The Type I Interferon Response Determines Differences in Choroid Plexus Susceptibility between Newborns and Adults in Herpes Simplex Virus Encephalitis

Highly restrictive and directional penetration of the blood cerebral spinal fluid barrier by JCPyV

The human polyomavirus JCPyV is an opportunistic pathogen that infects greater than 60% of the world's population. The virus establishes a persistent and asymptomatic infection in the urogenital system but can cause a fatal demyelinating disease in immunosuppressed or immunomodulated patients following invasion of the CNS. The mechanisms responsible for JCPyV invasion into CNS tissues are not known but direct invasion from the blood to the cerebral spinal fluid via the choroid plexus has been hypothesized. To study the potential of the choroid plexus as a site of neuroinvasion, we used an adult human choroid plexus epithelial cell line to model the blood-cerebrospinal fluid (B-CSF) barrier in a transwell system. We found that these cells formed a highly restrictive barrier to virus penetration either as free virus or as virus associated with extracellular vesicles (EVJC+). The restriction was not absolute and small amounts of virus or EVJC+ penetrated and were able to establish foci of infection in primary astrocytes. Disruption of the barrier with capsaicin did not increase virus or EVJC+ penetration leading us to hypothesize that virus and EVJC+ were highly cell-associated and crossed the barrier by an active process. An inhibitor of macropinocytosis increased virus penetration from the basolateral (blood side) to the apical side (CSF side). In contrast, inhibitors of clathrin and raft dependent transcytosis reduced virus transport from the basolateral to the apical side of the barrier. None of the drugs inhibited apical to basolateral transport suggesting directionality. Pretreatment with cyclosporin A, an inhibitor of P-gp, MRP2 and BCRP multidrug resistance transporters, restored viral penetration in cells treated with raft and clathrin dependent transcytosis inhibitors. Because choroid plexus epithelial cells are known to be susceptible to JCPyV infection both in vitro and in vivo we also examined the release of infectious virus from the barrier. We found that virus was preferentially released from the cells into the apical (CSF) chamber. These data show clearly that there are two mechanisms of penetration, direct transcytosis which is capable of seeding the CSF with small amounts of virus, and infection followed by directional release of infectious virions into the CSF compartment.

JCPyV infection of primary choroid plexus epithelial cells reduces expression of critical junctional proteins and increases expression of barrier disrupting inflammatory cytokines

The human polyomavirus, JCPyV, establishes a lifelong persistent infection in the peripheral organs of a majority of the human population worldwide. Patients who are immunocompromised due to underlying infections, cancer, or to immunomodulatory treatments for autoimmune disease are at risk for developing progressive multifocal leukoencephalopathy (PML) when the virus invades the CNS and infects macroglial cells in the brain parenchyma. It is not yet known how the virus enters the CNS to cause disease. The blood-choroid plexus barrier is a potential site of virus invasion as the cells that make up this barrier are known to be infected with virus both in vivo and in vitro. To understand the effects of virus infection on these cells we challenged primary human choroid plexus epithelial cells with JCPyV and profiled changes in host gene expression. We found that viral infection induced the expression of proinflammatory chemokines and downregulated junctional proteins essential for maintaining blood-CSF and blood-brain barrier function. These data contribute to our understanding of how JCPyV infection of the choroid plexus can modulate the host cell response to neuroinvasive pathogens.

IMPORTANCE

The human polyomavirus, JCPyV, causes a rapidly progressing demyelinating disease in the CNS of patients whose immune systems are compromised. JCPyV infection has been demonstrated in the choroid plexus both in vivo and in vitro and this highly vascularized organ may be important in viral invasion of brain parenchyma. Our data show that infection of primary choroid plexus epithelial cells results in increased expression of pro-inflammatory chemokines and downregulation of critical junctional proteins that maintain the blood-CSF barrier. These data have direct implications for mechanisms used by JCPyV to invade the CNS and cause neurological disease.

Type I interferon shapes brain distribution and tropism of tick-borne flavivirus

Viral tropism within the brain and the role(s) of vertebrate immune response to neurotropic flaviviruses infection is largely understudied. We combine multimodal imaging (cm-nm scale) with single nuclei RNA-sequencing to study Langat virus in wildtype and interferon alpha/beta receptor knockout (Ifnar^-/-) mice to visualize viral pathogenesis and define molecular mechanisms. Whole brain viral infection is imaged by Optical Projection Tomography coregistered to ex vivo MRI. Infection is limited to grey matter of sensory systems in wildtype mice, but extends into white matter, meninges and choroid plexus in Ifnar^-/- mice. Cells in wildtype display strong type I and II IFN responses, likely due to Ifnb expressing astrocytes, infiltration of macrophages and Ifng-expressing CD8+ NK cells, whereas in Ifnar^-/-, the absence of this response contributes to a shift in cellular tropism towards non-activated resident microglia. Multimodal imaging-transcriptomics exemplifies a powerful way to characterize mechanisms of viral pathogenesis and tropism.

Severity of neonatal influenza infection is driven by type I interferon and oxidative stress

Neonates exhibit increased susceptibility to respiratory viral infections, attributed to inflammation at the developing pulmonary air-blood interface. IFN I are antiviral cytokines critical to control viral replication, but also promote inflammation. Previously, we established a neonatal murine influenza virus (IV) model, which demonstrates increased mortality. Here, we sought to determine the role of IFN I in this increased mortality. We found that three-day-old IFNAR-deficient mice are highly protected from IV-induced mortality. In addition, exposure to IFNβ 24 h post IV infection accelerated death in WT neonatal animals but did not impact adult mortality. In contrast, IFN IIIs are protective to neonatal mice. IFNβ induced an oxidative stress imbalance specifically in primary neonatal IV-infected pulmonary type II epithelial cells (TIIEC), not in adult TIIECs. Moreover, neonates did not have an infection-induced increase in antioxidants, including a key antioxidant, superoxide dismutase 3, as compared to adults. Importantly, antioxidant treatment rescued IV-infected neonatal mice, but had no impact on adult morbidity. We propose that IFN I exacerbate an oxidative stress imbalance in the neonate because of IFN I-induced pulmonary TIIEC ROS production coupled with developmentally regulated, defective antioxidant production in response to IV infection. This age-specific imbalance contributes to mortality after respiratory infections in this vulnerable population.

The Astrocyte Type I Interferon Response is Essential for Protection Against Herpes Simplex Encephalitis

Innate immune activation by central nervous system (CNS) resident cells is critical for controlling HSV-1 replication.….

A sustained type I IFN-neutrophil-IL-18 axis drives pathology during mucosal viral infection

Neutrophil responses against pathogens must be balanced between protection and immunopathology. Factors that determine these outcomes are not well-understood. In a mouse model of genital herpes simplex virus-2 (HSV-2) infection, which results in severe genital inflammation, antibody-mediated neutrophil depletion reduced disease. Comparative single-cell RNA-sequencing analysis of vaginal cells against a model of genital HSV-1 infection, which results in mild inflammation, demonstrated sustained expression of interferon-stimulated genes (ISGs) only after HSV-2 infection primarily within the neutrophil population. Both therapeutic blockade of IFNα/β receptor 1 (IFNAR1) and genetic deletion of IFNAR1 in neutrophils concomitantly decreased HSV-2 genital disease severity and vaginal IL-18 levels. Therapeutic neutralization of IL-18 also diminished genital inflammation, indicating an important role for this cytokine in promoting neutrophil-dependent immunopathology. Our study reveals that sustained type I interferon (IFN) signaling is a driver of pathogenic neutrophil responses and identifies IL-18 as a novel component of disease during genital HSV-2 infection.

ASC-dependent inflammasomes contribute to immunopathology and mortality in herpes simplex encephalitis

Herpes simplex virus encephalitis (HSE) is the most common cause of sporadic viral encephalitis, and despite targeted antiviral therapy, outcomes remain poor. Although the innate immune system is critical for restricting herpes simplex virus type I (HSV-1) in the brain, there is evidence that prolonged neuroinflammation contributes to HSE pathogenesis. In this study, we investigated the contribution of inflammasomes to disease pathogenesis in a murine model of HSE. Inflammasomes are signaling platforms that activate the pro-inflammatory cytokines interleukin-1β (IL-1β) and IL-18. We found that mice deficient in the inflammasome adaptor protein, apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), had significantly improved survival and lower levels of IL-1β and IL-18 in the brain. Importantly, this difference in survival was independent of viral replication in the central nervous system (CNS). We found that microglia, the resident macrophages of the CNS, are the primary mediators of the ASC-dependent inflammasome response during infection. Using in vitro glial infections and a murine HSE model, we demonstrate that inflammasome activation contributes to the expression of chemokine (C-C motif) ligand 6 (CCL6), a leukocyte chemoattractant. The lower concentration of CCL6 in the brains of ASC-/- mice correlated with lower numbers of infiltrating macrophages during infection. Together, these data suggest that inflammasomes contribute to pathogenic inflammation in HSE and provide a mechanistic link between glial inflammasome activation and leukocyte infiltration. The contribution of inflammasomes to survival was independent of viral replication in our study, suggesting a promising new target in combating harmful inflammation in HSE.

Eastern equine encephalitis and use of IV immunoglobulin therapy and high-dose steroids

OBJECTIVE

To determine the clinical presentation and patient outcomes after treatment with IV immunoglobulin (IVIG), high-dose steroids, or standard of care alone in Eastern equine encephalitis (EEE), a mosquito-borne viral infection with significant neurologic morbidity and mortality.

METHODS

A retrospective observational study of patients admitted to 2 tertiary academic medical centers in Boston, Massachusetts, with EEE from 2005 to 2019.

RESULTS

Of 17 patients (median [IQR] age, 63 [36-70] years; 10 (59%) male, and 16 (94%) White race), 17 patients had fever (100%), 15 had encephalopathy (88%), and 12 had headache (71%). Eleven of 14 patients with CSF cell count differential had a neutrophil predominance (mean = 60.6% of white blood cells) with an elevated protein level (median [IQR], 100 mg/dL [75-145]). Affected neuroanatomic regions included the basal ganglia (n = 9/17), thalamus (n = 7/17), and mesial temporal lobe (n = 7/17). A total of 11 patients (65%) received IVIG; 8 (47%) received steroids. Of the patients who received IVIG, increased time from hospital admission to IVIG administration correlated with worse long-term disability as assessed by the modified Rankin Scale (mRS) (r = 0.72, p = 0.02); steroid use was not associated with the mRS score. The mortality was 12%.

CONCLUSIONS

Clinicians should suspect EEE in immunocompetent patients with early subcortical neuroimaging abnormalities and CSF neutrophilic predominance. This study suggests a lower mortality than previously reported, but a high morbidity rate in EEE. IVIG as an adjunctive to standard of care may be considered early during hospitalization.

Polar Infection of Echovirus-30 Causes Differential Barrier Affection and Gene Regulation at the Blood-Cerebrospinal Fluid Barrier

Echovirus-30 (E-30) is responsible for the extensive global outbreaks of meningitis in children. To gain access to the central nervous system, E-30 first has to cross the epithelial blood-cerebrospinal fluid barrier. Several meningitis causing bacteria preferentially infect human choroid plexus papilloma (HIBCPP) cells in a polar fashion from the basolateral cell side. Here, we investigated the polar infection of HIBCPP cells with E-30. Both apical and basolateral infections caused a significant decrease in the transepithelial electrical resistance of HIBCPP cells. However, to reach the same impact on the barrier properties, the multiplicity of infection of the apical side had to be higher than that of the basolateral infection. Furthermore, the number of infected cells at respective time-points after basolateral infection was significantly higher compared to apical infection. Cytotoxic effects of E-30 on HIBCPP cells during basolateral infection were observed following prolonged infection and appeared more drastically compared to the apical infection. Gene expression profiles determined by massive analysis of cDNA ends revealed distinct regulation of specific genes depending on the side of HIBCPP cells' infection. Altogether, our data highlights the polar effects of E-30 infection in a human in vitro model of the blood-cerebrospinal fluid barrier leading to central nervous system inflammation.

Herpes Simplex Virus Type 1 Interactions with the Interferon System

The interferon (IFN) system is one of the first lines of defense activated against invading viral pathogens. Upon secretion, IFNs activate a signaling cascade resulting in the production of several interferon stimulated genes (ISGs), which work to limit viral replication and establish an overall anti-viral state. Herpes simplex virus type 1 is a ubiquitous human pathogen that has evolved to downregulate the IFN response and establish lifelong latent infection in sensory neurons of the host. This review will focus on the mechanisms by which the host innate immune system detects invading HSV-1 virions, the subsequent IFN response generated to limit viral infection, and the evasion strategies developed by HSV-1 to evade the immune system and establish latency in the host.

Interferon-independent STING signaling promotes resistance to HSV-1 in vivo

The Stimulator of Interferon Genes (STING) pathway initiates potent immune responses upon recognition of DNA. To initiate signaling, serine 365 (S365) in the C-terminal tail (CTT) of STING is phosphorylated, leading to induction of type I interferons (IFNs). Additionally, evolutionary conserved responses such as autophagy also occur downstream of STING, but their relative importance during in vivo infections remains unclear. Here we report that mice harboring a serine 365-to-alanine (S365A) mutation in STING are unexpectedly resistant to Herpes Simplex Virus (HSV)-1, despite lacking STING-induced type I IFN responses. By contrast, resistance to HSV-1 is abolished in mice lacking the STING CTT, suggesting that the STING CTT initiates protective responses against HSV-1, independently of type I IFNs. Interestingly, we find that STING-induced autophagy is a CTT- and TBK1-dependent but IRF3-independent process that is conserved in the STING S365A mice. Thus, interferon-independent functions of STING mediate STING-dependent antiviral responses in vivo.

The Innate Immune Response to Herpes Simplex Virus 1 Infection Is Dampened in the Newborn Brain and Can Be Modulated by Exogenous Interferon Beta To Improve Survival

Herpes simplex virus (HSV) is a ubiquitous human pathogen affecting 50 to 80% of the population in North America and Europe. HSV infection is commonly asymptomatic in the adult population but can result in fatal encephalitis in the newborn. Current treatment with acyclovir has improved mortality in the newborn; however, severe neurologic sequelae are still a major concern following HSV encephalitis. For this reason, there is a critical need to better understand the underlying differences in the immune response between the two age groups that could be used to develop more effective treatments. In this study, we investigated differences in the innate immune response to viral infection in the brains of newborn and adult mice. We found that, similar to humans, newborn mice are more susceptible to HSV infection than the adult. Increased susceptibility was associated with dampened innate immune responses in the newborn brain that could be rescued by administering interferon beta.

Newborns are particularly susceptible to severe forms of herpes simplex virus 1 (HSV-1) infection, including encephalitis and multisystemic disseminated disease. The underlying age-dependent differences in the immune response that explain this increased susceptibility relative to the adult population remain largely understudied. Using a murine model of HSV-1 infection, we found that newborn mice are largely susceptible to intracranial and intraperitoneal challenge while adult mice are highly resistant. This age-dependent difference correlated with differential basal-level expression of components of innate immune signaling pathways, which resulted in dampened interferon (IFN) signaling in the newborn brain. To explore the possibility of modulating the IFN response in the newborn brain to recapitulate the adult phenotype, we administered exogenous IFN-β in the context of disseminated HSV-1 infection. IFN-β treatment resulted in significantly increased survival and delayed viral neuroinvasion in the newborn. These effects were associated with changes in the type I IFN response in the brain, reduced viral replication in the periphery, and the stabilization of the blood-brain barrier (BBB). Our study reveals important age-dependent differences in the innate immune response to HSV-1 infection and suggests a contribution of the BBB and the brain parenchyma in mediating the increased susceptibility to HSV-1 infection observed in the newborn. These results could provide the basis for potential new therapeutic strategies for life-threatening HSV-1 infection in newborns.

Zika virus infects pericytes in the choroid plexus and enters the central nervous system through the blood-cerebrospinal fluid barrier

Zika virus (ZIKV) can infect and cause microcephaly and Zika-associated neurological complications in the developing fetal and adult brains. In terms of pathogenesis, a critical question is how ZIKV overcomes the barriers separating the brain from the circulation and gains access to the central nervous system (CNS). Despite the importance of ZIKV pathogenesis, the route ZIKV utilizes to cross CNS barriers remains unclear. Here we show that in mouse models, ZIKV-infected cells initially appeared in the periventricular regions of the brain, including the choroid plexus and the meninges, prior to infection of the cortex. The appearance of ZIKV in cerebrospinal fluid (CSF) preceded infection of the brain parenchyma. Further the brain infection was significantly attenuated by neutralization of the virus in the CSF, indicating that ZIKV in the CSF at the early stage of infection might be responsible for establishing a lethal infection of the brain. We show that cells infected by ZIKV in the choroid plexus were pericytes. Using in vitro systems, we highlight the possibility that ZIKV crosses the blood-CSF barrier by disrupting the choroid plexus epithelial layer. Taken together, our results suggest that ZIKV might exploit the blood-CSF barrier rather than the blood-brain barrier to invade the CNS.

JC Virus infected choroid plexus epithelial cells produce extracellular vesicles that infect glial cells independently of the virus attachment receptor

The human polyomavirus, JCPyV, is the causative agent of progressive multifocal leukoencephalopathy (PML) in immunosuppressed and immunomodulated patients. Initial infection with JCPyV is common and the virus establishes a long-term persistent infection in the urogenital system of 50-70% of the human population worldwide. A major gap in the field is that we do not know how the virus traffics from the periphery to the brain to cause disease. Our recent discovery that human choroid plexus epithelial cells are fully susceptible to virus infection together with reports of JCPyV infection of choroid plexus in vivo has led us to hypothesize that the choroid plexus plays a fundamental role in this process. The choroid plexus is known to relay information between the blood and the brain by the release of extracellular vesicles. This is particularly important because human macroglia (oligodendrocytes and astrocytes), the major targets of virus infection in the central nervous system (CNS), do not express the known attachment receptors for the virus and do not bind virus in human tissue sections. In this report we show that JCPyV infected choroid plexus epithelial cells produce extracellular vesicles that contain JCPyV and readily transmit the infection to human glial cells. Transmission of the virus by extracellular vesicles is independent of the known virus attachment receptors and is not neutralized by antisera directed at the virus. We also show that extracellular vesicles containing virus are taken into target glial cells by both clathrin dependent endocytosis and macropinocytosis. Our data support the hypothesis that the choroid plexus plays a fundamental role in the dissemination of virus to brain parenchyma.

Interferon Control of Neurotropic Viral Infections

Interferons (IFNs) comprise a pleiotropic family of signaling molecules that are often the first line of defense against viral infection. Inflammatory responses induced by IFN are generally well tolerated during peripheral infections; yet, the same degree of inflammation during infection of the central nervous system (CNS) could be catastrophic. Thus, IFN responses must be modified within the CNS to ensure host survival. In this review, we discuss emerging principles highlighting unique aspects of antiviral effects of IFN protection following neurotropic viral infection, chiefly using new techniques in rodent models. Evaluation of these unique responses provides insights into how the immune system eradicates or controls pathogens, while avoiding host damage. Defining these principles may have direct impact on the development of novel clinical approaches.

Shared and Distinct Functions of Type I and Type III Interferons

Type I interferons (IFNs) (IFN-α, IFN-β) and type III IFNs (IFN-λ) share many properties, including induction by viral infection, activation of shared signaling pathways, and transcriptional programs. However, recent discoveries have revealed context-specific functional differences. Here, we provide a comprehensive review of type I and type III IFN activities, highlighting shared and distinct features from molecular mechanisms through physiological responses. Beyond discussing canonical antiviral functions, we consider the adaptive immune priming, anti-tumor, and autoimmune functions of IFNs. We discuss a model wherein type III IFNs serve as a front-line defense that controls infection at epithelial barriers while minimizing damaging inflammatory responses, reserving the more potent type I IFN response for when local responses are insufficient. In this context, we discuss current therapeutic applications targeting these cytokine pathways and highlight gaps in understanding of the biology of type I and type III IFNs in health and disease.

Complexities of Type I Interferon Biology: Lessons from LCMV

Over the past decades, infection of mice with lymphocytic choriomeningitis virus (LCMV) has provided an invaluable insight into our understanding of immune responses to viruses. In particular, this model has clarified the central roles that type I interferons play in initiating and regulating host responses. The use of different strains of LCMV and routes of infection has allowed us to understand how type I interferons are critical in controlling virus replication and fostering effective antiviral immunity, but also how they promote virus persistence and functional exhaustion of the immune response. Accordingly, these discoveries have formed the foundation for the development of novel treatments for acute and chronic viral infections and even extend into the management of malignant tumors. Here we review the fundamental insights into type I interferon biology gained using LCMV as a model and how the diversity of LCMV strains, dose, and route of administration have been used to dissect the molecular mechanisms underpinning acute versus persistent infection. We also identify gaps in the knowledge regarding LCMV regulation of antiviral immunity. Due to its unique properties, LCMV will continue to remain a vital part of the immunologists' toolbox.

Age-dependent susceptibility to reovirus encephalitis in mice is influenced by maturation of the type-I interferon response

BackgroundInfants and young children are particularly susceptible to viral encephalitis; however, the mechanisms are unknown. We determined the age-dependent contribution of innate and adaptive immune functions to reovirus-induced encephalitis in mice.MethodsNewborn wild-type mice, 2-20 days of age, were inoculated with reovirus or diluent and monitored for mortality, weight gain, and viral load. Four- and fifteen-day-old IFNAR-/- and RAG2-/- mice were inoculated with reovirus and similarly monitored.ResultsWeight gain was impaired in mice inoculated with reovirus at 8 days of age or less. Clinical signs of encephalitis were detected in mice inoculated at 10 days of age or less. Mortality decreased when mice were inoculated after 6 days of age. Survival was ≤15% in wild type (WT), RAG2-/-, and IFNAR-/- mice inoculated at 4 days of age. All WT mice, 92% of RAG2-/- mice, and only 48% of IFNAR-/- mice survived following inoculation at 15 days of age.ConclusionsSusceptibility of mice to reovirus-induced disease decreases between 6 and 8 days of age. Enhanced reovirus virulence in IFNAR-/- mice relative to WT and RAG2-/- mice inoculated at 15 days of age suggests that maturation of the type-I interferon response contributes to age-related mortality following reovirus infection.

Interferon Lambda Genetics and Biology in Regulation of Viral Control

Type III interferons, also known as interferon lambdas (IFNλs), are the most recent addition to the IFN family following their discovery in 2003. Initially, IFNλ was demonstrated to induce expression of interferon-stimulated genes and exert antiviral properties in a similar manner to type I IFNs. However, while IFNλ has been described to have largely overlapping expression and function with type I IFNs, it has become increasingly clear that type III IFNs also have distinct functions from type I IFNs. In contrast to type I IFNs, whose receptor is ubiquitously expressed, type III IFNs signal and function largely at barrier epithelial surfaces, such as the respiratory and gastrointestinal tracts, as well as the blood–brain barrier. In further support of unique functions for type III IFNs, single nucleotide polymorphisms in IFNL genes in humans are strongly associated with outcomes to viral infection. These biological linkages have also been more directly supported by studies in mice highlighting roles of IFNλ in promoting antiviral immune responses. In this review, we discuss the current understanding of type III IFNs, and how their functions are similar to, and different from, type I IFN in various immune cell subtypes and viral infections.

The diverse cellular responses of the choroid plexus during infection of the central nervous system

The choroid plexus (CP) is responsible for the production of a large amount of the cerebrospinal fluid (CSF). As a highly vascularized structure, the CP also presents a significant frontier between the blood and the central nervous system (CNS). To seal this border, the epithelium of the CP forms the blood-CSF barrier, one of the most important barriers separating the CNS from the blood. During the course of infectious disease, cells of the CP can experience interactions with intruding pathogens, especially when the CP is used as gateway for entry into the CNS. In return, the CP answers to these encounters with diverse measures. Here, we will review the distinct responses of the CP during infection of the CNS, which include engaging of signal transduction pathways, the regulation of gene expression in the host cells, inflammatory cell response, alterations of the barrier, and, under certain circumstances, cell death. Many of these actions may contribute to stage an immunological response against the pathogen and subsequently help in the clearance of the infection.

Spontaneous activation of a MAVS-dependent antiviral signaling pathway determines high basal interferon-β expression in cardiac myocytes

Viral myocarditis is a leading cause of sudden death in young adults as the limited turnover of cardiac myocytes renders the heart particularly vulnerable to viral damage. Viruses induce an antiviral type I interferon (IFN-α/β) response in essentially all cell types, providing an immediate innate protection. Cardiac myocytes express high basal levels of IFN-β to help pre-arm them against viral infections, however the mechanism underlying this expression remains unclear. Using primary cultures of murine cardiac and skeletal muscle cells, we demonstrate here that the mitochondrial antiviral signaling (MAVS) pathway is spontaneously activated in unstimulated cardiac myocytes but not cardiac fibroblasts or skeletal muscle cells. Results suggest that MAVS association with the mitochondrial-associated ER membranes (MAM) is a determinant of high basal IFN-β expression, and demonstrate that MAVS is essential for spontaneous high basal expression of IFN-β in cardiac myocytes and the heart. Together, results provide the first mechanism for spontaneous high expression of the antiviral cytokine IFN-β in a poorly replenished and essential cell type.

The Type I Interferon Response and Age-Dependent Susceptibility to Herpes Simplex Virus Infection

Herpes simplex virus type 1 (HSV-1) is a highly prevalent human neurotropic pathogen. HSV-1 infection is associated with a variety of diseases ranging from benign orolabial lesions to more serious and even life-threatening conditions such as herpes simplex keratitis and herpes simplex encephalitis (HSE). HSE is a rare occurrence among healthy adult individuals, but newborns are a particularly susceptible population. Type I IFN signaling has been identified as a crucial component of the innate immune response to the control of HSV-1 infection. In this study, we review the contribution of the type I IFN response to controlling HSV-1 infection, and differences in the early host response between adults and newborns that may contribute to the increased susceptibility to infection and central nervous system disease in newborns.

Treatment of perinatal viral infections to improve neurologic outcomes

Viral infections in the fetus or newborn often involve the central nervous system (CNS) and can lead to significant morbidity and mortality. Substantial progress has been made in identifying interventions decreasing adverse neurodevelopmental outcomes in this population. This review highlights progress in treatment of important viruses affecting the CNS in these susceptible hosts, focusing on herpes simplex virus (HSV), cytomegalovirus (CMV), human immunodeficiency virus (HIV), and enteroviruses. The observation that high-dose acyclovir improves mortality in neonatal HSV disease culminated decades of antiviral research for this disease. More recently, prolonged oral acyclovir was found to improve neurologic morbidity after neonatal HSV encephalitis. Ganciclovir, and more recently its oral prodrug valganciclovir, is effective in improving hearing and neurodevelopment after congenital CMV infection. Increasing evidence suggests early control of perinatal HIV infection has implications for neurocognitive functioning into school age. Lastly, the antiviral pleconaril has been studied for nearly two decades for treating severe enteroviral infections, with newer data supporting a role for this drug in neonates. Identifying common mechanisms for pathogenesis of viral CNS disease during this critical period of brain development is an important research goal, highlighted by the recent emergence of Zika virus as a potential cause of fetal neurodevelopmental abnormalities.

Type I Interferons in Newborns-Neurotoxicity versus Antiviral Defense

In most children and adults, primary infection with herpes simplex virus 1 (HSV-1) is asymptomatic. However, very rarely (incidence of 1 in 1,000,000), it can cause herpes simplex encephalitis (HSE). HSE also occurs in infants but with a much starker incidence of one in three. This age difference in susceptibility to HSV-1-caused HSE is not well understood. In a recent article in mBio, authors have identified the choroid plexus as the anatomical site of robust HSV-1 replication in the brain. They point to low levels of type I interferon (IFN) receptor as causal of the lack of HSV-1 replication control in neonates, in contrast to adults. Here, I discuss these findings in the context of human genetic evidence. I point to the balancing act of type I IFN acting as a neurotoxin and an antiviral agent, an evolutionary choice of a lesser evil.