epigenetic hallmarks of SLE. We will herein discuss briefly how genetic studies fail to completely elucidate the pathogenesis of autoimmune diseases and present a comprehensive review on landmark epigenetic findings in autoimmune diseases, taking SLE as an extensively studied example. The epigenetics of other autoimmune diseases such as rheumatic arthritis, systemic sclerosis and primary biliary cirrhosis will also be summarized. Importantly we emphasize that the stochastic processes that lead to DNA modification may be the lynch pins that drive the initial break in tolerance.

Novel Phospholipid-Protein Conjugates Allow Improved Detection of Antibodies in Patients with Autoimmune Diseases

Reliable measurement of clinically relevant autoimmune antibodies toward phospholipid-protein conjugates is highly desirable in research and clinical assays. To date, the development in this field has been limited to the use of natural heterogeneous antigens. However, this approach does not take structural features of biologically active antigens into account and leads to low reliability and poor scientific test value. Here we describe novel phospholipid-protein conjugates for specific detection of human autoimmune antibodies. Our synthetic approach includes mild oxidation of synthetic phospholipid cardiolipin, and as the last step, coupling of the product with azide-containing linker and copper-catalyzed click chemistry with β2-glycoprotein I and prothrombin. To prove utility of the product antigens, we used enzyme-linked immunosorbent assay and three cohorts of samples obtained from patients in Denmark (n = 34) and the USA (n = 27 and n = 14). Afterwards we analyzed correlation of the obtained autoantibody titers with clinical parameters for each patient. Our results prove that using novel antigens clinically relevant autoantibodies can be detected with high repeatability, sensitivity and specificity. Unlike previously used antigens the obtained autoantibody titers strongly correlate with high disease activity and in particular, with arthritis, renal involvement, anti-Smith antibodies and high lymphocyte count. Importantly, chemical composition of antigens has a strong influence on the correlation of detected autoantibodies with disease activity and manifestations. This confirms the crucial importance of antigens’ composition on research and diagnostic assays, and opens up exciting perspectives for synthetic antigens in future studies of autoimmunity.

Secreted autoantibody repertoires in Sjögren's syndrome and systemic lupus erythematosus: A proteomic approach

The structures of epitopes bound by autoantibodies against RNA-protein complexes have been well-defined over several decades, but little is known of the clonality, immunoglobulin (Ig) variable (V) gene usage and mutational status of the autoantibodies themselves at the level of the secreted (serum) proteome. A novel proteomic workflow is presented based on affinity purification of specific Igs from serum, high-resolution two-dimensional gel electrophoresis, and de novo and database-driven sequencing of V-region proteins by mass spectrometry. Analysis of anti-Ro52/Ro60/La proteomes in primary Sjögren's syndrome (SS) and anti-Sm and anti-ribosomal P proteomes in systemic lupus erythematosus (SLE) has revealed that these antibody responses are dominated by restricted sets of public (shared) clonotypes, consistent with common pathways of production across unrelated individuals. The discovery of shared sets of specific V-region peptides can be exploited for diagnostic biomarkers in targeted mass spectrometry platforms and for tracking and removal of pathogenic clones.

IFI44L promoter methylation as a blood biomarker for systemic lupus erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) is a clinically heterogeneous disease with limited reliable diagnostic biomarkers. We investigated whether gene methylation could meet sensitivity and specificity criteria for a robust biomarker.

METHODS

IFI44L promoter methylation was examined using DNA samples from a discovery set including 377 patients with SLE, 358 healthy controls (HCs) and 353 patients with rheumatoid arthritis (RA). Two independent sets including 1144 patients with SLE, 1350 HCs, 429 patients with RA and 199 patients with primary Sjögren's syndrome (pSS) were used for validation.

RESULTS

Significant hypomethylation of two CpG sites within IFI44L promoter, Site1 (Chr1: 79 085 222) and Site2 (Chr1: 79 085 250; cg06872964), was identified in patients with SLE compared with HCs, patients with RA and patients with pSS. In a comparison between patients with SLE and HCs included in the first validation cohort, Site1 methylation had a sensitivity of 93.6% and a specificity of 96.8% at a cut-off methylation level of 75.5% and Site2 methylation had a sensitivity of 94.1% and a specificity of 98.2% at a cut-off methylation level of 25.5%. The IFI44L promoter methylation marker was also validated in an European-derived cohort. In addition, the methylation levels of Site1 and Site2 within IFI44L promoter were significantly lower in patients with SLE with renal damage than those without renal damage. Patients with SLE showed significantly increased methylation levels of Site1 and Site2 during remission compared with active stage.

CONCLUSIONS

The methylation level of IFI44L promoter can distinguish patients with SLE from healthy persons and other autoimmune diseases, and is a highly sensitive and specific diagnostic marker for SLE.

Autoantibodies in SLE: Specificities, Isotypes and Receptors

Systemic Lupus Erythematosus (SLE) is characterized by a wide spectrum of auto-antibodies which recognize several cellular components. The production of these self-reactive antibodies fluctuates during the course of the disease and the involvement of different antibody-secreting cell populations are considered highly relevant for the disease pathogenesis. These cells are developed and stimulated through different ways leading to the secretion of a variety of isotypes, affinities and idiotypes. Each of them has a particular mechanism of action binding to a specific antigen and recognized by distinct receptors. The effector responses triggered lead to a chronic tissue inflammation. DsDNA autoantibodies are the most studied as well as the first in being characterized for its pathogenic role in Lupus nephritis. However, others are of growing interest since they have been associated with other organ-specific damage, such as anti-NMDAR antibodies in neuropsychiatric clinical manifestations or anti-β2GP1 antibodies in vascular symptomatology. In this review, we describe the different auto-antibodies reported to be involved in SLE. How autoantibody isotypes and affinity-binding to their antigen might result in different pathogenic responses is also discussed.

Systemic lupus erythematosus and Raynaud's phenomenon

BACKGROUND

Patients with systemic lupus erythematosus seem to belong to different serological and clinical subgroups of the disease. Genetic background can cause the appearance of these subgroups.

OBJECTIVE

To determine whether Brazilian patients who have systemic lupus erythematosus and Raynaud's phenomenon differ from those who do not.

METHODS

Retrospective analysis of 373 medical records of systemic lupus erythematosus patients studied for demographic, clinical and serological data. A comparative analysis was performed of individuals with and without RP.

RESULTS

There was a positive association between Raynaud's phenomenon and age at diagnosis (p=0.02), presence of anti-Sm (p=0.01) antibodies and anti-RNP (p<0.0001). Furthermore, a negative association was found between Raynaud's phenomenon and hemolysis (p=0.01), serositis (p=0.01), glomerulonephritis (p=0.0004) and IgM aCL (p=0.004) antibodies.

CONCLUSION

Raynaud's phenomenon patients appear to belong to a systemic lupus erythematosus subset with a spectrum of clinical manifestations located in a more benign pole of the disease.

Autoantibodies Affect Brain Density Reduction in Nonneuropsychiatric Systemic Lupus Erythematosus Patients

This study explores the relationship between autoantibodies and brain density reduction in SLE patients without major neuropsychiatric manifestation (NPSLE). Ninety-five NPSLE patients without obvious cerebral deficits, as determined by conventional MRI, as well as 89 control subjects, underwent high-resolution structural MRI. Whole-brain density of grey matter (GMD) and white matter (WMD) were calculated for each individual, and correlations between the brain density, symptom severity, immunosuppressive agent (ISA), and autoantibody levels were assessed. The GMD and WMD of the SLE group decreased compared to controls. GMD was negatively associated with SLE activity. The WMD of patients who received ISA treatment were higher than that in the patients who did not. The WMD of patients with anticardiolipin (ACL) or anti-SSB/La antibodies was lower than in patients without these antibodies, while the GMD was lower in patients with anti-SM or anti-U1RNP antibodies. Thus, obvious brain atrophy can occur very early even before the development of significant symptoms and specific autoantibodies might contribute to the reduction of GMD or WMD in NPSLE patients. However, ISAs showed protective effects in minimizing GMD and WMD reduction. The presence of these specific autoantibodies might help identify early brain damage in NPSLE patients.

Characterization of anti-P monoclonal antibodies directed against the ribosomal protein-RNA complex antigen and produced using Murphy Roths large autoimmune-prone mice

Autoantibodies, including anti-ribosomal P proteins (anti-P), are thought to be produced by an antigen-driven immune response in systemic lupus erythematosus (SLE). To test this hypothesis, we reconstituted the ribosomal antigenic complex in vitro using human P0, phosphorylated P1 and P2 and a 28S rRNA fragment covering the P0 binding site, and immunized Murphy Roths large (MRL)/lrp lupus mice with this complex without any added adjuvant to generate anti-P antibodies. Using hybridoma technology, we subsequently obtained 34 clones, each producing an anti-P monoclonal antibody (mAb) that recognized the conserved C-terminal tail sequence common to all three P proteins. We also obtained two P0-specific monoclonal antibodies, but no antibody specific to P1, P2 or rRNA fragment. Two types of mAbs were found among these anti-P antibodies: one type (e.g. 9D5) reacted more strongly with the phosphorylated P1 and P2 than that with their non-phosphorylated forms, whereas the other type (e.g. 4H11) reacted equally with both phosphorylated and non-phosphorylated forms of P1/P2. Both 9D5 and 4H11 inhibited the ribosome/eukaryotic elongation factor-2 (eEF-2)-coupled guanosine triphosphate (GTP)ase activity. However, preincubation with a synthetic peptide corresponding to the C-terminal sequence common to all three P proteins, but not the peptide that lacked the last three C-terminal amino acids, mostly prevented the mAb-induced inhibition of GTPase activity. Thus, at least two types of anti-P were produced preferentially following the immunization of MRL mice with the reconstituted antigenic complex. Presence of multiple copies of the C-termini, particularly that of the last three C-terminal amino acid residues, in the antigenic complex appears to contribute to the immunogenic stimulus.

Low complements and high titre of anti-Sm antibody as predictors of histopathologically proven silent lupus nephritis without abnormal urinalysis in patients with systemic lupus erythematosus

OBJECTIVE

The aim of this study was to clarify the clinical characteristics and predictors of silent LN (SLN), a type of LN in SLE without abnormal urinalysis or renal impairment.

METHODS

Of 182 patients who underwent renal biopsy, 48 did not present with abnormal urinalysis or renal impairment at the time of biopsy. The patients with LN (SLN group, n = 36) and those without LN (non-LN group, n = 12) were compared with respect to their baseline characteristics. Bivariate analysis comprised Fisher's exact test and the Mann-Whitney test, whereas multivariate analysis employed binomial logistic regression analysis.

RESULTS

LN was histopathologically identified in 36 of 48 patients. According to the International Society of Nephrology/Renal Pathology Society classification, 72% of the SLN patients were classified as having class I/II, with a further 17% having class III/IV. Bivariate analyses indicated that platelet count, serum albumin, complement components (C3 and C4), complement haemolytic activity (CH50), anti-Sm antibody titre and anti-ribonucleoprotein antibody titre were significantly different between groups. Multivariate analysis indicated that CH50 and C3 titres were significantly lower in the SLN group, whereas anti-Sm antibody titre was significantly higher. The cut-off titre, calculated based on the receiver operating characteristic curve for CH50, was 33 U/ml, with a sensitivity and specificity of 89% and 83%, respectively. The cut-off titre for anti-Sm antibodies was 9 U/ml, with a sensitivity and specificity of 74% and 83%, respectively.

CONCLUSION

Low titres of CH50 and C3 and a high titre of anti-Sm antibody were identified as predictors of SLN.

Cluster Analysis of Autoantibodies in 852 Patients with Systemic Lupus Erythematosus from a Single Center

Objective.

Associations between autoantibodies and clinical features have been described in systemic lupus erythematosus (SLE). Herein, we aimed to define autoantibody clusters and their clinical correlations in a large cohort of patients with SLE.

Methods.

We analyzed 852 patients with SLE who attended our clinic. Seven autoantibodies were selected for cluster analysis: anti-DNA, anti-Sm, anti-RNP, anticardiolipin (aCL) immunoglobulin (Ig)G or IgM, lupus anticoagulant (LAC), anti-Ro, and anti-La. Two-step clustering and Kaplan-Meier survival analyses were used.

Results.

Five clusters were identified. A cluster consisted of patients with only anti-dsDNA antibodies, a cluster of anti-Sm and anti-RNP, a cluster of aCL IgG/M and LAC, and a cluster of anti-Ro and anti-La antibodies. Analysis revealed 1 more cluster that consisted of patients who did not belong to any of the clusters formed by antibodies chosen for cluster analysis. Sm/RNP cluster had significantly higher incidence of pulmonary hypertension and Raynaud phenomenon. DsDNA cluster had the highest incidence of renal involvement. In the aCL/LAC cluster, there were significantly more patients with neuropsychiatric involvement, antiphospholipid syndrome, autoimmune hemolytic anemia, and thrombocytopenia. According to the Systemic Lupus International Collaborating Clinics damage index, the highest frequency of damage was in the aCL/LAC cluster. Comparison of 10 and 20 years survival showed reduced survival in the aCL/LAC cluster.

Conclusion.

This study supports the existence of autoantibody clusters with distinct clinical features in SLE and shows that forming clinical subsets according to autoantibody clusters may be useful in predicting the outcome of the disease. Autoantibody clusters in SLE may exhibit differences according to the clinical setting or population.

Serology of Lupus Erythematosus: Correlation between Immunopathological Features and Clinical Aspects

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the aberrant production of a broad and heterogenous group of autoantibodies. Even though the presence of autoantibodies in SLE has been known, for more than 60 years, still nowadays a great effort is being made to understand the pathogenetic, diagnostic, and prognostic meaning of such autoantibodies. Antibodies to ds-DNA are useful for the diagnosis of SLE, to monitor the disease activity, and correlate with renal and central nervous involvements. Anti-Sm antibodies are highly specific for SLE. Anti-nucleosome antibodies are an excellent marker for SLE and good predictors of flares in quiescent lupus. Anti-histone antibodies characterize drug-induced lupus, while anti-SSA/Ro and anti-SSB/La antibodies are associated with neonatal lupus erythematosus and photosensitivity. Anti-ribosomal P antibodies play a role in neuropsychiatric lupus, but their association with clinical manifestations is still unclear. Anti-phospholipid antibodies are associated with the anti-phospholipid syndrome, cerebral vascular disease, and neuropsychiatric lupus. Anti-C1q antibodies amplify glomerular injury, and the elevation of their titers may predict renal flares. Anti-RNP antibodies are a marker of Sharp's syndrome but can be found in SLE as well. Anti-PCNA antibodies are present in 5–10% of SLE patients especially those with arthritis and hypocomplementemia.

Cofactors required for TLR7- and TLR9-dependent innate immune responses

Pathogens commonly utilize endocytic pathways to gain cellular access. The endosomal pattern recognition receptors TLR7 and TLR9 detect pathogen-encoded nucleic acids to initiate MyD88-dependent proinflammatory responses to microbial infection. Using genome-wide RNAi screening and integrative systems-based analysis, we identify 190 cofactors required for TLR7- and TLR9-directed signaling responses. A set of cofactors were crossprofiled for their activities downstream of several immunoreceptors and then functionally mapped based on the known architecture of NF-κB signaling pathways. Protein complexes and pathways involved in ubiquitin-protein ligase activities, sphingolipid metabolism, chromatin modifications, and ancient stress responses were found to modulate innate recognition of endosomal nucleic acids. Additionally, hepatocyte growth factor-regulated tyrosine kinase substrate (HRS) was characterized as necessary for ubiquitin-dependent TLR9 targeting to the endolysosome. Proteins and pathways identified here should prove useful in delineating strategies to manipulate innate responses for treatment of autoimmune disorders and microbial infection.

Epitope mapping of the U1 small nuclear ribonucleoprotein particle in patients with systemic lupus erythematosus and mixed connective tissue disease

Systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) are autoimmune illnesses characterized by the presence of high titers of autoantibodies directed against a wide range of 'self ' antigens. Proteins of the U1 small nuclear ribonucleoprotein particle (U1 snRNP) are among the most immunogenic molecules in patients with SLE and MCTD. The recent release of a crystallized U1 snRNP provides a unique opportunity to evaluate the effects of tertiary and quaternary structures on autoantigenicity within the U1 snRNP. In the present study, an epitope map was created using the U1 snRNP crystal structure. A total of 15 peptides were tested in a cohort of 68 patients with SLE, 29 with MCTD and 26 healthy individuals and mapped onto the U1 snRNP structure. Antigenic sites were detected in a variety of structures and appear to include RNA binding domains, but mostly exclude regions necessary for protein-protein interactions. These data suggest that while some autoantibodies may target U1 snRNP proteins as monomers or apoptosis-induced, protease-digested fragments, others may recognize epitopes on assembled protein subcomplexes of the U1 snRNP. Although nearly all of the peptides are strong predictors of autoimmune illness, none were successful at distinguishing between SLE and MCTD. The antigenicity of some peptides significantly correlated with several clinical symptoms. This investigation implicitly highlights the complexities of autoimmune epitopes, and autoimmune illnesses in general, and demonstrates the variability of antigens in patient populations, all of which contribute to difficult clinical diagnoses.

Sm peptides in differentiation of autoimmune diseases

Systemic lupus erythematosus (SLE) and related diseases are characterized by circulating autoantibodies to defined intracellular targets. Among the earliest identified autoantibodies were those directed to components of U2-U6 small nuclear ribonucleoproteins (snRNPs) known as Smith (Sm) antigen, which are highly specific for SLE. The Sm-antigen is composed of at least nine different polypeptides with molecular weights ranging from 9 to 29.5 kDa (B (B1, 28 kDa), B' (B2, 29 kDa), N (B3, 29.5 kDa), D1 (16 kDa), D2 (16.5 kDa), D3 (18 kDa), E (12 kDa), F (11 kDa), and G (9 kDa)). All of the nine core proteins, but most frequently the B and D polypeptides, are targets of the anti-Sm autoimmune response. However, since SmBB' and U1 specific RNPs share the cross-reactive epitope motif PPPGMRPP, SmD is regarded as the most SLE specific Sm-antigen. It has been shown that the polypeptides D1, D3, and BB' contain symmetrical dimethylarginine, constituting a major autoepitope within the C-terminus of SmD1 and SmD3. Several synthetic peptides have been used for the detection of anti-Sm antibodies and thus for the diagnosis of SLE. Anti-Sm antibodies have been reported to occur later than other SLE associated autoantibodies and, on average, around 1 year before the clinical onset of SLE. The present review provides a comprehensive summary on the history of anti-Sm antibodies and their use as biochemical tools to study cellular processes and as biomarker in the diagnosis of SLE. Additionally, a meta-analysis focused on recent data analyzes the prevalence of anti-Sm antibodies in SLE.

The autoimmunity of primary biliary cirrhosis and the clonal selection theory

Primary biliary cirrhosis (PBC) is a chronic cholestatic liver disease in which an immune-mediated injury targets the small intrahepatic bile ducts. PBC is further characterized by highly specific serum antimitochondrial autoantibodies (AMA) and autoreactive T cells, a striking female predominance, a strong genetic susceptibility, and a plethora of candidate environmental factors to trigger the disease onset. For these reasons PBC appears ideal to represent the developments of the clonal selection theory over the past decades. First, a sufficiently potent autoimmunogenic stimulus in PBC would require the coexistence of numerous pre-existing conditions (mostly genetic, as recently illustrated by genome-wide association studies and animal models) to perpetuate the destruction of the biliary epithelium by the immune system via the persistence of forbidden clones. Second, the proposed modifications of mitochondrial autoantigens caused by infectious agents and/or xenobiotics well illustrate the possibility that peculiar changes in the antigen structure and flexibility may contribute to tolerance breakdown. Third, the unique apoptotic features demonstrated for cholangiocytes are the ideal setting for the development of mitochondrial autoantigen presentation to the immune system through macrophages and AMA thus turning the non traditional mitochondrial antigen into a traditional one. This article will review the current knowledge on PBC etiology and pathogenesis in light of the clonal selection theory developments.

Methylation of ribosomal protein S10 by protein-arginine methyltransferase 5 regulates ribosome biogenesis

Modulation of ribosomal assembly is a fine tuning mechanism for cell number and organ size control. Many ribosomal proteins undergo post-translational modification, but their exact roles remain elusive. Here, we report that ribosomal protein s10 (RPS10) is a novel substrate of an oncoprotein, protein-arginine methyltransferase 5 (PRMT5). We show that PRMT5 interacts with RPS10 and catalyzes its methylation at the Arg(158) and Arg(160) residues. The methylation of RPS10 at Arg(158) and Arg(160) plays a role in the proper assembly of ribosomes, protein synthesis, and optimal cell proliferation. The RPS10-R158K/R160K mutant is not efficiently assembled into ribosomes and is unstable and prone to degradation by the proteasomal pathway. In nucleoli, RPS10 interacts with nucleophosmin/B23 and is predominantly concentrated in the granular component region, which is required for ribosome assembly. The RPS10 methylation mutant interacts weakly with nucleophosmin/B23 and fails to concentrate in the granular component region. Our results suggest that PRMT5 is likely to regulate cell proliferation through the methylation of ribosome proteins, and thus reveal a novel mechanism for PRMT5 in tumorigenesis.

Anti-Sm and anti-RNP antibodies

Among anti-nuclear antibodies, anti-Sm and anti-RNP antibodies are of the utmost importance in clinical practice. Anti-Sm antibodies are directed against 7 proteins (B/B', D1, D2, D3, E, F, G) that constitute the common core of U1, U2, U4 and U5 small nuclear ribonucleoprotein (snRNP) particles; B/B', D1 and D3 are more frequently targeted. Anti-RNP antibodies react with proteins (70 Kd, A, C) that are associated with U1 RNA and form U1snRNP. Anti-Sm and anti-RNP antibodies are directed towards both discontinuous and linear epitopes which are either contained in the protein sequence or are post-translationally modified. The assays to detect anti-Sm and anti-RNP antibodies are counterimmunoelectrophoresis (CIE), immunoblot, and ELISA, based on purified or recombinant proteins or synthetic peptides. Anti-Sm antibodies are detectable in a percentage of SLE patients comprised between 5 and 30%; they are more prevalent in blacks and because of their high specificity for SLE have been included in the serological criteria for diagnosing the disease.Anti-RNP are detectable in 25-47% of SLE patients; high titers of anti-RNP antibodies are diagnostic of mixed connective tissue disorder (MCTD). The measurement of anti-Sm and anti-RNP antibodies is more important in the diagnosis of SLE than in the follow-up of patients. However, anti-RNP antibodies are more prevalent in patients with Raynaud's phenomenon and are associated with milder renal involvement. On the contrary, anti-Sm antibodies are associated with the severity and the activity of renal involvement. The specificity of anti-Sm antibodies, together with epidemiological data, suggest that Epstein-Barr virus infection has the potential to induce anti-Sm antibodies by molecular mimicry.Anti-nuclear antibodies, a hallmark of the systemic autoimmune diseases, include several populations of antibodies with different specificities. Among them, anti-Sm and anti-RNP antibodies are of the utmost importance in clinical practice; in research, the study of the mechanisms inducing their production has opened up new perspectives and helped to elucidate the pathogenesis of autoimmune disorders.

Protein arginine methylation in health and disease

Protein arginine methylation is a rapidly growing field of biomedical research that holds great promise for extending our understanding of developmental and pathological processes. Less than ten years ago, fewer than two dozen proteins were verified to contain methylarginine. Currently, however, hundreds of methylarginine proteins have been detected and many have been confirmed by mass spectrometry and other proteomic and molecular techniques. Several of these proteins are products of disease genes or are implicated in disease processes by recent experimental or clinical observations. The purpose of this chapter is twofold; (1) to re-examine the role of protein arginine methylation placed within the context of cell growth and differentiation, as well as within the rich variety of cellular metabolic methylation pathways and (2) to review the implications of recent advances in protein methylarginine detection and the analysis of protein methylarginine function for our understanding of human disease.

ADMA metabolism and clearance

The plasma concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is the resultant of many processes at cellular and organ levels. Post-translational methylation of arginine residues of proteins plays a crucial role in the regulation of their functions, which include processes such as transcription, translation and RNA splicing. Because protein methylation is irreversible, the methylation signal can be turned off only by proteolysis of the entire protein. Consequently, most methylated proteins have high turnover rates. Free ADMA, which is formed during proteolysis, is actively degraded by the intracellular enzyme dimethylarginine dimethylaminohydrolase (DDAH). Some ADMA escapes degradation and leaves the cell via cationic amino acid transporters. These transporters also mediate uptake of ADMA by neighboring cells or distant organs, thereby facilitating active interorgan transport. Clearance of ADMA from the plasma occurs in small part by urinary excretion, but the bulk of ADMA is degraded by intracellular DDAH, after uptake from the circulation. This review discusses the various processes involved in ADMA metabolism: protein methylation, proteolysis of methylated proteins, metabolism by DDAH, and interorgan transport. In addition, the role of the kidney and the liver in the clearance of ADMA is highlighted.

Genetic control of anti-Sm autoantibody production in NOD congenic mice narrowed to the Idd9.3 region

Anti-Smith (anti-Sm) autoantibodies are directed to proteins in the small-nuclear ribonucleoprotein (snRNP) family and are considered specific for systemic lupus erythematosus (SLE) in both humans and mice. We previously established that NOD.c3c4 mice, carrying B6 and B10 congenic segments from chromosomes 3 to 4 on an nonobese diabetic (NOD) background, and NOD.Idd9R28 mice, carrying a B10 segment on c4 alone, developed significant penetrance of anti-Sm antibody production. Here we determine autoantibody incidence in additional NOD.Idd9 congenic strains and use a congenic mapping approach to narrow the interval necessary for enhanced autoantibody production to a approximately 5.6-Mb region containing insulin-dependent diabetes (Idd)9.3. The Idd9.3 interval contains the candidate molecule cluster of differentiation (CD)137, which is a member of the tumor necrosis factor (TNF) receptor superfamily, functions as an inducible costimulator of T cells, and controls T-B interactions. The NOD and B10 CD137 alleles have sequence polymorphisms and different functional effects on T cells; the NOD CD137 allele mediates weaker T cell proliferative responses and decreased interleukin (IL)-2 production after CD137-mediated costimulation. Our work establishes CD137 as a candidate gene for control of autoantibody production in NOD.Idd9.3 congenic mice.

Effectiveness of different methods for anti-Sm antibody identification. A multicentre study

Methods for the measurement of autoantibodies frequently provide controversial results. The objective of the present study was to evaluate the performance of Spanish Clinical Laboratories in the measurement of anti-Sm antibodies. A total of 23 laboratories participated, analysing 30 serum samples from patients with systemic lupus erythematosus and other autoimmune and non-autoimmune diseases. The laboratories used four extractable nuclear antigen screens, eight enzyme-linked immunosorbent assays (ELISAs) specific for anti-Sm, one line-blot, one dot-blot and one double immunodiffusion assay, from 15 different manufacturers. A total of 871 results were obtained. In general, very good sensitivity was obtained (95-100%), but specificity was moderate (52-86%) and must be improved. Most ELISAs and the line-blot were valid assays for anti-Sm detection and could serve as tests both for analysis and/or confirmation. The likelihood ratios indicated that both methods can be considered very useful or useful for the determination of anti-Sm antibodies. Nevertheless, the analytical quality of the methods for the measurement of anti-Sm antibodies could probably be improved by standardisation of the methods and the participation of laboratories in external quality control programs.

SLE: challenges and candidates in human disease

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by immunological hyperactivity and multi-system organ damage. A complex genetic trait involving multiple genes, with both genetic heterogeneity and a threshold effect for disease expression, SLE involves abnormalities of both the innate and adaptive immune systems. Recognition of an 'interferon signature' in SLE leukocytes, of the role of B cells in promoting disease activity, and of FCGR3A alleles as a biomarker of end organ damage, provide important insights into disease pathogenesis. Nonetheless, coordinated studies in humans and model systems hold promise for an even more rapid advance in understanding pathways of disease development and strategies for intervention. More effective markers of disease risk, disease activity, severity of organ damage and outcomes would facilitate earlier diagnosis and guide appropriately targeted treatment.

Most nuclear systemic autoantigens are extremely disordered proteins: implications for the etiology of systemic autoimmunity

Patients with systemic autoimmune diseases usually produce high levels of antibodies to self-antigens (autoantigens). The repertoire of common autoantigens is remarkably limited, yet no readily understandable shared thread links these apparently diverse proteins. Using computer prediction algorithms, we have found that most nuclear systemic autoantigens are predicted to contain long regions of extreme structural disorder. Such disordered regions would generally make poor B cell epitopes and are predicted to be under-represented as potential T cell epitopes. Consideration of the potential role of protein disorder may give novel insights into the possible role of molecular mimicry in the pathogenesis of autoimmunity. The recognition of extreme autoantigen protein disorder has led us to an explicit model of epitope spreading that explains many of the paradoxical aspects of autoimmunity - in particular, the difficulty in identifying autoantigen-specific helper T cells that might collaborate with the B cells activated in systemic autoimmunity. The model also explains the experimentally observed breakdown of major histocompatibility complex (MHC) class specificity in peptides associated with the MHC II proteins of activated autoimmune B cells, and sheds light on the selection of particular T cell epitopes in autoimmunity. Finally, the model helps to rationalize the relative rarity of clinically significant autoimmunity despite the prevalence of low specificity/low avidity autoantibodies in normal individuals.

The symmetrical dimethylarginine post-translational modification of the SmD3 protein is not required for snRNP assembly and nuclear transport

The SmB, SmD1, and SmD3 proteins have the rare symmetrical dimethylarginine post-translational modification in their C-termini. In this report, we investigate the function of this modification in the assembly and intracellular transport of the SmD3 protein. We show that the elimination of this methylation in the SmD3 protein, by mutating the modified arginines to leucines, does not interfere with the assembly and the nuclear transport of the transiently expressed SmD3 variant. This suggests this modification is not essential for maturation of the SmD3 protein.

Antinuclear autoantibodies in systemic lupus erythematosus

PURPOSE OF REVIEW

The production of autoantibodies against nuclear antigens is the hallmark of systemic lupus erythematosus. Among the large number of autoantibodies known, only a limited number appear to be clinically important. The various autoantibodies have different clinical significance in lupus patients. In this review, we will discuss the various antinuclear autoantibodies detected in lupus patients, their potential pathogenic role, and their usefulness in clinical practice.

RECENT FINDINGS

Recent advances include the clear demonstration of autoantibody transport into living cells, a process that clearly includes interactions with a number of cellular components that may play a role in cellular dysfunction and disease. Also, the anti-Sm B/B' response originates from a single antigenic epitope that appears to be the same structure in different patients, before spreading to other epitopes and becoming the typically mature, complex humoral autoimmune anti-Sm autoantibody response.

SUMMARY

The existing data strongly support a central role of autoantibodies in the pathogenesis of lupus. Better characterization of autoantibodies, their mechanisms of production, and their interactions with various cellular constituents will clarify the pathogenesis of this disease.