Increased ribonuclease expression reduces inflammation and prolongs survival in TLR7 transgenic mice

Ribonuclease activity undermines immune sensing of naked extracellular RNA

The plasma membrane and the membrane of endosomal vesicles are considered physical barriers preventing extracellular RNA uptake. While naked RNA can be spontaneously internalized by certain cells types, functional delivery of naked RNA into the cytosol has been rarely observed. Here we show that extracellular ribonucleases, mainly derived from cell culture supplements, have so far hindered the study of extracellular RNA functionality. In the presence of active ribonuclease inhibitors (RI), naked bacterial RNA is pro-inflammatory when spiked in the media of dendritic cells and macrophages. In murine cells, this response mainly depends on the action of endosomal Toll-like receptors. However, we also show that naked RNA can perform endosomal escape and engage with cytosolic RNA sensors and ribosomes. For example, naked mRNAs encoding reporter proteins can be spontaneously internalized and translated by a variety of cell types, in an RI-dependent manner. In vivo, RI co-injection enhances the activation induced by naked extracellular RNA on splenic lymphocytes and myeloid-derived leukocytes. Furthermore, naked extracellular RNA is inherently pro-inflammatory in ribonuclease-poor compartments such as the peritoneal cavity. Overall, these results demonstrate that naked RNA is bioactive and does not need encapsulation inside synthetic or biological lipid vesicles for functional uptake, making a case for nonvesicular extracellular RNA-mediated intercellular communication.

Evaluation of RNase therapy in systemic lupus erythematosus: a randomised phase 2a clinical trial of RSLV-132

BACKGROUND

Circulating, extracellular RNA is the primary trigger of type I interferon in systemic lupus erythematosus (SLE), and interferon is known to play a central pathogenic role in the disease. RSLV-132 is a catalytically active human RNase molecule fused to human IgG1 Fc designed to digest RNA and thereby decrease the chronic inflammation associated with SLE. The drug was evaluated in a cohort of patients with SLE with moderate-severe cutaneous disease activity and the presence of RNA immune complexes. The primary objective of the study was the assessment of the impact of 13 doses of 10 mg/kg RSLV-132 over 6 months on the mean Cutaneous Lupus Erythematosus Disease Area and Severity Index (CLASI) score.

METHODS

Sixty-five patients meeting the entry criteria of a baseline CLASI score of 10 or greater and positivity of at least one of five autoantibodies to RNA-binding proteins (SM/RNP, SSA/Ro, SSB/La, Sm, RNP) were randomly assigned (2:1) to receive 13 doses of RSLV-132 10 mg/kg or placebo, respectively. Participants received study drug for 24 weeks on days 1, 8, 15, 29, 43, 57, 71, 85, 99, 113, 127, 141 and 155 with an end-of-treatment visit on day 169 and a follow-up visit at the end of the study on day 215. The primary objective was assessed on days 85 and 169. Secondary objectives included assessment of systemic disease activity using the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K), the British Isles Lupus Assessment Group 2004 Index and the Physician's Global Assessment. Data from these instruments were used to calculate the SLE Responder Index 4 (SRI-4) and the British Isles Lupus Assessment Group-based Composite Lupus Assessment (BICLA) scores.

RESULTS

The mean CLASI score change from baseline at day 169 was -5.7 (±7.0) in the placebo group and -6.2 (±8.5) in the RSLV-132 group. A subgroup of participants with moderate-severe systemic disease activity and high baseline SLEDAI scores (≥9) were analysed with respect to BICLA and SRI-4 responses. The RSLV-132 treated participants in the high SLEDAI subgroup had a greater percentage of BICLA responses (62% vs 44%) and SRI-4 responses (23% vs 11%) as compared with placebo. A second subgroup of participants with high baseline CLASI scores (≥21) were analysed with respect to BICLA and SRI-4 responses. The RSLV-132 treated participants in the high CLASI subgroup had a greater percentage of BICLA responses (28% vs 8%) and SRI-4 responses (39% vs 8%) as compared with placebo.

CONCLUSIONS

Six months of RSLV-132 therapy consisting of a weekly loading dose of RSLV-132 for 1 month, followed by 5 months of biweekly administrations did not significantly improve the mean CLASI score relative to placebo in this cohort of patients with SLE. The study entry criteria selected patients with moderate-severe cutaneous disease activity and no minimum SLEDAI score, which resulted in a wide range of systemic disease activity from inactive to severe as measured by SLEDAI. When the participants with higher SLEDAI and CLASI scores were analysed, a trend towards clinical improvement favouring RSLV-132 was observed. The results warrant further evaluation of RSLV-132 in SLE and suggest that patients with more active systemic disease are most likely to benefit from RNase therapy.

Edge Length-Programmed Single-Stranded RNA Origami for Predictive Innate Immune Activation and Therapy

Ligands targeting nucleic acid-sensing receptors activate the innate immune system and play a critical role in antiviral and antitumoral therapy. However, ligand design for in situ stability, targeted delivery, and predictive immunogenicity is largely hampered by the sophisticated mechanism of the nucleic acid-sensing process. Here, we utilize single-stranded RNA (ssRNA) origami with precise structural designability as nucleic acid sensor-based ligands to achieve improved biostability, organelle-level targeting, and predictive immunogenicity. The natural ssRNAs self-fold into compact nanoparticles with defined shapes and morphologies and exhibit resistance against RNase digestion in vitro and prolonged retention in macrophage endolysosomes. We find that programming the edge length of ssRNA origami can precisely regulate the degree of macrophage activation via a toll-like receptor-dependent pathway. Further, we demonstrate that the ssRNA origami-based ligand elicits an anti-tumoral immune response of macrophages and neutrophils in the tumor microenvironment and retards tumor growth in the mouse pancreatic tumor model. Our ssRNA origami strategy utilizes structured RNA ligands to achieve predictive immune activation, providing a new solution for nucleic acid sensor-based ligand design and biomedical applications.

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.

Regulatory strategies limiting endosomal Toll-like receptor activation in B cells

The recognition of pathogen-associated nucleic acid (NA) promotes effective immunity against invading pathogens. However, endosomal Toll-like receptor (TLR) activation by self-NA also underlies the pathogenesis of systemic autoimmune diseases, such as systemic lupus erythematosus (SLE). For this reason, the activation thresholds of NA-sensing TLRs must be tightly regulated to balance protective and pathogenic immune responses. In this study, we will provide an overview of the evolutionary mechanisms designed to limit the aberrant activation of endosomal TLRs by self-ligands, focusing on four broad strategies. These include the following: 1) the production of nucleases able to degrade self-DNA and RNA; 2) the cell-specific regulation of endosomal TLR expression; 3) the spatial and temporal control of TLR positioning at a sub-cellular level; and 4) the modulation of downstream TLR signaling cascades. Given the critical role of B cells in lupus pathogenesis, where possible, we will describe evidence for B cell-specific induction of these regulatory mechanisms. We will also highlight our own work showing how modulation of B cell endolysosomal flux tunes NA-sensing TLR activation signals. In the face of inevitable generation of self-NA during normal cellular turnover, these parallel mechanisms are vital to protect against pathogenic inflammation.

Emerging biological functions of ribonuclease 1 and angiogenin

Pancreatic-type ribonucleases (ptRNases) are a large family of vertebrate-specific secretory endoribonucleases. These enzymes catalyze the degradation of many RNA substrates and thereby mediate a variety of biological functions. Though the homology of ptRNases has informed biochemical characterization and evolutionary analyses, the understanding of their biological roles is incomplete. Here, we review the functions of two ptRNases: RNase 1 and angiogenin. RNase 1, which is an abundant ptRNase with high catalytic activity, has newly discovered roles in inflammation and blood coagulation. Angiogenin, which promotes neovascularization, is now known to play roles in the progression of cancer and amyotrophic lateral sclerosis, as well as in the cellular stress response. Ongoing work is illuminating the biology of these and other ptRNases.

Regulation of the nucleic acid-sensing Toll-like receptors

Many of the ligands for Toll-like receptors (TLRs) are unique to microorganisms, such that receptor activation unequivocally indicates the presence of something foreign. However, a subset of TLRs recognizes nucleic acids, which are present in both the host and foreign microorganisms. This specificity enables broad recognition by virtue of the ubiquity of nucleic acids but also introduces the possibility of self-recognition and autoinflammatory or autoimmune disease. Defining the regulatory mechanisms required to ensure proper discrimination between foreign and self-nucleic acids by TLRs is an area of intense research. Progress over the past decade has revealed a complex array of regulatory mechanisms that ensure maintenance of this delicate balance. These regulatory mechanisms can be divided into a conceptual framework with four categories: compartmentalization, ligand availability, receptor expression and signal transduction. In this Review, we discuss our current understanding of each of these layers of regulation.

Activation of nucleic acid-sensing Toll-like receptors is finely tuned to limit self-reactivity while maintaining recognition of foreign microorganisms. The authors describe recent progress made in defining the regulatory mechanisms that facilitate this delicate balance.

Nucleic Acid Sensors as Therapeutic Targets for Human Disease

Innate immune sensors that detect nucleic acids are attractive targets for therapeutic intervention because of their diverse roles in many disease processes. In detecting RNA and DNA from either self or non-self, nucleic acid sensors mediate the pathogenesis of many autoimmune and inflammatory conditions. Despite promising pre-clinical data and investigational use in the clinic, relatively few drugs targeting nucleic acid sensors are approved for therapeutic use. Nevertheless, there is growing appreciation for the untapped potential of nucleic acid sensors as therapeutic targets, driven by the need for better therapies for cancer, infectious diseases, and autoimmune disorders. This review highlights the diverse mechanisms by which nucleic acid sensors are activated and exert their biological effects in the context of various disease settings. We discuss current therapeutic strategies utilizing agonists and antagonists targeting nucleic acid sensors to treat infectious disease, cancer, and autoimmune and inflammatory disorders.

Lupus Autoimmunity and Metabolic Parameters Are Exacerbated Upon High Fat Diet-Induced Obesity Due to TLR7 Signaling

Systemic lupus erythematosus (SLE) patients have increased prevalence of metabolic syndrome but the underlying mechanisms are unknown. Toll-like receptor 7 (TLR7) that detects single stranded-RNA plays a key role in antimicrobial host defense and also contributes to the initiation and progression of SLE both in mice and humans. Here, we report the implication of TLR7 signaling in high fat diet (HFD)-induced metabolic syndrome and exacerbation of lupus autoimmunity in TLR8-deficient (TLR8ko) mice, which develop spontaneous lupus-like disease due to increased TLR7 signaling by dendritic cells (DCs). The aggravated SLE pathogenesis in HFD-fed TLR8ko mice was characterized by increased overall immune activation, anti-DNA autoantibody production, and IgG/IgM glomerular deposition that were coupled with increased kidney histopathology. Moreover, upon HFD TLR8ko mice developed metabolic abnormalities, including liver inflammation. In contrast, upon HFD TLR7/8ko mice did not develop SLE and both TLR7ko and TLR7/8ko mice were fully protected from metabolic abnormalities, including body weight gain, insulin resistance, and liver inflammation. Interestingly, HFD led to an increase of TLR7 expression in WT mice, that was coupled with increased TNF production by DCs, and this phenotype was more profound in TLR8ko mice. Our study uncovers the implication of TLR7 signaling in the interconnection of SLE and metabolic abnormalities, indicating that TLR7 might be a novel approach as a tailored therapy in SLE and metabolic diseases.

Whole exome sequencing in childhood-onset lupus frequently detects single gene etiologies

BACKGROUND

Systemic lupus erythematosus (SLE) comprise a diverse range of clinical manifestations. To date, more than 30 single gene causes of lupus/lupus like syndromes in humans have been identified. In the clinical setting, identifying the underlying molecular diagnosis is challenging due to phenotypic and genetic heterogeneity.

METHODS

We employed whole exome sequencing (WES) in patients presenting with childhood-onset lupus with severe and/or atypical presentations to identify cases that are explained by a single-gene (monogenic) cause.

RESULTS

From January 2015 to June 2018 15 new cases of childhood-onset SLE were diagnosed in Edmond and Lily Safra Children's Hospital. By WES we identified causative mutations in four subjects in five different genes: C1QC, SLC7A7, MAN2B1, PTEN and STAT1. No molecular diagnoses were established on clinical grounds prior to genetic testing.

CONCLUSIONS

We identified a significant fraction of monogenic SLE etiologies using WES and confirm the genetic locus heterogeneity in childhood-onset lupus. These results highlight the importance of establishing a genetic diagnosis for children with severe or atypical lupus by providing accurate and early etiology-based diagnoses and improving subsequent clinical management.

Peripheral blood and hepatic Toll-like receptor 7 expression and interferon lambda 1 levels in chronic hepatitis C: Relation to virus replication and liver injury

BACKGROUND AND AIM

Toll-like receptor 7 (TLR7) can recognize single-stranded RNA viruses like hepatitis C virus (HCV) with subsequent induction of different interferon (IFN) types including IFN lambda (IFNL), which activate an immediate anti-viral response. However, the role of TLR7 in inflammation and fibrosis, characteristics of HCV-induced liver injury, is still controversial. The present work was designed to investigate the potential role of TLR7 and IFNL1 in chronic hepatitis C (CHC) in relation to viral replication and liver injury.

METHODS

Forty two treatment-naïve patients with CHC and 20 healthy subjects were enrolled in the study. TLR7 expression on peripheral blood CD14+ monocytes was studied by color flow cytometry and the frequency of TLR7+CD14+ cells was expressed as percentage of total monocyte count. Quantification of IFNL1 levels in serum was determined using enzyme-linked immunosorbant assay. Liver biopsies were examined for assessment of histological activity grade (A0-A3) and fibrosis stage (F0-F4) according to METAVIR scoring system as well as steatosis grade. Immunohistochemical staining was performed using human antibodies against TLR7 and IFNL1 and was scored semi-quantitatively (score 0-3). Hepatic expression of TLR7 and IFNL1 was further classified using a two-grade scale as low expression (score 0 or 1) and high expression (score 2 or 3).

RESULTS

Percentages of circulating TLR7+CD14+ monocytes and serum IFNL1 levels were significantly higher in patients with CHC than in healthy controls (P = 0.025 and P < 0.001 respectively) and were positively correlated with corresponding hepatic TLR7 and IFNL1 expression (P < 0.001 and P = 0.010 respectively). Significantly lower peripheral blood and hepatic TLR7 expression and IFNL1 levels were found in patients with viral loads between 200,000-600,000 IU/ml and >600,000 IU/ml than in those with viral load <200,000 IU/ml (P < 0.05), in patients with severe necroinflammation than in those with mild-to-moderate necroinflammation (P < 0.05) and in patients with advanced fibrosis than in those with early fibrosis (P < 0.01). Also, changes in TLR7 expression and IFNL1 production in peripheral blood and the liver were inversely correlated with serum levels of aspartate and alanine aminotransferases (P < 0.05) and HCV RNA (P < 0.01), histological activity grade (P < 0.01) and fibrosis stage (P < 0.01). By plotting receiver operating characteristics (ROC) curve, serum IFNL1 showed higher sensitivity and specificity than percentages of circulating TLR7+CD14+ monocytes in discriminating patients with CHC according to the severity of hepatic necroinflammation (area under the curve (AUC) = 0.901 vs. 0.816 respectively) and fibrosis (AUC = 0.971 vs. 0.825 respectively) at a cut-off value of 44.75 pg/ml and 10.25% respectively.

CONCLUSIONS

TLR7 activation and IFNL1 production in CHC may play an important role in controlling viral replication and limiting hepatic inflammation and fibrosis and their downregulation may result in viral persistence and disease progression. The immunoregulatory role of TLR7-IFNL1 pathway in the pathogenesis of chronic HCV infection should be further studied. Clinical trials with a large number of patients are needed to assess the usefulness of serum IFNL1 as a potential biomarker for severity of liver injury in chronic HCV infection and other liver diseases.

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.

Role of interferons in SLE

Systemic lupus erythematosus (SLE) is a chronic inflammatory autoimmune disease that affects many different organ systems, with excessive production of type I interferons (IFNs) and autoantibodies against nucleic acids as hallmarks. Activation of the type I IFN system in SLE is due to continuous stimulation of plasmacytoid dendritic cells by endogenous nucleic acids, leading to sustained type I IFN production. This is reflected by an overexpression of type I IFN-regulated genes or an IFN signature. Type I IFNs have effects on both the innate and adaptive immune systems, which contribute to both loss of tolerance and the autoimmune disease process. In this review, we discuss the current understanding of IFNs in SLE, focusing on their regulation, the influence of genetic background, and environmental factors and therapies that are under development aiming to inhibit the type I IFN system in SLE.

Intracellular B Lymphocyte Signalling and the Regulation of Humoral Immunity and Autoimmunity

B lymphocytes are critical for effective immunity; they produce antibodies and cytokines, present antigens to T lymphocytes and regulate immune responses. However, because of the inherent randomness in the process of generating their vast repertoire of antigen-specific receptors, B cells can also cause diseases through recognizing and reacting to self. Therefore, B lymphocyte selection and responses require tight regulation at multiple levels and at all stages of their development and activation to avoid diseases. Indeed, newly generated B lymphocytes undergo rigorous tolerance mechanisms in the bone marrow and, subsequently, in the periphery after their migration. Furthermore, activation of mature B cells is regulated through controlled expression of co-stimulatory receptors and intracellular signalling thresholds. All these regulatory events determine whether and how B lymphocytes respond to antigens, by undergoing apoptosis or proliferation. However, defects that alter regulated co-stimulatory receptor expression or intracellular signalling thresholds can lead to diseases. For example, autoimmune diseases can result from altered regulation of B cell responses leading to the emergence of high-affinity autoreactive B cells, autoantibody production and tissue damage. The exact cause(s) of defective B cell responses in autoimmune diseases remains unknown. However, there is evidence that defects or mutations in genes that encode individual intracellular signalling proteins lead to autoimmune diseases, thus confirming that defects in intracellular pathways mediate autoimmune diseases. This review provides a synopsis of current knowledge of signalling proteins and pathways that regulate B lymphocyte responses and how defects in these could promote autoimmune diseases. Most of the evidence comes from studies of mouse models of disease and from genetically engineered mice. Some, however, also come from studying B lymphocytes from patients and from genome-wide association studies. Defining proteins and signalling pathways that underpin atypical B cell response in diseases will help in understanding disease mechanisms and provide new therapeutic avenues for precision therapy.

Small RNAs induce the activation of the pro-inflammatory TLR7 signaling pathway in aged rat kidney

We have recently reported that TLR-related genes, including TLR7, are upregulated during aging. However, the role of TLR7 and its endogenous ligand in inflammation related to aging is not well defined. Here, we established that small RNAs trigger age-related renal inflammation via TLR7 signaling pathway. We first investigated the expression changes of nine different TLRs in kidney of 6-month-old young rats and 20-month-old aged rats. The results revealed that the expression of TLR7 was the highest among nine TLRs in kidney of old rats compared to the young aged rats. Next, to assess the role of cellular RNA as a TLR7 ligand, we treated a renal tubular epithelial cell line with total RNA isolated from the kidney of young and old rats. The results showed that RNA isolated from old rats showed higher expression of TLR7, IL1β, and TNFα compared to that from young rats. Furthermore, RNA isolated from old rats induced IKKα/β/JNK/NF-κB activation. To identify RNA that activates TLR7, we isolated small and large RNAs from old rat kidney and found that small RNAs increased TLR7 expression in cells. Finally, to investigate the local inflammatory response by small RNA, C57B/L6 mice were intraperitoneally injected with small RNAs isolated from young and old rats; thereby, RNA isolated from old rats induced higher inflammatory responses. Our study demonstrates that renal small RNAs from aged rats induce pro-inflammatory processes via the activation of the TLR7/IKKα/β/JNK/NF-κB signaling pathway, and highlights its causative role as a possible therapeutic target in age-related chronic renal inflammation.

Cellular and Molecular Mechanisms of Autoimmunity and Lupus Nephritis

Autoimmunity involves immune responses directed against self, which are a result of defective self/foreign distinction of the immune system, leading to proliferation of self-reactive lymphocytes, and is characterized by systemic, as well as tissue-specific, inflammation. Numerous mechanisms operate to ensure the immune tolerance to self-antigens. However, monogenetic defects or genetic variants that weaken immune tolerance render susceptibility to the loss of immune tolerance, which is further triggered by environmental factors. In this review, we discuss the phenomenon of immune tolerance, genetic and environmental factors that influence the immune tolerance, factors that induce autoimmunity such as epigenetic and transcription factors, neutrophil extracellular trap formation, extracellular vesicles, ion channels, and lipid mediators, as well as costimulatory or coinhibitory molecules that contribute to an autoimmune response. Further, we discuss the cellular and molecular mechanisms of autoimmune tissue injury and inflammation during systemic lupus erythematosus and lupus nephritis.

Autophagy in Dendritic Cells and B Cells Is Critical for the Inflammatory State of TLR7-Mediated Autoimmunity

Individuals suffering from autoimmune disorders possess a hyperactive cellular phenotype where tolerance to self-antigens is lost. Autophagy has been implicated in both the induction and prevention of autoimmunity, and modulators of this cellular recycling process hold high potential for the treatment of autoimmune diseases. In this study, we determine the effects of a loss of autophagy in dendritic cells (DCs), as well as both B cells and DCs, in a TLR7-mediated model of autoimmunity, similar to systemic lupus erythematosus, where both cell types are critical for disease. Although a loss of DC autophagy slowed disease, the combined loss of autophagy in both cell types resulted in a lethal sepsis-like environment, which included tissue inflammation and hyperproduction of inflammasome-associated cytokines. Ablation of B cell signaling reversed this phenotype, indicating that activation of these cells is an essential step in disease induction. Thus, autophagy plays a dichotomous role in this model of disease.

Characterization of promoter of the tuberculosis-resistant gene intracellular pathogen resistance 1

Tuberculosis is an infectious disease caused by Mycobacterium tuberculosis, which most commonly affects the lungs and causes over 1.3 million people die annually. Variation in host genes is known to influence susceptibility to tuberculosis. Expression of the intracellular pathogen resistance 1 (Ipr1) gene could enhance the host resistance to mycobacterium. Here, we analyzed the coding region sequence and promoter of Ipr1 gene of mouse strains C57BL/6 and BALB/c. We found that the coding sequences of Ipr1 gene both in C57BL/6 and in BALB/c mice encode the same protein, while the Ipr1 promoter of BALB/c exists a short deletion and showed a slight of decreased transcriptional activity when compared with C57BL/6. Moreover, the optimal and minimal Ipr1 promoter was identified by luciferase assays using truncated reporter constructs, and the region from -293 to +95 bp showed the highest transcriptional activity and responsible for IFN-γ stimulation. Furthermore, the results showed that IFN-γ activates JAK/STAT and NF-κB signaling pathways to induce Ipr1 expression, and the signal transducer and activator of transcription 1 (Stat1) are critical for IFN-γ-induced Ipr1 expression, because overexpression of Stat1 promotes Ipr1 transcription, but knockdown of Stat1 reduced Ipr1 expression. Collectively, for the first time, our study characterizes Ipr1 promoter and investigates the positive and negative regulation of Ipr1 expression, providing basic data for application of Ipr1 in animal breeding.

An L-RNA Aptamer that Binds and Inhibits RNase

L-RNA aptamers were developed that bind to barnase RNase and thereby inhibit the function of the enzyme. These aptamers were obtained by first carrying out in vitro selection of D-RNAs that bind to the full-length synthetic D-enantiomer of barnase, then reversing the mirror and preparing L-RNAs of identical sequence that similarly bind to natural L-barnase. The resulting L-aptamers bind L-barnase with an affinity of ∼100 nM and function as competitive inhibitors of enzyme cleavage of D-RNA substrates. L-RNA aptamers are resistant to degradation by ribonucleases, thus enabling them to function in biological samples, most notably for applications in molecular diagnostics and therapeutics. In addition to the irony of using RNA to inhibit RNase, L-RNA aptamers such as those described here could be used to measure the concentration or inhibit the function of RNase in the laboratory or in biological systems.

Scavenging nucleic acid debris to combat autoimmunity and infectious disease

Nucleic acid-containing debris released from dead and dying cells can be recognized as damage-associated molecular patterns (DAMPs) or pattern-associated molecular patterns (PAMPs) by the innate immune system. Inappropriate activation of the innate immune response can engender pathological inflammation and autoimmune disease. To combat such diseases, major efforts have been made to therapeutically target the pattern recognition receptors (PRRs) such as the Toll-like receptors (TLRs) that recognize such DAMPs and PAMPs, or the downstream effector molecules they engender, to limit inflammation. Unfortunately, such strategies can limit the ability of the immune system to combat infection. Previously, we demonstrated that nucleic acid-binding polymers can act as molecular scavengers and limit the ability of artificial nucleic acid ligands to activate PRRs. Herein, we demonstrate that nucleic acid scavengers (NASs) can limit pathological inflammation and nucleic acid-associated autoimmunity in lupus-prone mice. Moreover, we observe that such NASs do not limit an animal's ability to combat viral infection, but rather their administration improves survival when animals are challenged with lethal doses of influenza. These results indicate that molecules that scavenge extracellular nucleic acid debris represent potentially safer agents to control pathological inflammation associated with a wide range of autoimmune and infectious diseases.

Targeted therapeutics in SLE: emerging strategies to modulate the interferon pathway

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by impaired immune tolerance, resulting in the generation of pathogenic autoantibodies and immune complexes. Although autoreactive B lymphocytes have been the first targets for biologic therapies in SLE, the importance of the innate immune system, and in particular, pathways involved in interferon (IFN) signaling, has emerged. There are now data supporting a central role for a plasmacytoid dendritic cell-derived type I IFN pathway in SLE, with a number of biologic therapeutics and small-molecule inhibitors undergoing clinical trials. Monoclonal antibodies targeting IFN-α have completed phase II clinical trials, and an antibody against the type I IFN receptor is entering a phase III trial. However, other IFNs, such as IFN gamma, and the more recently discovered type III IFNs, are also emerging as targets in SLE; and blockade of upstream components of the IFN signaling pathway may enable inhibition of more than one IFN subtype. In this review, we discuss the current understanding of IFNs in SLE, focusing on emerging therapies.

Cause and consequences of the activated type I interferon system in SLE

Patients with systemic lupus erythematosus (SLE) have an increased expression of type I interferon (IFN)-regulated genes (an IFN signature), which is caused by an ongoing production of type I IFNs by plasmacytoid dendritic cells (pDCs). The reasons behind the continuous IFN production in SLE are the presence of self-derived IFN inducers and a lack of negative feed-back signals that downregulate the IFN response. In addition, several cells in the immune system promote the IFN production by pDCs and gene variants in the type I IFN signaling pathway contribute to the IFN signature. The type I IFNs act as an immune adjuvant and stimulate T cells, B cells, and monocytes, which all play an important role in the loss of tolerance and persistent autoimmune reaction in SLE. Consequently, new treatments aiming to inhibit the activated type I IFN system in SLE are now being developed and investigated in clinical trials.

B cell autophagy mediates TLR7-dependent autoimmunity and inflammation

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease, defined by loss of B cell self-tolerance that results in production of antinuclear antibodies (ANA) and chronic inflammation. While the initiating events in lupus development are not well defined, overexpression of the RNA-recognizing toll-like receptor (TLR)7 has been linked to SLE in humans and mice. We postulated that autophagy plays an essential role in TLR7 activation of B cells for the induction of SLE by delivering RNA ligands to the endosomes, where this innate immune receptor resides. To test this hypothesis, we compared SLE development in Tlr7 transgenic (Tg) mice with or without B cell-specific ablation of autophagy (Cd19-Cre Atg5(f/f)). We observed that in the absence of B cell autophagy the 2 hallmarks of SLE, ANA and inflammation, were eliminated, thus curing these mice of lupus. This was also evident in the significantly extended survival of the autophagy-deficient mice compared to Tlr7.1 Tg mice. Furthermore, glomerulonephritis was ameliorated, and the serum levels of inflammatory cytokines in the knockout (KO) mice were indistinguishable from those of control mice. These data provide direct evidence that B cells require TLR7-dependent priming through an autophagy-dependent mechanism before autoimmunity is induced, thereafter involving many cell types. Surprisingly, hyper-IgM production persisted in Tlr7.1 Tg mice in the absence of autophagy, likely involving a different activation pathway than the production of autoantibodies. Furthermore, these mice still presented with anemia, but responded with a striking increase in extramedullary hematopoiesis (EMH), possibly due to the absence of pro-inflammatory cytokines.

What can pestiviral endonucleases teach us about innate immunotolerance?

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In this review, we describe the identification of the PRRs involved in the recognition of pestiviruses, and the mechanisms of these viruses to prevent the activation of host’s innate immune response with special emphasis on viral RNases.

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Most importantly, we extend these data and present our model of innate immunotolerance requiring continuous prevention of detection of immunostimulatory self nucleic acids, in contrast to the well-known long-term tolerance of the adaptive immune system targeted predominantly against proteins.

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This hypothesis is very likely relevant beyond the bovine species and might answer more fundamental questions on the discrimination between “self” and “viral nonself RNA”, which are relevant also for the prevention and treatment of chronic IFN induction and autoimmunity induced by “self-RNAs”.

Pestiviruses including bovine viral diarrhea virus (BVDV), border disease virus (BDV) and classical swine fever virus (CSFV), occur worldwide and are important pathogens of livestock. A large part of their success can be attributed to the induction of central immunotolerance including B- and T-cells upon fetal infection leading to the generation of persistently infected (PI) animals. In the past few years, it became evident that evasion of innate immunity is a central element to induce and maintain persistent infection. Hence, the viral non-structural protease N^pro heads the transcription factor IRF-3 for proteasomal degradation, whereas an extracellularly secreted, soluble form of the envelope glycoprotein E^rns degrades immunostimulatory viral single- and double-stranded RNA, which makes this RNase unique among viral endoribonucleases. We propose that these pestiviral interferon (IFN) antagonists maintain a state of innate immunotolerance mainly pertaining its viral nucleic acids, in contrast to the well-established immunotolerance of the adaptive immune system, which is mainly targeted at proteins. In particular, the unique extension of ‘self’ to include the viral genome by degrading immunostimulatory viral RNA by E^rns is reminiscent of various host nucleases that are important to prevent inappropriate IFN activation by the host’s own nucleic acids in autoimmune diseases such as Aicardi-Goutières syndrome or systemic lupus erythematosus. This mechanism of “innate tolerance” might thus provide a new facet to the role of extracellular RNases in the sustained prevention of the body’s own immunostimulatory RNA to act as a danger-associated molecular pattern that is relevant across various species.

Nucleic Acid-Sensing Receptors: Rheostats of Autoimmunity and Autoinflammation

Distinct families of germline-encoded pattern recognition receptors can sense both microbial and endogenous nucleic acids. These DNA and RNA sensors include endosomal TLRs and cytosolic sensors upstream of stimulator of type I IFN genes (STING) and MAVS. The existence of overlapping specificities for both foreign and self nucleic acids suggests that, under optimal conditions, the activity of these receptors is finely tuned to effectively mediate host defense yet constrain pathogenic self-reactivity. This equilibrium becomes disrupted with the loss of either TLR9 or STING. To maintain immune protection, this loss can be counterbalanced by the elevated response of an alternative receptor(s). Unfortunately, this adjustment can lead to an increased risk for the development of systemic autoimmunity, as evidenced by the exacerbated clinical disease manifestations of TLR9-deficient and STING-deficient autoimmune-prone mice. These studies underscore the delicate balance normally maintained by tonic signals that prevent unchecked immune responses to nucleic acids released during infections and cellular duress or death.

Systemic Lupus Erythematosus--A Disease with A Dysregulated Type I Interferon System

Systemic lupus erythematosus (SLE) is a complex systemic autoimmune disease characterized by the loss of tolerance to nuclear antigens, immune complex formation and inflammation in multiple organs. The disease is very heterogeneous, and most clinicians consider SLE as a group of diseases with similar features where the pathogenesis is driven by a combination of genetic and environmental factors. One of the most prominent features, shared by the majority of patients with SLE, is a continuous activation of the type I interferon (IFN) system, which manifests as increased serum levels of IFNα and/or an increased expression of type I IFN-induced genes, a so-called type I IFN signature. The mechanisms behind this IFN signature have partly been clarified during recent years, although the exact function of the IFN-regulated genes in the disease process is unclear. In this review, we will describe the type I IFN system and its regulation and summarize the numerous findings implicating an important ethiopathogenic role of a dysregulated type I IFN system in SLE. Furthermore, strategies to therapeutically target the type I IFN system that are currently evaluated preclinically and in clinical trials will be mentioned.

Translating nucleic acid-sensing pathways into therapies

Nucleic acid sensing by innate receptors initiates immune defences against viruses and other pathogens. A hallmark of this response is the release of interferons (IFNs), which promote protective immunity by inducing IFN-stimulated genes (ISGs). A similar ISG signature is found in autoinflammatory and autoimmune conditions, indicating that chronic activation of nucleic acid-sensing pathways may contribute to these diseases. Here, we review how nucleic acid-sensing pathways are currently being targeted pharmacologically with both agonists and antagonists. We discuss how an improved understanding of the biology of these pathways is leading to novel therapies for infections, cancer, and autoimmune and autoinflammatory disorders, and how new therapeutics will, in turn, generate a deeper understanding of these complex diseases.

Beyond apoptosis in lupus

PURPOSE OF REVIEW

Systemic lupus erythematosus (SLE) is characterized by autoantibodies directed against nuclear autoantigens normally concealed from immune recognition in healthy individuals. Here, we summarize recently identified mechanisms of abnormal cell death leading to exposure and aberrant processing of nucleoprotein self antigens, and discuss their role in the SLE pathogenesis.

RECENT FINDINGS

During the past few years, the unveiling of several new forms of cell death has expanded our understanding beyond the simple view of 'apoptotic' versus 'necrotic' cell death. SLE patients show abnormalities in cell death at several levels, including increased rates of apoptosis, necrosis, and autophagy, as well as reduced clearance of dying cells. These abnormalities lead to an increased autoantigen burden and antigen modifications, such as nucleic acid oxidation that increases the inflammatory properties of self antigens. Recent investigations have highlighted the role of opsonins in determining the immunogenic versus tolerogenic characteristics of self antigens.

SUMMARY

Dysregulation of different forms of programmed cell death contributes to increased exposure, availability, and immunogenic characteristics of intracellular self antigens, which all participate in development of lupus autoimmunity. As our understanding of abnormalities of cell death in SLE advances, potential therapeutic opportunities await human implementation.

Advances in understanding the role of type I interferons in systemic lupus erythematosus

PURPOSE OF REVIEW

Advances in understanding the genetic and molecular basis of innate immune system activation and function have supported the hypothesis that type I interferons (IFN-I), the essential mediators of antiviral host defense, are central contributors to the pathogenesis of systemic lupus erythematosus (SLE). This review addresses the recent data that support the rationale for therapeutic targeting of the IFN-I pathway in SLE.

RECENT FINDINGS

New insights into the mechanisms of cell-intrinsic innate immune system activation, driven by endogenous virus-like nucleic acids and potentially modified by environmental stressors, provide a model for the induction of IFN-I that may precede the clinically apparent autoimmunity in patients with lupus. Further amplification of IFN-α production, induced by nucleic-acid-containing immune complexes that activate endosomal Toll-like receptors, augments and sustains immune system activation, autoimmunity and tissue damage.

SUMMARY

As demonstrated in the murine studies of persistent virus infection accompanied by sustained production of IFN-I, blockade of the IFN-I pathway may reverse the immune dysregulation and tissue damage that are the essential features of the immunopathogenesis of SLE. Recent research progress has identified numerous therapeutic targets, and specific candidate therapeutics relevant to the IFN-I pathway are under investigation.

B cells take the front seat: dysregulated B cell signals orchestrate loss of tolerance and autoantibody production

A significant proportion of autoimmune-associated genetic variants are expressed in B cells, suggesting that B cells may play multiple roles in autoimmune pathogenesis. In this review, we highlight recent studies demonstrating that even modest alterations in B cell signaling are sufficient to promote autoimmunity. First, we describe several examples of genetic variations promoting B cell-intrinsic initiation of autoimmune germinal centers and autoantibody production. We highlight how dual antigen receptor/toll-like receptor signals greatly facilitate this process and how activated, self-reactive B cells may function as antigen presenting cells, leading to loss of T cell tolerance. Further, we propose that B cell-derived cytokines may initiate and/or sustain autoimmune germinal centers, likely also contributing, in parallel, to programing of self-reactive T cells.

Targeting of type I interferon in systemic autoimmune diseases

Increased blood levels of type I interferon (IFN-I) and expression of a broad signature of gene transcripts that reflect induction by IFN-I are observed in many patients with systemic autoimmune diseases, and that pattern is most striking in systemic lupus erythematosus (SLE). Persistent production of IFN-α, the most abundant subtype measured in these patients, is an important feature of the immunopathogenesis of lupus and has stimulated current efforts to develop and test therapeutics that either block IFN-I or its receptor directly or target components of the IFN-I pathway involved in induction of or response to IFN-I. In this review data from animal models of chronic viral infection, examples of lupus-like syndromes associated with single-gene mutations that impact the IFN-I pathway, and longitudinal studies of patients with lupus are described and support the rationale for therapeutic targeting of the IFN-I pathway. However, the complexity of IFN-I regulation and the diversity of its effects on immune system function suggest that the definitive demonstration of that pathway as a valid and productive therapeutic target will only come from clinical trials of agents tested in patients with systemic autoimmune disease, with patients with lupus likely to be the most informative.

Toll-like receptors in systemic lupus erythematosus: potential for personalized treatment

Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterized by the loss of tolerance to self-nuclear antigens. The symptoms of SLE, progression of pathology and the array of autoantibodies present in the serum differ significantly from patient to patient, which calls for a personalized approach to treatment. SLE is polygenic and strongly influenced by gender, ethnicity, and environmental factors. Data from genome-wide association studies suggests that polymorphisms in as many as 100 genes contribute to SLE susceptibility. Recent research has focused on genes associated with Toll-like receptors (TLRs), type I interferons, immune regulation pathways, and immune-complex clearance. TLR7 and TLR9 have been extensively studied using lupus-prone mouse models. In multiple systems overexpression of TLR7 drives disease progression but interestingly, a loss of TLR9 results in an almost identical phenotype. While TLR7 overexpression has been linked to human SLE, the possible role of TLR9 in human disease remains elusive. In the present review, we focus on TLR polymorphisms and TLR expression in SLE patients and discuss their potential as biomarkers for individualized treatment.

B cell-intrinsic TLR7 signaling is essential for the development of spontaneous germinal centers

Spontaneous germinal center (Spt-GC) B cells and follicular helper T cells generate high-affinity autoantibodies that are involved in the development of systemic lupus erythematosus. TLRs play a pivotal role in systemic lupus erythematosus pathogenesis. Although previous studies focused on the B cell-intrinsic role of TLR-MyD88 signaling on immune activation, autoantibody repertoire, and systemic inflammation, the mechanisms by which TLRs control the formation of Spt-GCs remain unclear. Using nonautoimmune C57BL/6 (B6) mice deficient in MyD88, TLR2, TLR3, TLR4, TLR7, or TLR9, we identified B cell-intrinsic TLR7 signaling as a prerequisite to Spt-GC formation without the confounding effects of autoimmune susceptibility genes and the overexpression of TLRs. TLR7 deficiency also rendered autoimmune B6.Sle1b mice unable to form Spt-GCs, leading to markedly decreased autoantibodies. Conversely, B6.yaa and B6.Sle1b.yaa mice expressing an extra copy of TLR7 and B6.Sle1b mice treated with a TLR7 agonist had increased Spt-GCs and follicular helper T cells. Further, TLR7/MyD88 deficiency led to compromised B cell proliferation and survival after B cell stimulation both in vitro and in vivo. In contrast, TLR9 inhibited Spt-GC development. Our findings demonstrate an absolute requirement for TLR7 and a negative regulatory function for TLR9 in Spt-GC formation under nonautoimmune and autoimmune conditions. Our data suggest that, under nonautoimmune conditions, Spt-GCs initiated by TLR7 produce protective Abs. However, in the presence of autoimmune susceptibility genes, TLR7-dependent Spt-GCs produce pathogenic autoantibodies. Thus, a single copy of TLR7 in B cells is the minimal requirement for breaking the GC-tolerance checkpoint.

Type I interferon in the pathogenesis of lupus

Investigations of patients with systemic lupus erythematosus have applied insights from studies of the innate immune response to define IFN-I, with IFN-α as the dominant mediator, as central to the pathogenesis of this prototype systemic autoimmune disease. Genetic association data identify regulators of nucleic acid degradation and components of TLR-independent, endosomal TLR-dependent, and IFN-I-signaling pathways as contributors to lupus disease susceptibility. Together with a gene expression signature characterized by IFN-I-induced gene transcripts in lupus blood and tissue, those data support the conclusion that many of the immunologic and pathologic features of this disease are a consequence of a persistent self-directed immune reaction driven by IFN-I and mimicking a sustained antivirus response. This expanding knowledge of the role of IFN-I and the innate immune response suggests candidate therapeutic targets that are being tested in lupus patients.

Bovine brain ribonuclease is the functional homolog of human ribonuclease 1

Mounting evidence suggests that human pancreatic ribonuclease (RNase 1) plays important roles in vivo, ranging from regulating blood clotting and inflammation to directly counteracting tumorigenic cells. Understanding these putative roles has been pursued with continual comparisons of human RNase 1 to bovine RNase A, an enzyme that appears to function primarily in the ruminant gut. Our results imply a different physiology for human RNase 1. We demonstrate distinct functional differences between human RNase 1 and bovine RNase A. Moreover, we characterize another RNase 1 homolog, bovine brain ribonuclease, and find pronounced similarities between that enzyme and human RNase 1. We report that human RNase 1 and bovine brain ribonuclease share high catalytic activity against double-stranded RNA substrates, a rare quality among ribonucleases. Both human RNase 1 and bovine brain RNase are readily endocytosed by mammalian cells, aided by tight interactions with cell surface glycans. Finally, we show that both human RNase 1 and bovine brain RNase are secreted from endothelial cells in a regulated manner, implying a potential role in vascular homeostasis. Our results suggest that brain ribonuclease, not RNase A, is the true bovine homolog of human RNase 1, and provide fundamental insight into the ancestral roles and functional adaptations of RNase 1 in mammals.

Spontaneous activation of RNA-sensing pathways in autoimmune disease

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

Type I IFN signature in primary Sjögren's syndrome patients

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease characterized by lymphocytic infiltrates in salivary and lacrimal glands. Clinical manifestations range from ocular and oral dryness to vasculitis and severe fatigue. pSS is a disease with heterogeneous symptoms and a variable response to the available treatment. Recently, a key role for Interferon (IFN) type I has been implicated in the pathogenesis of pSS. As type I IFN consists of 17 different subtypes, it cannot be easily assessed using a conventional ELISA. Therefore the expression of type I IFN inducible genes--the so-called type I IFN signature--is assessed in salivary gland tissue and blood from patients as a readout for type I IFN activity. In this review we discuss the potential of type I IFN as a novel biomarker for disease activity, subclassification of patients, prediction of therapy response and most importantly as a target for therapeutic intervention.

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.