Deficiency of the type I interferon receptor protects mice from experimental lupus

MEK1/2 and ERK1/2 mediated lung endothelial injury and altered hemostasis promote diffuse alveolar hemorrhage in murine lupus

Objective

About 3% of lupus patients develop severe diffuse alveolar hemorrhage (DAH) with pulmonary vasculitis. B6 mice with pristane-induced lupus also develop DAH, but BALB/c mice are resistant. DAH is independent of TLR signaling and other inflammatory pathways. This study examined the role of the mitogen-activated protein kinase pathway (MEK1/2-ERK1/2, JNK, p38).

Methods

B6 and BALB/c mice were treated with pristane ± inhibitors of MEK1/2 (trametinib/GSK1120212, "GSK"), ERK1/2 (SCH772984, "SCH"), JNK, or p38. Effects on lung hemorrhage and hemostasis were determined.

Results

GSK and SCH abolished DAH, whereas JNK and p38 inhibitors were ineffective. Apoptotic cells were present in lung from pristane-treated mice, but not mice receiving pristane+GSK and endothelial dysfunction was normalized. Expression of the ERK1/2-regulated transcription factor Egr1 increased in pristane-treated B6, but not BALB/c, mice and was normalized by GSK. Pristane also increased expression of the anticoagulant genes Tfpi (tissue factor pathway inhibitor) and Thbd (thrombomodulin) in B6 mice. The ratio of tissue factor ( F3 ) to Tfpi increased in B6 (but not BALB/c) mice and was normalized by GSK. Circulating Thbd protein increased in B6 mice and returned to normal after GSK treatment. Consistent with augmented endothelial anticoagulant activity, pristane treatment increased tail bleeding in B6 mice.

Conclusion

Pristane treatment promotes lung endothelial injury and DAH in B6 mice by activating the MEK1/2-ERK1/2 pathway and impairing hemostasis. The hereditary factors determining susceptibility to lung injury and bleeding in pristane-induced lupus are relevant to the pathophysiology of life-threatening DAH in SLE and may help to optimize therapy.

Type I IFN in Glomerular Disease: Scarring beyond the STING

The field of nephrology has recently directed a considerable amount of attention towards the stimulator of interferon genes (STING) molecule since it appears to be a potent driver of chronic kidney disease (CKD). STING and its activator, the cyclic GMP-AMP synthase (cGAS), along with intracellular RIG-like receptors (RLRs) and toll-like receptors (TLRs), are potent inducers of type I interferon (IFN-I) expression. These cytokines have been long recognized as part of the mechanism used by the innate immune system to battle viral infections; however, their involvement in sterile inflammation remains unclear. Mounting evidence pointing to the involvement of the IFN-I pathway in sterile kidney inflammation provides potential insights into the complex interplay between the innate immune system and damage to the most sensitive segment of the nephron, the glomerulus. The STING pathway is often cited as one cause of renal disease not attributed to viral infections. Instead, this pathway can recognize and signal in response to host-derived nucleic acids, which are also recognized by RLRs and TLRs. It is still unclear, however, whether the development of renal diseases depends on subsequent IFN-I induction or other processes involved. This review aims to explore the main endogenous inducers of IFN-I in glomerular cells, to discuss what effects autocrine and paracrine signaling have on IFN-I induction, and to identify the pathways that are implicated in the development of glomerular damage.

Potential role of RhoA GTPase regulation in type interferon signaling in systemic lupus erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by abnormal activation of the type I interferon (IFN) pathway, which results in tissue inflammation and organ damage. We explored the role of the RhoA GTPase in the type I IFN activation pathway to provide a potential basis for targeting GTPase signaling for the treatment of SLE.

METHODS

Total RNA was extracted from peripheral blood mononuclear cells (PBMCs) of SLE patients and healthy controls, and the mRNA expression levels of RhoA and IFN-stimulated genes were measured by SYBR Green quantitative reverse transcriptase-polymerase chain reaction. IFN-a-stimulated response element (ISRE)-luciferase reporter gene assays and Western blotting were conducted to assess the biologic function of RhoA. An enzyme-linked immunoassay (ELISA) measured C-X-C motif chemokine ligand 10 (CXCL10) protein expression.

RESULTS

Our studies demonstrate that the expression of RhoA in the PBMCs of SLE subjects was significantly higher than in healthy controls and positively correlated with type I IFN scores and type I IFN-stimulated gene (ISGs) expression levels. SiRNA-mediated knockdown of RhoA and the RhoA/ROCK inhibitor Y27632 reduced the activity of the type I IFN-induced ISRE, the signal transducer and activator of transcription 1 (STAT-1) phosphorylation, and the expression of CXCL10 and 2'-5'-oligoadenylate synthetase 1 (OAS1). Finally, we verified that Y27632 could significantly down-regulate the OAS1 and CXCL10 expression levels in the PBMCs of SLE patients.

CONCLUSION

Our study shows that RhoA positively regulates the activation of the type I IFN response pathway. Reducing the expression level of RhoA inhibits the abnormal activation of the type I IFN system, and the RhoA/ROCK inhibitor Y27632 decreases aberrant type I IFN signaling in SLE PBMCs, suggesting the possibility of targeting the RhoA GTPase for the treatment of SLE.

The RhoA GTPase regulates Type I Interferon Signaling in Systemic lupus erythematosus

Objective

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by abnormal activation of the type I interferon (IFN) pathway, which results in tissue inflammation and organ damage. We explored the role of the RhoA GTPase in the type I IFN activation pathway to provide a potential basis for targeting GTPase signaling for the treatment of SLE.

Methods

Total RNA was extracted from peripheral blood mononuclear cells (PBMCs) of SLE patients and healthy controls, and the mRNA expression levels of RhoA and IFN-stimulated genes were measured by SYBR Green quantitative reverse transcriptase-polymerase chain reaction. IFN-stimulated response element (ISRE)-luciferase reporter gene assays and Western blotting were conducted to asssess the biologic function of RhoA. An Enzyme-Linked Immunoassay (ELISA) measured C-X-C motif chemokine ligand 10(CXCL10)protein expression.

Results

Our studies demonstrated that the expression of RhoA in the PBMCs of SLE subjects was significantly higher than healthy controls and positively correlated with type I IFN scores and type I IFN-stimulated gene (ISGs) expression levels. SiRNA-mediated knockdown of RhoA and the RhoA/ROCK inhibitor Y27632 reduced the activity of the type I IFN-induced ISRE, the signal transducer and activator of transcription 1 (STAT-1) phosphorylation, and the expression of CXCL10 and 2'-5'-oligoadenylate synthetase 1(OAS1). Finally,we verified that Y27632 could significantly down-regulate the OAS1 and CXCL10 expression levels in PBMCs of SLE patients.

Conclusion

Our study shows that RhoA positively regulates the activation of the type I IFN response pathway. Reducing the expression level of RhoA inhibits the abnormal activation of the type I IFN system, and the RhoA/ROCK inhibitor Y27632 decreases aberrant type I IFN signaling in SLE PBMCs, suggesting the possibility of targeting the RhoA GTPase for the treatment of SLE.

Targeting type I interferons in systemic lupus erythematous

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with systemic clinical manifestations including, but not limited to, rash, inflammatory arthritis, serositis, glomerulonephritis, and cerebritis. Treatment options for SLE are expanding and the increase in our understanding of the immune pathogenesis is leading to the development of new therapeutics. Autoantibody formation and immune complex formation are important mediators in lupus pathogenesis, but an important role of the type I interferon (IFN) pathway has been identified in SLE patients and mouse models of lupus. These studies have led to the development of therapeutics targeting type I IFN and related pathways for the treatment of certain manifestations of SLE. In the current narrative review, we will discuss the role of type I IFN in SLE pathogenesis and the potential translation of these data into strategies using type I IFN as a biomarker and therapeutic target for patients with SLE.

B cell-activating factor (BAFF) from dendritic cells, monocytes and neutrophils is required for B cell maturation and autoantibody production in SLE-like autoimmune disease

Purpose and methods

B cell-activating factor (BAFF) contributes to the pathogenesis of autoimmune diseases including systemic lupus erythematosus (SLE). Although several anti-BAFF Abs and derivatives have been developed for the treatment of SLE, the specific sources of BAFF that sustain autoantibody (auto-Ab) producing cells have not been definitively identified. Using BAFF-RFP reporter mice, we identified major changes in BAFF-producing cells in two mouse spontaneous lupus models (Tlr7 Tg mice and Sle1), and in a pristane-induced lupus (PIL) model.

Results

First, we confirmed that similar to their wildtype Tlr7 Tg and Sle1 mice counterparts, BAFF-RFP Tlr7 Tg mice and BAFF-RFP Sle1 mice had increased BAFF serum levels, which correlated with increases in plasma cells and auto-Ab production. Next, using the RFP reporter, we defined which cells had dysregulated BAFF production. BAFF-producing neutrophils (Nphs), monocytes (MOs), cDCs, T cells and B cells were all expanded in the spleens of BAFF-RFP Tlr7 Tg mice and BAFF-RFP Sle1 mice compared to controls. Furthermore, Ly6C^hi inflammatory MOs and T cells had significantly increased BAFF expression per cell in both spontaneous lupus models, while CD8^- DCs up-regulated BAFF expression only in the Tlr7 Tg mice. Similarly, pristane injection of BAFF-RFP mice induced increases in serum BAFF levels, auto-Abs, and the expansion of BAFF-producing Nphs, MOs, and DCs in both the spleen and peritoneal cavity. BAFF expression in MOs and DCs, in contrast to BAFF from Nphs, was required to maintain homeostatic and pristane-induced systemic BAFF levels and to sustain mature B cell pools in spleens and BMs. Although acting through different mechanisms, Nph, MO and DC sources of BAFF were each required for the development of auto-Abs in PIL mice.

Conclusions

Our findings underscore the importance of considering the relative roles of specific myeloid BAFF sources and B cell niches when developing treatments for SLE and other BAFF-associated autoimmune diseases.

cGAS deficiency enhances inflammasome activation in macrophages and inflammatory pathology in pristane-induced lupus

Introduction

Type I interferon (IFN) plays a vital role in the pathogenesis of systemic lupus erythematosus. Cyclic GMP AMP synthase (cGAS) is a cytosolic DNA sensor that recognizes dsDNA and creates cGAMP to activate STING-mediated type I IFN production. The activation of STING induces lupus disease in Fcgr2b deficient mice through the differentiation of dendritic cells. In contrast, Cgas-deficient mice could be generated more autoantibody production and proteinuria in pristane-induced lupus (PIL). These data suggested that the other dsDNA sensors could be involved in lupus development mechanisms.

Methods

This study aimed to identify the cGAS-mediated mechanisms contributing to lupus pathogenesis in PIL. The Cgas-deficient and WT mice were induced lupus disease with pristane and subsequently analyzed autoantibody, histopathology, and immunophenotypes. The lung tissues were analyzed with the expression profiles by RT-PCR and western blot. The bone marrow-derived macrophages were stimulated with inflammasome activators and observed pyroptosis.

Results

The Cgas-/- mice developed more severe pulmonary hemorrhage and autoantibody production than WT mice. The activated dendritic cells, IFN-g-, and IL-17a-producing T helper cells, and infiltrated macrophages in the lung were detected in Cgas-/- mice higher than in WT mice. We observed an increase in expression of Aim2, Casp11, and Ifi16 in the lung and serum IL-1a but IL-1b in pristane-injected Cgas-/- mice. The rise of Caspase-11 in the lung of pristane-injected Cgas-/- mice suggested noncanonical inflammasome activation. The activation of AIM2 and NLRP3 inflammasomes in bone marrow-derived macrophages (BMDMs) enhanced the number of dead cells in Cgas-/- mice compared with WT mice. Activation of the inflammasome significantly induced pyroptosis in Cgas-/- BMDMs. The dsDNA level, but not mitochondrial DNA, increased dramatically in pristane-injected Cgas-/- mice suggesting the dsDNA could be a ligand activating inflammasomes. The cGAS agonist-induced BMDM activation in the Cgas-/- mice indicated that the activation of DNA sensors other than cGAS enhanced activated macrophages.

Conclusion

These findings suggested that cGAS hampers the unusual noncanonical inflammasome activation through other DNA sensors.

Role of inhibitory B cell co-receptors in B cell self-tolerance to non-protein antigens

Antibodies to non-protein antigens such as nucleic acids, polysaccharides, and glycolipids play important roles in both host defense against microbes and development of autoimmune diseases. Although non-protein antigens are not recognized by T cells, antibody production to non-protein antigens involve T cell-independent mechanisms such as signaling through TLR7 and TLR9 in antibody production to nucleic acids. Although self-reactive B cells are tolerized by various mechanisms including deletion, anergy, and receptor editing, T cell tolerance is also crucial in self-tolerance of B cells to protein self-antigen because self-reactive T cells induce autoantibody production to these self-antigens. However, presence of T cell-independent mechanism suggests that T cell tolerance is not able to maintain B cell tolerance to non-protein self-antigens. Lines of evidence suggest that B cell response to non-protein self-antigens such as nucleic acids and gangliosides, sialic acid-containing glycolipids, are suppressed by inhibitory B cell co-receptors CD72 and Siglec-G, respectively. These inhibitory co-receptors recognize non-protein self-antigens and suppress BCR signaling induced by these antigens, thereby inhibiting B cell response to these self-antigens. Inhibitory B cell co-receptors appear to be involved in B cell self-tolerance to non-protein self-antigens that can activate B cells by T cell-independent mechanisms.

Interferon Lambda Regulates Cellular and Humoral Immunity in Pristane-Induced Lupus

A pivotal role of type I interferons in systemic lupus erythematosus (SLE) is widely accepted. Type III interferons (IFN-λ) however, the most recently discovered cytokines grouped within the interferon family, have not been extensively studied in lupus disease models yet. Growing evidence suggests a role for IFN-λ in regulating both innate and adaptive immune responses, and increased serum concentrations have been described in multiple autoimmune diseases including SLE. Using the pristane-induced lupus model, we found that mice with defective IFN-λ receptors (Ifnlr1^−/−) showed increased survival rates, decreased lipogranuloma formation and reduced anti-dsDNA autoantibody titers in the early phase of autoimmunity development compared to pristane-treated wild-type mice. Moreover, Ifnlr1^−/− mice treated with pristane had reduced numbers of inflammatory mononuclear phagocytes and cNK cells in their kidneys, resembling untreated control mice. Systemically, circulating B cells and monocytes (CD115⁺Ly6C⁺) were reduced in pristane-treated Ifnlr1^−/− mice. The present study supports a significant role for type III interferons in the pathogenesis of pristane-induced murine autoimmunity as well as in systemic and renal inflammation. Although the absence of type III interferon receptors does not completely prevent the development of autoantibodies, type III interferon signaling accelerates the development of autoimmunity and promotes a pro-inflammatory environment in autoimmune-prone hosts.

Type I Interferon Promotes Humoral Immunity in Viral Vector Vaccination

Recombinant viral vectors represent an important platform for vaccine delivery. Our recent studies have demonstrated distinct innate immune profiles in responding to viral vectors of different families (e.g., adenovirus versus poxvirus): while human Ad5 vector is minimally innate immune stimulatory, the poxviral vector ALVAC induces strong innate response and stimulates type I interferon (IFN) and inflammasome activation. However, the impact of the innate immune signaling on vaccine-induced adaptive immunity in viral vector vaccination is less clear. Here, we show that Modified Vaccinia Ankara (MVA), another poxviral vector, stimulated a type I IFN response in innate immune cells through cGAS-STING. Using MVA-HIV vaccine as a model, we found that type I IFN signaling promoted the generation of humoral immunity in MVA-HIV vaccination in vivo. Following vaccination, type I IFN receptor-knockout (IFNAR1-/-) mice produced significantly lower levels of total and HIV gp120-specific antibodies compared to wild-type (WT) mice. Consistent with the antibody response, a type I IFN signaling deficiency also led to reduced levels of plasma cells and memory-like B cells compared to WT mice. Furthermore, analysis of vaccine-induced CD4 T cells showed that type I IFN signaling also promoted the generation of a vaccine-specific CD4 T-cell response and a T follicular helper (Tfh) response in mice. Together, our data indicate a role for type I IFN signaling in promoting humoral immunity in poxviral vector vaccination. The study suggests that modulating type I IFN and its associated innate immune pathways will likely affect vaccine efficacy. IMPORTANCE Viral vectors, including MVA, are an important antigen delivery platform and have been commonly used in vaccine development. Understanding the innate host-viral vector interactions and their impact on vaccine-induced immunity is critical but understudied. Using MVA-HIV vaccination of WT and IFNAR1-/- mice as a model, we report that type I IFN signaling promotes humoral immunity in MVA vaccination, including vaccine-induced antibody, B-cell, and Tfh responses. Our findings provide insights that not only add to our basic understanding of host-viral vector interactions but also will aid in improving vaccine design by potentially modulating type I IFN and its associated innate immune pathways in viral vector vaccination.

Interferons in Systemic Lupus Erythematosus

Skewing of type I interferon (IFN) production and responses is a hallmark of systemic lupus erythematosus (SLE). Genetic and environmental contributions to IFN production lead to aberrant innate and adaptive immune activation even before clinical development of disease. Basic and translational research in this arena continues to identify contributions of IFNs to disease pathogenesis, and several promising therapeutic options for targeting of type I IFNs and their signaling pathways are in development for treatment of SLE patients.

Genetic and chemical inhibition of IRF5 suppresses pre-existing mouse lupus-like disease

The transcription factor IRF5 has been implicated as a therapeutic target for the autoimmune disease systemic lupus erythematosus (SLE). However, IRF5 activation status during the disease course and the effects of IRF5 inhibition after disease onset are unclear. Here, we show that SLE patients in both the active and remission phase have aberrant activation of IRF5 and interferon-stimulated genes. Partial inhibition of IRF5 is superior to full inhibition of type I interferon signaling in suppressing disease in a mouse model of SLE, possibly due to the function of IRF5 in oxidative phosphorylation. We further demonstrate that inhibition of IRF5 via conditional Irf5 deletion and a newly developed small-molecule inhibitor of IRF5 after disease onset suppresses disease progression and is effective for maintenance of remission in mice. These results suggest that IRF5 inhibition might overcome the limitations of current SLE therapies, thus promoting drug discovery research on IRF5 inhibitors.

IRF5 is a potential target for therapy in systemic lupus erythematosus (SLE). Here the authors show using mouse SLE-like models that genetic or chemical inhibition of IRF5 after SLE onset could be more effective than, or an add on for, currently utilised type I interferon inhibition.

Aim2 Couples With Ube2i for Sumoylation-Mediated Repression of Interferon Signatures in Systemic Lupus Erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) involves kidney damage, and the inflammasome-caspase-1 axis has been demonstrated to promote renal pathogenesis. The present study was designed to explore the function of the Absent in Melanoma 2 (Aim2) protein in SLE.

METHODS

Female wild-type Aim2^-/- , Aim2^-/- Ifnar1^-/- , Aim2^-/- Rag1^-/- , and Asc^-/- mice ages 8-10 weeks received 1 intraperitoneal injection of 500 μl pristane or saline, and survival of mice was monitored twice a week for 6 months.

RESULTS

The absence of Aim2, but not Asc, led to enhanced SLE in mice that received pristane treatment. Increased immune cell infiltration and type I interferon (IFN) signatures in the kidneys of Aim2^-/- mice coincided with severity of lupus, which was alleviated by blockade of Ifnar1-mediated signal. Adaptive immune cells were also involved in the glomerular lesions of Aim2^-/- mice after pristane challenge. Importantly, even in the absence of pristane, plasmacytoid dendritic cells in the kidneys of Aim2^-/- mice were significantly increased compared to control animals. Accordingly, transcriptome analysis revealed that Aim2 deficiency led to enhanced expression of type I IFN-induced genes in the kidneys even at an early developmental stage. Mechanistically, Aim2 bound ubiquitin-conjugating enzyme 2i (Ube2i), which mediates sumoylation-based suppression of type I IFN expression deficiency of Aim2 decreased cellular sumoylation, resulting in an augmented type I IFN signature and kidney pathogenesis.

CONCLUSION

The present study demonstrates a critical role for Aim2 in an optimal Ube2i-mediated sumoylation-based suppression of type I IFN generation and development of SLE. As such, the Aim2-Ube2i axis can thus be a novel target for intervention in SLE.

STINGing the Tumor Microenvironment to Promote Therapeutic Tertiary Lymphoid Structure Development

Tertiary lymphoid structures (TLS), also known as ectopic lymphoid structures (ELS) or tertiary lymphoid organs (TLO), represent a unique subset of lymphoid tissues noted for their architectural similarity to lymph nodes, but which conditionally form in peripheral tissues in a milieu of sustained inflammation. TLS serve as regional sites for induction and expansion of the host B and T cell repertoires via an operational paradigm involving mature dendritic cells (DC) and specialized endothelial cells (i.e. high endothelial venules; HEV) in a process directed by TLS-associated cytokines and chemokines. Recent clinical correlations have been reported for the presence of TLS within tumor biopsies with overall patient survival and responsiveness to interventional immunotherapy. Hence, therapeutic strategies to conditionally reinforce TLS formation within the tumor microenvironment (TME) via the targeting of DC, vascular endothelial cells (VEC) and local cytokine/chemokine profiles are actively being developed and tested in translational tumor models and early phase clinical trials. In this regard, a subset of agents that promote tumor vascular normalization (VN) have been observed to coordinately support the development of a pro-inflammatory TME, maturation of DC and VEC, local production of TLS-inducing cytokines and chemokines, and therapeutic TLS formation. This mini-review will focus on STING agonists, which were originally developed as anti-angiogenic agents, but which have recently been shown to be effective in promoting VN and TLS formation within the therapeutic TME. Future application of these drugs in combination immunotherapy approaches for greater therapeutic efficacy is further discussed.

Structural integrity with functional plasticity: what type I IFN receptor polymorphisms reveal

The type I IFNs activate an array of signaling pathways, which are initiated after IFNs bind their cognate receptors, IFNα/β receptor (IFNAR)1 and IFNAR2. These signals contribute to many aspects of human health including defense against pathogens, cancer immunosurveillance, and regulation of inflammation. How these cytokines interact with their receptors influences the quality of these signals. As such, the integrity of receptor structure is pivotal to maintaining human health and the response to immune stimuli. This review brings together genome wide association studies and clinical reports describing the association of nonsynonymous IFNAR1 and IFNAR2 polymorphisms with clinical disease, including altered susceptibility to viral and bacterial pathogens, autoimmune diseases, cancer, and adverse reactions to live-attenuated vaccines. We describe the amino acid substitutions or truncations induced by these polymorphisms and, using the knowledge of IFNAR conformational changes, IFNAR-IFN interfaces and overall structure-function relationship of the signaling complexes, we hypothesize the effect of these polymorphisms on receptor structure. That these predicted changes to IFNAR structure are associated with clinical manifestations of human disease, highlights the importance of IFNAR structural integrity to maintaining functional quality of these receptor-mediated responses. Type I IFNs are pivotal to innate immune responses and ultimately, to human health. Understanding the consequences of altered structure on the actions of these clinically significant cell receptors provides important information on the roles of IFNARs in health and disease.

The peptide symporter SLC15a4 is essential for the development of systemic lupus erythematosus in murine models

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease representing a serious unmet medical need. The disease is associated with the loss of self-tolerance and exaggerated B cell activation, resulting in autoantibody production and the formation of immune complexes that accumulate in the kidney, causing glomerulonephritis. TLR7, an important mediator of the innate immune response, drives the expression of type-1 interferon (IFN), which leads to expression of type-1 IFN induced genes and aggravates lupus pathology. Because the lysosomal peptide symporter slc15a4 is critically required for type-1 interferon production by pDC, and for certain B cell functions in response to TLR7 and TLR9 signals, we considered it as a potential target for pharmacological intervention in SLE. We deleted the slc15a4 gene in C57BL/6, NZB, and NZW mice and found that pristane-challenged slc15a4-/- mice in the C57BL/6 background and lupus prone slc15a4-/- NZB/W F1 mice were both completely protected from lupus like disease. In the NZB/W F1 model, protection persisted even when disease development was accelerated with an adenovirus encoding IFNα, emphasizing a broad role of slc15a4 in disease initiation. Our results establish a non-redundant function of slc15a4 in regulating both innate and adaptive components of the immune response in SLE pathobiology and suggest that it may be an attractive drug target.

Partial Protection From Lupus-Like Disease by B-Cell Specific Type I Interferon Receptor Deficiency

Systemic lupus erythematosus (SLE) is an autoimmune disease that can present with many different permutations of symptom presentation. A large subset of SLE patients have been shown to present with elevated interferon stimulated gene (ISG) expression, and Type I IFNs (IFNαβ) have been shown to drive disease in murine models through global IFNα Receptor (IFNAR) knockouts. However, the disease contribution of distinct immune cell subsets in response to constitutively increased levels of IFNαβ is not fully understood. We utilized a B-cell specific IFNAR knockout (BΔIFNAR) on the B6.Nba2 spontaneous-lupus background to determine the contribution of IFNαβ stimulated B cells in disease. We found that IFNαβ signaling in B cells is driving increased splenomegaly, increased populations of activated B cells, and increased populations of germinal center (GC) B cells, memory B cells, and plasma blasts/cells, but did not affect the development of glomerulonephritis and immune-complex deposition. IFNAR expression by B cells also drove production of anti-chromatin IgG, and anti-dsDNA and -nRNP IgG and IgG_2C auto-antibody levels, as well as increased Bcl2 expression, affecting GC B cell survival in B6.Nba2 mice.

Preclinical Testing of Viral Therapeutic Efficacy in Pristane-Induced Lupus Nephritis and Diffuse Alveolar Hemorrhage Mouse Models

Systemic lupus erythematosus (SLE) is a multifactorial and heterogeneous autoimmune disease involving multiple organ systems and tissues. Lupus nephritis occurs in approximately 60% of patients with SLE and is the leading cause of morbidity. Diffuse alveolar hemorrhage (DAH) is a rare but very serious complication of SLE with a greater than 50% associated mortality. The etiology of SLE is unclear but has proposed genetic, hormonal, and environmental aspects. Pristane is a saturated terpenoid alkane and has become the most popular laboratory model for inducing lupus in mice. The pristane model of SLE has the capacity to reproduce many components of the human presentation of the disease. Previous studies have demonstrated that virus-derived immune-modulating proteins have the potential to control inflammatory and autoimmune disorders. Serp-1, a 55 kDa secreted and highly glycosylated immune modulator derived from myxoma virus (MYXV), has potent immunomodulatory activity in models of vasculitis, viral sepsis, collagen-induced arthritis, and transplant rejection. This chapter describes the mouse preclinical pristane lupus model as a method to examine virus-derived protein efficacy for treating autoimmune diseases and specifically lupus nephritis and DAH.

Lupus animal models and neuropsychiatric implications

Systemic lupus erythematosus (SLE) that involves neurological complications is known as neuropsychiatric systemic lupus erythematosus (NPSLE). Research in humans is difficult due to the disease's great heterogeneity. Animal models are a resource for new discoveries. In this review, we examine experimental models of lupus that present neuropsychiatric manifestations. Spontaneous animal models such as NZB/W F1 and MRL/lpr are commonly used in NPSLE research; these models present few SLE symptoms compared to induced animal models, such as pristane-induced lupus (PIL). The PIL model is known to present eight of the main clinical and laboratory manifestations of SLE described by the American College of Rheumatology. Many cytokines associated with NPSLE are expressed in the PIL model, such as IL-6, TNF-α, and IFN. However, to date, NPSLE manifestations have been poorly studied in the PIL model. In this review article, we discuss whether the PIL model can mimic neuropsychiatric manifestations of SLE. Key Points • PIL model have a strong interferon signature. • Animals with PIL express learning and memory deficit.

LncRNA Malat1 inhibition of TDP43 cleavage suppresses IRF3-initiated antiviral innate immunity

Long noncoding RNAs (lncRNAs) involved in the regulation of antiviral innate immune responses need to be further identified. By functionally screening the lncRNAs in macrophages, here we identified lncRNA Malat1, abundant in the nucleus but significantly down-regulated after viral infection, as a negative regulator of antiviral type I IFN (IFN-I) production. Malat1 directly bound to the transactive response DNA-binding protein (TDP43) in the nucleus and prevented activation of TDP43 by blocking the activated caspase-3-mediated TDP43 cleavage to TDP35. The cleaved TDP35 increased the nuclear IRF3 protein level by binding and degrading Rbck1 pre-mRNA to prevent IRF3 proteasomal degradation upon viral infection, thus selectively promoting antiviral IFN-I production. Deficiency of Malat1 enhanced antiviral innate responses in vivo, accompanying the increased IFN-I production and reduced viral burden. Importantly, the reduced MALAT1, augmented IRF3, and increased IFNA mRNA were found in peripheral blood mononuclear cells (PBMCs) from systemic lupus erythematosus (SLE) patients. Therefore, the down-regulation of MALAT1 in virus-infected cells or in human cells from autoimmune diseases will increase host resistance against viral infection or lead to autoinflammatory interferonopathies via the increased type I IFN production. Our results demonstrate that the nuclear Malat1 suppresses antiviral innate responses by targeting TDP43 activation via RNA-RBP interactive network, adding insight to the molecular regulation of innate responses and autoimmune pathogenesis.

NF-E2-Related Factor 2 Regulates Interferon Receptor Expression and Alters Macrophage Polarization in Lupus

OBJECTIVE

Pristane-induced lupus is associated with nonresolving inflammation and deficiency of proresolving macrophages. Proresolving nonclassic macrophages (NCMs) are less responsive to type I interferon (IFN) than classic macrophages (CMs; which are proinflammatory), reflecting their relative expression levels of the type I IFN receptor (IFNAR). This study was undertaken to investigate the regulation of IFNAR expression in macrophages.

METHODS

We carried out gene expression profiling of purified CMs and NCMs from mice treated with pristane (which develop lupus) or mineral oil (non-lupus controls). Macrophage differentiation and IFNAR expression were examined in mice treated with NF-E2-related factor 2 (Nrf2) activators and inhibitors and in Nrf2-deficient mice. Nrf2 activity was also assessed in blood cells from patients with systemic lupus erythematosus (SLE). Significant differences were determined by Student's t-test.

RESULTS

RNA sequencing revealed increased expression of genes regulated by the transcription factor Nrf2 in NCMs from mineral oil-treated versus pristane-treated mice and in NCMs versus CMs. The Nrf2 activator CDDO-imidazole (CDDO-Im) decreased CMs (P < 0.0001) and promoted the development of proresolving NCMs (P = 0.06), whereas the Nrf2 inhibitor brusatol increased CMs (P < 0.05) and decreased NCMs (P < 0.001). CDDO-Im decreased Ifnar1 (P < 0.001) and IFN-stimulated gene (ISG) expression in macrophages and alleviated oxidative stress (P < 0.05), whereas brusatol had the opposite effect (P < 0.01). Moreover, Ifnar1 and ISG expression levels were higher in Nrf2-knockout mice than controls (P < 0.05). As seen in mice with lupus, SLE patients showed evidence of low Nrf2 activity.

CONCLUSION

Our findings indicate that Nrf2 activation favors the resolution of chronic inflammation in lupus. Since autoantibody production and lupus nephritis depend on IFNAR signaling, the ability of Nrf2 activators to repolarize macrophages and reduce the INF signature suggests that these agents may warrant consideration for treating lupus.

Inflammatory monocyte-derived dendritic cells mediate autoimmunity in murine model of systemic lupus erythematosus

Using a mouse model of systemic lupus erythematosus (SLE), we recently demonstrated that the two major manifestations of SLE are mechanistically independent because the type I IFN pathway leads to the autoantibody production whereas the NF-κB activation is sufficient for the development of glomerulonephritis. To further advance our understandings on the molecular pathways regulating the development of SLE, we studied the role of IRF8 because it controls both type I IFN and NF-κB pathways and saw that IRF8-deficient mice failed to develop either glomerulonephritis or the autoantibody production. Furthermore, these genetically engineered mice prompted us to realize the important role of Ly6C^high inflammatory monocytes in the development of SLE. These monocytes migrate to the peritoneal cavity in WT and IRF7-deficient mice but not in IRF8-deficient mice, and there they produce both type I IFN and proinflammatory cytokines in WT mice, while in IRF7-deficient mice they only produce proinflammatory cytokines. Upon migration to the spleen, Ly6C^high inflammatory monocytes differentiate into dendritic cells (DCs) which are capable of producing proinflammatory cytokines in response to dsDNA autoantigen. Collectively, type I IFN produced from inflammatory monocytes/monocyte-derived DCs might be essential for autoantibody production whereas proinflammatory cytokines produced from them might mediate tissue damages in this model. Our study reveals a specialized role for monocyte-derived antigen presenting cells in autoimmunity. Plasticity of monocyte might play an important role not only in the pathogenesis of the disease but also in flare-ups of the disease.

Contribution of mouse models in our understanding of lupus

Laboratory animal models are beneficial when they recapitulate all or just some of the clinical and immunological manifestations of the disease. Various animals such as cats, rats, dogs, hamsters, guinea pigs, rabbits, horses, minks, pigs, and primates have been described lupus-like phenotype. However, a mouse has remained the preferable animal for scientific investigations as a result of their reduced lifespan, easy reproduction, markedly low costs, public acceptance, ease of genetic management, and the probability to stay under standardized conditions. It is highly challenging to establish a mouse model with all features of lupus because of the difficulty and the heterogeneity of the clinical features in systemic lupus erythematous (SLE). Additionally, due to the multiple differences between the mouse and human immune system, the direct translation usually fails. Each mouse model has specific characteristics and shares many subsets of aspects with the disease observed in humans, which gives researchers a tool to select their particular needs. Over 50 years, many mice models have been developed and used to dissect the pathogenesis of lupus, also to test novel drugs and therapies. In general, mice models that contribute considerably in SLE understanding can be divided into four groups: Spontaneous models, induced models, genetically modified models, along with humanizing mouse models that are the link between the mouse and human immune system. In this updated review, we will present what has been learned from different lupus mice models and how these models have contributed to a better understanding of lupus pathogenesis and treatment.

Type I IFN Drives Experimental Systemic Lupus Erythematosus by Distinct Mechanisms in CD4 T Cells and B Cells

Myriad studies have linked type I IFN to the pathogenesis of autoimmune diseases, including systemic lupus erythematosus (SLE). Although increased levels of type I IFN are found in patients with SLE, and IFN blockade ameliorates disease in many mouse models of lupus, its precise roles in driving SLE pathogenesis remain largely unknown. In this study, we dissected the effect of type I IFN sensing by CD4 T cells and B cells on the development of T follicular helper cells (TFH), germinal center (GC) B cells, plasmablasts, and antinuclear dsDNA IgG levels using the bm12 chronic graft-versus-host disease model of SLE-like disease. Type I IFN sensing by B cells decreased their threshold for BCR signaling and increased their expression of MHC class II, CD40, and Bcl-6, requirements for optimal GC B cell functions. In line with these data, ablation of type I IFN sensing in B cells significantly reduced the accumulation of GC B cells, plasmablasts, and autoantibodies. Ablation of type I IFN sensing in T cells significantly inhibited TFH expansion and subsequent B cell responses. In contrast to the effect in B cells, type I IFN did not promote proliferation in the T cells but protected them from NK cell-mediated killing. Consequently, ablation of either perforin or NK cells completely restored TFH expansion of IFNAR-/- TFH and, subsequently, restored the B cell responses. Together, our data provide evidence for novel roles of type I IFN and immunoregulatory NK cells in the context of sterile inflammation and SLE-like disease.

ADP-ribosylation factor-like 8b is required for the development of mouse models of systemic lupus erythematosus

Toll-like receptor 7 (TLR7) and type I interferons (IFN-1) are essential for the development of systemic lupus erythematosus (SLE) models such as BXSB.Yaa and 2,6,10,14-tetramethyl-pentadecane (TMPD)-induced experimental lupus. However, the mechanism underlying the development of SLE remains undefined. We report a requirement for ADP-ribosylation factor-like 8b (Arl8b) for TLR7-dependent IFN-1 production in plasmacytoid dendritic cells (pDCs). We analyzed whether Arl8b plays a role in two SLE models by comparing wild-type and Arl8b-deficient Arl8b GeneTrap (Arl8bGt/Gt) mice. We found that BXSB.Yaa Arl8bGt/Gt mice showed none of the abnormalities characterized in BXSB.Yaa mice. TMPD treatment of Arl8bGt/Gt mice significantly inhibited the development of SLE. pDCs were required for TMPD-induced peritonitis. Our data demonstrate that Arl8b contributes to disease pathogenesis in two SLE models via IFN-1-dependent and -independent mechanisms and suggest that Arl8b is an attractive new target for therapeutic intervention in SLE.

Differential Responsiveness of Monocyte and Macrophage Subsets to Interferon

OBJECTIVE

Peripheral blood mononuclear cells (PBMCs) in systemic lupus erythematosus (SLE) patients exhibit a gene expression program (interferon [IFN] signature) that is attributed to overproduction of type I IFNs by plasmacytoid dendritic cells. Type I IFNs have been thought to play a role in the pathogenesis of SLE. This study was undertaken to examine an unexpected influence of monocyte/macrophages on the IFN signature.

METHODS

Proinflammatory (classic) and antiinflammatory (nonclassic) monocyte/macrophages were sorted from mice and analyzed by RNA sequencing and quantitative polymerase chain reaction (qPCR). Type I IFN-α/β/ω receptor (IFNAR-1) expression was determined by qPCR and flow cytometry. Macrophages were stimulated in vitro with IFNα, and pSTAT1was measured.

RESULTS

Transcriptional profiling of peritoneal macrophages from mice with pristane-induced SLE unexpectedly indicated a strong IFN signature in classic, but not nonclassic, monocyte/macrophages exposed to the same type I IFN concentrations. Ifnar1 messenger RNA and IFNAR surface staining were higher in classic monocyte/macrophages versus nonclassic monocyte/macrophages (P < 0.0001 and P < 0.05, respectively, by Student's t-test). Nonclassic monocyte/macrophages were also relatively insensitive to IFNα-driven STAT1 phosphorylation. Humans exhibited a similar pattern: higher IFNAR expression (P < 0.0001 by Student's t-test) and IFNα-stimulated gene expression (P < 0.01 by paired Wilcoxon's rank sum test) in classic monocyte/macrophages and lower levels in nonclassic monocyte/macrophages.

CONCLUSION

This study revealed that the relative abundance of different monocyte/macrophage subsets helps determine the magnitude of the IFN signature. Responsiveness to IFNα signaling reflects differences in IFNAR expression in classic (high IFNAR) compared to nonclassic (low IFNAR) monocyte/macrophages. Thus, the IFN signature depends on both type I IFN production and the responsiveness of monocyte/macrophages to IFNAR signaling.

Long Noncoding RNA Signatures Induced by Toll-Like Receptor 7 and Type I Interferon Signaling in Activated Human Plasmacytoid Dendritic Cells

Long noncoding RNAs (lncRNAs) exhibit highly lineage-specific expression and act through diverse mechanisms to exert control over a wide range of cellular processes. lncRNAs can function as potent modulators of innate immune responses through control of transcriptional and posttranscriptional regulation of mRNA expression and processing. Recent studies have demonstrated that lncRNAs participate in the regulation of antiviral responses and autoimmune disease. Despite their emerging role as immune mediators, the mechanisms that govern lncRNA expression and function have only begun to be characterized. In this study, we explore the role of lncRNAs in human plasmacytoid dendritic cells (pDCs), which are critical sentinel sensors of viral infection and contribute to the development of autoimmune disease. Using genome-wide sequencing approaches, we dissect the contributions of Toll-like receptor 7 (TLR7) and type I interferon (IFN-I) in the regulation of coding and noncoding RNA expression in CAL-1 pDCs treated with R848 or IFNβ. Functional enrichment analysis reveals both the unique and synergistic roles of TLR7 and IFN-I signaling in the orchestration of pDC function. These observations were consistent with primary cell immune responses elicited by detection of viral infection. We identified and characterized the conditional TLR7- and IFN-I-dependent regulation of 588 lncRNAs. Dysregulation of these lncRNAs could significantly alter pDC maturation, IFN-I and inflammatory cytokine production, antigen presentation, costimulation or tolerance cues, turnover, or localization, all consequential events during viral infection or IFN-I-driven autoimmune diseases such as systemic lupus erythematosus. These findings demonstrate the differential responsiveness of lncRNAs to unique immune stimuli, uncover regulatory mechanisms of lncRNA expression, and reveal a novel and tractable platform for the study of lncRNA expression and function.

When the balance is broken: X-linked gene dosage from two X chromosomes and female-biased autoimmunity

Women and men exhibit differences in innate and adaptive immunity, and women are more susceptible to numerous autoimmune disorders. Two or more X chromosomes increases the risk for some autoimmune diseases, and increased expression of some X-linked immune genes is frequently observed in female lymphocytes from autoimmune patients. Evidence from mouse models of autoimmunity also supports the idea that increased expression of X-linked genes is a feature of female-biased autoimmunity. Recent studies have begun to elucidate the correlation between abnormal X-chromosome inactivation (XCI), an essential mechanism female somatic cells use to equalize X-linked gene dosage between the sexes, and autoimmunity in lymphocytes. In this review, we highlight research describing overexpression of X-linked immunity-related genes and female-biased autoimmunity in both humans and mouse models, and make connections with our recent work elucidating lymphocyte-specific mechanisms of XCI maintenance that become altered in lupus patients.

High-dimensional analysis reveals a pathogenic role of inflammatory monocytes in experimental diffuse alveolar hemorrhage

Diffuse alveolar hemorrhage (DAH) is a life-threatening pulmonary complication associated with systemic lupus erythematosus, vasculitis, and stem cell transplant. Little is known about the pathophysiology of DAH, and no targeted therapy is currently available. Pristane treatment in mice induces systemic autoimmunity and lung hemorrhage that recapitulates hallmark pathologic features of human DAH. Using this experimental model, we performed high-dimensional analysis of lung immune cells in DAH by mass cytometry and single-cell RNA sequencing. We found a large influx of myeloid cells to the lungs in DAH and defined the gene expression profile of infiltrating monocytes. Bone marrow-derived inflammatory monocytes actively migrated to the lungs and homed adjacent to blood vessels. Using 3 models of monocyte deficiency and complementary transfer studies, we established a central role of inflammatory monocytes in the development of DAH. We further found that the myeloid transcription factor interferon regulatory factor 8 is essential to the development of both DAH and type I interferon-dependent autoimmunity. These findings collectively reveal monocytes as a potential treatment target in DAH.

Conditional Upregulation of IFN-α Alone Is Sufficient to Induce Systemic Lupus Erythematosus

The cause of systemic lupus erythematosus (SLE) is unknown. IFN-α has been suggested as a causative agent of SLE; however, it was not proven, and to what extent and how IFN-α contributes to the disease is unknown. We studied the contribution of IFN-α to SLE by generating inducible IFN-α transgenic mice and directly show that conditional upregulation of IFN-α alone induces a typical manifestation of SLE in the mice not prone to autoimmunity, such as serum immune complex, autoantibody against dsDNA (anti-dsDNA Ab), and the organ manifestations classical to SLE, such as immune complex-deposited glomerulonephritis, classical splenic onion-skin lesion, alopecia, epidermal liquefaction, and positive lupus band test of the skin. In the spleen of mice, activated effector CD4 T cells, IFN-γ-producing CD8 T cells, B220⁺CD86⁺ cells, and CD11c⁺CD86⁺ cells were increased, and the T cells produced increased amounts of IL-4, IL-6, IL-17, and IFN-γ and decreased IL-2. In particular, activated CD3⁺CD4^-CD8^- double-negative T cells positive for TCRαβ, B220, CD1d-teteramer, PD-1, and Helios (that produced increased amounts of IFN-γ, IL-4, IL-17, and TNF-α) were significantly expanded. They infiltrated into kidney and induced de novo glomerulonephritis and alopecia when transferred into naive recipients. Thus, sole upregulation of IFN-α is sufficient to induce SLE, and the double-negative T cells expanded by IFN-α are directly responsible for the organ manifestations, such as lupus skin disease or nephritis.

Metformin Inhibits the Type 1 IFN Response in Human CD4+ T Cells

In systemic lupus erythematosus, defective clearance of apoptotic debris and activation of innate cells result in a chronically activated type 1 IFN response, which can be measured in PBMCs of most patients. Metformin, a widely used prescription drug for Type 2 diabetes, has a therapeutic effect in several mouse models of lupus through mechanisms involving inhibition of oxidative phosphorylation and a decrease in CD4⁺ T cell activation. In this study, we report that in CD4⁺ T cells from human healthy controls and human systemic lupus erythematosus patients, metformin inhibits the transcription of IFN-stimulated genes (ISGs) after IFN-α treatment. Accordingly, metformin inhibited the phosphorylation of pSTAT1 (Y701) and its binding to IFN-stimulated response elements that control ISG expression. These effects were independent of AMPK activation or mTORC1 inhibition but were replicated using inhibitors of the electron transport chain respiratory complexes I, III, and IV. This indicates that mitochondrial respiration is required for ISG expression in CD4⁺ T cells and provides a novel mechanism by which metformin may exert a therapeutic effect in autoimmune diseases.

Identification of Renal Long Non-coding RNA RP11-2B6.2 as a Positive Regulator of Type I Interferon Signaling Pathway in Lupus Nephritis

Objective: Lupus nephritis (LN) is one of the most serious complications of systemic lupus erythematosus (SLE). Type I interferon (IFN-I) is associated with the pathogenesis of LN. Long non-coding RNAs (lncRNAs) have been implicated in the pathogenesis of SLE, however, the roles of lncRNAs in LN are still poorly understood. Here, we identified and investigated the function of LN-associated lncRNA RP11-2B6.2 in regulating IFN-I signaling pathway.

Methods: RNA sequencing was used to analyze the expression of lncRNAs in kidney biopsies from LN patients and controls. Antisense oligonucleotides and CRISPRi system or overexpression plasmids and CRISPRa system were used to perform loss or gain of function experiments. In situ hybridization, imaging flow cytometry, dual-luciferase reporter assay, and ATAC sequencing were used to study the functions of lncRNA RP11-2B6.2. RT-qPCR, ELISA, and western blotting were done to detect RNA and protein levels of specific genes.

Results: Elevated lncRNA RP11-2B6.2 was observed in kidney biopsies from LN patients and positively correlated with disease activity and IFN scores. Knockdown of lncRNA RP11-2B6.2 in renal cells inhibited the expression of IFN stimulated genes (ISGs), while overexpression of lncRNA RP11-2B6.2 enhanced ISG expression. Knockdown of LncRNA RP11-2B6.2 inhibited the phosphorylation of JAK1, TYK2, and STAT1 in IFN-I pathway, while promoted the chromatin accessibility and the transcription of SOCS1.

Conclusion: The expression of lncRNAs is abnormal in the kidney of LN. LncRNA RP11-2B6.2 is a novel positive regulator of IFN-I pathway through epigenetic inhibition of SOCS1, which provides a new therapeutic target to alleviate over-activated IFN-I signaling in LN.

Hes1 attenuates type I IFN responses via VEGF-C and WDFY1

Transcription factor Hes1 acts as a homeostatic negative regulator of type I interferon production to restrain interferon-mediated immune responses, including antiviral immunity and autoimmune conditions. Mechanistically, Hes1 suppresses interferon expression by targeting a regulatory circuit composed of WDFY1 and VEGF-C.

Induction of type I interferons (IFNs) is critical for eliciting competent immune responses, especially antiviral immunity. However, uncontrolled IFN production contributes to pathogenesis of autoimmune and inflammatory diseases. We found that transcription factor Hes1 suppressed production of type I IFNs and expression of IFN-stimulated genes. Functionally, Hes1-deficient mice displayed a heightened IFN signature in vivo, mounted enhanced resistance against encephalomyocarditis virus infection, and showed signs of exacerbated experimental lupus nephritis. Mechanistically, Hes1 did not suppress IFNs via direct transcriptional repression of IFN-encoding genes. Instead, Hes1 attenuated activation of TLR upstream signaling by inhibition of an adaptor molecule, WDFY1. Genome-wide assessment of Hes1 occupancy revealed that suppression of WDFY1 was secondary to direct binding and thus enhancement of expression of VEGF-C by Hes1, making Vegfc a rare example of an Hes1 positively regulated gene. In summary, these results identified Hes1 as a homeostatic negative regulator of type I IFNs for the maintenance of immune balance in the context of antiviral immunity and autoimmune diseases.

Deletion of the Mitochondrial Complex-IV Cofactor Heme A:Farnesyltransferase Causes Focal Segmental Glomerulosclerosis and Interferon Response

Mutations in mitochondrial DNA as well as nuclear-encoded mitochondrial proteins have been reported to cause tubulointerstitial kidney diseases and focal segmental glomerulosclerosis (FSGS). Recently, genes and pathways affecting mitochondrial turnover and permeability have been implicated in adult-onset FSGS. Furthermore, dysfunctioning mitochondria may be capable of engaging intracellular innate immune-sensing pathways. To determine the impact of mitochondrial dysfunction in FSGS and secondary innate immune responses, we generated Cre/loxP transgenic mice to generate a loss-of-function deletion mutation of the complex IV assembly cofactor heme A:farnesyltransferase (COX10) restricted to cells of the developing nephrons. These mice develop severe, early-onset FSGS with innate immune activation and die prematurely with kidney failure. Mutant kidneys showed loss of glomerular and tubular epithelial function, epithelial apoptosis, and, in addition, a marked interferon response. In vitro modeling of Cox10 deletion in primary kidney epithelium compromises oxygen consumption, ATP generation, and induces oxidative stress. In addition, loss of Cox10 triggers a selective interferon response, which may be caused by the leak of mitochondrial DNA into the cytosol activating the intracellular DNA sensor, stimulator of interferon genes. This new animal model provides a mechanism to study mitochondrial dysfunction in vivo and demonstrates a direct link between mitochondrial dysfunction and intracellular innate immune response.

Ectonucleotidase-Mediated Suppression of Lupus Autoimmunity and Vascular Dysfunction

Objectives

CD39 and CD73 are surface enzymes that jut into the extracellular space where they mediate the step-wise phosphohydrolysis of the autocrine and paracrine danger signals ATP and ADP into anti-inflammatory adenosine. Given the role of vascular and immune cells' "purinergic halo" in maintaining homeostasis, we hypothesized that the ectonucleotidases CD39 and CD73 might play a protective role in lupus.

Methods

Lupus was modeled by intraperitoneal administration of pristane to three groups of mice: wild-type (WT), CD39^-/-, and CD73^-/-. After 36 weeks, autoantibodies, endothelial function, kidney disease, splenocyte activation/polarization, and neutrophil activation were characterized.

Results

As compared with WT mice, CD39^-/- mice developed exaggerated splenomegaly in response to pristane, while both groups of ectonucleotidase-deficient mice demonstrated heightened anti-ribonucleoprotein production. The administration of pristane to WT mice triggered only subtle dysfunction of the arterial endothelium; however, both CD39^-/- and CD73^-/- mice demonstrated striking endothelial dysfunction following induction of lupus, which could be reversed by superoxide dismutase. Activated B cells and plasma cells were expanded in CD73^-/- mice, while deficiency of either ectonucleotidase led to expansion of T_H17 cells. CD39^-/- and CD73^-/- mice demonstrated exaggerated neutrophil extracellular trap release, while CD73^-/- mice additionally had higher levels of plasma cell-free DNA.

Conclusion

These data are the first to link ectonucleotidases with lupus autoimmunity and vascular disease. New therapeutic strategies may harness purinergic nucleotide dissipation or signaling to limit the damage inflicted upon organs and blood vessels by lupus.

TLR7-Mediated Lupus Nephritis Is Independent of Type I IFN Signaling

Systemic lupus erythematosus is an autoimmune disease characterized by increased type I IFNs, autoantibodies, and inflammatory-mediated multiorgan damage. TLR7 activation is an important contributor to systemic lupus erythematosus pathogenesis, but the mechanisms by which type I IFNs participate in TLR7-driven pathologic conditions remain uncertain. In this study, we examined the requirement for type I IFNs in TLR7-stimulated lupus nephritis. Lupus-prone NZM2328, INZM (which lack a functional type I IFN receptor), and NZM2328 IL-1β^-/- mice were treated at 10 wk of age on the right ear with R848 (TLR7 agonist) or control (DMSO). Autoantibody production and proteinuria were assessed throughout treatment. Multiorgan inflammation was assessed at the time of decline in health. Renal infiltrates and mRNA expression were also examined after 14 d of treatment. Both NZM2328 and INZM mice exhibited a decline in survival after 3-4 wk of R848 but not vehicle treatment. Development of splenomegaly and liver inflammation were dependent on type I IFN. Interestingly, autoantibody production, early renal infiltration of dendritic cells, upregulation of IL-1β, and lupus nephritis occurred independent of type I IFN signaling. Development of TLR7-driven lupus nephritis was not abolished by the deletion of IL-1β. Thus, although IFN-α is sufficient to induce nephritis acceleration, our data emphasize a critical role for IFN-independent signaling in TLR7-mediated lupus nephritis. Further, despite upregulation of IL-1β after TLR7 stimulation, deletion of IL-1β is not sufficient to reduce lupus nephritis development in this model.

TANK-Binding Kinase 1-Dependent Responses in Health and Autoimmunity

The pathogenesis of autoimmune diseases, such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) is driven by genetic predisposition and environmental triggers that lead to dysregulated immune responses. These include the generation of pathogenic autoantibodies and aberrant production of inflammatory cytokines. Current therapies for RA and other autoimmune diseases reduce inflammation by targeting inflammatory mediators, most of which are innate response cytokines, resulting in generalized immunosuppression. Overall, this strategy has been very successful, but not all patients respond, responses can diminish over time and numerous side effects can occur. Therapies that target the germinal center (GC) reaction and/or antibody-secreting plasma cells (PC) potentially provide a novel approach. TANK-binding kinase 1 (TBK1) is an IKK-related serine/threonine kinase best characterized for its involvement in innate antiviral responses through the induction of type I interferons. TBK1 is also gaining attention for its roles in humoral immune responses. In this review, we discuss the role of TBK1 in immunological pathways involved in the development and maintenance of antibody responses, with particular emphasis on its potential relevance in the pathogenesis of humoral autoimmunity. First, we review the role of TBK1 in the induction of type I IFNs. Second, we highlight how TBK1 mediates inducible T cell co-stimulator signaling to the GC T follicular B helper population. Third, we discuss emerging evidence on the contribution of TBK1 to autophagic pathways and the potential implications for immune cell function. Finally, we discuss the therapeutic potential of TBK1 inhibition in autoimmunity.

The association between expression of IFIT1 in podocytes of MRL/lpr mice and the renal pathological changes it causes: An animal study

Renal damage is the major cause of SLE associated mortality, and IFIT1expression was elevated in SLE cases in accordance of previous studies. Therefore, we conducted an animal study to identify the role of IFIT1 expression in renal pathological changes.18 female MRL/lpr mice and same number of female BALB/c mice were enrolled in present study. Quantitative analysis of urine protein, Complement C3 and C4, and anti-ds DNA antibody were conducted. HE and PAS staining and TEM analysis were employed to observe the pathological changes in renal tissue. Significant elevation on urine protein and anti-dsDNA and reduction on Complement C3 and C4 were observed in MRL/lpr mice when comparing the controls in same age. Staining and TEM analysis observed several pathological changes in glomerulus among MRL/lpr mice, including cellular enlargement, basement membrane thickening, and increased cellularcasts. The linear regression analysis found the optical density of IFIT1 was inversely associated with F-actin, Nephrin, and Podocin, but not Synatopodin. In summary, IFIT1 expression is associated with podocytes damage, and capable of suppressing some proteins essential to glomerular filtration.

Mouse models of lupus: what they tell us and what they don't

Lupus is a complex heterogeneous disease characterised by autoantibody production and immune complex deposition followed by damage to target tissues. Animal models of human diseases are an invaluable tool for defining pathogenic mechanisms and testing of novel therapeutic agents. There are perhaps more applicable murine models of lupus than any other human disease. There are spontaneous models of lupus, inducible models of lupus, transgenic-induced lupus, gene knockout induced lupus and humanised mouse models of lupus. These mouse models of lupus have contributed significantly to our knowledge of the pathogenesis of lupus and served as valuable preclinical models for proof of concept for new therapies. Despite their utility, mouse models of lupus have their distinct limitations. Although similar, mouse and human immune systems are different and thus one cannot assume a mechanism for disease in one is translatable to the other. Efficacy and toxicity of compounds can vary significantly between humans and mice, also limiting direct translation. Finally, the heterogeneous aspects of human lupus, both in clinical presentation, underlying pathogenesis and genetics, are not completely represented in current mouse models. Thus, proving a therapy or mechanism of disease in one mouse model is similar to proving a mechanism/therapy in a limited subset of human lupus. These limitations, however, do not marginalise the importance of animal models nor the significant contributions they have made to our understanding of lupus.

Induction of Systemic Autoimmunity by a Xenobiotic Requires Endosomal TLR Trafficking and Signaling from the Late Endosome and Endolysosome but Not Type I IFN

Type I IFN and nucleic acid-sensing TLRs are both strongly implicated in the pathogenesis of lupus, with most patients expressing IFN-induced genes in peripheral blood cells and with TLRs promoting type I IFNs and autoreactive B cells. About a third of systemic lupus erythematosus patients, however, lack the IFN signature, suggesting the possibility of type I IFN-independent mechanisms. In this study, we examined the role of type I IFN and TLR trafficking and signaling in xenobiotic systemic mercury-induced autoimmunity (HgIA). Strikingly, autoantibody production in HgIA was not dependent on the type I IFN receptor even in NZB mice that require type I IFN signaling for spontaneous disease, but was dependent on the endosomal TLR transporter UNC93B1 and the endosomal proton transporter, solute carrier family 15, member 4. HgIA also required the adaptor protein-3 complex, which transports TLRs from the early endosome to the late endolysosomal compartments. Examination of TLR signaling pathways implicated the canonical NF-κB pathway and the proinflammatory cytokine IL-6 in autoantibody production, but not IFN regulatory factor 7. These findings identify HgIA as a novel type I IFN-independent model of systemic autoimmunity and implicate TLR-mediated NF-κB proinflammatory signaling from the late endocytic pathway compartments in autoantibody generation.

Pristane-induced lupus: considerations on this experimental model

Systemic lupus erythematosus (SLE) is a multifactorial, autoimmune inflammatory disease with pleomorphic clinical manifestations involving different organs and tissues. The etiology of this disease has been associated with a dysfunctional response of B and T lymphocytes against environmental stimuli in individuals genetically susceptible to SLE, which determines an immune response against different autoantigens and, consequently, tissue damage. The study of different murine models has provided a better understanding of these autoimmune phenomena. This review primarily focuses on that has been learned from the pristane-induced lupus (PIL) model and how this model can be used to supplement recent advances in understanding the pathogenesis of SLE. We also consider both current and future therapies for this disease. The PubMed, SciELO, and Embase databases were searched for relevant articles published from 1950 to 2016. PIL has been shown to be a useful tool for understanding the multiple mechanisms involved in systemic autoimmunity. In addition, it can be considered an efficient model to evaluate the environmental contributions and interferon signatures present in patients with SLE.

Recent advances in the understanding of renal inflammation and fibrosis in lupus nephritis

Lupus nephritis is a potentially reversible cause of severe acute kidney injury and is an important cause of end-stage renal failure in Asians and patients of African or Hispanic descent. It is characterized by aberrant exaggerated innate and adaptive immune responses, autoantibody production and their deposition in the kidney parenchyma, triggering complement activation, activation and proliferation of resident renal cells, and expression of pro-inflammatory and chemotactic molecules leading to the influx of inflammatory cells, all of which culminate in destruction of normal nephrons and their replacement by fibrous tissue. Anti-double-stranded DNA (anti-dsDNA) antibody level correlates with disease activity in most patients. There is evidence that apart from mediating pathogenic processes through the formation of immune complexes, pathogenic anti-dsDNA antibodies can bind to resident renal cells and induce downstream pro-apoptotic, pro-inflammatory, or pro-fibrotic processes or a combination of these. Recent data also highlight the critical role of macrophages in acute and chronic kidney injury. Though clinically effective, current treatments for lupus nephritis encompass non-specific immunosuppression and the anti-inflammatory action of high-dose corticosteroids. The clinical and histological impact of novel biologics targeting pro-inflammatory molecules remains to be investigated. Insight into the underlying mechanisms that induce inflammatory and fibrotic processes in the kidney of lupus nephritis could present opportunities for more specific novel treatment options to improve clinical outcomes while minimizing off-target untoward effects. This review discusses recent advances in the understanding of pathogenic mechanisms leading to inflammation and fibrosis of the kidney in lupus nephritis in the context of established standard-of-care and emerging therapies.

Pathogenesis of Diffuse Alveolar Hemorrhage in Murine Lupus

OBJECTIVE

Diffuse alveolar hemorrhage (DAH) in lupus patients confers >50% mortality, and the cause is unknown. We undertook this study to examine the pathogenesis of DAH in C57BL/6 mice with pristane-induced lupus, a model of human lupus-associated DAH.

METHODS

Clinical/pathologic and immunologic manifestations of DAH in pristane-induced lupus were compared with those of DAH in humans. Tissue distribution of pristane was examined by mass spectrometry. Cell types responsible for disease were determined by in vivo depletion using clodronate liposomes and antineutrophil monoclonal antibodies (anti-Ly-6G). The effect of complement depletion with cobra venom factor (CVF) was examined.

RESULTS

After intraperitoneal injection, pristane migrated to the lung, causing cell death, small vessel vasculitis, and alveolar hemorrhage similar to that seen in DAH in humans. B cell-deficient mice were resistant to induction of DAH, but susceptibility was restored by infusing IgM. C3^-/- and CD18^-/- mice were also resistant, and DAH was prevented in wild-type mice by CVF. Induction of DAH was independent of Toll-like receptors, inflammasomes, and inducible nitric oxide. Mortality was increased in interleukin-10 (IL-10)-deficient mice, and pristane treatment decreased IL-10 receptor expression in monocytes and STAT-3 phosphorylation in lung macrophages. In vivo neutrophil depletion was not protective, while treatment with clodronate liposomes prevented DAH, which suggests that macrophage activation is central to DAH pathogenesis.

CONCLUSION

The pathogenesis of DAH involves opsonization of dead cells by natural IgM and complement followed by complement receptor-mediated lung inflammation. The disease is macrophage dependent, and IL-10 is protective. Complement inhibition and/or macrophage-targeted therapies may reduce mortality in lupus-associated DAH.

B-cell tolerance and autoimmunity

Self-reactive B cells are tolerized at various stages of B-cell development and differentiation, including the immature B-cell stage (central tolerance) and the germinal center (GC) B-cell stage, and B-cell tolerance involves various mechanisms such as deletion, anergy, and receptor editing. Self-reactive B cells generated by random immunoglobulin variable gene rearrangements are tolerized by central tolerance and anergy in the periphery, and these processes involve apoptosis regulated by Bim, a pro-apoptotic member of the Bcl-2 family, and regulation of B-cell signaling by various phosphatases, including SHIP-1 and SHP-1. Self-reactive B cells generated by somatic mutations during GC reaction are also eliminated. Fas is not directly involved in this process but prevents persistence of GC reaction that allows generation of less stringently regulated B cells, including self-reactive B cells. Defects in self-tolerance preferentially cause lupus-like disease with production of anti-nuclear antibodies, probably due to the presence of a large potential B-cell repertoire reactive to nucleic acids and the presence of nucleic acid-induced activation mechanisms in various immune cells, including B cells and dendritic cells. A feed-forward loop composed of anti-nuclear antibodies produced by B cells and type 1 interferons secreted from nucleic acid-activated dendritic cells plays a crucial role in the development of systemic lupus erythematosus.

Regulation of type I interferon signaling in immunity and inflammation: A comprehensive review

Type I interferons (IFNs) play essential roles in establishing and modulating host defense against microbial infection via induction of IFN-stimulated genes (ISGs) through Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway. However, dysregulation of IFNs production and function could also mediate immune pathogenesis such as inflammatory autoimmune diseases and infectious diseases via aberrantly activating inflammatory responses or improperly suppressing microbial controls. Thus, IFN responses need to be tightly regulated to achieve protective immunity against microbial infection while avoiding harmful toxicity caused by improper or prolonged IFN signaling. Multiple levels of cellular and molecular events act in a cooperated manner to regulate IFN responses, in especial, post-translational modification (PTMs) of signaling molecules and epigenetic modification of gene expression programs are two important mechanisms for regulation of IFN signaling and thus critical for orchestrating IFN-mediated host immune response to the complex pathogenic or environmental stimuli. Conventional PTMs such as phosphorylation and polyubiquitylation, as well as numerous other PTMs including acetylation, ISGylation, SUMOylation and methylation have been shown to potently modulate type I IFN signaling transduction via targeting distinct signaling steps or components. Moreover, epigenetic mechanisms, such as histone modification, DNA methylation, non-coding RNAs play critical roles in regulating chromatin structure and function, leading to flexible and dynamic gene expression patterns downstream type I IFN signaling. Herein, we summarize the recent advances in the PTMs and epigenetic mechanisms in regulation of type I IFN signaling and responses. The involvement of dysregulated IFN signaling in inflammatory and autoimmune diseases are also discussed.