The genetics and biology of Irf5-mediated signaling in lupus

Genetic polymorphisms in genes involved in the type I interferon system (STAT4 and IRF5): association with Asian SLE patients

Systemic lupus erythematosus (SLE) is a common autoimmune disease with a polymorphic clinical presentation involving multisystem damages with significant differences in prevalence and disease severity among different ethnic groups. Although genetic, hormonal, and environmental factors have been demonstrated to contribute a lot to SLE, the pathogenesis of SLE is still unknown. Numerous evidence revealed that gene variants within the type I interferons (IFN) signaling pathway performed the great genetic associations with autoimmune diseases including SLE. To date, through genome-wide association studies (GWAS), genetic association studies showed that more than 100 susceptibility genes have been linked to the pathogenesis of SLE, among which TYK2, STAT1, STAT4, and IRF5 are important molecules directly connected to the type I interferon signaling system. The review summarized the genetic associations and the detailed risk loci of STAT4 and IRF5 with Asian SLE patients, explored the genotype distributions associated with the main clinical manifestations of SLE, and sorted out the potential reasons for the differences in susceptibility in Asia and Europe. Moreover, the therapies targeting STAT4 and IRF5 were also evaluated in order to propose more personalized and targeted treatment plans in SLE.

Alternative Splicing: A New Cause and Potential Therapeutic Target in Autoimmune Disease

Alternative splicing (AS) is a complex coordinated transcriptional regulatory mechanism. It affects nearly 95% of all protein-coding genes and occurs in nearly all human organs. Aberrant alternative splicing can lead to various neurological diseases and cancers and is responsible for aging, infection, inflammation, immune and metabolic disorders, and so on. Though aberrant alternative splicing events and their regulatory mechanisms are widely recognized, the association between autoimmune disease and alternative splicing has not been extensively examined. Autoimmune diseases are characterized by the loss of tolerance of the immune system towards self-antigens and organ-specific or systemic inflammation and subsequent tissue damage. In the present review, we summarized the most recent reports on splicing events that occur in the immunopathogenesis of systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) and attempted to clarify the role that splicing events play in regulating autoimmune disease progression. We also identified the changes that occur in splicing factor expression. The foregoing information might improve our understanding of autoimmune diseases and help develop new diagnostic and therapeutic tools for them.

Coordination between innate immune cells, type I IFNs and IRF5 drives SLE pathogenesis

Systemic lupus erythematosus (SLE) is a complex autoimmune disease which affects multiple organs. The type I interferon (IFN) gene signature and circulating autoantibodies are hallmarks of SLE. Plasmacytoid dendritic cells (pDCs) are considered the main producers of type I IFN and production is modulated by multiple other immune cell types. In SLE, essentially every immune cell type is dysregulated and aberrant deregulation is thought to be due, in part, to direct or indirect exposure to IFN. Genetic variants within or around the transcription factor interferon regulatory factor 5 (IRF5) associate with SLE risk. Elevated IFNα activity was detected in the sera of SLE patients carrying IRF5 risk polymorphisms who were positive for either anti-RNA binding protein (anti-RBP) or anti-double-stranded DNA (anti-dsDNA) autoantibodies. Neutrophils are also an important source of type I IFNs and are found in abundance in human blood. Neutrophil extracellular traps (NETs) are considered a potential source of antigenic trigger in SLE that can lead to type I IFN gene induction, as well as increased autoantibody production. In this review, we will focus on immune cell types that produce type I IFNs and/or are affected by type I IFN in SLE. In addition, we will discuss potential inducers of endogenous type I IFN production in SLE. Last, we will postulate how the different immune cell populations may be affected by an IRF5-SLE risk haplotype.

Association between the interferon regulatory factor 5 rs2004640 functional polymorphism and systemic lupus erythematosus: an updated meta-analysis

OBJECTIVE

The aim of this study is to determine whether the functional interferon regulatory factor 5 ( IRF5) polymorphism rs2004640 is associated with susceptibility to systemic lupus erythematosus (SLE) in multiple ethnic populations.

METHODS

A meta-analysis was conducted on the T allele of the IRF5 rs2004640 polymorphism in all study participants as well as each ethnic population.

RESULTS

Twenty research articles that included 28 comparative studies of 20,892 patients and 24,930 controls were included in the meta-analysis. The Asian population had a much lower prevalence of the T allele than any other study population at 28%, and the European population had the highest prevalence of the T allele at 52%. Meta-analysis showed an association between the IRF5 rs2004640 polymorphism and SLE in all participants (odds ratio = 1.472, 95% confidence interval = 1.370-1.582, p < 0.001). Analysis after stratification by ethnicity indicated that the IRF5 rs2004640 T allele is significantly associated with SLE in Europeans, Asians, Latin Americans and Arabs.

CONCLUSIONS

This meta-analysis confirms that the IRF5 rs2004640 polymorphism is associated with SLE susceptibility in different ethnic groups, and that its prevalence is ethnicity dependent.

IRF5-mediated immune responses and its implications in immunological disorders

Transcription factors are gene regulators that activate or repress target genes. One family of the transcription factors that have been extensively studied for their crucial role in regulating gene network in the immune system is the interferon regulatory factors (IRFs). IRFs possess a novel turn-helix turn motif that recognizes a specific DNA consensus found in the promoters of many genes that are involved in immune responses. IRF5, a member of IRFs has recently gained much attention for its role in regulating inflammatory responses and autoimmune diseases. Here, we discuss the role of IRF5 in regulating immune cells functions and how the dysregulation of IRF5 contributes to the pathogenesis of immune disorders. We also review the latest findings of potential IRF5 inhibitors that modulate IRF5 activity in the effort of developing therapeutic approaches for treating inflammatory disorders.

Interferon regulatory factor 5 (IRF5) regulates the expression of matrix metalloproteinase-3 (MMP-3) in human chondrocytes

Matrix metalloproteinase-3 (MMP-3) plays a pivotal role in the destruction of articular cartilage in osteoarthritis (OA). The regulation of gene expression of MMP-3 is complicated. Interferon regulatory factor 5 (IRF5) is a member of the interferon regulatory factor family of transcription factors. Little information regarding the biological function of IRF5 on chondrocytes and the pathogenesis of OA has been reported. In the current study, for the first time, we report that IRF5 is expressed in human primary chondrocytes and human chondrosarcoma cell line SW1353 cells. In addition, IRF5 is upregulated in response to TNF-α treatment in a dose dependent manner. Interestingly, IRF5 is significantly higher in chondrocytes from OA patients compared to those from normal subjects. Notably, IRF5 mediates TNF-α- induced expression of MMP-3 in chondrocytes. Overexpression of IRF5 promotes the expression of MMP-3, however, knockdown of IRF5 reduces the expression of MMP-3. Mechanistically, IRF5 is able to enhance the transcription of MMP-3 by binding to its promoter. Also, we found that NF-κB was involved in the effects of IRF-5 on MMP-3 expression. These findings suggest that IRF5 might be a novel pharmacological target for the treatment of OA and RA.

The genetic basis of systemic lupus erythematosus: What are the risk factors and what have we learned

The genome-wide association study is a free-hypothesis approach based on screening of thousands or even millions of genetic variants distributed throughout the whole human genome in relation to a phenotype. The relevant role of the genome-wide association studies in the last decade is undisputed because it has permitted to elucidate multiple risk genetic factors associated with the susceptibility to several human complex diseases. Regarding systemic lupus erythematosus (SLE) this approach has allowed to identify more than 60 risk loci for SLE susceptibility across populations to date, increasing our understanding on the pathogenesis of this disease. We present the latest findings in the genetic of SLE across populations using genome-wide approaches. These studies revealed that most of the genetic risk is shared across borders and ethnicities. Finally, we focus on describing the most important risk loci for SLE attempting to cover the genetic findings in relation to functional polymorphisms, such as missense single nucleotide polymorphisms (SNPs) or regulatory variants involved in the development of the disease. The functional studies try to identify the causality of some GWAS-associated variants, many of which fall in non-coding regions of the genome, suggesting a regulatory role. Many loci show an environmental interaction, another aspect revealed by the studies of epigenetic modifications and those associated with genetic variants. Finally, new-generation sequencing technologies can open other paths in the research on SLE genetics, the role of rare variants and the detailed identification of causal regulatory variation. The clinical relevance of the genetic factors will be shown when we are able to use them or in combination with other molecular measurements to re-classify a heterogeneous disease such as SLE.

Interferon regulatory factor 5 in human autoimmunity and murine models of autoimmune disease

Interferon regulatory factor 5 (IRF5) has been demonstrated as a key transcription factor of the immune system, playing important roles in modulating inflammatory immune responses in numerous cell types including dendritic cells, macrophages, and B cells. As well as driving the expression of type I interferon in antiviral responses, IRF5 is also crucial for driving macrophages toward a proinflammatory phenotype by regulating cytokine and chemokine expression and modulating B-cell maturity and antibody production. This review highlights the functional importance of IRF5 in a disease setting, by discussing polymorphic mutations at the human Irf5 locus that lead to susceptibility to systemic lupus erythematosus, rheumatoid arthritis, and inflammatory bowel disease. In concordance with this, we also discuss lessons in IRF5 functionality learned from murine in vivo models of autoimmune disease and inflammation and hypothesize that modulation of IRF5 activity and expression could provide potential therapeutic benefits in the clinic.

Genetic, genomic and epigenetic studies as tools for elucidating disease pathogenesis in primary Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is characterized by lymphoid infiltration of lacrimal and salivary glands leading to xerophthalmia and xerostomia. pSS is a complex disease involving both genetic and environmental risk factors. Technological advances over the past 10 years have revolutionized genetics and genomics research enabling high-throughput characterization and analysis of DNA and RNA in patient samples on a genome-wide scale. Further, application of high-throughput methods for characterization of epigenetic variation, such as DNA methylation status, is increasingly being applied to AID populations and will likely further define additional risk factors for disease risk and outcome. Main results obtain in pSS through these various approaches are reviewed here.

Genetics of the type I interferon pathway in systemic lupus erythematosus

Genetic studies of systemic lupus erythematosus (SLE) have been successful, identifying numerous risk factors for human disease. While the list is not yet complete, it is clear that important immune system pathways are represented, one of which being type I interferon (IFN). Circulating type I IFN levels are high in SLE patients and this IFN pathway activation is heritable in families with SLE. We summarize our current understanding of the genetics of the type I IFN pathway in SLE, with an emphasis on studies that demonstrate an impact of the SLE-risk alleles upon type I IFN pathway activation in SLE patients. These studies illustrate that variations in type I IFN pathway genes represent a common genetic feature of SLE. By understanding the genetic regulation of type I IFN, we may be able to intervene in a more personalized fashion, based upon the molecular dysregulation present in a given individual.

Interferon regulatory factor 5 and autoimmune lupus

Systemic lupus erythematosus (SLE) is a severe multi-system autoimmune disease, whereas interferon regulatory factor (IRF) 5 belongs to the family of transcription factors that modulate immune system activities. Recently, many lines of investigations suggested that IRF5 gene polymorphisms are closely associated with the disease onset of SLE. Indeed, expressed in B cells, dendritic cells (DCs), monocytes and macrophages, IRF5 could significantly affect these immune cells participating in the pathogenesis of SLE, and numerous studies implied that this transcription factor is mechanistically linked to the disease progression. Here, we comprehensively review the updated evidence indicating the roles of IRF5 in autoimmune lupus. Hopefully, the information obtained will lead to a better understanding of the pathogenesis and development of novel therapeutic strategies for the systemic autoimmune disease.

Use of biomarkers in the management of children with lupus

Childhood systemic lupus erythematosus (SLE) is known to have a worse prognosis than adult-onset disease, and monitoring and treatment of the disease are still a challenge. Thus, there is an urgent need for highly reliable, non-invasive biomarkers for early detection of relapses, to avoid long-term complications and to optimize the management of children with LN. Recent studies of pediatric patients have yielded novel specific biomarkers for SLE diagnosis which can be used for monitoring disease activity and response to treatment. The most promising biomarkers in juvenile-onset SLE include cell-bound complement activation products, some genomic profiles, and urinary proteins such as neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and alpha-1-acid glycoprotein. None of these might be suitable for use as a single SLE-biomarker. More likely a combination of novel biomarkers with traditionally used data, including autoantibodies and complement, might help to enhance sensitivity and specificity for early diagnosis, disease monitoring, and prediction of relapses.cp.

The systemic lupus erythematosus IRF5 risk haplotype is associated with systemic sclerosis

Systemic sclerosis (SSc) is a fibrotic autoimmune disease in which the genetic component plays an important role. One of the strongest SSc association signals outside the human leukocyte antigen (HLA) region corresponds to interferon (IFN) regulatory factor 5 (IRF5), a major regulator of the type I IFN pathway. In this study we aimed to evaluate whether three different haplotypic blocks within this locus, which have been shown to alter the protein function influencing systemic lupus erythematosus (SLE) susceptibility, are involved in SSc susceptibility and clinical phenotypes. For that purpose, we genotyped one representative single-nucleotide polymorphism (SNP) of each block (rs10488631, rs2004640, and rs4728142) in a total of 3,361 SSc patients and 4,012 unaffected controls of Caucasian origin from Spain, Germany, The Netherlands, Italy and United Kingdom. A meta-analysis of the allele frequencies was performed to analyse the overall effect of these IRF5 genetic variants on SSc. Allelic combination and dependency tests were also carried out. The three SNPs showed strong associations with the global disease (rs4728142: P  = 1.34×10(-8), OR  = 1.22, CI 95%  = 1.14-1.30; rs2004640: P  = 4.60×10(-7), OR  = 0.84, CI 95%  = 0.78-0.90; rs10488631: P  = 7.53×10(-20), OR  = 1.63, CI 95%  = 1.47-1.81). However, the association of rs2004640 with SSc was not independent of rs4728142 (conditioned P  = 0.598). The haplotype containing the risk alleles (rs4728142*A-rs2004640*T-rs10488631*C: P  = 9.04×10(-22), OR  = 1.75, CI 95%  = 1.56-1.97) better explained the observed association (likelihood P-value  = 1.48×10(-4)), suggesting an additive effect of the three haplotypic blocks. No statistical significance was observed in the comparisons amongst SSc patients with and without the main clinical characteristics. Our data clearly indicate that the SLE risk haplotype also influences SSc predisposition, and that this association is not sub-phenotype-specific.

RNA-Seq for enrichment and analysis of IRF5 transcript expression in SLE

Polymorphisms in the interferon regulatory factor 5 (IRF5) gene have been consistently replicated and shown to confer risk for or protection from the development of systemic lupus erythematosus (SLE). IRF5 expression is significantly upregulated in SLE patients and upregulation associates with IRF5-SLE risk haplotypes. IRF5 alternative splicing has also been shown to be elevated in SLE patients. Given that human IRF5 exists as multiple alternatively spliced transcripts with distinct function(s), it is important to determine whether the IRF5 transcript profile expressed in healthy donor immune cells is different from that expressed in SLE patients. Moreover, it is not currently known whether an IRF5-SLE risk haplotype defines the profile of IRF5 transcripts expressed. Using standard molecular cloning techniques, we identified and isolated 14 new differentially spliced IRF5 transcript variants from purified monocytes of healthy donors and SLE patients to generate an IRF5 variant transcriptome. Next-generation sequencing was then used to perform in-depth and quantitative analysis of full-length IRF5 transcript expression in primary immune cells of SLE patients and healthy donors by next-generation sequencing. Evidence for additional alternatively spliced transcripts was obtained from de novo junction discovery. Data from these studies support the overall complexity of IRF5 alternative splicing in SLE. Results from next-generation sequencing correlated with cloning and gave similar abundance rankings in SLE patients thus supporting the use of this new technology for in-depth single gene transcript profiling. Results from this study provide the first proof that 1) SLE patients express an IRF5 transcript signature that is distinct from healthy donors, 2) an IRF5-SLE risk haplotype defines the top four most abundant IRF5 transcripts expressed in SLE patients, and 3) an IRF5 transcript signature enables clustering of SLE patients with the H2 risk haplotype.

4F decreases IRF5 expression and activation in hearts of tight skin mice

The apoAI mimetic 4F was designed to inhibit atherosclerosis by improving HDL. We reported that treating tight skin (Tsk^−/+) mice, a model of systemic sclerosis (SSc), with 4F decreases inflammation and restores angiogenic potential in Tsk^−/+ hearts. Interferon regulating factor 5 (IRF5) is important in autoimmunity and apoptosis in immune cells. However, no studies were performed investigating IRF5 in myocardium. We hypothesize that 4F differentially modulates IRF5 expression and activation in Tsk^−/+ hearts. Posterior wall thickness was significantly increased in Tsk^−/+ compared to C57Bl/6J (control) and Tsk^−/+ mice with 4F treatment assessed by echoradiography highlighting reduction of fibrosis in 4F treated Tsk^−/+ mice. IRF5 in heart lysates from control and Tsk/+ with and without 4F treatment (sc, 1 mg/kg/d, 6–8 weeks) was determined. Phosphoserine, ubiquitin, ubiquitin K⁶³ on IRF5 were determined on immunoprecipitates of IRF5. Immunofluorescence and TUNEL assays in heart sections were used to determine positive nuclei for IRF5 and apoptosis, respectively. Fluorescence-labeled streptavidin (SA) was used to determine endothelial cell uptake of biotinylated 4F. SA-agarose pulldown and immunoblotting for IRF5 were used to determine 4F binding IRF5 in endothelial cell cytosolic fractions and to confirm biolayer interferometry studies. IRF5 levels in Tsk^−/+ hearts were similar to control. 4F treatments decrease IRF5 in Tsk^−/+ hearts and decrease phosphoserine and ubiquitin K⁶³ but increase total ubiquitin on IRF5 in Tsk^−/+ compared with levels on IRF5 in control hearts. 4F binds IRF5 by mechanisms favoring association over dissociation strong enough to pull down IRF5 from a mixture of endothelial cell cytosolic proteins. IRF5 positive nuclei and apoptotic cells in Tsk^−/+ hearts were increased compared with controls. 4F treatments decreased both measurements in Tsk^−/+ hearts. IRF5 activation in Tsk^−/+ hearts is increased. 4F treatments decrease IRF5 expression and activation in Tsk^−/+ hearts by a mechanism related to 4F’s ability to bind IRF5.

Interferon regulatory factor 5 in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by multiple genetic risk factors, high levels of interferon alpha (IFN-α), and the production of autoantibodies against components of the cell nucleus. Interferon regulatory factor 5 (IRF5) is a transcription factor which induces the transcription of IFN-α and other cytokines, and genetic variants of IRF5 have been strongly linked to SLE pathogenesis. IRF5 functions downstream of Toll-like receptors and other microbial pattern-recognition receptors, and immune complexes made up of SLE-associated autoantibodies seem to function as a chronic endogenous stimulus to this pathway. In this paper, we discuss the physiologic role of IRF5 in immune defense and the ways in which IRF5 variants may contribute to the pathogenesis of human SLE. Recent data regarding the role of IRF5 in both serologic autoimmunity and the overproduction of IFN-α in human SLE are summarized. These data support a model in which SLE-risk variants of IRF5 participate in a “feed-forward” mechanism, predisposing to SLE-associated autoantibody formation, and subsequently facilitating IFN-α production downstream of Toll-like receptors stimulated by immune complexes composed of these autoantibodies.

Associations between interferon regulatory factor 5 polymorphisms and rheumatoid arthritis: a meta-analysis

The aim of this study was to determine whether interferon regulatory factor 5 (IRF5) polymorphisms confers susceptibility to rheumatoid arthritis (RA) in populations with different ethnicities. We searched the literature using the Pubmed and Embase databases and conducted meta-analyses on associations between the four IRF5 polymorphisms (rs2004640, rs729302, rs752637, and rs2280714) and RA susceptibility, using fixed and random effects models. A total of 12 comparison studies were considered in this meta-analysis, which in total involved 7,916 RA patients and 6,452 controls, and eight European, three Asian, and one Argentinean population. Meta-analysis showed an association between the minor allele of rs2004640 and RA in all subjects (odds ratio [OR] = 0.928, 95 % confidence interval [CI] = 0.865-0.996, P = 0.037). After stratification by ethnicity, analysis indicated that the minor allele was significantly associated with RA in Europeans (OR = 0.889, 95 % CI = 0.839-0.941, P = 5.03 × 10(-6)), but not in Asians (OR = 1.057, 95 % CI = 0.978-1.144, P = 0.164). A direct comparison between anti-citrullinated peptide antibody-positive and -negative patients revealed no difference of the frequency of the rs2004640 minor allele (OR = 1.047, 95 % CI = 0.813-1.348, P = 0.724). Meta-analysis identified a significant association between RA and the minor allele of the rs729302 polymorphism in the overall population (OR = 0.896, 95 % CI = 0.826-0.972, P = 0.009) and in Asians (OR = 0.862, 95 % CI = 0.795-0.935, P = 3.50 × 10(-5)), but not in Europeans (OR = 0.951, 95 % CI = 0.877-1.031, P = 0.225). Meta-analysis showed an association between the minor allele of rs752637 and RA in Europeans (OR = 0.858, 95 % CI = 0.789-0.932, P = 3.03 × 10(-5)), but not in Asians (OR = 1.035, 95 % CI = 0.918-1.168, P = 0.572). No association was found between the rs2280714 polymorphism and RA susceptibility. This meta-analysis confirms that the IRF5 rs2004640, rs729302 and rs752637 polymorphisms are associated with RA susceptibility in different ethnic groups, especially in Europeans and Asians, but further study of this association is required in other ethnic groups.

Genetics of SLE: functional relevance for monocytes/macrophages in disease

Genetic studies in the last 5 years have greatly facilitated our understanding of how the dysregulation of diverse components of the innate immune system contributes to pathophysiology of SLE. A role for macrophages in the pathogenesis of SLE was first proposed as early as the 1980s following the discovery that SLE macrophages were defective in their ability to clear apoptotic cell debris, thus prolonging exposure of potential autoantigens to the adaptive immune response. More recently, there is an emerging appreciation of the contribution both monocytes and macrophages play in orchestrating immune responses with perturbations in their activation or regulation leading to immune dysregulation. This paper will focus on understanding the relevance of genes identified as being associated with innate immune function of monocytes and macrophages and development of SLE, particularly with respect to their role in (1) immune complex (IC) recognition and clearance, (2) nucleic acid recognition via toll-like receptors (TLRs) and downstream signalling, and (3) interferon signalling. Particular attention will be paid to the functional consequences these genetic associations have for disease susceptibility or pathogenesis.

Genetics of myasthenia gravis: a case-control association study in the Hellenic population

Myasthenia gravis (MG) is an heterogeneous autoimmune disease characterized by the production of autoantibodies against proteins of the postsynaptic membrane, in the neuromuscular junction. The contribution of genetic factors to MG susceptibility has been evaluated through family and twin studies however, the precise genetic background of the disease remains elusive. We conducted a case-control association study in 101 unrelated MG patients of Hellenic origin and 101 healthy volunteers in order to assess the involvement of common genetic variants in susceptibility to MG. We focused on three candidate genes which have been clearly associated with several autoimmune diseases, aiming to investigate their potential implication in MG pathogenesis. These are interferon regulatory factor 5 (IRF-5), TNFα-induced protein 3 (TNFAIP3), also known as A20, and interleukin-10 (IL-10), key molecules in the regulation of immune function. A statistical trend of association (P = 0.068) between IL-10 promoter single nucleotide polymorphisms (SNPs) and the subgroups of early and late-onset MG patients was revealed. No statistically significant differences were observed in the rest of the variants examined. As far as we are aware, this is the first worldwide attempt to address the possible association between IRF-5 and TNFAIP3 common genetic variants and the genetic basis of MG.

Irf5-deficient mice are protected from pristane-induced lupus via increased Th2 cytokines and altered IgG class switching

Polymorphisms in the transcription factor interferon (IFN) regulatory factor 5 (IRF5) have been identified that show a strong association with an increased risk of developing the autoimmune disease systemic lupus erythematosus (SLE). A potential pathological role for IRF5 in SLE development is supported by the fact that increased IRF5 mRNA and protein are observed in primary blood cells of SLE patients and this correlates with an increased risk of developing the disease. Here, we demonstrate that IRF5 is required for pristane-induced SLE via its ability to control multiple facets of autoimmunity. We show that IRF5 is required for pathological hypergammaglobulinemia and, in the absence of IRF5, IgG class switching is reduced. Examination of in vivo cytokine expression (and autoantibody production) identified an increase in Irf5(-/-) mice of Th2 cytokines. In addition, we provide clear evidence that loss of Irf5 significantly weakens the in vivo type I IFN signature critical for disease pathogenesis in this model of murine lupus. Together, these findings demonstrate the importance of IRF5 for autoimmunity and provide a significant new insight into how overexpression of IRF5 in blood cells of SLE patients may contribute to disease pathogenesis.

Interferon-inducible Ifi200-family genes as modifiers of lupus susceptibility

Both genetic and environmental factors contribute to the development and progression of systemic lupus erythematosus (SLE), a complex autoimmune disease. The disease exhibits a strong gender bias and develops predominantly in females. Additionally, most SLE patients exhibit increased serum levels of interferon-α (IFN-α) and the "IFN signature". Studies using the mouse models of lupus have identified several lupus susceptibility loci, including the New Zealand Black (NZB)-derived autoimmunity 2 (Nba2) interval on the chromosome 1. The interval, which is syntenic to the human chromosome 1q region, harbors the FcγR family, SLAM/CD2-family, and the IFN-inducible Ifi200-family genes (encoding for the p200-family proteins). Studies involving the B6.Nba2 congenic mice revealed that the development of antinuclear autoantibodies (ANAs) depends on the age, gender, and activation of type I IFN-signaling. Interestingly, recent studies involving the generation of Nba2 subcongenic mouse lines and generation of mice deficient for the Fcgr2b or Aim2 gene within the interval have provided evidence that epistatic interactions among the Nba2 genes contribute to increased lupus susceptibility. Given that the expression of some of the p200-family proteins is differentially regulated by sex hormones and these proteins differentially regulate cytosolic DNA-induced production of type I IFN and proinflammatory cytokines (IL-1β and IL-18), the major known contributors of SLE-associated inflammation, we discuss the recent advancements in our understanding of the role of p200-family proteins in lupus susceptibility modification. An improved understanding of the role of p200-family proteins in the development of autoimmunity is likely to identify new approaches to treat SLE patients.

Interferons in autoimmune and inflammatory diseases: regulation and roles

Several lines of evidence strongly implicate type I interferons (IFN-α and β) and IFN-signaling in the pathogenesis of certain autoimmune inflammatory diseases. Accordingly, genome-wide association studies have identified polymorphisms in the type I IFN-signaling pathways. Other studies also indicate that a feed-forward loop of type I IFN production, which involves sensing of cytoplasmic nucleic acids by sensors, contributes to the development of immunopathology. In addition, a mutually positive regulatory feedback loop between type I IFNs and estrogen receptor-α may contribute to a gender bias, thus resulting in an increased production of type I IFNs and associated immunopathology in women. Increased levels of type I IFNs have numerous immunomodulatory functions for both the innate and adaptive immune responses. Given that the IFN-β also has some anti-inflammatory roles, identifying molecular links among certain genotypes, cytokine profiles, and associated phenotypes in patients with autoimmune inflammatory diseases is likely to improve our understanding of autoimmunity-associated pathogenesis and suboptimal outcomes following standard therapies.

Unique contribution of IRF-5-Ikaros axis to the B-cell IgG2a response

IRF-5 is a transcription factor activated by toll like receptor (TLR)7 and TLR9 during innate immune responses. IRF-5 activates not only Type I IFN, but also inflammatory cytokines. Most importantly, a genetic variation in the IRF-5 gene shows a strong association with autoimmune diseases such as Lupus. Here, we report that IRF5-deficient mice have attenuated IgG2a/c responses to T-cell-dependent and -independent antigens and to polyoma virus infection. This defect is due to the intrinsic deletion of IRF-5 in B cells, as SCID mice reconstituted with Irf5-/- B cells show a decrease in IgG2a/c expression after viral infection compared with mice that received wild-type B cells. Irf5-/-B cells in vitro have diminished TLR and cytokine-induced class switching to IgG2a/c. Addressing the molecular mechanism, we show that IRF-5 regulates IgG2a/c expression by decreasing Ikaros expression; reconstitution of IRF-5 in Irf5-/- B cells downregulates Ikaros levels and increases switching to IgG2a/c. The IRF site in ikzf1 promoter binds IRF-5, IRF-4 and IRF-8. We show that IRF-8 but not IRF-4 activates the ikzf1 promoter, and IRF-5 inhibits the transcriptional activity of IRF-8. Collectively, these results identify the IRF-5-Ikaros axis as a critical modulator of IgG2a/c class switching.

Biomarkers for systemic lupus erythematosus

The urgent need for lupus biomarkers was demonstrated in September 2011 during a Workshop sponsored by the Food and Drug Administration: Potential Biomarkers Predictive of Disease Flare. After 2 days of discussion and more than 2 dozen presentations from thought leaders in both industry and academia, it became apparent that highly sought biomarkers to predict lupus flare have not yet been identified. Even short of the elusive biomarker of flare, few biomarkers for systemic lupus erythematosus (SLE) diagnosis, monitoring, and stratification have been validated and employed for making clinical decisions. This lack of reliable, specific biomarkers for SLE hampers proper clinical management of patients with SLE and impedes development of new lupus therapeutics. As such, the intensity of investigation to identify lupus biomarkers is climbing a steep trajectory, lending cautious optimism that a validated panel of biomarkers for lupus diagnosis, monitoring, stratification, and prediction of flare may soon be in hand.

Effects of IRF5 lupus risk haplotype on pathways predicted to influence B cell functions

Both genetic and environmental interactions affect systemic lupus erythematosus (SLE) development and pathogenesis. One known genetic factor associated with lupus is a haplotype of the interferon regulatory factor 5 (IRF5) gene. Analysis of global gene expression microarray data using gene set enrichment analysis identified multiple interferon- and inflammation-related gene sets significantly overrepresented in cells with the risk haplotype. Pathway analysis using expressed genes from the significant gene sets impacted by the IRF5 risk haplotype confirmed significant correlation with the interferon pathway, Toll-like receptor pathway, and the B-cell receptor pathway. SLE patients with the IRF5 risk haplotype have a heightened interferon signature, even in an unstimulated state (P = 0.011), while patients with the IRF5 protective haplotype have a B cell interferon signature similar to that of controls. These results identify multiple genes in functionally significant pathways which are affected by IRF5 genotype. They also establish the IRF5 risk haplotype as a key determinant of not only the interferon response, but also other B-cell pathways involved in SLE.

Distinct regulation of murine lupus susceptibility genes by the IRF5/Blimp-1 axis

Genome-wide association studies have identified lupus susceptibility genes such as IRF5 and PRDM1 (encoding for IFN regulatory factor 5 [IRF]5 and Blimp-1) in the human genome. Accordingly, the murine Irf5 and Prdm1 genes have been shown to play a role in lupus susceptibility. However, it remains unclear how IRF5 and Blimp-1 (a transcriptional target of IRF5) contribute to lupus susceptibility. Given that the murine lupus susceptibility locus Nba2 includes the IFN-regulated genes Ifi202 (encoding for the p202 protein), Aim2 (encoding for the Aim2 protein), and Fcgr2b (encoding for the FcγRIIB receptor), we investigated whether the IRF5/Blimp-1 axis could regulate the expression of these genes. We found that an Irf5 deficiency in mice decreased the expression of Blimp-1 and reduced the expression of the Ifi202. However, the deficiency increased the expression of Aim2 and Fcgr2b. Correspondingly, increased expression of IRF5 in cells increased levels of Blimp-1 and p202 protein. Moreover, Blimp-1 expression increased the expression of Ifi202, whereas it reduced the expression of Aim2. Interestingly, an Aim2 deficiency in female mice increased the expression of IRF5. Similarly, the Fcgr2b-deficient mice expressed increased levels of IRF5. Moreover, increased expression of IRF5 and Blimp-1 in lupus-prone C57BL/6.Nba2, New Zealand Black, and C57BL/6.Sle123 female mice (as compared with age-matched C57BL/6 female mice) was associated with increased levels of the p202 protein. Taken together, our observations demonstrate that the IRF5/Blimp-1 axis differentially regulates the expression of Nba2 lupus susceptibility genes, and they suggest an important role for the IRF5/Blimp-1/p202 axis in murine lupus susceptibility.

Novel insights on the role of the innate immune system in systemic sclerosis

Over the last several years the involvement of the innate immune system in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus (SLE) has become well established. As systemic sclerosis (SSc; scleroderma) shares clinical features and autoantibodies with SLE, investigation has recently focused on the role of innate immunity in SSc. This has been supported by recent genetic studies. However, unlike SLE and other related autoimmune diseases, SSc patients suffer from pathologic fibrosis of skin and internal organs. The fibrotic component of SSc shares several features with syndromes following environmental exposures to agents such as organic solvents, silica dust and bleomycin. Recent work in SSc and these related fibrotic diseases have identified several areas in which innate immunity can stimulate inflammation as well as fibrosis. This article will focus on the recent discoveries identifying a prominent role of cells of the innate immune system, pattern recognition receptors, and activation of dendritic cells in the pathogenesis of SSc.

Cell type and gender-dependent differential regulation of the p202 and Aim2 proteins: implications for the regulation of innate immune responses in SLE

Upon sensing cytosolic double-stranded DNA (dsDNA), the murine Aim2 (encoded by the Aim2 gene) protein forms an inflammasome and promotes the secretion of proinflammatory cytokines, such as IL-1β and IL-18. In contrast, the p202 protein (encoded by the Ifi202 gene) does not form an inflammasome. Previously, we have reported that the interferon (IFN) and female sex hormone-induced increased nuclear levels of p202 protein in immune cells are associated with increased susceptibility to develop a lupus-like disease. However, signaling pathways that regulate the expression of Aim2 protein remain unknown. Here we report that the expression of Aim2 gene is induced in bone marrow-derived macrophages (BMDMs) by IFN-α treatment and the expression is, in part, STAT1-dependent. However, treatment of splenic T or B cells with IFN-α or their stimulation, which induced the expression of Ifi202 gene, did not induce the expression of Aim2 gene. Furthermore, treatment of cells with the male hormone androgen increased levels of Aim2 mRNA and protein. Moreover, treatment of murine macrophage cell lines (RAW264.7 and J774A.1) with IFN-α differentially induced the expression of Aim2 and p202 proteins and regulated their sub-cellular localization. Additionally, activation of Toll-like receptors (TLR3, 4, and 9) in BMDMs and cell lines also differentially regulated the expression of Aim2 and Ifi202 genes. Our observations demonstrate that cell type and gender-dependent factors differentially regulate the expression of the Aim2 and p202 proteins, thus, suggesting opposing roles for these two proteins in innate immune responses in lupus disease.

Emerging roles for the interferon-inducible p200-family proteins in sex bias in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease involving multiple organs. The disease is characterized by the production of pathogenic autoantibodies to DNA and certain nuclear antigens, chronic inflammation, and immune dysregulation. Genetic studies involving SLE patients and mouse models have indicated that multiple lupus susceptible genes contribute to the disease phenotype. Notably, the development of SLE in patients and in certain mouse models exhibits a strong sex bias. In addition, several lines of evidence indicates that activation of interferon-α (IFN-α) signaling in immune cells and alterations in the expression of certain immunomodulatory cytokines contribute to lupus pathogenesis. Studies have implicated factors, such as the X chromosomal gene dosage effect and the sex hormones, in gender bias in SLE. However, the molecular mechanisms remain unclear. Additionally, it remains unclear whether these factors influence the "IFN-signature," which is associated with SLE. In this regard, a mutually positive regulatory feedback loop between IFNs and estrogen receptor-α (ERα) has been identified in immune cells. Moreover, studies indicate that the expression of certain IFN-inducible p200-family proteins that act as innate immune sensors for cytosolic DNA is differentially regulated by sex hormones. In this review, we discuss how the modulation of the expression of the p200-family proteins in immune cells by sex hormones and IFNs contributes to sex bias in SLE. An improved understanding of the regulation and roles of the p200-family proteins in immune cells is critical to understand lupus pathogenesis as well as response (or the lack of it) to various therapies.

Genetic analyses of interferon pathway-related genes reveal multiple new loci associated with systemic lupus erythematosus

OBJECTIVE

The overexpression of interferon (IFN)-inducible genes is a prominent feature of systemic lupus erythematosus (SLE); it serves as a marker for active and more severe disease, and is also observed in other autoimmune and inflammatory conditions. This study was undertaken to investigate the genetic variations responsible for sustained activation of IFN-responsive genes in SLE.

METHODS

We systematically evaluated association of SLE with a total of 1,754 IFN pathway-related genes, including IFN-inducible genes known to be differentially expressed in SLE patients and their direct regulators. We used a 3-stage study design in which 2 cohorts (total of 939 SLE cases and 3,398 controls) were analyzed independently and jointly for association with SLE, and the results were adjusted for the number of comparisons.

RESULTS

A total of 15,166 single-nucleotide polymorphisms (SNPs) passed all quality control filters; 305 of these SNPs demonstrated replicated association with SLE in both cohorts. Nine variants were further genotyped for confirmation in an average of 1,316 independent SLE cases and 3,215 independent controls. Association with SLE was confirmed for several genes, including those for the transmembrane receptor CD44 (CD44 [rs507230]; P = 3.98 × 10⁻¹²), the cytokine pleiotrophin (PTN [rs919581]; P = 5.38 × 10⁻⁴), the heat-shock protein DnaJ (DNAJA1 [rs10971259]; P = 6.31 × 10⁻³), and the nuclear import protein karyopherin α1 (KPNA [rs6810306]; P = 4.91 × 10⁻²).

CONCLUSION

This study expands the number of candidate genes that have been shown to be associated with SLE and highlights potential of pathway-based approaches for gene discovery. Identification of the causal alleles will help elucidate the molecular mechanisms responsible for activation of the IFN system in SLE.

Replicated association of 17q12-21 with susceptibility of primary biliary cirrhosis in a Japanese cohort

To examine the genetics of susceptibility to primary biliary cirrhosis (PBC), genome-wide association studies GWAS have been performed in patients of European ancestry and have shown the significant associations of IL12-related pathways, SPIB, IRF5-TNPO3, and 17q12-21. We tested whether these findings could be extended to a Japanese cohort, 303 Japanese PBC and 298 controls. We failed to detect significant associations at IL12A (rs574808, rs1075498) and IL12RB2 (rs3790567). There was no genetic variance at IRF5-TNPO3 (rs10488631) in Japanese. A single nucleotide polymorphism (SNP) at SPIB (rs3745516) reached nominal significance, but the corrected P value did not reach significance. For the 17q12-21 region, two SNPs had nominally significant associations [GSDMB (rs2305480, P = 0.022) and ZPBP2 (rs11557467, P = 0.021)] and we noted a significant P value at a SNP in IKZF3 (rs939327, P = 0.0024, P(c) = 0.017) after correction for multiple comparisons. Thus, these results indicate a haplotype on 17q12-21 with a similar association in Japanese and European PBC.

Differential requirement of histone acetylase and deacetylase activities for IRF5-mediated proinflammatory cytokine expression

Recent evidence indicates a new role for histone deacetylases (HDACs) in the activation of genes governing the host immune response. Virus, along with other pathogenic stimuli, triggers an antiviral defense mechanism through the induction of IFN, IFN-stimulated genes, and other proinflammatory cytokines. Many of these genes have been shown to be regulated by transcription factors of the IFN regulatory factor (IRF) family. Recent studies from IRF5 knockout mice have confirmed a critical role for IRF5 in virus-induced type I IFN expression and proinflammatory cytokines IL-6, IL-12, and TNF-α; yet, little is known of the molecular mechanism of IRF5-mediated proinflammatory cytokine expression. In this study, we show that both HDACs and histone acetyltransferases (HATs) associate with IRF5, leading to alterations in its transactivation ability. Using the HDAC inhibitor trichostatin A, we demonstrate that ISRE, IFNA, and IL6 promoters require HDAC activity for transactivation and transcription, whereas TNFα does not. Mapping the interaction of corepressor proteins (HDAC1, silencing mediator of retinoid and thyroid receptor/nuclear corepressor of retinoid receptor, and Sin3a) and HATs to IRF5 revealed distinct differences, including the dependence of IRF5 phosphorylation on HAT association resulting in IRF5 acetylation. Data presented in this study support a mechanism whereby virus triggers the dynamic conversion of an IRF5-mediated silencing complex to that of an activating complex on promoters of target genes. These data provide the first evidence, to our knowledge, of a tightly controlled transcriptional mechanism whereby IRF5 regulates proinflammatory cytokine expression in conjunction with HATs and HDACs.

Gender-dependent expression of murine Irf5 gene: implications for sex bias in autoimmunity

Molecular mechanisms that contribute to sex bias in the development of systemic lupus erythematosus (SLE), an autoimmune disease, remain unknown. We found that the expression levels of interferon regulatory factor 5 (IRF5), a lupus susceptibility factor, depend on gender of mice. We found that steady-state levels of the Irf5 mRNA were relatively higher in splenic cells from certain autoimmune-prone mice (for example, NZB and NZB/W F(1)) than in non-autoimmune C57BL/6 mice. Additionally, levels of Irf5 mRNA and protein were higher in females than in strain and age-matched males. Accordingly, splenic cells from estrogen receptor-alpha (ERα) knockout, when compared with the wild-type (ERα(+/+)), female mice expressed relatively lower levels of Irf5 mRNA and the treatment of splenic cells with 17β-estradiol increased the levels. Furthermore, splenic B cells from the female mice had relatively more IRF5 protein in the nucleus than the male mice. Collectively, our observations demonstrate a gender bias in the expression and sub-cellular localization of the murine IRF5.

Cardiovascular disease complications in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a highly variable autoimmune disease characterized by aberrant host-immune responses and chronic inflammation. Recently, a strong association between cardiovascular (CV) disease and SLE has emerged. Thus, low serum, high-density lipoprotein strongly correlated with elevated erythrocyte sedimentation rate, IL-6, TNF-alpha and the SLE disease activity index after adjusting for age, gender, race, BMI, insulin sensitivity and any concurrent drug use. In SLE, CV disease is characterized by increased VEGF, which may alter vascular hemostasis and promote neoangiogenesis. Increased low-density lipoprotein-cholesterol and proinflammatory high-density lipoprotein-cholesterol uptake by monocytes together with enhanced low-density lipoprotein-cholesterol oxidation results in the deposition of altered cholesterol forms into the vascular wall. This contributes to precocious and accelerated development of coronary artery plaques. Cholesterol-reducing drugs should be considered in the standard of care of SLE patients, especially in those with an unfavorable CV disease risk profile, which could reduce the probability of atherosclerosis progressing to CV disease or stroke in these patients.

Aberrant responses to TLR agonists in pediatric IBD patients; the possible association with increased production of Th1/Th17 cytokines in response to candida, a luminal antigen

Toll like receptors (TLR) regulate innate immune responses sensing byproducts of intestinal microbiota. We examined responses to TLR agonists in children with inflammatory bowel disease (IBD). Peripheral blood mononuclear cells (PBMC) obtained from children with IBD [Crohn's disease (CD, n = 10), ulcerative colitis (UC, n = 10)], children with non-IgE-mediated food allergy (NFA, n = 20), and controls (n = 15) were tested for their production of proinflammatory and counter-regulatory cytokines with TLR agonists in comparison with their cytokine production against milk protein and candida. IBD patients were all in the inactive state. IBD PBMC produced more IL-6 with all the TLR agonists tested than controls. CD PBMC produced more counter-regulatory cytokines with TLR agonists, while UC PBMC produced more IL-1ss and IL-10 with TLR 7/8 agonist than controls. Cytokine production by NFA PBMC did not differ from controls. CD but not UC PBMC produced more IFN-gamma and IL-17 with candida. Aberrant responses to TLR agonists may be associated with increase in IFN-gamma/IL-17 production against candida in CD children.

Contribution of IRF5 in B cells to the development of murine SLE-like disease through its transcriptional control of the IgG2a locus

Interferon regulatory factor (IRF) 5 is a key transcription factor for the activation of innate immune responses downstream of Toll-like receptor signaling. Based on recent genetic analyses, IRF5 is a focus for its potential involvement in systemic lupus erythematosus (SLE), although how IRF5 contributes to SLE is uncertain. In this study, we demonstrate a requirement for IRF5 in the development of murine SLE via its role in B lymphocytes. We show that antinuclear autoantibodies and Ig glomerular deposits, hallmarks of SLE, are absent in Irf5(-/-) mice challenged to develop SLE by pristane injection. In particular, production of autoantibodies of the IgG2a subtype, the most prominent isotype in inducing autoimmunity, requires IRF5. Finally, we provide evidence for the critical role of this transcription factor in the secretion of pathogenic antibodies through its direct control of class switch recombination of the gamma2a locus. By demonstrating a B-cell-intrinsic role, this study places IRF5 in a context that may have implications for understanding the pathogenesis of human SLE.

Genetic risk factors in lupus nephritis and IgA nephropathy--no support of an overlap

Background

IgA nephropathy (IgAN) and nephritis in Systemic Lupus Erythematosus (SLE) are two common forms of glomerulonephritis in which genetic findings are of importance for disease development. We have recently reported an association of IgAN with variants of TGFB1. In several autoimmune diseases, particularly in SLE, IRF5, STAT4 genes and TRAF1-C5 locus have been shown to be important candidate genes. The aim of this study was to compare genetic variants from the TGFB1, IRF5, STAT4 genes and TRAF1-C5 locus with susceptibility to IgAN and lupus nephritis in two Swedish cohorts.

Patients and Methods

We genotyped 13 single nucleotide polymorphisms (SNPs) in four genetic loci in 1252 DNA samples from patients with biopsy proven IgAN or with SLE (with and without nephritis) and healthy age- and sex-matched controls from the same population in Sweden.

Results

Genotype and allelic frequencies for SNPs from selected genes did not differ significantly between lupus nephritis patients and SLE patients without nephritis. In addition, haplotype analysis for seven selected SNPs did not reveal a difference for the SLE patient groups with and without nephritis. Moreover, none of these SPNs showed a significant difference between IgAN patients and healthy controls. IRF5 and STAT4 variants remained significantly different between SLE cases and healthy controls. In addition, the data did not show an association of TRAF1-C5 polymorphism with susceptibility to SLE in this Swedish population.

Conclusion

Our data do not support an overlap in genetic susceptibility between patients with IgAN or SLE and reveal no specific importance of SLE associated SNPs for the presence of lupus nephritis.

Genetic associations in type I interferon related pathways with autoimmunity

Type I interferons play an outstanding role in innate and adaptive immunity by enhancing functions of dendritic cells, inducing differentiation of monocytes, promoting immunoglobulin class switching in B cells and stimulating effector functions of T cells. The increased production of IFNα/β by plasmacytoid dendritic cells could be responsible for not only efficient antiviral defence, but it also may be a pathological factor in the development of various autoimmune disorders. The first evidence of a genetic link between type I interferons and autoimmune diseases was the observation that elevated IFNα activity is frequently detected in the sera of patients with systemic lupus erythematosus, and that this trait shows high heritability and familial aggregation in their first-degree healthy relatives. To date, a number of genes involved in interferon signalling have been associated with various autoimmune diseases. Patients with systemic lupus erythematosus, Sjögren's syndrome, dermatomyositis, psoriasis, and a fraction of patients with rheumatoid arthritis display a specific expression pattern of interferon-dependent genes in their leukocytes, termed the interferon signature. Here, in an attempt to understand the role of type I interferons in the pathogenesis of autoimmunity, we review the recent advances in the genetics of autoimmune diseases focusing on the association of genes involved in type I interferon pathways.

Overview of the biology of type I interferons

Type I interferons are pleiotropic cytokines with antiviral, antitumor and immunoregulatory functions. An aspect of their complex biology is the paradox that, depending on context, type I interferons can be anti-inflammatory and tissue protective or can be proinflammatory and promote autoimmunity. Along these lines, the activation of type I interferon pathways is effective in suppressing disease activity in patients with multiple sclerosis and in animal models of arthritis and colitis, while there is an expectation that blockade of the same pathways will be beneficial in the treatment of patients with systemic lupus erythematosus.

IFN regulatory factor 5 is required for disease development in the FcgammaRIIB-/-Yaa and FcgammaRIIB-/- mouse models of systemic lupus erythematosus

Polymorphisms in the transcription factor IFN regulatory factor 5 (IRF5) are strongly associated in human genetic studies with an increased risk of developing the autoimmune disease systemic lupus erythematosus. However, the biological role of IRF5 in lupus pathogenesis has not previously been tested in an animal model. In this study, we show that IRF5 is absolutely required for disease development in the FcgammaRIIB(-/-)Yaa and FcgammaRIIB(-/-) lupus models. In contrast to IRF5-sufficient FcgammaRIIB(-/-)Yaa mice, IRF5-deficient FcgammaRIIB(-/-)Yaa mice do not develop lupus manifestations and have a phenotype comparable to wild-type mice. Strikingly, full expression of IRF5 is required for the development of autoimmunity, as IRF5 heterozygotes had dramatically reduced disease. One effect of IRF5 is to induce the production of the type I IFN, IFN-alpha, a cytokine implicated in lupus pathogenesis. To address the mechanism by which IRF5 promotes disease, we evaluated FcgammaRIIB(-/-)Yaa mice lacking the type I IFN receptor subunit 1. Unlike the IRF5-deficient and IRF5-heterozygous FcgammaRIIB(-/-)Yaa mice, type I IFN receptor subunit 1-deficient FcgammaRIIB(-/-)Yaa mice maintained a substantial level of residual disease. Furthermore, in FcgammaRIIB(-/-) mice lacking Yaa, IRF5-deficiency also markedly reduced disease manifestations, indicating that the beneficial effects of IRF5 deficiency in FcgammaRIIB(-/-)Yaa mice are not due only to inhibition of the enhanced TLR7 signaling associated with the Yaa mutation. Overall, we demonstrate that IRF5 plays an essential role in lupus pathogenesis in murine models and that this is mediated through pathways beyond that of type I IFN production.

Promoter insertion/deletion in the IRF5 gene is highly associated with susceptibility to systemic lupus erythematosus in distinct populations, but exerts a modest effect on gene expression in peripheral blood mononuclear cells

OBJECTIVE

We examined the genetic association of the promoter insertion/deletion (indel) in IRF5 gene with systemic lupus erythematosus (SLE) in distinct populations and assessed its role in gene expression.

METHODS

Four IRF5 polymorphisms were genotyped in 1488 SLE patients and 1466 controls. Gene expression was analyzed by quantitative real-time PCR using RNA from peripheral blood mononuclear cells (PBMC).

RESULTS

The promoter indel and rs2070197 had independent genetic effects, which accounted for the association of rs2004640 and rs10954213. Gene expression analysis revealed that rs10954213 exerted the greatest influence on IRF5 transcript levels.

CONCLUSION

We corroborated the association of the promoter indel with SLE in 5 different populations and revealed that rs10954213 is the main single-nucleotide polymorphism responsible for altered IRF5 expression in PBMC.

The search for lupus biomarkers

Few biomarkers for systemic lupus erythematosus (SLE) have been validated and employed for making clinical decisions. The lack of reliable, specific biomarkers for SLE hampers the proper clinical management of patients with SLE and impedes the development of new lupus therapeutics. This void has led to renewed enthusiasm for identifying biomarkers that precisely and specifically reflect the pathophysiological and clinical changes of SLE. Several laboratory markers have shown early promise as biomarkers for lupus susceptibility, diagnosis and monitoring. These include polymorphisms and copy-number variations of complement C4 and Fcgamma receptor genes (disease susceptibility), cell-bound complement C4d (diagnosis and/or disease activity), CD27(high) plasma cells (disease activity), 'interferon signature' (disease activity) and anti-C1q and anti-NMDA (disease activity and organ involvement). Although these and other promising candidate biomarkers have been identified, they still need to be validated through rigorous, large-scale multicentre studies. This article briefly reviews the historical aspects of lupus biomarkers and summarises current efforts to advance the field.

Estradiol targets T cell signaling pathways in human systemic lupus

The major risk factor for developing systemic lupus erythematosus (SLE) is being female. The present study utilized gene profiles of activated T cells from females with SLE and healthy controls to identify signaling pathways uniquely regulated by estradiol that could contribute to SLE pathogenesis. Selected downstream pathway genes (+/- estradiol) were measured by real time polymerase chain amplification. Estradiol uniquely upregulated six pathways in SLE T cells that control T cell function including interferon-alpha signaling. Measurement of interferon-alpha pathway target gene expression revealed significant differences (p= 0.043) in DRIP150 (+/- estradiol) in SLE T cell samples while IFIT1 expression was bimodal and correlated moderately (r= 0.55) with disease activity. The results indicate that estradiol alters signaling pathways in activated SLE T cells that control T cell function. Differential expression of transcriptional coactivators could influence estrogen-dependent gene regulation in T cell signaling and contribute to SLE onset and disease pathogenesis.

Type I IFNs and their role in the development of autoimmune diseases

BACKGROUND

Since their initial use in the 1980s, IFNs have become an essential component of the therapy for many diseases such as hepatitis and multiple sclerosis. Although they have been extremely useful in conditions that pose therapeutic challenges, complications associated with their use have been widely reported including emerging reports of several autoimmune diseases. Many of these reports have shed light on the pathogenesis of autoimmune disorders and helped to highlight not only the critical role of type I IFNs in defense against viral infections but also the pivotal role they occupy in the interface between innate and adaptive immunity. Many patients with autoimmune disease have increased responsiveness to type I IFNs (alpha/beta), and therapy with these cytokines has induced or unmasked autoimmune disease in many additional patients.

OBJECTIVE

The objective of this paper is to discuss the role of type I IFNs in autoimmunity.

METHODS

The literature regarding type I IFNs and autoimmunity was reviewed using the Medline database from 1950 to 2009. Search terms included 'interferon alpha' and 'autoimmune disease' and 'interferon beta' and 'autoimmune disease'. Case reports, case series, reviews and prospective studies were included in the analysis.

RESULTS/CONCLUSIONS

In the literature a variety of autoimmune disorders have reportedly been induced by the use of type I IFNs, being used, although these are primarily in the form of case reports and case series. Nevertheless, there is a growing body of molecular evidence to support the clinical association. The role of IFNs in the induction of autoimmunity is complex with interplay of many genetic and environmental factors that influence the balance between normal and aberrant immune responsiveness, ultimately leading to the observed clinical manifestations.

Vicious circle: systemic autoreactivity in Ro52/TRIM21-deficient mice

Dysregulated innate responses, particularly excessive activation of interferon (IFN) pathways, have been implicated in the development of autoimmune pathologies. Autoreactivity frequently targets IFN-inducible genes such as the Ro autoantigens, which ubiquitinate and inhibit interferon regulatory factors (IRFs). A new study validates the role of these common autoantigens in preventing autoimmunity. The findings reveal that injury-induced systemic autoimmune disease is exacerbated in the absence of Ro52/Trim21 and is driven by the IL-23–Th17 pathway.

Evidence for genetic association and interaction between the TYK2 and IRF5 genes in systemic lupus erythematosus

OBJECTIVE

Several candidate genes have been implicated in susceptibility for systemic lupus erythematosus (SLE), a complex autoimmune disease. The proposed genes include members of the type I interferon (IFN) pathway and genes involved in immunological defense functions. Our aim was to systematically replicate 6 such genes, TYK2, IRF5, CTLA4, PDCD1, FCGR2A, and NOD2.

METHODS

Single-nucleotide polymorphisms in TYK2, IRF5, CTLA4, PDCD1, FCGR2A, and NOD2 were genotyped in 277 SLE patients and 356 healthy controls from Finland, giving a power of 42%-70% for different genes at published allele frequencies.

RESULTS

Significant association was seen for rs2304256 (p = 0.0001) and rs12720270 (p = 0.0031) in TYK2 and rs10954213 (p = 0.0043) in IRF5 in our samples, but not for the other genes. We found evidence for genetic interaction (p = 0.014) between rs2304256 in TYK2 and rs10954213 in IRF5, both members of the type I IFN pathway, strengthening the role of the type I IFN pathway in the pathogenesis of SLE.

CONCLUSION

The IFN pathway genes IRF5 and TYK2 may act epistatically in increasing risk for SLE, but our lack of replication does not exclude effects of the other genes studied.

Cytokines in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the production of autoantibodies that can form immune complexes and deposit in tissues, causing inflammation and organ damage. There is evidence that interferons and some interleukins can have an active role in the pathogenesis of SLE and can contribute significantly to the immune imbalance in the disease, whereas the role of some cytokines (such as TNF) is still debated. This review discusses the activity of several cytokines in SLE, their effects on the immune cells in relation to the disease pathogenesis, and the promise and limitations of cytokine-based therapies in clinical trials for lupus patients.

Association between the rs2004640 functional polymorphism of interferon regulatory factor 5 and systemic lupus erythematosus: a meta-analysis

The aim of this study is to determine whether the functional interferon regulatory factor 5 (IRF5) polymorphism, rs2004640, confers susceptibility to systemic lupus erythematosus (SLE) in multiple ethic populations. A meta-analysis was conducted on the T allele of the IRF5 rs2004640 polymorphism and 12 studies were included in the meta-analysis. Meta-analysis revealed an association between SLE and the IRF5 rs2004640 T allele in all subjects without inter-study heterogeneity (OR 1.429, 95% CI 1.359-1.503, P < 0.001). The IRF5 rs2004640 T allele was significantly associated with SLE in European and Asians. The Asian population had a much lower prevalence of the T allele (34.4%) than any other population studied. and Europeans had the highest frequency of the IRF5 rs2004640 T allele (51.8%). In conclusion, this meta-analysis confirms that the IRF5 rs2004640 polymorphism is associated with SLE susceptibility in different ethnic groups, and that its prevalence is ethnicity dependent.