Cutting Edge: TLR3 stimulation suppresses experimental autoimmune encephalomyelitis by inducing endogenous IFN-beta

Proteome Profiling of Experimental Autoimmune Encephalomyelitis Mouse Model and the Effect of a SUMO E1 Inhibitor

Multiple sclerosis (MS) is one of the most common neurodegenerative diseases, causing demyelination and inflammation in the central nervous system. The pathology of MS has been extensively studied using the experimental autoimmune encephalomyelitis (EAE) mouse model. However, the molecular mechanisms are still largely unclear and require further investigation. In this study, we carried out quantitative proteomic analysis of the brain and spinal cord tissues in mice induced with EAE using a data-independent acquisition strategy and identified 744 differentially regulated proteins in the brain and 741 in the spinal cord. The changed proteins were highly related with phagocytosis, lysosomal enzymes, inflammasome activation, complements, and synaptic loss processes. Moreover, gene set enrichment analysis revealed the elevation of the SUMOylation process in EAE with the increase of SUMOylation-related enzymes and modification targets. Furthermore, to test the possibility of treating MS by targeting SUMOylation, we explored the application of a selective SUMO E1 inhibitor, TAK-981. Intriguingly, TAK-981 suppressed the global SUMOylation level in the brain and significantly alleviated the symptoms of EAE in mice. Our findings contribute to a better understanding of MS pathology, reveal the important role of SUMOylation in disease progression, and demonstrate the potential of the SUMO E1 inhibitor as a novel treatment for MS.

Potential therapeutic and diagnostic approaches of exosomes in multiple sclerosis pathophysiology

Exosomes are bilayer lipid vesicles that are released by cells and contain proteins, nucleic acids, and lipids. They can be internalized by other cells, inducing inflammatory responses and instigating toxicities in the recipient cells. Exosomes can also serve as therapeutic vehicles by transporting protective cargo to maintain homeostasis. Multiple studies have shown that exosomes can initiate and participate in the regulation of neuroinflammation, improve neurogenesis, and are closely related to the pathogenesis of central nervous system (CNS) diseases, including multiple sclerosis (MS). Exosomes can be secreted by both neurons and glial cells in the CNS, and their contents change with disease occurrence. Due to their ability to penetrate the blood-brain barrier and their stability in peripheral fluids, exosomes are attractive biomarkers of CNS diseases. In recent years, exosomes have emerged as potential therapeutic agents for CNS diseases, including MS. However, the molecular pathways in the pathogenesis of MS are still unknown, and further research is needed to fully understand the role of exosomes in the occurrence or improvement of MS disease. Thereby, in this review, we intend to provide a more complete understanding of the pathways in which exosomes are involved and affect the occurrence or improvement of MS disease.

Toll-like receptor signalling as a cannabinoid target

Toll-like receptors (TLRs) have become a focus in biomedicine and biomedical research given the roles of this unique family of innate immune proteins in immune activation, infection, and autoimmunity. It is evident that TLR dysregulation, and subsequent alterations in TLR-mediated inflammatory signalling, can contribute to disease pathogenesis, and TLR targeted therapies are in development. This review highlights evidence that cannabinoids are key regulators of TLR signalling. Cannabinoids include component of the plant Cannabis sativa L. (C. sativa), synthetic and endogenous ligands, and overall represent a class of compounds whose therapeutic potential and mechanism of action continues to be elucidated. Cannabinoid-based medicines are in the clinic, and are furthermore under intense investigation for broad clinical development to manage symptoms of a range of disorders. In this review, we present an overview of research evidence that signalling linked to a range of TLRs is targeted by cannabinoids, and such cannabinoid mediated effects represent therapeutic avenues for further investigation. First, we provide an overview of TLRs, adaptors and key signalling events, alongside a summary of evidence that TLRs are linked to disease pathologies. Next, we discuss the cannabinoids system and the development of cannabinoid-based therapeutics. Finally, for the bulk of this review, we systematically outline the evidence that cannabinoids (plant-derived cannabinoids, synthetic cannabinoids, and endogenous cannabinoid ligands) can cross-talk with innate immune signalling governed by TLRs, focusing specifically on each member of the TLR family. Cannabinoids should be considered as key regulators of signalling controlled by TLRs, and such regulation should be a major focus in terms of the anti-inflammatory propensity of the cannabinoid system.

Consecutive Injection of High-Dose Lipopolysaccharide Modulates Microglia Polarization via TREM2 to Alter Status of Septic Mice

BACKGROUND

The neuroinflammation of the central nervous system (CNS) is a prevalent syndrome of brain dysfunction secondary to severe sepsis and is regulated by microglia. Triggering the receptor expressed on myeloid cells 2 (TREM2) is known to have protective functions that modulate the microglial polarization of M2 type to reduce inflammatory responses, thereby improving cognition.

METHODS

We examined the effect of TREM2 on the polarization state of microglia during the progression of neuroinflammation. After consecutive intraperitoneal injections of lipopolysaccharide for 7 days, we evaluated the inflammation of a septic mice model by hematoxylin-eosin (H&E) and electron microscopy, and we used immunofluorescence (IF) assays and Western blotting to visualize hippocampal sections in C57BL/6 mice to assess TREM2 expression. In addition, we analyzed the state of microglia polarization with quantitative RT-PCR.

RESULT

The consecutive injection of LPS for 4 days elevated systemic inflammation and caused behavioral cognitive dysfunction in the septic model. However, on Day 7, the neuroinflammation was considerably attenuated. Meanwhile, TREM2 decreased on Day 4 and increased on Day 7 in vivo. Consistently, LPS could reduce the expression of TREM2 while IFN-β enhanced TREM2 expression in vitro. TREM2 regulated the microglial M1 phenotype's conversion to the M2 phenotype.

CONCLUSION

Our aim in this study was to investigate the interconnection between microglia polarization and TREM2 in neuroinflammation. Our results suggested that IFN-β could modulate TREM2 expression to alter the polarization state of microglia, thereby reducing LPS-induced neuroinflammation. Therefore, TREM2 is a novel potential therapeutic target for neuroinflammation.

Analysis of Differential TLR Activation in a Mouse Model of Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative and autoimmune disease affecting the central nervous system (CNS). The precise etiology of MS is still undeciphered, and signs and symptoms of the disease are varied and complex, ranging from axonal degeneration, synaptic, and neuronal loss to demyelination. Inflammation plays a critical role in determining the onset and the progression of MS, but there is still a lot of information missing before scientists come to understand what are the factors that contribute to the establishment of the neuroinflammation. Thus, various murine models, each representative of a specific hallmark of MS, are used to study the processes underlying the pathogenetic mechanisms of the disease in an attempt to find effective drugs for its treatment. Among the many causes of MS, viral infections appear to be one of the most prominent ones. In this scenario, the comprehension of the role of receptors activated upon the recognition of viral, and in general microbial, components in determining onset and progression of the neuroinflammation is of paramount importance. Toll-like receptors (TLRs) are evolutionarily conserved receptors that recognize several pathogen-associated molecular patterns (PAMPs), common structures of the pathogens, or the damage caused by the pathogens within the host. TLRs are thus directly involved in the regulation of inflammatory reactions and in the activation of the innate and, subsequently, the adaptive immune responses crucial for the elimination of infectious pathogens. The role of TLR activation in the development of MS is widely studied in various murine models of MS, as well as in MS patients. In this chapter, we will summarize the current knowledge about the contribution of TLRs to the development or progression of MS, and we will illustrate different methods commonly used for the investigation of the role of different TLRs in various murine models of the disease.

Toll-like receptor-mediated neuroinflammation: relevance for cognitive dysfunctions

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) with a well-documented role in the innate and adaptive immune responses. Interestingly, TLR activation has also been linked to several brain functions including neurogenesis and synaptogenesis. Increasing evidence supports TLR involvement in peripheral and central inflammation underlying normal aging and the pathogenesis of clinical conditions characterized by cognitive decline. These include not only major neurodegenerative diseases but also traumatic brain injuries, surgeries, and alcohol consumption- and chemotherapy-induced cognitive impairment. We first summarize the physiological roles of TLRs in the nervous system, and then illustrate the emerging involvement of TLRs in cognitive functions, pointing to these receptors as novel enticing pharmacological targets to develop more efficient drugs for the treatment of cognitive impairment.

Supramolecular organizing centers at the interface of inflammation and neurodegeneration

The pathogenesis of neurodegenerative diseases involves the accumulation of misfolded protein aggregates. These deposits are both directly toxic to neurons, invoking loss of cell connectivity and cell death, and recognized by innate sensors that upon activation release neurotoxic cytokines, chemokines, and various reactive species. This neuroinflammation is propagated through signaling cascades where activated sensors/receptors, adaptors, and effectors associate into multiprotein complexes known as supramolecular organizing centers (SMOCs). This review provides a comprehensive overview of the SMOCs, involved in neuroinflammation and neurotoxicity, such as myddosomes, inflammasomes, and necrosomes, their assembly, and evidence for their involvement in common neurodegenerative diseases. We discuss the multifaceted role of neuroinflammation in the progression of neurodegeneration. Recent progress in the understanding of particular SMOC participation in common neurodegenerative diseases such as Alzheimer's disease offers novel therapeutic strategies for currently absent disease-modifying treatments.

Role of Toll-Like Receptors in Neuroimmune Diseases: Therapeutic Targets and Problems

Toll-like receptors (TLRs) are a class of proteins playing a key role in innate and adaptive immune responses. TLRs are involved in the development and progression of neuroimmune diseases via initiating inflammatory responses. Thus, targeting TLRs signaling pathway may be considered as a potential therapy for neuroimmune diseases. However, the role of TLRs is elusive and complex in neuroimmune diseases. In addition to the inadequate immune response of TLRs inhibitors in the experiments, the recent studies also demonstrated that partial activation of TLRs is conducive to the production of anti-inflammatory factors and nervous system repair. Exploring the mechanism of TLRs in neuroimmune diseases and combining with developing the emerging drug may conquer neuroimmune diseases in the future. Herein, we provide an overview of the role of TLRs in several neuroimmune diseases, including multiple sclerosis, neuromyelitis optica spectrum disorder, Guillain-Barré syndrome and myasthenia gravis. Emerging difficulties and potential solutions in clinical application of TLRs inhibitors will also be discussed.

Role of Peripheral Immune Cells in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a chronic autoimmune disease that affects the myelination of the neurons present in the central nervous system (CNS). The exact etiology of MS development is unclear, but various environmental and genetic factors might play a role in initiating the disease. Experimental autoimmune encephalomyelitis (EAE) is a mouse model that is used to study the pathophysiology of MS disease as well as the effects of possible therapeutic agents. In addition, autoreactive immune cells trigger an inflammatory process upon the recognition of CNS antigens, which leads to destruction of the neurons. These include innate immune cells such as macrophages, dendritic cells, and natural killer cells. Additionally, the activation and extravasation of adaptive immune cells such as CD4+ T cells into the CNS may lead to further exacerbation of the disease. However, many studies revealed that immune cells could have either a protective or pathological role in MS. In this review, we highlight the roles of innate and adaptive immune cellular and soluble players that contribute to the pathogenesis of MS and EAE, which may be used as potential targets for therapy.

Transcription cofactor GRIP1 differentially affects myeloid cell-driven neuroinflammation and response to IFN-β therapy

Macrophages (MФ) and microglia (MG) are critical in the pathogenesis of multiple sclerosis (MS) and its mouse model, experimental autoimmune encephalomyelitis (EAE). Glucocorticoids (GCs) and interferon β (IFN-β) are frontline treatments for MS, and disrupting each pathway in mice aggravates EAE. Glucocorticoid receptor-interacting protein 1 (GRIP1) facilitates both GR and type I IFN transcriptional actions; hence, we evaluated the role of GRIP1 in neuroinflammation. Surprisingly, myeloid cell-specific loss of GRIP1 dramatically reduced EAE severity, immune cell infiltration of the CNS, and MG activation and demyelination specifically during the neuroinflammatory phase of the disease, yet also blunted therapeutic properties of IFN-β. MФ/MG transcriptome analyses at the bulk and single-cell levels revealed that GRIP1 deletion attenuated nuclear receptor, inflammatory and, interestingly, type I IFN pathways and promoted the persistence of a homeostatic MG signature. Together, these results uncover the multifaceted function of type I IFN in MS/EAE pathogenesis and therapy, and an unexpectedly permissive role of myeloid cell GRIP1 in neuroinflammation.

Context Is Key: Delineating the Unique Functions of IFNα and IFNβ in Disease

Type I interferons (IFNs) are critical effector cytokines of the immune system and were originally known for their important role in protecting against viral infections; however, they have more recently been shown to play protective or detrimental roles in many disease states. Type I IFNs consist of IFNα, IFNβ, IFNϵ, IFNκ, IFNω, and a few others, and they all signal through a shared receptor to exert a wide range of biological activities, including antiviral, antiproliferative, proapoptotic, and immunomodulatory effects. Though the individual type I IFN subtypes possess overlapping functions, there is growing appreciation that they also have unique properties. In this review, we summarize some of the mechanisms underlying differential expression of and signaling by type I IFNs, and we discuss examples of differential functions of IFNα and IFNβ in models of infectious disease, cancer, and autoimmunity.

Modulation of the Innate Immune Response by Targeting Toll-like Receptors: A Perspective on Their Agonists and Antagonists

Toll-like receptors (TLRs) are a class of proteins that recognize pathogen-associated molecular patterns (PAMPs) and damaged-associated molecular patterns (DAMPs), and they are involved in the regulation of innate immune system. These transmembrane receptors, localized at the cellular or endosomal membrane, trigger inflammatory processes through either myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) signaling pathways. In the last decades, extensive research has been performed on TLR modulators and their therapeutic implication under several pathological conditions, spanning from infections to cancer, from metabolic disorders to neurodegeneration and autoimmune diseases. This Perspective will highlight the recent discoveries in this field, emphasizing the role of TLRs in different diseases and the therapeutic effect of their natural and synthetic modulators, and it will discuss insights for the future exploitation of TLR modulators in human health.

MyD88-dependent and -independent signalling via TLR3 and TLR4 are differentially modulated by Δ9-tetrahydrocannabinol and cannabidiol in human macrophages

Toll-like receptors (TLRs) are sensors of pathogen-associated molecules that trigger inflammatory signalling in innate immune cells including macrophages. All TLRs, with the exception of TLR3, promote intracellular signalling via recruitment of the myeloid differentiation factor 88 (MyD88) adaptor, while TLR3 signals via Toll-Interleukin-1 Receptor (TIR)-domain-containing adaptor-inducing interferon (IFN)-β (TRIF) adaptor to induce MyD88-independent signalling. Furthermore, TLR4 can activate both MyD88-dependent and -independent signalling (via TRIF). The study aim was to decipher the impact of the highly purified plant-derived (phyto) cannabinoids Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD), when delivered in isolation and in combination (1:1), on MyD88-dependent and -independent signalling in macrophages. We employed the use of the viral dsRNA mimetic poly(I:C) and endotoxin lipopolysaccharide (LPS), to induce viral TLR3 and bacterial TLR4 signalling in human Tamm-Horsfall protein-1 (THP-1)-derived macrophages, respectively. TLR3/TLR4 stimulation promoted the activation of interferon (IFN) regulatory factor 3 (IRF3) and TLR4 promoted the activation of nuclear factor (NF)-κB signalling, with downstream production of the type I IFN-β, the chemokines CXCL10 and CXCL8, and cytokine TNF-α. THC and CBD (both at 10 μM) attenuated TLR3/4-induced IRF3 activation and induction of CXCL10/IFN-β, while both phytocannabinoids failed to impact TLR4-induced IκB-α degradation and TNF-α/CXCL8 expression. The role of CB₁, CB₂ and PPARγ receptors in mediating the effect of THC and CBD on MyD88-independent signalling was investigated. TLRs are attractive therapeutic targets given their role in inflammation and initiation of adaptive immunity, and data herein indicate that both CBD and THC preferentially modulate TLR3 and TLR4 signalling via MyD88-independent mechanisms in macrophages. This offers mechanistic insight into the role of phytocannabinoids in modulating cellular inflammation.

Inflammatory Role of TLR-MyD88 Signaling in Multiple Sclerosis

Multiple sclerosis (MS) is a neuro-autoimmune and neurodegenerative disorder leading to chronic inflammation, demyelination, axonal, and neuronal loss in the central nervous system (CNS). Despite intense research efforts, the pathogenesis of MS still remains unclear. Toll-like receptors (TLRs) are a family of type I transmembrane receptors that play a crucial role in the innate immune response. Myeloid differentiation factor 88 (MyD88) is the adaptor of major TLRs. It has been widely considered that the TLR-MyD88 signaling pathway plays an important role in the occurrence and development of autoimmune disease. Data have revealed that the TLR-MyD88 signaling may be involved in the pathogenesis of MS and experimental autoimmune encephalomyelitis (EAE), an animal model for MS, by regulating the antigen presentation of dendritic cells, the integrity of blood-brain barrier (BBB), and the activation of T cells and B cells. Here, we summarize the role of TLRs and MyD88 in MS and discuss the possible therapies that are based on these molecules.

Pattern Recognition Receptors in Multiple Sclerosis and Its Animal Models

Pattern recognition receptors (PRRs) coordinate the innate immune response and have a significant role in the development of multiple sclerosis (MS). Accumulating evidence has identified both pathogenic and protective functions of PRR signaling in MS and its animal model, experimental autoimmune encephalomyelitis (EAE). Additionally, evidence for PRR signaling in non-immune cells and PRR responses to host-derived endogenous ligands has also revealed new pathways controlling the development of CNS autoimmunity. Many PRRs remain uncharacterized in MS and EAE, and understanding the distinct triggers and functions of PRR signaling in CNS autoimmunity requires further investigation. In this brief review, we discuss the diverse pathogenic and protective functions of PRRs in MS and EAE, and highlight major avenues for future research.

TLR3 preconditioning induces anti-inflammatory and anti-ictogenic effects in mice mediated by the IRF3/IFN-β axis

Activation of Toll-like receptor 3 (TLR3) was previously shown to contribute to the generation of epileptic seizures in rodents by evoking a proinflammatory response in the forebrain. This suggests that TLR3 blockade may provide therapeutic effects in epilepsy. We report that brain activation of TLR3 using the synthetic receptor ligand Poly I:C may also result in remarkable dose- and time-dependent inhibitory effects on acute seizures in mice without inducing inflammation. These inhibitory effects are associated with reduced neuronal excitability in the hippocampus as shown by a decrease in the population spike amplitude of CA1 pyramidal neurons following Schaffer collaterals stimulation. TLR3 activation which results in seizure inhibition does not evoke NF-kB-dependent inflammatory molecules or morphological activation of glia, however, it induces the alternative interferon (IFN) regulatory factor (IRF)-3/IFN-β signaling pathway. IFN-β reproduced the inhibitory effects of Poly I:C on neuronal excitability in hippocampal slices. Seizure inhibition attained with activation the TLR3-IRF3/IFN-β axis should be carefully considered when TLR3 are targeted for therapeutic purposes.

Altered Levels of Toll-Like Receptors in Circulating Extracellular Vesicles in Multiple Sclerosis

Extracellular vesicles (EVs) are involved in inter-cellular communication and their cargo may provide prognostic/diagnostic biomarkers. To discover EV-associated biomarkers for Multiple Sclerosis (MS), we used an immune marker array to identify surface proteins on circulating EVs that differ between MS patients and controls (n = 3 each). We identified toll-like receptor-3 (TLR3) as a potential target for further validation. We utilized prospectively collected serum from relapsing-remitting MS patients (n = 18) and controls (n = 16) and confirmed lower concentration of TLR3 and higher concentration of mechanistically related TLR4 in MS EVs compared to controls. Future studies may further evaluate the utility of EV-associated TLRs as MS biomarkers and uncover their mechanistic significance.

Interferon β-Mediated Protective Functions of Microglia in Central Nervous System Autoimmunity

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) leading to demyelination and axonal damage. It often affects young adults and can lead to neurological disability. Interferon β (IFNβ) preparations represent widely used treatment regimens for patients with relapsing-remitting MS (RRMS) with therapeutic efficacy in reducing disease progression and frequency of acute exacerbations. In mice, IFNβ therapy has been shown to ameliorate experimental autoimmune encephalomyelitis (EAE), an animal model of MS while genetic deletion of IFNβ or its receptor augments clinical severity of disease. However, the complex mechanism of action of IFNβ in CNS autoimmunity has not been fully elucidated. Here, we review our current understanding of the origin, phenotype, and function of microglia and CNS immigrating macrophages in the pathogenesis of MS and EAE. In addition, we highlight the emerging roles of microglia as IFNβ-producing cells and vice versa the impact of IFNβ on microglia in CNS autoimmunity. We finally discuss recent progress in unraveling the underlying molecular mechanisms of IFNβ-mediated effects in EAE.

Effects of Aspirin in Rats With Ouabain Intracerebral Treatment-Possible Involvement of Inflammatory Modulation?

Bipolar disorder (BD) is a chronic and refractory disease with high probability of morbidity and mortality. Although epidemiological studies have established a strong association between BD and immune dysfunction, the precise etiology is still debatable, and the underpinning mechanism remains poorly investigated and understood. In the present study, manic-like symptoms of BD were induced in rats after intracerebroventricular administration of ouabain. Aspirin, a commonly used anti-inflammatory agent, was used to treat the induced manic-like symptoms and inflammation. Concentrations of a spectrum of inflammatory cytokines were examined by enzyme-linked immunosorbent assay in both plasma and brain tissues, and expression of Toll-like receptors 3 and 4 were determined in rat brains. Locomotor activity was monitored with open-field test to assess the effects of ouabain challenge and to evaluate the treatment efficacy of aspirin. Ouabain administration recapitulated many mania-like features such as increased stereotypic counts, traveling distance in open-field test, and decreased expression of brain-derived neurotrophic factor, interferon gamma, and Toll-like receptor 3, which were frequently found in patients with BD. These abnormalities could be partially reversed by aspirin. Our findings suggest that aspirin could be used as a promising adjunctive therapy for BD.

Differential role of MyD88 and TRIF signaling in myeloid cells in the pathogenesis of autoimmune diabetes

Type 1 diabetes (T1D) is caused by the autoimmune destruction of the insulin-producing pancreatic beta cells. While the role of adaptive immunity has been extensively studied, the role of innate immune responses and particularly of Toll- like Receptor (TLR) signaling in T1D remains poorly understood. Here we show that myeloid cell-specific MyD88 deficiency considerably protected mice from the development of streptozotocin (STZ)-induced diabetes. The protective effect of MyD88 deficiency correlated with increased expression of the immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO) in pancreatic lymph nodes from STZ-treated mice and in bone marrow-derived dendritic cells (BMDC) stimulated with apoptotic cells. Mice with myeloid cell specific TIR-domain-containing adapter-inducing interferon-β (TRIF) knockout showed a trend towards accelerated onset of STZ-induced diabetes, while TRIF deficiency resulted in reduced IDO expression in vivo and in vitro. Moreover, myeloid cell specific MyD88 deficiency delayed the onset of diabetes in Non-Obese Diabetic (NOD) mice, whereas TRIF deficiency had no effect. Taken together, these results identify MyD88 signaling in myeloid cells as a critical pathogenic factor in autoimmune diabetes, which is antagonized by TRIF-dependent responses. This differential function of MyD88 and TRIF depends at least in part on their opposite effects in regulating IDO expression in phagocytes exposed to apoptotic cells.

Cathepsin H deficiency in mice induces excess Th1 cell activation and early-onset of EAE though impairment of toll-like receptor 3 cascade

OBJECTIVE

The objective of this study is to investigate the role of cathepsin H (CatH), a lysosomal cysteine protease, in the development of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis.

METHODS

EAE was induced in CatH-deficient mice (CatH^-/-) and wild-type littermates (+/+) using myelin oligodendrocyte glycoprotein (MOG) 35-55. The effects of CatH deficiency were determined by clinical scoring, mRNA expression levels of Tbx21, Rorc and FoxP3, protein levels of poly(I:C)-induced toll-like receptor 3 (TLR3) and phosphorylation of IRF3, and secretion of interferon-β (IFN-β) by splenocytes.

RESULTS AND CONCLUSIONS

CatH^-/- showed a significantly earlier disease onset of EAE and increased Th1 cell differentiation in splenocytes. Splenocytes prepared from immunized CatH^-/- showed a significant decrease in poly(I:C)-induced increased TLR3 expression, interferon regulatory factor 3 (IRF3) phospholylation and IFN-β secretion. Therefore, CatH deficiency impaired TLR3-mediated activation of IRF3 and consequent secretion of IFN-β from dendritic cells, leading to the enhancement of Th1 cell differentiation and consequent early disease onset of EAE.

The Role of Astrocytes in Multiple Sclerosis

The role traditionally assigned to astrocytes in the pathogenesis of multiple sclerosis (MS) lesions has been the formation of the glial scar once inflammation has subsided. Astrocytes are now recognized to be early and highly active players during lesion formation and key for providing peripheral immune cells access to the central nervous system. Here, we review the role of astrocytes in the formation and evolution of MS lesions, including the recently described functional polarization of astrocytes, discuss prototypical pathways for astrocyte activation, and summarize mechanisms by which MS treatments affect astrocyte function.

TLR7 Signaling Regulates Th17 Cells and Autoimmunity: Novel Potential for Autoimmune Therapy

Innate regulation through TLR signaling has been shown to be important for promoting T cell subset development and function. However, limited information is known about whether differential TLR signaling can selectively inhibit Th17 and/or Th1 cells, which are important for controlling excessive inflammation and autoimmune responses. In this article, we demonstrate that activation of TLR7 signaling in T cells can inhibit Th17 cell differentiation from naive T cells and IL-17 production in established Th17 cells. We further report that downregulation of STAT3 signaling is responsible for TLR7-mediated inhibition of Th17 cells due to induction of suppressor of cytokine signaling 3 and 5. TLR7-mediated suppression of Th17 cells does not require dendritic cell involvement. In addition, we show that TLR7 signaling can suppress Th1 cell development and function through a mechanism different from Th17 cell suppression. Importantly, our complementary in vivo studies demonstrate that treatment with the TLR7 ligand imiquimod can inhibit Th1 and Th17 cells, resulting in the prevention of, and an immunotherapeutic reduction in, experimental autoimmune encephalomyelitis. These studies identify a new strategy to manipulate Th17/Th1 cells through TLR7 signaling, with important implications for successful immunotherapy against autoimmune and inflammatory diseases.

Interferon-β regulates the production of IL-10 by toll-like receptor-activated microglia

Pattern recognition receptors, such as toll‐like receptors (TLRs), perceive tissue alterations and initiate local innate immune responses. Microglia, the resident macrophages of the brain, encode TLRs which primary role is to protect the tissue integrity. However, deregulated activation of TLRs in microglia may lead to chronic neurodegeneration. This double role of microglial responses is often reported in immune‐driven neurologic diseases, as in multiple sclerosis (MS). Consequently, strategies to manipulate microglia inflammatory responses may help to ameliorate disease progression. In this context, the anti‐inflammatory cytokine interleukin (IL)‐10 appears as an attractive target. In this study, we investigated how activation of microglia by TLRs with distinct roles in MS impacts on IL‐10 production. We found that activation of TLR2, TLR4, and TLR9 induced the production of IL‐10 to a greater extent than activation of TLR3. This was surprising as both TLR3 and IL‐10 play protective roles in animal models of MS. Interestingly, combination of TLR3 triggering with the other TLRs, enhanced IL‐10 through the modulation of its transcription, via interferon (IFN)‐β, but independently of IL‐27. Thus, in addition to the modulation of inflammatory responses of the periphery described for the axis TLR3/IFN‐β, we now report a direct modulation of microglial responses. We further show that the presence of IFN‐γ in the microenvironment abrogated the modulation of IL‐10 by TLR3, whereas that of IL‐17 had no effect. Considering the therapeutic application of IFN‐β in MS, our study bears important implications for the understanding of the cytokine network regulating microglia responses in this setting.

Review on Toll-Like Receptor Activation in Myasthenia Gravis: Application to the Development of New Experimental Models

Abnormal toll-like receptor (TLR) activation and uncontrolled resolution of inflammation are suspected to play a key role in the development of autoimmune diseases. Acquired myasthenia gravis (MG) is an invalidating neuromuscular disease leading to muscle weaknesses. MG is mainly mediated by anti-acetylcholine receptor (AChR) autoantibodies, and thymic hyperplasia characterized by ectopic germinal centers is a common feature in MG. An abnormal expression of certain TLRs is observed in the thymus of MG patients associated with the overexpression of interferon (IFN)-β, the orchestrator of thymic changes in MG. Experimental models have been developed for numerous autoimmune diseases. These models are induced by animal immunization with a purified antigen solubilized in complete Freund's adjuvant (CFA) containing heat-inactivated mycobacterium tuberculosis (MTB). Sensitization against the antigen is mainly due to the activation of TLR signaling pathways by the pathogen motifs displayed by MTB, and attempts have been made to substitute the use of CFA by TLR agonists. AChR emulsified in CFA is used to induce the classical experimental autoimmune MG model (EAMG). However, the TLR4 activator lipopolysaccharide (LPS) has proved to be efficient to replace MTB and induce a sensitization against purified AChR. Poly(I:C), the well-known TLR3 agonist, is also able by itself to induce MG symptoms in mice associated with early thymic changes as observed in human MG. In this review, we discuss the abnormal expression of TLRs in MG patients and we describe the use of TLR agonists to induce EAMG in comparison with other autoimmune experimental models.

Innate immune regulation of autoimmunity in multiple sclerosis: Focus on the role of Toll-like receptor 2

Innate immunity relies on a set of germline-encoded receptors including Toll-like receptors (TLRs) that enable the host to discriminate between self and non-self. Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease of the central nervous system (CNS). Infections are thought to play an important role in disease susceptibility. The role of innate immunity in MS has been recently appreciated. TLR2, a member of the TLR family, forms heterodimers with either TLR1 or TLR6 and detects a wide range of microbial as well as self-derived molecular structures. It may thus be important both in fighting infection and in activating autoimmunity. In this review, we discuss innate regulation of autoimmunity in MS with a focus on the role of TLR2 signaling.

TLR3-Induced Maturation of Murine Dendritic Cells Regulates CTL Responses by Modulating PD-L1 Trafficking

Targeting TLR3 through formulations of polyI:C is widely studied as an adjuvant in cancer immunotherapy. The efficacy of such targeting has been shown to increase in combination with anti-PD-L1 treatment. Nevertheless, the mechanistic details of the effect of polyI:C on DC maturation and the impact on T-DC interactions upon PD-L1 blockade is largely unknown. Here we found that although DC treatment with polyI:C induced a potent inflammatory response including the production of type I interferon, polyI:C treatment of DCs impaired activation of peptide specific CD8+ T cells mainly due to PD-L1. Interestingly, we found that PD-L1 trafficking to the cell surface is regulated in two waves in polyI:C-treated DCs. One induced upon overnight treatment and a second more rapid one, specific to polyI:C treatment, was induced upon CD40 signaling leading to a further increase in surface PD-L1 in DCs. The polyI:C-induced cell surface PD-L1 reduced the times of contact between DCs and T cells, potentially accounting for limited T cell activation. Our results reveal a novel CD40-dependent regulation of PD-L1 trafficking induced upon TLR3 signaling that dictates its inhibitory activity. These results provide a mechanistic framework to understand the efficacy of anti-PD-L1 cancer immunotherapy combined with TLR agonists.

An inhibitory alternative splice isoform of Toll-like receptor 3 is induced by type I interferons in human astrocyte cell lines

Toll-like receptor 3 (TLR3) recognizes viral double-stranded RNA. It stimulates pro-inflammatory cytokine and interferon production. Here we reported the expression of a novel isoform of TLR3 in human astrocyte cell lines whose message is generated by alternative splicing. The isoform represents the N-terminus of the protein. It lacks many of the leucine-rich repeat domains, the transmembrane domain, and the intracellular Toll/interleukin-1 receptor domain of TLR3. Type I interferons (interferon-α and interferon-β) induced the expression of this isoform. Exogenous overexpression of this isoform inhibited interferon regulatory factor 3, signal transducers and activators of transcription 1, and Inhibitor of kappa B α signaling following stimulation. This isoform of TLR3 also inhibited the production of chemokine interferon-γ-inducible protein 10. Our study clearly demonstrated that the expression of this isoform of TLR3 was a negative regulator of signaling pathways and that it was inducible by type I interferons. We also found that this isoform could modulate inflammation in the brain. [BMB Reports 2015; 48(12): 696-701]

Cross-talk between pathogen recognizing Toll-like receptors and immunoglobulin Fc receptors in immunity

The individual role of pathogen-binding Toll-like receptors (TLRs) and antibody-binding Fc receptors (FcRs) during pathogenic infections has been studied extensively. However, combined activation of these different receptor classes has received little attention, even though they are triggered simultaneously when immune cells bind antibody-opsonized pathogens. In the last few years, it has become evident that joined activation of TLRs and FcRs substantially tailors inflammatory immune responses, which is an efficient and controlled mechanism of the host to act upon invading pathogens. In this review, we discuss the mechanisms of cross-talk between different TLRs and FcRs and the resulting inflammatory immune responses. Furthermore, we propose how chronic activation via this cross-talk might be detrimental in inflammatory (auto) immune diseases. We conclude with the potential exploitation of the interplay between TLRs and FcRs for monoclonal antibody therapy to target tumors. Future interests in this field of research include establishing a more detailed and mechanistic understanding of the mode of action of TLR and FcR cross-talk and exploration of its physiological importance in health and disease. This may furthermore open up novel therapeutic options for intervention in inflammatory diseases or cancer.

Impact of Exercise on Innate Immunity in Multiple Sclerosis Progression and Symptomatology

Multiple Sclerosis (MS), an idiopathic progressive immune-mediated neurological disorder of the central nervous system (CNS), is characterized by recurrent episodes of inflammatory demyelination and consequent axonal deterioration. It accounts for functional deterioration and lasting disability among young adults. A body of literature demonstrates that physical activity counteracts fatigue and depression and may improve overall quality of life in MS patients. Furthermore, much data indicates that exercise ameliorates chronic neuroinflammation and its related pathologies by tipping cytokine profiles toward an anti-inflammatory signature. Recent data has focused on the direct impact of exercise training on the innate immune system by targeting toll-like receptors (TLRs), signaling pattern recognition receptors that govern the innate immune response, shedding light on the physiological role of TLRs in health and disease. Indeed, TLRs continue to emerge as players in the neuroinflammatory processes underpinning MS. This review will highlight evidence that physical activity and exercise are potential immunomodulatory therapies, targeting innate signaling mechanism(s) to modulate MS symptom development and progression.

Interferon-beta signaling in retinal mononuclear phagocytes attenuates pathological neovascularization

Age-related macular degeneration (AMD) is a leading cause of vision loss among the elderly. AMD pathogenesis involves chronic activation of the innate immune system including complement factors and microglia/macrophage reactivity in the retina. Here, we show that lack of interferon-β signaling in the retina accelerates mononuclear phagocyte reactivity and promotes choroidal neovascularization (CNV) in the laser model of neovascular AMD Complete deletion of interferon-α/β receptor (Ifnar) using Ifnar1(-/-) mice significantly enhanced early microglia and macrophage activation in lesion areas. This triggered subsequent vascular leakage and CNV at later stages. Similar findings were obtained in laser-treated Cx3cr1(Cre) (ER):Ifnar1(fl/fl) animals that allowed the tamoxifen-induced conditional depletion of Ifnar in resident mononuclear phagocytes only. Conversely, systemic IFN-β therapy of laser-treated wild-type animals effectively attenuated microgliosis and macrophage responses in the early stage of disease and significantly reduced CNV size in the late phase. Our results reveal a protective role of Ifnar signaling in retinal immune homeostasis and highlight a potential use for IFN-β therapy in the eye to limit chronic inflammation and pathological angiogenesis in AMD.

Toll-like receptor signalling as a cannabinoid target in Multiple Sclerosis

Toll-like receptors (TLRs) are the sensors of pathogen-associated molecules that trigger tailored innate immune intracellular signalling responses to initiate innate immune reactions. Data from the experimental autoimmune encephalomyelitis (EAE) model indicates that TLR signalling machinery is a pivotal player in the development of murine EAE. To compound this, data from human studies indicate that complex interplay exists between TLR signalling and Multiple Sclerosis (MS) pathogenesis. Cannabis-based therapies are in clinical development for the management of a variety of medical conditions, including MS. In particular Sativex^®, a combination of plant-derived cannabinoids, is an oromucosal spray with efficacy in MS patients, particularly those with neuropathic pain and spasticity. Despite this, the precise cellular and molecular mechanisms of action of Sativex^® in MS patients remains unclear. This review will highlight evidence that novel interplay exists between the TLR and cannabinoid systems, both centrally and peripherally, with relevance to the pathogenesis of MS. This article is part of the Special Issue entitled 'Lipid Sensing G Protein-Coupled Receptors in the CNS'.

TLR3 Agonist Poly-IC Induces IL-33 and Promotes Myelin Repair

Background

Impaired remyelination of demyelinated axons is a major cause of neurological disability. In inflammatory demyelinating disease of the central nervous system (CNS), although remyelination does happen, it is often incomplete, resulting in poor clinical recovery. Poly-IC a known TLR3 agonist and IL-33, a cytokine which is induced by poly-IC are known to influence recovery and promote repair in experimental models of CNS demyelination.

Methodology and Principal Findings

We examined the effect of addition of poly-IC and IL-33 on the differentiation and maturation of oligodendrocyte precursor cells (OPC) cultured in vitro. Both Poly-IC and IL-33 induced transcription of myelin genes and the differentiation of OPC to mature myelin forming cells. Poly-IC induced IL-33 in OPC and addition of IL-33 to in vitro cultures, amplified further, IL-33 expression suggesting an autocrine regulation of IL-33. Poly-IC and IL-33 also induced phosphorylation of p38MAPK, a signaling molecule involved in myelination. Following the induction of gliotoxic injury with lysolecithin to the corpus callosum (CC), treatment of animals with poly-IC resulted in greater recruitment of OPC and increased staining for myelin in areas of demyelination. Also, poly-IC treated animals showed greater expression of IL-33 and higher expression of M2 phenotype macrophages in the CC.

Conclusion/Significance

Our studies suggest that poly-IC and IL-33 play a role in myelin repair by enhancing expression of myelin genes and are therefore attractive therapeutic agents for use as remyelinating agents in human demyelinating disease.

IL-10 Modulates Th17 Pathogenicity during Autoimmune Diseases

The immune system is essential for host defense against pathogen infections; however dysregulated immune response may lead to inflammatory or autoimmune diseases. Elevated activation of both innate immune cells and T cells such as Th17 cells are linked to many autoimmune diseases, including Multiple Sclerosis (MS), arthritis and inflammatory bowel disease (IBD). To keep immune homeostasis, the immune system develops a number of negative feedback mechanisms, such as the production of anti-inflammatory cytokine IL-10, to dampen excessive production of inflammatory cytokines and uncontrolled activation of immune cells. Our recent studies uncover a novel immunoregulatory function of interferon (IFN) pathways on the innate and antigen-specific immune response. Our results show that IFNα/β induced IL-10 production from macrophages and Th17 cells, which in turn negatively regulated Th17 function in autoimmune diseases such as Experimental Allergic Encephalomyelitis (EAE), an animal model of human MS. In a chronic colitis model resembling human IBD, we also found that IL-10 inhibited inflammasome/IL-1 pathway, and the pathogenicity of Th17 cells, leading to reduced chronic intestinal inflammation. Results from our and other studies further suggest that IL-10 produced by both macrophages and regulatory T cells may shift Th17 into more regulatory phenotypes, leading to reduced inflammatory response.

Early IFN-γ production together with decreased expression of TLR3 and TLR9 characterizes EAE development conditional on the presence of myelin

Experimental autoimmune encephalomyelitis (EAE) is a model for the study of multiple sclerosis, which is an inflammatory and demyelinating disease of the central nervous system (CNS). Despite increased efforts to elucidate the function of toll-like receptors (TLRs) in autoimmune diseases of the CNS, the relative contribution of other factors, including the immunomodulatory properties of TLR signaling, role of the innate response and the presence or absence of myelin peptides remain unclear. The aim was to evaluate TLR expression in the CNS during EAE development by investigating the expression of TLRs in the initial phase of EAE and establishing correlations with the modulation of inflammatory factors. Mice were subcutaneously immunized at the tail base with 100 μg of myelin oligodendrocyte glycoprotein peptide (MOG35-55), emulsified in complete Freund's adjuvant (CFA) supplemented with 400 μg of attenuated Mycobacterium tuberculosis H37RA. Pertussis toxin (300 ng per animal) was intraperitoneally injected on the day of immunization and 48 h later. Another group (MOG(-)) received an equal emulsion of CFA and M. tuberculosis, without MOG35-55, and the same protocol of Pertussis toxin. The immunized mice presented signs of disease with increased IFN-γ production and presence of NK cells on Day 2 postimmunization and reduced the expression of TLR-3 and TLR-9. In the spinal cord, CCL5 and CCL20 were higher in EAE. This study establishes a correlation between TLR-3 and TLR-9 expression with the development of EAE. In addition, evidence of a role for the myelin peptide in targeting the innate inflammatory response to the CNS is presented.

Close Encounters of the First Kind: Innate Sensors and Multiple Sclerosis

Although autoimmune diseases by definition imply adaptive immune system pathologies, growing evidence points to the relevance of innate receptors in modulating the initiation and progression of the autoreactive response. Multiple sclerosis (MS) is a chronic autoimmune disease characterised by central nervous system (CNS) demyelination, inflammation and axonal damage, in which the role of several pathogens such as herpes viruses have long been described as potential triggers. Encounters of these pathogens with altered innate receptors in susceptible individuals might drive pathological autoreactivity and inflammation, overcoming tolerance and causing subsequent CNS damage. In particular, functional and genetic studies reveal that Toll-like receptor (TLR) 2 and the Nod-like receptor (NLR) P3 could be involved in MS pathogenesis, whereas TLR3, the triggering receptor expressed on myeloid cells (TREM)-2 and the C-type lectin receptors (CLRs) MBL and MASP-3 would have a putative protective role. A better understanding of these interactions will provide important insights into the aetiopathogenesis of MS and could help design potential targets for novel therapies.

Toll-Like Receptors in the Pathogenesis of Autoimmune Diseases

Human Toll-like receptors (TLRs) are a family of transmembrane receptors, which play a key role in both innate and adaptive immune responses. Beside of recognizing specific molecular patterns that associated with different types of pathogens, TLRs may also detect a number of self-proteins and endogenous nucleic acids. Activating TLRs lead to the heightened expression of various inflammatory genes, which have a protective role against infection. Data rising predominantly from human patients and animal models of autoimmune disease indicate that, inappropriate triggering of TLR pathways by exogenous or endogenous ligands may cause the initiation and/or perpetuation of autoimmune reactions and tissue damage. Given their important role in infectious and non-infectious disease process, TLRs and its signaling pathways emerge as appealing targets for therapeutics. In this review, we demonstrate how TLRs pathways could be involved in autoimmune disorders and their therapeutic application.

Role of TRIF Small Interference RNA (siRNA) in Chronic Experimental Allergic Encephalomyelitis (EAE)

BACKGROUND

Multiple sclerosis (MS) is an autoimmune disease causing multifocal demyelination and axonal injuries in the central nervous system (CNS). Toll-interleukin-1 receptor (TIR)-domain containing adaptor protein-inducing interferon beta (TRIF) is an important adaptor protein for Toll-like receptors (TLRs) and can modulate the immune response via regulating cytokine secretion. This study investigated the potential function of TRIF in MS mice via small interference RNA (siRNA).

MATERIAL AND METHODS

Isolated mouse lymphocytes were processed using TRIF siRNA, followed by RT-PCR assay to quantify TRIF expression level. An experimental allergic encephalomyelitis (EAE) model was prepared in C57BL/6 mice immunized with MOG 35-55. TRIF siRNA or controlled siRNA were intravenously applied to evaluate the neurological function of animals. Serum levels of IFN-γ and IL-2 were observed.

RESULTS

Specific siRNA effectively decreased the TRIF expression in mouse dendritic cells and this siRNA improved the EAE severity and neurological scores. Further assays showed that both IFN-γ and IL-2 levels in the siRNA treatment group were significantly lower than in controls.

CONCLUSIONS

The expression of TRIF can be down-regulated by siRNA, thereby alleviating the severity of EAE via its inhibition of interleukin and cytokine release. This may provide new insights for future treatment of MS.

Modulation of TLR3/TLR4 inflammatory signaling by the GABAB receptor agonist baclofen in glia and immune cells: relevance to therapeutic effects in multiple sclerosis

The GABAB receptor agonist, baclofen, is used to treat muscle tightness and cramping caused by spasticity in a number of disorders including multiple sclerosis (MS), but its precise mechanism of action is unknown. Neuroinflammation drives the central pathology in MS and is mediated by both immunoreactive glial cells and invading lymphocytes. Furthermore, a body of data indicates that the Toll-like receptor (TLR) family of innate immune receptors is implicated in MS progression. In the present study we investigated whether modulation of GABAB receptors using baclofen can exert anti-inflammatory effects by targeting TLR3 and(or) TLR4-induced inflammatory signaling in murine glial cells and human peripheral blood mononuclear cells (PBMCs) isolated from healthy control individuals and patients with the relapse-remitting (RR) form of MS. TLR3 and TLR4 stimulation promoted the nuclear sequestration of NF-κB and pro-inflammatory cytokine expression in murine glia, while TLR4, but not TLR3, promoted pro-inflammatory cytokine expression in PBMCs isolated from both healthy donors and RR-MS patients. Importantly, this effect was exacerbated in RR-MS patient immune cells. We present further evidence that baclofen dose-dependently attenuated TLR3- and TLR4-induced inflammatory signaling in primary glial cells. Pre-exposure of PBMCs isolated from healthy donors to baclofen attenuated TLR4-induced TNF-α expression, but did not affect TLR4-induced TNF-α expression in RR-MS patient PBMCs. Interestingly, mRNA expression of the GABAB receptor was reduced in PBMCs from RR-MS donors when compared to healthy controls, an effect that might contribute to the differential sensitivity to baclofen seen in healthy and RR-MS patient cells. Overall these findings indicate that baclofen differentially regulates TLR3 and TLR4 signaling in glia and immune cells, and offers insight on the role of baclofen in the treatment of neuroinflammatory disease states including MS.

Induction of endogenous Type I interferon within the central nervous system plays a protective role in experimental autoimmune encephalomyelitis

The Type I interferons (IFN), beta (IFN-β) and the alpha family (IFN-α), act through a common receptor and have anti-inflammatory effects. IFN-β is used to treat multiple sclerosis (MS) and is effective against experimental autoimmune encephalomyelitis (EAE), an animal model for MS. Mice with EAE show elevated levels of Type I IFNs in the central nervous system (CNS), suggesting a role for endogenous Type I IFN during inflammation. However, the therapeutic benefit of Type I IFN produced in the CNS remains to be established. The aim of this study was to examine whether experimentally induced CNS-endogenous Type I IFN influences EAE. Using IFN-β reporter mice, we showed that direct administration of polyinosinic–polycytidylic acid (poly I:C), a potent inducer of IFN-β, into the cerebrospinal fluid induced increased leukocyte numbers and transient upregulation of IFN-β in CD45/CD11b-positive cells located in the meninges and choroid plexus, as well as enhanced IFN-β expression by parenchymal microglial cells. Intrathecal injection of poly I:C to mice showing first symptoms of EAE substantially increased the normal disease-associated expression of IFN-α, IFN-β, interferon regulatory factor-7 and IL-10 in CNS, and disease worsening was prevented for as long as IFN-α/β was expressed. In contrast, there was no therapeutic effect on EAE in poly I:C-treated IFN receptor-deficient mice. IFN-dependent microglial and astrocyte response included production of the chemokine CXCL10. These results show that Type I IFN induced within the CNS can play a protective role in EAE and highlight the role of endogenous type I IFN in mediating neuroprotection.

IFNβ secreted by microglia mediates clearance of myelin debris in CNS autoimmunity

Introduction

Multiple sclerosis (MS) is a chronic demyelinating disorder of the central nervous system (CNS) leading to progressive neurological disability. Interferon β (IFNβ) represents a standard treatment for relapsing-remitting MS and exogenous administration of IFNβ exhibits protective effects in experimentally induced CNS autoimmunity. Also, genetic deletion of IFNβ in mice leads to an aggravation of disease symptoms in the MS model of experimental autoimmune encephalomyelitis (EAE). However, neither the underlying mechanisms mediating the beneficial effects nor the cellular source of IFNβ have been fully elucidated.

Results

In this report, a subpopulation of activated microglia was identified as the major producers of IFNβ in the CNS at the peak of EAE using an IFNβ-fluorescence reporter mouse model. These IFNβ expressing microglia specifically localized to active CNS lesions and were associated with myelin debris in demyelinated cerebellar organotypic slice cultures (OSCs). In response to IFNβ microglia showed an enhanced capacity to phagocytose myelin in vitro and up-regulated the expression of phagocytosis-associated genes. IFNβ treatment was further sufficient to stimulate association of microglia with myelin debris in OSCs. Moreover, IFNβ-producing microglia mediated an enhanced removal of myelin debris when co-transplanted onto demyelinated OSCs as compared to IFNβ non-producing microglia.

Conclusions

These data identify activated microglia as the major producers of protective IFNβ at the peak of EAE and as orchestrators of IFNβ-induced clearance of myelin debris.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0192-4) contains supplementary material, which is available to authorized users.

Using Poly I:C as an adjuvant does not induce or exacerbate models of systemic lupus erythematosus

Subunit vaccines are typically poorly immunogenic when administered alone, and require adjuvants for robust responses. Triggering TLRs to boost antigen-specific adaptive immunity is an attractive approach to increase the potency and quality of vaccines. However, recent reports suggest that alterations in TLR expression are associated with the pathogenesis of inflammatory and autoimmune diseases. To compare genetic studies with adjuvant studies, we examined whether stimulation through a TLR agonist induces or increases the autoimmune phenotype of healthy or autoimmune mice. C57BL/6, MRL/lpr, and Fcγr2b-deficient mice were dosed i.p. with Poly I:C every other day for 3 weeks, and monitored for signs of autoimmunity over 3 months. A separate group of mice was vaccinated three times i.m. with rPA anthrax antigen with or without Poly I:C with 2 weeks between doses. Immunized groups exhibited robust responses to vaccine and C57BL/6 and MRL/lpr mice showed a statistically significant increase in anti-rPA IgG responses in the presence of Poly I:C. Interestingly, Fcγr2b-/- mice showed increases with the base rPA vaccine, which was not significantly increased when Poly I:C was used as an adjuvant. In the chronically dosed groups, we also observed subtle alterations in levels of total antibody and some autoantibodies. However, there were no statistically significant differences in autoimmune syndrome, as measured by proteinurea, kidney pathology, weight loss, and mortality, with Poly I:C administration in chronic or vaccination mode. Taken together, these results suggest that administration of TLR3 agonists in chronic or vaccination mode does not induce or exacerbate models of systemic lupus erythematosus.

Interferon regulatory factor 3 in adaptive immune responses

Interferon regulatory factor (IRF) 3 plays a key role in innate responses against viruses. Indeed, activation of this transcription factor triggers the expression of type I interferons and downstream interferon-stimulated genes in infected cells. Recent evidences indicate that this pathway also modulates adaptive immune responses. This review focuses on the different mechanisms that are implicated in this process. We discuss the role of IRF3 within antigen-presenting cells and T lymphocytes in the polarization of the cellular immune response and its implication in the pathogenesis of immune disorders.

Interferon regulatory factor (IRF) 3 is critical for the development of experimental autoimmune encephalomyelitis

Background

Experimental autoimmune encephalomyelitis (EAE) is an animal model of autoimmune inflammatory demyelination that is mediated by Th1 and Th17 cells. The transcription factor interferon regulatory factor 3 (IRF3) is activated by pathogen recognition receptors and induces interferon-β production.

Methods

To determine the role of IRF3 in autoimmune inflammation, we immunised wild-type (WT) and irf3^−/− mice to induce EAE. Splenocytes from WT and irf3^−/− mice were also activated in vitro in Th17-polarising conditions.

Results

Clinical signs of disease were significantly lower in mice lacking IRF3, with reduced Th1 and Th17 cells in the central nervous system. Peripheral T-cell responses were also diminished, including impaired proliferation and Th17 development in irf3^−/− mice. Myelin-reactive CD4⁺ cells lacking IRF3 completely failed to transfer EAE in Th17-polarised models as did WT cells transferred into irf3^−/− recipients. Furthermore, IRF3 deficiency in non-CD4⁺ cells conferred impairment of Th17 development in antigen-activated cultures.

Conclusion

These data show that IRF3 plays a crucial role in development of Th17 responses and EAE and warrants investigation in human multiple sclerosis.