Evolutionarily conserved Otub1 suppresses antiviral immune response by promoting Irf3 proteasomal degradation in miiuy croaker, Miichthys miiuy

Increasing evidence has been shown that OTUB1, a member of OTU deubiquitinases, is of importance in regulating the immune system. However, its molecular identification and functional characterization in teleosts are still rarely known. In this work, we cloned the otub1 of miiuy croaker (Miichthys miiuy), analyzed its sequence, structure, and evolution at genetic and protein levels, and determined its function in the antiviral immune response. The complete open reading frame (ORF) of miiuy croaker otub1 is 843 bp in length, encoding 280 amino acids. Miiuy croaker Otub1 has an OTU domain at the carboxyl terminus, which is a common functional domain that exists in OTU deubiquitinases. Molecular characteristics and evolution analysis results indicated that miiuy croaker Otub1, especially its functional domain, is highly conserved during evolution. The luciferase reporter assays showed that miiuy croaker Otub1 could significantly inhibit the poly(I:C) and Irf3-induced IFN1 and IFN-stimulated response element (ISRE) activation. Further experiments showed that miiuy croaker Otub1 decreases Irf3 protein abundance by promoting its proteasomal degradation. These data suggest that the evolutionarily conserved Otub1 acts as a suppressor in controlling antiviral immune response by promoting Irf3 proteasomal degradation in miiuy croaker.

cGAS-STING pathway in systemic lupus erythematosus: biological implications and therapeutic opportunities

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has been identified as a significant modulator of inflammation in various clinical contexts, including infection, cellular stress, and tissue injury. The extensive participation of the cGAS-STING pathway can be attributed to its ability to detect and control the cellular reaction to DNAs originating from both microorganisms and hosts. These DNAs are well recognized as molecules linked with potential risks. At physiological levels, the STING signaling system exhibits protective effects. However, prolonged stimulation of this pathway contributes to autoimmune disorder pathogenesis. The present paper provides an overview of the activation mechanism of the cGAS-STING signaling pathways and their associated significant functions, as well as therapeutic interventions in the context of systemic lupus erythematosus (SLE). The primary objective is to enhance our comprehension of SLE and facilitate more effective diagnosis and treatment strategies for this condition.

Nucleic Acid Materials-Mediated Innate Immune Activation for Cancer Immunotherapy

Abnormally localized nucleic acids (NAs) are considered as pathogen associated molecular patterns (PAMPs) in innate immunity. They are recognized by NAs-specific pattern recognition receptors (PRRs), leading to the activation of associated signaling pathways and subsequent production of type I interferons (IFNs) and pro-inflammatory cytokines, which further trigger the adaptive immunity. Notably, NAs-mediated innate immune activation is highly dependent on the conformation changes, especially the aggregation of PRRs. Evidence indicates that the characteristics of NAs including their length, concentration and even spatial structure play essential roles in inducing the aggregation of PRRs. Therefore, nucleic acid materials (NAMs) with high valency of NAs and high-order structures hold great potential for activating innate and adaptive immunity, making them promising candidates for cancer immunotherapy. In recent years, a variety of NAMs have been developed and have demonstrated significant efficacy in achieving satisfactory anti-tumor immunity in multiple mouse models, exhibiting huge potential for clinical application in cancer treatment. This review aims to discuss the mechanisms of NAMs-mediated innate immune response, and summarize their applications in cancer immunotherapy.

Harnessing cGAS-STING axis for therapeutic benefits in systemic lupus erythematosus

The cyclic GMP-AMP synthase (cGAS), a prominent intracellular DNA sensor in mammalian cells, controls the innate immune response and the stimulator of interferon genes (STING)-mediated synthesis of pro-inflammatory cytokines, such as type-I interferon (IFN-I). For decades, IFN-I has been hypothesized to be essential in the development of systemic lupus erythematosus (SLE), a chronic multisystem autoimmunity characterized by immune complex (IC) deposition in small vessels. Recent findings revealed that the activation of the cGAS-STING pathway by self-DNA would propagate the autoimmune responses via upregulating IFN-I production in SLE. In this review, we aimed to provide a comprehensive outlook of the role of the cGAS-STING pathway in SLE pathobiology, as well as, a better understanding of current therapeutic opportunities targeting this axis.

MHC class I-dressing is mediated via phosphatidylserine recognition and is enhanced by polyI:C

In addition to cross-presentation, cross-dressing plays an important role in the induction of CD8+ T cell immunity. In the process of cross-dressing, conventional dendritic cells (DCs) acquire major histocompatibility complex class I (MHCI) from other cells and subsequently prime CD8+ T cells via the pre-formed antigen-MHCI complexes without antigen processing. However, the mechanisms underlying the cross-dressing pathway, as well as the relative contributions of cross-presentation and cross-dressing to CD8+ T cell priming are not fully understood. Here, we demonstrate that DCs rapidly acquire MHCI-containing membrane fragments from dead cells via the phosphatidylserine recognition-dependent mechanism for cross-dressing. The MHCI dressing is enhanced by a TLR3 ligand polyinosinic-polycytidylic acid (polyI:C). Further, polyI:C promotes not only cross-presentation but also cross-dressing in vivo. Taken together, these results suggest that cross-dressing as well as cross-presentation is involved in inflammatory diseases associated with cell death and type I IFN production.

Modulation of plasmacytoid dendritic cells response in inflammation and autoimmunity

The discovery of toll-like receptors (TLRs) and the subsequent recognition that endogenous nucleic acids (NAs) could serve as TLR ligands have led to essential insights into mechanisms of healthy immune responses as well as pathogenic mechanisms relevant to systemic autoimmune and inflammatory diseases. In systemic lupus erythematosus, systemic sclerosis, and rheumatoid arthritis, NA-containing immune complexes serve as TLR ligands, with distinct implications depending on the additional immune stimuli available. Plasmacytoid dendritic cells (pDCs), the robust producers of type I interferon (IFN-I), are providing critical insights relevant to TLR-mediated healthy immune responses and tissue repair, as well as generation of inflammation, autoimmunity and fibrosis, processes central to the pathogenesis of many autoimmune diseases. In this review, we describe recent data characterizing the role of platelets and NA-binding chemokines in modulation of TLR signaling in pDCs, as well as implications for how the IFN-I products of pDCs contribute to the generation of inflammation and wound healing responses by monocyte/macrophages. Chemokine modulators of TLR-mediated B cell tolerance mechanisms and interactions between TLR signaling and metabolic pathways are also considered. The modulators of TLR signaling and their contribution to the pathogenesis of systemic autoimmune diseases suggest new opportunities for identification of novel therapeutic targets.

Immunostimulation of Asian elephant (Elephas maximus) blood cells by parapoxvirus ovis and CpG motif-containing bacterial plasmid DNA upregulates innate immune gene expression

The immune system of Asian elephants (Elephas maximus) is poorly studied, compared to that of livestock, rodents or humans. The innate immune response has become a focus of interest in relation to Elephant endotheliotropic herpesviruses (EEHVs). EEHVs cause a fatal hemorrhagic disease (EEHV-HD) and are a significant threat to captive Asian elephant populations worldwide. Similar to other herpesvirus infections, nearly all animals become infected, but only some develop disease. As progression to EEHV-HD is often acute, a robust innate immune response is crucial to control EEHV infections. This is invariably true of the host in the first instance, but it can also potentially be modulated by intervention strategies. Here, two immunostimulant veterinary medicinal products, authorized for use in domestic species, were tested for their ability to induce innate anti-viral immune responses in Asian elephant blood cells. Sequence data were obtained for a range of previously unidentified Asian elephant immune genes, including C-X-C motif chemokine ligand 10 (CXCL10), interferon stimulated gene 15 (ISG15) and myxovirus GTPase 1 (Mx1), and were employed in the design of species-specific qPCR assays. These assays were subsequently used in analyses to determine fold changes in gene expression over a period of 24 hours. This study demonstrates that both immunostimulant medications are capable of inducing significant innate anti-viral immune responses which suggests that both could be beneficial in controlling EEHV infections in Asian elephants.

Major low-energy trauma results in non-specific immunoglobulin generation without evidence for specific autoantibody production: A prospective cohort study

Cellular debris resulting from large trauma might overwhelm the scavenger mechanisms and lead to autoimmune reactions. We analysed whether a major well-defined trauma in humans induces laboratory signs of transient autoimmunity in the months after the insult. We included 50 patients with pertrochanteric femur fracture undergoing intramedullary nail osteosynthesis in a prospective cohort study and followed them at 3-4 days, 6 weeks, 12 weeks and 12 months postoperatively. By standard techniques, we assessed levels of total immunoglobulins, anti-nuclear antibodies (ANA), anti-cardiolipin antibodies, anti-dsDNA antibodies and anti-C1q antibodies, as well as antibodies against cytomegalovirus (CMV) as a control. Blood leukocyte differential and lymphocyte subpopulations were determined at baseline and in the first two postoperative samples. The mean age of the patients reached 80.1 years, and 23 (46%) completed all visits. Serum concentrations of total IgG, IgM and IgA increased at all follow-up time points. The ANA fluorescence light intensity units increased at 12 weeks and 12 months postoperatively (p < 0.0001), but the proportion of ANA-positive patients did not change (35%). The values of anti-C1q mildly increased at all follow-up visits, but not the ratio to total IgG. Anti-dsDNA remained negative in all patients, and anti-cardiolipin IgG/IgM antibodies did not change. Anti-CMV IgG antibodies increased significantly at all follow-up visits, without change in the ratio to total IgG. Flow cytometry showed an increased proportion of B-cells 3-4 days postoperatively. In conclusion, major musculoskeletal trauma in elderly patients induces a generalized non-specific increase in immunoglobulin production without laboratory signs for enhanced systemic autoimmunity.

Dichotomous roles of RIPK3 in regulating the IFN response and NLRP3 inflammasome in human monocytes

Regulation of the profile and magnitude of toll-like receptor (TLR) responses is important for effective host defense against infections while minimizing inflammatory toxicity. The chemokine CXCL4 regulates the TLR8 response to amplify inflammatory gene and inflammasome activation while attenuating the interferon (IFN) response in primary monocytes. In this study, we describe an unexpected role for the kinase RIPK3 in suppressing the CXCL4 + TLR8-induced IFN response and providing signal 2 to activate the NLRP3 inflammasome and interleukin (IL)-1 production in primary human monocytes. RIPK3 also amplifies induction of inflammatory genes such as TNF, IL6, and IL1B while suppressing IL12B. Mechanistically, RIPK3 inhibits STAT1 activation and activates PI3K-Akt-dependent and XBP1- and NRF2-mediated stress responses to regulate downstream genes in a dichotomous manner. These findings identify new functions for RIPK3 in modulating TLR responses and provide potential mechanisms by which RIPK3 plays roles in inflammatory diseases and suggest targeting RIPK3 and XBP1- and NRF2-mediated stress responses as therapeutic strategies to suppress inflammation while preserving the IFN response for host defense.

The E3 ligase Riplet promotes RIG-I signaling independent of RIG-I oligomerization

RIG-I is an essential innate immune receptor that responds to infection by RNA viruses. The RIG-I signaling cascade is mediated by a series of post-translational modifications, the most important of which is ubiquitination of the RIG-I Caspase Recruitment Domains (CARDs) by E3 ligase Riplet. This is required for interaction between RIG-I and its downstream adapter protein MAVS, but the mechanism of action remains unclear. Here we show that Riplet is required for RIG-I signaling in the presence of both short and long dsRNAs, establishing that Riplet activation does not depend upon RIG-I filament formation on long dsRNAs. Likewise, quantitative Riplet-RIG-I affinity measurements establish that Riplet interacts with RIG-I regardless of whether the receptor is bound to RNA. To understand this, we solved high-resolution cryo-EM structures of RIG-I/RNA/Riplet complexes, revealing molecular interfaces that control Riplet-mediated activation and enabling the formulation of a unified model for the role of Riplet in signaling.

Development of cyclopeptide inhibitors of cGAS targeting protein-DNA interaction and phase separation

Cyclic GMP-AMP synthase (cGAS) is an essential sensor of aberrant cytosolic DNA for initiating innate immunity upon invading pathogens and cellular stress, which is considered as a potential drug target for autoimmune and autoinflammatory diseases. Here, we report the discovery of a class of cyclopeptide inhibitors of cGAS identified by an in vitro screening assay from a focused library of cyclic peptides. These cyclopeptides specifically bind to the DNA binding site of cGAS and block the binding of dsDNA with cGAS, subsequently inhibit dsDNA-induced liquid phase condensation and activation of cGAS. The specificity and potency of one optimal lead XQ2B were characterized in cellular assays. Concordantly, XQ2B inhibited herpes simplex virus-1 (HSV-1)-induced antiviral immune responses and enhanced HSV-1 infection in vitro and in vivo. Furthermore, XQ2B significantly suppressed the elevated levels of type I interferon and proinflammatory cytokines in primary macrophages from Trex1-/- mice and systemic inflammation in Trex1-/- mice. XQ2B represents the specific cGAS inhibitor targeting protein-DNA interaction and phase separation and serves as a scaffold for the development of therapies in the treatment of cGAS-dependent inflammatory diseases.

TLR8 escapes X chromosome inactivation in human monocytes and CD4+ T cells

BACKGROUND

Human endosomal Toll-like receptors TLR7 and TLR8 recognize self and non-self RNA ligands, and are important mediators of innate immunity and autoimmune pathogenesis. TLR7 and TLR8 are, respectively, encoded by adjacent X-linked genes. We previously established that TLR7 evades X chromosome inactivation (XCI) in female immune cells. Whether TLR8 also evades XCI, however, has not yet been explored.

METHOD

In the current study, we used RNA fluorescence in situ hybridization (RNA FISH) to directly visualize, on a single-cell basis, primary transcripts of TLR7 and TLR8 relative to X chromosome territories in CD14+ monocytes and CD4+ T lymphocytes from women, Klinefelter syndrome (KS) men, and euploid men. To assign X chromosome territories in cells lacking robust expression of a XIST compartment, we designed probes specific for X-linked genes that do not escape XCI and therefore robustly label the active X chromosome. We also assessed whether XCI escape of TLR8 was associated with sexual dimorphism in TLR8 protein expression by western blot and flow cytometry.

RESULTS

Using RNA FISH, we show that TLR8, like TLR7, evades XCI in immune cells, and that cells harboring simultaneously TLR7 and TLR8 transcript foci are more frequent in women and KS men than in euploid men, resulting in a sevenfold difference in frequency. This transcriptional bias was again observable when comparing the single X of XY males with the active X of cells from females or KS males. Interestingly, TLR8 protein expression was significantly higher in female mononuclear blood cells, including all monocyte subsets, than in male cells.

CONCLUSIONS

TLR8, mirroring TLR7, escapes XCI in human monocytes and CD4+ T cells. Co-dependent transcription from the active X chromosome and escape from XCI could both contribute to higher TLR8 protein abundance in female cells, which may have implications for the response to viruses and bacteria, and the risk of developing inflammatory and autoimmune diseases.

Amplification-Free Nucleic Acid Testing with a Fluorescence One-Step-Branched DNA-Based Lateral Flow Assay (FOB-LFA)

The emergence of the global pandemic and the discovery of nucleic acid biomarkers in cancer diagnosis have fostered the development of more accurate and adaptive molecular diagnosis technologies. Current nucleic acid testing (NAT) methods either lack sensitivity or require tedious amplification operations, which could not meet the need for point-of-care (POC) NAT for on-site and community-based diagnosis. Here, we present a fluorescence one-step-bDNA-based lateral flow assay (FOB-LFA) method for amplification-free NAT to realize point-of-care pathogen detection and disease diagnosis. Take COVID-19 as an example, the developed FOB-LFA demonstrated a high sensitivity of 300 copies/mL for the RNA of the SARS-CoV-2 pseudovirus and exhibited high specificity among various homologous pseudoviruses. Further, the result of oropharyngeal swab sample detection suggested the great potential of FOB-LFA in clinical examination. The outstanding performance of FOB-LFA, including high sensitivity, high specificity, low cost, excellent portability, and minimized risk of nucleic acid leakage and contamination, can meet the POC testing demand for the diagnosis of various infectious and genetic diseases.

TLR pathway signaling molecules in burbot (Lota lota): molecular characterization, basal expression, and their response to Poly(I:C)

Burbot (Lota lota), a fish species of economic and ecological significance found across northern hemisphere freshwater ecosystems, was the focus of this study. We characterized 19 Toll-like receptor (TLR) genes in burbot, tracing their expression patterns following pathogen exposure. TLR genes, crucial to the innate immune system, including TLR13-1/2/3, TLR2/2-2/2-3/2-4/2-5, and TLR22a/22b/22c/22d, were discovered to be tandemly repeated, signifying an evolution in the fish's immune system. Notably, different TLR subfamilies displayed tissue-specific expressions, with TLR1 primarily in spleen and head kidney, TLR13 in head kidney, trunk kidney, and heart, TLR22 in trunk kidney and liver, and TLR3 and TLR9 predominantly in spleen and head kidney, but also in trunk kidney. Further, we investigated the response of TLR genes in burbot to pathogen exposure using qRT-PCR. This involved measuring mRNA expressions of identified TLR genes in spleen and liver tissues after injecting Poly(I:C) to simulate a double-stranded RNA viral infection. The results revealed a time and tissue-specific expression pattern. Specifically, LoTLR3 reached peak expression in the spleen 12 h post-injection, declining thereafter, while TLR2 subfamily members only began expressing after 24 h. In the liver, activation of the TLR3-IRF7 and TLR3-IRF3 signaling pathways was noted. Integrating these results with transcriptomic data illuminated the pivotal role of TLR genes in the burbot's immune response. Such findings are vital in shaping future disease prevention and treatment strategies.

Secreted mammalian DNases protect against systemic bacterial infection by digesting biofilms

Extracellular DNase DNASE1L3 maintains tolerance to self-DNA in humans and mice, whereas the role of its homolog DNASE1 remains controversial, and the overall function of secreted DNases in immunity is unclear. We report that deletion of murine DNASE1 neither caused autoreactivity in isolation nor exacerbated lupus-like disease in DNASE1L3-deficient mice. However, combined deficiency of DNASE1 and DNASE1L3 rendered mice susceptible to bloodstream infection with Staphylococcus aureus. DNASE1/DNASE1L3 double-deficient mice mounted a normal innate response to S. aureus and did not accumulate neutrophil extracellular traps (NETs). However, their kidneys manifested severe pathology, increased bacterial burden, and biofilm-like bacterial lesions that contained bacterial DNA and excluded neutrophils. Furthermore, systemic administration of recombinant DNASE1 protein during S. aureus infection rescued the mortality of DNase-deficient mice and ameliorated the disease in wild-type mice. Thus, DNASE1 and DNASE1L3 jointly facilitate the control of bacterial infection by digesting extracellular microbial DNA in biofilms, suggesting the original evolutionary function of secreted DNases as antimicrobial agents.

Pathogenic cellular and molecular mediators in lupus nephritis

Kidney involvement in patients with systemic lupus erythematosus - lupus nephritis (LN) - is one of the most important and common clinical manifestations of this disease and occurs in 40-60% of patients. Current treatment regimens achieve a complete kidney response in only a minority of affected individuals, and 10-15% of patients with LN develop kidney failure, with its attendant morbidity and considerable prognostic implications. Moreover, the medications most often used to treat LN - corticosteroids in combination with immunosuppressive or cytotoxic drugs - are associated with substantial side effects. Advances in proteomics, flow cytometry and RNA sequencing have led to important new insights into immune cells, molecules and mechanistic pathways that are instrumental in the pathogenesis of LN. These insights, together with a renewed focus on the study of human LN kidney tissue, suggest new therapeutic targets that are already being tested in lupus animal models and early-phase clinical trials and, as such, are hoped to eventually lead to meaningful improvements in the care of patients with systemic lupus erythematosus-associated kidney disease.

Pathogenesis and treatment of Sjogren's syndrome: Review and update

Sjogren's syndrome (SS) is a chronic autoimmune disease accompanied by multiple lesions. The main manifestations include dryness of the mouth and eyes, along with systemic complications (e.g., pulmonary disease, kidney injury, and lymphoma). In this review, we highlight that IFNs, Th17 cell-related cytokines (IL-17 and IL-23), and B cell-related cytokines (TNF and BAFF) are crucial for the pathogenesis of SS. We also summarize the advances in experimental treatment strategies, including targeting Treg/Th17, mesenchymal stem cell treatment, targeting BAFF, inhibiting JAK pathway, et al. Similar to that of SLE, RA, and MS, biotherapeutic strategies of SS consist of neutralizing antibodies and inflammation-related receptor blockers targeting proinflammatory signaling pathways. However, clinical research on SS therapy is comparatively rare. Moreover, the differences in the curative effects of immunotherapies among SS and other autoimmune diseases are not fully understood. We emphasize that targeted drugs, low-side-effect drugs, and combination therapies should be the focus of future research.

Transcriptome-wide N6-methyladenosine modification profiling of mRNAs during infection of Newcastle disease virus in chicken macrophages

N6-methyladenosine (m6A) modification, the most prevalent post-transcriptional modification of eukaryotic mRNAs, is reported to play a crucial role in viral infection. However, the role of m6A modification during Newcastle disease virus (NDV) infection has remained unclear. In this study, we performed MeRIP-seq to investigate the transcriptome-wide m6A methylome and m6A-modified genes in NDV-infected chicken macrophages. A total of 9496 altered peaks were identified, of which 7015 peaks were significantly upregulated across 3320 genes, and 2481 peaks were significantly down-regulated across 1264 genes. Combined analysis of m6A peaks and mRNA expression showed that 1234 mRNAs had significantly altered levels of methylation and expression after NDV infection, and m6A modification tended to have a negative relationship with mRNA expression, suggesting that m6A modification may regulate the process of NDV infection by regulating gene expression, particularly of the genes important in the innate immune response. To the best of our knowledge, this is the first comprehensive characterization of m6A patterns in chicken macrophage mRNA after NDV infection, providing a valuable basis for further exploring the role of m6A modification mechanisms during the course of NDV infection.

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.

Chronic activation of pDCs in autoimmunity is linked to dysregulated ER stress and metabolic responses

Plasmacytoid dendritic cells (pDCs) chronically produce type I interferon (IFN-I) in autoimmune diseases, including systemic sclerosis (SSc) and systemic lupus erythematosus (SLE). We report that the IRE1α-XBP1 branch of the unfolded protein response (UPR) inhibits IFN-α production by TLR7- or TLR9-activated pDCs. In SSc patients, UPR gene expression was reduced in pDCs, which inversely correlated with IFN-I-stimulated gene expression. CXCL4, a chemokine highly secreted in SSc patients, downregulated IRE1α-XBP1-controlled genes and promoted IFN-α production by pDCs. Mechanistically, IRE1α-XBP1 activation rewired glycolysis to serine biosynthesis by inducing phosphoglycerate dehydrogenase (PHGDH) expression. This process reduced pyruvate access to the tricarboxylic acid (TCA) cycle and blunted mitochondrial ATP generation, which are essential for pDC IFN-I responses. Notably, PHGDH expression was reduced in pDCs from patients with SSc and SLE, and pharmacological blockade of TCA cycle reactions inhibited IFN-I responses in pDCs from these patients. Hence, modulating the IRE1α-XBP1-PHGDH axis may represent a hitherto unexplored strategy for alleviating chronic pDC activation in autoimmune disorders.

Post-Translational Modifications of cGAS-STING: A Critical Switch for Immune Regulation

Innate immune mechanisms initiate immune responses via pattern-recognition receptors (PRRs). Cyclic GMP-AMP synthase (cGAS), a member of the PRRs, senses diverse pathogenic or endogenous DNA and activates innate immune signaling pathways, including the expression of stimulator of interferon genes (STING), type I interferon, and other inflammatory cytokines, which, in turn, instructs the adaptive immune response development. This groundbreaking discovery has rapidly advanced research on host defense, cancer biology, and autoimmune disorders. Since cGAS/STING has enormous potential in eliciting an innate immune response, understanding its functional regulation is critical. As the most widespread and efficient regulatory mode of the cGAS-STING pathway, post-translational modifications (PTMs), such as the covalent linkage of functional groups to amino acid chains, are generally considered a regulatory mechanism for protein destruction or renewal. In this review, we discuss cGAS-STING signaling transduction and its mechanism in related diseases and focus on the current different regulatory modalities of PTMs in the control of the cGAS-STING-triggered innate immune and inflammatory responses.

The distinct roles of exosomes in innate immune responses and therapeutic applications in cancer

The innate immune system is one of the major constituents of the host's defense against invading pathogens and extracellular vesicles (EVs) are involved in regulating its responses. Exosomes, a subclass of EVs, released from eukaryotic cells, contribute to intracellular communication and drive various biological processes by transferring nuclei acids, proteins, lipids, and carbohydrates between cells, protecting cargo from enzymatic degradation and immune recognition and consequent elimination by the immune system. A growing body of evidence has revealed that exosomes produced from host cells, infected cells, tumor cells, and immune cells regulate innate immune signaling and responses and thus play a significant role in the propagation of pathogens. Immune cells can recognize exosomes-bearing components including DNA strands, viral RNAs, and even proteins by various mechanisms such as through Toll-like receptor/NF-κB signaling, inducing cytokine production and reprogramming the innate immune responses, immunosuppression or immunesupportive. There is persuasive preclinical and clinical evidence that exosomes are therapeutic strategies for immunotherapy, cancer vaccine, drug-delivery system, and diagnostic biomarker. However, further scrutiny is essential to validate these findings. In this review, we describe the current facts on the regulation of innate immune responses by exosomes. We also describe the translational application of exosomes as cancer-therapy agents and immunotherapy.

The intersection molecule MDA5 in Cancer and COVID-19

The connections between pattern recognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs) constitutes the crucial signaling pathways in the innate immune system. Cytoplasmic nucleic acid sensor melanoma differentiation-associated gene 5 (MDA5) serves as an important pattern recognition receptor in the innate immune system by recognizing viral RNA. MDA5 also plays a role in identifying the cytoplasmic RNA from damaged, dead cancer cells or autoimmune diseases. MDA5’s recognition of RNA triggers innate immune responses, induces interferon (IFN) response and a series of subsequent signaling pathways to produce immunomodulatory factors and inflammatory cytokines. Here we review the latest progress of MDA5 functions in triggering anti-tumor immunity by sensing cytoplasmic dsRNA, and recognizing SARS-CoV-2 virus infection for antiviral response, in which the virus utilizes multiple ways to evade the host defense mechanism.

Monocyte-derived macrophages aggravate pulmonary vasculitis via cGAS/STING/IFN-mediated nucleic acid sensing

Autoimmune vasculitis is a group of life-threatening diseases, whose underlying pathogenic mechanisms are incompletely understood, hampering development of targeted therapies. Here, we demonstrate that patients suffering from anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) showed increased levels of cGAMP and enhanced IFN-I signature. To identify disease mechanisms and potential therapeutic targets, we developed a mouse model for pulmonary AAV that mimics severe disease in patients. Immunogenic DNA accumulated during disease onset, triggering cGAS/STING/IRF3-dependent IFN-I release that promoted endothelial damage, pulmonary hemorrhages, and lung dysfunction. Macrophage subsets played dichotomic roles in disease. While recruited monocyte-derived macrophages were major disease drivers by producing most IFN-β, resident alveolar macrophages contributed to tissue homeostasis by clearing red blood cells and limiting infiltration of IFN-β-producing macrophages. Moreover, pharmacological inhibition of STING, IFNAR-I, or its downstream JAK/STAT signaling reduced disease severity and accelerated recovery. Our study unveils the importance of STING/IFN-I axis in promoting pulmonary AAV progression and identifies cellular and molecular targets to ameliorate disease outcomes.

Blocking CD47 promotes antitumour immunity through CD103+ dendritic cell-NK cell axis in murine hepatocellular carcinoma model

BACKGROUND & AIMS

The CD47-signal regulatory protein α (SIRPα) axis inhibits dendritic cell (DC) phagocytosis and contributes to immune evasion. However, the behaviour of DCs and the potential crosstalk between DCs and natural killer (NK) cells in the hepatocellular carcinoma (HCC) microenvironment after CD47 blockade remain unclear.

METHODS

The infiltration of CD103⁺ DCs and NK cells were analysed by immunohistochemistry and immunofluorescence in both human and murine HCC specimens. An orthotopic liver tumour model was used to evaluate the function of the CD103⁺ DC-NK cell axis after CD47 blockade in vivo in wild-type, Rag1^-/-, Batf3^-/-, and STING1^-/- mice. Phagocytosis assays were performed in CD103⁺ DC and HCC cell lines. CD103⁺ DC-derived cytokines were analysed by chemokine array. Spleen-derived NK cells in C57BL/6J mice were used to evaluate cytotoxic functions in vitro.

RESULTS

Higher CD47 expression was associated with worse prognosis in patients with HCC. CD47 blockade enhanced antitumour efficacy by stimulating the CD103⁺ DC-NK cell axis. The hypoxic microenvironment promoted CD47 blockade-induced tumour DNA phagocytosis by CD103⁺ DCs. By releasing IL-12 and CXCL9, activated CD103⁺ DCs induced the recruitment of NK cells with upregulated expression of granzyme B, NKG2D, interferon-γ, and tumour necrosis factor-α and downregulated expression of NKG2A. The antitumour effects of CD47 blockade could be abolished by cyclic GMP-AMP synthase (cGAS)-STING pathway inhibition.

CONCLUSIONS

In addition to the classical DC-T cell axis, CD47 blockade significantly enhanced the ability of CD103⁺ DCs to take up tumour DNA, resulting in the stimulation of the cGAS-STING pathway, which promoted the infiltration and activation of NK cells in liver cancer.

LAY SUMMARY

Hypoxia (low oxygen levels) is prevalent in the hepatocellular carcinoma microenvironment and promotes the phagocytosis (ingestion and elimination) of tumour DNA by CD103⁺ dendritic cells (a type of immune cell). Blockade of the cell surface protein CD47 resulted in activation of CD103⁺ dendritic cells which led to the recruitment and activation of natural killer cells (a different immune cell). When activated, these cells exhibit an antitumour effect.

Varicella-Zoster virus ORF9 is an antagonist of the DNA sensor cGAS

Varicella-Zoster virus (VZV) causes chickenpox and shingles. Although the infection is associated with severe morbidity in some individuals, molecular mechanisms that determine innate immune responses remain poorly defined. We found that the cGAS/STING DNA sensing pathway was required for type I interferon (IFN) induction during VZV infection and that recognition of VZV by cGAS restricted its replication. Screening of a VZV ORF expression library identified the essential VZV tegument protein ORF9 as a cGAS antagonist. Ectopically or virally expressed ORF9 bound to endogenous cGAS leading to reduced type I IFN responses to transfected DNA. Confocal microscopy revealed co-localisation of cGAS and ORF9. ORF9 and cGAS also interacted directly in a cell-free system and phase-separated together with DNA. Furthermore, ORF9 inhibited cGAMP production by cGAS. Taken together, these results reveal the importance of the cGAS/STING DNA sensing pathway for VZV recognition and identify a VZV immune antagonist that partially but directly interferes with DNA sensing via cGAS.

Chemokines form nanoparticles with DNA and can superinduce TLR-driven immune inflammation

Chemokines control the migratory patterns and positioning of immune cells to organize immune responses to pathogens. However, many chemokines have been associated with systemic autoimmune diseases that have chronic IFN signatures. We report that a series of chemokines, including CXCL4, CXCL10, CXCL12, and CCL5, can superinduce type I IFN (IFN-I) by TLR9-activated plasmacytoid DCs (pDCs), independently of their respective known chemokine receptors. Mechanistically, we show that chemokines such as CXCL4 mediate transcriptional and epigenetic changes in pDCs, mostly targeted to the IFN-I pathways. We describe that chemokines physically interact with DNA to form nanoparticles that promote clathrin-mediated cellular uptake and delivery of DNA in the early endosomes of pDCs. Using two separate mouse models of skin inflammation, we observed the presence of CXCL4 associated with DNA in vivo. These data reveal a noncanonical role for chemokines to serve as nucleic acid delivery vectors to modulate TLR signaling, with implications for the chronic presence of IFN-I by pDCs in autoimmune diseases.

CXCL4 synergizes with TLR8 for TBK1-IRF5 activation, epigenomic remodeling and inflammatory response in human monocytes

Regulation of endosomal Toll-like receptor (TLR) responses by the chemokine CXCL4 is implicated in inflammatory and fibrotic diseases, with CXCL4 proposed to potentiate TLR responses by binding to nucleic acid TLR ligands and facilitating their endosomal delivery. Here we report that in human monocytes/macrophages, CXCL4 initiates signaling cascades and downstream epigenomic reprogramming that change the profile of the TLR8 response by selectively amplifying inflammatory gene transcription and interleukin (IL)-1β production, while partially attenuating the interferon response. Mechanistically, costimulation by CXCL4 and TLR8 synergistically activates TBK1 and IKKε, repurposes these kinases towards an inflammatory response via coupling with IRF5, and activates the NLRP3 inflammasome. CXCL4 signaling, in a cooperative and synergistic manner with TLR8, induces chromatin remodeling and activates de novo enhancers associated with inflammatory genes. Our findings thus identify new regulatory mechanisms of TLR responses relevant for cytokine storm, and suggest targeting the TBK1-IKKε-IRF5 axis may be beneficial in inflammatory diseases.

Bat Employs a Conserved MDA5 Gene to Trigger Antiviral Innate Immune Responses

Bats are important hosts for various zoonotic viral diseases. However, they rarely show signs of disease infection with such viruses. As the first line for virus control, the innate immune system of bats attracted our full attention. In this study, the Tadarida brasiliensis MDA5 gene (batMDA5), a major sensor for anti-RNA viral infection, was first cloned, and its biological functions in antiviral innate immunity were identified. Bioinformatics analysis shows that the amino acid sequence of batMDA5 is poorly conserved among species, and it is evolutionarily closer to humans. The mRNA of batMDA5 was significantly upregulated in Newcastle disease virus (NDV), avian influenza virus (AIV), and vesicular stomatitis virus (VSV)-infected bat TB 1 Lu cells. Overexpression of batMDA5 could activate IFNβ and inhibit vesicular stomatitis virus (VSV-GFP) replication in TB 1 Lu cells, while knockdown of batMDA5 yielded the opposite result. In addition, we found that the CARD domain was essential for MDA5 to activate IFNβ by constructing MDA5 domain mutant plasmids. These results indicated that bat employs a conserved MDA5 gene to trigger anti-RNA virus innate immune response. This study helps understand the biological role of MDA5 in innate immunity during evolution.

DNA damage contributes to neurotoxic inflammation in Aicardi-Goutières syndrome astrocytes

Aberrant induction of type I IFN is a hallmark of the inherited encephalopathy Aicardi-Goutières syndrome (AGS), but the mechanisms triggering disease in the human central nervous system (CNS) remain elusive. Here, we generated human models of AGS using genetically modified and patient-derived pluripotent stem cells harboring TREX1 or RNASEH2B loss-of-function alleles. Genome-wide transcriptomic analysis reveals that spontaneous proinflammatory activation in AGS astrocytes initiates signaling cascades impacting multiple CNS cell subsets analyzed at the single-cell level. We identify accumulating DNA damage, with elevated R-loop and micronuclei formation, as a driver of STING- and NLRP3-related inflammatory responses leading to the secretion of neurotoxic mediators. Importantly, pharmacological inhibition of proapoptotic or inflammatory cascades in AGS astrocytes prevents neurotoxicity without apparent impact on their increased type I IFN responses. Together, our work identifies DNA damage as a major driver of neurotoxic inflammation in AGS astrocytes, suggests a role for AGS gene products in R-loop homeostasis, and identifies common denominators of disease that can be targeted to prevent astrocyte-mediated neurotoxicity in AGS.

Pathogenesis and treatment of cytokine storm in COVID-19

COVID-19 is a viral infection caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that killed a large number of patients around the world. A hyperinflammatory state resulting in a cytokine storm and adult respiratory distress syndrome seems to be the major cause of the death. Many mechanisms have been suggested in the pathogenesis of COVID-19 associated cytokine storm (COVID-CS). Insufficient viral clearance and persistence of a strong cytokine response despite inadequate antiviral immunity seem to be the main mechanisms underlying the pathogenesis. The diagnosis of COVID-19 is based on relatively constant clinical symptoms, clinical findings, laboratory tests, and imaging techniques, while the diagnosis of COVID-CS is a rather dynamic process, based on evolving or newly emerging findings during the clinical course. Management of COVID-19 consists of using antiviral agents to inhibit SARS-CoV-2 replication and treating potential complications including the cytokine storm together with general supportive measures. COVID-CS may be treated using appropriate immunosuppressive and immunomodulatory drugs that reduce the level of inappropriate systemic inflammation, which has the potential to cause organ damage. Currently corticosteroids, IL-6 blockers, or IL-1 blockers are most widely used for treating COVID-CS.

Regulation of antiviral innate immune signaling and viral evasion following viral genome sensing

A harmonized balance between positive and negative regulation of pattern recognition receptor (PRR)-initiated immune responses is required to achieve the most favorable outcome for the host. This balance is crucial because it must not only ensure activation of the first line of defense against viral infection but also prevent inappropriate immune activation, which results in autoimmune diseases. Recent studies have shown how signal transduction pathways initiated by PRRs are positively and negatively regulated by diverse modulators to maintain host immune homeostasis. However, viruses have developed strategies to subvert the host antiviral response and establish infection. Viruses have evolved numerous genes encoding immunomodulatory proteins that antagonize the host immune system. This review focuses on the current state of knowledge regarding key host factors that regulate innate immune signaling molecules upon viral infection and discusses evidence showing how specific viral proteins counteract antiviral responses via immunomodulatory strategies.

An Integrated View of Deubiquitinating Enzymes Involved in Type I Interferon Signaling, Host Defense and Antiviral Activities

Viral infectious diseases pose a great challenge to human health around the world. Type I interferons (IFN-Is) function as the first line of host defense and thus play critical roles during virus infection by mediating the transcriptional induction of hundreds of genes. Nevertheless, overactive cytokine immune responses also cause autoimmune diseases, and thus, tight regulation of the innate immune response is needed to achieve viral clearance without causing excessive immune responses. Emerging studies have recently uncovered that the ubiquitin system, particularly deubiquitinating enzymes (DUBs), plays a critical role in regulating innate immune responses. In this review, we highlight recent advances on the diverse mechanisms of human DUBs implicated in IFN-I signaling. These DUBs function dynamically to calibrate host defenses against various virus infections by targeting hub proteins in the IFN-I signaling transduction pathway. We also present a future perspective on the roles of DUB-substrate interaction networks in innate antiviral activities, discuss the promises and challenges of DUB-based drug development, and identify the open questions that remain to be clarified. Our review provides a comprehensive description of DUBs, particularly their differential mechanisms that have evolved in the host to regulate IFN-I-signaling-mediated antiviral responses.

COVID-19 and the lungs: A review

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) attacks pulmonary alveolar cells via angiotensin-converting enzyme 2 (ACE2) receptors and causes pulmonary infections that result in coronavirus disease (COVID-19), inducing immune responses that can result in severe pneumonia. We reviewed the clinical experiences of lung diseases during the COVID-19 pandemic to offer insights into the adaptations made by experts in the diagnosis and treatment of these comorbidities. Various lung comorbidities increase the severity of COVID-19 and associated mortality by amplifying ACE2 expression. Additionally, the COVID-19 pandemic has changed the use of routine diagnostic pulmonary imaging methods, making chest sonography scoring the most convenient, as it can be conducted bedside. Treatment protocols for SARS-CoV-2 infection and the underlying lung diseases are also affected owing to potential interactions. The optimal diagnostic methods and treatment protocols for lung diseases have been adapted worldwide to increase survival rates and attenuate acute lung injuries during the COVID-19 pandemic.

Role of nucleic acid sensing in the pathogenesis of type 1 diabetes

During infections, nucleic acids of pathogens are also engaged in recognition via several exogenous and cytosolic pattern recognition receptors, such as the toll-like receptors, retinoic acid inducible gene-I-like receptors, and nucleotide-binding and oligomerization domain-like receptors. The binding of the pathogen-derived nucleic acids to their corresponding sensors initiates certain downstream signaling cascades culminating in the release of type-I interferons (IFNs), especially IFN-α and other cytokines to induce proinflammatory responses towards invading pathogens leading to their clearance from the host. Although these sensors are hardwired to recognize pathogen associated molecular patterns, like viral and bacterial nucleic acids, under unusual physiological conditions, such as excessive cellular stress and increased apoptosis, endogenous self-nucleic acids like DNA, RNA, and mitochondrial DNA are also released. The presence of these self-nucleic acids in extranuclear compartments or extracellular spaces or their association with certain proteins sometimes leads to the failure of discriminating mechanisms of nucleic acid sensors leading to proinflammatory responses as seen in autoimmune disorders, like systemic lupus erythematosus, psoriasis and to some extent in type 1 diabetes (T1D). This review discusses the involvement of various nucleic acid sensors in autoimmunity and discusses how aberrant recognition of self-nucleic acids by their sensors activates the innate immune responses during the pathogenesis of T1D.

Enhanced cGAS-STING-dependent interferon signaling associated with mutations in ATAD3A

Mitochondrial DNA (mtDNA) has been suggested to drive immune system activation, but the induction of interferon signaling by mtDNA has not been demonstrated in a Mendelian mitochondrial disease. We initially ascertained two patients, one with a purely neurological phenotype and one with features suggestive of systemic sclerosis in a syndromic context, and found them both to demonstrate enhanced interferon-stimulated gene (ISG) expression in blood. We determined each to harbor a previously described de novo dominant-negative heterozygous mutation in ATAD3A, encoding ATPase family AAA domain-containing protein 3A (ATAD3A). We identified five further patients with mutations in ATAD3A and recorded up-regulated ISG expression and interferon α protein in four of them. Knockdown of ATAD3A in THP-1 cells resulted in increased interferon signaling, mediated by cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING). Enhanced interferon signaling was abrogated in THP-1 cells and patient fibroblasts depleted of mtDNA. Thus, mutations in the mitochondrial membrane protein ATAD3A define a novel type I interferonopathy.

KAP1-Mediated Epigenetic Suppression in Anti-RNA Viral Responses by Direct Targeting RIG-I and MDA5

Retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), including RIG-I (encoded by Ddx58) and melanoma differentiation-associated gene 5 (MDA5) (encoded by Ifih1), are crucial for initiating antiviral responses. Endogenous retroviral elements (ERVs) are transposable elements derived from exogenous retroviruses that are integrated into the genome. KRAB-associated protein 1 (KAP1) is a key epigenetic suppressor of ERVs that protects cells from detrimental genome instability. Increased ERV transcripts are sensed by RLRs and trigger innate immune signaling. However, whether KAP1 directly controls RLRs activity remains unclear. In this study, we show that KAP1 attenuates RNA viral infection-induced type I IFNs and facilitates viral replication by inhibiting RIG-I/MDA5 expression in primary peritoneal macrophages (PMs) of C57BL/6J mice. Kap1 deficiency increases IFN-β expression and inhibits vesicular stomatitis virus replication in C57BL/6J mice in vivo. Mechanistically, KAP1 binds to the promoter regions of Ddx58 and Ifih1 and promotes the establishment of repressive histone marks in primary PMs of C57BL/6J mice. Concordantly, KAP1 suppresses the expression of RIG-I and MDA5 at the transcriptional level in primary PMs of C57BL/6J mice. Our results establish that KAP1 epigenetically suppresses host antiviral responses by directly targeting RIG-1 and MDA5, thus facilitating the immune escape of RNA viruses.

Transcriptome analysis of host response to porcine epidemic diarrhea virus nsp15 in IPEC-J2 cells

BACKGROUND

Porcine epidemic diarrhea virus (PEDV) is an enveloped positive-sense ssRNA virus which is highly lethal to piglets, causing enormous economic losses to swine industry worldwide. Nsp15 protein is an endoribonuclease of PEDV and plays an indispensable role in the viral proliferation. We reported the transcription files of nsp15 transfected IPEC-J2 cells for the first time to broaden our understanding of PEDV pathogenesis.

METHODS

RNA-seq was performed to compare gene expression profiles between pCAGGS-HA-nsp15 transfected IPEC-J2 cells and pCAGGS-HA (empty vector) transfected IPEC-J2 cells. Immune-related genes and pathways were identified and analyzed to deepen our understanding of nsp15 for PEDV pathogenicity. IPEC-J2 cells transfected with pCAGGS-HA-CCL5/CXCL8/CXCL10 were infected with CV777 and the virus load of PEDV was detected by qRT-PCR.

RESULTS

A total of 21,654 genes were obtained by RNA-Seq and 415 differential expressed genes (DEGs) were identified, including 136 up-regulated and 279 down-regulated genes. A number of effect genes involved in immune responses and inflammation were differentially expressed. GO and KEGG enrichment analysis showed that 32 GO terms were significantly enriched and the DEGs were mainly enriched in immune-related pathways such as TNF signaling pathway, RIG-I-like receptor signaling pathway and Cytosolic DNA-sensing pathway. qRT-PCR results indicated the overexpression of selected chemokines, CCL5/CXCL8/CXCL10, can inhibit PEDV proliferation in IPEC-J2 cells.

CONCLUSIONS

Our transcriptome profile illustrated a number of genes involving in immune responses and inflammation were inhibited by nsp15, such as CCL5, CXCL8, CXCL10, OAS, MXs, STAT1 and IRF9. The results suggested that nsp15 can antagonize IFNs and block chemokine system to provide an adequate intracellular environment for viral proliferation.

Mitochondrial Nucleic Acid as a Driver of Pathogenic Type I Interferon Induction in Mendelian Disease

The immune response to viral infection involves the recognition of pathogen-derived nucleic acids by intracellular sensors, leading to type I interferon (IFN), and downstream IFN-stimulated gene, induction. Ineffective discrimination of self from non-self nucleic acid can lead to autoinflammation, a phenomenon implicated in an increasing number of disease states, and well highlighted by the group of rare genetic disorders referred to as the type I interferonopathies. To understand the pathogenesis of these monogenic disorders, and polyfactorial diseases associated with pathogenic IFN upregulation, such as systemic lupus erythematosus and dermatomyositis, it is important to define the self-derived nucleic acid species responsible for such abnormal IFN induction. Recently, attention has focused on mitochondria as a novel source of immunogenic self nucleic acid. Best appreciated for their function in oxidative phosphorylation, metabolism and apoptosis, mitochondria are double membrane-bound organelles that represent vestigial bacteria in the cytosol of eukaryotic cells, containing their own DNA and RNA enclosed within the inner mitochondrial membrane. There is increasing recognition that a loss of mitochondrial integrity and compartmentalization can allow the release of mitochondrial nucleic acid into the cytosol, leading to IFN induction. Here, we provide recent insights into the potential of mitochondrial-derived DNA and RNA to drive IFN production in Mendelian disease. Specifically, we summarize current understanding of how nucleic acids are detected as foreign when released into the cytosol, and then consider the findings implicating mitochondrial nucleic acid in type I interferonopathy disease states. Finally, we discuss the potential for IFN-driven pathology in primary mitochondrial disorders.

Resveratrol as an Adjunctive Therapy for Excessive Oxidative Stress in Aging COVID-19 Patients

The coronavirus disease 2019 (COVID-19) pandemic continues to burden healthcare systems worldwide. COVID-19 symptoms are highly heterogeneous, and the patient may be asymptomatic or may present with mild to severe or fatal symptoms. Factors, such as age, sex, and comorbidities, are key determinants of illness severity and progression. Aging is accompanied by multiple deficiencies in interferon production by dendritic cells or macrophages in response to viral infections, resulting in dysregulation of inflammatory immune responses and excess oxidative stress. Age-related dysregulation of immune function may cause a more obvious pathophysiological response to SARS-CoV-2 infection in elderly patients and may accelerate the risk of biological aging, even after recovery. For more favorable treatment outcomes, inhibiting viral replication and dampening inflammatory and oxidative responses before induction of an overt cytokine storm is crucial. Resveratrol is a potent antioxidant with antiviral activity. Herein, we describe the reasons for impaired interferon production, owing to aging, and the impact of aging on innate and adaptive immune responses to infection, which leads to inflammation distress and immunosuppression, thereby causing fulminant disease. Additionally, the molecular mechanism by which resveratrol could reverse a state of excessive basal inflammatory and oxidative stress and low antiviral immunity is discussed.

Anti-Viral Pattern Recognition Receptors as Therapeutic Targets

Pattern recognition receptors (PRRs) play a central role in the inflammation that ensues following microbial infection by their recognition of molecular patterns present in invading microorganisms but also following tissue damage by recognising molecules released during disease states. Such receptors are expressed in a variety of cells and in various compartments of these cells. PRR binding of molecular patterns results in an intracellular signalling cascade and the eventual activation of transcription factors and the release of cytokines, chemokines, and vasoactive molecules. PRRs and their accessory molecules are subject to tight regulation in these cells so as to not overreact or react in unnecessary circumstances. They are also key to reacting to infection and in stimulating the immune system when needed. Therefore, targeting PRRs offers a potential therapeutic approach for chronic inflammatory disease, infections and as vaccine adjuvants. In this review, the current knowledge on anti-viral PRRs and their signalling pathways is reviewed. Finally, compounds that target PRRs and that have been tested in clinical trials for chronic infections and as adjuvants in vaccine trials are discussed.

Type I interferon detection in autoimmune diseases: challenges and clinical applications

INTRODUCTION

Accumulating data highlights that the dysregulation of type I interferon (IFN) pathways plays a central role in the pathogenesis of several systemic and organ-specific autoimmune diseases. Advances in understanding the role of type I IFNs in these disorders can lead to targeted drug development as well as establishing potential disease biomarkers.

AREAS COVERED

Here, we summarize current knowledge regarding the role of type I IFNs in the major systemic, as well as organ-specific, autoimmune disorders, including prominent inflammatory CNS disorders like multiple sclerosis.

EXPERT OPINION

Type I IFN involvement and its clinical associations in a wide spectrum of autoimmune diseases represents a promising area for research aiming to unveil common pathogenetic pathways in systemic and organ-specific autoimmunity.

Molecular mechanisms of nonself nucleic acid recognition by the innate immune system

Nucleic acids (NAs) represent one of the most important classes of molecules recognized by the innate immune system. However, NAs are not limited to pathogens, but are also present within the host. As such, the immune system has evolved an elaborate set of pathogen recognition receptors (PRRs) that employ various strategies to recognize distinct types of NAs, while reliably distinguishing between self and nonself. The here-employed strategies encompass the positioning of NA-sensing PRRs in certain subcellular compartments that potentially come in contact with pathogens but not host NAs, the existence of counterregulatory measures that keep endogenous NAs below a certain threshold, and also the specific identification of certain nonself patterns. Here, we review recent advances in the molecular mechanisms of NA recognition by TLRs, RLRs, and the cGAS-STING axis. We highlight the differences in NA-PRR interfaces that confer specificity and selectivity toward an NA ligand, as well as the NA-dependent induced conformational changes required for signal transduction.

Targeting human plasmacytoid dendritic cells through BDCA2 prevents skin inflammation and fibrosis in a novel xenotransplant mouse model of scleroderma

OBJECTIVES

Plasmacytoid dendritic cells (pDC) have been implicated in the pathogenesis of autoimmune diseases, such as scleroderma (SSc). However, this has been derived from indirect evidence using ex vivo human samples or mouse pDC in vivo. We have developed human-specific pDC models to directly identify their role in inflammation and fibrosis, as well as attenuation of pDC function with BDCA2-targeting to determine its therapeutic application.

METHODS

RNAseq of human pDC with TLR9 agonist ODN2216 and humanised monoclonal BDCA2 antibody, CBS004. Organotypic skin rafts consisting of fibroblasts and keratinocytes were stimulated with supernatant from TLR9-stimulated pDC and with CBS004. Human pDC were xenotransplanted into Nonobese diabetic/severe combined immunodeficiency (NOD SCID) mice treated with Aldara (inflammatory model), or bleomycin (fibrotic model) with CBS004 or human IgG control. Skin punch biopsies were used to assess gene and protein expression.

RESULTS

RNAseq shows TLR9-induced activation of human pDC goes beyond type I interferon (IFN) secretion, which is functionally inactivated by BDCA2-targeting. Consistent with these findings, we show that BDCA2-targeting of pDC can completely suppress in vitro skin IFN-induced response. Most importantly, xenotransplantation of human pDC significantly increased in vivo skin IFN-induced response to TLR agonist and strongly enhanced fibrotic and immune response to bleomycin compared with controls. In these contexts, BDCA2-targeting suppressed human pDC-specific pathological responses.

CONCLUSIONS

Our data indicate that human pDC play a key role in inflammation and immune-driven skin fibrosis, which can be effectively blocked by BDCA2-targeting, providing direct evidence supporting the development of attenuation of pDC function as a therapeutic application for SSc.

Functional characterization of the cnidarian antiviral immune response reveals ancestral complexity

Animals evolved a broad repertoire of innate immune sensors and downstream effector cascades for defense against RNA viruses. Yet, this system varies greatly among different bilaterian animals, masking its ancestral state. In this study, we aimed to characterize the antiviral immune response of the cnidarian Nematostella vectensis and decipher the function of the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) known to detect viral double-stranded RNA (dsRNA) in bilaterians but activate different antiviral pathways in vertebrates and nematodes. We show that polyinosinic:polycytidylic acid (poly(I:C)), a mimic of long viral dsRNA and a primary ligand for the vertebrate RLR melanoma differentiation-associated protein 5 (MDA5), triggers a complex antiviral immune response bearing features distinctive for both vertebrate and invertebrate systems. Importantly, a well-characterized agonist of the vertebrate RIG-I receptor does not induce a significant transcriptomic response that bears signature of the antiviral immune response, which experimentally supports the results of a phylogenetic analysis indicating clustering of the two N. vectensis RLR paralogs (NveRLRa and NveRLRb) with MDA5. Furthermore, the results of affinity assays reveal that NveRLRb binds poly(I:C) and long dsRNA and its knockdown impairs the expression of putative downstream effector genes including RNA interference components. Our study provides for the first time the functional evidence for the conserved role of RLRs in initiating immune response to dsRNA that originated before the cnidarian–bilaterian split and lay a strong foundation for future research on the evolution of the immune responses to RNA viruses.

Extracellular Nucleic Acids Present in the Candida albicans Biofilm Trigger the Release of Neutrophil Extracellular Traps

Neutrophils, the first line of the host's defense, use a variety of antimicrobial mechanisms to fight invading pathogens. One of the most crucial is the production of neutrophil extracellular traps (NETs) in the process called NETosis. The unique structure of NETs effectively inhibits the spread of pathogens and ensures their exposure to a high concentration of NET-embedded antimicrobial compounds. NETosis strategy is often used by the host to defend against fungal infection caused by Candida albicans. In immunocompromised patients, this microorganism is responsible for developing systemic fungal infections (candidiasis). This is correlated with the use of a vast array of virulence factors, leading to the acquisition of specific resistance to host defense factors and available drug therapies. One of the most important features favoring the development of drug resistance is a C. albicans ability to form biofilms that protect fungal cells mainly through the production of an extracellular matrix (ECM). Among the main ECM-building macromolecules extracellular nucleic acids have been identified and their role is probably associated with the stbilization of the biofilm structure. The complex interactions of immune cells with the thick ECM layer, comprising the first line of contact between these cells and the biofilm structure, are still poorly understood. Therefore, the current studies aimed to assess the release of extracellular nucleic acids by C. albicans strains at different stages of biofilm formation, and to determine the role of these molecules in triggering the NETosis. We showed for the first time that fungal nucleic acids, purified directly from mature C. albicans biofilm structure or obtained from the whole fungal cells, have the potential to induce NET release in vitro. In this study, we considered the involvement of TLR8 and TLR9 in NETosis activation. We showed that DNA and RNA molecules initiated the production of reactive oxygen species (ROS) by activation of the NADPH oxidase complex, essential for ROS-dependent NETosis. Furthermore, analysis of the cell migration showed that the nucleic acids located in the extracellular space surrounding the biofilm may be also effective chemotactic factors, driving the dynamic migration of human neutrophils to the site of ongoing fungal infection.

Self-DNA Sensing by cGAS-STING and TLR9 in Autoimmunity: Is the Cytoskeleton in Control?

Modified or misplaced DNA can be recognized as a danger signal by mammalian cells. Activation of cellular responses to DNA has evolved as a defense mechanism to microbial infections, cellular stress, and tissue damage, yet failure to control this mechanism can lead to autoimmune diseases. Several monogenic and multifactorial autoimmune diseases have been associated with type-I interferons and interferon-stimulated genes (ISGs) induced by deregulated recognition of self-DNA. Hence, understanding how cellular mechanism controls the pathogenic responses to self-nucleic acid has important clinical implications. Fine-tuned membrane trafficking and cellular compartmentalization are two major factors that balance activation of DNA sensors and availability of self-DNA ligands. Intracellular transport and organelle architecture are in turn regulated by cytoskeletal dynamics, yet the precise impact of actin remodeling on DNA sensing remains elusive. This review proposes a critical analysis of the established and hypothetical connections between self-DNA recognition and actin dynamics. As a paradigm of this concept, we discuss recent evidence of deregulated self-DNA sensing in the prototypical actin-related primary immune deficiency (Wiskott-Aldrich syndrome). We anticipate a broader impact of actin-dependent processes on tolerance to self-DNA in autoimmune disorders.