Type I interferons as ambiguous modulators of chronic inflammation in the central nervous system

Type I interferon response in astrocytes promotes brain metastasis by enhancing monocytic myeloid cell recruitment

Cancer metastasis to the brain is a significant clinical problem. Metastasis is the consequence of favorable interactions between invaded cancer cells and the microenvironment. Here, we demonstrate that cancer-activated astrocytes create a sustained low-level activated type I interferon (IFN) microenvironment in brain metastatic lesions. We further confirm that the IFN response in astrocytes facilitates brain metastasis. Mechanistically, IFN signaling in astrocytes activates C-C Motif Chemokine Ligand 2 (CCL2) production, which further increases the recruitment of monocytic myeloid cells. The correlation between CCL2 and monocytic myeloid cells is confirmed in clinical brain metastasis samples. Lastly, genetically or pharmacologically inhibiting C-C Motif Chemokine Receptor 2 (CCR2) reduces brain metastases. Our study clarifies a pro-metastatic effect of type I IFN in the brain even though IFN response has been considered to have anti-tumor effects. Moreover, this work expands our understandings on the interactions between cancer-activated astrocytes and immune cells in brain metastasis.

Chronic Cortical Inflammation, Cognitive Impairment, and Immune Reactivity Associated with Diffuse Brain Injury Are Ameliorated by Forced Turnover of Microglia

Traumatic brain injury (TBI) is associated with an increased risk of cognitive, psychiatric, and neurodegenerative complications that may develop after injury. Increased microglial reactivity following TBI may underlie chronic neuroinflammation, neuropathology, and exaggerated responses to immune challenges. Therefore, the goal of this study was to force turnover of trauma-associated microglia that develop after diffuse TBI and determine whether this alleviated chronic inflammation, improved functional recovery and attenuated reduced immune reactivity to lipopolysaccharide (LPS) challenge. Male mice received a midline fluid percussion injury (mFPI) and 7 d later were subjected to a forced microglia turnover paradigm using CSF1R antagonism (PLX5622). At 30 d postinjury (dpi), cortical gene expression, dendritic complexity, myelin content, neuronal connectivity, cognition, and immune reactivity were assessed. Myriad neuropathology-related genes were increased 30 dpi in the cortex, and 90% of these gene changes were reversed by microglial turnover. Reduced neuronal connectivity was evident 30 dpi and these deficits were attenuated by microglial turnover. TBI-associated dendritic remodeling and myelin alterations, however, remained 30 dpi independent of microglial turnover. In assessments of functional recovery, increased depressive-like behavior, and cognitive impairment 30 dpi were ameliorated by microglia turnover. To investigate microglial priming and reactivity 30 dpi, mice were injected intraperitoneally with LPS. This immune challenge caused prolonged lethargy, sickness behavior, and microglial reactivity in the TBI mice. These extended complications with LPS in TBI mice were prevented by microglia turnover. Collectively, microglial turnover 7 dpi alleviated behavioral and cognitive impairments associated with microglial priming and immune reactivity 30 dpi.SIGNIFICANCE STATEMENT A striking feature of traumatic brain injury (TBI), even mild injuries, is that over 70% of individuals have long-term neuropsychiatric complications. Chronic inflammatory processes are implicated in the pathology of these complications and these issues can be exaggerated by immune challenge. Therefore, our goal was to force the turnover of microglia 7 d after TBI. This subacute 7 d postinjury (dpi) time point is a critical transitional period in the shift toward chronic inflammatory processes and microglia priming. This forced microglia turnover intervention in mice attenuated the deficits in behavior and cognition 30 dpi. Moreover, microglia priming and immune reactivity after TBI were also reduced with microglia turnover. Therefore, microglia represent therapeutic targets after TBI to reduce persistent neuroinflammation and improve recovery.

Interferon-α promotes MHC I antigen presentation of islet β cells through STAT1-IRF7 pathway in type 1 diabetes

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease. Increased incidence of T1D was reported in patients receiving IFN-α treatment. However, the exact mechanisms of IFN-α that facilitate the pathogenesis of T1D are not fully understood. To explore the mechanism of IFN-α on the immune system and islets, non-obese diabetic (NOD) mice were injected with IFN-α and the progression of autoimmune insulitis was assessed by haematoxylin and eosin (HE) staining, immunohistochemical and flow cytometry analysis. Transcriptional profiling of islets treated with IFN-α was explored by RNA-seq. IFN-α induced antigen presentation was evaluated by qRT-PCR, western blot and immunofluorescence, and key transcription factors were inhibited by small interfering RNAs (siRNAs). Our data show that IFN-α contributed to the progression of autoimmune insulitis in NOD mice by promoting the proliferation of CD8+ T cells. IFN-α upregulated antigen presentation related genes MHC I, TAP1, B2M, PSMB8, NLRC5 and transcriptional regulator STAT1, STAT2, IRF7 at a time and dose-dependent manner. The silence of STAT1 or STAT2 both weakened IFN-α-induced increase of antigen presenting related molecules. IRF7 was also merely influenced by STAT1 silence. The knockdown of IRF7 decreased the IFN-α induced expressions of TAP1, PSMB8 and MHC I and prevented the expression of STAT2 but not STAT1. Our study demonstrated that STAT1-IRF7-MHC I complex axis were crucial for IFN-α signalling in islets, and created positive feedback through IRF7-STAT2 cascade amplifying signals which accelerated the process of T1D.

Spectrum of Neuroradiologic Findings Associated with Monogenic Interferonopathies

The genetic interferonopathies are a heterogeneous group of disorders thought to be caused by the dysregulated expression of interferons and are now commonly considered in the differential diagnosis of children presenting with recurrent or persistent inflammatory phenotypes. With emerging therapeutic options, recognition of these disorders is increasingly important, and neuroimaging plays a vital role. In this article, we discuss the wide spectrum of neuroradiologic features associated with monogenic interferonopathies by reviewing the literature and illustrate these with cases from our institutions. These cases include intracerebral calcifications, white matter T2 hyperintensities, deep WM cysts, cerebral atrophy, large cerebral artery disease, bilateral striatal necrosis, and masslike lesions. A better understanding of the breadth of the neuroimaging phenotypes in conjunction with clinical and laboratory findings will enable earlier diagnosis and direct therapeutic strategies.

Type 1 interferon mediates chronic stress-induced neuroinflammation and behavioral deficits via complement component 3-dependent pathway

Chronic stress is a major risk factor in the pathophysiology of many neuropsychiatric disorders. Further, chronic stress conditions can promote neuroinflammation and inflammatory responses in both humans and animal models. Type I interferons (IFN-I) are critical mediators of the inflammatory response in the periphery and responsible for the altered mood and behavior. However, the underlying mechanisms are not well understood. In the present study, we investigated the role of IFN-I signaling in chronic stress-induced changes in neuroinflammation and behavior. Using the chronic restraint stress model, we found that chronic stress induces a significant increase in serum IFNβ levels in mice, and systemic blockade of IFN-I signaling attenuated chronic stress-induced infiltration of macrophages into prefrontal cortex and behavioral abnormalities. Furthermore, complement component 3 (C3) mediates systemic IFNβ-induced changes in neuroinflammation and behavior. Also, we found significant increases in the mRNA expression levels of IFN-I stimulated genes in the prefrontal cortex of depressed suicide subjects and significant correlation with C3 and inflammatory markers. Together, these findings from animal and human postmortem brain studies identify a crucial role of C3 in IFN-I-mediated changes in neuroinflammation and behavior under chronic stress conditions.

Agent-based modeling reveals benefits of heterogeneous and stochastic cell populations during cGAS-mediated IFNβ production

MOTIVATION

The cGAS pathway is a component of the innate immune system responsible for the detection of pathogenic DNA and upregulation of interferon beta (IFNβ). Experimental evidence shows that IFNβ signaling occurs in highly heterogeneous cells and is stochastic in nature; however, the benefits of these attributes remain unclear. To investigate how stochasticity and heterogeneity affect IFNβ production, an agent-based model is developed to simulate both DNA transfection and viral infection.

RESULTS

We show that heterogeneity can enhance IFNβ responses during infection. Furthermore, by varying the degree of IFNβ stochasticity, we find that only a percentage of cells (20-30%) need to respond during infection. Going beyond this range provides no additional protection against cell death or reduction of viral load. Overall, these simulations suggest that heterogeneity and stochasticity are important for moderating immune potency while minimizing cell death during infection.

AVAILABILITY AND IMPLEMENTATION

Model repository is available at: https://github.com/ImmuSystems-Lab/AgentBasedModel-cGASPathway.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Decoding the Transcriptional Response to Ischemic Stroke in Young and Aged Mouse Brain

Ischemic stroke is a well-recognized disease of aging, yet it is unclear how the age-dependent vulnerability occurs and what are the underlying mechanisms. To address these issues, we perform a comprehensive RNA-seq analysis of aging, ischemic stroke, and their interaction in 3- and 18-month-old mice. We assess differential gene expression across injury status and age, estimate cell type proportion changes, assay the results against a range of transcriptional signatures from the literature, and perform unsupervised co-expression analysis, identifying modules of genes with varying response to injury. We uncover downregulation of axonal and synaptic maintenance genetic program, and increased activation of type I interferon (IFN-I) signaling following stroke in aged mice. Together, these results paint a picture of ischemic stroke as a complex age-related disease and provide insights into interaction of aging and stroke on cellular and molecular level.

Integrative analysis of transcriptomic data related to the liver of laying hens: from physiological basics to newly identified functions

BACKGROUND

At sexual maturity, the liver of laying hens undergoes many metabolic changes to support vitellogenesis. In published transcriptomic approaches, hundreds of genes were reported to be overexpressed in laying hens and functional gene annotation using gene ontology tools have essentially revealed an enrichment in lipid and protein metabolisms. We reanalyzed some data from a previously published article comparing 38-week old versus 10-week old hens to give a more integrative view of the functions stimulated in the liver at sexual maturity and to move beyond current physiological knowledge. Functions were defined based on information available in Uniprot database and published literature.

RESULTS

Of the 516 genes previously shown to be overexpressed in the liver of laying hens, 475 were intracellular (1.23-50.72 fold changes), while only 36 were predicted to be secreted (1.35-66.93 fold changes) and 5 had no related information on their cellular location. Besides lipogenesis and protein metabolism, we demonstrated that the liver of laying hens overexpresses several clock genes (which supports the circadian control of liver metabolic functions) and was likely to be involved in a liver/brain/liver circuit (neurotransmitter transport), in thyroid and steroid hormones metabolisms. Many genes were associated with anatomical structure development, organ homeostasis but also regulation of blood pressure. As expected, several secreted proteins are incorporated in yolky follicles but we also evidenced that some proteins are likely participating in fertilization (ZP1, MFGE8, LINC00954, OVOCH1) and in thyroid hormone maturation (CPQ). We also proposed that secreted proteins (PHOSPHO1, FGF23, BMP7 but also vitamin-binding proteins) may contribute to the development of peripheral organs including the formation of medullar bones to provide labile calcium for eggshell formation. Thirteen genes are uniquely found in chicken/bird but not in human species, which strengthens that some of these genes may be specifically related to avian reproduction.

CONCLUSIONS

This study gives additional hypotheses on some molecular actors and mechanisms that are involved in basic physiological function of the liver at sexual maturity of hen. It also revealed some additional functions that accompany reproductive capacities of laying hens, and that are usually underestimated when using classical gene ontology approaches.

The regulation of interferon type I pathway-related genes RSAD2 and ETV7 specifically indicates antibody-mediated rejection after kidney transplantation

CONTEXT

Antibody-mediated rejection (ABMR) after kidney transplantation (KTx) remains the crucial obstacle to successful long-term graft function. The identification of gene signatures involved in ABMR could grant the basis for better prevention and treatment strategies.

OBJECTIVE

The identification of gene signatures in whole blood cells specific for ABMR after KTx.

MATERIALS AND METHODS

Total RNA from blood cells of 16 kidney-transplanted patients with ABMR, stable graft function (SGF), and with T-cell-mediated rejection (TCMR) was isolated. Gene expression was determined by high-throughput sequencing followed by validation and analyses of differentially expressed candidates on mRNA level and on protein level in a large patient cohort (n = 185) in patients with SGF, urinary tract infection (UTI), borderline rejection (BL), TCMR, ABMR, and interstitial fibrosis and tubular atrophy.

RESULTS

From the 570 genes detected, 111 discriminated ABMR from SGF and TCMR. A distinct enrichment of interferon (IFN) type I and type II signature gene set was observed. The expression of candidate genes IFIT1, ETV7, and RSAD2 distinguished ABMR patients from patients with SGF and also TCMR, whereas ETV7 and RSAD2 differentiated ABMR also from BL.

CONCLUSION

The IFN-inducible genes ETV7 and RSAD2 represent specific biomarkers for ABMR episodes after KTx.

Human Induced Pluripotent Stem Cell-Derived Astrocytes Are Differentially Activated by Multiple Sclerosis-Associated Cytokines

Recent studies highlighted the importance of astrocytes in neuroinflammatory diseases, interacting closely with other CNS cells but also with the immune system. However, due to the difficulty in obtaining human astrocytes, their role in these pathologies is still poorly characterized. Here, we develop a serum-free protocol to differentiate human induced pluripotent stem cells (hiPSCs) into astrocytes. Gene expression and functional assays show that our protocol consistently yields a highly enriched population of resting mature astrocytes across the 13 hiPSC lines differentiated. Using this model, we first highlight the importance of serum-free media for astrocyte culture to generate resting astrocytes. Second, we assess the astrocytic response to IL-1β, TNF-α, and IL-6, all cytokines important in neuroinflammation, such as multiple sclerosis. Our study reveals very specific profiles of reactive astrocytes depending on the triggering stimulus. This model provides ideal conditions for in-depth and unbiased characterization of astrocyte reactivity in neuroinflammatory conditions.

Lentiviral infection of proliferating brain macrophages in HIV and simian immunodeficiency virus encephalitis despite sterile alpha motif and histidine-aspartate domain-containing protein 1 expression

Objective:

HIV-1 infection of the brain and related cognitive impairment remain prevalent in HIV-1-infected individuals despite combination antiretroviral therapy. Sterile alpha motif and histidine-aspartate domain-containing protein 1 (SAMHD1) is a newly identified host restriction factor that blocks the replication of HIV-1 and other retroviruses in myeloid cells. Cell cycle-regulated phosphorylation at residue Thr592 and viral protein X (Vpx)-mediated degradation of SAMHD1 have been shown to bypass SAMHD1 restriction in vitro. Herein, we investigated expression and phosphorylation of SAMHD1 in vivo in relation to macrophage infection and proliferation during the neuropathogenesis of HIV-1 and simian immunodeficiency virus (SIV) encephalitis.

Methods:

Using brain and other tissues from uninfected and SIV-infected macaques with or without encephalitis, we performed immunohistochemistry, multilabel fluorescence microscopy and western blot to examine the expression, localization and phosphorylation of SAMHD1.

Results:

The number of SAMHD1⁺ nuclei increased in encephalitic brains despite the presence of Vpx. Many of these cells were perivascular macrophages, although subsets of SAMHD1⁺ microglia and endothelial cells were also observed. The SAMHD1⁺ macrophages were shown to be both infected and proliferating. Moreover, the presence of cycling SAMHD1⁺ brain macrophages was confirmed in the tissue of HIV-1-infected patients with encephalitis. Finally, western blot analysis of brain-protein extracts from SIV-infected macaques showed that SAMHD1 protein exists in the brain mainly as an inactive Thr592-phosphorylated form.

Conclusion:

The ability of SAMHD1 to act as a restriction factor for SIV/HIV in the brain is likely bypassed in proliferating brain macrophages through the phosphorylation-mediated inactivation, not Vpx-mediated degradation of SAMHD1.

Post-nano strategies for drug delivery: Multistage porous silicon microvectors

Nanodelivery systems usually improve the biodistribution of drugs, leading to reduced side effects and enhanced therapeutic efficacy. However, only a small portion of the injected nanoparticle dose accumulates in pathological tissue. Challenges in drug delivery arise due to a multitude of transport obstacles in the body, including the endothelium, the extracellular matrix, and the cell membrane. In general, nanoparticles are designed to overcome only a few biological barriers, making them inadequate for localized drug delivery. Accordingly, a multifunctional and multicomponent systems are required to effectively address a wide variety of transport obstacles. A suitable approach to obtain high levels of multifunctionality is to bring together the nanoscale with the microscale, resulting in post-nano strategies for drug delivery. This review discusses several such post-nano approaches, with an emphasis on the multistage vector (MSV) platform. The MSV consists of three components on different spatial scales, each intended to address biological barriers that exist in a specific compartment in the body. The first stage vector is a microparticle that is designed to navigate in the vascular compartment. The second stage vector consists of nanoparticles that are released from the microparticle into the tissue interstitium, where they address biological barriers in extracellular and intracellular compartments. The final component of the system is a small molecule therapeutic agent. A new generation of microparticle-based strategies with expanded applications has recently been developed, including injectable nanoparticle generators and silicon particles for immunotherapy. Notably, the advantage of incorporating microstructures in drug delivery vehicles is apparent from the observation that superior functionality only appears on the microscale, highlighting the inherent functional limitations of nanostructures.

Brain Endothelial- and Epithelial-Specific Interferon Receptor Chain 1 Drives Virus-Induced Sickness Behavior and Cognitive Impairment

Sickness behavior and cognitive dysfunction occur frequently by unknown mechanisms in virus-infected individuals with malignancies treated with type I interferons (IFNs) and in patients with autoimmune disorders. We found that during sickness behavior, single-stranded RNA viruses, double-stranded RNA ligands, and IFNs shared pathways involving engagement of melanoma differentiation-associated protein 5 (MDA5), retinoic acid-inducible gene 1 (RIG-I), and mitochondrial antiviral signaling protein (MAVS), and subsequently induced IFN responses specifically in brain endothelia and epithelia of mice. Behavioral alterations were specifically dependent on brain endothelial and epithelial IFN receptor chain 1 (IFNAR). Using gene profiling, we identified that the endothelia-derived chemokine ligand CXCL10 mediated behavioral changes through impairment of synaptic plasticity. These results identified brain endothelial and epithelial cells as natural gatekeepers for virus-induced sickness behavior, demonstrated tissue specific IFNAR engagement, and established the CXCL10-CXCR3 axis as target for the treatment of behavioral changes during virus infection and type I IFN therapy.

Gene-Expression Profiling Suggests Impaired Signaling via the Interferon Pathway in Cstb-/- Microglia

Progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1, OMIM254800) is an autosomal recessive neurodegenerative disorder characterized by stimulus-sensitive and action-activated myoclonus, tonic-clonic epileptic seizures, and ataxia. Loss-of-function mutations in the gene encoding the cysteine protease inhibitor cystatin B (CSTB) underlie EPM1. The deficiency of CSTB in mice (Cstb^-/- mice) generates a phenotype resembling the symptoms of EPM1 patients and is accompanied by microglial activation at two weeks of age and an upregulation of immune system-associated genes in the cerebellum at one month of age. To shed light on molecular pathways and processes linked to CSTB deficiency in microglia we characterized the transcriptome of cultured Cstb^-/- mouse microglia using microarray hybridization and RNA sequencing (RNA-seq). The gene expression profiles obtained with these two techniques were in good accordance and not polarized to either pro- or anti-inflammatory status. In Cstb^-/- microglia, altogether 184 genes were differentially expressed. Of these, 33 genes were identified by both methods. Several interferon-regulated genes were weaker expressed in Cstb^-/- microglia compared to control. This was confirmed by quantitative real-time PCR of the transcripts Irf7 and Stat1. Subsequently, we explored the biological context of CSTB deficiency in microglia more deeply by functional enrichment and canonical pathway analysis. This uncovered a potential role for CSTB in chemotaxis, antigen-presentation, and in immune- and defense response-associated processes by altering JAK-STAT pathway signaling. These data support and expand the previously suggested involvement of inflammatory processes to the disease pathogenesis of EPM1 and connect CSTB deficiency in microglia to altered expression of interferon-regulated genes.

β-Catenin Upregulates the Constitutive and Virus-Induced Transcriptional Capacity of the Interferon Beta Promoter through T-Cell Factor Binding Sites

Rapid upregulation of interferon beta (IFN-β) expression following virus infection is essential to set up an efficient innate antiviral response. Biological roles related to the antiviral and immune response have also been associated with the constitutive production of IFN-β in naive cells. However, the mechanisms capable of modulating constitutive IFN-β expression in the absence of infection remain largely unknown. In this work, we demonstrate that inhibition of the kinase glycogen synthase kinase 3 (GSK-3) leads to the upregulation of the constitutive level of IFN-β expression in noninfected cells, provided that GSK-3 inhibition is correlated with the binding of β-catenin to the IFN-β promoter. Under these conditions, IFN-β expression occurred through the T-cell factor (TCF) binding sites present on the IFN-β promoter independently of interferon regulatory factor 3 (IRF3). Enhancement of the constitutive level of IFN-β per se was able to confer an efficient antiviral state to naive cells and acted in synergy with virus infection to stimulate virus-induced IFN-β expression. Further emphasizing the role of β-catenin in the innate antiviral response, we show here that highly pathogenic Rift Valley fever virus (RVFV) targets the Wnt/β-catenin pathway and the formation of active TCF/β-catenin complexes at the transcriptional and protein level in RVFV-infected cells and mice.

Porous silicon microparticle potentiates anti-tumor immunity by enhancing cross-presentation and inducing type I interferon response

Micro- and nanometer-size particles have become popular candidates for cancer vaccine adjuvants. However, the mechanism by which such particles enhance immune responses remains unclear. Here, we report a porous silicon microparticle (PSM)-based cancer vaccine that greatly enhances cross-presentation and activates type I interferon (IFN-I) response in dendritic cells (DCs). PSM-loaded antigen exhibited prolonged early endosome localization and enhanced cross-presentation through both proteasome- and lysosome-dependent pathways. Phagocytosis of PSM by DCs induced IFN-I responses through a TRIF- and MAVS-dependent pathway. DCs primed with PSM-loaded HER2 antigen produced robust CD8 T cell-dependent anti-tumor immunity in mice bearing HER2+ mammary gland tumors. Importantly, this vaccination activated the tumor immune microenvironment with elevated levels of intra-tumor IFN-I and MHCII expression, abundant CD11c+ DC infiltration, and tumor-specific cytotoxic T cell responses. These findings highlight the potential of PSM as an immune adjuvant to potentiate DC-based cancer immunotherapy.

USP18 lack in microglia causes destructive interferonopathy of the mouse brain

Microglia are tissue macrophages of the central nervous system (CNS) that control tissue homeostasis. Microglia dysregulation is thought to be causal for a group of neuropsychiatric, neurodegenerative and neuroinflammatory diseases, called "microgliopathies". However, how the intracellular stimulation machinery in microglia is controlled is poorly understood. Here, we identified the ubiquitin-specific protease (Usp) 18 in white matter microglia that essentially contributes to microglial quiescence. We further found that microglial Usp18 negatively regulates the activation of Stat1 and concomitant induction of interferon-induced genes, thereby terminating IFN signaling. The Usp18-mediated control was independent from its catalytic activity but instead required the interaction with Ifnar2. Additionally, the absence of Ifnar1 restored microglial activation, indicating a tonic IFN signal which needs to be negatively controlled by Usp18 under non-diseased conditions. These results identify Usp18 as a critical negative regulator of microglia activation and demonstrate a protective role of Usp18 for microglia function by regulating the Ifnar pathway. The findings establish Usp18 as a new molecule preventing destructive microgliopathy.

Interferons, signal transduction pathways, and the central nervous system

The interferon (IFN) family of cytokines participates in the development of innate and acquired immune defenses against various pathogens and pathogenic stimuli. Discovered originally as a proteinaceous substance secreted from virus-infected cells that afforded immunity to neighboring cells from virus infection, these cytokines are now implicated in various human pathologies, including control of tumor development, cell differentiation, and autoimmunity. It is now believed that the IFN system (IFN genes and the genes induced by them, and the factors that regulate these processes) is a generalized alarm of cellular stress, including DNA damage. IFNs exert both beneficial and deleterious effects on the central nervous system (CNS). Our knowledge of the IFN-regulated processes in the CNS is far from being clear. In this article, we reviewed the current understanding of IFN signal transduction pathways and gene products that might have potential relevance to diseases of the CNS.

Apoptotic caspases suppress mtDNA-induced STING-mediated type I IFN production

Activated caspases are a hallmark of apoptosis induced by the intrinsic pathway, but they are dispensable for cell death and the apoptotic clearance of cells in vivo. This has led to the suggestion that caspases are activated not just to kill but to prevent dying cells from triggering a host immune response. Here, we show that the caspase cascade suppresses type I interferon (IFN) production by cells undergoing Bak/Bax-mediated apoptosis. Bak and Bax trigger the release of mitochondrial DNA. This is recognized by the cGAS/STING-dependent DNA sensing pathway, which initiates IFN production. Activated caspases attenuate this response. Pharmacological caspase inhibition or genetic deletion of caspase-9, Apaf-1, or caspase-3/7 causes dying cells to secrete IFN-β. In vivo, this precipitates an elevation in IFN-β levels and consequent hematopoietic stem cell dysfunction, which is corrected by loss of Bak and Bax. Thus, the apoptotic caspase cascade functions to render mitochondrial apoptosis immunologically silent.

Role and therapeutic value of dendritic cells in central nervous system autoimmunity

Dendritic cells (DCs) are professional antigen-presenting cells that control the generation of adaptive immunity. Consequently, DCs have a central role in the induction of protective immunity to pathogens and also in the pathogenic immune response responsible for the development and progression of autoimmune disorders. Thus the study of the molecular pathways that control DC development and function is likely to result in new strategies for the therapeutic manipulation of the immune response. In this review, we discuss the role and therapeutic value of DCs in autoimmune diseases, with a special focus on multiple sclerosis.

Regulation of experimental autoimmune encephalomyelitis by TPL-2 kinase

Tumor progression locus 2 (TPL-2) expression is required for efficient polarization of naive T cells to Th1 effector cells in vitro, as well as for Th1-mediated immune responses. In the present study, we investigated the potential role of TPL-2 in Th17 cells. TPL-2 was found to be dispensable for Th17 cell differentiation in vitro, and for the initial priming of Th17 cells in experimental autoimmune encephalomyelitis (EAE), a Th17 cell-mediated disease model for multiple sclerosis. Nevertheless, TPL-2-deficient mice were protected from EAE, which correlated with reduced immune cell infiltration, demyelination, and axonal damage in the CNS. Adoptive transfer experiments demonstrated that there was no T cell-intrinsic function for TPL-2 in EAE, and that TPL-2 signaling was not required in radiation-sensitive hematopoietic cells. Rather, TPL-2 signaling in radiation-resistant stromal cells promoted the effector phase of the disease. Importantly, using a newly generated mouse strain expressing a kinase-inactive form of TPL-2, we demonstrated that stimulation of EAE was dependent on the catalytic activity of TPL-2 and not its adaptor function to stabilize the associated ubiquitin-binding protein ABIN-2. Our data therefore raise the possibility that small molecule inhibitors of TPL-2 may be beneficial in multiple sclerosis therapy.

Interferon regulatory factor-1 protects from fatal neurotropic infection with vesicular stomatitis virus by specific inhibition of viral replication in neurons

The innate immune system protects cells against invading viral pathogens by the auto- and paracrine action of type I interferon (IFN). In addition, the interferon regulatory factor (IRF)-1 can induce alternative intrinsic antiviral responses. Although both, type I IFN and IRF-1 mediate their antiviral action by inducing overlapping subsets of IFN stimulated genes, the functional role of this alternative antiviral action of IRF-1 in context of viral infections in vivo remains unknown. Here, we report that IRF-1 is essential to counteract the neuropathology of vesicular stomatitis virus (VSV). IFN- and IRF-1-dependent antiviral responses act sequentially to create a layered antiviral protection program against VSV infections. Upon intranasal infection, VSV is cleared in the presence or absence of IRF-1 in peripheral organs, but IRF-1^−/− mice continue to propagate the virus in the brain and succumb. Although rapid IFN induction leads to a decline in VSV titers early on, viral replication is re-enforced in the brains of IRF-1^−/− mice. While IFN provides short-term protection, IRF-1 is induced with delayed kinetics and controls viral replication at later stages of infection. IRF-1 has no influence on viral entry but inhibits viral replication in neurons and viral spread through the CNS, which leads to fatal inflammatory responses in the CNS. These data support a temporal, non-redundant antiviral function of type I IFN and IRF-1, the latter playing a crucial role in late time points of VSV infection in the brain.

IRFs are a family of transcription factors that play a key role in viral defense. Apart from their function in the adaptive immune system, recent work revealed that several IRFs contribute to antiviral response independent of secreted IFN. IRFs have been developed earlier in evolution than IFN and are regarded as precursor of today's IFN system, acting only on an intrinsic level. IRF-1 by itself exhibits antiviral effects that are exerted by the induction of a set of genes that overlaps the set of IFN-induced genes (ISGs). Our data show that IRF-1 contributes decisively for the protection of mice from neurotropic Vesicular stomatitis virus (VSV), a virus similar to rabies virus. Mice, deficient in IRF-1, are highly vulnerable to VSV infection and succumb with signs of encephalitis. Although type I IFN action is a prerequisite for survival from the infection, IRF-1 becomes increasingly crucial in neuronal tissue at a time point where clearance of the virus has not been achieved. The data highlight the importance of IRF-1 as an antiviral agent that acts in combination with the IFN system.

Effects of interferon β-1a and interferon β-1b monotherapies on selected serum cytokines and nitrite levels in patients with relapsing-remitting multiple sclerosis: a 3-year longitudinal study

OBJECTIVE

Interferon (IFN)β treatment is a mainstay of relapsing-remitting multiple sclerosis (RRMS) immunotherapy. Its efficacy is supposedly a consequence of impaired trafficking of inflammatory cells into the central nervous system and modification of the proinflammatory/antiinflammatory cytokine balance. However, the effects of long-term monotherapy using various IFNβ preparations on cytokine profiles and the relevance of these effects for the therapy outcome have not yet been elucidated.

METHODS

Changes were compared in serum levels of TNFα, IFNγ, interleukin (IL)-6, IL-10 and nitrite between RRMS patients given 3-year treatment with intramuscular IFNβ-1a (30 μg once a week) or subcutaneous IFNβ-1b (250 μg every other day). Only the data from patients who completed the 3-year study (n = 20 and n = 18, respectively) were analyzed.

RESULTS

Three-year IFNβ-1a or IFNβ-1b monotherapy reduced serum nitrite levels by 77 and 71%, respectively, lowered multiple sclerosis relapse annual rate by 70 and 71%, respectively, and significantly and similarly lowered Expanded Disability Status Scale scores in both study groups (by 0.9 on average). The two monotherapies showed little if any effect on cytokine levels and cytokine level ratios after the first year, but exerted diverging effects on these indices later on; the only exception was the IFNγ/IL-6 ratio that showed a monotonous rise in both study groups over the entire study period.

CONCLUSION

During long-term IFNβ monotherapy, the levels of the studied cytokines show no relevance to the course of RRMS and neurological status of patients, whereas there seems to be a link between these clinical indices and the activity of nitric oxide-mediated pathways.

Cytokine control of inflammation and repair in the pathology of multiple sclerosis

Cytokines are secreted signaling proteins that play an essential role in propagating and regulating immune responses during experimental autoimmune encephalomyelitis (EAE), the mouse model of the neurodegenerative, autoimmune disease multiple sclerosis (MS). EAE pathology is driven by a myelin-specific T cell response that is activated in the periphery and mediates the destruction of myelin upon T cell infiltration into the central nervous system (CNS). Cytokines provide cell signals both in the immune and CNS compartment, but interestingly, some have detrimental effects in the immune compartment while having beneficial effects in the CNS compartment. The complex nature of these signals will be reviewed.

Restricting HIV the SAMHD1 way: through nucleotide starvation

HIV replication is limited by cellular restriction factors, such as APOBEC and tetherin, which themselves are counteracted by viral proteins. SAMHD1 was recently identified as a novel HIV restriction factor in myeloid cells, and was shown to be blocked by the lentiviral protein Vpx. SAMHD1 limits viral replication through an original mechanism: it hydrolyses intracellular dNTPs in non-cycling cells, thus decreasing the amount of these key substrates, which are required for viral DNA synthesis. In this Progress article, we describe how SAMHD1 regulates the pool of intracellular nucleotides to control HIV replication and the innate immune response.