Mutations in the TLR3 signaling pathway and beyond in adult patients with herpes simplex encephalitis

The multidisciplinary approach to diagnosing inborn errors of immunity: a comprehensive review of discipline-based manifestations

INTRODUCTION

Congenital immunodeficiency is named primary immunodeficiency (PID), and more recently inborn errors of immunity (IEI). There are more than 485 conditions classified as IEI, with a wide spectrum of clinical and laboratory manifestations.

AREAS COVERED

Regardless of the developing knowledge of IEI, many physicians do not think of IEI when approaching the patient's complaint, which leads to delayed diagnosis, misdiagnosis, serious infectious and noninfectious complications, permanent end-organ damage, and even death. Due to the various manifestations of IEI and the wide spectrum of associated conditions, patients refer to specialists in different disciplines of medicine and undergo - mainly symptomatic - treatments, and because IEI are not included in physicians' differential diagnosis, the main disease remains undiagnosed.

EXPERT OPINION

A multidisciplinary approach may be a proper solution. Manifestations and the importance of a multidisciplinary approach in the diagnosis of main groups of IEI are discussed in this article.

UL56 Is Essential for Herpes Simplex Virus-1 Virulence In Vivo but Is Dispensable for Induction of Host-Protective Immunity

Herpes simplex virus-1 (HSV-1) is common and can cause significant disease in humans. Unfortunately, efforts to develop effective vaccines against HSV-1 have so far failed. A detailed understanding of how the virus infects its host and how the host mounts potent immune responses against the virus may inform new vaccine approaches. Here, using a zosteriform mouse model, we examined how the HSV-1 gene UL56 affects the ability of the virus to cause morbidity and generate protective immunity. A UL56 deletion mutant, ΔUL56, was derived from the wild-type HSV-1 strain SC16, alongside a revertant strain in which UL56 was reintroduced in ΔUL56. In vitro, the three virus strains replicated in a similar manner; however, in vivo, only the wild type and the revertant strains caused shingles-like skin lesions and death. Mice previously infected with ΔUL56 became resistant to a lethal challenge with the wild-type SC16. The protective immunity induced by ΔUL56 was independent of IL-1, IL-33, and IL-36 signaling through IL-1RAP. Both skin and intramuscular ΔUL56 inoculation generated protective immunity against a lethal SC16 challenge. After 6 months, female mice remained resistant to infection, while male mice exhibited signs of declining protection. Our data demonstrate that UL56 is important for the ability of HSV-1 to spread within the infected host and that a ∆UL56 strain elicits an effective immune response against HSV-1 despite this loss of virulence. These findings may guide further HSV-1 vaccine development.

Inhibition of herpes simplex virus by wedelolactone via targeting viral envelope and cellular TBK1/IRF3 and SOCS1/STAT3 pathways

OBJECTIVES

Development of novel antiherpes simplex virus (HSV) agents with active mechanisms different from nucleoside analogues is of high importance. Herein, we investigated the anti-HSV activities and mechanisms of wedelolactone (WDL) both in vitro and in vivo.

METHODS

Cytopathic effect (CPE) inhibition assay, plaque assay, and western blot assay were used to evaluate the anti-HSV effects of WDL in vitro. The immunofluorescence assay, RT-PCR assay, plaque reduction assay, sandwich ELISA assay, syncytium formation assay, tanscriptome analysis and western blot assay were used to explore the anti-HSV mechanisms of WDL. The murine encephalitis and vaginal models of HSV infection were performed to evaluate the anti-HSV effects of WDL in vivo.

RESULTS

WDL possessed inhibitory effects against both HSV-1 and HSV-2 in different cells with low toxicity, superior to the effects of acyclovir. WDL can directly inactivate the HSV particle via destruction of viral envelope and block HSV replication process after virus adsorption, different from the mechanisms of acyclovir. WDL may influence the host genes and signaling pathways related to HSV infection and immune responses. WDL can mainly interfere with the TBK1/IRF3 and SOCS1/STAT3 pathways to reduce HSV infection and inflammatory responses. Importantly, WDL treatment markedly improved mice survival, attenuated inflammatory symptoms, and reduced the virus titres in both HSV-1 and HSV-2 infected mice.

CONCLUSIONS

Thus, the natural compound WDL has the potential to be developed into a novel anti-HSV agent targeting both viral envelope and cellular TBK1/IRF3 and SOCS1/STAT3 pathways.

Whole exome sequencing of patients with varicella-zoster virus and herpes simplex virus induced acute retinal necrosis reveals rare disease-associated genetic variants

Purpose

Herpes simplex virus (HSV) and varicella-zoster virus (VZV) are neurotropic human alphaherpesviruses endemic worldwide. Upon primary infection, both viruses establish lifelong latency in neurons and reactivate intermittently to cause a variety of mild to severe diseases. Acute retinal necrosis (ARN) is a rare, sight-threatening eye disease induced by ocular VZV or HSV infection. The virus and host factors involved in ARN pathogenesis remain incompletely described. We hypothesize an underlying genetic defect in at least part of ARN cases.

Methods

We collected blood from 17 patients with HSV-or VZV-induced ARN, isolated DNA and performed Whole Exome Sequencing by Illumina followed by analysis in Varseq with criteria of CADD score > 15 and frequency in GnomAD < 0.1% combined with biological filters. Gene modifications relative to healthy control genomes were filtered according to high quality and read-depth, low frequency, high deleteriousness predictions and biological relevance.

Results

We identified a total of 50 potentially disease-causing genetic variants, including missense, frameshift and splice site variants and on in-frame deletion in 16 of the 17 patients. The vast majority of these genes are involved in innate immunity, followed by adaptive immunity, autophagy, and apoptosis; in several instances variants within a given gene or pathway was identified in several patients.

Discussion

We propose that the identified variants may contribute to insufficient viral control and increased necrosis ocular disease presentation in the patients and serve as a knowledge base and starting point for the development of improved diagnostic, prophylactic, and therapeutic applications.

Susceptibility to Zika virus in a Collaborative Cross mouse strain is induced by Irf3 deficiency in vitro but requires other variants in vivo

Zika virus (ZIKV) is a Flavivirus responsible for recent epidemics in Pacific Islands and in the Americas. In humans, the consequences of ZIKV infection range from asymptomatic infection to severe neurological disease such as Guillain-Barré syndrome or fetal neurodevelopmental defects, suggesting, among other factors, the influence of host genetic variants. We previously reported similar diverse outcomes of ZIKV infection in mice of the Collaborative Cross (CC), a collection of inbred strains with large genetic diversity. CC071/TauUnc (CC071) was the most susceptible CC strain with severe symptoms and lethality. Notably, CC071 has been recently reported to be also susceptible to other flaviviruses including dengue virus, Powassan virus, West Nile virus, and to Rift Valley fever virus. To identify the genetic origin of this broad susceptibility, we investigated ZIKV replication in mouse embryonic fibroblasts (MEFs) from CC071 and two resistant strains. CC071 showed uncontrolled ZIKV replication associated with delayed induction of type-I interferons (IFN-I). Genetic analysis identified a mutation in the Irf3 gene specific to the CC071 strain which prevents the protein phosphorylation required to activate interferon beta transcription. We demonstrated that this mutation induces the same defective IFN-I response and uncontrolled viral replication in MEFs as an Irf3 knock-out allele. By contrast, we also showed that Irf3 deficiency did not induce the high plasma viral load and clinical severity observed in CC071 mice and that susceptibility alleles at other genes, not associated with the IFN-I response, are required. Our results provide new insight into the in vitro and in vivo roles of Irf3, and into the genetic complexity of host responses to flaviviruses.

Human inherited complete STAT2 deficiency underlies inflammatory viral diseases

STAT2 is a transcription factor activated by type I and III IFNs. We report 23 patients with loss-of-function variants causing autosomal recessive (AR) complete STAT2 deficiency. Both cells transfected with mutant STAT2 alleles and the patients' cells displayed impaired expression of IFN-stimulated genes and impaired control of in vitro viral infections. Clinical manifestations from early childhood onward included severe adverse reaction to live attenuated viral vaccines (LAV) and severe viral infections, particularly critical influenza pneumonia, critical COVID-19 pneumonia, and herpes simplex virus type 1 (HSV-1) encephalitis. The patients displayed various types of hyperinflammation, often triggered by viral infection or after LAV administration, which probably attested to unresolved viral infection in the absence of STAT2-dependent types I and III IFN immunity. Transcriptomic analysis revealed that circulating monocytes, neutrophils, and CD8+ memory T cells contributed to this inflammation. Several patients died from viral infection or heart failure during a febrile illness with no identified etiology. Notably, the highest mortality occurred during early childhood. These findings show that AR complete STAT2 deficiency underlay severe viral diseases and substantially impacts survival.

Epilepsy following herpes simplex encephalitis - A case series

BACKGROUND

Herpes simplex encephalitis (HSE) is associated with severe mortality and morbidity. Its incidence is estimated at 1:250 000, and the typical symptomatology of acute disease including headaches, mental state disturbances, confusion, sleepiness, and seizures. The chronic phase of the disease is occasionally characterized by epilepsy and neurological deficits.

STUDY RATIONALE

The present retrospective single-center study aims to identify risk factors for predicting the development of epilepsy (epileptogenesis) following HSE.

METHODS

Medical records were screened for patients older than 18 years, hospitalized between January 2005 and September 2019 with a diagnosis of "encephalitis" and "herpes simplex virus, HSV" infection. HSE diagnosis was based on an analysis of the cerebrospinal fluid with positive HSV testing results.

RESULTS

Twenty-three patients fit our inclusion criteria: fever and behavioral changes, followed by seizures, were reported in 58.3 % of patients. On follow-up (59.7 ± 38.8 months), eight patients (34.8 %) developed epilepsy. Pathological imaging and EEG were correlated with acute symptomatic seizures (ASS). ASS was associated with an 8-fold risk increase to develop post-encephalitis epilepsy (PE). PE was associated with younger age but not with CSF results, imaging, or EEG.

CONCLUSION

Our retrospective single-center study on PE, following HSE, shows that younger age and ASS were associated with PE. Brain imaging, CSF analysis, and EEG were not associated with the development of epilepsy following HSE.

Inborn Errors of Immunity Predisposing to Herpes Simplex Virus Infections of the Central Nervous System

Herpesvirus infections can lead to a number of severe clinical manifestations, particularly when involving the central nervous system (CNS), causing encephalitis and meningitis. However, understanding of the host factors conferring increased susceptibility to these diseases and their complications remains incomplete. Previous studies have uncovered defects in the innate Toll-like receptor 3 pathway and production of type I interferon (IFN-I) in children and adults that predispose them to herpes simplex encephalitis. More recently, there is accumulating evidence for an important role of IFN-independent cell-autonomous intrinsic mechanisms, including small nucleolar RNAs, RNA lariat metabolism, and autophagy, in restricting herpesvirus replication and conferring protection against CNS infection. The present review first describes clinical manifestations of HSV infection with a focus on neurological complications and then summarizes the host-pathogen interactions and innate immune pathways responsible for sensing herpesviruses and triggering antiviral responses and immunity. Next, we review the current landscape of inborn errors of immunity and the underlying genetic defects and disturbances of cellular immune pathways that confer increased susceptibility to HSV infection in CNS. Ultimately, we discuss some of the present outstanding unanswered questions relating to inborn errors of immunity and HSV CNS infection together with some perspectives and future directions for research in the pathogenesis of these severe diseases in humans.

Infection and inflammation: radiological insights into patterns of pediatric immune-mediated CNS injury

The central nervous system (CNS) undergoes constant immune surveillance enabled via regionally specialized mechanisms. These include selectively permissive barriers and modifications to interlinked innate and adaptive immune systems that detect and remove an inciting trigger. The end-points of brain injury and edema from these triggers are varied but often follow recognizable patterns due to shared underlying immune drivers. Imaging provides insights to understanding these patterns that often arise from unique interplays of infection, inflammation and genetics. We review the current updates in our understanding of these intersections and through examples of cases from our practice, highlight that infection and inflammation follow diverse yet convergent mechanisms that can challenge the CNS in children.

Nuclear antiviral innate responses at the intersection of DNA sensing and DNA repair

The coevolution of vertebrate and mammalian hosts with DNA viruses has driven the ability of host cells to distinguish viral from cellular DNA in the nucleus to induce intrinsic immune responses. Concomitant viral mechanisms have arisen to inhibit DNA sensing. At this virus-host interface, emerging evidence links cytokine responses and cellular homeostasis pathways, particularly the DNA damage response (DDR). Nuclear DNA sensors, such as the interferon (IFN)-γ inducible protein 16 (IFI16), functionally intersect with the DDR regulators ataxia telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNA-PK). Here, we discuss accumulating knowledge for the DDR-innate immunity signaling axis. Through the lens of this infection-driven signaling axis, we present host and viral molecular strategies acquired to regulate autoinflammation and antiviral responses.

Added Value of Reanalysis of Whole Exome- and Whole Genome Sequencing Data From Patients Suspected of Primary Immune Deficiency Using an Extended Gene Panel and Structural Variation Calling

Background

Knowledge of the genetic variation underlying Primary Immune Deficiency (PID) is increasing. Reanalysis of genome-wide sequencing data from undiagnosed patients with suspected PID may improve the diagnostic rate.

Methods

We included patients monitored at the Department of Infectious Diseases or the Child and Adolescent Department, Rigshospitalet, Denmark, for a suspected PID, who had been analysed previously using a targeted PID gene panel (457 PID-related genes) on whole exome- (WES) or whole genome sequencing (WGS) data. A literature review was performed to extend the PID gene panel used for reanalysis of single nucleotide variation (SNV) and small indels. Structural variant (SV) calling was added on WGS data.

Results

Genetic data from 94 patients (86 adults) including 36 WES and 58 WGS was reanalysed a median of 23 months after the initial analysis. The extended gene panel included 208 additional PID-related genes. Genetic reanalysis led to a small increase in the proportion of patients with new suspicious PID related variants of uncertain significance (VUS). The proportion of patients with a causal genetic diagnosis was constant. In total, five patients (5%, including three WES and two WGS) had a new suspicious PID VUS identified due to reanalysis. Among these, two patients had a variant added due to the expansion of the PID gene panel, and three patients had a variant reclassified to a VUS in a gene included in the initial PID gene panel. The total proportion of patients with PID related VUS, likely pathogenic, and pathogenic variants increased from 43 (46%) to 47 (50%), as one patient had a VUS detected in both initial- and reanalysis. In addition, we detected new suspicious SNVs and SVs of uncertain significance in PID candidate genes with unknown inheritance and/or as heterozygous variants in genes with autosomal recessive inheritance in 8 patients.

Conclusion

These data indicate a possible diagnostic gain of reassessing WES/WGS data from patients with suspected PID. Reasons for the possible gain included improved knowledge of genotype-phenotype correlation, expanding the gene panel, and adding SV analyses. Future studies of genotype-phenotype correlations may provide additional knowledge on the impact of the new suspicious VUSs.

Life-threatening viral disease in a novel form of autosomal recessive IFNAR2 deficiency in the Arctic

Type I interferons (IFN-I) play a critical role in human antiviral immunity, as demonstrated by the exceptionally rare deleterious variants of IFNAR1 or IFNAR2. We investigated five children from Greenland, Canada, and Alaska presenting with viral diseases, including life-threatening COVID-19 or influenza, in addition to meningoencephalitis and/or hemophagocytic lymphohistiocytosis following live-attenuated viral vaccination. The affected individuals bore the same homozygous IFNAR2 c.157T>C, p.Ser53Pro missense variant. Although absent from reference databases, p.Ser53Pro occurred with a minor allele frequency of 0.034 in their Inuit ancestry. The serine to proline substitution prevented cell surface expression of IFNAR2 protein, small amounts of which persisted intracellularly in an aberrantly glycosylated state. Cells exclusively expressing the p.Ser53Pro variant lacked responses to recombinant IFN-I and displayed heightened vulnerability to multiple viruses in vitro-a phenotype rescued by wild-type IFNAR2 complementation. This novel form of autosomal recessive IFNAR2 deficiency reinforces the essential role of IFN-I in viral immunity. Further studies are warranted to assess the need for population screening.

Fascinating Molecular and Immune Escape Mechanisms in the Treatment of STIs (Syphilis, Gonorrhea, Chlamydia, and Herpes Simplex)

The incidence of syphilis, gonorrhea, chlamydia, and herpes simplex has increased over the last decade, despite the numerous prevention strategies. Worldwide scientists report a surge in drug-resistant infections, particularly in immunocompromised patients. Antigenic variations in syphilis enable long-term infection, but benzathine penicillin G maintains its efficiency, whereas macrolides should be recommended with caution. Mupirocin and zoliflodacin were recently introduced as therapies against ceftriaxone-resistant gonococcus, which poses a larger global threat. The gastrointestinal and prostatic potential reservoirs of Chlamydia trachomatis may represent the key towards complete eradication. Similar to syphilis, macrolides resistance has to be considered in genital chlamydiosis. Acyclovir-resistant HSV may respond to the novel helicase-primase inhibitors and topical imiquimod, particularly in HIV-positive patients. Novel drugs can overcome these challenges while nanocarriers enhance their potency, particularly in mucosal areas. This review summarizes the most recent and valuable discoveries regarding the immunopathogenic mechanisms of these sexually transmitted infections and discusses the challenges and opportunities of the novel molecules and nanomaterials.

Respiratory tract infection of fatal severe human bocavirus 1 in a 13-month-old child: A case report and literature review

Human bocavirus 1 (HBoV1) belongs to the family Parvoviridae and it is acknowledged that HBoV1 is a respiratory pathogen. We report the case of a 13-month-old boy who presented with a cough, shortness of breath, and wheezing, and who eventually died of severe pneumonia and acute respiratory distress syndrome (ARDS). Metagenomics next-generation sequencing (mNGS) showed that HBoV1 was the only detected pathogen. The nasopharyngeal aspirate viral load was 2.08 × 10¹⁰ copies/ml and the serum viral load was 2.37 × 10⁵ copies/ml. The child was still oxygen deficient under mechanical ventilation. Chest imaging suggested diffuse lesions in both lungs, an injury caused by ARDS. In this case, the clinical symptoms and signs of the child, the high viral load, viremia, and the detection of mNGS in the tracheal aspirate all supported that HBoV1 could cause severe acute respiratory tract infection in children without other pathogen infections.

Prevalence of Pathogenic and Potentially Pathogenic Inborn Error of Immunity Associated Variants in Children with Severe Sepsis

Purpose

Our understanding of inborn errors of immunity is increasing; however, their contribution to pediatric sepsis is unknown.

Methods

We used whole-exome sequencing (WES) to characterize variants in genes related to monogenic immunologic disorders in 330 children admitted to intensive care for severe sepsis. We defined candidate variants as rare variants classified as pathogenic or potentially pathogenic in QIAGEN’s Human Gene Mutation Database or novel null variants in a disease-consistent inheritance pattern. We investigated variant correlation with infection and inflammatory phenotype.

Results

More than one in two children overall and three of four African American children had immunodeficiency-associated variants. Children with variants had increased odds of isolating a blood or urinary pathogen (blood: OR 2.82, 95% CI: 1.12–7.10, p = 0.023, urine: OR: 8.23, 95% CI: 1.06–64.11, p = 0.016) and demonstrating increased inflammation with hyperferritinemia (ferritin \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\ge 500$$\end{document}≥500 ng/mL, OR: 2.16, 95% CI: 1.28–3.66, p = 0.004), lymphopenia (lymphocyte count < 1000/µL, OR: 1.66, 95% CI: 1.06 – 2.60, p = 0.027), thrombocytopenia (platelet count < 150,000/µL, OR: 1.76, 95% CI: 1.12–2.76, p = 0.013), and CRP greater than 10 mg/dl (OR: 1.71, 95% CI: 1.10–2.68, p = 0.017). They also had increased odds of requiring extracorporeal membrane oxygenation (ECMO, OR: 4.19, 95% CI: 1.21–14.5, p = 0.019).

Conclusion

Herein, we describe the genetic findings in this severe pediatric sepsis cohort and their microbiologic and immunologic significance, providing evidence for the phenotypic effect of these variants and rationale for screening children with life-threatening infections for potential inborn errors of immunity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10875-021-01183-4.

Disrupting Neurons and Glial Cells Oneness in the Brain-The Possible Causal Role of Herpes Simplex Virus Type 1 (HSV-1) in Alzheimer's Disease

Current data strongly suggest herpes simplex virus type 1 (HSV-1) infection in the brain as a contributing factor to Alzheimer's disease (AD). The consequences of HSV-1 brain infection are multilateral, not only are neurons and glial cells damaged, but modifications also occur in their environment, preventing the transmission of signals and fulfillment of homeostatic and immune functions, which can greatly contribute to the development of disease. In this review, we discuss the pathological alterations in the central nervous system (CNS) cells that occur, following HSV-1 infection. We describe the changes in neurons, astrocytes, microglia, and oligodendrocytes related to the production of inflammatory factors, transition of glial cells into a reactive state, oxidative damage, Aβ secretion, tau hyperphosphorylation, apoptosis, and autophagy. Further, HSV-1 infection can affect processes observed during brain aging, and advanced age favors HSV-1 reactivation as well as the entry of the virus into the brain. The host activates pattern recognition receptors (PRRs) for an effective antiviral response during HSV-1 brain infection, which primarily engages type I interferons (IFNs). Future studies regarding the influence of innate immune deficits on AD development, as well as supporting the neuroprotective properties of glial cells, would reveal valuable information on how to harness cytotoxic inflammatory milieu to counter AD initiation and progression.

Dynamics of IL-15/IL-15R-α expression in response to HSV-1 infection reveal a novel mode of viral immune evasion counteracted by iNKT cells

Herpes simplex virus type 1 (HSV-1) infects and persists in most of the human population. Interleukin-15 (IL-15) has an important role in the activation of cell-mediated immune responses and acts in complex with IL-15 receptor alpha (IL-15R-α) through cell surface transpresentation. Here, we have examined the IL-15/IL-15R-α complex response dynamics during HSV-1 infection in human keratinocytes. Surface expression of the IL-15/IL-15R-α complex rapidly increased in response to HSV-1, reaching a peak around 12 h after infection. This response was dependent on detection of viral replication by TLR3, and enhancement of IL15 and IL15RA gene expression. Beyond the peak of expression, levels of IL-15 and IL-15R-α gradually declined, reaching a profound loss of surface expression beyond 24 h of infection. This involved the loss of IL15 and IL15RA transcription. Interestingly, invariant natural killer T (iNKT) cells inhibited the viral interference with IL-15/IL-15R-α complex expression in an IFNγ-dependent manner. These results indicate that rapid upregulation of the IL-15/IL-15R-α complex occurs in HSV-1 infected keratinocytes, and that this response is targeted by viral interference. Shutdown of the IL-15 axis represents a novel mode of HSV-1 immune evasion, which can be inhibited by the host iNKT cell response.

Neuron-intrinsic immunity to viruses in mice and humans

Viral encephalitis is a major neglected medical problem. Host defense mechanisms against viral infection of the central nervous system (CNS) have long remained unclear. The few previous studies of CNS-specific immunity to viruses in mice in vivo and humans in vitro have focused on the contributions of circulating leukocytes, resident microglial cells and astrocytes, with neurons long considered passive victims of viral infection requiring protection from extrinsic antiviral mechanisms. The last decade has witnessed the gradual emergence of the notion that neurons also combat viruses through cell-intrinsic mechanisms. Forward genetic approaches in humans have shown that monogenic inborn errors of TLR3, IFN-α/β, or snoRNA31 immunity confer susceptibility to herpes simplex virus 1 (HSV-1) infection of the forebrain, whereas inborn errors of DBR1 underlie brainstem infections due to various viruses, including HSV-1. The study of human pluripotent stem cell (hPSC)-derived CNS-resident cells has unraveled known (i.e. TLR3-dependent IFN-α/β immunity) and new (i.e. snoRNA31-dependent or DBR1-dependent immunity) cell-intrinsic antiviral mechanisms operating in neurons. Reverse genetic approaches in mice have confirmed that some known antiviral mechanisms also operate in mouse neurons (e.g. TLR3 and IFN-α/β immunity). The search for human inborn errors of immunity (IEIs) underlying various forms of viral encephalitis, coupled with mouse models in vivo, and hPSC-based culture models of CNS and peripheral nervous system cells and organoids in vitro, should shed further light on the cell-specific and tissue-specific mechanisms of host defense against viruses in the human brain.

TLR3 controls constitutive IFN-β antiviral immunity in human fibroblasts and cortical neurons

Human herpes simplex virus 1 (HSV-1) encephalitis can be caused by inborn errors of the TLR3 pathway, resulting in impairment of CNS cell-intrinsic antiviral immunity. Deficiencies of the TLR3 pathway impair cell-intrinsic immunity to vesicular stomatitis virus (VSV) and HSV-1 in fibroblasts, and to HSV-1 in cortical but not trigeminal neurons. The underlying molecular mechanism is thought to involve impaired IFN-α/β induction by the TLR3 recognition of dsRNA viral intermediates or by-products. However, we show here that human TLR3 controls constitutive levels of IFNB mRNA and secreted bioactive IFN-β protein, and thereby also controls constitutive mRNA levels for IFN-stimulated genes (ISGs) in fibroblasts. Tlr3-/- mouse embryonic fibroblasts also have lower basal ISG levels. Moreover, human TLR3 controls basal levels of IFN-β secretion and ISG mRNA in induced pluripotent stem cell-derived cortical neurons. Consistently, TLR3-deficient human fibroblasts and cortical neurons are vulnerable not only to both VSV and HSV-1, but also to several other families of viruses. The mechanism by which TLR3 restricts viral growth in human fibroblasts and cortical neurons in vitro and, by inference, by which the human CNS prevents infection by HSV-1 in vivo, is therefore based on the control of early viral infection by basal IFN-β immunity.

Nuclear ADP-ribosylation drives IFNγ-dependent STAT1α enhancer formation in macrophages

STAT1α is a key transcription factor driving pro-inflammatory responses in macrophages. We found that the interferon gamma (IFNγ)-regulated transcriptional program in macrophages is controlled by ADP-ribosylation (ADPRylation) of STAT1α, a post-translational modification resulting in the site-specific covalent attachment of ADP-ribose moieties. PARP-1, the major nuclear poly(ADP-ribose) polymerase (PARP), supports IFNγ-stimulated enhancer formation by regulating the genome-wide binding and IFNγ-dependent transcriptional activation of STAT1α. It does so by ADPRylating STAT1α on specific residues in its DNA-binding domain (DBD) and transcription activation (TA) domain. ADPRylation of the DBD controls STAT1α binding to its cognate DNA elements, whereas ADPRylation of the TA domain regulates enhancer activation by modulating STAT1α phosphorylation and p300 acetyltransferase activity. Loss of ADPRylation at either site leads to diminished IFNγ-dependent transcription and downstream pro-inflammatory responses. We conclude that PARP-1-mediated ADPRylation of STAT1α drives distinct enhancer activation mechanisms and is a critical regulator of inflammatory responses in macrophages.

Toll-Like Receptor Signaling in the Establishment and Function of the Immune System

Toll-like receptors (TLRs) are pattern recognition receptors that play a central role in the development and function of the immune system. TLR signaling promotes the earliest emergence of hematopoietic cells during development, and thereafter influences the fate and function of both primitive and effector immune cell types. Aberrant TLR signaling is associated with hematopoietic and immune system dysfunction, and both loss- and gain-of- function variants in TLR signaling-associated genes have been linked to specific infection susceptibilities and immune defects. Herein, we will review the role of TLR signaling in immune system development and the growing number of heritable defects in TLR signaling that lead to inborn errors of immunity.

Constitutive and latent immune mechanisms exert 'silent' control of virus infections in the central nervous system

Viral infections in the central nervous system (CNS) can lead to severe disease manifestations often mediated by a combination of viral cytopathic effects and immunopathology. Moreover, neuronal tissue and brain activities are highly sensitive to excessive inflammation that disturb homeostasis. Immune responses to virus infections in the CNS should therefore be tightly balanced and limited in magnitude and duration to avoid immunopathology and tissue damage. Recent data from genetic studies of patients with viral infections in the CNS as well as experimental cell and animal models have provided evidence of non-redundant roles for constitutive and latent immune mechanisms, which mediate a first line of antiviral control without significantly triggering inflammatory activities. Collectively, accumulating data suggest the existence of a layer of immune mechanisms in the CNS exerting immediate control of infection, hence buffering the need for activation of more potent immune reactions with inherent potential to induce immunopathology and disease.

The Potential Role of Herpes Simplex Virus Type 1 and Neuroinflammation in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease affecting ~50 million people worldwide. To date, there is no cure and current therapies have not been effective in delaying disease progression. Therefore, there is an urgent need for better understanding of the pathogenesis of AD and to rethink possible therapies. Herpes simplex virus type 1 (HSV1) has recently received growing attention for its potential role in sporadic AD. The virus is a ubiquitous human pathogen that infects mucosal epithelia and invades the peripheral nervous system (PNS) of its host to establish a reactivable, latent infection. Upon reactivation, HSV1 spreads back to the epithelium and initiates a new infection, causing epithelial lesions. Occasionally, the virus spreads from the PNS to the brain after reactivation. In this review, we discuss current work on the pathogenesis of AD and summarize research results that support a potential role for HSV1 in the infectious hypothesis of AD. We also highlight recent findings on the neuroinflammatory response, which has been proposed to be the main driving force of AD, starting early in the course of the disease. Relevant rodent models to study neuroinflammation in AD and novel therapeutic approaches are also discussed. Throughout this review, we focus on several aspects of HSV1 pathogenesis, including its primary role as an invader of the PNS, that should be considered in the etiology of AD. We also point out some of the contradictory data and remaining knowledge gaps that require further research to finally fully understand the cause of AD in humans.

The herpesvirus accessory protein γ134.5 facilitates viral replication by disabling mitochondrial translocation of RIG-I

RIG-I and MDA5 are cytoplasmic RNA sensors that mediate cell intrinsic immunity against viral pathogens. While it has been well-established that RIG-I and MDA5 recognize RNA viruses, their interactive network with DNA viruses, including herpes simplex virus 1 (HSV-1), remains less clear. Using a combination of RNA-deep sequencing and genetic studies, we show that the γ134.5 gene product, a virus-encoded virulence factor, enables HSV growth by neutralization of RIG-I dependent restriction. When expressed in mammalian cells, HSV-1 γ134.5 targets RIG-I, which cripples cytosolic RNA sensing and subsequently suppresses antiviral gene expression. Rather than inhibition of RIG-I K63-linked ubiquitination, the γ134.5 protein precludes the assembly of RIG-I and cellular chaperone 14-3-3ε into an active complex for mitochondrial translocation. The γ134.5-mediated inhibition of RIG-I-14-3-3ε binding abrogates the access of RIG-I to mitochondrial antiviral-signaling protein (MAVS) and activation of interferon regulatory factor 3. As such, unlike wild type virus HSV-1, a recombinant HSV-1 in which γ134.5 is deleted elicits efficient cytokine induction and replicates poorly, while genetic ablation of RIG-I expression, but not of MDA5 expression, rescues viral growth. Collectively, these findings suggest that viral suppression of cytosolic RNA sensing is a key determinant in the evolutionary arms race of a large DNA virus and its host.

Recurrent Herpes Zoster Ophthalmicus in a Patient With a Novel Toll-Like Receptor 3 Variant Linked to Compromised Activation Capacity in Fibroblasts

BACKGROUND

Herpes zoster ophthalmicus occurs primarily in elderly or immunocompromised individuals after reactivation of varicella zoster virus (VZV). Recurrences of zoster ophthalmicus are uncommon because the reactivation efficiently boosts anti-VZV immunity. A 28-year-old female presented to our clinic with a history of multiple recurrences of zoster ophthalmicus.

METHODS

Whole-exome sequencing (WES), analyses of VZV T-cell immunity, and pathogen recognition receptor function in primary antigen-presenting cells (APCs) and fibroblasts were performed.

RESULTS

Normal VZV-specific T-cell immunity and antibody response were detected. Whole-exome sequencing identified a heterozygous nonsynonymous variant (c.2324C > T) in the Toll-like receptor 3 (TLR3) gene resulting in formation of a premature stop-codon. This alteration could potentially undermine TLR3 signaling in a dominant-negative fashion. Therefore, we investigated TLR3 signaling responses in APCs and fibroblasts from the patient. The APCs responded efficiently to stimulation with TLR3 ligands, whereas the responses from the fibroblasts were compromised.

CONCLUSIONS

We report a novel TLR3 variant associated with recurrent zoster ophthalmicus. Toll-like receptor 3 responses that were unaffected in APCs but diminished in fibroblasts are in line with previous reports linking TLR3 deficiency with herpes simplex virus encephalitis. Mechanisms involving compromised viral sensing in infected cells may thus be central to the described immunodeficiency.

Rare Genetic Variants in Immune Genes and Neonatal Herpes Simplex Viral Infections

Neonatal herpes simplex virus (HSV) infection is a devastating disease with high mortality, particularly when disseminated. Studies in adults and children suggest that susceptibility to herpes simplex encephalitis (HSE) may represent phenotypes for inborn errors in toll-like receptor 3 (TLR3) signaling. However, the genetic basis of susceptibility to neonatal HSV including disseminated disease remains unknown. To test the hypothesis that variants in known HSE-susceptible genes as well as genes mediating HSV immunity will be identified in neonatal HSV, we performed an unbiased exome sequencing study in 10 newborns with disseminated, HSE, and skin, eyes, and mouth disease. Determination of potential impact on function was determined by following American College of Medical Genetics and Genomics guidelines. We identified deleterious and potentially deleterious, rare variants in known HSE-related genes including a stop IRF3 variant (disseminated), nonsynonymous variants in TLR3 and TRAF3 (HSE), STAT1 (skin, eyes, and mouth), and DBR1 (disseminated) in our cohort. Novel and rare variants in other immunodeficiency genes or HSV-related immune genes GRB2, RAG2, PRF1, C6, C7, and MSR1 were found in 4 infants. The variant in GRB2, essential for T-lymphocyte cell responses to HSV, is a novel stop variant not found in public databases. In this pilot study, we identified deleterious or potentially deleterious variants in TLR3 pathway and genes that regulate anti-HSV immunity in neonates with HSV including disseminated disease. Larger, definitive studies incorporating functional analysis of genetic variants are required to validate these data and determine the role of immune genetic variants in neonatal HSV susceptibility.

Defects in LC3B2 and ATG4A underlie HSV2 meningitis and reveal a critical role for autophagy in antiviral defense in humans

Recurrent herpesvirus infections can manifest in different forms of disease, including cold sores, genital herpes, and encephalitis. There is an incomplete understanding of the genetic and immunological factors conferring susceptibility to recurrent herpes simplex virus 2 (HSV2) infection in the central nervous system (CNS). Here, we describe two adult patients with recurrent HSV2 lymphocytic Mollaret's meningitis that each carry a rare monoallelic variant in the autophagy proteins ATG4A or LC3B2. HSV2-activated autophagy was abrogated in patient primary fibroblasts, which also exhibited significantly increased viral replication and enhanced cell death. HSV2 antigen was captured in autophagosomes of infected cells, and genetic inhibition of autophagy by disruption of autophagy genes, including ATG4A and LC3B2, led to enhanced viral replication and cell death in primary fibroblasts and a neuroblastoma cell line. Activation of autophagy by HSV2 was sensitive to ultraviolet (UV) irradiation of the virus and inhibited in the presence of acyclovir, but HSV2-induced autophagy was independent of the DNA-activated STING pathway. Reconstitution of wild-type ATG4A and LC3B2 expression using lentiviral gene delivery or electroporation of in vitro transcribed mRNA into patient cells restored virus-induced autophagy and the ability to control HSV2 replication. This study describes a previously unknown link between defective autophagy and an inborn error of immunity that can lead to increased susceptibility to HSV2 infection, suggesting an important role for autophagy in antiviral immunity in the CNS.

Host genetic susceptibility to viral infections: the role of type I interferon induction

The innate immune response is the major front line of defense against viral infections. It involves hundreds of genes with antiviral properties which expression is induced by type I interferons (IFNs) and are therefore called interferon stimulated genes (ISGs). Type I IFNs are produced after viral recognition by pathogen recognition receptors, which trigger a cascade of activation events. Human and mouse studies have shown that defective type I IFNs induction may hamper the ability to control viral infections. In humans, moderate to high-effect variants have been identified in individuals with particularly severe complications following viral infection. In mice, functional studies using knock-out alleles have revealed the specific role of most genes of the IFN pathway. Here, we review the role of the molecular partners of the type I IFNs induction pathway and their implication in the control of viral infections and of their complications.

Participation of Endosomes in Toll-Like Receptor 3 Transportation Pathway in Murine Astrocytes

TLR3 provides immediate type I IFN response following entry of stimulatory PAMPs into the CNS, as it is in HSV infection. The receptor plays a vital role in astrocytes, contributing to rapid infection sensing and suppression of viral replication, precluding the spread of virus beyond neurons. The route of TLR3 mobilization culminating in the receptor activation remains unexplained. In this research, we investigated the involvement of various types of endosomes in the regulation of the TLR3 mobility in C8-D1A murine astrocyte cell line. TLR3 was transported rapidly to early EEA1-positive endosomes as well as LAMP1-lysosomes following stimulation with the poly(I:C). Later, TLR3 largely associated with late Rab7-positive endosomes. Twenty-four hours after stimulation, TLR3 co-localized with LAMP1 abundantly in lysosomes of astrocytes. TLR3 interacted with poly(I:C) intracellularly from 1 min to 8 h following cell stimulation. We detected TLR3 on the surface of astrocytes indicating constitutive expression, which increased after poly(I:C) stimulation. Our findings contribute to the understanding of cellular modulation of TLR3 trafficking. Detailed analysis of the TLR3 transportation pathway is an important component in disclosing the fate of the receptor in HSV-infected CNS and may help in the search for rationale therapeutics to control the replication of neuropathic viruses.

The role of host genetics in susceptibility to severe viral infections in humans and insights into host genetics of severe COVID-19: A systematic review

BACKGROUND

Susceptibility to severe viral infections was reported to be associated with genetic variants in immune response genes using case reports and GWAS studies. SARS-CoV-2 is an emergent viral disease that caused millions of COVID-19 cases all over the world. Around 15 % of cases are severe and some of them are accompanied by dysregulated immune system and cytokine storm. There is increasing evidence that severe manifestations of COVID-19 might be attributed to human genetic variants in genes related to immune deficiency and or inflammasome activation (cytokine storm).

OBJECTIVE

Identify the candidate genes that are likely to aid in explaining severe COVID-19 and provide insights to understand the pathogenesis of severe COVID-19.

METHODS

In this article, we systematically reviewed genes related to viral susceptibility that were reported in human genetic studies (Case-reports and GWAS) to understand the role of host viral interactions and to provide insights into the pathogenesis of severe COVID-19.

RESULTS

We found 40 genes associated with viral susceptibility and 21 of them were associated with severe SARS-CoV disease and severe COVID-19. Some of those genes were implicated in TLR pathways, others in C-lectin pathways, and others were related to inflammasome activation (cytokine storm).

CONCLUSION

This compilation represents a list of candidate genes that are likely to aid in explaining severe COVID-19 which are worthy of inclusion in gene panels and during meta-analysis of different variants in host genetics studies of COVID-19. In addition, we provide several hypotheses for severe COVID-19 and possible therapeutic targets.

Whole-Exome Sequencing of Patients With Recurrent HSV-2 Lymphocytic Mollaret Meningitis

Recurrent lymphocytic meningitis, also referred to as Mollaret meningitis, is a rare neurological disease characterized mainly by reactivation of herpes simplex virus 2 (HSV-2) from sensory ganglia. However, the underlying host immune determinants and viral factors rendering some individuals unable to maintain HSV-2 latency are largely unknown. We collected a cohort of 15 patients diagnosed with Mollaret meningitis. By whole-exome sequencing we identified rare host genetic variants predicted to be deleterious in molecules involved in (1) ubiquitin-proteasome pathways, (2) the autophagy machinery, and (3) cell proliferation/apoptosis. Moreover, infection of patient cells with HSV-2 or stimulation by virus-derived double-stranded DNA ligands revealed reduced antiviral interferon responses in most patients. These findings may contribute to a better understanding of disease pathogenesis and protective immunity to HSV in the central nervous system, and may ultimately be of importance for identification of targets for development of improved prophylaxis and treatment of this disease.

Next generation sequencing analysis of consecutive Russian patients with clinical suspicion of inborn errors of immunity

Primary immune deficiencies are usually attributed to genetic defects and, therefore, frequently referred to as inborn errors of immunity (IEI). We subjected the genomic DNA of 333 patients with clinical signs of IEI to next generation sequencing (NGS) analysis of 344 immunity-related genes and, in some instances, additional genetic techniques. Genetic causes of the disease were identified in 69/333 (21%) of subjects, including 11/18 (61%) of children with syndrome-associated IEIs, 45/202 (22%) of nonsyndromic patients with Jeffrey Modell Foundation (JMF) warning signs, 9/56 (16%) of subjects with periodic fever, 3/30 (10%) of cases of autoimmune cytopenia, 1/21 (5%) of patients with unusually severe infections and 0/6 (0%) of individuals with isolated elevation of IgE level. There were unusual clinical observations: twins with severe immunodeficiency carried a de novo CHARGE syndrome-associated SEMA3E c.2108C>T (p.S703L) allele; however, they lacked clinical features of CHARGE syndrome. Additionally, there were genetically proven instances of Netherton syndrome, Х-linked agammaglobulinemia, severe combined immune deficiency (SCID), IPEX and APECED syndromes, among others. Some patients carried recurrent pathogenic alleles, such as AIRE c.769C>T (p.R257*), NBN c.657del5, DCLRE1C c.103C>G (p.H35D), NLRP12 c.1054C>T (p.R352C) and c.910C>T (p.H304Y). NGS is a powerful tool for high-throughput examination of patients with malfunction of immunity.

TBK1, a central kinase in innate immune sensing of nucleic acids and beyond

Sensing of intracellular and extracellular environments is one of the fundamental processes of cell. Surveillance of aberrant nucleic acids, derived either from invading pathogens or damaged organelle, is conducted by pattern recognition receptors (PRRs) including RIG-I-like receptors, cyclic GMP-AMP synthase, absent in melanoma 2, and a few members of toll-like receptors. TANK-binding kinase 1 (TBK1), along with its close analogue I-kappa-B kinase epsilon, is a central kinase in innate adaptor complexes linking activation of PRRs to mobilization of transcriptional factors that transcribe proinflammatory cytokines, type I interferon (IFN-α/β), and myriads interferon stimulated genes. However, it still remains elusive for the precise mechanisms of activation and execution of TBK1 in signaling platforms formed by innate adaptors mitochondrial antiviral signaling protein (MAVS), stimulator of interferon genes protein (STING), and TIR-domain-containing adapter-inducing interferon-β (TRIF), as well as its complex regulations. An atlas of TBK1 substrates is in constant expanding, setting TBK1 as a key node of signaling network and a dominant player in contexts of cell biology, animal models, and human diseases. Here, we review recent advancements of activation, regulations, and functions of TBK1 under these physiological and pathological contexts.

Incomplete penetrance in primary immunodeficiency: a skeleton in the closet

Primary immunodeficiencies (PIDs) comprise a diverse group of over 400 genetic disorders that result in clinically apparent immune dysfunction. Although PIDs are classically considered as Mendelian disorders with complete penetrance, we now understand that absent or partial clinical disease is often noted in individuals harboring disease-causing genotypes. Despite the frequency of incomplete penetrance in PID, no conceptual framework exists to categorize and explain these occurrences. Here, by reviewing decades of reports on incomplete penetrance in PID we identify four recurrent themes of incomplete penetrance, namely genotype quality, (epi)genetic modification, environmental influence, and mosaicism. For each of these principles, we review what is known, underscore what remains unknown, and propose future experimental approaches to fill the gaps in our understanding. Although the content herein relates specifically to inborn errors of immunity, the concepts are generalizable across genetic diseases.

Immunomodulatory Strategies in Herpes Simplex Virus Encephalitis

Herpes simplex virus 1 (HSV-1) can be responsible for life-threatening HSV encephalitis (HSE). The mortality rate of patients with HSE who do not receive antiviral treatment is 70%, with most survivors suffering from permanent neurological sequelae. The use of intravenous acyclovir together with improved diagnostic technologies such as PCR and magnetic resonance imaging has resulted in a reduction in the mortality rate to close to 20%. However, 70% of surviving patients still do not recover complete neurological functions. Thus, there is an urgent need to develop more effective treatments for a better clinical outcome. It is well recognized that cerebral damage resulting from HSE is caused by viral replication together with an overzealous inflammatory response. Both of these processes constitute potential targets for the development of innovative therapies against HSE. In this review, we discuss recent progress in therapy that may be used to ameliorate the outcome of patients with HSE, with a particular emphasis on immunomodulatory agents. Ideally, the administration of adjunctive immunomodulatory drugs should be initiated during the rise of the inflammatory response, and its duration should be limited in time to reduce undesired effects. This critical time frame should be optimized by the identification of reliable biomarkers of inflammation.

Herpes simplex virus encephalitis of childhood: inborn errors of central nervous system cell-intrinsic immunity

Herpes simplex virus 1 (HSV-1) encephalitis (HSE) is the most common sporadic viral encephalitis in Western countries. Over the last 15 years, human genetic and immunological studies have provided proof-of-principle that childhood HSE can result from inborn errors of central nervous system (CNS)-specific, cell-intrinsic immunity to HSV-1. HSE-causing mutations of eight genes disrupt known (TLR3-dependent IFN-α/β immunity) and novel (dependent on DBR1 or snoRNA31) antiviral mechanisms. Monogenic inborn errors confer susceptibility to forebrain (TLR3-IFN or snoRNA31) or brainstem (DBR1) HSE. Most of these disorders display incomplete clinical penetrance, with the possible exception of DBR1 deficiency. They account for a small, but non-negligible proportion of cases (about 7%). These findings pave the way for the gradual definition of the genetic and immunological architecture of childhood HSE, with both biological and clinical implications.

Human inborn errors of immunity to herpes viruses

Infections with any of the nine human herpes viruses (HHV) can be asymptomatic or life-threatening. The study of patients with severe diseases caused by HHVs, in the absence of overt acquired immunodeficiency, has led to the discovery or diagnosis of various inborn errors of immunity. The related inborn errors of adaptive immunity disrupt α/β T-cell rather than B-cell immunity. Affected patients typically develop HHV infections in the context of other infectious diseases. However, this is not always the case, as illustrated by inborn errors of SAP-dependent T-cell immunity to EBV-infected B cells. The related inborn errors of innate immunity disrupt leukocytes other than T and B cells, non-hematopoietic cells, or both. Patients typically develop only a single type of infection due to HHV, although, again, this is not always the case, as illustrated by inborn errors of TLR3 immunity resulting in HSV1 encephalitis in some patients and influenza pneumonitis in others. Most severe HHV infections in otherwise healthy patients remains unexplained. The forward human genetic dissection of isolated and syndromic HHV-driven illnesses will establish the molecular and cellular basis of protective immunity to HHVs, paving the way for novel diagnosis and management strategies.

Herpes simplex encephalitis in adult patients with MASP-2 deficiency

We report here two cases of Herpes simplex virus encephalitis (HSE) in adult patients with very rare, previously uncharacterized, non synonymous heterozygous G634R and R203W substitution in mannan-binding lectin serine protease 2 (MASP2), a gene encoding a key protease of the lectin pathway of the complement system. None of the 2 patients had variants in genes involved in the TLR3-interferon signaling pathway. Both MASP2 variants induced functional defects in vitro, including a reduced (R203W) or abolished (G634R) protein secretion, a lost capability to cleave MASP-2 precursor into its active form (G634R) and an in vivo reduced antiviral activity (G634R). In a murine model of HSE, animals deficient in mannose binding lectins (MBL, the main pattern recognition molecule associated with MASP-2) had a decreased survival rate and an increased brain burden of HSV-1 compared to WT C57BL/6J mice. Altogether, these data suggest that MASP-2 deficiency can increase susceptibility to adult HSE.

Human herpes virus type 1 (HSV-1) infects a large number of individuals during their life, with manifestations usually limited to mild and self-limiting inflammation of the oral mucosa (cold sore). However, HSV-1 can cause a very severe disease of the brain called Herpes simplex encephalitis (HSE) in 1 out of 250’000–500’000 individuals per year. The reasons why HSV-1 can cause such a devastating disease in a very limited number of individuals are unknown. Increasing evidence suggests that susceptibility to HSE in children can results from genetic variations in the immune system, in particular in a viral detection pathway called the Toll-like receptor 3 (TLR3)–interferon (IFN) axis. Fewer data are available to explain HSE in adult patients. Here, we describe two adult patients with HSE who carry mutations in a gene called mannan-binding lectin serine protease 2 (MASP2), which is part of an immune pathway different from the TLR3-IFN axis, called the lectin pathway of the complement system. We demonstrate that MASP2 mutations induce functional defects in immune defense against HSV-1 that prevent viral replication. Mice deficient in the lectin pathway have higher mortality compared to wild-type mice after HSV-1 infection. Altogether, our study suggests that susceptibility to HSE in adults relies of immune deficiencies that are different from those causing HSE in children.

Host Intrinsic and Innate Intracellular Immunity During Herpes Simplex Virus Type 1 (HSV-1) Infection

When host cells are invaded by viruses, they deploy multifaceted intracellular defense mechanisms to control infections and limit the damage they may cause. Host intracellular antiviral immunity can be classified into two main branches: (i) intrinsic immunity, an interferon (IFN)-independent antiviral response mediated by constitutively expressed cellular proteins (so-called intrinsic host restriction factors); and (ii) innate immunity, an IFN-dependent antiviral response conferred by IFN-stimulated gene (ISG) products, which are (as indicated by their name) upregulated in response to IFN secretion following the recognition of pathogen-associated molecular patterns (PAMPs) by host pattern recognition receptors (PRRs). Recent evidence has demonstrated temporal regulation and specific viral requirements for the induction of these two arms of immunity during herpes simplex virus type 1 (HSV-1) infection. Moreover, they exert differential antiviral effects to control viral replication. Although they are distinct from one another, the words "intrinsic" and "innate" have been interchangeably and/or simultaneously used in the field of virology. Hence, the aims of this review are to (1) elucidate the current knowledge about host intrinsic and innate immunity during HSV-1 infection, (2) clarify the recent advances in the understanding of their regulation and address the distinctions between them with respect to their induction requirements and effects on viral infection, and (3) highlight the key roles of the viral E3 ubiquitin ligase ICP0 in counteracting both aspects of immunity. This review emphasizes that intrinsic and innate immunity are temporally and functionally distinct arms of host intracellular immunity during HSV-1 infection; the findings are likely pertinent to other clinically important viral infections.

The Goldilocks Zone of Type I IFNs: Lessons from Human Genetics

Type I IFNs (IFN-Is) are powerful cytokines. They provide remarkable protection against viral infections, but their indiscriminate production causes severe self-inflicted damage that can be lethal, particularly in early development. In humans, inappropriately high IFN-I levels caused by defects in the regulatory mechanisms that control IFN-I production and response result in clinical conditions known as type I interferonopathies. In essence, type I interferonopathies define the upper limit of safe, IFN-related inflammation in vivo. Conversely, the loss of IFN-I responsiveness increases susceptibility to viral infections, but, surprisingly, most affected individuals survive despite these inborn errors of immunity. These findings suggest that too much IFN-I early in life is toxic, but that insensitivity to IFN-I is perhaps not the death sentence it was initially thought to be. Human genetic analyses have suggested that seemingly insignificant levels of IFN-regulated gene activity may be sufficient for most of the antiviral defenses used by humans in natura.

Host Genetics, Innate Immune Responses, and Cellular Death Pathways in Poliomyelitis Patients

Purpose

Poliovirus (PV) is one of the most studied viruses. Despite efforts to understand PV infection within the host, fundamental questions remain unanswered. These include the mechanisms determining the progression to viremia, the pathogenesis of neuronal infection and paralysis in only a minority of patients. Because of the rare disease phenotype of paralytic poliomyelitis (PPM), we hypothesize that a genetic etiology may contribute to the disease course and outcome.

Methods

We used whole-exome sequencing (WES) to investigate the genetic profile of 18 patients with PPM. Functional analyses were performed on peripheral blood mononuclear cells (PBMCs) and monocyte-derived macrophages (MdMs).

Results

We identified rare variants in host genes involved in interferon signaling, viral replication, apoptosis, and autophagy. Upon PV infection of MdMs, we observed a tendency toward increased viral burden in patients compared to controls, suggesting reduced control of PV infection. In MdMs from patients, the IFNβ response correlated with the viral burden.

Conclusion

We suggest that genetic variants in innate immune defenses and cell death pathways contribute to the clinical presentation of PV infection. Importantly, this study is the first to uncover the genetic profile in patients with PPM combined with investigations of immune responses and viral burden in primary cells.

Identification and characterization of rare toll-like receptor 3 variants in patients with autoimmune Addison's disease

Autoimmune Addison's disease (AAD) is a classic organ-specific autoimmune disease characterized by an immune-mediated attack on the adrenal cortex. As most autoimmune diseases, AAD is believed to be caused by a combination of genetic and environmental factors, and probably interactions between the two. Persistent viral infections have been suggested to play a triggering role, by invoking inflammation and autoimmune destruction. The inability of clearing infections can be due to aberrations in innate immunity, including mutations in genes involved in the recognition of conserved microbial patterns. In a whole exome sequencing study of anonymized AAD patients, we discovered several rare variants predicted to be damaging in the gene encoding Toll-like receptor 3 (TLR3). TLR3 recognizes double stranded RNAs, and is therefore a major factor in antiviral defense. We here report the occurrence and functional characterization of five rare missense variants in TLR3 of patients with AAD. Most of these variants occurred together with a common TLR3 variant that has been associated with a wide range of immunopathologies. The biological implications of these variants on TLR3 function were evaluated in a cell-based assay, revealing a partial loss-of-function effect of three of the rare variants. In addition, rare mutations in other members of the TLR3-interferon (IFN) signaling pathway were detected in the AAD patients. Together, these findings indicate a potential role for TLR3 and downstream signaling proteins in the pathogenesis in a subset of AAD patients.

Syk and Hrs Regulate TLR3-Mediated Antiviral Response in Murine Astrocytes

Toll-like receptors (TLRs) sense the presence of pathogen-associated molecular patterns. Nevertheless, the mechanisms modulating TLR-triggered innate immune responses are not yet fully understood. Complex regulatory systems exist to appropriately direct immune responses against foreign or self-nucleic acids, and a critical role of hepatocyte growth factor-regulated tyrosine kinase substrate (HRS), endosomal sorting complex required for transportation-0 (ESCRT-0) subunit, has recently been implicated in the endolysosomal transportation of TLR7 and TLR9. We investigated the involvement of Syk, Hrs, and STAM in the regulation of the TLR3 signaling pathway in a murine astrocyte cell line C8-D1A following cell stimulation with a viral dsRNA mimetic. Our data uncover a relationship between TLR3 and ESCRT-0, point out Syk as dsRNA-activated kinase, and suggest the role for Syk in mediating TLR3 signaling in murine astrocytes. We show molecular events that occur shortly after dsRNA stimulation of astrocytes and result in Syk Tyr-342 phosphorylation. Further, TLR3 undergoes proteolytic processing; the resulting TLR3 N-terminal form interacts with Hrs. The knockdown of Syk and Hrs enhances TLR3-mediated antiviral response in the form of IFN-β, IL-6, and CXCL8 secretion. Understanding the role of Syk and Hrs in TLR3 immune responses is of high importance since activation and precise execution of the TLR3 signaling pathway in the brain seem to be particularly significant in mounting an effective antiviral defense. Infection of the brain with herpes simplex type 1 virus may increase the secretion of amyloid-β by neurons and astrocytes and be a causal factor in degenerative diseases such as Alzheimer's disease. Errors in TLR3 signaling, especially related to the precise regulation of the receptor transportation and degradation, need careful observation as they may disclose foundations to identify novel or sustain known therapeutic targets.

Insights into the dynamic nature of the dsRNA-bound TLR3 complex

Toll-like receptor 3 (TLR3), an endosomal receptor crucial for immune responses upon viral invasion. The TLR3 ectodomain (ECD) is responsible for double-stranded RNA (dsRNA) recognition and mutational analysis suggested that TLR3 ECD C-terminal dimerization is essential for dsRNA binding. Moreover, the L412F polymorphism of TLR3 is associated with human diseases. Although the mouse structure of the TLR3-dsRNA complex provides valuable insights, the structural dynamic behavior of the TLR3-dsRNA complex in humans is not completely understood. Hence, in this study, we performed molecular dynamic simulations of human wild-type and mutant TLR3 complexes. Our results suggested that apoTLR3 ECD dimers are unlikely to be stable due to the distance between the monomers are largely varied during simulations. The observed interaction energies and hydrogen bonds in dsRNA-bound TLR3 wild-type and mutant complexes indicate the presence of a weak dimer interface at the TLR3 ECD C-terminal site, which is required for effective dsRNA binding. The L412F mutant exhibited similar dominant motion compared to wild-type. Additionally, we identified the distribution of crucial residues for signal propagation in TLR3-dsRNA complex through the evaluation of residue betweenness centrality (C_B). The results of this study extend our understanding of TLR3-dsRNA complex, which may assist in TLR3 therapeutics.

Herpes Simplex Virus Type 1 Infection of the Central Nervous System: Insights Into Proposed Interrelationships With Neurodegenerative Disorders

Herpes simplex virus type 1 (HSV-1) is highly prevalent in humans and can reach the brain without evident clinical symptoms. Once in the central nervous system (CNS), the virus can either reside in a quiescent latent state in this tissue, or eventually actively lead to severe acute necrotizing encephalitis, which is characterized by exacerbated neuroinflammation and prolonged neuroimmune activation producing a life-threatening disease. Although HSV-1 encephalitis can be treated with antivirals that limit virus replication, neurological sequelae are common and the virus will nevertheless remain for life in the neural tissue. Importantly, there is accumulating evidence that suggests that HSV-1 infection of the brain both, in symptomatic and asymptomatic individuals could lead to neuronal damage and eventually, neurodegenerative disorders. Here, we review and discuss acute and chronic infection of particular brain regions by HSV-1 and how this may affect neuron and cognitive functions in the host. We review potential cellular and molecular mechanisms leading to neurodegeneration, such as protein aggregation, dysregulation of autophagy, oxidative cell damage and apoptosis, among others. Furthermore, we discuss the impact of HSV-1 infection on brain inflammation and its potential relationship with neurodegenerative diseases.

IRF and STAT Transcription Factors - From Basic Biology to Roles in Infection, Protective Immunity, and Primary Immunodeficiencies

The induction and action of type I interferon (IFN) is of fundamental importance in human immune defenses toward microbial pathogens, particularly viruses. Basic discoveries within the molecular and cellular signaling pathways regulating type I IFN induction and downstream actions have shown the essential role of the IFN regulatory factor (IRF) and the signal transducer and activator of transcription (STAT) families, respectively. However, the exact biological and immunological functions of these factors have been most clearly revealed through the study of inborn errors of immunity and the resultant infectious phenotypes in humans. The spectrum of human inborn errors of immunity caused by mutations in IRFs and STATs has proven very diverse. These diseases encompass herpes simplex encephalitis (HSE) and severe influenza in IRF3- and IRF7/IRF9 deficiency, respectively. They also include Mendelian susceptibility to mycobacterial infection (MSMD) in STAT1 deficiency, through disseminated measles infection associated with STAT2 deficiency, and finally staphylococcal abscesses and chronic mucocutaneous candidiasis (CMC) classically described with Hyper-IgE syndrome (HIES) in the case of STAT3 deficiency. More recently, increasing focus has been on aspects of autoimmunity and autoinflammation playing an important part in many primary immunodeficiency diseases (PID)s, as exemplified by STAT1 gain-of-function causing CMC and autoimmune thyroiditis, as well as a recently described autoinflammatory syndrome with hypogammaglobulinemia and lymphoproliferation as a result of STAT3 gain-of-function. Here I review the infectious, inflammatory, and autoimmune disorders arising from mutations in IRF and STAT transcription factors in humans, highlightning the underlying molecular mechanisms and immunopathogenesis as well as the clinical/therapeutic perspectives of these new insights.

Whole Exome Sequencing of HIV-1 long-term non-progressors identifies rare variants in genes encoding innate immune sensors and signaling molecules

Common CCR5-∆32 and HLA alleles only explain a minority of the HIV long-term non-progressor (LTNP) and elite controller (EC) phenotypes. To identify rare genetic variants contributing to the slow disease progression phenotypes, we performed whole exome sequencing (WES) on seven LTNPs and four ECs. HLA and CCR5 allele status, total HIV DNA reservoir size, as well as variant-related functional differences between the ECs, LTNPs, and eleven age- and gender-matched HIV-infected non-controllers on antiretroviral therapy (NCARTs) were investigated. Several rare variants were identified in genes involved in innate immune sensing, CD4-dependent infectivity, HIV trafficking, and HIV transcription mainly within the LTNP group. ECs and LTNPs had a significantly lower HIV reservoir compared to NCARTs. Furthermore, three LTNPs with variants affecting HIV nuclear import showed integrated HIV DNA levels below detection limit after in vitro infection. HIV slow progressors with variants in the TLR and NOD2 pathways showed reduced pro-inflammatory responses compared to matched controls. Low-range plasma levels of fibronectin was observed in a LTNP harboring two FN1 variants. Taken together, this study identified rare variants in LTNPs as well as in one EC, which may contribute to understanding of HIV pathogenesis and these slow progressor phenotypes, especially in individuals without protecting CCR5-∆32 and HLA alleles.

RNA Polymerase III as a Gatekeeper to Prevent Severe VZV Infections

In most individuals, varicella zoster virus (VZV) causes varicella upon primary infection and zoster during reactivation. However, in a subset of individuals, VZV may cause severe disease, including encephalitis. Host genetics is believed to be the main determinant of exacerbated disease manifestations. Recent studies have demonstrated that defects in the DNA sensor RNA polymerase III (POL III) confer selective increased susceptibility to VZV infection, thus providing fundamental new insight into VZV immunity. Here we describe the roles of POL III in housekeeping and immune surveillance during VZV infection. We present the latest knowledge on the role of POL III in VZV infection and discuss outstanding questions related to the role of POL III in VZV immunity, and how this insight can be translated into clinical medicine.