IFN-beta gene deletion leads to augmented and chronic demyelinating experimental autoimmune encephalomyelitis

Pathogenicity and transcriptomic resolution in dengue virus serotype 1 infected AGB6 mouse model

Dengue viruses are the causative agents of dengue fever, dengue hemorrhagic fever, and dengue shock syndrome, which are mainly transmitted by Aedes aegypti and Aedes albopictus mosquitoes, and cost billions of dollars annually in patient treatment and mosquito control. Progress in understanding DENV pathogenesis and developing effective treatments has been hampered by the lack of a suitable small pathological animal model. Until now, the candidate vaccine, antibody, and drug for DENV have not been effectively evaluated. Here, we analyzed the pathogenicity of DENV-1 in type Ⅰ and type Ⅱ interferon receptor-deficient mice (AGB6) by intraperitoneal inoculation. Infected mice showed such neurological symptoms as opisthotonus, hunching, ataxia, and paralysis of one or both hind limbs. Viremia can be detected 3 days after infection. It was found that 6.98 × 103 PFU or higher dose induce 100% mortality. To determine the cause of lethality in mice, heart, liver, spleen, lung, kidney, intestinal, and brain tissues were collected from AGB6 mice (at an attack dose of 6.98 × 103 PFU) for RNA quantification, and it was found that the viral load in brain tissues peaked at moribund states (14 dpi) and that the viral loads in the other tissues and organs decreased over time. Significant histopathologic changes were observed in brain tissue (hippocampal region and cerebral cortex). Hematological analysis showed hemorrhage and hemoconcentration in infected mice. DENV-1 can be isolated from the brain tissue of infected mice. Subsequently, brain tissue transcriptome sequencing was performed to assess host response characteristics in infected AGB6 mice. Transcriptional patterns in brain tissue suggest that aberrant expression of pro-inflammatory cytokines induces antiviral responses and tissue damage. Screening of hub genes and their characterization by qPCR and ELISA, it was hypothesized that IL-6 and IFN-γ might be the key factors in dengue virus-induced inflammatory response. Therefore, this study provides an opportunity to decipher certain aspects of dengue pathogenesis further and provides a new platform for drug, antibody, and vaccine testing.

The brain cytokine orchestra in multiple sclerosis: from neuroinflammation to synaptopathology

The central nervous system (CNS) is finely protected by the blood-brain barrier (BBB). Immune soluble factors such as cytokines (CKs) are normally produced in the CNS, contributing to physiological immunosurveillance and homeostatic synaptic scaling. CKs are peptide, pleiotropic molecules involved in a broad range of cellular functions, with a pivotal role in resolving the inflammation and promoting tissue healing. However, pro-inflammatory CKs can exert a detrimental effect in pathological conditions, spreading the damage. In the inflamed CNS, CKs recruit immune cells, stimulate the local production of other inflammatory mediators, and promote synaptic dysfunction. Our understanding of neuroinflammation in humans owes much to the study of multiple sclerosis (MS), the most common autoimmune and demyelinating disease, in which autoreactive T cells migrate from the periphery to the CNS after the encounter with a still unknown antigen. CNS-infiltrating T cells produce pro-inflammatory CKs that aggravate local demyelination and neurodegeneration. This review aims to recapitulate the state of the art about CKs role in the healthy and inflamed CNS, with focus on recent advances bridging the study of adaptive immune system and neurophysiology.

FTY720 requires vitamin B12-TCN2-CD320 signaling in astrocytes to reduce disease in an animal model of multiple sclerosis

Vitamin B12 (B12) deficiency causes neurological manifestations resembling multiple sclerosis (MS); however, a molecular explanation for the similarity is unknown. FTY720 (fingolimod) is a sphingosine 1-phosphate (S1P) receptor modulator and sphingosine analog approved for MS therapy that can functionally antagonize S1P1. Here, we report that FTY720 suppresses neuroinflammation by functionally and physically regulating the B12 pathways. Genetic and pharmacological S1P1 inhibition upregulates a transcobalamin 2 (TCN2)-B12 receptor, CD320, in immediate-early astrocytes (ieAstrocytes; a c-Fos-activated astrocyte subset that tracks with experimental autoimmune encephalomyelitis [EAE] severity). CD320 is also reduced in MS plaques. Deficiency of CD320 or dietary B12 restriction worsens EAE and eliminates FTY720's efficacy while concomitantly downregulating type I interferon signaling. TCN2 functions as a chaperone for FTY720 and sphingosine, whose complex induces astrocytic CD320 internalization, suggesting a delivery mechanism of FTY720/sphingosine via the TCN2-CD320 pathway. Taken together, the B12-TCN2-CD320 pathway is essential for the mechanism of action of FTY720.

Inhibition of Microglial Activation by Amitriptyline and Doxepin in Interferon-β Pre-Treated Astrocyte–Microglia Co-Culture Model of Inflammation

Depression may occur in patients with multiple sclerosis, especially during interferon-β (IFN-β) treatment, and therapy with antidepressants may be necessary. Interactions of IFN-β with antidepressants concerning glia-mediated inflammation have not yet been studied. Primary rat co-cultures of astrocytes containing 5% (M5, consistent with “physiological” conditions) or 30% (M30, consistent with “pathological, inflammatory” conditions) of microglia were incubated with 10 ng/mL amitriptyline or doxepin for 2 h, or with 2000 U/mL IFN-β for 22 h. To investigate the effects of antidepressants on IFN-β treatment, amitriptyline or doxepin was added to IFN-β pre-treated co-cultures. An MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was performed to measure the glial cell viability, immunocytochemistry was performed to evaluate the microglial activation state, and ELISA was performed to measure pro-inflammatory TNF-α and IL-6 cytokine concentrations. Incubation of inflammatory astrocyte–microglia co-cultures with amitriptyline, doxepin or IFN-β alone, or co-incubation of IFN-β pre-treated co-cultures with both antidepressants, significantly reduced the extent of inflammation, with the inhibition of microglial activation. TNF-α and IL-6 levels were not affected. Accordingly, the two antidepressants did not interfere with the anti-inflammatory effect of IFN-β on astrocytes and microglia. Furthermore, no cytotoxic effects on glial cells were observed. This is the first in vitro study offering novel perspectives in IFN-β treatment and accompanying depression regarding glia.

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.

The role of type I IFN in autoimmune and autoinflammatory diseases with CNS involvement

Type I interferons (IFNs) are major mediators of innate immunity, with well-known antiviral, antiproliferative, and immunomodulatory properties. A growing body of evidence suggests the involvement of type I IFNs in the pathogenesis of central nervous system (CNS) manifestations in the setting of chronic autoimmune and autoinflammatory disorders, while IFN-β has been for years, a well-established therapeutic modality for multiple sclerosis (MS). In the present review, we summarize the current evidence on the mechanisms of type I IFN production by CNS cellular populations as well as its local effects on the CNS. Additionally, the beneficial effects of IFN-β in the pathophysiology of MS are discussed, along with the contributory role of type I IFNs in the pathogenesis of neuropsychiatric lupus erythematosus and type I interferonopathies.

STAT1 signaling protects self-reactive T cells from control by innate cells during neuroinflammation

The transcription factor STAT1 plays a critical role in modulating the differentiation of CD4⁺ T cells producing IL-17 and GM-CSF, which promote the development of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). The protective role of STAT1 in MS and EAE has been largely attributed to its ability to limit pathogenic Th cells and promote Tregs. Using mice with selective deletion of STAT1 in T cells (STAT1^CD4-Cre), we identified a potentially novel mechanism by which STAT1 regulates neuroinflammation independently of Foxp3⁺ Tregs. STAT1-deficient effector T cells became the target of NK cell–mediated killing, limiting their capacity to induce EAE. STAT1-deficient T cells promoted their own killing by producing more IL-2 that, in return, activated NK cells. Elimination of NK cells restored EAE susceptibility in STAT1^CD4-Cre mice. Therefore, our study suggests that the STAT1 pathway can be manipulated to limit autoreactive T cells during autoimmunity directed against the CNS.

The host inflammatory response contributes to disease severity in Crimean-Congo hemorrhagic fever virus infected mice

Crimean-Congo hemorrhagic fever virus (CCHFV) is an important human pathogen. In cell culture, CCHFV is sensed by the cytoplasmic RNA sensor retinoic acid-inducible gene I (RIG-I) molecule and its adaptor molecule mitochondrial antiviral signaling (MAVS) protein. MAVS initiates both type I interferon (IFN-I) and proinflammatory responses. Here, we studied the role MAVS plays in CCHFV infection in mice in both the presence and absence of IFN-I activity. MAVS-deficient mice were not susceptible to CCHFV infection when IFN-I signaling was active and showed no signs of disease. When IFN-I signaling was blocked by antibody, MAVS-deficient mice lost significant weight, but were uniformly protected from lethal disease, whereas all control mice succumbed to infection. Cytokine activity in the infected MAVS-deficient mice was markedly blunted. Subsequent investigation revealed that CCHFV infected mice lacking TNF-α receptor signaling (TNFA-R-deficient), but not IL-6 or IL-1 activity, had more limited liver injury and were largely protected from lethal outcomes. Treatment of mice with an anti-TNF-α neutralizing antibody also conferred partial protection in a post-virus exposure setting. Additionally, we found that a disease causing, but non-lethal strain of CCHFV produced more blunted inflammatory cytokine responses compared to a lethal strain in mice. Our work reveals that MAVS activation and cytokine production both contribute to CCHFV pathogenesis, potentially identifying new therapeutic targets to treat this disease.

IFN-β Deficiency Results in Fatal or Demyelinating Disease in C57BL/6 Mice Infected With Theiler's Murine Encephalomyelitis Viruses

Type I Interferons (IFN-I) are important inducers of the antiviral immune response and immune modulators. IFN-β is the most highly expressed IFN-I in the central nervous system (CNS). The infection of SJL mice with the BeAn or the DA strain of Theiler's murine encephalomyelitis virus (TMEV) results in a progressive demyelinating disease. C57BL/6 mice are usually resistant to TMEV-induced demyelination and eliminate these strains from the CNS within several weeks. Using C57BL/6 IFN-β knockout (IFN-β^-/-) mice infected with TMEV, we evaluated the role of IFN-β in neuroinfection. Despite the resistance of C57BL/6 wild type (WT) mice to TMEV infection, DA-infected IFN-β^-/- mice had to be killed at 7 to 8 days post infection (dpi) due to severe clinical disease. In contrast, BeAn-infected IFN-β^-/- mice survived until 98 dpi. Nevertheless at 14 dpi, BeAn-infected IFN-β^-/- mice showed a stronger encephalitis and astrogliosis, higher viral load as well as higher mRNA levels of Isg15, Eif2ak2 (PKR), Tnfa, Il1b, Il10, Il12 and Ifng in the cerebrum than BeAn-infected WT mice. Moreover, the majority of IFN-β^-/- mice did not clear the virus from the CNS and developed mild demyelination in the spinal cord at 98 dpi, whereas virus and lesions were absent in the spinal cord of WT mice. Persistently infected IFN-β^-/- mice also had higher Isg15, Eif2ak1, Tnfa, Il1a, Il1b and Ifng mRNA levels in the spinal cord at 98 dpi than their virus-negative counterparts indicating an activation of IFN-I signaling and ongoing inflammation. Most importantly, BeAn-infected NesCre^+/- IFN-β^fl/fl mice, which do not express IFN-β in neurons, astrocytes and oligodendrocytes, only developed mild brain lesions similar to WT mice. Consequently, IFN-β produced by neuroectodermal cells does not seem to play a critical role in the resistance of C57BL/6 mice against fatal and demyelinating disease induced by TMEV strains.

cGAS-STING-mediated IFN-I response in host defense and neuro-inflammatory diseases

The presence of foreign or misplaced nucleic acids is a danger signal that triggers innate immune responses through activating cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) and binding to its downstream signaling effector stimulator of interferon genes (STING). Then the cGAS-STING pathway activation links nucleic acid sensing to immune responses and pathogenic entities clearance. However, overactivation of this signaling pathway leads to fatal immune disorders and contributes to the progression of many human inflammatory diseases. Therefore, optimal activation of this pathway is crucial for the elimination of invading pathogens and the maintenance of immune homeostasis. In this review, we will summarize its fundamental roles in initiating host defense against invading pathogens and discuss its pathogenic roles in multiple neuro-inflammatory diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS) and other neurodegenerative diseases.

ADAM12 is a costimulatory molecule that determines Th1 cell fate and mediates tissue inflammation

A disintegrin and metalloproteinase (ADAM)12 was previously found to be expressed in T cells in the inflamed brain. However, the function of ADAM12 in T-cell responses in general and in tissue inflammation has not been examined. Here, we studied the role of ADAM12 in T-cell responses, fate determination on activation, and its functions in T cells to mediate tissue inflammation. We identified ADAM12 as a costimulatory molecule that is expressed on naive T cells and downregulated on stimulation. ADAM12 mimics CD28 costimulatory signaling to activate and induce the proliferation of T-helper 1 (Th1) cells. Monoclonal ADAM12 Fab antibodies trigger T-cell activation by amplifying TCR signaling to stimulate T-bet-mediated IFNγ production. Lack of genomic ADAM12 and its knockdown in T cells diminished T-bet and IFNγ production in Th1 cells, whereas other T cells, including Th17 cells, were unaffected. ADAM12 had similar functions in vivo on myelin antigen (MOG35-55)-induced T-cell activation. We found that genetic loss of ADAM12 profoundly alleviated Th1-mediated neuroinflammation and thus disease severity in experimental autoimmune encephalomyelitis, a model of multiple sclerosis. Transcriptomic profiling of MOG35-55-specific ADAM12-/- T cells revealed differentially expressed genes that are important for T-cell activation, proliferation, and costimulatory signaling and Th1 pathogenicity, consistent with their inability to cause T-cell-mediated skin inflammation in a model of adoptive delayed-type hypersensitivity. We conclude that ADAM12 is a T-cell costimulatory molecule that contributes to the pathogenesis of tissue inflammation and a potential target for the treatment of Th1-mediated diseases.

Central Nervous System-Endogenous TLR7 and TLR9 Induce Different Immune Responses and Effects on Experimental Autoimmune Encephalomyelitis

Innate receptors, including Toll like receptors (TLRs), are implicated in pathogenesis of CNS inflammatory diseases such as multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). TLR response to pathogens or endogenous signals includes production of immunoregulatory mediators. One of these, interferon (IFN)β, a Type I IFN, plays a protective role in MS and EAE. We have previously shown that intrathecal administration of selected TLR ligands induced IFNβ and infiltration of blood-derived myeloid cells into the central nervous system (CNS), and suppressed EAE in mice. We have now extended these studies to evaluate a potential therapeutic role for CNS-endogenous TLR7 and TLR9. Intrathecal application of Imiquimod (TLR7 ligand) or CpG oligonucleotide (TLR9 ligand) into CNS of otherwise unmanipulated mice induced IFNβ expression, with greater magnitude in response to CpG. CD45+ cells in the meninges were identified as source of IFNβ. Intrathecal CpG induced infiltration of monocytes, neutrophils, CD4+ T cells and NK cells whereas Imiquimod did not recruit blood-derived CD45+ cells. CpG, but not Imiquimod, had a beneficial effect on EAE, when given at time of disease onset. This therapeutic effect of CpG on EAE was not seen in mice lacking the Type I IFN receptor. In mice with EAE treated with CpG, the proportion of monocytes was significantly increased in the CNS. Infiltrating cells were predominantly localized to spinal cord meninges and demyelination was significantly reduced compared to non-treated mice with EAE. Our findings show that TLR7 and TLR9 signaling induce distinct inflammatory responses in the CNS with different outcome in EAE and point to recruitment of blood-derived cells and IFNβ induction as possible mechanistic links between TLR9 stimulation and amelioration of EAE. The protective role of TLR9 signaling in the CNS may have application in treatment of diseases such as MS.

IFN-β rescues neurodegeneration by regulating mitochondrial fission via STAT5, PGAM5, and Drp1

Mitochondrial homeostasis is essential for providing cellular energy, particularly in resource-demanding neurons, defects in which cause neurodegeneration, but the function of interferons (IFNs) in regulating neuronal mitochondrial homeostasis is unknown. We found that neuronal IFN-β is indispensable for mitochondrial homeostasis and metabolism, sustaining ATP levels and preventing excessive ROS by controlling mitochondrial fission. IFN-β induces events that are required for mitochondrial fission, phosphorylating STAT5 and upregulating PGAM5, which phosphorylates serine 622 of Drp1. IFN-β signaling then recruits Drp1 to mitochondria, oligomerizes it, and engages INF2 to stabilize mitochondria-endoplasmic reticulum (ER) platforms. This process tethers damaged mitochondria to the ER to separate them via fission. Lack of neuronal IFN-β in the Ifnb^-/- model of Parkinson disease (PD) disrupts STAT5-PGAM5-Drp1 signaling, impairing fission and causing large multibranched, damaged mitochondria with insufficient ATP production and excessive oxidative stress to accumulate. In other PD models, IFN-β rescues dopaminergic neuronal cell death and pathology, associated with preserved mitochondrial homeostasis. Thus, IFN-β activates mitochondrial fission in neurons through the pSTAT5/PGAM5/^S622 Drp1 pathway to stabilize mitochondria/ER platforms, constituting an essential neuroprotective mechanism.

Selected Clostridia Strains from The Human Microbiota and their Metabolite, Butyrate, Improve Experimental Autoimmune Encephalomyelitis

Gut microbiome studies in multiple sclerosis (MS) patients are unravelling some consistent but modest patterns of gut dysbiosis. Among these, a significant decrease of Clostridia cluster IV and XIVa has been reported. In the present study, we investigated the therapeutic effect of a previously selected mixture of human gut-derived 17 Clostridia strains, which belong to Clostridia clusters IV, XIVa, and XVIII, on the clinical outcome of experimental autoimmune encephalomyelitis (EAE). The observed clinical improvement was related to lower demyelination and astrocyte reactivity as well as a tendency to lower microglia reactivity/infiltrating macrophages and axonal damage in the central nervous system (CNS), and to an enhanced immunoregulatory response of regulatory T cells in the periphery. Transcriptome studies also highlighted increased antiinflammatory responses related to interferon beta in the periphery and lower immune responses in the CNS. Since Clostridia-treated mice were found to present higher levels of the immunomodulatory short-chain fatty acid (SCFA) butyrate in the serum, we studied if this clinical effect could be reproduced by butyrate administration alone. Further EAE experiments proved its preventive but slight therapeutic impact on CNS autoimmunity. Thus, this smaller therapeutic effect highlighted that the Clostridia-induced clinical effect was not exclusively related to the SCFA and could not be reproduced by butyrate administration alone. Although it is still unknown if these Clostridia strains will have the same effect on MS patients, gut dysbiosis in MS patients could be partially rebalanced by these commensal bacteria and their immunoregulatory properties could have a beneficial effect on MS clinical course.

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.

PIAS2-mediated blockade of IFN-β signaling: a basis for sporadic Parkinson disease dementia

Familial Parkinson disease (PD) is associated with rare genetic mutations, but the etiology in most patients with sporadic (s)PD is largely unknown, and the basis for its progression to dementia (sPDD) is poorly characterized. We have identified that loss of IFNβ or IFNAR1, the receptor for IFNα/β, causes pathological and behavioral changes resembling PDD, prompting us to hypothesize that dysregulated genes in IFNβ-IFNAR signaling pathway predispose one to sPD. By transcriptomic analysis, we found defective neuronal IFNβ-IFNAR signaling, including particularly elevated PIAS2 associated with sPDD. With meta-analysis of GWASs, we identified sequence variants in IFNβ-IFNAR-related genes in sPD patients. Furthermore, sPDD patients expressed higher levels of PIAS2 mRNA and protein in neurons. To determine its function in brain, we overexpressed PIAS2 under a neuronal promoter, alone or with human α-synuclein, in the brains of mice, which caused motor and cognitive impairments and correlated with intraneuronal phosphorylated (p)α-synuclein accumulation and dopaminergic neuron loss. Ectopic expression of neuronal PIAS2 blocked mitophagy, increased the accumulation of senescent mitochondrial and oxidative stress, as evidenced by excessive oxDJ1 and 8OHdG, by inactivating ERK1/2-P53 signaling. Conversely, PIAS2 knockdown rescued the clinicopathological manifestations of PDD in Ifnb^-/- mice on restoring mitochondrial homeostasis, oxidative stress, and pERK1/2-pP53 signaling. The regulation of JAK-STAT2-PIAS2 signaling was crucial for neurite outgrowth and neuronal survival and excitability and thus might prevent cognitive impairments. Our findings provide insights into the progression of sPD and dementia and have implications for new therapeutic approaches.

Caspase-11 Noncanonical Inflammasome: A Novel Key Player in Murine Models of Neuroinflammation and Multiple Sclerosis

Inflammasomes are intracellular protein complexes consisting of the pattern recognition receptors and inflammatory molecules in the inflamed cells. In response to various ligands, inflammasomes play a pivotal role to execute the inflammatory responses by inducing the pyroptosis and the secretion of pro-inflammatory cytokines, interleukin (IL)-1β, and IL-18. Unlike canonical inflammasomes, including NOD-like receptor family inflammasomes, such as NLRP1, NLRP3, NLRC4, and absence in melanoma 2 inflammasomes, noncanonical inflammasomes, such as mouse caspase-11 and human caspase-4/5 were recently discovered, and their roles in the inflammatory responses have been poorly understood. However, emerging studies have been successfully demonstrating the regulatory roles of these noncanonical inflammasomes on inflammatory responses and the pathogenesis of inflammatory/autoimmune diseases. This review summarizes and discusses the recent studies investigating the regulatory roles of the caspase-11 noncanonical inflammasome in neuroinflammation and the pathogenesis of multiple sclerosis (MS), which provides the insight for the validation of caspase-11 noncanonical inflammasome to develop novel and promising therapeutics for MS.

Vitamin D and IFN-β Modulate the Inflammatory Gene Expression Program of Primary Human T Lymphocytes

IFN-β treatment is a commonly used therapy for relapsing-remitting multiple sclerosis (MS), while vitamin D deficiency correlates with an increased risk of MS and/or its activity. MS is a demyelinating chronic inflammatory disease of the central nervous system, in which activated T lymphocytes play a major role, and may represent direct targets of IFN-β and vitamin D activities. However, the underlying mechanism of action of vitamin D and IFN-β, alone or in combination, remains incompletely understood, especially when considering their direct effects on the ability of T lymphocytes to produce inflammatory cytokines. We profiled the expression of immune-related genes and microRNAs in primary human T lymphocytes in response to vitamin D and IFN-β, and we dissected the impact of these treatments on cytokine production and T cell proliferation. We found that the treatments influenced primarily memory T cell plasticity, rather than polarization toward a stable phenotype. Moreover, our data revealed extensive reprogramming of the transcriptional output of primary T cells in response to vitamin D and IFN-β and provide the bases for further mechanistic insights into these commonly used treatments.

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.

IFN-β signaling dampens microglia reactivity but does not prevent from light-induced retinal degeneration

Chronic activation of microglia is associated with retinal degeneration, which makes them a potential therapeutic target for retinal degenerative diseases including age-related macular degeneration (AMD). Interferon-beta (IFN-β) is a potent immune regulator, commonly used for the treatment of multiple sclerosis patients. We have previously shown that IFN-β prevents microgliosis and choroidal neovascularization in a laser model of wet AMD. Here, we hypothesized that microglia modulation via IFN-β may also dampen mononuclear phagocyte reactivity and thereby protect from retinal degeneration in a light-damage paradigm mimicking some features of dry AMD. BALB/cJ mice received intraperitoneal injections of 10,000 U IFN-β or vehicle every other day; starting at the day of exposure to 15,000 lux white light for 1 h. Systemic treatment with IFN-β partially enhanced IFN-α/β receptor (IFNAR) signaling in the retina and reduced the number of reactivated microglia in the subretinal space. However, four days after light damage neither decreased expression of complement factors nor rescue of retinal thickness was found. We conclude that IFNAR signaling modulate retinal microglia but cannot prevent strong retinal degeneration as elicited by acute white light damage.

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Intraperitoneal application of IFN-β increases IFNAR signaling in the retina.

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IFN-β administration reduces microglia migration to the subretinal space.

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Light-induced retinal degeneration is not restored by IFN-β therapy.

Function of multiple sclerosis-protective HLA class I alleles revealed by genome-wide protein-quantitative trait loci mapping of interferon signalling

Interferons (IFNs) are cytokines that are central to the host defence against viruses and other microorganisms. If not properly regulated, IFNs may contribute to the pathogenesis of inflammatory autoimmune, or infectious diseases. To identify genetic polymorphisms regulating the IFN system we performed an unbiased genome-wide protein-quantitative trait loci (pQTL) mapping of cell-type specific type I and type II IFN receptor levels and their responses in immune cells from 303 healthy individuals. Seven genome-wide significant (p < 5.0E-8) pQTLs were identified. Two independent SNPs that tagged the multiple sclerosis (MS)-protective HLA class I alleles A*02/A*68 and B*44, respectively, were associated with increased levels of IFNAR2 in B and T cells, with the most prominent effect in IgD^–CD27⁺ memory B cells. The increased IFNAR2 levels in B cells were replicated in cells from an independent set of healthy individuals and in MS patients. Despite increased IFNAR2 levels, B and T cells carrying the MS-protective alleles displayed a reduced response to type I IFN stimulation. Expression and methylation-QTL analysis demonstrated increased mRNA expression of the pseudogene HLA-J in B cells carrying the MS-protective class I alleles, possibly driven via methylation-dependent transcriptional regulation. Together these data suggest that the MS-protective effects of HLA class I alleles are unrelated to their antigen-presenting function, and propose a previously unappreciated function of type I IFN signalling in B and T cells in MS immune-pathogenesis.

Genetic association studies have been very successful in identifying disease-associated single nucleotide polymorphisms (SNPs), but it has been challenging to define the molecular mechanisms underlying these associations. As interferons (IFNs) have a central role in the immune system, we hypothesized that some of the SNPs associated to immune-mediated diseases would affect the IFN system. By combining genetic data with characterization of interferon receptor levels and their responses on the protein level in immune cells from 303 genotyped healthy individuals, we show that two SNPs tagging the HLA class I alleles A*02/A*68 and B*44 are associated with a decreased response to type I IFN stimulation in B cells and T cells. Notably, both HLA-A*02 and HLA-B*44 confer protection from developing multiple sclerosis (MS), which is a chronic inflammatory neurologic disease. In addition to suggesting a pathogenic role of enhanced type I interferon signalling in B cells and T cells in MS, our data emphasize the fact that genetic associations in the HLA locus can affect functions not directly associated to antigen presentation, which conceptually may be important for other diseases genetically associated to the HLA locus.

Protective roles for myeloid cells in neuroinflammation

Myeloid cells represent the major cellular component of innate immune responses. Myeloid cells include monocytes and macrophages, granulocytes (neutrophils, basophils and eosinophils) and dendritic cells (DC). The role of myeloid cells has been broadly described both in physiological and in pathological conditions. All tissues or organs are equipped with resident myeloid cells, such as parenchymal microglia in the brain, which contribute to maintaining homeostasis. Moreover, in case of infection or tissue damage, other myeloid cells such as monocytes or granulocytes (especially neutrophils) can be recruited from the circulation, at first to promote inflammation and later to participate in repair and regeneration. This review aims to address the regulatory roles of myeloid cells in inflammatory diseases of the central nervous system (CNS), with a particular focus on recent work showing induction of suppressive function via stimulation of innate signalling in multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE).

Innate signaling within the central nervous system recruits protective neutrophils

There is great interest in understanding how the central nervous system (CNS) communicates with the immune system for recruitment of protective responses. Infiltrating phagocytic monocytes and granulocytes are implicated in neuroinflammation in multiple sclerosis and its animal model experimental autoimmune encephalomyelitis (EAE). To investigate how CNS endogenous signals can be harnessed to promote anti-inflammatory programs, we have used a particulate Toll-like receptor 9 and nucleotide-oligomerization domain 2 bispecific innate ligand (MIS416), to address whether its phagocytosis within the CNS recruits protective myeloid cells. We find that MIS416 injected intrathecally into the cerebrospinal fluid via the cisterna magna induced a local chemokine response that recruited blood-derived monocytes and neutrophils to the CNS. These cells phagocytosed MIS416. The increase in EAE severity normally seen from time of onset did not occur in mice receiving MIS416. This suppression of disease symptoms was dependent on expression of the type I interferon receptor (IFNAR). Transfer of intrathecal MIS416-induced neutrophils suppressed EAE in recipient mice, while monocytes did not transfer protection. MIS416-induced neutrophils showed increased IL-10 expression that was IFNAR1-driven. In contrast to intrathecal administration, intravenous administration of MIS416 led to monocyte but not neutrophil infiltration to the CNS. We thus identify a CNS-intrinsic and -specific phagocytosis-induced recruitment of anti-inflammatory neutrophils that contribute to CNS homeostasis and may have therapeutic potential.

Cannabidiol Regulates Gene Expression in Encephalitogenic T cells Using Histone Methylation and noncoding RNA during Experimental Autoimmune Encephalomyelitis

Cannabidiol (CBD) has been shown by our laboratory to attenuate experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). In this study, we used microarray and next generation sequencing (NGS)-based approaches to determine whether CBD would alter genome-wide histone modification and gene expression in MOG sensitized lymphocytes. We compared H3K4me3 and H3K27me3 marks in CD4+ T cells from naïve, EAE and CBD treated EAE mice by ChIP-seq. Although the overall methylation level of these two histone marks did not change significantly, the signal intensity and coverage differed in individual genes, suggesting that CBD may modulate gene expression by altering histone methylation. Further analysis showed that these histone methylation signals were differentially enriched in the binding sites of certain transcription factors, such as ZNF143 and FoxA1, suggesting that these transcription factors may play important roles in CBD mediated immune modulation. Using microarray analysis, we found that the expression pattern of many EAE-induced genes was reversed by CBD treatment which was consistent with its effect on attenuating the clinical symptoms of EAE. A unique finding of this study was that the expression of many miRNAs and lncRNAs was dramatically affected by CBD. In summary, this study demonstrates that CBD suppresses inflammation through multiple mechanisms, from histone methylation to miRNA to lncRNA.

Interferon beta ameliorates cognitive dysfunction in a rat model of Alzheimer's disease: Modulation of hippocampal neurogenesis and apoptosis as underlying mechanism

Neuronal apoptosis and impaired hippocampal neurogenesis are major players in cognitive/memory dysfunctions including Alzheimer's disease (AD). Interferon beta (IFNβ) is a cytokine with anti-apoptotic and neuroprotective properties on the central nervous system (CNS) cells which specifically affects neural progenitor cells (NPCs) even in the adult brain. In this study, we examined the effect of IFNβ on memory impairment as well as hippocampal neurogenesis and apoptosis in a rat model of AD. AD model was induced by lentiviral-mediated overexpression of mutant APP in the hippocampus of adult rats. Intranasal (IN) administration of IFNβ (0.5 μg/kg and 1 μg/kg doses) was started from day 23 after virus injection and continued every other day to the final day of experiments. The expression levels of APP, neurogenesis (Nestin, Ki67, DCX, and Reelin) and apoptosis (Bax/Bcl-2 ratio, cleaved-caspase-3 and seladin-1) markers were evaluated by immunohistochemistry, real-time PCR, immunofluorescence and western blotting. Moreover, thioflavin T and Nissl stainings were used to assess Aβ plaque levels and neuronal degeneration in the hippocampus, respectively. Our results showed that IFNβ treatment reduced APP expression and Aβ plaque formation, and concomitantly ameliorated spatial learning and memory deficits examined in Y-maze and Morris water maze tests. Moreover, in parallel with reducing apoptosis and neural loss in the hippocampal subfields, IFNβ decreased ectopic neurogenesis in the CA1 and CA3 regions of the AD rat hippocampus. However, IFNβ increased neurogenesis in the dentate gyrus neurogenic niche. Our findings suggest that IFNβ exerts neuroprotective effects at least partly by inhibition of apoptosis and modulation of neurogenesis. Taken together, IFNβ can be a promising therapeutic approach to improve cognitive performance in AD-like neurodegenerative context.

Modulation of three key innate immune pathways for the most common retinal degenerative diseases

This review highlights the role of three key immune pathways in the pathophysiology of major retinal degenerative diseases including diabetic retinopathy, age‐related macular degeneration, and rare retinal dystrophies. We first discuss the mechanisms how loss of retinal homeostasis evokes an unbalanced retinal immune reaction involving responses of local microglia and recruited macrophages, activity of the alternative complement system, and inflammasome assembly in the retinal pigment epithelium. Presenting these key mechanisms as complementary targets, we specifically emphasize the concept of immunomodulation as potential treatment strategy to prevent or delay vision loss. Promising molecules are ligands for phagocyte receptors, specific inhibitors of complement activation products, and inflammasome inhibitors. We comprehensively summarize the scientific evidence for this strategy from preclinical animal models, human ocular tissue analyses, and clinical trials evolving in the last few years.

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.

Type I Interferons in NeuroHIV

Infection with Human Immunodeficiency Virus (HIV)-1 continues to cause HIV-associated neurocognitive disorders despite combined antiretroviral therapy. Interferons (IFNs) are important for any antiviral immune response, but the lasting production of IFNα causes exhaustive activation leading eventually to progression to AIDS. Expression of IFNα in the HIV-exposed central nervous system has been linked to cognitive impairment and inflammatory neuropathology. In contrast, IFNβ exerts anti-inflammatory effects, appears to control, at least temporarily, lentiviral infection in the brain and provides neuroprotection. The dichotomy of type I IFN effects on HIV-1 infection and the associated brain injury will be discussed in this review, because the underlying mechanisms require further investigation to allow harnessing these innate immune factors for therapeutic purposes.

New Therapies of Neovascular AMD-Beyond Anti-VEGFs

Neovascular age-related macular degeneration (nAMD) is one of the leading causes of blindness among the aging population. The current treatment options for nAMD include intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF). However, standardized frequent administration of anti-VEGF injections only improves vision in approximately 30–40% of nAMD patients. Current therapies targeting nAMD pose a significant risk of retinal fibrosis and geographic atrophy (GA) development in nAMD patients. A need exists to develop new therapies to treat nAMD with effective and long-term anti-angiogenic effects. Recent research on nAMD has identified novel therapeutic targets and angiogenic signaling mechanisms involved in its pathogenesis. For example, tissue factor, human intravenous immune globulin, interferon-β signaling, cyclooxygenase-2 (COX-2) and cytochrome P450 monooxygenase lipid metabolites have been identified as key players in the development of angiogenesis in AMD disease models. Furthermore, novel therapies such as NACHT, LRR and PYD domains containing protein 3 (NLRP3) inflammasome inhibition, inhibitors of integrins and tissue factor are currently being tested at the level of clinical trials to treat nAMD. The aim of this review is to discuss the scope for alternative therapies proposed as anti-VEGFs for the treatment of nAMD.

RhoA Drives T-Cell Activation and Encephalitogenic Potential in an Animal Model of Multiple Sclerosis

T-cells are known to be intimately involved in the pathogenesis of multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). T-cell activation is controlled by a range of intracellular signaling pathways regulating cellular responses such as proliferation, cytokine production, integrin expression, and migration. These processes are crucial for the T-cells’ ability to mediate inflammatory processes in autoimmune diseases such as MS. RhoA is a ubiquitously expressed small GTPase well described as a regulator of the actin cytoskeleton. It is essential for embryonic development and together with other Rho GTPases controls various cellular processes such as cell development, shaping, proliferation, and locomotion. However, the specific contribution of RhoA to these processes in T-cells in general, and in autoreactive T-cells in particular, has not been fully characterized. Using mice with a T-cell specific deletion of the RhoA gene (RhoA^fl/flLckCre⁺), we investigated the role of RhoA in T-cell development, functionality, and encephalitogenic potential in EAE. We show that lack of RhoA specifically in T-cells results in reduced numbers of mature T-cells in thymus and spleen but normal counts in peripheral blood. EAE induction in RhoA^fl/flLckCre⁺ mice results in significantly reduced disease incidence and severity, which coincides with a reduced CNS T-cell infiltration. Besides presenting reduced migratory capacity, both naïve and autoreactive effector T-cells from RhoA^fl/flLckCre⁺ mice show decreased viability, proliferative capacity, and an activation profile associated with reduced production of Th1 pro-inflammatory cytokines. Our study demonstrates that RhoA is a central regulator of several archetypical T-cell responses, and furthermore points toward RhoA as a new potential therapeutic target in diseases such as MS, where T-cell activity plays a central role.

The Role of Macrophages in Neuroinflammatory and Neurodegenerative Pathways of Alzheimer's Disease, Amyotrophic Lateral Sclerosis, and Multiple Sclerosis: Pathogenetic Cellular Effectors and Potential Therapeutic Targets

In physiological conditions, different types of macrophages can be found within the central nervous system (CNS), i.e., microglia, meningeal macrophages, and perivascular (blood-brain barrier) and choroid plexus (blood-cerebrospinal fluid barrier) macrophages. Microglia and tissue-resident macrophages, as well as blood-borne monocytes, have different origins, as the former derive from yolk sac erythromyeloid precursors and the latter from the fetal liver or bone marrow. Accordingly, specific phenotypic patterns characterize each population. These cells function to maintain homeostasis and are directly involved in the development and resolution of neuroinflammatory processes. Also, following inflammation, circulating monocytes can be recruited and enter the CNS, therefore contributing to brain pathology. These cell populations have now been identified as key players in CNS pathology, including autoimmune diseases, such as multiple sclerosis, and degenerative diseases, such as Amyotrophic Lateral Sclerosis and Alzheimer’s disease. Here, we review the evidence on the involvement of CNS macrophages in neuroinflammation and the advantages, pitfalls, and translational opportunities of pharmacological interventions targeting these heterogeneous cellular populations for the treatment of brain diseases.

Interferon-β deficiency at asthma exacerbation promotes MLKL mediated necroptosis

Defective production of antiviral interferon (IFN)-β is thought to contribute to rhinovirus-induced asthma exacerbations. These exacerbations are associated with elevated lung levels of lactate dehydrogenase (LDH), indicating occurrence of cell necrosis. We thus hypothesized that reduced lung IFN-β could contribute to necrotic cell death in a model of asthma exacerbations. Wild-type and IFN-β^−/− mice were given saline or house dust mite (HDM) intranasally for 3 weeks to induce inflammation. Double-stranded RNA (dsRNA) was then given for additional 3 days to induce exacerbation. HDM induced an eosinophilic inflammation, which was not associated with increased expression of cleaved caspase-3, cleaved PARP or elevated bronchoalveolar lavage fluid (BALF) LDH levels in wild-type. However, exacerbation evoked by HDM + dsRNA challenges increased BALF levels of LDH, apoptotic markers and the necroptotic markers receptor-interacting protein (RIP)-3 and phosphorylation of mixed linage kinase domain-like protein (pMLKL), compared to HDM + saline. Absence of IFN-β at exacerbation further increased BALF LDH and protein expression of pMLKL compared to wild-type. We demonstrate that cell death markers are increased at viral stimulus-induced exacerbation in mouse lungs, and that absence of IFN-β augments markers of necroptotic cell death at exacerbation. Our data thus suggest a novel role of deficient IFN-β production at viral-induced exacerbation.

Cytokine signaling in multiple sclerosis: Lost in translation

Multiple sclerosis (MS) is a common neurological disorder of putative autoimmune origin. Clinical studies delineate abnormal expression of specific cytokines over the course of disease. Preclinical studies using animal models of MS have yielded promising results in manipulating the activity of certain cytokines to improve the clinical outcome. However, the translation of these findings into the clinic is often disappointing. The reason for this might be the complex nature of cytokine networks and the pathogenesis of neuroinflammation, as well as an oversimplified interpretation of preclinical observations. This review presents an overview on cytokines that potentially contribute to the development of MS and provides examples of success and failure in translating basic science into clinical benefit for people with MS.

Microglial Phenotypes and Functions in Multiple Sclerosis

Microglia are the resident immune cells that constantly survey the central nervous system. They can adapt to their environment and respond to injury or insult by altering their morphology, phenotype, and functions. It has long been debated whether microglial activation is detrimental or beneficial in multiple sclerosis (MS). Recently, the two opposing yet connected roles of microglial activation have been described with the aid of novel microglial markers, RNA profiling, and in vivo models. In this review, microglial phenotypes and functions in the context of MS will be discussed with evidence from both human pathological studies, in vitro and in vivo models. Microglial functional diversity-phagocytosis, antigen presentation, immunomodulation, support, and repair-will also be examined in detail. In addition, this review discusses the emerging evidence for microglia-related targets as biomarkers and therapeutic targets for MS.

Cytokine Signaling in Multiple Sclerosis and Its Therapeutic Applications

Multiple sclerosis (MS) is one of the most common neurological disorders in young adults. The etiology of MS is not known but it is widely accepted that it is autoimmune in nature. Disease onset is believed to be initiated by the activation of CD4+ T cells that target autoantigens of the central nervous system (CNS) and their infiltration into the CNS, followed by the expansion of local and infiltrated peripheral effector myeloid cells that create an inflammatory milieu within the CNS, which ultimately lead to tissue damage and demyelination. Clinical studies have shown that progression of MS correlates with the abnormal expression of certain cytokines. The use of experimental autoimmune encephalomyelitis (EAE) model further delineates the role of these cytokines in neuroinflammation and the therapeutic potential of manipulating their biological activity in vivo. In this review, we will first present an overview on cytokines that may contribute to the pathogenesis of MS or EAE, and provide successful examples and roadblock of translating data obtained from EAE to MS. We will then focus in depth on recent findings that demonstrate the pathological role of granulocyte-macrophage colony-stimulating factor (GM-CSF) in MS and EAE, and briefly discuss the potential of targeting effector myeloid cells as a treatment strategy for MS.

Interferon-β regulates dendritic cell activation and migration in experimental autoimmune encephalomyelitis

CD11c⁺ dendritic cells (DCs) exert a critical role as antigen-presenting cells in regulating pathogenic T cells in multiple sclerosis (MS). To determine whether the therapeutic benefit of interferon-β (IFN-β) treatment for MS is in part influenced by IFN regulation of DC function, we examined the immunophenotype of DCs derived from IFN-β^+/+ and IFN-β^-/- mice using a myelin oligodendrocyte glycoprotein (MOG) peptide-induced mouse model of MS, experimental autoimmune encephalomyelitis (EAE). Our earlier work identified that IFN-β^-/- mice exhibit earlier onset and more rapid progression of neurological impairment compared with IFN-β^+/+ mice. In this study we show that lipopolysaccharide-/MOG peptide-stimulated IFN-β^-/- DCs secrete cytokines associated with pathological T helper type 17 rather than regulatory T-cell polarization and exhibit increased CD80 and MHCII expression when compared with stimulated IFN-β^+/+ DCs. IFN-β^-/- DCs from mice immunized to develop EAE induce greater proliferation of MOG-transgenic CD4⁺ T cells and promote interleukin-17 production by these T cells. Adoptive transfer of MOG peptide-primed IFN-β^-/- DCs into IFN-β^+/+ and IFN-β^-/- mice immunized to develop EAE resulted in their rapid migration into the central nervous system of recipient mice, before onset of disease, which we attribute to failed signal transducer and activator of transcription 1-mediated inhibition of CCR7. Taken together, our data support immunoregulatory roles for IFN-β in the activation and migration of DCs during EAE.

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.

Getting "Inside" Type I IFNs: Type I IFNs in Intracellular Bacterial Infections

Type I interferons represent a unique and complex group of cytokines, serving many purposes during innate and adaptive immunity. Discovered in the context of viral infections, type I IFNs are now known to have myriad effects in infectious and autoimmune disease settings. Type I IFN signaling during bacterial infections is dependent on many factors including whether the infecting bacterium is intracellular or extracellular, as different signaling pathways are activated. As such, the repercussions of type I IFN induction can positively or negatively impact the disease outcome. This review focuses on type I IFN induction and downstream consequences during infection with the following intracellular bacteria: Chlamydia trachomatis, Listeria monocytogenes, Mycobacterium tuberculosis, Salmonella enterica serovar Typhimurium, Francisella tularensis, Brucella abortus, Legionella pneumophila, and Coxiella burnetii. Intracellular bacterial infections are unique because the bacteria must avoid, circumvent, and even co-opt microbial "sensing" mechanisms in order to reside and replicate within a host cell. Furthermore, life inside a host cell makes intracellular bacteria more difficult to target with antibiotics. Because type I IFNs are important immune effectors, modulating this pathway may improve disease outcomes. But first, it is critical to understand the context-dependent effects of the type I IFN pathway in intracellular bacterial infections.

Neuronal IFN-beta-induced PI3K/Akt-FoxA1 signalling is essential for generation of FoxA1+Treg cells

Neurons reprogramme encephalitogenic T cells (T_enc) to regulatory T cells (T_regs), either FoxP3⁺T_regs or FoxA1⁺T_regs. We reported previously that neuronal ability to generate FoxA1⁺T_regs was central to preventing neuroinflammation in experimental autoimmune encephalomyelitis (EAE). Mice lacking interferon (IFN)-β were defective in generating FoxA1⁺T_regs in the brain. Here we show that lack of neuronal IFNβ signalling is associated with the absence of programme death ligand-1 (PDL1), which prevents their ability to reprogramme T_enc cells to FoxA1⁺T_regs. Passive transfer-EAE via IFNβ-competent T_enc cells to mice lacking IFNβ and active induced-EAE in mice lacking its receptor, IFNAR, in the brain (Nes^Cre:Ifnar^fl/fl) result in defective FoxA1⁺T_regs generation and aggravated neuroinflammation. IFNβ activates neuronal PI3K/Akt signalling and Akt binds to transcription factor FoxA1 that translocates to the nucleus and induces PDL1. Conversely, inhibition of PI3K/Akt, FoxA1 and PDL1 blocked neuronal ability to generate FoxA1⁺T_regs. We characterize molecular factors central for neuronal ability to reprogramme pathogenic T cells to FoxA1⁺T_regs preventing neuroinflammation.

Clash of the Cytokine Titans: counter-regulation of interleukin-1 and type I interferon-mediated inflammatory responses

Over the past decades the notion of 'inflammation' has been extended beyond the original hallmarks of rubor (redness), calor (heat), tumor (swelling) and dolor (pain) described by Celsus. We have gained a more detailed understanding of the cellular players and molecular mediators of inflammation which is now being applied and extended to areas of biomedical research such as cancer, obesity, heart disease, metabolism, auto-inflammatory disorders, autoimmunity and infectious diseases. Innate cytokines are often central components of inflammatory responses. Here, we discuss how the type I interferon and interleukin-1 cytokine pathways represent distinct and specialized categories of inflammatory responses and how these key mediators of inflammation counter-regulate each other.

2'-5' oligoadenylate synthetase-like 1 (OASL1) deficiency suppresses central nervous system damage in a murine MOG-induced multiple sclerosis model

Type I Interferon (IFN-I) is critical for antiviral and antitumor defense. Additionally, IFN-I has been used for treating multiple sclerosis (MS), a chronic autoimmune disease of the central nervous system (CNS). Recently, we reported that 2'-5' oligoadenylate synthetase-like 1 (OASL1) negatively regulates IFN-I production upon viral infection and tumor challenge. Therefore, OASL1 deficient (Oasl1(-)(/)(-)) mice are resistant to viral infections and tumor challenge. In this study, we examined whether OASL1 plays a negative role in the development of autoimmune MS by using Oasl1(-)(/)(-) mice and a murine MS model, myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE). Oasl1(-)(/)(-) mice showed enhanced resistance to EAE development compared to wild-type (WT) mice. Additionally, EAE-induced Oasl1(-)(/)(-) mice showed fewer infiltrated immune cells such as T cells and macrophages in the CNS and less CNS inflammation, compared to WT mice. Collectively, these results indicate that OASL1 deficiency suppresses the development of MS-like autoimmunity and suggest that negative regulators of IFN-I could be good therapeutic targets for treating MS in humans.

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.

Interferons and inflammasomes: Cooperation and counterregulation in disease

Interferons and the IL-1 family of cytokines have important roles in host defense against invading viruses and bacteria. Inflammasomes, multimeric cytosolic sensors of infection, are required for IL-1β and IL-18 processing and release. Interferons, IL-1β, and IL-18 are also implicated in autoimmune disease and chronic inflammation. Although independent but complementary pathways induce these cytokine subsets during infection, in some circumstances the cross-talk between these key inflammatory mediators is a particular requirement for effective host defense. In this review we will summarize recent discoveries concerning the potentiation of inflammasome responses by type I interferons, particularly in patients with gram-negative bacterial infections, and reflect on the molecular mechanisms of IFN-β's immunosuppressive effects through modulation of inflammasome and IL-1β signaling in patients with tuberculosis and multiple sclerosis.

Experimental Neuromyelitis Optica Induces a Type I Interferon Signature in the Spinal Cord

Neuromyelitis optica (NMO) is an acute inflammatory disease of the central nervous system (CNS) which predominantly affects spinal cord and optic nerves. Most patients harbor pathogenic autoantibodies, the so-called NMO-IgGs, which are directed against the water channel aquaporin 4 (AQP4) on astrocytes. When these antibodies gain access to the CNS, they mediate astrocyte destruction by complement-dependent and by antibody-dependent cellular cytotoxicity. In contrast to multiple sclerosis (MS) patients who benefit from therapies involving type I interferons (I-IFN), NMO patients typically do not profit from such treatments. How is I-IFN involved in NMO pathogenesis? To address this question, we made gene expression profiles of spinal cords from Lewis rat models of experimental neuromyelitis optica (ENMO) and experimental autoimmune encephalomyelitis (EAE). We found an upregulation of I-IFN signature genes in EAE spinal cords, and a further upregulation of these genes in ENMO. To learn whether the local I-IFN signature is harmful or beneficial, we induced ENMO by transfer of CNS antigen-specific T cells and NMO-IgG, and treated the animals with I-IFN at the very onset of clinical symptoms, when the blood-brain barrier was open. With this treatment regimen, we could amplify possible effects of the I-IFN induced genes on the transmigration of infiltrating cells through the blood brain barrier, and on lesion formation and expansion, but could avoid effects of I-IFN on the differentiation of pathogenic T and B cells in the lymph nodes. We observed that I-IFN treated ENMO rats had spinal cord lesions with fewer T cells, macrophages/activated microglia and activated neutrophils, and less astrocyte damage than their vehicle treated counterparts, suggesting beneficial effects of I-IFN.

Type I/II Interferon Balance in the Regulation of Brain Physiology and Pathology

Recent findings have revealed distinct roles for type I and II interferons (IFN-I and IFN-γ) in the recruitment of immune cells to the central nervous system (CNS) and highlighted the importance of this process for brain maintenance and protection/repair. Furthermore, manipulation of IFN-I and IFN-γ pathways in pathological contexts has yielded conflicting results. We discuss these findings, focusing on two distinct conditions; relapsing remitting multiple sclerosis (RRMS) and brain aging. Using these examples, we propose that regulation of immune cell entry to the CNS is a mechanism through which interaction between IFN-I and -II can affect brain function from its anatomical borders. Deviation from homeostatic IFN-I/-II balance may contribute to distinct brain pathologies, resulting from either insufficient immune surveillance of the CNS and loss of immune-dependent protection, or overwhelming leukocyte entry and immune-mediated destruction.

Lack of Neuronal IFN-β-IFNAR Causes Lewy Body- and Parkinson's Disease-like Dementia

Neurodegenerative diseases have been linked to inflammation, but whether altered immunomodulation plays a causative role in neurodegeneration is not clear. We show that lack of cytokine interferon-β (IFN-β) signaling causes spontaneous neurodegeneration in the absence of neurodegenerative disease-causing mutant proteins. Mice lacking Ifnb function exhibited motor and cognitive learning impairments with accompanying α-synuclein-containing Lewy bodies in the brain, as well as a reduction in dopaminergic neurons and defective dopamine signaling in the nigrostriatal region. Lack of IFN-β signaling caused defects in neuronal autophagy prior to α-synucleinopathy, which was associated with accumulation of senescent mitochondria. Recombinant IFN-β promoted neurite growth and branching, autophagy flux, and α-synuclein degradation in neurons. In addition, lentiviral IFN-β overexpression prevented dopaminergic neuron loss in a familial Parkinson's disease model. These results indicate a protective role for IFN-β in neuronal homeostasis and validate Ifnb mutant mice as a model for sporadic Lewy body and Parkinson's disease dementia.

Endogenous IFN-β signaling exerts anti-inflammatory actions in experimentally induced focal cerebral ischemia

Background

Interferon (IFN)-β exerts anti-inflammatory effects, coupled to remarkable neurological improvements in multiple sclerosis, a neuroinflammatory condition of the central nervous system. Analogously, it has been hypothesized that IFN-β, by limiting inflammation, decreases neuronal death and promotes functional recovery after stroke. However, the core actions of endogenous IFN-β signaling in stroke are unclear.

Methods

To address this question, we used two clinically relevant models of focal cerebral ischemia, transient and permanent middle cerebral artery occlusion, and two genetically modified mouse lines, lacking either IFN-β or its receptor, the IFN-α/β receptor. Subsets of inflammatory and immune cells isolated from the brain, blood, and spleen were studied using flow cytometry. Sensorimotor deficits were assessed by a modified composite neuroscore, the rotating pole and grip strength tests, and cerebral infarct volumes were given by lack of neuronal nuclei immunoreactivity.

Results

Here, we report alterations in local and systemic inflammation in IFN-β knockout (IFN-βKO) mice over 8 days after induction of focal cerebral ischemia. Notably, IFN-βKO mice showed a higher number of infiltrating leukocytes in the brain 2 days after stroke. Concomitantly, in the blood of IFN-βKO mice, we found a higher percentage of total B cells but a similar percentage of mature and activated B cells, collectively indicating a higher proliferation rate. The additional differential regulation of circulating cytokines and splenic immune cell populations in wild-type and IFN-βKO mice further supports an important immunoregulatory function of IFN-β in stroke. Moreover, we observed a significant weight loss 2–3 days and a reduction in grip strength 2 days after stroke in the IFN-βKO group, while endogenous IFN-β signaling did not affect the infarct volume.

Conclusions

We conclude that endogenous IFN-β signaling attenuates local inflammation, regulates peripheral immune cells, and, thereby, may contribute positively to stroke outcome.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0427-0) contains supplementary material, which is available to authorized users.