Coronavirus infection of the central nervous system: host-virus stand-off

The international European Academy of Neurology survey on neurological symptoms in patients with COVID-19 infection

BACKGROUND AND PURPOSE

Although the main clinical features of COVID-19 infection are pulmonary, several associated neurological signs, symptoms and diseases are emerging. The incidence and characteristics of neurological complications are unclear. For this reason, the European Academy of Neurology (EAN) core COVID-19 Task Force initiated a survey on neurological symptoms observed in patients with COVID-19 infection.

METHODS

A 17-question online survey was made available on the EAN website and distributed to EAN members and other worldwide physicians starting on 9 April 2020.

RESULTS

By 27 April 2020, proper data were collected from 2343 responders (out of 4199), of whom 82.0% were neurologists, mostly from Europe. Most responders (74.7%) consulted patients with COVID-19 mainly in emergency rooms and in COVID-19 units. The majority (67.0%) had evaluated fewer than 10 patients with neurological manifestations of COVID-19 (neuro COVID-19). The most frequently reported neurological findings were headache (61.9%), myalgia (50.4%), anosmia (49.2%), ageusia (39.8%), impaired consciousness (29.3%) and psychomotor agitation (26.7%). Encephalopathy and acute cerebrovascular disorders were reported at 21.0%. Neurological manifestations were generally interpreted as being possibly related to COVID-19; they were most commonly recognized in patients with multiple general symptoms and occurred at any time during infection.

CONCLUSION

Neurologists are currently and actively involved in the management of neurological issues related to the COVID-19 pandemic. This survey justifies setting up a prospective registry to better capture the prevalence of patients with neuro COVID-19, neurological disease characteristics and the contribution of neurological manifestations to outcome.

Neurobiology of coronaviruses: Potential relevance for COVID-19

In the first two decades of the 21st century, there have been three outbreaks of severe respiratory infections caused by highly pathogenic coronaviruses (CoVs) around the world: the severe acute respiratory syndrome (SARS) by the SARS-CoV in 2002-2003, the Middle East respiratory syndrome (MERS) by the MERS-CoV in June 2012, and Coronavirus Disease 2019 (COVID-19) by the SARS-CoV-2 presently affecting most countries In all of these, fatalities are a consequence of a multiorgan dysregulation caused by pulmonary, renal, cardiac, and circulatory damage; however, COVID patients may show significant neurological signs and symptoms such as headache, nausea, vomiting, and sensory disturbances, the most prominent being anosmia and ageusia. The neuroinvasive potential of CoVs might be responsible for at least part of these symptoms and may contribute to the respiratory failure observed in affected patients. Therefore, in the present manuscript, we have reviewed the available preclinical evidence on the mechanisms and consequences of CoVs-induced CNS damage, and highlighted the potential role of CoVs in determining or aggravating acute and long-term neurological diseases in infected individuals. We consider that a widespread awareness of the significant neurotropism of CoVs might contribute to an earlier recognition of the signs and symptoms of viral-induced CNS damage. Moreover, a better understanding of the cellular and molecular mechanisms by which CoVs affect CNS function and cause CNS damage could help in planning new strategies for prognostic evaluation and targeted therapeutic intervention.

Possible routes of SARS-CoV-2 invasion in brain: In context of neurological symptoms in COVID-19 patients

Manifestation of neurological symptoms in certain patients of coronavirus disease-2019 (COVID-19) has warranted for their virus-induced etiogenesis. SARS-CoV-2, the causative agent of COVID-19, belongs to the genus of betacoronaviruses which also includes SARS-CoV-1 and MERS-CoV; causative agents for severe acute respiratory syndrome (SARS) in 2002 and Middle East respiratory syndrome (MERS) in 2012, respectively. Studies demonstrating the neural invasion of SARS-CoV-2 in vivo are still scarce, although such characteristics of certain other betacoronaviruses are well demonstrated in the literature. Based on the recent evidence for the presence of SARS-CoV-2 host cell entry receptors in specific components of the human nervous and vascular tissue, a neural (olfactory and/or vagal), and a hematogenous-crossing the blood-brain barrier, routes have been proposed. The neurological symptoms in COVID-19 may also arise as a consequence of the "cytokine storm" (characteristically present in severe disease) induced neuroinflammation, or co-morbidities. There is also a possibility that, there may be multiple routes of SARS-CoV-2 entry into the brain, or multiple mechanisms can be involved in the pathogenesis of the neurological symptoms. In this review article, we have discussed the possible routes of SARS-CoV-2 brain entry based on the emerging evidence for this virus, and that available for other betacoronaviruses in literature.

Lessons for COVID-19 Immunity from Other Coronavirus Infections

A key goal to controlling coronavirus disease 2019 (COVID-19) is developing an effective vaccine. Development of a vaccine requires knowledge of what constitutes a protective immune response and also features that might be pathogenic. Protective and pathogenic aspects of the response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are not well understood, partly because the virus has infected humans for only 6 months. However, insight into coronavirus immunity can be informed by previous studies of immune responses to non-human coronaviruses, common cold coronaviruses, and SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV). Here, we review the literature describing these responses and discuss their relevance to the SARS-CoV-2 immune response.

Lessons for COVID-19 Immunity from Other Coronavirus Infections

A key goal to controlling coronavirus disease 2019 (COVID-19) is developing an effective vaccine. Development of a vaccine requires knowledge of what constitutes a protective immune response and also features that might be pathogenic. Protective and pathogenic aspects of the response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are not well understood, partly because the virus has infected humans for only 6 months. However, insight into coronavirus immunity can be informed by previous studies of immune responses to non-human coronaviruses, common cold coronaviruses, and SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV). Here, we review the literature describing these responses and discuss their relevance to the SARS-CoV-2 immune response.

Neurological Manifestations of Severe SARS-CoV-2 Infection: Potential Mechanisms and Implications of Individualized Mechanical Ventilation Settings

In December 2019, an outbreak of illness caused by a novel coronavirus (2019-nCoV, subsequently renamed SARS-CoV-2) was reported in Wuhan, China. Coronavirus disease 2019 (COVID-19) quickly spread worldwide to become a pandemic. Typical manifestations of COVID-19 include fever, dry cough, fatigue, and respiratory distress. In addition, both the central and peripheral nervous system can be affected by SARS-CoV-2 infection. These neurological changes may be caused by viral neurotropism, by a hyperinflammatory and hypercoagulative state, or even by mechanical ventilation-associated impairment. Hypoxia, endothelial cell damage, and the different impacts of different ventilatory strategies may all lead to increased stress and strain, potentially exacerbating the inflammatory response and leading to a complex interaction between the lungs and the brain. To date, no studies have taken into consideration the possible secondary effect of mechanical ventilation on brain recovery and outcomes. The aim of our review is to provide an updated overview of the potential pathogenic mechanisms of neurological manifestations in COVID-19, discuss the physiological issues related to brain-lung interactions, and propose strategies for optimization of respiratory support in critically ill patients with SARS-CoV-2 pneumonia.

mRNA induced expression of human angiotensin-converting enzyme 2 in mice for the study of the adaptive immune response to severe acute respiratory syndrome coronavirus 2

The novel human coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a pandemic resulting in nearly 20 million infections across the globe, as of August 2020. Critical to the rapid evaluation of vaccines and antivirals is the development of tractable animal models of infection. The use of common laboratory strains of mice to this end is hindered by significant divergence of the angiotensin-converting enzyme 2 (ACE2), which is the receptor required for entry of SARS-CoV-2. In the current study, we designed and utilized an mRNA-based transfection system to induce expression of the hACE2 receptor in order to confer entry of SARS-CoV-2 in otherwise non-permissive cells. By employing this expression system in an in vivo setting, we were able to interrogate the adaptive immune response to SARS-CoV-2 in type 1 interferon receptor deficient mice. In doing so, we showed that the T cell response to SARS-CoV-2 is enhanced when hACE2 is expressed during infection. Moreover, we demonstrated that these responses are preserved in memory and are boosted upon secondary infection. Interestingly, we did not observe an enhancement of SARS-CoV-2 specific antibody responses with hACE2 induction. Importantly, using this system, we functionally identified the CD4+ and CD8+ peptide epitopes targeted during SARS-CoV-2 infection in H2b restricted mice. Antigen-specific CD8+ T cells in mice of this MHC haplotype primarily target peptides of the spike and membrane proteins, while the antigen-specific CD4+ T cells target peptides of the nucleocapsid, membrane, and spike proteins. The functional identification of these T cell epitopes will be critical for evaluation of vaccine efficacy in murine models of SARS-CoV-2. The use of this tractable expression system has the potential to be used in other instances of emerging infections in which the rapid development of an animal model is hindered by a lack of host susceptibility factors.

The neurological insights of the emerging coronaviruses

Emerging Viral diseases are incredibly infectious and proficient in inducing pandemics. Unlike the previous emerging coronaviruses (ECoVs) which neurological complexities were uncommon, with neurological features exhibition at 14-25 days post-onset, yet with critical outcomes exhibiting >50% mortality in central nervous (CNS) presenting pathologies. The COVID 19 neurological consequences occur more frequently even in mild cases, presenting with CNS involvement in up to 25%, musculoskeletal and peripheral manifestation (PNM). Through preceding ECoVs case reports, the PNM not linked to fatal outcomes, however, required, repeated neuro-imaging as notable CT and MRI changes appeared as late as 21 days while the likelihood of Cerebrospinal fluid to test positive for ECoV was 25%, only in the CNS presenting cases. Owing to 44-60% myalgia presentation, risk of the high inflammatory state, and coagulation cascade abnormalities reported in ECoVs, testing for C-reactive protein, serum creatine kinase, and D-dimer level is mandatory. Presently, there is no antiviral medication or vaccination for the ECoVs, early induction of antiviral drugs remains the backbone of management. Neurologically, the therapeutic dosages of anticoagulants are linked to the high incidence of thrombotic complexities, while methylprednisolone is associated with myopathy. Future studies expected to apply more neuro-imaging techniques for CNS exploration and further explore the pathogenesis of the COVID 19 myalgia, anosmia/ageusia reported in the majority of the initial cases.

Coronaviruses and the central nervous system

Seven coronavirus (CoV) species are known human pathogens: the epidemic viruses SARS-CoV, SARS-CoV-2, and MERS-CoV and those continuously circulating in human populations since initial isolation: HCoV-OC43, HCoV-229E, HCoV-HKU1, and HCoV-NL63. All have associations with human central nervous system (CNS) dysfunction. In infants and young children, the most common CNS phenomena are febrile seizures; in adults, non-focal abnormalities that may be either neurologic or constitutional. Neurotropism and neurovirulence are dependent in part on CNS expression of cell surface receptors mediating viral entry, and host immune response. In adults, CNS receptors for epidemic viruses are largely expressed on brain vasculature, whereas receptors for less pathogenic viruses are present in vasculature, brain parenchyma, and olfactory neuroepithelium, dependent upon viral species. Human coronaviruses can infect circulating mononuclear cells, but meningoencephalitis is rare. Well-documented human neuropathologies are infrequent and, for SARS, MERS, and COVID-19, can entail cerebrovascular accidents originating extrinsically to brain. There is evidence of neuronal infection in the absence of inflammatory infiltrates with SARS-CoV, and CSF studies of rare patients with seizures have demonstrated virus but no pleocytosis. In contrast to human disease, animal models of neuropathogenesis are well developed, and pathologies including demyelination, neuronal necrosis, and meningoencephalitis are seen with both native CoVs as well as human CoVs inoculated into nasal cavities or brain. This review covers basic CoV biology pertinent to CNS disease; the spectrum of clinical abnormalities encountered in infants, children, and adults; and the evidence for CoV infection of human brain, with reference to pertinent animal models of neuropathogenesis.

Neuropathogenic human coronaviruses: A review

Human Coronaviruses (HCoVs) have long been known as respiratory viruses. However, there are reports of neurological findings in HCoV infections, particularly in patients infected with the novel severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) amid Coronavirus disease 2019 (COVID‐19) pandemic. Therefore, it is essential to interpret the interaction of HCoVs and the nervous system and apply this understanding to the COVID‐19 pandemic. This review of the literature analyses how HCoVs, in general, and SARS‐CoV‐2, in particular, affect the nervous system, highlights the various underlying mechanisms, addresses the associated neurological and psychiatric manifestations, and identifies the neurological risk factors involved. This review of literature shows the magnitude of neurological conditions associated with HCoV infections, including SARS‐CoV‐2. This review emphasises, that, during HCoV outbreaks, such as COVID‐19, a focus on early detection of neurotropism, alertness for the resulting neurological complications, and the recognition of neurological risk factors are crucial to reduce the workload on hospitals, particularly intensive‐care units and neurological departments.

COVID-19 Pulmonary and Olfactory Dysfunctions: Is the Chemokine CXCL10 the Common Denominator?

COVID-19 is an ongoing viral pandemic that emerged from East Asia and quickly spread to the rest of the world. SARS-CoV-2 is the virus causing COVID-19. Acute respiratory distress syndrome (ARDS) is definitely one of the main clinically relevant consequences in patients with COVID-19. Starting from the earliest reports of the COVID-19 pandemic, two peculiar neurological manifestations (namely, hyposmia/anosmia and dysgeusia) were reported in a relevant proportion of patients infected by SARS-CoV-2. At present, the physiopathologic mechanisms accounting for the onset of these symptoms are not yet clarified. CXCL10 is a pro-inflammatory chemokine with a well-established role in the COVID-19-related cytokine storm and in subsequent development of ARDS. CXCL10 is also known to be involved in coronavirus-induced demyelination. On these bases, a role for CXCL10 as the common denominator between pulmonary and olfactory dysfunctions could be envisaged. The aim of the present report will be to hypothesize a role for CXCL10 in COVID-19 olfactory dysfunctions. Previous evidences supporting our hypothesis, with special emphasis to the role of CXCL10 in coronavirus-induced demyelination, the anatomical and physiological peculiarity of the olfactory system, and the available data supporting their link during COVID-19 infections, will be overviewed.

Identification of COVID-19 Infection-Related Human Genes Based on a Random Walk Model in a Virus-Human Protein Interaction Network

Coronaviruses are specific crown-shaped viruses that were first identified in the 1960s, and three typical examples of the most recent coronavirus disease outbreaks include severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and COVID-19. Particularly, COVID-19 is currently causing a worldwide pandemic, threatening the health of human beings globally. The identification of viral pathogenic mechanisms is important for further developing effective drugs and targeted clinical treatment methods. The delayed revelation of viral infectious mechanisms is currently one of the technical obstacles in the prevention and treatment of infectious diseases. In this study, we proposed a random walk model to identify the potential pathological mechanisms of COVID-19 on a virus–human protein interaction network, and we effectively identified a group of proteins that have already been determined to be potentially important for COVID-19 infection and for similar SARS infections, which help further developing drugs and targeted therapeutic methods against COVID-19. Moreover, we constructed a standard computational workflow for predicting the pathological biomarkers and related pharmacological targets of infectious diseases.

Oligodendrocytes that survive acute coronavirus infection induce prolonged inflammatory responses in the CNS

Neurotropic strains of mouse hepatitis virus (MHV), a coronavirus, cause acute and chronic demyelinating encephalomyelitis with similarities to the human disease multiple sclerosis. Here, using a lineage-tracking system, we show that some cells, primarily oligodendrocytes (OLs) and oligodendrocyte precursor cells (OPCs), survive the acute MHV infection, are associated with regions of demyelination, and persist in the central nervous system (CNS) for at least 150 d. These surviving OLs express major histocompatibility complex (MHC) class I and other genes associated with an inflammatory response. Notably, the extent of inflammatory cell infiltration was variable, dependent on anatomic location within the CNS, and without obvious correlation with numbers of surviving cells. We detected more demyelination in regions with larger numbers of T cells and microglia/macrophages compared to those with fewer infiltrating cells. Conversely, in regions with less inflammation, these previously infected OLs more rapidly extended processes, consistent with normal myelinating function. Together, these results show that OLs are inducers as well as targets of the host immune response and demonstrate how a CNS infection, even after resolution, can induce prolonged inflammatory changes with CNS region-dependent impairment in remyelination.

A candidate multi-epitope vaccine against SARS-CoV-2

In the past two decades, 7 coronaviruses have infected the human population, with two major outbreaks caused by SARS-CoV and MERS-CoV in the year 2002 and 2012, respectively. Currently, the entire world is facing a pandemic of another coronavirus, SARS-CoV-2, with a high fatality rate. The spike glycoprotein of SARS-CoV-2 mediates entry of virus into the host cell and is one of the most important antigenic determinants, making it a potential candidate for a vaccine. In this study, we have computationally designed a multi-epitope vaccine using spike glycoprotein of SARS-CoV-2. The overall quality of the candidate vaccine was validated in silico and Molecular Dynamics Simulation confirmed the stability of the designed vaccine. Docking studies revealed stable interactions of the vaccine with Toll-Like Receptors and MHC Receptors. The in silico cloning and codon optimization supported the proficient expression of the designed vaccine in E. coli expression system. The efficiency of the candidate vaccine to trigger an effective immune response was assessed by an in silico immune simulation. The computational analyses suggest that the designed multi-epitope vaccine is structurally stable which can induce specific immune responses and thus, can be a potential vaccine candidate against SARS-CoV-2.

Regulatory T cells promote remyelination in the murine experimental autoimmune encephalomyelitis model of multiple sclerosis following human neural stem cell transplant

Multiple sclerosis (MS) is a chronic, inflammatory autoimmune disease that affects the central nervous system (CNS) for which there is no cure. In MS, encephalitogenic T cells infiltrate the CNS causing demyelination and neuroinflammation; however, little is known about the role of regulatory T cells (Tregs) in CNS tissue repair. Transplantation of neural stem and progenitor cells (NSCs and NPCs) is a promising therapeutic strategy to promote repair through cell replacement, although recent findings suggest transplanted NSCs also instruct endogenous repair mechanisms. We have recently described that dampened neuroinflammation and increased remyelination is correlated with emergence of Tregs following human NPC transplantation in a murine viral model of immune-mediated demyelination. In the current study we utilized the prototypic murine autoimmune model of demyelination experimental autoimmune encephalomyelitis (EAE) to test the efficacy of hNSC transplantation. Eight-week-old, male EAE mice receiving an intraspinal transplant of hNSCs during the chronic phase of disease displayed remyelination, dampened neuroinflammation, and an increase in CNS CD4⁺CD25⁺FoxP3⁺ regulatory T cells (Tregs). Importantly, ablation of Tregs abrogated histopathological improvement. Tregs are essential for maintenance of T cell homeostasis and prevention of autoimmunity, and an emerging role for Tregs in maintenance of tissue homeostasis through interactions with stem and progenitor cells has recently been suggested. The data presented here provide direct evidence for collaboration between CNS Tregs and hNSCs promoting remyelination.

Persistent SARS-CoV-2 infection and the risk for cancer

The current SARS-CoV-2 has put significant strain on healthcare services worldwide due to acute COVID-19. However, the potential long-term effects of this infection haven’t been extensively discussed.

We hypothesize that SARS-CoV-2 may be able to cause persistent infection in some individuals, and should this be the case, that in a few years we may see a rise in cancer incidence due to carcinogenic effects of this coronavirus.

Non-retroviral RNA viruses such as Coronaviridae have been shown to cause persistent infection in hosts. Empirical evidence of viral genomic material shedding weeks after apparent clinical and laboratorial resolution of COVID-19 may be an indirect proof for persistent viral infection. Furthermore, tropism towards certain immune-privileged territories may facilitate immune evasion by this virus.

Structural homology with SARS-CoV-1 indicates that SARS-CoV-2 may be able to directly impair pRb and p53, which are key gatekeepers with tumor suppressor functions. Additionally, COVID-19 features preeminent inflammatory response with marked oxidative stress, which acts as both as initiator and promotor of carcinogenesis.

Should there be a carcinogenic risk associated with SARS-CoV-2, the implications for public health are plenty, as infected patients should be closely watched during long periods of follow-up.

Additional investigation to establish or exclude the possibility for persistent infection is paramount to identify and prevent possible complications in the future.

SARS-CoV-2 Infection Leads to Neurological Dysfunction

A number of neurological disease complications have been seen following infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While most person with COVID-19 respiratory disease demonstrate headache, nausea and vomiting, up to 40% present also experience dizziness, confusion, cerebrovascular disease, muscle pain, ataxia and seizures. Loss of taste and smell, defects in visual acuity and pain occur in parallel. Such central nervous system (CNS) signs and symptoms linked to laboratory-confirmed SARS-CoV-2 infection is often life threatening. Health care providers currently evaluating patients with neurologic symptoms need consider COVID-19 in any differential diagnosis. These considerations will facilitate prompt testing, isolation and prevention of viral transmission speeding best clinical outcomes.

Does SARS-Cov-2 invade the brain? Translational lessons from animal models

The current coronavirus disease (COVID‐19) outbreak, caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), has raised the possibility of potential neurotropic properties of this virus. Indeed, neurological sequelae of SARS‐CoV‐2 infection have already been reported and highlight the relevance of considering the neurological impact of coronavirus (CoV) from a translational perspective. Animal models of SARS and Middle East respiratory syndrome, caused by structurally similar CoVs during the 2002 and 2012 epidemics, have provided valuable data on nervous system involvement by CoVs and the potential for central nervous system spread of SARS‐CoV‐2. One key finding that may unify these pathogens is that all require angiotensin‐converting enzyme 2 as a cell entry receptor. The CoV spike glycoprotein, by which SARS‐CoV‐2 binds to cell membranes, binds angiotensin‐converting enzyme 2 with a higher affinity compared with SARS‐CoV. The expression of this receptor in neurons and endothelial cells hints that SARS‐CoV‐2 may have higher neuroinvasive potential compared with previous CoVs. However, it remains to be determined how such invasiveness might contribute to respiratory failure or cause direct neurological damage. Both direct and indirect mechanisms may be of relevance. Clinical heterogeneity potentially driven by differential host immune‐mediated responses will require extensive investigation. Development of disease models to anticipate emerging neurological complications and to explore mechanisms of direct or immune‐mediated pathogenicity in the short and medium term is therefore of great importance. In this brief review, we describe the current knowledge from models of previous CoV infections and discuss their potential relevance to COVID‐19.

Neurosurgery and Neurology Practices during the Novel COVID-19 Pandemic: A Consensus Statement from India

Background

The COVID-19 infection outbreak has aroused increasing attention and affected thousands of people nationwide. The long incubation period, high infectious rate, varied manifestation, and absence of effective treatment make it difficult to manage the disease transmission.

Objective

The intended goals are to encourage efficient management of neurological and neurosurgical patients, resource utilization, and protecting the healthcare provider during the COVID-19 epidemic. Herein, we present a consensus statement from various centers in India.

Methodology

In addition to the literature review, recommendations were included from neurologists and neurosurgeons from various centers in India.

Results

Every patient presenting for treatment should be treated as a potential asymptomatic infected case. Patients should be categorized based upon the priority as acute (require immediate treatment/surgery within 24 h), sub-acute (requiring treatment within a maximum of 7-10 days), or chronic (requiring treatment within a month). Non-essential elective surgeries and outpatient clinics should be avoided after informing the patient(s). There is a high risk of aerosol dispersion during intubation and certain neurosurgical procedures particularly those involving drills and endoscopes. These procedures should be performed wearing full personal protective equipment. The workflow of the operating rooms should also be modified significantly. Minor modifications in personal and professional lifestyles and routine training to use the PPE will ensure efficient management of resources.

Conclusion

These recommendations could be used to mitigate the risks and reduce exposure to other patients, public, and healthcare staff.

COVID-19 and Stroke: Incidental, Triggered or Causative

Stroke is a serious neurological comorbidity observed during the ongoing COVID-19 (coronavirus associated disease 2019) pandemic caused by SARS-CoV-2 (severe acute respiratory syndrome, corona virus 2) and includes ischemic stroke, intracerebral haemorrhage and cerebral venous thrombosis. We reviewed factors that could potentially contribute to the occurrence of stroke among patients with COVID-19. There could be an interaction between the conventional risk factors of stroke, infection, systemic inflammatory response and plaque destabilisation. Inflammatory markers, D-dimer elevation and increased cytokine activity have been observed in patients with COVID-19. Other probable contributing factors include cardiac injury leading to embolism, a prothrombotic state and a possibility of direct neuroinvasive potential causing vasculopathy. Data from stroke patients gathered in large multicentric cohorts could help shed more light on the occurrence, behaviour, aetiology, pathophysiology, biomarkers and outcomes of stroke occurring during the ongoing pandemic.

Immune-epidemiological parameters of the novel coronavirus - a perspective

INTRODUCTION

At the end of 2019, Wuhan, a city in China with a population of about 11 million, witnessed the outbreak of unusual pneumonia. As of 29 March 2020, the disease has spread to more 199 countries and territories worldwide. The 2019 novel coronavirus, 2019-nCoV, is known as the probable causative agent of the illness.

AREAS COVERED

Here, the epidemiological dynamics of the coronavirus disease 2019 (COVID-19) that stand in close relation to distinct immunogenetic characters of the pathogen are discussed, to understand the ability and inability of the immune system in combatting COVID-19.

EXPERT OPINION

The elderly population is at increased risk of developing and dying from COVID-19. Comorbidity is present in more than 30% of cases with COVID-19. Except for less than 1% of the total, a chronic condition has been found in all cases that died from COVID-19. Men are more than 1.5 times more likely to die from COVID-19. Evidence links aging to cytokine dysregulation and T-cell repertoire reduction, male population to relatively reduced anti-viral immunity, and COVID-19-related comorbidities to hyper inflammation. The transmission of COVID-19 is influenced by the host-related factors that are known to be associated with immune dysregulation.

Perspectives for the use of therapeutic Botulinum toxin as a multifaceted candidate drug to attenuate COVID-19

The recent outbreak of coronavirus disease (COVID-19) resulting from a distinctive severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) continues to evolve in many countries and pose life-threatening clinical issues to global public health. While the lungs are the primary target for the SARS-CoV-2-mediated pathological consequence, the virus appears to invade the brain and cause unpredicted neurological deficits. In the later stage, COVID-19 can progress to pneumonia, acute respiratory failure, neurodegeneration and multi-organ dysfunctions leading to death. Though a significant portion of individuals with COVID-19 has been recovering from clinical symptoms, the pathological impact of the SARS-CoV-2 infection on the structural and functional properties of the lungs, heart, brain and other organs at the post-recovery state remains unknown. Presently, there is an urgent need for a remedial measure to combat this devastating COVID-19. Botulinum toxins (BoNTs) are potent neurotoxins that can induce paralysis of muscle and acute respiratory arrest in humans. However, a mild dose of the purified form of BoNT has been known to attenuate chronic cough, dyspnoea, pneumonia, acute respiratory failure, abnormal circulation, cardiac defects and various neurological deficits that have been recognised as the prominent clinical symptoms of COVID-19. Considering the fact, this review article provides 1) an overview of the SARS-CoV-2 mediated pathological impact on the lungs, heart and brain, 2) signifies the therapeutic uses of BoNTs against pulmonary failure, cardiac arrest and neurological deficits, and 3) emphasize the rationality for the possible use of BoNT to prevent SARS-CoV-2 infection and manage COVID-19.

COVID-19: ICU delirium management during SARS-CoV-2 pandemic

The novel coronavirus, SARS-CoV-2-causing Coronavirus Disease 19 (COVID-19), emerged as a public health threat in December 2019 and was declared a pandemic by the World Health Organization in March 2020. Delirium, a dangerous untoward prognostic development, serves as a barometer of systemic injury in critical illness. The early reports of 25% encephalopathy from China are likely a gross underestimation, which we know occurs whenever delirium is not monitored with a valid tool. Indeed, patients with COVID-19 are at accelerated risk for delirium due to at least seven factors including (1) direct central nervous system (CNS) invasion, (2) induction of CNS inflammatory mediators, (3) secondary effect of other organ system failure, (4) effect of sedative strategies, (5) prolonged mechanical ventilation time, (6) immobilization, and (7) other needed but unfortunate environmental factors including social isolation and quarantine without family. Given early insights into the pathobiology of the virus, as well as the emerging interventions utilized to treat the critically ill patients, delirium prevention and management will prove exceedingly challenging, especially in the intensive care unit (ICU). The main focus during the COVID-19 pandemic lies within organizational issues, i.e., lack of ventilators, shortage of personal protection equipment, resource allocation, prioritization of limited mechanical ventilation options, and end-of-life care. However, the standard of care for ICU patients, including delirium management, must remain the highest quality possible with an eye towards long-term survival and minimization of issues related to post-intensive care syndrome (PICS). This article discusses how ICU professionals (e.g., physicians, nurses, physiotherapists, pharmacologists) can use our knowledge and resources to limit the burden of delirium on patients by reducing modifiable risk factors despite the imposed heavy workload and difficult clinical challenges posed by the pandemic.

Regulatory T cells promote remyelination in the murine experimental autoimmune encephalomyelitis model of multiple sclerosis following human neural stem cell transplant

Multiple sclerosis (MS) is a chronic, inflammatory autoimmune disease that affects the central nervous system (CNS) for which there is no cure. In MS, encephalitogenic T cells infiltrate the CNS causing demyelination and neuroinflammation; however, little is known about the role of regulatory T cells (Tregs) in CNS tissue repair. Transplantation of neural stem and progenitor cells (NSCs and NPCs) is a promising therapeutic strategy to promote repair through cell replacement, although recent findings suggest transplanted NSCs also instruct endogenous repair mechanisms. We have recently described that dampened neuroinflammation and increased remyelination is correlated with emergence of Tregs following human NPC transplantation in a murine viral model of immune-mediated demyelination. In the current study we utilized the prototypic murine autoimmune model of demyelination experimental autoimmune encephalomyelitis (EAE) to test the efficacy of hNSC transplantation. Eight-week-old, male EAE mice receiving an intraspinal transplant of hNSCs during the chronic phase of disease displayed remyelination, dampened neuroinflammation, and an increase in CNS CD4⁺CD25⁺FoxP3⁺ regulatory T cells (Tregs). Importantly, ablation of Tregs abrogated histopathological improvement. Tregs are essential for maintenance of T cell homeostasis and prevention of autoimmunity, and an emerging role for Tregs in maintenance of tissue homeostasis through interactions with stem and progenitor cells has recently been suggested. The data presented here provide direct evidence for collaboration between CNS Tregs and hNSCs promoting remyelination.

Murine Coronavirus Infection Activates the Aryl Hydrocarbon Receptor in an Indoleamine 2,3-Dioxygenase-Independent Manner, Contributing to Cytokine Modulation and Proviral TCDD-Inducible-PARP Expression

The aryl hydrocarbon receptor (AhR) is a cytoplasmic receptor/transcription factor that modulates several cellular and immunological processes following activation by pathogen-associated stimuli, though its role during virus infection is largely unknown. Here, we show that AhR is activated in cells infected with mouse hepatitis virus (MHV), a coronavirus (CoV), and contributes to the upregulation of downstream effector TCDD-inducible poly(ADP-ribose) polymerase (TiPARP) during infection. Knockdown of TiPARP reduced viral replication and increased interferon expression, suggesting that TiPARP functions in a proviral manner during MHV infection. We also show that MHV replication induced the expression of other genes known to be downstream of AhR in macrophages and dendritic cells and in livers of infected mice. Further, we found that chemically inhibiting or activating AhR reciprocally modulated the expression levels of cytokines induced by infection, specifically, interleukin 1β (IL-1β), IL-10, and tumor necrosis factor alpha (TNF-α), consistent with a role for AhR activation in the host response to MHV infection. Furthermore, while indoleamine 2,3-dioxygenase (IDO1) drives AhR activation in other settings, MHV infection induced equal expression of downstream genes in wild-type (WT) and IDO1-/- macrophages, suggesting an alternative pathway of AhR activation. In summary, we show that coronaviruses elicit AhR activation by an IDO1-independent pathway, contributing to upregulation of downstream effectors, including the proviral factor TiPARP, and to modulation of cytokine gene expression, and we identify a previously unappreciated role for AhR signaling in CoV pathogenesis.IMPORTANCE Coronaviruses are a family of positive-sense RNA viruses with human and agricultural significance. Characterizing the mechanisms by which coronavirus infection dictates pathogenesis or counters the host immune response would provide targets for the development of therapeutics. Here, we show that the aryl hydrocarbon receptor (AhR) is activated in cells infected with a prototypic coronavirus, mouse hepatitis virus (MHV), resulting in the expression of several effector genes. AhR is important for modulation of the host immune response to MHV and plays a role in the expression of TiPARP, which we show is required for maximal viral replication. Taken together, our findings highlight a previously unidentified role for AhR in regulating coronavirus replication and the immune response to the virus.

Parkinsonism as a Third Wave of the COVID-19 Pandemic?

Since the initial reports of COVID-19 in December 2019, the world has been gripped by the disastrous acute respiratory disease caused by the SARS-CoV-2 virus. There are an ever-increasing number of reports of neurological symptoms in patients, from severe (encephalitis), to mild (hyposmia), suggesting the potential for neurotropism of SARS-CoV-2. This Perspective investigates the hypothesis that the reliance on self-reporting of hyposmia has resulted in an underestimation of neurological symptoms in COVID-19 patients. While the acute effect of the virus on the nervous system function is vastly overshadowed by the respiratory effects, we propose that it will be important to monitor convalescent individuals for potential long-term implications that may include neurodegenerative sequelae such as viral-associated parkinsonism. As it is possible to identify premorbid harbingers of Parkinson's disease, we propose long-term screening of SARS-CoV-2 cases post-recovery for these expressions of neurodegenerative disease. An accurate understanding of the incidence of neurological complications in COVID-19 requires long-term monitoring for sequelae after remission and a strategized health policy to ensure healthcare systems all over the world are prepared for a third wave of the virus in the form of parkinsonism.

COVID-19: What do we need to know about ICU delirium during the SARS-CoV-2 pandemic?

In March 2020, the World Health Organisation announced the COVID-19 pandemic caused by the SARS-CoV-2 virus. As well as respiratory failure, the SARS-CoV-2 may cause central nervous system (CNS) involvement, including delirium occurring in critically ill patients (ICU delirium). Due attention must be paid to this subject in the face of the COVID-19 pandemic. Delirium, the detection of which takes less than two minutes, is frequently underestimated during daily routine ICU care, but it may be a prodromal symptom of infection or hypoxia associated with severe respiratory failure. During the COVID-19 pandemic, systematic delirium monitoring using validated tests (CAM-ICU or ICDSC) may be sacrificed. This is likely to be due to the fact that the main emphasis is placed on organisational issues, i.e. the lack of ventilators, setting priorities for limited mechanical ventilation options, and a shortage of personal protective equipment. Early identification of patients with delirium is critical in patients with COVID-19 because the occurrence of delirium may be an early symptom of worsening respiratory failure or of infectious spread to the CNS mediated by potential neuroinvasive mechanisms of the coronavirus. The purpose of this review is to identify problems related to the development of delirium during the COVID-19 epidemic, which are presented in three areas: i) factors contributing to delirium in COVID-19, ii) potential pathophysiological factors of delirium in COVID-19, and iii) long-term consequences of delirium in COVID-19. This article discusses how healthcare workers can reduce the burden of delirium by identifying potential risk factors and difficulties during challenges associated with SARS-CoV-2 infection.

Inflammation During Virus Infection: Swings and Roundabouts

Inflammation constitutes a concerted series of cellular and molecular responses that follow disturbance of systemic homeostasis, by either toxins or infectious organisms. Leukocytes modulate inflammation through production of secretory mediators, like cytokines and chemokines, which work in an autocrine and/or paracrine manner. These mediators can either promote or attenuate the inflammatory response and depending on differential temporal and spatial expression play a crucial role in the outcome of infection. Even though the objective is clearance of the pathogen with minimum damage to host, the pathogenesis of multiple human pathogenic viruses has been suggested to emanate from a dysregulation of the inflammatory response, sometimes with fatal consequences. This review discusses the nature and the outcome of inflammatory response, which is triggered in the human host subsequent to infection by single-sense plus-strand RNA viruses. In view of such harmful effects of a dysregulated inflammatory response, an exogenous regulation of these reactions by either interference or supplementation of critical regulators has been suggested. Currently multiple such factors are being tested for their beneficial and adverse effects. A successful use of such an approach in diseases of viral etiology can potentially protect the affected individual without directly affecting the virus life cycle. Further, such approaches whenever applicable would be useful in mitigating death and/or debility that is caused by the infection of those viruses which have proven particularly difficult to control by either prophylactic vaccines and/or therapeutic strategies using specific antiviral drugs.

The S2 Subunit of QX-type Infectious Bronchitis Coronavirus Spike Protein Is an Essential Determinant of Neurotropism

Some coronaviruses (CoVs) have an extra furin cleavage site (RRKR/S, furin-S2′ site) upstream of the fusion peptide in the spike protein, which plays roles in virion adsorption and fusion. Mutation of the S2′ site of QX genotype (QX-type) infectious bronchitis virus (IBV) spike protein (S) in a recombinant virus background results in higher pathogenicity, pronounced neural symptoms and neurotropism when compared with conditions in wild-type IBV (WT-IBV) infected chickens. In this study, we present evidence suggesting that recombinant IBV with a mutant S2′ site (furin-S2′ site) leads to higher mortality. Infection with mutant IBV induces severe encephalitis and breaks the blood–brain barrier. The results of a neutralization test and immunoprotection experiment show that an original serum and vaccine can still provide effective protection in vivo and in vitro. This is the first demonstration of IBV-induced neural symptoms in chickens with encephalitis and the furin-S2′ site as a determinant of neurotropism.

Disrupted CXCR2 Signaling in Oligodendroglia Lineage Cells Enhances Myelin Repair in a Viral Model of Multiple Sclerosis

CXCR2 is a chemokine receptor expressed on oligodendroglia that has been implicated in the pathogenesis of neuroinflammatory demyelinating diseases as well as enhancement of the migration, proliferation, and myelin production by oligodendroglia. Using an inducible proteolipid protein (Plp) promoter-driven Cre-loxP recombination system, we were able to assess how timed ablation of Cxcr2 in oligodendroglia affected disease following intracranial infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV). Generation of Plp-Cre-ER(T)::Cxcr2flox/flox transgenic mice (termed Cxcr2-CKO mice) allows for Cxcr2 to be silenced in oligodendrocytes in adult mice following treatment with tamoxifen. Ablation of oligodendroglia Cxcr2 did not influence clinical severity in response to intracranial infection with JHMV. Infiltration of activated T cells or myeloid cells into the central nervous system (CNS) was not affected, nor was the ability to control viral infection. In addition, the severity of demyelination was similar between tamoxifen-treated mice and vehicle-treated controls. Notably, deletion of Cxcr2 resulted in increased remyelination, as assessed by g-ratio (the ratio of the inner axonal diameter to the total outer fiber diameter) calculation, compared to that in vehicle-treated control mice. Collectively, our findings argue that CXCR2 signaling in oligodendroglia is dispensable with regard to contributing to neuroinflammation, but its deletion enhances remyelination in a preclinical model of the human demyelinating disease multiple sclerosis (MS).IMPORTANCE Signaling through the chemokine receptor CXCR2 in oligodendroglia is important for developmental myelination in rodents, while chemical inhibition or nonspecific genetic deletion of CXCR2 appears to augment myelin repair in animal models of the human demyelinating disease multiple sclerosis (MS). To better understand the biology of CXCR2 signaling on oligodendroglia, we generated transgenic mice in which Cxcr2 is selectively ablated in oligodendroglia upon treatment with tamoxifen. Using a viral model of neuroinflammation and demyelination, we demonstrate that genetic silencing of CXCR2 on oligodendroglia did not affect clinical disease, neuroinflammation, or demyelination, yet there was increased remyelination. These findings support and extend previous findings suggesting that targeting CXCR2 may offer a therapeutic avenue for enhancing remyelination in patients with demyelinating diseases.

The microbiota protects from viral-induced neurologic damage through microglia-intrinsic TLR signaling

Symbiotic microbes impact the function and development of the central nervous system (CNS); however, little is known about the contribution of the microbiota during viral-induced neurologic damage. We identify that commensals aid in host defense following infection with a neurotropic virus through enhancing microglia function. Germfree mice or animals that receive antibiotics are unable to control viral replication within the brain leading to increased paralysis. Microglia derived from germfree or antibiotic-treated animals cannot stimulate viral-specific immunity and microglia depletion leads to worsened demyelination. Oral administration of toll-like receptor (TLR) ligands to virally infected germfree mice limits neurologic damage. Homeostatic activation of microglia is dependent on intrinsic signaling through TLR4, as disruption of TLR4 within microglia, but not the entire CNS (excluding microglia), leads to increased viral-induced clinical disease. This work demonstrates that gut immune-stimulatory products can influence microglia function to prevent CNS damage following viral infection.

T cell-selective deletion of Oct1 protects animals from autoimmune neuroinflammation while maintaining neurotropic pathogen response

BACKGROUND

Treatments for autoimmune diseases aim to dampen autoreactivity while preserving normal immune function. In CD4+ T cells, the transcription factor Oct1/Pou2f1 is a dispensable transcription factor for T cell development and response to primary infection, but promotes expression of target genes, including Il2 and Ifng, under conditions of antigen reencounter. As a result, they are more strongly expressed upon secondary stimulation. Such repeated antigen encounters occur in memory recall responses, in autoimmunity where self-antigen can be recognized multiple times, and in chronic infection where foreign antigen is persistent. Based on these previous findings, we hypothesized that Oct1 loss would protect animals from autoimmunity but maintain normal responses to pathogens in the CNS.

OBJECTIVE

We used a conditional mouse Oct1 (Pou2f1) allele and a CD4-Cre driver to determine the effect of T cell-specific Oct1 loss on autoimmune- and viral-induced neuroinflammation using an autoantigen-driven EAE model of autoimmunity and a JHMV model of viral infection.

RESULTS

Oct1 conditional deletion mitigated clinical scores and reduced infiltrating T cells and cytokine production in the EAE model. Consistently, Oct1-deficient CD4+ T cells stimulated in vitro showed increased expression of markers associated with T cell anergy, particularly in the absence of co-stimulatory signals. In contrast, anti-viral T cell effector functions are intact in the absence of Oct1, with no changes in neuroinflammation, infiltrating T cells or cytokine production.

CONCLUSION

Our findings uncover a significant difference between the effect of Oct1 loss on autoimmune and anti-pathogen responses, which potentially could be exploited for therapeutic benefit.

The coronavirus macrodomain is required to prevent PARP-mediated inhibition of virus replication and enhancement of IFN expression

ADP-ribosylation is a ubiquitous post-translational addition of either monomers or polymers of ADP-ribose to target proteins by ADP-ribosyltransferases, usually by interferon-inducible diphtheria toxin-like enzymes known as PARPs. While several PARPs have known antiviral activities, these activities are mostly independent of ADP-ribosylation. Consequently, less is known about the antiviral effects of ADP-ribosylation. Several viral families, including Coronaviridae, Togaviridae, and Hepeviridae, encode for macrodomain proteins that bind to and hydrolyze ADP-ribose from proteins and are critical for optimal replication and virulence. These results suggest that macrodomains counter cellular ADP-ribosylation, but whether PARPs or, alternatively, other ADP-ribosyltransferases cause this modification is not clear. Here we show that pan-PARP inhibition enhanced replication and inhibited interferon production in primary macrophages infected with macrodomain-mutant but not wild-type coronavirus. Specifically, knockdown of two abundantly expressed PARPs, PARP12 and PARP14, led to increased replication of mutant but did not significantly affect wild-type virus. PARP14 was also important for the induction of interferon in mouse and human cells, indicating a critical role for this PARP in the regulation of innate immunity. In summary, these data demonstrate that the macrodomain is required to prevent PARP-mediated inhibition of coronavirus replication and enhancement of interferon production.

ADP-ribosylation, an understudied post-translational modification, facilitates the host response to virus infection. Several viruses, including all members of the coronavirus family, encode a macrodomain to reverse ADP-ribosylation and combat this immune response. As such, viruses with mutations in the macrodomain are highly attenuated and cause minimal disease in vivo. Here, using primary macrophages and mice infected with a pathogenic murine coronavirus, we identify PARPs, specifically PARP12 and PARP14, as host cell ADP-ribosylating enzymes important for the attenuation of these mutant viruses and confirm their importance using inhibitors and siRNAs. These data demonstrate a broad strategy of virus-host interactions and indicate that the macrodomain may be a useful target for antiviral therapy.

Innate Immune Responses and Viral-Induced Neurologic Disease

Multiple sclerosis (MS) is a disease of the central nervous system (CNS) characterized by chronic neuroinflammation, axonal damage, and demyelination. Cellular components of the adaptive immune response are viewed as important in initiating formation of demyelinating lesions in MS patients. This notion is supported by preclinical animal models, genome-wide association studies (GWAS), as well as approved disease modifying therapies (DMTs) that suppress clinical relapse and are designed to impede infiltration of activated lymphocytes into the CNS. Nonetheless, emerging evidence demonstrates that the innate immune response e.g., neutrophils can amplify white matter damage through a variety of different mechanisms. Indeed, using a model of coronavirus-induced neurologic disease, we have demonstrated that sustained neutrophil infiltration into the CNS of infected animals correlates with increased demyelination. This brief review highlights recent evidence arguing that targeting the innate immune response may offer new therapeutic avenues for treatment of demyelinating disease including MS.

Fine Tuning the Cytokine Storm by IFN and IL-10 Following Neurotropic Coronavirus Encephalomyelitis

The central nervous system (CNS) is vulnerable to several viral infections including herpes viruses, arboviruses and HIV to name a few. While a rapid and effective immune response is essential to limit viral spread and mortality, this anti-viral response needs to be tightly regulated in order to limit immune mediated tissue damage. This balance between effective virus control with limited pathology is especially important due to the highly specialized functions and limited regenerative capacity of neurons, which can be targets of direct virus cytolysis or bystander damage. CNS infection with the neurotropic strain of mouse hepatitis virus (MHV) induces an acute encephalomyelitis associated with focal areas of demyelination, which is sustained during viral persistence. Both innate and adaptive immune cells work in coordination to control virus replication. While type I interferons are essential to limit virus spread associated with early mortality, perforin, and interferon-γ promote further virus clearance in astrocytes/microglia and oligodendrocytes, respectively. Effective control of virus replication is nonetheless associated with tissue damage, characterized by demyelinating lesions. Interestingly, the anti-inflammatory cytokine IL-10 limits expansion of tissue lesions during chronic infection without affecting viral persistence. Thus, effective coordination of pro- and anti-inflammatory cytokines is essential during MHV induced encephalomyelitis in order to protect the host against viral infection at a limited cost.

Microglia have a protective role in viral encephalitis-induced seizure development and hippocampal damage

In the central nervous system (CNS), innate immune surveillance is mainly coordinated by microglia. These CNS resident myeloid cells are assumed to help orchestrate the immune response against infections of the brain. However, their specific role in this process and their interactions with CNS infiltrating immune cells, such as blood-borne monocytes and T cells are only incompletely understood. The recent development of PLX5622, a specific inhibitor of colony-stimulating factor 1 receptor that depletes microglia, allows studying the role of microglia in conditions of brain injury such as viral encephalitis, the most common form of brain infection. Here we used this inhibitor in a model of viral infection-induced epilepsy, in which C57BL/6 mice are infected by a picornavirus (Theiler's murine encephalomyelitis virus) and display seizures and hippocampal damage. Our results show that microglia are required early after infection to limit virus distribution and persistence, most likely by modulating T cell activation. Microglia depletion accelerated the occurrence of seizures, exacerbated hippocampal damage, and led to neurodegeneration in the spinal cord, which is normally not observed in this mouse strain. This study enhances our understanding of the role of microglia in viral encephalitis and adds to the concept of microglia-T cell crosstalk.

Neurologic Alterations Due to Respiratory Virus Infections

Central Nervous System (CNS) infections are one of the most critical problems in public health, as frequently patients exhibit neurologic sequelae. Usually, CNS pathologies are caused by known neurotropic viruses such as measles virus (MV), herpes virus and human immunodeficiency virus (HIV), among others. However, nowadays respiratory viruses have placed themselves as relevant agents responsible for CNS pathologies. Among these neuropathological viruses are the human respiratory syncytial virus (hRSV), the influenza virus (IV), the coronavirus (CoV) and the human metapneumovirus (hMPV). These viral agents are leading causes of acute respiratory infections every year affecting mainly children under 5 years old and also the elderly. Up to date, several reports have described the association between respiratory viral infections with neurological symptoms. The most frequent clinical manifestations described in these patients are febrile or afebrile seizures, status epilepticus, encephalopathies and encephalitis. All these viruses have been found in cerebrospinal fluid (CSF), which suggests that all these pathogens, once in the lungs, can spread throughout the body and eventually reach the CNS. The current knowledge about the mechanisms and routes used by these neuro-invasive viruses remains scarce. In this review article, we describe the most recent findings associated to neurologic complications, along with data about the possible invasion routes of these viruses in humans and their various effects on the CNS, as studied in animal models.

Intercellular Communication Is Key for Protective IFNα/β Signaling During Viral Central Nervous System Infection

A variety of viruses can induce central nervous system (CNS) infections and neurological diseases, although the incidence is rare. Similar to peripheral infections, IFNα/β induction and signaling constitutes a first line of defense to limit virus dissemination. However, CNS-resident cells differ widely in their repertoire and magnitude of both basal and inducible components in the IFNα/β pathway. While microglia as resident myeloid cells have been implicated as prominent sentinels of CNS invading pathogens or insults, astrocytes are emerging as key responders to many neurotropic RNA virus infections. Focusing on RNA viruses, this review discusses the role of astrocytes as IFNα/β inducers and responders and touches on the role of IFNα/β receptor signaling in regulating myeloid cell activation and IFNγ responsiveness. A summary picture emerges implicating IFNα/β not only as key in establishing the classical "antiviral" state, but also orchestrating cell mobility and IFNγ-mediated effector functions.

Promoting remyelination through cell transplantation therapies in a model of viral-induced neurodegenerative disease

Multiple sclerosis (MS) is a central nervous system (CNS) disease characterized by chronic neuroinflammation, demyelination, and axonal damage. Infiltration of activated lymphocytes and myeloid cells are thought to be primarily responsible for white matter damage and axonopathy. Several United States Food and Drug Administration-approved therapies exist that impede activated lymphocytes from entering the CNS thereby limiting new lesion formation in patients with relapse-remitting forms of MS. However, a significant challenge within the field of MS research is to develop effective and sustained therapies that allow for axonal protection and remyelination. In recent years, there has been increasing evidence that some kinds of stem cells and their derivatives seem to be able to mute neuroinflammation as well as promote remyelination and axonal integrity. Intracranial infection of mice with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in immune-mediated demyelination and axonopathy, making this an excellent model to interrogate the therapeutic potential of stem cell derivatives in evoking remyelination. This review provides a succinct overview of our recent findings using intraspinal injection of mouse CNS neural progenitor cells and human neural precursors into JHMV-infected mice. JHMV-infected mice receiving these cells display extensive remyelination associated with axonal sparing. In addition, we discuss possible mechanisms associated with sustained clinical recovery. Developmental Dynamics 248:43-52, 2019. © 2018 Wiley Periodicals, Inc.

Chemokine CXCL10 and Coronavirus-Induced Neurologic Disease

Chemokines (chemotactic cytokines) are involved in a wide variety of biological processes. Following microbial infection, there is often robust chemokine signaling elicited from infected cells, which contributes to both innate and adaptive immune responses that control growth of the invading pathogen. Infection of the central nervous system (CNS) by the neuroadapted John Howard Mueller (JHM) strain of mouse hepatitis virus (JHMV) provides an excellent example of how chemokines aid in host defense as well as contribute to disease. Intracranial inoculation of the CNS of susceptible mice with JHMV results in an acute encephalomyelitis characterized by widespread dissemination of virus throughout the parenchyma. Virus-specific T cells are recruited to the CNS, and control viral replication through release of antiviral cytokines and cytolytic activity. Sterile immunity is not acquired, and virus will persist primarily in white matter tracts leading to chronic neuroinflammation and demyelination. Chemokines are expressed and contribute to defense as well as chronic disease by attracting targeted populations of leukocytes to the CNS. The T cell chemoattractant chemokine CXCL10 (interferon-inducible protein 10 kDa, IP-10) is prominently expressed in both stages of disease, and serves to attract activated T and B lymphocytes expressing CXC chemokine receptor 3 (CXCR3), the receptor for CXCL10. Functional studies that have blocked expression of either CXCL10 or CXCR3 illuminate the important role of this signaling pathway in host defense and neurodegeneration in a model of viral-induced neurologic disease.

Distinct Gene Profiles of Bone Marrow-Derived Macrophages and Microglia During Neurotropic Coronavirus-Induced Demyelination

Multiple Sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) characterized by demyelination and axonal loss. Demyelinating lesions are associated with infiltrating T lymphocytes, bone marrow-derived macrophages (BMDM), and activated resident microglia. Tissue damage is thought to be mediated by T cell produced cytokines and chemokines, which activate microglia and/or BMDM to both strip myelin and produce toxic factors, ultimately damaging axons and promoting disability. However, the relative contributions of BMDM and microglia to demyelinating pathology are unclear, as their identification in MS tissue is difficult due to similar morphology and indistinguishable surface markers when activated. The CD4 T cell-induced autoimmune murine model of MS, experimental autoimmune encephalitis (EAE), in which BMDM are essential for demyelination, has revealed pathogenic and repair-promoting phenotypes associated with BMDM and microglia, respectively. Using a murine model of demyelination induced by a gliatropic coronavirus, in which BMDM are redundant for demyelination, we herein characterize gene expression profiles of BMDM versus microglia associated with demyelination. While gene expression in CNS infiltrating BMDM was upregulated early following infection and subsequently sustained, microglia expressed a more dynamic gene profile with extensive mRNA upregulation coinciding with peak demyelination after viral control. This delayed microglia response comprised a highly pro-inflammatory and phagocytic profile. Furthermore, while BMDM exhibited a mixed phenotype of M1 and M2 markers, microglia repressed the vast majority of M2-markers. Overall, these data support a pro-inflammatory and pathogenic role of microglia temporally remote from viral control, whereas BMDM retained their gene expression profile independent of the changing environment. As demyelination is caused by multifactorial insults, our results highlight the plasticity of microglia in responding to distinct inflammatory settings, which may be relevant for MS pathogenesis.

Nasal priming by a murine coronavirus provides protective immunity against lethal heterologous virus pneumonia

The nasal mucosa is an important component of mucosal immunity. Immunogenic particles in inspired air are known to activate the local nasal mucosal immune system and can lead to sinonasal inflammation; however, little is known about the effect of this activation on the lung immune environment. Here, we showed that nasal inoculation of murine coronavirus (CoV) in the absence of direct lung infection primes the lung immune environment by recruiting activated monocytes (Ly6C+ inflammatory monocytes) and NK cells into the lungs. Unlike infiltration of these cells into directly infected lungs, a process that requires type I IFN signaling, nasally induced infiltration of Ly6C+ inflammatory monocytes into the lungs is IFN-I independent. These activated macrophages ingested antigen and migrated to pulmonary lymph nodes, and enhanced both innate and adaptive immunity after heterologous virus infection. Clinically, such nasal-only inoculation of MHV-1 failed to cause pneumonia but significantly reduced mortality and morbidity of lethal pneumonia caused by severe acute respiratory syndrome CoV (SARS-CoV) or influenza A virus. Together, the data indicate that the nose and upper airway remotely prime the lung immunity to protect the lungs from direct viral infections.

Alpha/Beta Interferon (IFN-α/β) Signaling in Astrocytes Mediates Protection against Viral Encephalomyelitis and Regulates IFN-γ-Dependent Responses

The contribution of distinct central nervous system (CNS) resident cells to protective alpha/beta interferon (IFN-α/β) function following viral infections is poorly understood. Based on numerous immune regulatory functions of astrocytes, we evaluated the contribution of astrocyte IFN-α/β signaling toward protection against the nonlethal glia- and neuronotropic mouse hepatitis virus (MHV) strain A59. Analysis of gene expression associated with IFN-α/β function, e.g., pattern recognition receptors (PRRs) and interferon-stimulated genes (ISGs), revealed lower basal mRNA levels in brain-derived astrocytes than in microglia. Although astrocytes poorly induced Ifnβ mRNA following infection, they upregulated various mRNAs in the IFN-α/β pathway to a higher extent than microglia, supporting effective IFN-α/β responsiveness. Ablation of the IFN-α/β receptor (IFNAR) in astrocytes using mGFAPcre IFNAR^fl/fl mice resulted in severe encephalomyelitis and mortality, coincident with uncontrolled virus replication. Further, virus spread was not restricted to astrocytes but also affected microglia and neurons, despite increased and sustained Ifnα/β and ISG mRNA levels within the CNS. IFN-γ, a crucial mediator for MHV control, was not impaired in infected mGFAPcre IFNAR^fl/fl mice despite reduced T cell CNS infiltration. Unexpectedly however, poor induction of IFN-γ-dependent major histocompatibility complex (MHC) class II expression on microglia supported that defective IFN-γ signaling contributes to uncontrolled virus replication. A link between sustained elevated IFN-α/β and impaired responsiveness to IFN-γ supports the novel concept that temporally limited early IFN-α/β responses are critical for effective antiviral IFN-γ function. Overall, our results imply that IFN-α/β signaling in astrocytes is not only critical in limiting early CNS viral spread but also promotes protective antiviral IFN-γ function.IMPORTANCE An antiviral state established by IFN-α/β contains initial viral spread as adaptive immunity develops. While it is apparent that the CNS lacks professional IFN-α/β producers and that resident cells have distinct abilities to elicit innate IFN-α/β responses, protective interactions between inducer and responder cells require further investigation. Infection with a glia- and neuronotropic coronavirus demonstrates that astrocytes mount a delayed but more robust response to infection than microglia, despite their lower basal mRNA levels of IFN-α/β-inducing components. Lethal, uncontrolled viral dissemination following ablation of astrocyte IFN-α/β signaling revealed the importance of IFN-α/β responses in a single cell type for protection. Sustained global IFN-α/β expression associated with uncontrolled virus did not suffice to protect neurons and further impaired responsiveness to protective IFN-γ. The results support astrocytes as critical contributors to innate immunity and the concept that limited IFN-α/β responses are critical for effective subsequent antiviral IFN-γ function.

Microglia are required for protection against lethal coronavirus encephalitis in mice

Recent findings have highlighted the role of microglia in orchestrating normal development and refining neural network connectivity in the healthy CNS. Microglia are not only vital cells in maintaining CNS homeostasis, but also respond to injury, infection, and disease by undergoing proliferation and changes in transcription and morphology. A better understanding of the specific role of microglia in responding to viral infection is complicated by the presence of nonmicroglial myeloid cells with potentially overlapping function in the healthy brain and by the rapid infiltration of hematopoietic myeloid cells into the brain in diseased states. Here, we used an inhibitor of colony-stimulating factor 1 receptor (CSF1R) that depletes microglia to examine the specific roles of microglia in response to infection with the mouse hepatitis virus (MHV), a neurotropic coronavirus. Our results show that microglia were required during the early days after infection to limit MHV replication and subsequent morbidity and lethality. Additionally, microglia depletion resulted in ineffective T cell responses. These results reveal nonredundant, critical roles for microglia in the early innate and virus-specific T cell responses and for subsequent host protection from viral encephalitis.

Protective Humoral Immunity in the Central Nervous System Requires Peripheral CD19-Dependent Germinal Center Formation following Coronavirus Encephalomyelitis

B cell subsets with phenotypes characteristic of naive, non-isotype-switched, memory (B_mem) cells and antibody-secreting cells (ASC) accumulate in various models of central nervous system (CNS) inflammation, including viral encephalomyelitis. During neurotropic coronavirus JHMV infection, infiltration of protective ASC occurs after T cell-mediated viral control and is preceded by accumulation of non-isotype-switched IgD⁺ and IgM⁺ B cells. However, the contribution of peripheral activation events in cervical lymph nodes (CLN) to driving humoral immune responses in the infected CNS is poorly defined. CD19, a signaling component of the B cell receptor complex, is one of multiple regulators driving B cell differentiation and germinal center (GC) formation by lowering the threshold of antigen-driven activation. JHMV-infected CD19^-/- mice were thus used to determine how CD19 affects CNS recruitment of B cell subsets. Early polyclonal ASC expansion, GC formation, and virus-specific ASC were all significantly impaired in CLN of CD19^-/- mice compared to wild-type (WT) mice, consistent with lower and unsustained virus-specific serum antibody (Ab). ASC were also significantly reduced in the CNS, resulting in increased infectious virus during persistence. Nevertheless, CD19 deficiency did not affect early CNS IgD⁺ B cell accumulation. The results support the notion that CD19-independent factors drive early B cell mobilization and recruitment to the infected CNS, while delayed accumulation of virus-specific, isotype-switched ASC requires CD19-dependent GC formation in CLN. CD19 is thus essential for both sustained serum Ab and protective local Ab within the CNS following JHMV encephalomyelitis.IMPORTANCE CD19 activation is known to promote GC formation and to sustain serum Ab responses following antigen immunization and viral infections. However, the contribution of CD19 in the context of CNS infections has not been evaluated. This study demonstrates that antiviral protective ASC in the CNS are dependent on CD19 activation and peripheral GC formation, while accumulation of early-recruited IgD⁺ B cells is CD19 independent. This indicates that IgD⁺ B cells commonly found early in the CNS do not give rise to local ASC differentiation and that only antigen-primed, peripheral GC-derived ASC infiltrate the CNS, thereby limiting potentially harmful nonspecific Ab secretion. Expanding our understanding of activation signals driving CNS migration of distinct B cell subsets during neuroinflammatory insults is critical for preventing and managing acute encephalitic infections, as well as preempting reactivation of persistent viruses during immune-suppressive therapies targeting B cells in multiple sclerosis (MS), such as rituximab and ocrelizumab.

Murine Olfactory Bulb Interneurons Survive Infection with a Neurotropic Coronavirus

Viral infection of the central nervous system (CNS) is complicated by the mostly irreplaceable nature of neurons, as the loss of neurons has the potential to result in permanent damage to brain function. However, whether neurons or other cells in the CNS sometimes survive infection and the effects of infection on neuronal function is largely unknown. To address this question, we used the rJHM strain (rJ) of mouse hepatitis virus (MHV), a neurotropic coronavirus that causes acute encephalitis in susceptible strains of mice. To determine whether neurons or other CNS cells survive acute infection with this virulent virus, we developed a recombinant JHMV that expresses Cre recombinase (rJ-Cre) and infected mice that universally expressed a silent (floxed) version of tdTomato. Infection of these mice with rJ-Cre resulted in expression of tdTomato in host cells. The results showed that some cells were able to survive the infection, as demonstrated by continued tdTomato expression after virus antigen could no longer be detected. Most notably, interneurons in the olfactory bulb, which are known to be inhibitory, represented a large fraction of the surviving cells. In conclusion, our results indicated that some neurons are resistant to virus-mediated cell death and provide a framework for studying the effects of prior coronavirus infection on neuron function.IMPORTANCE We developed a novel recombinant virus that allows the study of cells that survive an infection by a central nervous system-specific strain of murine coronavirus. Using this virus, we identified neurons and, to a lesser extent, nonneuronal cells in the brain that were infected during the acute phase of the infection and survived for approximately 2 weeks until the mice succumbed to the infection. We focused on neurons and glial cells within the olfactory bulb because the virus enters the brain at this site. Our results show that interneurons of the olfactory bulb were the primary cell type able to survive infection. Further, these results indicate that this system will be useful for functional and gene expression studies of cells in the brain that survive acute infection.

Plasmonic silver nanoshells for drug and metabolite detection

In-vitro metabolite and drug detection rely on designed materials-based analytical platforms, which are universally used in biomedical research and clinical practice. However, metabolic analysis in bio-samples needs tedious sample preparation, due to the sample complexity and low molecular abundance. A further challenge is to construct diagnostic tools. Herein, we developed a platform using silver nanoshells. We synthesized SiO2@Ag with tunable shell structures by multi-cycled silver mirror reactions. Optimized nanoshells achieved direct laser desorption/ionization mass spectrometry in 0.5 μL of bio-fluids. We applied these nanoshells for disease diagnosis and therapeutic evaluation. We identified patients with postoperative brain infection through daily monitoring and glucose quantitation in cerebrospinal fluid. We measured drug distribution in blood and cerebrospinal fluid systems and validated the function of blood-brain/cerebrospinal fluid-barriers for pharmacokinetics. Our work sheds light on the design of materials for advanced metabolic analysis and precision diagnostics.Preparation of samples for diagnosis can affect the detection of biomarkers and metabolites. Here, the authors use a silver nanoparticle plasmonics approach for the detection of biomarkers in patients as well as investigate the distribution of drugs in serum and cerebral spinal fluid.

Virus-induced inflammasome activation is suppressed by prostaglandin D2/DP1 signaling

Prostaglandin D2 (PGD₂), an eicosanoid with both pro- and anti-inflammatory properties, is the most abundantly expressed prostaglandin in the brain. Here we show that PGD₂ signaling through the D-prostanoid receptor 1 (DP1) receptor is necessary for optimal microglia/macrophage activation and IFN expression after infection with a neurotropic coronavirus. Genome-wide expression analyses indicated that PGD₂/DP1 signaling is required for up-regulation of a putative inflammasome inhibitor, PYDC3, in CD11b⁺ cells in the CNS of infected mice. Our results also demonstrated that, in addition to PGD₂/DP1 signaling, type 1 IFN (IFN-I) signaling is required for PYDC3 expression. In the absence of Pydc3 up-regulation, IL-1β expression and, subsequently, mortality were increased in infected DP1^-/- mice. Notably, survival was enhanced by IL1 receptor blockade, indicating that the effects of the absence of DP1 signaling on clinical outcomes were mediated, at least in part, by inflammasomes. Using bone marrow-derived macrophages in vitro, we confirmed that PYDC3 expression is dependent upon DP1 signaling and that IFN priming is critical for PYDC3 up-regulation. In addition, Pydc3 silencing or overexpression augmented or diminished IL-1β secretion, respectively. Furthermore, DP1 signaling in human macrophages also resulted in the up-regulation of a putative functional analog, POP3, suggesting that PGD₂ similarly modulates inflammasomes in human cells. These findings demonstrate a previously undescribed role for prostaglandin signaling in preventing excessive inflammasome activation and, together with previously published results, suggest that eicosanoids and inflammasomes are reciprocally regulated.

Within host RNA virus persistence: mechanisms and consequences

In a prototypical response to an acute viral infection it would be expected that the adaptive immune response would eliminate all virally infected cells within a few weeks of infection. However many (non-retrovirus) RNA viruses can establish 'within host' persistent infections that occasionally lead to chronic or reactivated disease. Despite the importance of 'within host' persistent RNA virus infections, much has still to be learnt about the molecular mechanisms by which RNA viruses establish persistent infections, why innate and adaptive immune responses fail to rapidly clear these infections, and the epidemiological and potential disease consequences of such infections.