IRF9 and STAT1 are required for IgG autoantibody production and B cell expression of TLR7 in mice

Elevated unphosphorylated STAT1 and IRF9 in T and B cells of primary sjögren's syndrome: Novel biomarkers for disease activity and subsets

OBJECTIVES

Autoreactive B cells and interferon (IFN) signature are hallmarks of primary sjögren's syndrome (pSS), but how IFN signaling pathways influence autoantibody production and clinical manifestations remain unclear. More detailed studies hold promise for improved diagnostic methodologies and personalized treatment.

METHODS

We analyzed peripheral blood T and B cell subsets from 34 pSS patients and 38 healthy donors (HDs) at baseline and upon stimulation regarding their expression levels of type I and II IFN signaling molecules (STAT1/2, IRF1, IRF9). Additionally, we investigated how the levels of these molecules correlated with serological and clinical characteristics and performed ROC analysis.

RESULTS

Patients showed elevated IFN pathway molecules, including STAT1, STAT2 and IRF9 among most T and B cell subsets. We found a reduced ratio of phosphorylated STAT1 and STAT2 in patients in comparison to HDs, although B cells from patients were highly responsive by increased phosphorylation upon IFN stimulation. Correlation matrices showed further interrelations between STAT1, IRF1 and IRF9 in pSS. Levels of STAT1 and IRF9 in T and B cells correlated with the IFN type I marker Siglec-1 (CD169) on monocytes. High levels of STAT1 and IRF9 within pSS B cells were significantly associated with hypergammaglobulinemia as well as anti-SSA/anti-SSB autoantibodies. Elevated STAT1 levels were found in patients with extraglandular disease and could serve as a biomarker for this subgroup (p < 0.01). Notably, IRF9 levels in T and B cells correlated with EULAR Sjögren's syndrome disease activity index (ESSDAI).

CONCLUSION

Here, we provide evidence that in active pSS patients, enhanced IFN signaling incl. unphosphorylated STAT1 and STAT2 with IRFs entertain chronic T and B cell activation. Furthermore, increased STAT1 levels candidate as biomarker of extraglandular disease, while IRF9 levels can serve as biomarker for disease activity.

Insights gained from single-cell analysis of immune cells in tofacitinib treatment of Vogt-Koyanagi-Harada disease

Vogt-Koyanagi-Harada disease (VKH) is an important refractory uveitis mediated by pathological T cells (TCs). Tofacitinib (TOFA) is a JAK- targeted therapy for several autoimmune diseases. However, the specific pathogenesis and targeted therapeutics for VKH remain largely unknown. Based on single-cell RNA sequencing and mass cytometry, we present what we believe is the first multimodal, high-dimensional analysis to generate a comprehensive human immune atlas regarding subset composition, gene signatures, enriched pathways, and intercellular interactions of VKH patients undergoing TOFA therapy. Patients with VKH are characterized by TCs' polarization from naive to effector and memory subsets, together with accrued monocytes and upregulated cytokines and JAK/STAT signaling pathways. In vitro, TOFA reversed Th17/Treg imbalance and inhibited IL-2-induced STAT1/3 phosphorylation. TOFA alleviated VKH symptoms by restoring pathological TCs' polarization and functional marker expression and downregulating cytokine signaling and lymphocyte function. Remarkably, inflammation-related responses and intercellular interactions decreased after TOFA treatment, particularly in monocytes. Notably, we identified 2 inflammation- and JAK-associated monocyte subpopulations that were strongly implicated in VKH pathogenesis and mechanisms involved in TOFA treatment. Here, we provide a potentially novel JAK-targeted therapy for VKH and elaborate on the possible therapeutic mechanisms of TOFA, expanding our knowledge of VKH pathological patterns.

miR-196b-TLR7/8 Signaling Axis Regulates Innate Immune Signaling and Myeloid Maturation in DNMT3A-Mutant AML

PURPOSE

DNMT3A mutations confer a poor prognosis in acute myeloid leukemia (AML), but the molecular mechanisms downstream of DNMT3A mutations in disease pathogenesis are not completely understood, limiting targeted therapeutic options. The role of miRNA in DNMT3A-mutant AML pathogenesis is understudied.

EXPERIMENTAL DESIGN

DNA methylation and miRNA expression was evaluated in human AML patient samples and in Dnmt3a/Flt3-mutant AML mice. The treatment efficacy and molecular mechanisms of TLR7/8-directed therapies on DNMT3A-mutant AML were evaluated in vitro on human AML patient samples and in Dnmt3a/Flt3-mutant AML mice.

RESULTS

miR-196b is hypomethylated and overexpressed in DNMT3A-mutant AML and is associated with poor patient outcome. miR-196b overexpression in DNMT3A-mutant AML is important to maintain an immature state and leukemic cell survival through repression of TLR signaling. The TLR7/8 agonist resiquimod induces dendritic cell-like differentiation with costimulatory molecule expression in DNMT3A-mutant AML cells and provides a survival benefit to Dnmt3a/Flt3-mutant AML mice. The small molecule bryostatin-1 augments resiquimod-mediated AML growth inhibition and differentiation.

CONCLUSIONS

DNMT3A loss-of-function mutations cause miRNA locus-specific hypomethylation and overexpression important for mutant DNMT3A-mediated pathogenesis and clinical outcomes. Specifically, the overexpression of miR-196b in DNMT3A-mutant AML creates a novel therapeutic vulnerability by controlling sensitivity to TLR7/8-directed therapies.

The lupus susceptibility allele DRB1*03:01 encodes a disease-driving epitope

The HLA-DRB1*03:01 allele is a major genetic risk factor in systemic lupus erythematosus (SLE), but the mechanistic basis of the association is unclear. Here we show that in the presence of interferon gamma (IFN-γ), a short DRB1*03:01-encoded allelic epitope activates a characteristic lupus transcriptome in mouse and human macrophages. It also triggers a cascade of SLE-associated cellular aberrations, including endoplasmic reticulum stress, unfolded protein response, mitochondrial dysfunction, necroptotic cell death, and production of pro-inflammatory cytokines. Parenteral administration of IFN-γ to naïve DRB1*03:01 transgenic mice causes increased serum levels of anti-double stranded DNA antibodies, glomerular immune complex deposition and histopathological renal changes that resemble human lupus nephritis. This study provides evidence for a noncanonical, antigen presentation-independent mechanism of HLA-disease association in SLE and could lay new foundations for our understanding of key molecular mechanisms that trigger and propagate this devastating autoimmune disease.

Variation in blood microbial lipopolysaccharide (LPS) contributes to immune reconstitution in response to suppressive antiretroviral therapy in HIV

BACKGROUND

In HIV infection, even under long-term antiretroviral therapy (ART), up to 20% of HIV-infected individuals fail to restore CD4+ T cell counts to the levels similar to those of healthy controls. The mechanisms of poor CD4+ T cell reconstitution on suppressive ART are not fully understood.

METHODS

Here, we tested the hypothesis that lipopolysaccharide (LPS) from bacteria enriched in the plasma from immune non-responders (INRs) contributes to blunted CD4+ T cell recovery on suppressive ART in HIV. We characterized plasma microbiome in HIV INRs (aviremic, CD4+ T cell counts < 350 cells/μl), immune responders (IRs, CD4+ T cell counts > 500 cells/μl), and healthy controls. Next, we analyzed the structure of the lipid A domain of three bacterial species identified by mass spectrometry (MS) and evaluated the LPS function through LPS induced proinflammatory responses and CD4+ T cell apoptosis in PBMCs. In comparison, we also evaluated plasma levels of proinflammatory cytokine and chemokine patterns in these three groups. At last, to study the causality of microbiome-blunted CD4+ T cell recovery in HIV, B6 mice were intraperitoneally (i.p.) injected with heat-killed Burkholderia fungorum, Serratia marcescens, or Phyllobacterium myrsinacearum, twice per week for total of eight weeks.

FINDINGS

INRs exhibited elevated plasma levels of total microbial translocation compared to the IRs and healthy controls. The most enriched bacteria were Burkholderia and Serratia in INRs and were Phyllobacterium in IRs. Further, unlike P. myrsinacearum LPS, B. fungorum and S. marcescens LPS induced proinflammatory responses and CD4+ T cell apoptosis in PBMCs, and gene profiles of bacteria-mediated cell activation pathways in THP-1 cells in vitro. Notably, LPS structural analysis by mass spectrometry revealed that lipid A from P. myrsinacearum exhibited a divergent structure consistent with weak toll-like receptor (TLR) 4 agonism, similar to the biological profile of probiotic bacteria. In contrast, lipid A from B. fungorum and S. marcescens showed structures more consistent with canonical TLR4 agonists stemming from proinflammatory bacterial strains. Finally, intraperitoneal (i.p.) injection of inactivated B. fungorum and S. marcescens but not P. myrsinacearum resulted in cell apoptosis in mesenteric lymph nodes of C57BL/6 mice in vivo.

INTERPRETATION

These results suggest that the microbial products are causally associated with INR phenotype. In summary, variation in blood microbial LPS immunogenicity may contribute to immune reconstitution in response to suppressive ART. Collectively, this work is consistent with immunologically silencing microbiome being causal and targetable with therapy in HIV.

FUNDING

This work was supported by the National Institute of Allergy and Infectious Diseases (NIAID; R01 AI128864, Jiang) (NIAID; P30 AI027767, Saag/Health), the Medical Research Service at the Ralph H. Johnson VA Medical Center (merit grant VA CSRD MERIT I01 CX-002422, Jiang), and the National Institute of Aging (R21 AG074331, Scott). The SCOPE cohort was supported by the UCSF/Gladstone Institute of Virology & Immunology CFAR (P30 AI027763, Gandhi) and the CFAR Network of Integrated Clinical Systems (R24 AI067039, Saag). The National Center for Advancing Translational Sciences of the National Institutes of Health under Award Number UL1TR001450 (the pilot grant, Jiang). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Tissue-Specific Variations in Transcription Factors Elucidate Complex Immune System Regulation

Gene expression plays a key role in health and disease. Estimating the genetic components underlying gene expression can thus help understand disease etiology. Polygenic models termed “transcriptome imputation” are used to estimate the genetic component of gene expression, but these models typically consider only the cis regions of the gene. However, these cis-based models miss large variability in expression for multiple genes. Transcription factors (TFs) that regulate gene expression are natural candidates for looking for additional sources of the missing variability. We developed a hypothesis-driven approach to identify second-tier regulation by variability in TFs. Our approach tested two models representing possible mechanisms by which variations in TFs can affect gene expression: variability in the expression of the TF and genetic variants within the TF that may affect the binding affinity of the TF to the TF-binding site. We tested our TF models in whole blood and skeletal muscle tissues and identified TF variability that can partially explain missing gene expression for 1035 genes, 76% of which explains more than the cis-based models. While the discovered regulation patterns were tissue-specific, they were both enriched for immune system functionality, elucidating complex regulation patterns. Our hypothesis-driven approach is useful for identifying tissue-specific genetic regulation patterns involving variations in TF expression or binding.

High Interferon Signature Leads to Increased STAT1/3/5 Phosphorylation in PBMCs From SLE Patients by Single Cell Mass Cytometry

The establishment of an “interferon (IFN) signature” to subset SLE patients on disease severity has led to therapeutics targeting IFNα. Here, we investigate IFN signaling in SLE using multiplexed protein arrays and single cell cytometry by time of flight (CyTOF). First, the IFN signature for SLE patients (n=81) from the Stanford Lupus Registry is determined using fluidigm qPCR measuring 44 previously determined IFN-inducible transcripts. IFN-high (IFN-H) patients have increased SLE criteria and renal/CNS/immunologic involvement, and increased autoantibody reactivity against spliceosome-associated antigens. CyTOF analysis is performed on non-stimulated and stimulated (IFNα, IFNγ, IL-21) PBMCs from SLE patients (n=25) and HCs (n=9) in a panel identifying changes in phosphorylation of intracellular signaling proteins (pTOF). Another panel is utilized to detect changes in intracellular cytokine (ICTOF) production in non-stimulated and stimulated (PMA/ionomycin) PBMCs from SLE patients (n=31) and HCs (n=17). Bioinformatic analysis by MetaCyto and OMIQ reveal phenotypic changes in immune cell subsets between IFN-H and IFN-low (IFN-L) patients. Most notably, IFN-H patients exhibit increased STAT1/3/5 phosphorylation downstream of cytokine stimulation and increased phosphorylation of non-canonical STAT proteins. These results suggest that IFN signaling in SLE modulates STAT phosphorylation, potentially uncovering possible targets for future therapeutic approaches.

TLR7 Signaling in Lupus B Cells: New Insights into Synergizing Factors and Downstream Signals

PURPOSE OF THE REVIEW

Systemic lupus erythematosus (SLE) is driven by nucleic acid-containing antigens that stimulate endosomal TLRs. We review new advances in our understanding of how TLR7 signaling in B cells drives autoimmunity.

RECENT FINDINGS

Pathogenic B cell responses to TLR7 engagement are shaped by the disease-associated cytokine environment. TLR7, IFNγ, and IL-21 together promote the formation of autoreactive germinal centers and the ABC/DN2 B cell subset. BAFF and type 1 IFNs enhance autoantibody production from transitional B cells in concert with TLR7. TLR7 signaling components STAT1, BANK1, IRF5, SLC15A4, and CXorf21/TASL are associated genetically with SLE and important for lupus development in mice, while role of T-bet is controversial. Proper control of TLR7 trafficking by UNC93B1, syntenin-1, and αvβ3 integrin is critical for preventing autoimmunity. A better understanding of TLR7 signaling has revealed potential new therapeutic approaches for SLE, several of which are being tested in animal models or clinical trials.

The DNA co-vaccination using Sm antigen and IL-10 as prophylactic experimental therapy ameliorates nephritis in a model of lupus induced by pristane

Introduction

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies such as anti-Sm. Studies in patients with SLE and murine models of lupus reveal that the most critical anti-Sm autoantibodies are predominantly direct against D1_(83–119), D2, and B´/B epitopes.

Objectives

The present study aimed to analyze the induction of antigen-specific tolerance after prophylactic immunization with a DNA vaccine encoding the epitopes: D1_83-119, D2, B´/B, and B´/B_COOH in co-vaccination with IFN-γ or IL-10 in a murine model of lupus induced by pristane.

Material and methods

To obtain endotoxin-free DNA vaccines, direct cloning techniques using pcDNA were performed: D1_83-119, D2, B´/B, B´/B_COOH, IFN-γ, or IL-10. Lupus was induced by 0.5 mL of pristane via intraperitoneal in BALB/c female mice. Immunoprecipitation with K562 cells was metabolically labeled with ³⁵S and ELISA to detect serum antibodies or mice IgG1, IgG2a isotypes. ELISA determined IL-10 and IFN-γ from splenocytes supernatants. Proteinuria was assessed monthly, and lupus nephritis was evaluated by immunofluorescence, and electron microscopy.

Results

The prophylactic co-vaccination with D2/IL-10 reduced the expression of kidney damage observed by electron microscopy, direct immunofluorescence, and H & E, along with reduced level of anti-nRNP/Sm antibodies (P = 0.048).

Conclusion

The prophylactic co-vaccination of IL-10 with D2 in pristane-induced lupus ameliorates the renal damage maybe by acting as prophylactic DNA tolerizing therapy.

CD38 Deficiency Ameliorates Chronic Graft-Versus-Host Disease Murine Lupus via a B-Cell-Dependent Mechanism

The absence of the mouse cell surface receptor CD38 in Cd38^−/− mice suggests that this receptor acts as a positive regulator of inflammatory and autoimmune responses. Here, we report that, in the context of the chronic graft-versus-host disease (cGVHD) lupus inducible model, the transfer of B6.C-H2bm12/KhEg(bm12) spleen cells into co-isogenic Cd38^−/− B6 mice causes milder lupus-like autoimmunity with lower levels of anti-ssDNA autoantibodies than the transfer of bm12 spleen cells into WT B6 mice. In addition, significantly lower percentages of Tfh cells, as well as GC B cells, plasma cells, and T-bet⁺CD11c^hi B cells, were observed in Cd38^−/− mice than in WT mice, while the expansion of Treg cells and Tfr cells was normal, suggesting that the ability of Cd38^−/− B cells to respond to allogeneic help from bm12 CD4⁺ T cells is greatly diminished. The frequencies of T-bet⁺CD11c^hi B cells, which are considered the precursors of the autoantibody-secreting cells, correlate with anti-ssDNA autoantibody serum levels, IL-27, and sCD40L. Proteomics profiling of the spleens from WT cGVHD mice reflects a STAT1-driven type I IFN signature, which is absent in Cd38^−/− cGVHD mice. Kidney, spleen, and liver inflammation was mild and resolved faster in Cd38^−/− cGVHD mice than in WT cGVHD mice. We conclude that CD38 in B cells functions as a modulator receptor that controls autoimmune responses.

Interferon Regulatory Factor 9 Promotes Lung Cancer Progression via Regulation of Versican

Simple Summary

Lung cancer is the leading cause of cancer-related deaths worldwide, accounting for more than 1.6 million deaths per year. The tumor microenvironment (TME) has been shown to play a crucial role in tumor progression and metastasis, and transcription factors link TME signaling to oncogenesis. Type I interferons (IFNs) are strong immune modulators that possess antiproliferative and proapoptotic properties. In this study, we investigated the role of the transcription factor interferon regulatory factor 9 (IRF9) in the IFN pathway in lung cancer. We performed in vitro and in vivo experiments to reveal the oncogenic properties of IRF9, which was highly upregulated in lung adenocarcinoma. For the first time, we showed that IRF9 binds to the promoter of the known oncogene versican, regulates its expression, and thereby promotes oncogenic activity.

Abstract

Transcription factors can serve as links between tumor microenvironment signaling and oncogenesis. Interferon regulatory factor 9 (IRF9) is recruited and expressed upon interferon stimulation and is dependent on cofactors that exert in tumor-suppressing or oncogenic functions via the JAK-STAT pathway. IRF9 is frequently overexpressed in human lung cancer and is associated with decreased patient survival; however, the underlying mechanisms remain to be elucidated. Here, we used stably transduced lung adenocarcinoma cell lines (A549 and A427) to overexpress or knockdown IRF9. Overexpression led to increased oncogenic behavior in vitro, including enhanced proliferation and migration, whereas knockdown reduced these effects. These findings were confirmed in vivo using lung tumor xenografts in nude mice, and effects on both tumor growth and tumor mass were observed. Using RNA sequencing, we identified versican (VCAN) as a novel downstream target of IRF9. Indeed, IRF9 and VCAN expression levels were found to be correlated. We showed for the first time that IRF9 binds at a newly identified response element in the promoter region of VCAN to regulate its transcription. Using an siRNA approach, VCAN was found to enable the oncogenic properties (proliferation and migration) of IRF9 transduced cells, perhaps with CDKN1A involvement. The targeted inhibition of IRF9 in lung cancer could therefore be used as a new treatment option without multimodal interference in microenvironment JAK-STAT signaling.

Toll-like receptor signalling in B cells during systemic lupus erythematosus

B lymphocytes have a central role in autoimmune diseases, which are often defined by specific autoantibody patterns and feature a loss of B cell tolerance. A prototypic disease associated with B cell hyperactivity is systemic lupus erythematosus (SLE). In patients with SLE, the loss of B cell tolerance to autoantigens is controlled in a cell-intrinsic manner by Toll-like receptors (TLRs), which sense nucleic acids in endosomes. TLR7 drives the extrafollicular B cell response and the germinal centre reaction that are involved in autoantibody production and disease pathogenesis. Surprisingly, TLR9 seems to protect against SLE, even though it is required for the production of autoantibodies recognizing double-stranded DNA-associated antigens, which are abundant in SLE and are a hallmark of this disease. The protective function of TLR9 is at least partly mediated by its capacity to limit the stimulatory activity of TLR7. The roles of TLR7 and TLR9 in the effector function of B cells in lupus-like disease and in patients with SLE, and the unique features of TLR signalling in B cells, suggest that targeting TLR signalling in SLE might be therapeutically beneficial.

Loss of B cell tolerance to autoantigens in systemic lupus erythematosus (SLE) is driven by TLR7, whereas TLR9 appears to protect against SLE by limiting the stimulatory activity of TLR7. The unique features of Toll-like receptor signalling in B cells implicate it as a therapeutic target in SLE.

Intrinsic TLR7 and TLR9 signalling in B cells plays an important role in the development and pathogenesis of systemic lupus erythematosus (SLE).

In patients with SLE, effector plasma cells are generated via the extrafollicular response and via the formation of spontaneous germinal centres.

TLR7 plays key roles in the extrafollicular response and the response mediated by germinal centres.

Some plasma cells produce IL-10 and can have protective roles in lupus-like disease.

Serine Phosphorylation of the STAT1 Transactivation Domain Promotes Autoreactive B Cell and Systemic Autoimmunity Development

Although STAT1 tyrosine-701 phosphorylation (designated STAT1-pY701) is indispensable for STAT1 function, the requirement for STAT1 serine-727 phosphorylation (designated STAT1-pS727) during systemic autoimmune and antipathogen responses remains unclear. Using autoimmune-prone B6.Sle1b mice expressing a STAT1-S727A mutant in which serine is replaced by alanine, we report in this study that STAT1-pS727 promotes autoimmune Ab-forming cell (AFC) and germinal center (GC) responses, driving autoantibody production and systemic lupus erythematosus (SLE) development. In contrast, STAT1-pS727 is not required for GC, T follicular helper cell (Tfh), and Ab responses to various foreign Ags, including pathogens. STAT1-pS727 is also not required for gut microbiota and dietary Ag-driven GC and Tfh responses in B6.Sle1b mice. By generating B cell-specific bone marrow chimeras, we demonstrate that STAT1-pS727 plays an important B cell-intrinsic role in promoting autoimmune AFC, GC, and Tfh responses, leading to SLE-associated autoantibody production. Our analysis of the TLR7-accelerated B6.Sle1b.Yaa SLE disease model expressing a STAT1-S727A mutant reveals STAT1-pS727-mediated regulation of autoimmune AFC and GC responses and lupus nephritis development. Together, we identify previously unrecognized differential regulation of systemic autoimmune and antipathogen responses by STAT1-pS727. Our data implicate STAT1-pS727 as a therapeutic target for SLE without overtly affecting STAT1-mediated protection against pathogenic infections.

Type II but Not Type I IFN Signaling Is Indispensable for TLR7-Promoted Development of Autoreactive B Cells and Systemic Autoimmunity

TLR7 is associated with development of systemic lupus erythematosus (SLE), but the underlying mechanisms are incompletely understood. Although TLRs are known to activate type I IFN (T1IFN) signaling, the role of T1IFN and IFN-γ signaling in differential regulation of TLR7-mediated Ab-forming cell (AFC) and germinal center (GC) responses, and SLE development has never been directly investigated. Using TLR7-induced and TLR7 overexpression models of SLE, we report in this study a previously unrecognized indispensable role of TLR7-induced IFN-γ signaling in promoting AFC and GC responses, leading to autoreactive B cell and SLE development. T1IFN signaling in contrast, only modestly contributed to autoimmune responses and the disease process in these mice. TLR7 ligand imiquimod treated IFN-γ reporter mice show that CD4⁺ effector T cells including follicular helper T (Tfh) cells are the major producers of TLR7-induced IFN-γ. Transcriptomic analysis of splenic tissues from imiquimod-treated autoimmune-prone B6.Sle1b mice sufficient and deficient for IFN-γR indicates that TLR7-induced IFN-γ activates multiple signaling pathways to regulate TLR7-promoted SLE. Conditional deletion of Ifngr1 gene in peripheral B cells further demonstrates that TLR7-driven autoimmune AFC, GC and Tfh responses and SLE development are dependent on IFN-γ signaling in B cells. Finally, we show crucial B cell-intrinsic roles of STAT1 and T-bet in TLR7-driven GC, Tfh and plasma cell differentiation. Altogether, we uncover a nonredundant role for IFN-γ and its downstream signaling molecules STAT1 and T-bet in B cells in promoting TLR7-driven AFC, GC, and SLE development whereas T1IFN signaling moderately contributes to these processes.

Identification of U11snRNA as an endogenous agonist of TLR7-mediated immune pathogenesis

The activation of innate immune receptors by pathogen-associated molecular patterns (PAMPs) is central to host defense against infections. On the other hand, these receptors are also activated by immunogenic damage-associated molecular patterns (DAMPs), typically released from dying cells, and the activation can evoke chronic inflammatory or autoimmune disorders. One of the best known receptors involved in the immune pathogenesis is Toll-like receptor 7 (TLR7), which recognizes RNA with single-stranded structure. However, the causative DAMP RNA(s) in the pathogenesis has yet to be identified. Here, we first developed a chemical compound, termed KN69, that suppresses autoimmunity in several established mouse models. A subsequent search for KN69-binding partners led to the identification of U11 small nuclear RNA (U11snRNA) as a candidate DAMP RNA involved in TLR7-induced autoimmunity. We then showed that U11snRNA robustly activated the TLR7 pathway in vitro and induced arthritis disease in vivo. We also found a correlation between high serum level of U11snRNA and autoimmune diseases in human subjects and established mouse models. Finally, by revealing the structural basis for U11snRNA's ability to activate TLR7, we developed more potent TLR7 agonists and TLR7 antagonists, which may offer new therapeutic approaches for autoimmunity or other immune-driven diseases. Thus, our study has revealed a hitherto unknown immune function of U11snRNA, providing insight into TLR7-mediated autoimmunity and its potential for further therapeutic applications.

Direct Inhibition of IRF-Dependent Transcriptional Regulatory Mechanisms Associated With Disease

Interferon regulatory factors (IRFs) are a family of homologous proteins that regulate the transcription of interferons (IFNs) and IFN-induced gene expression. As such they are important modulating proteins in the Toll-like receptor (TLR) and IFN signaling pathways, which are vital elements of the innate immune system. IRFs have a multi-domain structure, with the N-terminal part acting as a DNA binding domain (DBD) that recognizes a DNA-binding motif similar to the IFN-stimulated response element (ISRE). The C-terminal part contains the IRF-association domain (IAD), with which they can self-associate, bind to IRF family members or interact with other transcription factors. This complex formation is crucial for DNA binding and the commencing of target-gene expression. IRFs bind DNA and exert their activating potential as homo or heterodimers with other IRFs. Moreover, they can form complexes (e.g., with Signal transducers and activators of transcription, STATs) and collaborate with other co-acting transcription factors such as Nuclear factor-κB (NF-κB) and PU.1. In time, more of these IRF co-activating mechanisms have been discovered, which may play a key role in the pathogenesis of many diseases, such as acute and chronic inflammation, autoimmune diseases, and cancer. Detailed knowledge of IRFs structure and activating mechanisms predisposes IRFs as potential targets for inhibition in therapeutic strategies connected to numerous immune system-originated diseases. Until now only indirect IRF modulation has been studied in terms of antiviral response regulation and cancer treatment, using mainly antisense oligonucleotides and siRNA knockdown strategies. However, none of these approaches so far entered clinical trials. Moreover, no direct IRF-inhibitory strategies have been reported. In this review, we summarize current knowledge of the different IRF-mediated transcriptional regulatory mechanisms and how they reflect the diverse functions of IRFs in homeostasis and in TLR and IFN signaling. Moreover, we present IRFs as promising inhibitory targets and propose a novel direct IRF-modulating strategy employing a pipeline approach that combines comparative in silico docking to the IRF-DBD with in vitro validation of IRF inhibition. We hypothesize that our methodology will enable the efficient identification of IRF-specific and pan-IRF inhibitors that can be used for the treatment of IRF-dependent disorders and malignancies.

T-bet Transcription Factor Promotes Antibody-Secreting Cell Differentiation by Limiting the Inflammatory Effects of IFN-γ on B Cells

Although viral infections elicit robust interferon-γ (IFN-γ) and long-lived antibody-secreting cell (ASC) responses, the roles for IFN-γ and IFN-γ-induced transcription factors (TFs) in ASC development are unclear. We showed that B cell intrinsic expression of IFN-γR and the IFN-γ-induced TF T-bet were required for T-helper 1 cell-induced differentiation of B cells into ASCs. IFN-γR signaling induced Blimp1 expression in B cells but also initiated an inflammatory gene program that, if not restrained, prevented ASC formation. T-bet did not affect Blimp1 upregulation in IFN-γ-activated B cells but instead regulated chromatin accessibility within the Ifng and Ifngr2 loci and repressed the IFN-γ-induced inflammatory gene program. Consistent with this, B cell intrinsic T-bet was required for formation of long-lived ASCs and secondary ASCs following viral, but not nematode, infection. Therefore, T-bet facilitates differentiation of IFN-γ-activated inflammatory effector B cells into ASCs in the setting of IFN-γ-, but not IL-4-, induced inflammatory responses.

IFNγ induces epigenetic programming of human T-bethi B cells and promotes TLR7/8 and IL-21 induced differentiation

Although B cells expressing the IFNγR or the IFNγ-inducible transcription factor T-bet promote autoimmunity in Systemic Lupus Erythematosus (SLE)-prone mouse models, the role for IFNγ signaling in human antibody responses is unknown. We show that elevated levels of IFNγ in SLE patients correlate with expansion of the T-bet expressing IgDnegCD27negCD11c+CXCR5neg (DN2) pre-antibody secreting cell (pre-ASC) subset. We demonstrate that naïve B cells form T-bethi pre-ASCs following stimulation with either Th1 cells or with IFNγ, IL-2, anti-Ig and TLR7/8 ligand and that IL-21 dependent ASC formation is significantly enhanced by IFNγ or IFNγ-producing T cells. IFNγ promotes ASC development by synergizing with IL-2 and TLR7/8 ligands to induce genome-wide epigenetic reprogramming of B cells, which results in increased chromatin accessibility surrounding IRF4 and BLIMP1 binding motifs and epigenetic remodeling of IL21R and PRDM1 loci. Finally, we show that IFNγ signals poise B cells to differentiate by increasing their responsiveness to IL-21.

Regulating IRFs in IFN Driven Disease

The Interferon regulatory factors (IRFs) are a family of transcription factors that play pivotal roles in many aspects of the immune response, including immune cell development and differentiation and regulating responses to pathogens. Three family members, IRF3, IRF5, and IRF7, are critical to production of type I interferons downstream of pathogen recognition receptors that detect viral RNA and DNA. A fourth family member, IRF9, regulates interferon-driven gene expression. In addition, IRF4, IRF8, and IRF5 regulate myeloid cell development and phenotype, thus playing important roles in regulating inflammatory responses. Thus, understanding how their levels and activity is regulated is of critical importance given that perturbations in either can result in dysregulated immune responses and potential autoimmune disease. This review will focus the role of IRF family members in regulating type I IFN production and responses and myeloid cell development or differentiation, with particular emphasis on how regulation of their levels and activity by ubiquitination and microRNAs may impact autoimmune disease.

Systemic translocation of Staphylococcus drives autoantibody production in HIV disease

BACKGROUND

Increased autoreactive antibodies have been reported in HIV disease; however, the mechanism accounting for autoantibody induction in HIV remains unknown.

RESULTS

Herein, we show that seasonal influenza vaccination induces autoantibody production (e.g., IgG anti-nuclear antibody (ANA) and anti-double-stranded DNA antibody (anti-dsDNA)) in some viral-suppressed antiretroviral therapy (ART)-treated HIV+ subjects, but not in healthy controls. These autoantibodies were not derived from antigen-specific B cells but from activated "bystander" B cells analyzed by single-cell assay and by study of purified polyclonal ANAs from plasma. To explore the mechanism of autoantibody generation in HIV+ subjects, plasma level of microbial products, gene expression profile of B cells, and B cell receptor (BCR) repertoires were analyzed. We found that autoantibody production was associated with increased plasma level of microbial translocation; the patients with high autoantibodies had skewed B cell repertoires and upregulation of genes related to innate immune activation in response to microbial translocation. By analyzing circulating microbial 16S rDNA in plasma, the relative abundance of Staphylococcus was found to be associated with autoantibody production in HIV+ subjects. Finally, we found that injection of heat-killed Staphylococcus aureus promoted germinal center B cell responses and autoantibody production in mice, consistent with the notion that autoantibody production in HIV+ patients is triggered by microbial products.

CONCLUSIONS

Our results showed that translocation of Staphylococcus can promote B cell activation through enhancing germinal center response and induces autoantibody production. It uncovers a potential mechanism linking microbial translocation and autoimmunity in HIV+ disease and provides a strong rationale for targeting Staphylococcus to prevent autoantibody production.

Distinct systemic microbiome and microbial translocation are associated with plasma level of anti-CD4 autoantibody in HIV infection

Microbial signals have been linked to autoantibody induction. Recently, we found that purified anti-CD4 autoantibodies from the plasma of chronic HIV-1-infected patients under viral-suppressed antiretroviral therapy (ART) play a pathologic role in poor CD4+ T cell recovery. The purpose of the study was to investigate the association of systemic microbiome and anti-CD4 autoantibody production in HIV. Plasma microbiome from 12 healthy controls and 22 HIV-infected subjects under viral-suppressed ART were analyzed by MiSeq sequencing. Plasma level of autoantibodies and microbial translocation (LPS, total bacterial 16S rDNA, soluble CD14, and LPS binding protein) were analyzed by ELISA, limulus amebocyte assay, and qPCR. We found that plasma level of anti-CD4 IgGs but not anti-CD8 IgGs was increased in HIV+ subjects compared to healthy controls. HIV+ subjects with plasma anti-CD4 IgG > 50 ng/mL (high) had reduced microbial diversity compared to HIV+ subjects with anti-CD4 IgG ≤ 50 ng/mL (low). Moreover, plasma anti-CD4 IgG level was associated with elevated microbial translocation and reduced microbial diversity in HIV+ subjects. The Alphaproteobacteria class was significantly enriched in HIV+ subjects with low anti-CD4 IgG compared to patients with high anti-CD4 IgG even after controlling for false discovery rate (FDR). The microbial components were different from the phylum to genus level in HIV+ subjects with high anti-CD4 IgGs compared to the other two groups, but these differences were not significant after controlling for FDR. These results suggest that systemic microbial translocation and microbiome may associate with anti-CD4 autoantibody production in ART-treated HIV disease.

Interferon Regulatory Factor 9 Structure and Regulation

Interferon regulatory factor 9 (IRF9) is an integral transcription factor in mediating the type I interferon antiviral response, as part of the interferon-stimulated gene factor 3. However, the role of IRF9 in many important non-communicable diseases has just begun to emerge. The duality of IRF9’s role in conferring protection but at the same time exacerbates diseases is certainly puzzling. The regulation of IRF9 during these conditions is not well understood. The high homology of IRF9 DNA-binding domain to other IRFs, as well as the recently resolved IRF9 IRF-associated domain structure can provide the necessary insights for progressive inroads on understanding the regulatory mechanism of IRF9. This review sought to outline the structural basis of IRF9 that guides its regulation and interaction in antiviral immunity and other diseases.

Development of Th17-Associated Interstitial Kidney Inflammation in Lupus-Prone Mice Lacking the Gene Encoding STAT-1

OBJECTIVE

Type I interferon (IFN) signaling is a central pathogenic pathway in systemic lupus erythematosus (SLE), and therapeutics targeting type I IFN signaling are in development. Multiple proteins with overlapping functions play a role in IFN signaling, but the signaling events downstream of receptor engagement are unclear. This study was undertaken to investigate the roles of the type I and type II IFN signaling components IFN-α/β/ω receptor 2 (IFNAR-2), IFN regulatory factor 9 (IRF-9), and STAT-1 in a mouse model of SLE.

METHODS

We used immunohistochemical staining and highly multiplexed assays to characterize pathologic changes in histology, autoantibody production, cytokine/chemokine profiles, and STAT phosphorylation in order to investigate the individual roles of IFNAR-2, IRF-9, and STAT-1 in MRL/lpr mice.

RESULTS

We found that STAT-1(-/-) mice, but not IRF-9(-/-) or IFNAR-2(-/-) mice, developed interstitial nephritis characterized by infiltration with retinoic acid receptor-related orphan nuclear receptor γt-positive lymphocytes, macrophages, and eosinophils. Despite pronounced interstitial kidney disease and abnormal kidney function, STAT-1(-/-) mice had decreased proteinuria, glomerulonephritis, and autoantibody production. Phosphospecific flow cytometry revealed shunting of STAT phosphorylation from STAT-1 to STAT-3/4.

CONCLUSION

We describe unique contributions of STAT-1 to pathology in different kidney compartments in a mouse model, and provide potentially novel insight into tubulointerstitial nephritis, a poorly understood complication that predicts end-stage kidney disease in SLE patients.

MicroRNA-302d targets IRF9 to regulate the IFN-induced gene expression in SLE

Systemic lupus erythematosus (SLE) is a complex disease targeting multiple organs as a result of overactivation of the type I interferon (IFN) system, a feature currently being targeted by multiple biologic therapies against IFN-α. We have identified an estrogen-regulated microRNA, miR-302d, whose expression is decreased in SLE patient monocytes and identify its target as interferon regulatory factor (IRF)-9, a critical component of the transcriptional complex that regulates expression of interferon-stimulated genes (ISGs). In keeping with the reduced expression of miR-302d in SLE patient monocytes, IRF9 levels were increased, as was expression of a number of ISGs including MX1 and OAS1. In vivo evaluation revealed that miR-302d protects against pristane-induced inflammation in mice by targeting IRF9 and hence ISG expression. Importantly, patients with enhanced disease activity have markedly reduced expression of miR-302d and enhanced IRF9 and ISG expression, with miR-302d negatively correlating with IFN score. Together these findings identify miR-302d as a key regulator of type I IFN driven gene expression via its ability to target IRF9 and regulate ISG expression, underscoring the importance of non-coding RNA in regulating the IFN pathway in SLE.

Interferon regulatory factor signaling in autoimmune disease

Interferon regulatory factors (IRFs) play critical roles in pathogen-induced innate immune responses and the subsequent induction of adaptive immune response. Dysregulation of IRF signaling is therefore thought to contribute to autoimmune disease pathogenesis. Indeed, numerous murine in vivo studies have documented protection from or enhanced susceptibility to particular autoimmune diseases in Irf-deficient mice. What has been lacking, however, is replication of these in vivo observations in primary immune cells from patients with autoimmune disease. These types of studies are essential as the majority of in vivo data support a protective role for IRFs in Irf-deficient mice, yet IRFs are often found to be overexpressed in patient immune cells. A significant body of work is beginning to emerge from both of these areas of study - mouse and human.

Effect of glucocorticoid on cytokines TLR9 and TLR7 in peripheral blood for patients with uveitis

The effect of glucocorticoid on cytokines Toll-like receptor (TLR)9 and TLR7 in peripheral blood of patients with uveitis was explored. Forty-six patients with uveitis admitted to our hospital from April 2014 to April 2015 were selected as the research observational group. Thirty-five able-bodied individuals in the same period were selected as the control group. To treat uveitis, the observational group was injected with glucocorticoid (1–2 mg/kg/day) daily, while the control group did not receive any treatment. The quantity of expression of peripheral blood cytokines TLR9 and TLR7 were detected by the methods of fluorescence quantitative PCR, enzyme-linked immunosorbent assay and western blotting. The content of peripheral blood TLR9 and TLR7 (0.21±0.01, 0.19±0.01) decreased significantly (P<0.05) in observational group after glucocorticoid treatment. Compared with data of control group (0.21±0.01, 0.19±0.01), TLR9 and TLR7 content in peripheral blood after glucocorticoid treatment on the patients with uveitis from observation group (0.19±0.01, 0.17±0.01) did not show any significant difference, for correlation between TLR9 and TLR7 in observation group before and after treatment. It was observed that the cytokine content of TLR9 was associated with TLR7 positively (r=0.653, P=0.012). In conclusion, glucocorticoid can improve uveitis by reducing the content of cytokines TLR9 and TLR7 in peripheral blood.

STAT1 regulates marginal zone B cell differentiation in response to inflammation and infection with blood-borne bacteria

Chen et al. show that STAT1 positively regulates TLR- and S. pneumoniae–induced IgM responses of MZ B cells through up-regulation of Prdm1 expression, and STAT1 is crucial for MZ B cell–mediated clearance of blood-borne S. pneumoniae infection.

Marginal zone B (MZ B) cells can rapidly produce antibody in response to infection with blood-borne encapsulated pathogens. Although TLR-mediated activation of MZ B is known to trigger humoral immune response, the signal cascade directing this response remains undefined. Here, we demonstrate that STAT1 plays an essential role in TLR-mediated antibody response of MZ B cells. Further, the TLR-induced IgM response is impaired in a type I and type II IFN-independent manner. Although activation, proliferation, and apoptosis are not affected, both differentiation into plasma cells and IgM production are impaired in Stat1^−/− MZ B cells. Interestingly, STAT1 directly regulates the expression of Prdm1 (encodes BLIMP-1) by binding to its promoter, and Prdm1 expression is reduced in Stat1^−/− MZ B cells. Restoration of BLIMP-1 to cells rescues TLR-induced IgM response. Moreover, Stat1^−/− mice are more susceptible to S. pneumoniae infection, which can be rescued by the serum of bacteria-primed WT mice. The increased susceptibility to S. pneumoniae infection in Stat1^−/− mice is also intrinsic to STAT1 requirement in MZ B cells. Collectively, these results define a differential regulation of TLR-mediated activation and differentiation of MZ B cells by STAT1 and reveal a STAT1-dependent, but IFN-independent, antibody response during infection and inflammation.

BANK1 Regulates IgG Production in a Lupus Model by Controlling TLR7-Dependent STAT1 Activation

The purpose of our study was to investigate the effects of the adaptor Bank1 in TLR7 signaling using the B6.Sle1.yaa mouse, a lupus model that develops disease through exacerbated TLR7 expression. Crosses of B6.Sle1.yaa with Bank1^-/- mice maintained several B and myeloid cell phenotypes close to normal wild-type levels. Most striking was the reduction in total serum IgG antibodies, but not of IgM, and reduced serum levels of autoantibodies, IL-6, and BAFF. Bank1 deficiency did modify numbers of MZ B cells and total B cell numbers, as well as expression of CXCR4 by follicular helper T cells. Other T cell changes were not observed. Bank1 deficiency did not modify numbers of germinal center B cells or plasma cells or clinical disease outcomes. Purified B cells from Bank1 deficient mice had strongly reduced Ifnb, Ifna4, Irf7, Aicda and Stat1 gene expression following TLR7 agonist stimulation. Interestingly, phosphorylation of Tyr701, but not of Ser727 of STAT1, was impaired in splenic B cells from B6.Sle1.yaa.Bank1-/- mice, as was the nuclear translocation of IRF7 in response to TLR7 agonist stimulation. Further, Bank1 deficiency in B6.Sle1.yaa mice reduced the production of IgG2c after in vitro TLR7 agonist stimulation. Our results demonstrate that Bank1 controls TLR7-mediated type I interferon production. Combined with the control of the nuclear translocation of IRF7, the modulation of STAT1 transcription and phosphorylation, Bank1 contributes to IgG production during development of autoimmune disease.

IFN-γ receptor and STAT1 signaling in B cells are central to spontaneous germinal center formation and autoimmunity

Spontaneously developed germinal centers (GCs [Spt-GCs]) harbor autoreactive B cells that generate somatically mutated and class-switched pathogenic autoantibodies (auto-Abs) to promote autoimmunity. However, the mechanisms that regulate Spt-GC development are not clear. In this study, we report that B cell-intrinsic IFN-γ receptor (IFN-γR) and STAT1 signaling are required for Spt-GC and follicular T helper cell (Tfh cell) development. We further demonstrate that IFN-γR and STAT1 signaling control Spt-GC and Tfh cell formation by driving T-bet expression and IFN-γ production by B cells. Global or B cell-specific IFN-γR deficiency in autoimmune B6.Sle1b mice leads to significantly reduced Spt-GC and Tfh cell responses, resulting in diminished antinuclear Ab reactivity and IgG2c and IgG2b auto-Ab titers compared with B6.Sle1b mice. Additionally, we observed that the proliferation and differentiation of DNA-reactive B cells into a GC B cell phenotype require B cell-intrinsic IFN-γR signaling, suggesting that IFN-γR signaling regulates GC B cell tolerance to nuclear self-antigens. The IFN-γR deficiency, however, does not affect GC, Tfh cell, or Ab responses against T cell-dependent foreign antigens, indicating that IFN-γR signaling regulates autoimmune, but not the foreign antigen-driven, GC and Tfh cell responses. Together, our data define a novel B cell-intrinsic IFN-γR signaling pathway specific to Spt-GC development and autoimmunity. This novel pathway can be targeted for future pharmacological intervention to treat systemic lupus erythematosus.

A Regulatory Feedback between Plasmacytoid Dendritic Cells and Regulatory B Cells Is Aberrant in Systemic Lupus Erythematosus

Signals controlling the generation of regulatory B (Breg) cells remain ill-defined. Here we report an “auto”-regulatory feedback mechanism between plasmacytoid dendritic cells (pDCs) and Breg cells. In healthy individuals, pDCs drive the differentiation of CD19⁺CD24^hiCD38^hi (immature) B cells into IL-10-producing CD24⁺CD38^hi Breg cells and plasmablasts, via the release of IFN-α and CD40 engagement. CD24⁺CD38^hi Breg cells conversely restrained IFN-α production by pDCs via IL-10 release. In systemic lupus erythematosus (SLE), this cross-talk was compromised; pDCs promoted plasmablast differentiation but failed to induce Breg cells. This defect was recapitulated in healthy B cells upon exposure to a high concentration of IFN-α. Defective pDC-mediated expansion of CD24⁺CD38^hi Breg cell numbers in SLE was associated with altered STAT1 and STAT3 activation. Both altered pDC-CD24⁺CD38^hi Breg cell interactions and STAT1-STAT3 activation were normalized in SLE patients responding to rituximab. We propose that alteration in pDC-CD24⁺CD38^hi Breg cell interaction contributes to the pathogenesis of SLE.

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pDCs induce the differentiation of Breg cells in an IFN-α-dependent manner

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Breg cells limit pDC-derived IFN-α in an IL-10-dependent mechanism

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pDCs are hyperactivated in SLE and fail to induce Breg cells

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Patients responding to rituximab display a normalized pDC-Breg cell interaction

The emerging role of interferon regulatory factor 9 in the antiviral host response and beyond

The host response to viral infections relies on tightly regulated and intricate signaling pathways involving type I interferons (IFN-Is). The IFN-Is mediate their antiviral effects predominantly through a signaling factor complex that comprises the transcription factors, interferon regulatory factor 9 (IRF9) and the signal transducers and activators of transcription (STAT) 1 and STAT2. While STAT1 and STAT2 have been studied extensively, the biological significance of IRF9 is only beginning to emerge. Recent studies have revealed a unique role for IRF9 as a conductor of the cellular responses to IFN-Is. Intriguingly, novel roles for IRF9 outside of the antiviral response are also being identified. Thus IRF9 may have a more extensive influence on cellular processes than previously recognized, ranging from antiviral immune responses to oncogenesis and gut homeostasis. In this review, we will focus on the distinct and emerging roles of IRF9 in the antiviral host response and beyond.

Defects in Germinal Center Selection in SLE

Germinal centers (GCs) are the primary site at which clonal expansion and affinity maturation of B cells occur. B cells encounter antigen and receive T cell help in the GC light zone (LZ) and then migrate to the dark zone where they proliferate and undergo somatic mutation before cycling back to the LZ for further rounds of selection. Tolerance to autoantigens is frequently lost de novo as GC B cells undergo class switching and somatic mutation. This loss of tolerance is regulated by a variety of mechanisms including cell death, failure to compete for T cell help, and failure to differentiate into effector cells. Systemic lupus erythematosus (SLE) is characterized by loss of tolerance to nucleic acid antigens. While defects in tolerance occur in the naïve repertoire of SLE patients, pathogenic autoantibodies also arise in the GC by somatic mutation from non-autoreactive precursors. Several B cell defects contribute to the loss of GC tolerance in SLE, including polymorphisms of genes encoded by the Sle1 locus, excess TLR7 signaling, defects in FcRIIB expression, or defects of B cell apoptosis. Extrinsic soluble factors, such as Type-1 IFN and B cell-activating factor, or an increased number of T follicular helper cells in the GC also alter B cell-negative selection. Finally, defects in clearance of apoptotic debris within the GC result in BCR-mediated internalization of nucleic acid containing material and stimulation of autoantibody production by endosomal TLR-driven mechanisms.

The receptor TREML4 amplifies TLR7-mediated signaling during antiviral responses and autoimmunity

The molecules and pathways that fine-tune innate inflammatory responses mediated by Toll-like receptor 7 (TLR7) remain to be fully elucidated. Using an unbiased genome-scale screen with short hairpin RNA (shRNA), we identified the receptor TREML4 as an essential positive regulator of TLR7 signaling. Macrophages from Treml4(-/-) mice were hyporesponsive to TLR7 agonists and failed to produce type I interferons due to impaired phosphorylation of the transcription factor STAT1 by the mitogen-activated protein kinase p38 and decreased recruitment of the adaptor MyD88 to TLR7. TREML4 deficiency reduced the production of inflammatory cytokines and autoantibodies in MRL/lpr mice, which are prone to systemic lupus erythematosus (SLE), and inhibited the antiviral immune response to influenza virus. Our data identify TREML4 as a positive regulator of TLR7 signaling and provide insight into the molecular mechanisms that control antiviral immunity and the development of autoimmunity.

Tetramers reveal IL-17-secreting CD4+ T cells that are specific for U1-70 in lupus and mixed connective tissue disease

Antigen-specific CD4(+) T cells are implicated in the autoimmune disease systemic lupus erythematosus (SLE), but little is known about the peptide antigens that they recognize and their precise function in disease. We generated a series of MHC class II tetramers of I-E(k)-containing peptides from the spliceosomal protein U1-70 that specifically stain distinct CD4(+) T-cell populations in MRL/lpr mice. The T-cell populations recognize an epitope differing only by the presence or absence of a single phosphate residue at position serine(140). The frequency of CD4(+) T cells specific for U1-70(131-150):I-E(k) (without phosphorylation) correlates with disease severity and anti-U1-70 autoantibody production. These T cells also express RORγt and produce IL-17A. Furthermore, the U1-70-specific CD4(+) T cells that produce IL-17A are detected in a subset of patients with SLE and are significantly increased in patients with mixed connective tissue disease. These studies provide tools for studying antigen-specific CD4(+) T cells in lupus, and demonstrate an antigen-specific source of IL-17A in autoimmune disease.

Role of osteopontin in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multisystemic disease, caused by a variety of factors, which lead to immunological abnormalities. Osteopontin (OPN) is a pleiotropic protein, important in bone remodeling and immune system signaling. OPN, produced by various cells, including immune cells, plays a key role in regulating T-helper 1/T-helper 2 balance, stimulating B lymphocytes to produce antibodies, regulating macrophages, neutrophils and inducing dendritic cells. OPN expression is influenced by genetic polymorphisms of its promoter, hormones and cytokines. Over expression of OPN has been associated with the pathogenesis of immune-mediated diseases. OPN has been implicated in the development of murine model of lupus and in humans with SLE. In this review, I will present current state of research on the role of OPN and OPN gene polymorphisms in pathogenesis and clinical course of SLE. A better understanding of the role of OPN in SLE will contribute to more precise diagnosis and treatment of the disease.

Overexpression of TLR7 promotes cell-intrinsic expansion and autoantibody production by transitional T1 B cells

Transgenic expression of TLR7 results in the expansion and hyperactivation of T1 B cells in response to endogenous RNA complexes, leading to increased autoantibody production.

Toll-like receptor (TLR), a ligand for single-stranded RNA, has been implicated in the development of pathogenic anti-RNA autoantibodies both in systemic lupus erythematous (SLE) patients and in murine models of lupus. It is still unclear, however, where and how TLR7-mediated interactions affect the development of autoreactive B cells. We found that overexpression of TLR7 in transgenic mice (TLR7.1Tg) leads to marked alterations of transitional (T1) B cells, associated with their expansion and proliferation within the splenic red pulp (RP). This phenotype was intrinsic to the T1 subset of B cells and occurred independently of type 1 IFN signals. Overexpression of RNase in TLR7.1Tg mice significantly limited the expansion and proliferation of T1 cells, indicating that endogenous RNA complexes are driving their activation. TLR7.1Tg T1 cells were hyper-responsive to anti-IgM and TLR7 ligand stimulation in vitro and produced high concentrations of class-switched IgG2b and IgG2c, including anti-RNA antibodies. Our results demonstrate that initial TLR7 stimulation of B cells occurs at the T1 stage of differentiation in the splenic RP and suggest that dysregulation of TLR7 expression in T1 cells can result in production of autoantibodies.

The role of cytokines in the pathogenesis of systemic lupus erythematosus - from bench to bedside

The pathogenesis of systemic lupus erythematosus (SLE) entails a complex interaction between the different arms of the immune system. While autoantibodies production and immune complex deposition are cornered as hallmark features of SLE, there is growing evidence to propose the pathogenic role of cytokines in this disease. Examples of these cytokines include BLys, interleukin-6, interleukin-17, interleukin-18, type I interferons and tumour necrosis factor alpha. These cytokines all assume pivotal functions to orchestrate the differentiation, maturation and activation of various cell types, which would mediate local inflammatory process and tissue injury. The knowledge on these cytokines not only fosters our understanding of the disease, but also provides insights in devising biomarkers and targeted therapies. In this review, we focus on cytokines which have substantial pathogenic significance and also highlight the possible clinical applications of these cytokines.

The regulation of inflammation by interferons and their STATs

Interferons (IFN) are subdivided into type I IFN (IFN-I, here synonymous with IFN-α/β), type II (IFN-γ) and type III IFN (IFN-III/IFN-λ) that reprogram nuclear gene expression through STATs 1 and 2 by forming STAT1 dimers (mainly IFN-γ) or the ISGF3 complex, a STAT1-STAT2-IRF9 heterotrimer (IFN-I and IFN-III). Dominant IFN activities in the immune system are to protect cells from viral replication and to activate macrophages for enhanced effector function. However, the impact of IFN and their STATs on the immune system stretches far beyond these activities and includes the control of inflammation. The goal of this review is to give an overview of the different facets of the inflammatory process that show regulatory input by IFN/STAT.

Anti-IFN-α/β receptor antibody treatment ameliorates disease in lupus-predisposed mice

The demonstration in humans and mice that nucleic acid-sensing TLRs and type I IFNs are essential disease mediators is a milestone in delineating the mechanisms of lupus pathogenesis. In this study, we show that Ifnb gene deletion does not modify disease progression in NZB mice, thereby strongly implicating IFN-α subtypes as the principal pathogenic effectors. We further document that long-term treatment of male BXSB mice with an anti-IFN-α/β receptor Ab of mouse origin reduced serologic, cellular, and histologic disease manifestations and extended survival, suggesting that disease acceleration by the Tlr7 gene duplication in this model is mediated by type I IFN signaling. The efficacy of this treatment in BXSB mice was clearly evident when applied early in the disease process, but only partial reductions in some disease characteristics were observed when treatment was initiated at later stages. A transient therapeutic effect was also noted in the MRL-Fas(lpr) model, although overall mortality was unaffected. The combined findings suggest that IFN-α/β receptor blockade, particularly when started at early disease stages, may be a useful treatment approach for human systemic lupus erythematosus and other autoimmune syndromes.

B cell TLR7 expression drives anti-RNA autoantibody production and exacerbates disease in systemic lupus erythematosus-prone mice

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disease characterized by the production of antinuclear autoantibodies. Antinuclear autoantibody development is recognized as one of the initial stages of disease that often results in systemic inflammation, kidney disease, and death. The etiology is complex, but it is clear that innate pathways may play an important role in disease progression. Recent data have highlighted an important role for the TLR family, particularly TLR7, in both human disease and murine models. In this study, we have presented a low copy conditional TLR7 transgenic (Tg7) mouse strain that does not develop spontaneous autoimmunity. When we combine Tg7 with the Sle1 lupus susceptibility locus, the mice develop severe disease. Using the CD19(Cre) recombinase system, we normalized expression of TLR7 solely within the B cells. Using this method we demonstrated that overexpression of TLR7 within the B cell compartment reduces the marginal zone B cell compartment and increases B and T cell activation but not T follicular helper cell development. Moreover, this enhanced B cell TLR7 expression permits the specific development of Abs to RNA/protein complexes and exacerbates SLE disease.

B-cell selection and the development of autoantibodies

The clearest evidence that B cells play an important role in human autoimmunity is that immunotherapies that deplete B cells are very effective treatments for many autoimmune diseases. All people, healthy or ill, have autoreactive B cells, but not at the same frequency. A number of genes influence the level of these autoreactive B cells and whether they are eliminated or not during development at a central checkpoint in the bone marrow (BM) or at a later checkpoint in peripheral lymphoid tissues. These genes include those encoding proteins that regulate signaling through the B-cell receptor complex such as Btk and PTPN22, proteins that regulate innate signaling via Toll-like receptors (TLRs) such as MyD88 and interleukin-1 receptor-associated kinase 4, as well as the gene encoding the activation-induced deaminase (AID) essential for B cells to undergo class switch recombination and somatic hypermutation. Recent studies have revealed that TLR signaling elements and AID function not only in peripheral B cells to help mediate effective antibody responses to foreign antigens, but also in the BM to help remove autoreactive B-lineage cells at a very early point in B-cell development. Newly arising B cells that leave the BM and enter the blood and splenic red pulp can express both AID and TLR signaling elements like TLR7, and thus are fully equipped to respond rapidly to antigens (including autoantigens), to isotype class switch, and to undergo somatic hypermutation. These red pulp B cells may thus be an important source of autoantibody-producing cells arising particularly in extrafollicular sites, and indeed may be as significant a source of autoantibody-producing cells as B cells arising from germinal centers.

The Yaa locus and IFN-α fine-tune germinal center B cell selection in murine systemic lupus erythematosus

Male NZW/BXSB.Yaa (W/B) mice express two copies of TLR7 and develop pathogenic autoantibodies, whereas females with only one copy of TLR7 have attenuated disease. Our goal was to analyze the regulation of the autoantibody response in male and female W/B mice bearing the autoreactive site-directed H chain transgene 3H9. Serum anti-dsDNA Abs appeared in males at 12 wk, and most had high-titer IgG anti-dsDNA and anti-cardiolipin Abs and developed >300 mg/dl proteinuria by 8 mo. Females had only low-titer IgG anti-cardiolipin Abs, and none developed proteinuria by 1 y. Males had a smaller marginal zone than females with a repertoire that was distinct from the follicular repertoire, indicating that the loss of marginal zone B cells was not due to diversion to the follicular compartment. Vk5-43 and Vk5-48, which were rare in the naive repertoire, were markedly overrepresented in the germinal center repertoire of both males and females, but the VJ junctions differed between males and females with higher-affinity autoreactive B cells being selected into the germinal centers of males. Administration of IFN-α to females induced anti-cardiolipin and anti-DNA autoantibodies and proteinuria and was associated with a male pattern of junctional diversity in Vk5-43 and Vk5-48. Our studies are consistent with the hypothesis that presence of the Yaa locus, which includes an extra copy of Tlr7, or administration of exogenous IFN-α relaxes the stringency for selection in the germinal centers resulting in increased autoreactivity of the Ag-driven B cell repertoire.

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.

New tools for classification and monitoring of autoimmune diseases

Rheumatologists see patients with a range of autoimmune diseases. Phenotyping these diseases for diagnosis, prognosis and selection of therapies is an ever increasing problem. Advances in multiplexed assay technology at the gene, protein, and cellular level have enabled the identification of 'actionable biomarkers'; that is, biological metrics that can inform clinical practice. Not only will such biomarkers yield insight into the development, remission, and exacerbation of a disease, they will undoubtedly improve diagnostic sensitivity and accuracy of classification, and ultimately guide treatment. This Review provides an introduction to these powerful technologies that could promote the identification of actionable biomarkers, including mass cytometry, protein arrays, and immunoglobulin and T-cell receptor high-throughput sequencing. In our opinion, these technologies should become part of routine clinical practice for the management of autoimmune diseases. The use of analytical tools to deconvolve the data obtained from use of these technologies is also presented here. These analyses are revealing a more comprehensive and interconnected view of the immune system than ever before and should have an important role in directing future treatment approaches for autoimmune diseases.

IFN type I and type II independent enhancement of B cell TLR7 expression by natural killer cells

The PRR TLR7 plays a key role in the activation of autoantigen-reactive B cells. This response is increased markedly by IFN-α, produced by accessory cells, as a result of the up-regulation of TLR7. We report herein an alternative pathway by which TLR7 expression can be augmented. This finding was derived from continuation of ongoing studies to uncover interactions between NK and B cells. Here, we have compared gene expression profiles by microarray analysis of B cells before and after their interaction with purified NK cells. The most outstanding alteration of genes transcribed in B cells is a significant increase in the expression of many members of the ISG family, among which is TLR7. Further analysis revealed that the enhancement of TLR7 on B cells is not mediated via type I or type II IFN but by another cytokine, IL-28, a type III IFN, which acts in concert with contact-mediated interactions with NK cells. This increased expression allows B cells to respond more readily upon stimulation by its ligand and may increase in vivo responses to other TLR7 ligands, such as autoantigens, prior to or jointly with stimulation by other cytokines.