Regulation of type I interferon responses

Impact of Type I and III Interferons on Respiratory Superinfections Due to Multidrug-Resistant Pathogens

The increased morbidity and mortality associated with bacterial pneumonias that are acquired following influenza infection are well appreciated by clinicians. One of the major components of the immune response to influenza is the induction of the types I and III interferon cascades, which encompasses the activation of over 300 genes. The immunological consequences of IFN activation, while important for viral clearance, modify the host proinflammatory responses through effects on the inflammasome, Th17 signaling and recruitment of phagocytic cells. IFN signaling affects both susceptibility to subsequent Streptococcus pneumoniae and Staphylococcus aureus infection as well as the intensity of the immune responses associated with pulmonary damage. Appreciation for the effects of IFN activation on anti-bacterial pulmonary defense mechanisms should help to inform therapeutic strategies in an ICU setting.

A prosurvival DNA damage-induced cytoplasmic interferon response is mediated by end resection factors and is limited by Trex1

Radiotherapy and chemotherapy are effective treatment methods for many types of cancer, but resistance is common. Recent findings indicate that antiviral type I interferon (IFN) signaling is induced by these treatments. However, the underlying mechanisms still need to be elucidated. Expression of a set of IFN-stimulated genes comprises an IFN-related DNA damage resistance signature (IRDS), which correlates strongly with resistance to radiotherapy and chemotherapy across different tumors. Classically, during viral infection, the presence of foreign DNA in the cytoplasm of host cells can initiate type I IFN signaling. Here, we demonstrate that DNA-damaging modalities used during cancer therapy lead to the release of ssDNA fragments from the cell nucleus into the cytosol, engaging this innate immune response. We found that the factors that control DNA end resection during double-strand break repair, including the Bloom syndrome (BLM) helicase and exonuclease 1 (EXO1), play a major role in generating these DNA fragments and that the cytoplasmic 3'-5' exonuclease Trex1 is required for their degradation. Analysis of mRNA expression profiles in breast tumors demonstrates that those with lower Trex1 and higher BLM and EXO1 expression levels are associated with poor prognosis. Targeting BLM and EXO1 could therefore represent a novel approach for circumventing the IRDS produced in response to cancer therapeutics.

Enteric helminth-induced type I interferon signaling protects against pulmonary virus infection through interaction with the microbiota

BACKGROUND

Helminth parasites have been reported to have beneficial immunomodulatory effects in patients with allergic and autoimmune conditions and detrimental consequences in patients with tuberculosis and some viral infections. Their role in coinfection with respiratory viruses is not clear.

OBJECTIVE

Here we investigated the effects of strictly enteric helminth infection with Heligmosomoides polygyrus on respiratory syncytial virus (RSV) infection in a mouse model.

METHODS

A murine helminth/RSV coinfection model was developed. Mice were infected by means of oral gavage with 200 stage 3 H polygyrus larvae. Ten days later, mice were infected intranasally with either RSV or UV-inactivated RSV.

RESULTS

H polygyrus-infected mice showed significantly less disease and pulmonary inflammation after RSV infection associated with reduced viral load. Adaptive immune responses, including T_H2 responses, were not essential because protection against RSV was maintained in Rag1^-/- and Il4rα^-/- mice. Importantly, H polygyrus infection upregulated expression of type I interferons and interferon-stimulated genes in both the duodenum and lung, and its protective effects were lost in both Ifnar1^-/- and germ-free mice, revealing essential roles for type I interferon signaling and microbiota in H polygyrus-induced protection against RSV.

CONCLUSION

These data demonstrate that a strictly enteric helminth infection can have remote protective antiviral effects in the lung through induction of a microbiota-dependent type I interferon response.

Cytosolic DNA Promotes Signal Transducer and Activator of Transcription 3 (STAT3) Phosphorylation by TANK-binding Kinase 1 (TBK1) to Restrain STAT3 Activity

Cytosolic DNA can elicit beneficial as well as undesirable immune responses. For example, viral or microbial DNA triggers cell-intrinsic immune responses to defend against infections, whereas aberrant cytosolic accumulation of self-DNA results in pathological conditions, such as autoimmunity. Given the importance of these DNA-provoked responses, a better understanding of their molecular mechanisms is needed. Cytosolic DNA engages stimulator of interferon genes (STING) to activate TANK-binding kinase 1 (TBK1), which subsequently phosphorylates the transcription factor interferon regulatory factor 3 (IRF3) to promote interferon expression. Recent studies have reported that additional transcription factors, including nuclear factor κB (NF-κB) and signal transducer and activator of transcription 6 (STAT6), are also activated by cytosolic DNA, suggesting that cytosolic DNA-induced gene expression is orchestrated by multiple factors. Here we show that cytosolic DNA activates STAT3, another member of the STAT family, via an autocrine mechanism involving interferon β (IFNβ) and IL-6. Additionally, we observed a novel cytosolic DNA-induced phosphorylation at serine 754 in the transactivation domain of STAT3. Upon cytosolic DNA stimulation, Ser⁷⁵⁴ is directly phosphorylated by TBK1 in a STING-dependent manner. Moreover, Ser⁷⁵⁴ phosphorylation inhibits cytosolic DNA-induced STAT3 transcriptional activity and selectively reduces STAT3 target genes that are up-regulated in response to cytosolic DNA. Taken together, our results suggest that cytosolic DNA-induced STAT3 activation via IFNβ and IL-6 is restrained by Ser⁷⁵⁴ phosphorylation of STAT3. Our findings reveal a new signaling axis downstream of the cytosolic DNA pathway and suggest potential interactions between innate immune responses and STAT3-driven oncogenic pathways.

Type I Interferons Modulate CD8+ T Cell Immunity to mRNA Vaccines

mRNA vaccines have emerged as potent tools to elicit antitumor T cell immunity. They are characterized by a strong induction of type I interferons (IFNs), potent inflammatory cytokines affecting T cell differentiation and survival. Recent reports have attributed opposing roles for type I IFNs in modulating CD8+ T cell immunity to mRNA vaccines, from profoundly stimulatory to strongly inhibitory. The mechanisms behind this duality are unclear. Disentangling the factors governing the beneficial or detrimental impact of type I IFNs on CD8+ T cell responses is vital to the design of mRNA vaccines of increased potency. In light of recent advancements regarding the complex role of type I IFNs in regulating CD8+ T cell immunity to infectious diseases, we posit that the dual outcome of type I IFNs on CD8+ T cell responses to mRNA vaccination is determined by the timing and intensity of type I IFN induction relative to T cell receptor (TCR) activation.

STAT2 is an essential adaptor in USP18-mediated suppression of type I interferon signaling

Type I interferons (IFNs) are multifunctional cytokines that regulate immune responses and cellular functions but also can have detrimental effects on human health. A tight regulatory network therefore controls IFN signaling, which in turn may interfere with medical interventions. The JAK-STAT signaling pathway transmits the IFN extracellular signal to the nucleus, thus resulting in alterations in gene expression. STAT2 is a well-known essential and specific positive effector of type I IFN signaling. Here, we report that STAT2 is also a previously unrecognized, crucial component of the USP18-mediated negative-feedback control in both human and mouse cells. We found that STAT2 recruits USP18 to the type I IFN receptor subunit IFNAR2 via its constitutive membrane-distal STAT2-binding site. This mechanistic coupling of effector and negative-feedback functions of STAT2 may provide novel strategies for treatment of IFN-signaling-related human diseases.

The host cell response to tick-borne encephalitis virus

Tick-borne encephalitis virus is the most prevalent autochthonous arbovirus in Europe and an important travel-associated virus. Complications of the infection could lead to lethal encephalitis in susceptible individuals. However, despite its clinical relevance and expanding geographical distribution, most of our knowledge on its pathogenesis is inferred from studies on other flaviviruses. Molecular details of the host cell response to infection are scarce leading to a poor understanding of the antiviral pathways and viral countermeasures that are critical to determine the outcome of the infection. In this work the relevant literature is reviewed and the key elements of tick-borne encephalitis virus infection of human cells are identified, which requires further investigation.

IFN-α/IFN-λ responses to respiratory viruses in paediatric asthma

We analysed the influence of rhinovirus (RV) in nasopharyngeal fluid (NPF) on type I and III interferon (IFN) responses (e.g. IFN-α and IFN -: λ) and their signal transduction, at baseline and during disease exacerbation, in cohorts of pre-school children with and without asthma.At the time of recruitment into the Europe-wide study PreDicta, and during symptoms, NPF was collected and the local RV colonisation was analysed. Peripheral blood mononuclear cells (PBMCs) were challenged in vitro with RV or not. RNA was analysed by quantitative real-time PCR and gene arrays. Serum was analysed with ELISA for IFNs and C-reactive protein.We found that PBMCs from asthmatic children infected in vitro with the RV1b serotype upregulated MYD88, IRF1, STAT1 and STAT2 mRNA, whereas MYD88, IRF1, STAT1 and IRF9 were predominantly induced in control children. Moreover, during symptomatic visits because of disease exacerbation associated with RV detection in NPF, IFN-α production was found increased, while IFN-λ secretion was already induced by RV in asthmatic children at baseline.During asthma exacerbations associated with RV, asthmatic children can induce IFN-α secretion, indicating a hyperactive immune response to repeated respiratory virus infection.

The conserved macrodomains of the non-structural proteins of Chikungunya virus and other pathogenic positive strand RNA viruses function as mono-ADP-ribosylhydrolases

Human pathogenic positive single strand RNA ((+)ssRNA) viruses, including Chikungunya virus, pose severe health problems as for many neither efficient vaccines nor therapeutic strategies exist. To interfere with propagation, viral enzymatic activities are considered potential targets. Here we addressed the function of the viral macrodomains, conserved folds of non-structural proteins of many (+)ssRNA viruses. Macrodomains are closely associated with ADP-ribose function and metabolism. ADP-ribosylation is a post-translational modification controlling various cellular processes, including DNA repair, transcription and stress response. We found that the viral macrodomains possess broad hydrolase activity towards mono-ADP-ribosylated substrates of the mono-ADP-ribosyltransferases ARTD7, ARTD8 and ARTD10 (aka PARP15, PARP14 and PARP10, respectively), reverting this post-translational modification both in vitro and in cells. In contrast, the viral macrodomains possess only weak activity towards poly-ADP-ribose chains synthesized by ARTD1 (aka PARP1). Unlike poly-ADP-ribosylglycohydrolase, which hydrolyzes poly-ADP-ribose chains to individual ADP-ribose units but cannot cleave the amino acid side chain - ADP-ribose bond, the different viral macrodomains release poly-ADP-ribose chains with distinct efficiency. Mutational and structural analyses identified key amino acids for hydrolase activity of the Chikungunya viral macrodomain. Moreover, ARTD8 and ARTD10 are induced by innate immune mechanisms, suggesting that the control of mono-ADP-ribosylation is part of a host-pathogen conflict.

ISG15: In Sickness and in Health

ISG15 is a type I interferon (IFN)-inducible gene encoding a protein with pleiotropic functions, acting both as a soluble molecule and as a protein modifier. Surprisingly, and despite the antiviral functions of ISG15 described in mice, humans born with inactivating mutations of ISG15 do not present with any overt viral phenotype, but are highly susceptible to environmental mycobacteria and have autoinflammatory disease presentations. In vitro, ISG15 deficiency also leads to persistently high levels of type I IFN-stimulated gene expression and to increased resistance to all viruses tested to date. This suggests that ISG15 deficiency increases antiviral responses in humans, in stark contrast to expectations based on mouse experiments. We discuss here the roles of each of the forms of ISG15 in health and disease, as well as the differences between species.

Familial chilblain lupus due to a gain-of-function mutation in STING

OBJECTIVES

Familial chilblain lupus is a monogenic form of cutaneous lupus erythematosus caused by loss-of-function mutations in the nucleases TREX1 or SAMHD1. In a family without TREX1 or SAMHD1 mutation, we sought to determine the causative gene and the underlying disease pathology.

METHODS

Exome sequencing was used for disease gene identification. Structural analysis was performed by homology modelling and docking simulations. Type I interferon (IFN) activation was assessed in cells transfected with STING cDNA using an IFN-β reporter and Western blotting. IFN signatures in patient blood in response to tofacitinib treatment were measured by RT-PCR of IFN-stimulated genes.

RESULTS

In a multigenerational family with five members affected with chilblain lupus, we identified a heterozygous mutation of STING, a signalling molecule in the cytosolic DNA sensing pathway. Structural and functional analyses indicate that mutant STING enhances homodimerisation in the absence of its ligand cGAMP resulting in constitutive type I IFN activation. Treatment of two affected family members with the Janus kinase (JAK) inhibitor tofacitinib led to a marked suppression of the IFN signature.

CONCLUSIONS

A heterozygous gain-of-function mutation in STING can cause familial chilblain lupus. These findings expand the genetic spectrum of type I IFN-dependent disorders and suggest that JAK inhibition may be of therapeutic value.

Paeoniflorin ameliorates interferon-alpha-induced neuroinflammation and depressive-like behaviors in mice

Long-term treatment with high-dose Interferon-alpha (IFN-α) has resulted in depression in 30-50% of the patients. Paeoniflorin may ameliorate the IFN-α-induced depression; however, the underlying mechanism is less studied. Here, we investigated the prophylactic antidepressant and anti-neuroinflammatory effects of paeoniflorin on the behaviors and specific emotion-related regions of the brain in mice with IFN-α-induced depression. A series of behavior assessments were conducted to identify the depressive state after subcutaneously IFN-α injections and with or without intragastrically paeoniflorin administration in C57BL/6J mice. Levels of many inflammatory-related cytokines in serum, mPFC, vHi and amygdala were determined by cytokine array analysis. Furthermore, microglia and astrocyte activation in these three regions were evaluated by immunohistochemistry. We found that the mice which were subcutaneously injected IFN-α 15×106 IU/kg for 4 successive weeks to mimic an IFN-α-induced depression model had distinct inflammatory changes in the amygdala. Interestingly, 4-week 20 mg/kg or 40 mg/kg paeoniflorin pretreatments reversed the depressive-like behaviors and the abnormal inflammatory cytokine levels in the serum, mPFC, vHi and amygdala. These cytokines were not limited to the commonly reported IL-6, IL-1β and TNF-α, but also IL-9, IL-10, IL-12, and MCP-1. Besides, the increased density of microglia in IFN-α-treated mice was reversed by paeoniflorin in these three brain areas. Taken together, our data suggest that paeoniflorin can reverse the long-term, high-dose IFN-α-induced depressive-like behaviors that were associated with local distinct neuroinflammation in the mPFC, vHi and particularly the amygdala. Paeoniflorin might have a preventive therapeutic potential in IFN-α-induced depression.

Transcriptional Regulation of Antiviral Interferon-Stimulated Genes

Interferon-stimulated genes (ISGs) are a group of gene products that coordinately combat pathogen invasions, in particular viral infections. Transcription of ISGs occurs rapidly upon pathogen invasion, and this is classically provoked via activation of the Janus kinase/signal transducer and activator of transcription (JAK–STAT) pathway, mainly by interferons (IFNs). However, a plethora of recent studies have reported a variety of non-canonical mechanisms regulating ISG transcription. These new studies are extremely important for understanding the quantitative and temporal differences in ISG transcription under specific circumstances. Because these canonical and non-canonical regulatory mechanisms are essential for defining the nature of host defense and associated detrimental proinflammatory effects, we comprehensively review the state of this rapidly evolving field and the clinical implications of recently acquired knowledge in this respect.

Transcriptional regulation of ISGs defines the state of host anti-pathogen defense.

In light of the recently identified regulatory elements and mechanisms of the IFN–JAK–STAT pathway, new insights have been gained into this classical cascade in regulating ISG transcription.

A variety of non-canonical mechanisms have been recently revealed that coordinately regulate ISG transcription.

With regards to the adverse effects of IFNs in clinic, ISG-based antiviral strategy could be the next promising frontier in drug discovery.

Phosphorylation-Dependent Feedback Inhibition of RIG-I by DAPK1 Identified by Kinome-wide siRNA Screening

Cell-autonomous induction of type I interferon must be stringently regulated. Rapid induction is key to control virus infection, whereas proper limitation of signaling is essential to prevent immunopathology and autoimmune disease. Using unbiased kinome-wide RNAi screening followed by thorough validation, we identified 22 factors that regulate RIG-I/IRF3 signaling activity. We describe a negative-feedback mechanism targeting RIG-I activity, which is mediated by death associated protein kinase 1 (DAPK1). RIG-I signaling triggers DAPK1 kinase activation, and active DAPK1 potently inhibits RIG-I stimulated IRF3 activity and interferon-beta production. DAPK1 phosphorylates RIG-I in vitro at previously reported as well as other sites that limit 5'ppp-dsRNA sensing and virtually abrogate RIG-I activation.

A paradox of transcriptional and functional innate interferon responses of human intestinal enteroids to enteric virus infection

The intestinal epithelium can limit enteric pathogens by producing antiviral cytokines, such as IFNs. Type I IFN (IFN-α/β) and type III IFN (IFN-λ) function at the epithelial level, and their respective efficacies depend on the specific pathogen and site of infection. However, the roles of type I and type III IFN in restricting human enteric viruses are poorly characterized as a result of the difficulties in cultivating these viruses in vitro and directly obtaining control and infected small intestinal human tissue. We infected nontransformed human intestinal enteroid cultures from multiple individuals with human rotavirus (HRV) and assessed the host epithelial response by using RNA-sequencing and functional assays. The dominant transcriptional pathway induced by HRV infection is a type III IFN-regulated response. Early after HRV infection, low levels of type III IFN protein activate IFN-stimulated genes. However, this endogenous response does not restrict HRV replication because replication-competent HRV antagonizes the type III IFN response at pre- and posttranscriptional levels. In contrast, exogenous IFN treatment restricts HRV replication, with type I IFN being more potent than type III IFN, suggesting that extraepithelial sources of type I IFN may be the critical IFN for limiting enteric virus replication in the human intestine.

Activation of the JAK-STAT Signaling Pathway after In Vitro Stimulation with IFNß in Multiple Sclerosis Patients According to the Therapeutic Response to IFNß

Interferon beta (IFNß) is a common treatment used for multiple sclerosis (MS) which acts through the activation of the JAK-STAT pathway. However, this therapy is not always effective and currently there are no reliable biomarkers to predict therapeutic response. We postulate that the heterogeneity in the response to IFNß therapy could be related to differential activation patterns of the JAK-STAT signaling pathway. Our aim was to evaluate the basal levels and the short term activation of this pathway after IFNß stimulation in untreated and IFNß treated patients, as well as according to therapeutic response. Therefore, cell surface levels of IFNAR subunits (IFNAR1 and IFNAR2) and the activated forms of STAT1 and STAT2 were assessed in peripheral blood mononuclear cells from MS patients by flow cytometry. Basal levels of each of the markers strongly correlated with the expression of the others in untreated patients, but many of these correlations lost significance in treated patients and after short term activation with IFNß. Patients who had undergone IFNß treatment showed higher basal levels of IFNAR1 and pSTAT1, but a reduced response to in vitro exposure to IFNß. Conversely, untreated patients, with lower basal levels, showed a greater ability of short term activation of this pathway. Monocytes from responder patients had lower IFNAR1 levels (p = 0.039) and higher IFNAR2 levels (p = 0.035) than non-responders just after IFNß stimulation. A cluster analysis showed that levels of IFNAR1, IFNAR2 and pSTAT1-2 in monocytes grouped 13 out of 19 responder patients with a similar expression pattern, showing an association of this pattern with the phenotype of good response to IFNß (p = 0.013). Our findings suggest that an activation pattern of the IFNß signaling pathway in monocytes could be associated with a clinical phenotype of good response to IFNß treatment and that a differential modulation of the IFNAR subunits in monocytes could be related with treatment effectiveness.

Protozoan Parasites and Type I IFNs

For many years, the role of interferon (IFN)-I has been characterized primarily in the context of viral infections. However, regulatory functions mediated by IFN-I have also been described against bacterial infections and in tumor immunology. Only recently, the interest in understanding the immune functions mediated by IFN-I has dramatically increased in the field of protozoan infections. In this review, we discuss the discrete role of IFN-I in the immune response against major protozoan infections: Plasmodium, Leishmania, Trypanosoma, and Toxoplasma.

The Many Faces of the Flavivirus NS5 Protein in Antagonism of Type I Interferon Signaling

The vector-borne flaviviruses cause severe disease in humans on every inhabited continent on earth. Their transmission by arthropods, particularly mosquitoes, facilitates large emergence events such as witnessed with Zika virus (ZIKV) or West Nile virus in the Americas. Every vector-borne flavivirus examined thus far that causes disease in humans, from dengue virus to ZIKV, antagonizes the host type I interferon (IFN-I) response by preventing JAK-STAT signaling, suggesting that suppression of this pathway is an important determinant of infection. The most direct and potent viral inhibitor of this pathway is the nonstructural protein NS5. However, the mechanisms utilized by NS5 from different flaviviruses are often quite different, sometimes despite close evolutionary relationships between viruses. The varied mechanisms of NS5 as an IFN-I antagonist are also surprising given that the evolution of NS5 is restrained by the requirement to maintain function of two enzymatic activities critical for virus replication, the methyltransferase and RNA-dependent RNA polymerase. This review discusses the different strategies used by flavivirus NS5 to evade the antiviral effects of IFN-I and how this information can be used to better model disease and develop antiviral countermeasures.

Polycythemia Vera Management and Challenges in the Community Health Setting

Patients with polycythemia vera (PV) experience shortened survival, increased risk of thromboembolic and hemorrhagic events, and burdensome symptoms. For all patients with PV, treatment with aspirin and hematocrit control with phlebotomy are recommended. In addition, patients with high-risk status or poor hematocrit control benefit from cytoreductive therapy with hydroxyurea, although approximately 1 in 4 patients develops resistance or intolerance. For patients who are resistant to or intolerant of hydroxyurea, studies have shown that ruxolitinib, a Janus kinase 1/2 inhibitor, provides hematocrit control, reduces spleen size, normalizes blood counts, and improves PV-related symptoms. For many patients, PV is managed in a community health setting, and it is important that community hematologists, oncologists, and internists are familiar with the contemporary management of PV to improve patient outcomes, including management for patients who present with unique health-care needs. This review provides an overview of current treatment options for patients with PV and discusses challenging circumstances encountered by community providers in the management of PV, including symptom assessment, identification of hydroxyurea resistance/intolerance, pregnancy, elective surgeries, concomitant immunosuppressants, and managing patients in areas with limited access to specialized hematologic care.

Engineered Aedes aegypti JAK/STAT Pathway-Mediated Immunity to Dengue Virus

We have developed genetically modified Ae. aegypti mosquitoes that activate the conserved antiviral JAK/STAT pathway in the fat body tissue, by overexpressing either the receptor Dome or the Janus kinase Hop by the blood feeding-induced vitellogenin (Vg) promoter. Transgene expression inhibits infection with several dengue virus (DENV) serotypes in the midgut as well as systemically and in the salivary glands. The impact of the transgenes Dome and Hop on mosquito longevity was minimal, but it resulted in a compromised fecundity when compared to wild-type mosquitoes. Overexpression of Dome and Hop resulted in profound transcriptome regulation in the fat body tissue as well as the midgut tissue, pinpointing several expression signatures that reflect mechanisms of DENV restriction. Our transcriptome studies and reverse genetic analyses suggested that enrichment of DENV restriction factor and depletion of DENV host factor transcripts likely accounts for the DENV inhibition, and they allowed us to identify novel factors that modulate infection. Interestingly, the fat body-specific activation of the JAK/STAT pathway did not result in any enhanced resistance to Zika virus (ZIKV) or chikungunya virus (CHIKV) infection, thereby indicating a possible specialization of the pathway’s antiviral role.

Dengue has represented a significant public health burden for a number of decades, and given the lack of dengue-specific drugs and limited availability of licensed vaccine, new methods for prevention and control are urgently needed. Here, we investigated whether genetic manipulation of the mosquitoes’ native JAK/STAT pathway-mediated anti-DENV defense system could be used to render mosquitoes more resistant to infection. We generated Ae. aegypti mosquitoes overexpressing the JAK/STAT pathway components Dome and Hop under the control of a bloodmeal-inducible, fat body-specific vitellogenin (Vg) promoter. These genetically modified mosquitoes showed an increased resistance to DENV infection, likely because of higher expression of DENV restriction factors and lower expression of DENV host factors, as indicated by transcriptome analyses. Expression of the transgenes had a minimal impact on mosquito longevity; however, it significantly impaired the mosquitoes’ fecundity. Interestingly, bloodmeal-inducible fat body-specific overexpression of either Hop or Dome did not affect mosquito permissiveness to either ZIKV or CHIKV infection, suggesting a possible specialization of JAK/STAT pathway antiviral defenses. Thus, our study is the first to provide a proof-of-concept that genetic engineering of the mosquitoes’ JAK/STAT immune pathway can be used to render this host more resistant to DENV infection.

Inflammatory myopathy in a patient with Aicardi-Goutières syndrome

Aicardi-Goutières syndrome (AGS) is an inflammatory disorder belonging to the recently characterized group of type I interferonopathies. The most consistently affected tissues in AGS are the central nervous system and skin, but various organ systems and tissues have been reported to be affected, pointing to the systemic nature of the disease. Here we describe a patient with AGS due to a homozygous p.Arg114His mutation in the TREX1 gene. The histologically proven inflammatory myopathy in our patient expands the range of clinical features of AGS. Histological signs of muscle biopsies in the proband, and in two other AGS patients described earlier, are similar to those seen in various autoimmune myositises and could be ascribed to inapproapriate IFN I activation. In view of signs of possible mitochondrial damage in AGS, we propose that mitochondrial DNA could be a trigger of autoimmune responses in AGS.

Absent in Melanoma 2 proteins in SLE

Type I interferons (IFN-α/β)-inducible PYRIN and HIN domain-containing protein family includes Absent in Melanoma 2 (murine Aim2 and human AIM2), murine p202, and human PYRIN-only protein 3 (POP3). The generation of Aim2-deficient mice indicated that the Aim2 protein is essential for inflammasome activation, resulting in the secretion of interleukin-1β (IL-1β) and IL-18 and cell death by pyroptosis. Further, Aim2-deficiency also increased constitutive expression of the IFN-β and expression of the p202 protein. Notably, an increased expression of p202 protein in female mice associated with the development of systemic lupus erythematosus (SLE). SLE in patients is characterized by a constitutive increase in serum levels of IFN-α and an increase in the expression IFN-stimulated genes. Recent studies indicate that p202 and POP3 proteins inhibit activation of the Aim2/AIM2 inflammasome and promote IFN-β expression. Therefore, we discuss the role of Aim2/AIM2 proteins in the suppression of type I IFNs production and lupus susceptibility.

Integrative Analysis of Immunological Data to Explore Chronic Immune T-Cell Activation in Successfully Treated HIV Patients

OBJECTIVES

To unravel the complex relationships between cytomegalovirus-induced-, autoimmune-induced responses, microbial translocation and chronic immune activation (CIA) in successfully treated HIV-infected patients and to explore the mediating role of alpha-interferon in these processes.

DESIGN

Cross-sectional study nested in the ANRS CO3 Aquitaine Cohort, a prospective hospital-based cohort of HIV-1-infected patients in South-Western France.

METHODS

Patients initiated antiretroviral therapy between 2005 and 2008 and were treated with sustained virological suppression for at least two years. CIA was defined by the percentage of HLA-DR+/CD38+ among CD8+T-cells. Integrative analyses were performed using structural equation modelling (SEM).

RESULTS

The main analysis was performed in 57 HLA-A*0201 positive patients, due to availability of percentages of actin-, vimentin-, lamin-specific CD8+T-cells (HLA-A2-restricted tests) to further characterize autoimmune response. Cytomegalovirus-induced response was assessed by Quantiferon and pp-65 ELISPOT. SEM revealed a direct effect of cytomegalovirus-induced response on CIA (standardized estimate βstd = 0.56, p-value = 0.0004). The effect of autoimmune-induced response on CIA was indirect through alpha-interferon pathway, assessed by expression levels of 5 alpha-interferon-stimulated genes ADAR, ISG15, IFIT1, Mx1 and OAS1 (effect of autoimmune response on alpha-interferon: βstd = 0.36, p-value = 0.0401; effect of alpha-interferon on CIA: βstd = 0.39, p-value = 0.0044). There was no direct effect of autoimmune-induced response on CIA (p-value = 0.3169). Microbial translocation as measured by 16SrDNA and sCD14 in plasma was not associated with CIA. Results were consistent in 142 patients in whom cytomegalovirus and auto-immunity responses were measured by Quantiferon and anti-nuclear antibodies, respectively. All analyses performed in HLA-A*0201 positive patients and in the overall population revealed a significant effect of IFN-α latent variable on CIA.

CONCLUSION

The role of cytomegalovirus-induced response on CIA was confirmed as well as the involvement of alpha-interferon on CIA. The indirect effect of auto-immunity response on CIA revealed through the alpha-interferon pathway requires further investigation to confirm the potential role of auto-immunity for CIA in HIV-infected patients.

Modulation of STAT1-Driven Transcriptional Activity by Histone Deacetylases

The luciferase (LUC) reporter assay is commonly used to study gene expression at the transcriptional level. It is convenient, fast, sensitive, inexpensive, and provides quantitative data about small changes in transcription. Signal transducer and activator of transcription 1 (STAT1) is a transcription factor that plays a crucial role in signaling by interferons (IFNs). Here, we describe LUC reporter studies that address the role of histone deacetylase (HDAC) activity in STAT1-dependent gene activation. These experiments include overexpression of HDAC1, HDAC2, HDAC3, and HDAC4 as well as silencing of HDAC1, HDAC2, and HDAC3 through RNA interference in mammalian cancer cells.

Type I Interferon Is a Catastrophic Feature of the Diabetic Islet Microenvironment

A detailed understanding of the molecular pathways and cellular interactions that result in islet beta cell (β cell) destruction is essential for the development and implementation of effective therapies for prevention or reversal of type 1 diabetes (T1D). However, events that define the pathogenesis of human T1D have remained elusive. This gap in our knowledge results from the complex interaction between genetics, the immune system, and environmental factors that precipitate T1D in humans. A link between genetics, the immune system, and environmental factors are type 1 interferons (T1-IFNs). These cytokines are well known for inducing antiviral factors that limit infection by regulating innate and adaptive immune responses. Further, several T1D genetic risk loci are within genes that link innate and adaptive immune cell responses to T1-IFN. An additional clue that links T1-IFN to T1D is that these cytokines are a known constituent of the autoinflammatory milieu within the pancreas of patients with T1D. The presence of IFNα/β is correlated with characteristic MHC class I (MHC-I) hyperexpression found in the islets of patients with T1D, suggesting that T1-IFNs modulate the cross-talk between autoreactive cytotoxic CD8⁺ T lymphocytes and insulin-producing pancreatic β cells. Here, we review the evidence supporting the diabetogenic potential of T1-IFN in the islet microenvironment.

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.

Biallelic JAK1 mutations in immunodeficient patient with mycobacterial infection

Mutations in genes encoding components of the immune system cause primary immunodeficiencies. Here, we study a patient with recurrent atypical mycobacterial infection and early-onset metastatic bladder carcinoma. Exome sequencing identified two homozygous missense germline mutations, P733L and P832S, in the JAK1 protein that mediates signalling from multiple cytokine receptors. Cells from this patient exhibit reduced JAK1 and STAT phosphorylation following cytokine stimulations, reduced induction of expression of interferon-regulated genes and dysregulated cytokine production; which are indicative of signalling defects in multiple immune response pathways including Interferon-γ production. Reconstitution experiments in the JAK1-deficient cells demonstrate that the impaired JAK1 function is mainly attributable to the effect of the P733L mutation. Further analyses of the mutant protein reveal a phosphorylation-independent role of JAK1 in signal transduction. These findings clarify JAK1 signalling mechanisms and demonstrate a critical function of JAK1 in protection against mycobacterial infection and possibly the immunological surveillance of cancer.

JAK1 mediates intracellular signalling from multiple cytokine receptors. Here, Eletto et al. identify JAK1 mutations that disrupt multiple signalling pathways and are associated with primary immunodeficiency, atypical mycobacterial infection susceptibility and early-onset metastatic bladder carcinoma.

Effects of Interferons and Viruses on Metabolism

Interferons (IFNs) are potent pleiotropic cytokines that broadly alter cellular functions in response to viral and other infections. These alterations include changes in protein synthesis, proliferation, membrane composition, and the nutritional microenvironment. Recent evidence suggests that antiviral responses are supported by an IFN-induced rewiring of the cellular metabolism. In this review, we discuss the roles of type I and type II IFNs in regulating the cellular metabolism and biosynthetic reactions. Furthermore, we give an overview of how viruses themselves affect these metabolic activities to promote their replication. In addition, we focus on the lipid as well as amino acid metabolisms, through which IFNs exert potent antiviral and immunomodulatory activities. Conversely, the expression of IFNs is controlled by the nutrient sensor mammalian target of rapamycin or by direct reprograming of lipid metabolic pathways. These findings establish a mutual relationship between IFN production and metabolic core processes.

Transcriptomic profiling of microglia reveals signatures of cell activation and immune response, during experimental cerebral malaria

Cerebral malaria is a pathology involving inflammation in the brain. There are many immune cell types activated during this process, but there is little information on the response of microglia, in this severe complication. We examined microglia by genome wide transcriptomic analysis in a model of experimental cerebral malaria (ECM), in which C57BL/6 mice are infected with Plasmodium berghei ANKA. Thousands of transcripts were differentially expressed in microglia at two different time points during infection. Proliferation of microglia was a dominant feature before the onset of ECM, and supporting this, we observed an increase in numbers of these cells in the brain. When cerebral malaria symptoms were manifest, genes involved in immune responses and chemokine production were upregulated, which were possibly driven by Type I Interferon. Consistent with this hypothesis, in vitro culture of a microglial cell line with Interferon-β, but not infected red blood cells, resulted in production of several of the chemokines shown to be upregulated in the gene expression analysis. It appears that these responses are associated with ECM, as microglia from mice infected with a mutant P. berghei parasite (ΔDPAP3), which does not cause ECM, did not show the same level of activation or proliferation.

Signal transducer and activator of transcription 3 (Stat3) regulates host defense and protects mice against herpes simplex virus-1 (HSV-1) infection

Signal transducer and activator of transcription 3 (STAT3) mediates cellular responses to multiple cytokines, governs gene expression, and regulates the development and activation of immune cells. STAT3 also modulates reactivation of latent herpes simplex virus-1 (HSV-1) in ganglia. However, it is unclear how STAT3 regulates the innate immune response during the early phase of HSV-1 lytic infection. Many cell types critical for the innate immunity are derived from the myeloid lineage. Therefore, in this study, we used myeloid-specific Stat3 knockout mice to investigate the role of STAT3 in the innate immune response against HSV-1. Our results demonstrate that Stat3 knockout bone marrow-derived macrophages (BMMs) expressed decreased levels of interferon-α (IFN-α) and interferon-stimulated genes (ISGs) upon HSV-1 infection. In vivo, knockout mice were more susceptible to HSV-1, as marked by higher viral loads and more significant weight loss. Splenic expression of IFN-α and ISGs was reduced in the absence of STAT3, indicating that STAT3 is required for optimal type I interferon response to HSV-1. Expression of TNF-α and IL-12, cytokines that have been shown to limit HSV-1 replication and pathogenesis, was also significantly lower in knockout mice. Interestingly, Stat3 knockout mice failed to expand the CD8⁺ conventional DC (cDC) population upon HSV-1 infection, and this was accompanied by impaired NK and CD8 T cell activation. Collectively, our data demonstrate that myeloid-specific Stat3 deletion causes defects in multiple aspects of the immune system and that STAT3 has a protective role at the early stage of systemic HSV-1 infection.

Computational identification and analysis of signaling subnetworks with distinct functional roles in the regulation of TNF production

Inflammation is a complex process driven by the coordinated action of a vast number of pro- and anti-inflammatory molecular mediators. While experimental studies have provided an abundance of information about the properties and mechanisms of action of individual mediators, essential system-level regulatory patterns that determine the time-course of inflammation are not sufficiently understood. In particular, it is not known how the contributions from distinct signaling pathways involved in cytokine regulation combine to shape the overall inflammatory response over different time scales. We investigated the kinetics of the intra- and extracellular signaling network controlling the production of the essential pro-inflammatory cytokine, tumor necrosis factor (TNF), and its anti-inflammatory counterpart, interleukin 10 (IL-10), in a macrophage culture. To tackle the intrinsic complexity of the network, we employed a computational modeling approach using the available literature data about specific molecular interactions. Our computational model successfully captured experimentally observed short- and long-term kinetics of key inflammatory mediators. Subsequent model analysis showed that distinct subnetworks regulate IL-10 production by impacting different temporal phases of the cAMP response element-binding protein (CREB) phosphorylation. Moreover, the model revealed that functionally similar inhibitory control circuits regulate the early and late activation phases of nuclear factor κB and CREB. Finally, we identified and investigated distinct signaling subnetworks that independently control the peak height and tail height of the TNF temporal trajectories. The knowledge of such subnetwork-specific regulatory effects may facilitate therapeutic interventions aimed at precise modulation of the inflammatory response.

Identification of context-dependent expression quantitative trait loci in whole blood

Genetic risk factors often localize to noncoding regions of the genome with unknown effects on disease etiology. Expression quantitative trait loci (eQTLs) help to explain the regulatory mechanisms underlying these genetic associations. Knowledge of the context that determines the nature and strength of eQTLs may help identify cell types relevant to pathophysiology and the regulatory networks underlying disease. Here we generated peripheral blood RNA-seq data from 2,116 unrelated individuals and systematically identified context-dependent eQTLs using a hypothesis-free strategy that does not require previous knowledge of the identity of the modifiers. Of the 23,060 significant cis-regulated genes (false discovery rate (FDR) ≤ 0.05), 2,743 (12%) showed context-dependent eQTL effects. The majority of these effects were influenced by cell type composition. A set of 145 cis-eQTLs depended on type I interferon signaling. Others were modulated by specific transcription factors binding to the eQTL SNPs.

Spatiotemporal control of interferon-induced JAK/STAT signalling and gene transcription by the retromer complex

Type-I interferons (IFNs) play a key role in the immune defences against viral and bacterial infections, and in cancer immunosurveillance. We have established that clathrin-dependent endocytosis of the type-I interferon (IFN-α/β) receptor (IFNAR) is required for JAK/STAT signalling. Here we show that the internalized IFNAR1 and IFNAR2 subunits of the IFNAR complex are differentially sorted by the retromer at the early endosome. Binding of the retromer VPS35 subunit to IFNAR2 results in IFNAR2 recycling to the plasma membrane, whereas IFNAR1 is sorted to the lysosome for degradation. Depletion of VPS35 leads to abnormally prolonged residency and association of the IFNAR subunits at the early endosome, resulting in increased activation of STAT1- and IFN-dependent gene transcription. These experimental data establish the retromer complex as a key spatiotemporal regulator of IFNAR endosomal sorting and a new factor in type-I IFN-induced JAK/STAT signalling and gene transcription.

The Ebola Interferon Inhibiting Domains Attenuate and Dysregulate Cell-Mediated Immune Responses

Ebola virus (EBOV) infections are characterized by deficient T-lymphocyte responses, T-lymphocyte apoptosis and lymphopenia. We previously showed that disabling of interferon-inhibiting domains (IIDs) in the VP24 and VP35 proteins effectively unblocks maturation of dendritic cells (DCs) and increases the secretion of cytokines and chemokines. Here, we investigated the role of IIDs in adaptive and innate cell-mediated responses using recombinant viruses carrying point mutations, which disabled IIDs in VP24 (EBOV/VP24m), VP35 (EBOV/VP35m) or both (EBOV/VP35m/VP24m). Peripheral blood mononuclear cells (PBMCs) from cytomegalovirus (CMV)-seropositive donors were inoculated with the panel of viruses and stimulated with CMV pp65 peptides. Disabling of the VP35 IID resulted in increased proliferation and higher percentages of CD4+ T cells secreting IFNγ and/or TNFα. To address the role of aberrant DC maturation in the IID-mediated suppression of T cell responses, CMV-stimulated DCs were infected with the panel of viruses and co-cultured with autologous T-lymphocytes. Infection with EBOV/VP35m infection resulted in a significant increase, as compared to wt EBOV, in proliferating CD4+ cells secreting IFNγ, TNFα and IL-2. Experiments with expanded CMV-specific T cells demonstrated their increased activation following co-cultivation with CMV-pulsed DCs pre-infected with EBOV/VP24m, EBOV/VP35m and EBOV/VP35m/VP24m, as compared to wt EBOV. Both IIDs were found to block phosphorylation of TCR complex-associated adaptors and downstream signaling molecules. Next, we examined the effects of IIDs on the function of B cells in infected PBMC. Infection with EBOV/VP35m and EBOV/VP35m/VP24m resulted in significant increases in the percentages of phenotypically distinct B-cell subsets and plasma cells, as compared to wt EBOV, suggesting inhibition of B cell function and differentiation by VP35 IID. Finally, infection with EBOV/VP35m increased activation of NK cells, as compared to wt EBOV. These results demonstrate a global suppression of cell-mediated responses by EBOV IIDs and identify the role of DCs in suppression of T-cell responses.

Vaccinia Virus Protein C6 Inhibits Type I IFN Signalling in the Nucleus and Binds to the Transactivation Domain of STAT2

The type I interferon (IFN) response is a crucial innate immune signalling pathway required for defense against viral infection. Accordingly, the great majority of mammalian viruses possess means to inhibit this important host immune response. Here we show that vaccinia virus (VACV) strain Western Reserve protein C6, is a dual function protein that inhibits the cellular response to type I IFNs in addition to its published function as an inhibitor of IRF-3 activation, thereby restricting type I IFN production from infected cells. Ectopic expression of C6 inhibits the induction of interferon stimulated genes (ISGs) in response to IFNα treatment at both the mRNA and protein level. C6 inhibits the IFNα-induced Janus kinase/signal transducer and activator of transcription (JAK/STAT) signalling pathway at a late stage, downstream of STAT1 and STAT2 phosphorylation, nuclear translocation and binding of the interferon stimulated gene factor 3 (ISGF3) complex to the interferon stimulated response element (ISRE). Mechanistically, C6 associates with the transactivation domain of STAT2 and this might explain how C6 inhibits the type I IFN signalling very late in the pathway. During virus infection C6 reduces ISRE-dependent gene expression despite the presence of the viral protein phosphatase VH1 that dephosphorylates STAT1 and STAT2. The ability of a cytoplasmic replicating virus to dampen the immune response within the nucleus, and the ability of viral immunomodulators such as C6 to inhibit multiple stages of the innate immune response by distinct mechanisms, emphasizes the intricacies of host-pathogen interactions and viral immune evasion.

In response to a viral infection, infected host cells mount an early, innate immune response to limit viral replication and spread. Type I interferons (IFNs) are produced by a cell when a viral infection is detected and are a crucial aspect of this early immune response. IFNs are released from the infected cell and can act on the infected cell itself or neighbouring cells to initiate a signalling pathway that results in the production of hundreds of anti-viral proteins. In this work we investigated a vaccinia virus protein called C6, a known inhibitor of type I IFN production. Here we show that C6 also inhibits signalling initiated in response to type I IFNs, therefore providing a dual defence against this essential immune response. The results show that, unlike the majority of viral inhibitors of IFN signalling, C6 inhibits the signalling pathway at a late stage once the proteins required for IFN-stimulated gene transcription have reached the nucleus and bound to the DNA. This work illustrates the complex relationship between infecting viruses and the host immune response and further investigation of the mechanism by which C6 inhibits this important immune pathway will likely increase our knowledge of the pathway itself.

Myeloid-Specific Gene Deletion of Protein Phosphatase 2A Magnifies MyD88- and TRIF-Dependent Inflammation following Endotoxin Challenge

Protein phosphatase 2A (PP2A) is a member of the intracellular serine/threonine phosphatases. Innate immune cell activation triggered by pathogen-associated molecular patterns is mediated by various protein kinases, and PP2A plays a counter-regulatory role by deactivating these kinases. In this study, we generated a conditional knockout of the α isoform of the catalytic subunit of PP2A (PP2ACα). After crossing with myeloid-specific cre-expressing mice, effective gene knockout was achieved in various myeloid cells. The myeloid-specific knockout mice (lyM-PP2A^fl/fl) showed higher mortality in response to endotoxin challenge and bacterial infection. Upon LPS challenge, serum levels of TNF-α, KC, IL-6, and IL-10 were significantly increased in lyM-PP2A^fl/fl mice, and increased phosphorylation was observed in MAPK pathways (p38, ERK, JNK) and the NF-κB pathway (IKKα/β, NF-κB p65) in bone marrow-derived macrophages (BMDMs) from knockout mice. Heightened NF-κB activation was not associated with degradation of IκBα; instead, enhanced phosphorylation of the NF-κB p65 subunit and p38 phosphorylation-mediated TNF-α mRNA stabilization appear to contribute to the increased TNF-α expression. In addition, increased IL-10 expression appears to be due to PP2ACα-knockout-induced IKKα/β hyperactivation. Microarray experiments indicated that the Toll/IL-1R domain-containing adaptor inducing IFN-β/ TNFR-associated factor 3 pathway was highly upregulated in LPS-treated PP2ACα-knockout BMDMs, and knockout BMDMs had elevated IFN-α/β production compared with control BMDMs. Serum IFN-β levels from PP2ACα-knockout mice treated with LPS were also greater than those in controls. Thus, we demonstrate that PP2A plays an important role in regulating inflammation and survival in the setting of septic insult by targeting MyD88- and Toll/IL-1R domain-containing adaptor inducing IFN-β-dependent pathways.

Cyclic di-AMP Released from Staphylococcus aureus Biofilm Induces a Macrophage Type I Interferon Response

Staphylococcus aureus is a leading cause of community- and nosocomial-acquired infections, with a propensity for biofilm formation. S. aureus biofilms actively skew the host immune response toward an anti-inflammatory state; however, the biofilm effector molecules and the mechanism(s) of action responsible for this phenomenon remain to be fully defined. The essential bacterial second messenger cyclic diadenylate monophosphate (c-di-AMP) is an emerging pathogen-associated molecular pattern during intracellular bacterial infections, as c-di-AMP secretion into the infected host cytosol induces a robust type I interferon (IFN) response. Type I IFNs have the potential to exacerbate infectious outcomes by promoting anti-inflammatory effects; however, the type I IFN response to S. aureus biofilms is unknown. Additionally, while several intracellular proteins function as c-di-AMP receptors in S. aureus, it has yet to be determined if any extracellular role for c-di-AMP exists and its release during biofilm formation has not yet been demonstrated. This study examined the possibility that c-di-AMP released during S. aureus biofilm growth polarizes macrophages toward an anti-inflammatory phenotype via type I interferon signaling. DacA, the enzyme responsible for c-di-AMP synthesis in S. aureus, was highly expressed during biofilm growth, and 30 to 50% of total c-di-AMP produced from S. aureus biofilm was released extracellularly due to autolytic activity. S. aureus biofilm c-di-AMP release induced macrophage type I IFN expression via a STING-dependent pathway and promoted S. aureus intracellular survival in macrophages. These findings identify c-di-AMP as another mechanism for how S. aureus biofilms promote macrophage anti-inflammatory activity, which likely contributes to biofilm persistence.

Type I IFN signaling facilitates the development of IL-10-producing effector CD8+ T cells during murine influenza virus infection

Recent evidence has suggested that IL‐10‐producing effector CD8⁺ T cells play an important role in regulating excessive inflammation during acute viral infections. However, the cellular and molecular cues regulating the development of IL‐10‐producing effector CD8⁺ T cells are not completely defined. Here, we show that type I interferons (IFNs) are required for the development of IL‐10‐producing effector CD8⁺ T cells during influenza virus infection in mice. We find that type I IFNs can enhance IL‐27 production by lung APCs, thereby facilitating IL‐10‐producing CD8⁺ T‐cell development through a CD8⁺ T‐cell‐nonautonomous way. Surprisingly, we also demonstrate that direct type I IFN signaling in CD8⁺ T cells is required for the maximal generation of IL‐10‐producing CD8⁺ T cells. Type I IFN signaling in CD8⁺ T cells, in cooperation with IL‐27 and IL‐2 signaling, promotes and sustains the expression of IFN regulatory factor 4 (IRF4) and B‐lymphocyte‐induced maturation protein‐1 (Blimp‐1), two transcription factors required for the production of IL‐10 by effector CD8⁺ T cells. Our data reveal a critical role of the innate antiviral effector cytokines in regulating the production of a regulatory cytokine by effector CD8⁺ T cells during respiratory virus infection.

The human papillomavirus E7 oncoprotein as a regulator of transcription

High-risk human papillomaviruses (HPVs) encode oncoproteins which manipulate gene expression patterns in the host keratinocytes to facilitate viral replication, regulate viral transcription, and promote immune evasion and persistence. In some cases, oncoprotein-induced changes in host cell behavior can cause progression to cancer, but a complete picture of the functions of the viral oncoproteins in the productive HPV life cycle remains elusive. E7 is the HPV-encoded factor most responsible for maintaining cell cycle competence in differentiating keratinocytes. Through interactions with dozens of host factors, E7 has an enormous impact on host gene expression patterns. In this review, we will examine the role of E7 specifically as a regulator of transcription. We will discuss mechanisms of regulation of cell cycle-related genes by E7 as well as genes involved in immune regulation, growth factor signaling, DNA damage responses, microRNAs, and others pathways. We will also discuss some unanswered questions about how transcriptional regulation by E7 impacts the biology of HPV in both benign and malignant conditions.

IFNAR1-Signalling Obstructs ICOS-mediated Humoral Immunity during Non-lethal Blood-Stage Plasmodium Infection

Parasite-specific antibodies protect against blood-stage Plasmodium infection. However, in malaria-endemic regions, it takes many months for naturally-exposed individuals to develop robust humoral immunity. Explanations for this have focused on antigenic variation by Plasmodium, but have considered less whether host production of parasite-specific antibody is sub-optimal. In particular, it is unclear whether host immune factors might limit antibody responses. Here, we explored the effect of Type I Interferon signalling via IFNAR1 on CD4⁺ T-cell and B-cell responses in two non-lethal murine models of malaria, P. chabaudi chabaudi AS (PcAS) and P. yoelii 17XNL (Py17XNL) infection. Firstly, we demonstrated that CD4⁺ T-cells and ICOS-signalling were crucial for generating germinal centre (GC) B-cells, plasmablasts and parasite-specific antibodies, and likewise that T follicular helper (Tfh) cell responses relied on B cells. Next, we found that IFNAR1-signalling impeded the resolution of non-lethal blood-stage infection, which was associated with impaired production of parasite-specific IgM and several IgG sub-classes. Consistent with this, GC B-cell formation, Ig-class switching, plasmablast and Tfh differentiation were all impaired by IFNAR1-signalling. IFNAR1-signalling proceeded via conventional dendritic cells, and acted early by limiting activation, proliferation and ICOS expression by CD4⁺ T-cells, by restricting the localization of activated CD4⁺ T-cells adjacent to and within B-cell areas of the spleen, and by simultaneously suppressing Th1 and Tfh responses. Finally, IFNAR1-deficiency accelerated humoral immune responses and parasite control by boosting ICOS-signalling. Thus, we provide evidence of a host innate cytokine response that impedes the onset of humoral immunity during experimental malaria.

Plasmodium parasites cause malaria by invading, replicating within, and rupturing out of red blood cells. Natural immunity to malaria, which depends on generating Plasmodium-specific antibodies, often takes years to develop. Explanations for this focus on antigenic variation by the parasite, but consider less whether antibody responses themselves may be sub-optimal. Surprisingly little is known about how Plasmodium-specific antibody responses are generated in the host, and whether these can be enhanced. Using mouse models, we found that cytokine-signalling via the receptor IFNAR1 delayed the production of Plasmodium-specific antibody responses. IFNAR1-signalling hindered the resolution of infection, and acted early via conventional dendritic cells to restrict CD4⁺ T-cell activation and their interactions with B-cells. Thus, we reveal that an innate cytokine response, which occurs during blood-stage Plasmodium infection in humans, obstructs the onset of antibody–mediated immunity during experimental malaria.

Multiple functions of USP18

Since the discovery of the ubiquitin system and the description of its important role in the degradation of proteins, many studies have shown the importance of ubiquitin-specific peptidases (USPs). One special member of this family is the USP18 protein (formerly UBP43). In the past two decades, several functions of USP18 have been discovered: this protein is not only an isopeptidase but also a potent inhibitor of interferon signaling. Therefore, USP18 functions as 'a' maestro of many biological pathways in various cell types. This review outlines multiple functions of USP18 in the regulation of various immunological processes, including pathogen control, cancer development, and autoimmune diseases.

T Cells Exacerbate Lyme Borreliosis in TLR2-Deficient Mice

Infection of humans with the spirochete, Borrelia burgdorferi, causes Lyme borreliosis and can lead to clinical manifestations such as arthritis, carditis, and neurological conditions. Experimental infection of mice recapitulates many of these symptoms and serves as a model system for the investigation of disease pathogenesis and immunity. Innate immunity is known to drive the development of Lyme arthritis and carditis, but the mechanisms driving this response remain unclear. Innate immune cells recognize B. burgdorferi surface lipoproteins primarily via toll-like receptor (TLR)2; however, previous work has demonstrated TLR2^−/− mice had exacerbated disease and increased bacterial burden. We demonstrate increased CD4 and CD8 T cell infiltrates in B. burgdorferi-infected joints and hearts of C3H TLR2^−/− mice. In vivo depletion of either CD4 or CD8 T cells reduced Borrelia-induced joint swelling and lowered tissue spirochete burden, whereas depletion of CD8 T cells alone reduced disease severity scores. Exacerbation of Lyme arthritis correlated with increased production of CXCL9 by synoviocytes, and this was reduced with CD8 T cell depletion. These results demonstrate T cells can exacerbate Lyme disease pathogenesis and prolong disease resolution possibly through dysregulation of inflammatory responses and inhibition of bacterial clearance.

The Type I Interferonopathies

Type I interferons (IFNs) play a central role in the immune defense against viral infections. Type I IFN activation is induced by pattern-recognition receptors of the innate immune system that sense pathogen-derived nucleic acids. Cellular responses to type I IFN signaling are orchestrated by a complex network of regulatory pathways that involve both the innate and adaptive immune system. The genetic and molecular dissection of rare Mendelian disorders associated with constitutive overproduction of type I IFN has provided unique insight into cell-intrinsic disease mechanisms that initiate and sustain autoinflammation and autoimmunity and that are caused by disturbances in the intracellular nucleic acid metabolism or in cytosolic nucleic acid-sensing pathways. Collectively, these findings have greatly advanced our understanding of mechanisms that protect the organism against inappropriate immune activation triggered by self nucleic acids while maintaining a prompt and efficient immune response to foreign nucleic acids derived from invading pathogens.

IFI44L promoter methylation as a blood biomarker for systemic lupus erythematosus

OBJECTIVE

Systemic lupus erythematosus (SLE) is a clinically heterogeneous disease with limited reliable diagnostic biomarkers. We investigated whether gene methylation could meet sensitivity and specificity criteria for a robust biomarker.

METHODS

IFI44L promoter methylation was examined using DNA samples from a discovery set including 377 patients with SLE, 358 healthy controls (HCs) and 353 patients with rheumatoid arthritis (RA). Two independent sets including 1144 patients with SLE, 1350 HCs, 429 patients with RA and 199 patients with primary Sjögren's syndrome (pSS) were used for validation.

RESULTS

Significant hypomethylation of two CpG sites within IFI44L promoter, Site1 (Chr1: 79 085 222) and Site2 (Chr1: 79 085 250; cg06872964), was identified in patients with SLE compared with HCs, patients with RA and patients with pSS. In a comparison between patients with SLE and HCs included in the first validation cohort, Site1 methylation had a sensitivity of 93.6% and a specificity of 96.8% at a cut-off methylation level of 75.5% and Site2 methylation had a sensitivity of 94.1% and a specificity of 98.2% at a cut-off methylation level of 25.5%. The IFI44L promoter methylation marker was also validated in an European-derived cohort. In addition, the methylation levels of Site1 and Site2 within IFI44L promoter were significantly lower in patients with SLE with renal damage than those without renal damage. Patients with SLE showed significantly increased methylation levels of Site1 and Site2 during remission compared with active stage.

CONCLUSIONS

The methylation level of IFI44L promoter can distinguish patients with SLE from healthy persons and other autoimmune diseases, and is a highly sensitive and specific diagnostic marker for SLE.

miR-145 and miR20a-5p Potentially Mediate Pleiotropic Effects of Interferon-Beta Through Mitogen-Activated Protein Kinase Signaling Pathway in Multiple Sclerosis Patients

MicroRNAs (miRNAs) are crucial to the immunopathogenesis of multiple sclerosis (MS). The mechanism of action of interferon beta (IFN-β) in relapsing-remitting (RR) MS patients is largely unknown. miR-145 and miR-20a-5p previously reported as diagnosis biomarker in treatment naïve RRMS patients and their expression after IFN-β therapy might be indicative of molecular mechanism of IFN-β. Cross-talking between JAK/STAT pathway and complementary pathways like MAPK is important in IFN-β signaling. Here, in order to clarify the ambiguous molecular mechanism of IFN-β and evaluate the potential use of them as a biomarker for monitoring of therapy, we investigated the expression of miR-145 and miR-20a-5p in blood sample of 15 treatment naïve RRMS patients, 15 IFN-β-treated RRMS patients, and 15 healthy volunteers (HVs). In silico molecular signaling pathway enrichment analysis was fulfilled on validated and predicted targets of miR-145 and miR-20a-5p to probe the plausible role of them on molecular effects of IFN-β. We identified miR-145 and miR-20a-5p level was normalized in IFN-β-treated patients, and MAPK pathway was one of the most relevant pathways that recognized by molecular signaling pathway enrichment analysis. Moreover, ROC curve analysis of miR-145 indicated that this miRNA could be used for monitoring of response to IFN-β therapy. Restoration of miR-145 and miR-20a expression in IFN-β-treated patients suggests that pleiotropic effects of IFN-β might be through miRNAs. Enrichment of MAPK pathway underscores the importance of non-canonical pathways in IFN-β signaling.