Recent insights into the genetic basis of systemic lupus erythematosus

Association of eNOS gene polymorphisms and systemic lupus erythematosus in southeast Iran

BACKGROUND AND OBJECTIVES

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with unknown etiology. Genetic and environmental factors play important roles in the pathogenesis of SLE. The primary objective of this study was to investigate the possible association of eNOS gene intron 4b/a, Glu298Asp and T-786C polymorphisms with SLE in southeast Iran populations.

PATIENTS AND METHODS

This was a case-control study comparing eNOS polymorphisms in 106 SLE patients and 196 age- and sex-matched healthy controls. The 4b/a, Glu298Asp and T-786C polymorphisms were analyzed using polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

Our findings indicated that the 4b/a polymorphism was associated with SLE, and the risk of SLE was 3.5- and 1.75-fold higher in patients with aa and ba genotypes than in patients with bb genotype. No association was observed between Glu298Asp and T-786C polymorphisms and SLE. There were no differences in eNOS gene polymorphisms between the Balouch and Fars population.

CONCLUSION

Statistically significant differences were observed in genotypes and allele frequencies of 4b/a polymorphism between patients with SLE and healthy controls in southeast Iran.

Prevalence and incidence of systemic lupus erythematosus in a population-based registry of American Indian and Alaska Native people, 2007-2009

OBJECTIVE

Few studies have investigated the epidemiology of systemic lupus erythematosus (SLE) in American Indian and Alaska Native populations. The objective of this study was to determine the prevalence and incidence of SLE in the Indian Health Service (IHS) active clinical population in 3 regions of the US.

METHODS

For this population-based registry within the IHS, the denominator consisted of individuals in the IHS active clinical population in 2007, 2008, and/or 2009 and residing in a community in 1 of 3 specified regions. Potential SLE cases were identified based on the presence of a diagnostic code for SLE or related disorder in the IHS National Data Warehouse. Detailed medical record abstraction was performed for each potential case. The primary case definition was documentation in the medical record of ≥4 of the revised American College of Rheumatology criteria for the classification of SLE. Prevalence was calculated for 2007, and the mean annual incidence was calculated for the years 2007 through 2009.

RESULTS

The age-adjusted prevalence and incidence of SLE according to the primary definition were 178 per 100,000 person-years (95% confidence interval [95% CI] 157-200) and 7.4 per 100,000 person-years (95% CI 5.1-10.4). Among women, the age-adjusted prevalence was 271, and the age-adjusted incidence was 10.4. The prevalence was highest in women ages 50-59 years and in the Phoenix Area IHS.

CONCLUSION

The first population-based lupus registry in the US American Indian and Alaska Native population has demonstrated that the prevalence and incidence of SLE are high. Our estimates are as high as or higher than the rates reported in the US black population.

IFNαR signaling in effector but not regulatory T cells is required for immune dysregulation during type I IFN-dependent inflammatory disease

Type I IFNs are a family of proinflammatory cytokines that are essential for antiviral immunity but whose overexpression is associated with several autoimmune disorders. In this study, we asked how chronic IFN overexpression regulates the activity of different cell types and how this contributes to immune dysfunction during IFN-associated inflammatory diseases. We show that in mice that chronically overproduce type I IFNs owing to loss of the DNA exonuclease Trex1, inflammatory disease completely depends on IFNαR signaling in T cells. Although IFNs directly inhibited the proliferation and activation of Foxp3(+) regulatory T cells, this was neither required nor sufficient for development of inflammatory disease. Rather, chronic IFN expression directly promoted the expansion and activation of effector T cells, and disease development was completely dependent on IFNαR signaling in these cells. Thus, chronic IFN expression can drive inflammatory disease via its direct effects on effector, but not regulatory, T cells.

Copy Number Variation of TLR-7 Gene and its Association with the Development of Systemic Lupus Erythematosus in Female Patients from Yucatan Mexico

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by the production of autoantibodies against self-antigens, which occurs most often in women between 15 and 40 years of age. The innate immunity is involved in the pathogenesis of SLE through TLR- 7. Genetic factors such as copy number variation (CNV) of target genes may contribute to disease development, but this possible risk has not yet been studied in SLE patients from Yucatan, Mexico. The CNV of TLR-7 gene was determined by quantitative polymerase chain reaction assay using TaqMan probes in 80 SLE women and 150 control subjects. The results showed that 10% of SLE patients exhibited more than two copies of TLR-7 gene, whereas no mRNA overexpression was detected. These data suggested that increased CNV of the TLR-7 gene in Yucatan SLE women can be a risk factor for this disease.

Integrin CD11b negatively regulates BCR signalling to maintain autoreactive B cell tolerance

A variant of the integrin-α-M (CD11b) gene has been linked to the pathogenesis of systemic lupus erythematosus. However, how this genotype results in the lupus phenotype is not fully understood. Here we show that autoreactive B cells lacking CD11b exhibit a hyperproliferative response to B cell receptor (BCR) crosslinking and enhanced survival. In vivo engagement of BCR in CD11b-deficient mice leads to increased autoAb production and kidney Ig deposition. In addition, CD11b-deficient autoreactive B cells have decreased tyrosine phosphorylation including Lyn and CD22 with decreased phosphatase SHP-1 recruitment but increased calcium influx. Results obtained using B cells transfected with the wild type or rs1143679 lupus-associated variant of CD11b suggest that this mutation completely abrogates the regulatory effect of CD11b on BCR signalling. This is through disruption of CD22-CD11b direct binding. These results reveal a previously unrecognized role of CD11b in maintaining autoreactive B cell tolerance.

Association of STAT4 rs7574865 with susceptibility to systemic lupus erythematosus in Iranian population

Systemic lupus erythematosus (SLE) is a multifactorial autoimmune disease with complex genetic inheritance that affecting different organs and systems. STAT4 has been newly identified as a susceptible gene in the development of SLE. According to recent studies, STAT4 has been associated with SLE in various populations. We investigated whether STAT4 single nucleotide polymorphisms (SNPs) were associated with susceptibility and clinical features of SLE in Iranian patients. The study group comprised 280 patients with SLE and 281 sex-, age-, and ethnicity-matched healthy controls of Iranian ancestry. Two SNPs (rs7574865 and rs7601754) were genotyped using the TaqMan MGB Allelic Discrimination method. Our results showed a significant association between rs7574865 T allele (odds ratio (OR) = 1.50, 95 % CI = 1.18-1.92, P = 0.002) and susceptibility to SLE. The rs7574865TT genotype (P = 0.02, OR = 1.94, 95 % CI = 1.74-3.19) and GT genotype (P = 0.008, OR = 1.71, 95 % CI = 1.19-2.45) showed a significant association with the risk of SLE in the Iranian population. We concluded that STAT4 rs7574865 is associated with SLE susceptibility in the Iranian population and this SNP might be a factor in the pathogenesis of SLE. However, further studies are required to investigate the mechanism by which polymorphisms in this gene lead to SLE.

Spontaneous activation of RNA-sensing pathways in autoimmune disease

Multiple intracellular RNA sensing innate immune pathways have been linked to autoimmune disease. RNA-related ligands taken up by the endocytic pathway activate TLRs, and affect primarily immune cells. This type of activation is enhanced by nucleic acid-specific antibodies and induces an inflammatory program. In contrast, spontaneous activation of cytoplasmic RNA sensing pathways targets mostly non-hematopoietic tissues and their effect on autoimmune disease is secondary to the release of interferon in the circulation. The fact that pathologies result from spontaneous activation of innate pathways implies that endogenous RNA ligands that might be sensed as pathogenic are commonly found in both immune and non-immune cells.

Clinical perspectives on lupus genetics: advances and opportunities

In recent years, genome-wide association studies have led to an expansion in the identification of regions containing confirmed genetic risk variants within complex human diseases, such as systemic lupus erythematosus (SLE). Many of the strongest SLE genetic associations can be divided into groups based on their potential roles in different processes implicated in lupus pathogenesis, including ubiquitination, DNA degradation, innate immunity, cellular immunity, lymphocyte development, and antigen presentation. Recent advances have also shown several genetic associations with SLE subphenotypes and subcriteria. Many areas for further exploration remain to move lupus genetic studies toward clinically informative end points.

Immunoglobulin-like transcripts 6 (ILT6) polymorphism influences the anti-Ro60/52 autoantibody status in south Indian SLE patients

Introduction

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disorder with complex etiology. Loss of immune tolerance against self-antigens results in activation of the immune system to produce autoantibodies, which in turn contribute to the clinical manifestations of the disease. Immune cells harbor a plethora of regulatory receptors. Immunoglobulin-like transcripts (ILTs) exhibit both immune activation and inhibitory properties. Genetic defects in genes encoding these receptors may predispose to development of autoimmune diseases secondary to loss of their function. The aim of our study was to analyze the presence or absence of the 6.7 kb segment in the ILT6 gene and its association with susceptibility to SLE and its different manifestations.

Method

A total of 188 SLE patients and 192 age-, sex similar-, ethnicity-matched controls were recruited. They were genotyped to test the presence or absence of the 6.7 kb segment of the ILT6 gene by polymerase chain reaction.

Results

The mutant allele lacking the 6.7 kb gene segment had an equal frequency in patients as well as controls (20% and 18%, respectively). The mutant allele was not associated with SLE or its clinical manifestations. However, the mutant allele was associated with the presence of anti-Ro60 ( p = 0.0005, OR 3.5, 95% CI 1.8–7.1) and anti-Ro52 ( p = 0.0027, OR 2.99, 95% CI 1.5–6.06) autoantibodies.

Conclusion

ILT6 deletion polymorphism does not appear to be a lupus susceptibility gene in South Indian Tamils, but may behave as a genetic modifier of autoantibody phenotype by influencing the production of anti-Ro60 and anti-Ro52 autoantibodies and thus indirectly contribute to autoimmune responses in SLE.

The development of genome-wide association studies and their application to complex diseases, including lupus

In this review, we explain the motivation for carrying out genome-wide association studies (GWAS), contrasting the achievements of linkage-based experiments for Mendelian traits with the difficulties found when applying that type of experiment to complex diseases. We explain the technical and organizational developments that were required to make GWAS feasible, as well as some of the theoretical concerns that were raised during the design of these studies. We describe the impressive achievements of GWAS in lupus, and compare them with the experiences in three other genetically complex disorders: rheumatoid arthritis, type 1 diabetes and coronary heart disease. GWAS have been successful in identifying many new susceptibility loci for these four diseases, and have provided the motivation for novel immunological work. We conclude by describing preliminary steps that have been taken towards translating the results of GWAS into improvements in patient care, explaining some of the difficulties involved, as well as successes that have already been achieved.

XRCC1 Arg399Gln and Arg194Trp polymorphisms and risk of systemic lupus erythematosus in an Iranian population: a pilot study

Background. Evidences are suggesting that DNA damage is implicated in development of systemic lupus erythematosus (SLE). Therefore we focused on two common XRCC1 polymorphisms (Arg399Gln and Arg194Trp) in SLE susceptibility in South East of Iran. Methods. Peripheral blood DNA was extracted from 163 SLE patients and 180 healthy controls. PCR-restriction fragment length polymorphism method was used for genotyping of XRCC1 Arg399Gln and Arg194Trp polymorphisms. Results. The frequency of Arg/Gln genotype of the XRCC1 Arg399Gln polymorphism was significantly lower in SLE patients than controls. Moreover, lower frequency of Arg/Gln genotype was found in SLE patients with malar rash compared to patients without this manifestation. No association was observed between XRCC1 Arg194Trp polymorphism and increased risk of SLE in studied population. Haplotype analysis revealed no correlation between four haplotypes of XRCC1 Arg399Gln and Arg194Trp polymorphisms and SLE risk. Conclusion. These findings suggest that XRCC1 399 Arg/Gln heterozygous genotype plays a protective role in SLE susceptibility.

Resequencing the susceptibility gene, ITGAM, identifies two functionally deleterious rare variants in systemic lupus erythematosus cases

Introduction

The majority of the genetic variance of systemic lupus erythematosus (SLE) remains unexplained by the common disease-common variant hypothesis. Rare variants, which are not detectable by genome-wide association studies because of their low frequencies, are predicted to explain part of this ”missing heritability.” However, recent studies identifying rare variants within known disease-susceptibility loci have failed to show genetic associations because of their extremely low frequencies, leading to the questioning of the contribution of rare variants to disease susceptibility. A common (minor allele frequency = 17.4% in cases) nonsynonymous coding variant rs1143679 (R77H) in ITGAM (CD11b), which forms half of the heterodimeric integrin receptor, complement receptor 3 (CR3), is robustly associated with SLE and has been shown to impair CR3-mediated phagocytosis.

Methods

We resequenced ITGAM in 73 SLE cases and identified two previously unidentified, case-specific nonsynonymous variants, F941V and G1145S. Both variants were genotyped in 2,107 and 949 additional SLE cases, respectively, to estimate their frequencies in a disease population. An in vitro model was used to assess the impact of F941V and G1145S, together with two nonsynonymous ITGAM polymorphisms, A858V (rs1143683) and M441T (rs11861251), on CR3-mediated phagocytosis. A paired two-tailed t test was used to compare the phagocytic capabilities of each variant with that of wild-type CR3.

Results

Both rare variants, F941V and G1145S, significantly impair CR3-mediated phagocytosis in an in vitro model (61% reduction, P = 0.006; 26% reduction, P = 0.0232). However, neither of the common variants, M441T and A858V, had an effect on phagocytosis. Neither rare variant was observed again in the genotyping of additional SLE cases, suggesting that there frequencies are extremely low.

Conclusions

Our results add further evidence to the functional importance of ITGAM in SLE pathogenesis through impaired phagocytosis. Additionally, this study provides a new example of the identification of rare variants in common-allele-associated loci, which, because of their extremely low frequencies, are not statistically associated. However, the demonstration of their functional effects adds support to their contribution to disease risk, and questions the current notion of dismissing the contribution of very rare variants on purely statistical analyses.

Liver X receptors alpha gene (NR1H3) promoter polymorphisms are associated with systemic lupus erythematosus in Koreans

Introduction

Liver X receptors are established sensors of lipid and cholesterol homeostasis. Recent studies have reported that these receptors are involved in the regulation of inflammation and immune responses. We attempted to identify single nucleotide polymorphisms (SNPs) of the NR1H3 gene associated with the susceptibility to systemic lupus erythematosus (SLE).

Methods

SNPs were genotyped using SNaPSHOT assay in 300 Korean patients with SLE and 217 normal controls (NC), and in replication samples (160 SLE patients and 143 NC). Also, the functional effects of NR1H3 gene promoter polymorphisms were analyzed using a luciferase assay, real-time polymerase chain reaction, B cell proliferation assay and an electrophoretic mobility shift assay.

Results

We identified five polymorphisms: -1851 T > C (rs3758673), -1830 T > C (rs3758674), -1003 G > A (new), -840 C > A (rs61896015) and -115 G > A (rs12221497). There was a significant and reproducible difference in the -1830 T > C, -1003 G > A and -115 G > A polymorphisms between the SLE and the NC. Luciferase activity of the structure containing -1830 C was less enhanced compared to the structure containing -1830 T in basal, GW3965 and T0901317 treated Hep3B cells (P = 0.009, P = 0.034 and P <0.001, respectively). Proliferation of the -1830 TC type was increased compared to the -1830 TT type in basal, GW3965 and T0901317 treated B cells from SLE patients (P = 0.011, P = 0.040 and P = 0.017, respectively). Transcription factor GATA-3 preferentially bound the -1830 T allele in the promoter.

Conclusions

NR1H3 genetic polymorphisms may be associated with disease susceptibility and clinical manifestations of SLE. Specifically, -1830 T > C polymorphism within NR1H3 promoter region may be involved in regulation of NR1H3 expression.

Systemic lupus erythematosus: epidemiology, pathophysiology, manifestations, and management

Systemic lupus erythematosus is a chronic autoimmune disorder characterized by production of autoantibodies directed against nuclear and cytoplasmic antigens, affecting several organs. Although cause is largely unknown, pathophysiology is attributed to several factors. Clinically, this disorder is characterized by periods of remission and relapse and may present with various constitutional and organ-specific symptoms. Diagnosis is achieved via clinical findings and laboratory examinations. Therapies are based on disease activity and severity. General treatment considerations include sun protection, diet and nutrition, smoking cessation, exercise, and appropriate immunization, whereas organ-specific treatments include use of steroidal and nonsteroidal anti-inflammatory drugs, immunosuppressive agents, and biologic agents.

Safeguard against DNA sensing: the role of TREX1 in HIV-1 infection and autoimmune diseases

Innate immune recognition is crucial for host responses against viral infections, including infection by human immunodeficiency virus 1 (HIV-1). Human cells detect such invading pathogens with a collection of pattern recognition receptors that activate the production of antiviral proteins, such as the cytokine interferon-type I, to initiate antiviral responses immediately as well as the adaptive immune response for long-term protection. To establish infection in the host, many viruses have thus evolved strategies for subversion of these mechanisms of innate immunity. For example, acute infection by HIV-1 and other retroviruses have long been thought to be non-immunogenic, signifying suppression of host defenses by these pathogens. Studies in the past few years have begun to uncover a multifaceted scheme of how HIV-1 evades innate immune detection, especially of its DNA, by exploiting host proteins. This review will discuss the host mechanisms of HIV-1 DNA sensing and viral immune evasion, with a particular focus on TREX1, three prime repair exonuclease 1, a host 3′ exonuclease (also known as DNase III).

Genetic variants of DNMT3A and systemic lupus erythematosus susceptibility

OBJECTIVES

A significant increase in DNA methyltransferase 3A (DNMT3A) transcript levels has recently been demonstrated in peripheral blood mononuclear cells from systemic lupus erythematosus (SLE) patients as compared to healthy individuals.

METHODS

Employing high resolution melting curve analysis (HRM) and PCR-restriction fragment length polymorphism analysis, we assessed the frequency of five single nucleotide polymorphisms (SNPs) of this gene: rs2289195, rs7590760, rs13401241, rs749131 and rs1550117, situated in different linkage disequilibrium blocks of the DNMT3A gene in two hundred and fifty seven women with SLE and six hundred and twenty five controls.

RESULTS

The lowest p values of the trend test were observed for the DNMT3A -448A> G (rs1550117) SNP (ptrend = 0.0111). We also found that, in a dominant inheritance model, the DNMT3A -448A> G SNP may protect from SLE development [odds ratio (OR) = 0.494 (0.294-0.830), p = 0.0068, pcorr = 0.034]. Furthermore, we observed that the DNMT3A -448A > G SNP in dominant inheritance models may protect from immunologic manifestations of SLE [OR = 0.1753 (95% CI = 0.04976-0.6176, p = 0.0026, pcorr = 0.0468).

CONCLUSIONS

Our study demonstrates that the DNMT3A -448A> G SNP might protect from SLE and its immunologic manifestations in a sample from the Polish population.

Asian ethnicity in systemic lupus erythematosus: an Australian perspective

Ethnic differences in both disease susceptibility and expression have been noted in systemic lupus erythematosus (SLE). This review focuses on the evidence of disparities between SLE patients of Asian and Caucasian descent, the two predominant ethnic groups affected by SLE in the Australian context. While epidemiological studies suggest higher rates of SLE among Asian patients, multi-ethnic cohort studies have allowed direct comparison of disease characteristics between different ethnic groups. Such studies suggest that Asians are affected by more severe SLE across several disease parameters, including increased renal involvement, autoantibody positivity, disease activity and damage accumulation. As delineation of these disparities becomes clearer, uncovering the biological basis of such differences poses a significant opportunity to progress understanding of SLE pathogenesis. Understanding ethnic variation in disease provides a platform for an individualised approach to risk assessment, monitoring and management of SLE.

Macrophage migration inhibitory factor: association of -794 CATT5-8 and -173 G>C polymorphisms with TNF-α in systemic lupus erythematosus

Macrophage migration inhibitory factor (MIF) is an upstream immunoregulatory cytokine associated with the pathogenesis of autoimmune inflammatory diseases. There is evidence that MIF functions in a positive feedback loop with TNF-α that could perpetuate the inflammatory process in systemic lupus erythematosus (SLE). In this case-control study we investigated whether commonly occurring functional MIF polymorphisms are associated with SLE as well as with MIF and TNF-α serum levels in a Mexican-Mestizo population. Genotyping of the -794 CATT5-8 (rs5844572) and -173 G>C (rs755622) MIF polymorphisms was performed by PCR and PCR-RFLP, respectively in 186 SLE patients and 200 healthy subjects. MIF and TNF-α serum levels were determined by ELISA. A significant increase of MIF and TNF-α levels was found in SLE patients. According to a genetic model, we found a significant association of genotypes carrying the -794 CATT7 and -173(∗)C risk alleles with susceptibility to SLE and with a significant increase of TNF-α. In conclusion, MIF gene polymorphisms are associated with SLE susceptibility and with an increase of TNF-α serum levels in a Mexican-Mestizo population.

USP21 negatively regulates antiviral response by acting as a RIG-I deubiquitinase

Lys63-linked polyubiquitination of RIG-I is essential in antiviral immune defense, yet the molecular mechanism that negatively regulates this critical step is poorly understood. Here, we report that USP21 acts as a novel negative regulator in antiviral responses through its ability to bind to and deubiquitinate RIG-I. Overexpression of USP21 inhibited RNA virus-induced RIG-I polyubiquitination and RIG-I-mediated interferon (IFN) signaling, whereas deletion of USP21 resulted in elevated RIG-I polyubiquitination, IRF3 phosphorylation, IFN-α/β production, and antiviral responses in MEFs in response to RNA virus infection. USP21 also restricted antiviral responses in peritoneal macrophages (PMs) and bone marrow-derived dendritic cells (BMDCs). USP21-deficient mice spontaneously developed splenomegaly and were more resistant to VSV infection with elevated production of IFNs. Chimeric mice with USP21-deficient hematopoietic cells developed virus-induced splenomegaly and were more resistant to VSV infection. Functional comparison of three deubiquitinases (USP21, A20, and CYLD) demonstrated that USP21 acts as a bona fide RIG-I deubiquitinase to down-regulate antiviral response independent of the A20 ubiquitin-editing complex. Our studies identify a previously unrecognized role for USP21 in the negative regulation of antiviral response through deubiquitinating RIG-I.

Immunopathology of lupus nephritis

When patients with systemic lupus erythematosus (SLE) present with urinary abnormalities, a renal biopsy is usually needed to rule out or confirm lupus nephritis. Renal biopsy is also needed to define the type of renal manifestation as different entities are associated with different outcomes; hence, renal biopsy results shape lupus management. But why does lupus nephritis come in different shapes? Why do patients with SLE often show change over time in class of lupus nephritis or have mixed forms? How does autoimmunity in SLE evolve? Why does loss of tolerance against nuclear antigens preferentially affect the kidney? Why are immune complex deposits in different glomerular compartments associated with different outcomes? What determines crescent formation in lupus? In this review, we discuss these questions by linking the latest information on lupus pathogenesis into the context of the different classes of lupus nephritis. This should help the basic scientist, the pathologist, and the clinician to gain a more conceptual view on the immunopathology of lupus nephritis.

Systemic lupus erythematosus diagnostics in the 'omics' era

Systemic lupus erythematosus is a complex autoimmune disease affecting multiple organ systems. Currently, diagnosis relies upon meeting at least four out of eleven criteria outlined by the ACR. The scientific community actively pursues discovery of novel diagnostics in the hope of better identifying susceptible individuals in early stages of disease. Comprehensive studies have been conducted at multiple biological levels including: DNA (or genomics), mRNA (or transcriptomics), protein (or proteomics) and metabolites (or metabolomics). The 'omics' platforms allow us to re-examine systemic lupus erythematosus at a greater degree of molecular resolution. More importantly, one is hopeful that these 'omics' platforms may yield newer biomarkers for systemic lupus erythematosus that can help clinicians track the disease course with greater sensitivity and specificity.

Toll-like receptor 4 gene polymorphism 1196 C/T does not influence the risk of neuropsychiatric systemic lupus erythematosus in Polish population – a preliminary report

Objective

Recent data indicate that Toll-like receptors (TLRs) participate in various neuropathologic conditions, including ictogenesis, myelin disruptions associated with chronic alcohol abuse, behavioral and cognitive dysfunctions associated with alcohol-induced neuroinflammatory damage, and activation of microglia to reduce amyloid β deposits. As seizures and depression are well known neuropsychiatric syndromes in systemic lupus erythematosus (SLE) the aim of the study was to investigate whether TLR4 gene polymorphism 1196C/T (rs4986791, Thr399Ile) was a candidate for susceptibility of development of neuropsychiatric systemic lupus erythematosus (NPSLE).

Methods

The study covered 60 patients with SLE and 100 healthy individuals. TLR4 1196C/T genotyping was performed by real-time polymerase chain reaction with the SimpleProbe.

Results

The SLE group comprised 86.7% of patients with wild-type homozygotes CC and 13.3% heterozygotes CT and no homozygotes TT. The control group consisted of 85% wild-type homozygotes CC, 15% heterozygotes CT and no homozygotes TT. The frequencies of genotype and allele distribution in SLE patients did not differ significantly from those of the control subjects. The probability of describing the possible risk of SLE imputed to genotype did not significantly differ in comparison with the healthy individuals ( p = 0.77, odds ratio = 0.87, 95% confidence interval 0.34–2.19). A significant genotype association of genotype CC with arthritis was found in SLE patients ( p = 0.02). It was further confirmed by a significant association of a dominant allele C with arthritis ( p = 0.02). No association between CC and CT genotypes of TLR4 1196C/T and NPSLE was found. Allele distribution of TLR4 1196C/T also was not associated with NPSLE. No other significant differences were found in genotype and allele frequencies regarding clinical manifestation of SLE patients.

Conclusion

In the Polish population of SLE patients, 1196C/T polymorphism of TLR4 gene does not increase the risk of development of NPSLE; however, genotype CC and a dominant allele C is associated with arthritis in the course of SLE.

Nucleic Acid sensors and type I interferon production in systemic lupus erythematosus

The characteristic serologic feature of systemic lupus erythematosus (SLE) is autoantibodies against one’s own nucleic acid or nucleic acid-binding proteins – DNA and RNA-binding nuclear proteins. Circulating autoantibodies can deposit in the tissue, causing inflammation and production of cytokines such as type 1 interferon (IFN). Investigations in human patients and animal models have implicated environmental as well as genetic factors in the biology of the SLE autoimmune response. Viral/Bacterial nucleic acid is a potent stimulant of innate immunity by both toll-like receptor (TLR) and non-TLR signaling cascades. Additionally, foreign DNA may act as an immunogen to drive an antigen-specific antibody response. Self nucleic acid is normally restricted to the nucleus or the mitochondria, away from the DNA/RNA sensors, and mechanisms exist to differentiate between foreign and self nucleic acid. In normal immunity, a diverse range of DNA and RNA sensors in different cell types form a dynamic and integrated molecular network to prevent viral infection. In SLE, pathologic activation of these sensors occurs via immune complexes consisting of autoantibodies bound to DNA or to nucleic acid-protein complexes. In this review, we will discuss recent studies outlining how mismanaged nucleic acid sensing networks promote autoimmunity and result in the over-production of type I IFN. This information is critical for improving therapeutic strategies for SLE disease.

Gene expression and regulation in systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is the prototypic systemic autoimmune disease. Genome-wide (GW) association studies have identified more than 40 disease-associated loci, together accounting for only 10-20% of disease heritability. Gene expression represents the intermediate phenotype between DNA and disease phenotypic variation, and provides insights regarding genetic and epigenetic effects. We review data on gene expression and regulation in SLE by our group and other investigators.

MATERIALS AND METHODS

Systematic PubMed search for GW expression studies in SLE published since the year 2000.

RESULTS

Deregulation of genes involved in type I interferon signaling is a consistent finding in the peripheral blood of active and severe SLE patients. Upregulation of granulocyte-specific transcripts especially in bone marrow mononuclear cells (BMMCs), and of myeloid lineage transcripts in lupus nephritis, provide evidence for pathogenic role of these cells. Gene network analysis in BMMCs identified central gene regulators which could represent therapeutic targets and a high similarity between SLE and non-Hodgkin lymphoma providing a molecular basis for the reported association of the two diseases. Gene expression abnormalities driven by deregulated expression of certain microRNAs in SLE contribute to interferon production, T- and B-cell hyperactivity, DNA hypomethylation, and defective tissue response to injury. Methylation arrays have revealed alterations in white blood cell DNA methylation in SLE suggesting an important role of epigenetics and the environment.

CONCLUSIONS

Gene expression studies have contributed to the characterization of pathogenic processes in SLE. Integrated approaches utilizing genetic variation, transcriptome and epigenome profiling will facilitate efforts towards a molecular-based disease taxonomy.

Detecting rare variants in case-parents association studies

Despite the success of genome-wide association studies (GWASs) in detecting common variants (minor allele frequency ≥0.05) many suggested that rare variants also contribute to the genetic architecture of diseases. Recently, researchers demonstrated that rare variants can show a strong stratification which may not be corrected by using existing methods. In this paper, we focus on a case-parents study and consider methods for testing group-wise association between multiple rare (and common) variants in a gene region and a disease. All tests depend on the numbers of transmitted mutant alleles from parents to their diseased children across variants and hence they are robust to the effect of population stratification. We use extensive simulation studies to compare the performance of four competing tests: the largest single-variant transmission disequilibrium test (TDT), multivariable test, combined TDT, and a likelihood ratio test based on a random-effects model. We find that the likelihood ratio test is most powerful in a wide range of settings and there is no negative impact to its power performance when common variants are also included in the analysis. If deleterious and protective variants are simultaneously analyzed, the likelihood ratio test was generally insensitive to the effect directionality, unless the effects are extremely inconsistent in one direction.

Association analyses identifying two common susceptibility loci shared by psoriasis and systemic lupus erythematosus in the Chinese Han population

BACKGROUND

Genome-wide association studies (GWASs) have revealed a large number of genetic risk loci for many autoimmune diseases. One clear finding emerging from the published genetic studies of autoimmunity is that different autoimmune diseases, such as psoriasis and systemic lupus erythematosus (SLE), share susceptibility loci. Our study explores additional susceptibility loci shared by psoriasis and SLE in the Chinese Han population.

METHODS

In total, 20 single nucleotide polymorphisms (SNPs) in 17 previously reported psoriasis susceptibility loci and 34 SNPs from 24 previously reported SLE susceptibility loci were investigated in our initial psoriasis and SLE GWAS dataset. Among these SNPs, we selected two SNPs (rs8016947 and rs4649203) with association values of p<5×10(-2) for both diseases in the GWAS data for further investigation in psoriasis (7260 cases and 9842 controls) and SLE (2207 cases and 9842 controls) using a Sequenom MassARRAY system.

RESULTS

We found that these two SNPs (rs8016947 and rs4649203) in two loci (NFKBIA and IL28RA) were associated with psoriasis and SLE with genome-wide significance (Pcombined<5×10(-8) in psoriasis and Pcombined<5×10(-8) in SLE): rs8016947 at NFKBIA (Pcombined-psoriasis=3.90×10(-10), Pcombined-SLE=1.08×10(-13)) and rs4649203 at IL28RA (Pcombined-psoriasis=3.91×10(-12), Pcombined-SLE=9.90×10(-9)).

CONCLUSIONS

These results showed that two common susceptibility loci (NFKBIA and IL28RA) are shared by psoriasis and SLE in the Chinese Han population.

Biomarkers in systemic lupus erythematosus: challenges and prospects for the future

The search for lupus biomarkers to diagnose, monitor, stratify, and predict individual response to therapy is currently more intense than ever before. This effort is essential for several reasons. First, epidemic overdiagnosis and underdiagnosis of lupus, even by certified rheumatologists, leads to errors in therapy with concomitant side effects which may be more serious than the disease itself. Second, identification of lupus flares remains as much an art as it is a science. Third, the capacity to stratify patients so as to predict those who will develop specific patterns of organ involvement is not currently possible but would potentially lead to preventive therapeutic strategies. Fourth, only one new drug for the treatment of lupus has been approved by the US Food and Drug Administration in over 50 years. A major obstacle in this pipeline is the dearth of biomarkers available to prove a patient has responded to an experimental therapeutic intervention. This review will summarize the challenges faced in the discovery and validation of lupus biomarkers, the most promising lupus biomarkers identified to date, and the promise of future directions.

Latest advances in connective tissue disorders

The connective tissue disorders comprise a number of related conditions that include systemic lupus erythematosus (SLE) and the antiphospholipid (Hughes) syndrome, scleroderma, myositis and Sjögren's syndrome. They are characterized by autoantibody production and other immune-mediated dysfunction. There are common clinical and serological features with some patients having multiple overlapping connective tissue disorders. The latest advances include new approaches to therapy, including more focused utilization of existing therapies and the introduction of biological therapies in SLE, more precise protocols for assessment of severe disease manifestations such as in interstitial lung disease and pulmonary artery hypertension in scleroderma, new antibodies for disease characterization in myositis and new approaches to patient assessment in Sjögren's syndrome. B cells have a critical role in most, if not all of these disorders such that B-cell depletion or suppression of B-cell activating cytokines improves disease in many patients. In particular, the introduction of rituximab, a monoclonal antibody targeting the CD20 molecule on B cells, into clinical practice for rheumatoid arthritis and B-cell lymphoma has been a key driver of experimental approaches to therapy in connective tissue disorders. Genetic studies also suggest a role for the innate immune system in disease pathogenesis, suggesting further future targets for biological therapies over the next few years.

Vitamin D Receptor Gene BsmI Polymorphism in Polish Patients with Systemic Lupus Erythematosus

The hormonally active form of vitamin D₃, 1,25(OH)₂D₃ (calcitriol), exerts actions through VDR receptor, which acts as a transcriptional factor. Calcitriol is an immunomodulator that affects various immune cells, and several studies link it to many autoimmune diseases. BsmI polymorphism affects the level of VDR gene transcription, transcript stability, and posttranscriptional modifications. It seems to be related to the systemic lupus erythematosus (SLE). Our study examined the characteristics of VDR gene BsmI polymorphism in Polish SLE patients and their relationship with clinical manifestations of the disease. We genotyped 62 patients with SLE and 100 healthy controls using the real-time PCR. There were no differences observed in the frequency of BsmI genotypes in SLE patients and in the control group. There was no significant correlation between BsmI genotypes and clinical symptoms of SLE, but the AA genotype correlates with higher levels of antinuclear antibodies (ANA) in this group (r = 0.438; P = 0.002). A larger study examining BsmI and other VDR gene polymorphisms is needed. It may allow explaining differences in the clinical picture of the disease and choosing a personalized therapy.

Gene-function studies in systemic lupus erythematosus

The aetiology of systemic lupus erythematosus (SLE) is complex and is known to involve both genetic and environmental factors. In a small number of patients, single-gene defects can lead to the development of SLE. Such genes include those encoding early components of the complement cascade and the 3'-5' DNA exonuclease TREX1. In addition, genome-wide association studies have identified single-nucleotide polymorphisms that confer some susceptibility to SLE. In this Review, we discuss selected examples of genes whose products have distinctly altered function in SLE and contribute to the pathogenic process. Specifically, we focus on the genes encoding integrin αM (ITGAM), IgG Fc receptors, sialic acid O-acetyl esterase (SIAE), the catalytic subunit of protein phosphatase PP2A (PPP2CA) and signalling lymphocytic activation molecule (SLAM) family members. Moreover, we highlight the changes in epigenetic signatures that occur in SLE. Such epigenetic modifications, which are abundantly present and might alter gene expression in the presence or absence of susceptibility variants, should be carefully considered when deconstructing the contribution of individual genes to the complex pathogenesis of SLE.

Coronary heart disease in systemic lupus erythematosus is associated with interferon regulatory factor-8 gene variants

BACKGROUND

Patients with systemic lupus erythematosus have increased morbidity and mortality in coronary heart disease (CHD). We asked whether there was a genetic influence on CHD in systemic lupus erythematosus.

METHODS AND RESULTS

The association between single-nucleotide polymorphisms (SNPs) and CHD in 2 populations of patients with systemic lupus erythematosus was assessed. Patients were genotyped on a custom 12k Illumina Array. The allele frequencies were compared between patients with (n=66) and without (n=509) CHD. We found 61 SNPs with an association (P<0.01) to CHD, with the strongest association for 3 SNPs located in the interferon regulatory factor-8 (IRF8) gene. Comparison of the allele frequencies of these 61 SNPs in patients with (n=27) and without (n=212) CHD in the second study population revealed that 2 SNPs, rs925994 and rs10514610 in IRF8 (linkage disequilibrium, r²=0.84), were associated with CHD in both study populations. Meta-analysis of the SNP rs925994 gave an odds ratio of 3.6 (2.1-6.3), P value 1.9×10⁻⁶. The identified IRF8 allele remained as a risk factor for CHD after adjustment for traditional CHD risk factors. The IRF8 risk allele was associated with the presence of carotid plaques (P<0.001) and increased intima-media thickness (P=0.01). By electrophoretic mobility shift assays, we show weaker binding of protein to the risk allele of the highly linked SNP rs11117415, and by flow cytometry, a reduced frequency of circulating B cells was detected in patients with the IRF8 risk allele.

CONCLUSIONS

There is a considerable genetic component for CHD in systemic lupus erythematosus, with IRF8 as a strong susceptibility locus.

Inducible expression of kallikrein in renal tubular cells protects mice against spontaneous lupus nephritis

OBJECTIVE

To ascertain whether engineered expression of kallikreins within the kidneys, using an inducible Cre/loxP system, can ameliorate murine lupus nephritis.

METHODS

In mice with a lupus-prone genetic background, we engineered the expression of tamoxifen-inducible Cre recombinase under the control of a kidney-specific promoter whose activation initiates murine kallikrein-1 expression within the kidneys. These transgenic mice were injected with either tamoxifen or vehicle at age 2 months and then were monitored for 8 months for kallikrein expression and disease.

RESULTS

Elevated expression of kallikrein was detected in the kidney and urine of tamoxifen-injected mice but not in controls. At age 10 months, all vehicle-injected mice developed severe lupus nephritis, as evidenced by increased proteinuria (mean ± SD 13.43 ± 5.65 mg/24 hours), increased blood urea nitrogen (BUN) and serum creatinine levels (39.86 ± 13.45 mg/dl and 15.23 ± 6.89 mg/dl, respectively), and severe renal pathology. In contrast, the tamoxifen-injected mice showed significantly reduced proteinuria (6.6 ± 4.12 mg/24 hours), decreased BUN and serum creatinine levels (15.71 ± 8.17 mg/dl and 6.64 ± 3.39 mg/dl, respectively), and milder renal pathology. Tamoxifen-induced up-regulation of renal kallikrein expression increased nitric oxide production and dampened renal superoxide production and inflammatory cell infiltration, alluding to some of the pathways through which kallikreins may be operating within the kidneys.

CONCLUSION

Local expression of kallikreins within the kidney has the capacity to dampen lupus nephritis, possibly by modulating inflammation and oxidative stress.

Toll-like receptors in systemic lupus erythematosus: potential targets for therapeutic intervention

Toll-like receptors (TLRs) have attracted increased attention in recent years, not only for their role in sensing conserved microbial components, but also in the realm of autoimmunity. Although TLRs are most widely known for their capacity to detect conserved motifs of infectious agents, mounting evidence indicates that these innate receptors also promote autoimmune conditions by causing uncontrolled autoinflammation as a result of chronic recognition of self. In response to the need for modern approaches to treatment of autoimmune diseases, several groups have begun investigating ways to target TLRs as new therapeutic options for autoimmune conditions. Here we discuss recent data describing advances in TLRs as therapeutic targets for treatment of autoimmune diseases, with a focus on systemic lupus erythematosus.

cAMP responsive element modulator: a critical regulator of cytokine production

T lymphocytes from patients with systemic lupus erythematosus (SLE) display a complex array of cellular, molecular, and signaling anomalies, many of which have been attributed to increased expression of the transcriptional regulator cAMP responsive element modulator α (CREMα). Recent evidence indicates that CREMα, in addition to its regulatory functions on gene promoters in T lymphocytes, alters the epigenetic conformation of cytokine genes by interacting with enzymes that control histone methylation and acetylation as well as cytosine-phosphate-guanosine (CpG) DNA methylation. This review summarizes the most recent findings on CREM protein expression in various cell types, in particular its effects on T lymphocyte biology in the context of both health and SLE. We emphasize CREMα as a key molecule that drives autoimmunity.

Fine mapping of Xq28: both MECP2 and IRAK1 contribute to risk for systemic lupus erythematosus in multiple ancestral groups

OBJECTIVES

The Xq28 region containing IRAK1 and MECP2 has been identified as a risk locus for systemic lupus erythematosus (SLE) in previous genetic association studies. However, due to the strong linkage disequilibrium between IRAK1 and MECP2, it remains unclear which gene is affected by the underlying causal variant(s) conferring risk of SLE.

METHODS

We fine-mapped ≥136 SNPs in a ∼227 kb region on Xq28, containing IRAK1, MECP2 and seven adjacent genes (L1CAM, AVPR2, ARHGAP4, NAA10, RENBP, HCFC1 and TMEM187), for association with SLE in 15 783 case-control subjects derived from four different ancestral groups.

RESULTS

Multiple SNPs showed strong association with SLE in European Americans, Asians and Hispanics at p<5×10(-8) with consistent association in subjects with African ancestry. Of these, six SNPs located in the TMEM187-IRAK1-MECP2 region captured the underlying causal variant(s) residing in a common risk haplotype shared by all four ancestral groups. Among them, rs1059702 best explained the Xq28 association signals in conditional testings and exhibited the strongest p value in transancestral meta-analysis (p(meta )= 1.3×10(-27), OR=1.43), and thus was considered to be the most likely causal variant. The risk allele of rs1059702 results in the amino acid substitution S196F in IRAK1 and had previously been shown to increase NF-κB activity in vitro. We also found that the homozygous risk genotype of rs1059702 was associated with lower mRNA levels of MECP2, but not IRAK1, in SLE patients (p=0.0012) and healthy controls (p=0.0064).

CONCLUSIONS

These data suggest contributions of both IRAK1 and MECP2 to SLE susceptibility.

Association of a functional IRF7 variant with systemic lupus erythematosus

OBJECTIVE

A previous genome-wide association study conducted in a population of European ancestry identified rs4963128, a KIAA1542 single-nucleotide polymorphism (SNP) 23 kb telomeric to IRF7 (the gene for interferon regulatory factor 7 [IRF-7]), to be strongly associated with systemic lupus erythematosus (SLE). This study was undertaken to investigate whether genetic polymorphism within IRF7 is a risk factor for the development of SLE.

METHODS

We genotyped one KIAA1542 SNP (rs4963128) and one IRF7 SNP (rs1131665 [Q412R]) in an Asian population (1,302 cases, 1,479 controls), to assess their association with SLE. Subsequently, rs1131665 was further genotyped in independent panels of Chinese subjects (528 cases, 527 controls), European American subjects (446 cases, 461 controls), and African American subjects (159 cases, 115 controls) by TaqMan genotyping assay, to seek confirmation of association in various ethnic groups. A luciferase reporter assay was used to assess the effect of Q412R polymorphism on the activation of IRF-7.

RESULTS

Consistent association of rs1131665 (Q412R) with SLE was identified in Asian, European American, and African American populations (total 2,435 cases and 2,582 controls) (P(meta) = 6.18 × 10(-6) , odds ratio 1.42 [95% confidence interval 1.22-1.65]). Expression of the IRF7 412Q risk allele resulted in a 2-fold increase in interferon-stimulated response element transcriptional activity compared with expression of IRF7 412R (P = 0.0003), suggesting that IRF7 412Q confers elevated IRF-7 activity and may therefore affect a downstream interferon pathway.

CONCLUSION

These findings show that the major allele of a nonsynonymous SNP, rs1131665 (412Q) in IRF7, confers elevated activation of IRF-7 and predisposes to the development of SLE in multiple ethnic groups. This result provides direct genetic evidence that IRF7 may be a risk gene for human SLE.

Neutrophils come of age in chronic inflammation

Neutrophils have long been known to participate in acute inflammation, but a role in chronic inflammatory and autoimmune diseases is now emerging. These cells are key players in the recognition and elimination of pathogens, but they also sense self components, including nucleic acids and products of sterile tissue damage. While this normally contributes to tissue repair, it can also lead to the release of highly immunogenic products that can trigger and/or amplify autoimmune pathogenic loops. Understanding the mechanisms that underlie neutrophil activation, migration, survival and their various forms of death in health and disease might provide us with new approaches to treat chronic inflammatory conditions.

TLR7 and TLR9 in SLE: when sensing self goes wrong

Autoreactive B and T cells are present in healthy, autoimmunity-free individuals, but they are kept in check by various regulatory mechanisms. In systemic lupus erythematosus (SLE) patients, however, autoreactive cells are expanded, activated, and produce large quantities of autoantibodies, directed especially against nuclear antigens. These antibodies form immune complexes with self-nucleic acids present in SLE serum. Since self-DNA and self-RNA in the form of protein complexes can act as TLR9 and TLR7 ligands, respectively, TLR stimulation is suggested as an additional signal contributing to activation and/or modulation of the aberrant adaptive immune response. Data from mouse models suggest a pathogenic role for TLR7 and a protective role for TLR9 in the pathogenesis of SLE. Future investigations are needed to elucidate the underlying modulatory mechanisms and the role of TLR7 and TLR9 in the complex pathogenesis of human SLE.

Trex1 regulates lysosomal biogenesis and interferon-independent activation of antiviral genes

The sensing of viral nucleic acids by the innate immune system triggers the production of type I interferons, which activates interferon-stimulated genes (ISGs) and directs a multifaceted antiviral response. ISGs can also be activated through interferon-independent pathways, although the precise mechanisms remain elusive. Here we found that the cytosolic exonuclease Trex1 regulated the activation of a subset of ISGs independently of interferon. Both Trex1(-/-) mouse cells and Trex1-mutant human cells had high expression of genes encoding antiviral molecules ('antiviral genes') and were refractory to viral infection. The interferon-independent activation of antiviral genes in Trex1(-/-) cells required the adaptor STING, the kinase TBK1 and the transcription factors IRF3 and IRF7. We also found that Trex1-deficient cells had an expanded lysosomal compartment, altered subcellular localization of the transcription factor TFEB and diminished activity of the regulator mTORC1. Together our data identify Trex1 as a regulator of lysosomal biogenesis and interferon-independent activation of antiviral genes and show that dysregulation of lysosomes can elicit innate immune responses.

Unraveling multiple MHC gene associations with systemic lupus erythematosus: model choice indicates a role for HLA alleles and non-HLA genes in Europeans

We have performed a meta-analysis of the major-histocompatibility-complex (MHC) region in systemic lupus erythematosus (SLE) to determine the association with both SNPs and classical human-leukocyte-antigen (HLA) alleles. More specifically, we combined results from six studies and well-known out-of-study control data sets, providing us with 3,701 independent SLE cases and 12,110 independent controls of European ancestry. This study used genotypes for 7,199 SNPs within the MHC region and for classical HLA alleles (typed and imputed). Our results from conditional analysis and model choice with the use of the Bayesian information criterion show that the best model for SLE association includes both classical loci (HLA-DRB1(∗)03:01, HLA-DRB1(∗)08:01, and HLA-DQA1(∗)01:02) and two SNPs, rs8192591 (in class III and upstream of NOTCH4) and rs2246618 (MICB in class I). Our approach was to perform a stepwise search from multiple baseline models deduced from a priori evidence on HLA-DRB1 lupus-associated alleles, a stepwise regression on SNPs alone, and a stepwise regression on HLA alleles. With this approach, we were able to identify a model that was an overwhelmingly better fit to the data than one identified by simple stepwise regression either on SNPs alone (Bayes factor [BF] > 50) or on classical HLA alleles alone (BF > 1,000).

Association of two independent functional risk haplotypes in TNIP1 with systemic lupus erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by autoantibody production and altered type I interferon expression. Genetic surveys and genome-wide association studies have identified >30 SLE susceptibility genes. One of these genes, TNIP1, encodes the ABIN1 protein. ABIN1 functions in the immune system by restricting NF-κB signaling. The present study was undertaken to investigate the genetic factors that influence association with SLE in genes that regulate the NF-κB pathway.

METHODS

We analyzed a dense set of genetic markers spanning TNIP1 and TAX1BP1, as well as the TNIP1 homolog TNIP2, in case-control populations of diverse ethnic origins. TNIP1, TNIP2, and TAX1BP1 were fine-mapped in a total of 8,372 SLE cases and 7,492 healthy controls from European-ancestry, African American, Hispanic, East Asian, and African American Gullah populations. Levels of TNIP1 messenger RNA (mRNA) and ABIN1 protein in Epstein-Barr virus-transformed human B cell lines were analyzed by quantitative reverse transcription-polymerase chain reaction and Western blotting, respectively.

RESULTS

We found significant associations between SLE and genetic variants within TNIP1, but not in TNIP2 or TAX1BP1. After resequencing and imputation, we identified 2 independent risk haplotypes within TNIP1 in individuals of European ancestry that were also present in African American and Hispanic populations. Levels of TNIP1 mRNA and ABIN1 protein were reduced among subjects with these haplotypes, suggesting that they harbor hypomorphic functional variants that influence susceptibility to SLE by restricting ABIN1 expression.

CONCLUSION

Our results confirm the association signals between SLE and TNIP1 variants in multiple populations and provide new insight into the mechanism by which TNIP1 variants may contribute to SLE pathogenesis.

Carabin deficiency in B cells increases BCR-TLR9 costimulation-induced autoimmunity

The mechanisms behind flares of human autoimmune diseases in general, and of systemic lupus in particular, are poorly understood. The present scenario proposes that predisposing gene defects favour clinical flares under the influence of external stimuli. Here, we show that Carabin is low in B cells of (NZB × NZW) F1 mice (murine SLE model) long before the disease onset, and is low in B cells of lupus patients during the inactive phases of the disease. Using knock-out and B-cell-conditional knock-out murine models, we identify Carabin as a new negative regulator of B-cell function, whose deficiency in B cells speeds up early B-cell responses and makes the mice more susceptible to anti-dsDNA production and renal lupus flare after stimulation with a Toll-like Receptor 9 agonist, CpG-DNA. Finally, in vitro analysis of NFκB activation and Erk phosphorylation in TLR9- and B-cell receptor (BCR)-stimulated Carabin-deficient B cells strongly suggests how the internal defect synergizes with the external stimulus and proposes Carabin as a natural inhibitor of the potentially dangerous crosstalk between BCR and TLR9 pathways in self-reactive B cells.

Association of RANTES and MBL gene polymorphisms with systemic lupus erythematosus: a meta-analysis

The RANTES (regulated on activation normal T cell expressed and secreted) and MBL (mannose binding lectin) single-nucleotide polymorphisms have been repeatedly associated with systemic lupus erythematosus (SLE), but the findings are not consistent across studies. The aim of this study was to determine whether the functional RANTES-28, -403 and MBL2 A/O polymorphisms confer susceptibility to SLE in multiple ethnic populations. A meta-analysis was conducted (allelic contrast, the additive model, the dominant model and the recessive model) on RANTES with seven studies (four studies for RANTES-28: three Asian and one American studies; three studies for RANTES-403: two Asian and one European studies), MBL with eight studies (five European and three American studies). OR is used as a measure of the effect of the association in a fixed/random effects model. The meta-analysis indicated that none of the two polymorphisms in gene of the RANTES showed any significant association with SLE risk, respectively, except for the recessive model (OR = 1.24, 95 % CI: 1.01-1.52, P = 0.04) in all study subjects combined with the two polymorphisms. According to the MBL2 A/O polymorphism, the results indicated a significant association between the polymorphism and SLE in allelic contrast (OR = 0.83, 95 % CI: 0.73-0.93, P = 0.002). While stratified by ethnicity in European, no significant association was found. In summary, the present study suggests that the RANTES-28, -403 polymorphisms do not associate with SLE, but the MBL2 A/O polymorphism might associate with SLE.