Neurotropism of human coronavirus 229E

Evaluating the Virology and Evolution of Seasonal Human Coronaviruses Associated with the Common Cold in the COVID-19 Era

Approximately 15-30% of all cases of the common cold are due to human coronavirus infections. More recently, the emergence of the more severe respiratory coronaviruses, SARS-CoV and MERS-CoV, have highlighted the increased pathogenic potential of emergent coronaviruses. Lastly, the current emergence of SARS-CoV-2 has demonstrated not only the potential for significant disease caused by emerging coronaviruses, but also the capacity of novel coronaviruses to promote pandemic spread. Largely driven by the global response to the COVID-19 pandemic, significant research in coronavirus biology has led to advances in our understanding of these viruses. In this review, we evaluate the virology, emergence, and evolution of the four endemic coronaviruses associated with the common cold, their relationship to pandemic SARS-CoV-2, and discuss the potential for future emergent human coronaviruses.

Long-term Consequences of COVID-19: Chemosensory Disorders

PURPOSE OF REVIEW

A number of sequelae after acute coronavirus disease 2019 (COVID-19) significantly affect the quality of life of patients. The chemosensory disorders including olfactory dysfunction (OD) and gustatory dysfunction (GD) are two of the commonest symptoms complained by patients with COVID-19. Although chemosensory function has been reported improved in over 60% of COVID-19 patients in a short time after acute infection, it may last as a major symptom for patients with long COVID-19. This narrative review discussed current literatures on OD and GD in long COVID-19 including the prevalence, risk factors, possible mechanisms, and potential therapies.

RECENT FINDINGS

Although the prevalence of OD and GD has declined continuously after acute COVID-19, a considerable number of patients had persistent chemosensory disorders 3 months to 2 years after symptom onset. Female gender, initial severity of dysfunction, nasal congestion, emotional distress and depression, and SARS-CoV-2 variants have been identified as risk factors for persistent OD and GD in long COVID-19. The pathogenesis of OD and GD in long COVID-19 remains unknown, but may be analogous to the persistent OD and GD post common respiratory viral infection. Corticosteroids and olfactory training might be a potential choice regarding the treatment of lasting OD and GD after SARS-CoV-2 infection; however, more studies are needed to prove it. OD and GD are common long-term consequences of COVID-19 and influenced by gender, initial severity of dysfunction, emotional distress and depression, and SARS-CoV-2 variants. More studies are needed to illustrate their pathogenesis and to establish therapeutic strategies.

Suppression of porcine hemagglutinating encephalomyelitis virus replication by resveratrol

BACKGROUND

Porcine hemagglutinating encephalomyelitis virus (PHEV), a member of the genus Betacoronavirus, is the causative agent of neurological disease in pigs. No effective therapeutics are currently available for PHEV infection. Resveratrol has been shown to exert neuroprotective and antiviral effects. Here resveratrol was investigated for its ability to inhibit PHEV replication in nerve cells and central nervous system tissues.

METHODS

Anti-PHEV effect of resveratrol was evaluated using an in vitro cell-based PHEV infection model and employing a mouse PHEV infection model. The collected cells or tissues were used for quantitative PCR analysis, western blot analysis, or indirect immunofluorescence assay. The supernatants were collected to quantify viral loads by TCID₅₀ assay in vitro. EC50 and CC50 were determined by dose-response experiments, and the ratio (EC50/CC50) was used as a selectivity index (SI) to measure the antiviral versus cytotoxic activity.

RESULTS

Our results showed that resveratrol treatment reduced PHEV titer in a dose-dependent manner, with a 50% inhibition concentration of 6.24 μM. A reduction of > 70% of viral protein expression and mRNA copy number and a 19-fold reduction of virus titer were achieved when infected cells were treated with 10 µM resveratrol in a pre-treatment assay. Quantitative PCR analysis and TCID₅₀ assay results revealed that the addition of 10 μM resveratrol to cells after adsorption of PHEV significantly reduced 56% PHEV mRNA copy number and eightfold virus titer. 10 µM resveratrol treatment reduced 46% PHEV mRNA copy number and fourfold virus titer in virus inactivation assay. Moreover, the in vivo data obtained in this work also demonstrated that resveratrol inhibited PHEV replication, and anti-PHEV activities of resveratrol treatment via intranasal installation displayed better than oral gavage.

CONCLUSION

These results indicated that resveratrol exerted antiviral effects under various drug treatment and virus infection conditions in vitro and holds promise as a treatment for PHEV infection in vivo.

Emerging COVID-19 variants and their impact on SARS-CoV-2 diagnosis, therapeutics and vaccines

The emergence of novel and evolving variants of SARS-CoV-2 has fostered the need for change in the form of newer and more adaptive diagnostic methods for the detection of SARS-CoV-2 infections. On the other hand, developing rapid and sensitive diagnostic technologies is now more challenging due to emerging variants and varying symptoms exhibited among the infected individuals. In addition to this, vaccines remain the major mainstay of prevention and protection against infection. Novel vaccines and drugs are constantly being developed to unleash an immune response for the robust targeting of SARS-CoV-2 and its associated variants. In this review, we provide an updated perspective on the current challenges posed by the emergence of novel SARS-CoV-2 mutants/variants and the evolution of diagnostic techniques to enable their detection. In addition, we also discuss the development, formulation, working mechanisms, advantages, and drawbacks of some of the most used vaccines/therapeutic drugs and their subsequent immunological impact.Key messageThe emergence of novel variants of the SARS-CoV-2 in the past couple of months, highlights one of the primary challenges in the diagnostics, treatment, as well as vaccine development against the virus.Advancements in SARS-CoV-2 detection include nucleic acid based, antigen and immuno- assay-based and antibody-based detection methodologies for efficient, robust, and quick testing; while advancements in COVID-19 preventive and therapeutic strategies include novel antiviral and immunomodulatory drugs and SARS-CoV-2 targeted vaccines.The varied COVID-19 vaccine platforms and the immune responses induced by each one of them as well as their ability to battle post-vaccination infections have all been discussed in this review.

SARS-CoV-2 infects neurons and induces neuroinflammation in a non-human primate model of COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiologic agent of coronavirus disease 2019 (COVID-19), can induce a plethora of neurological complications in some patients. However, it is still under debate if SARS-CoV-2 directly infects the brain or if CNS sequelae result from systemic inflammatory responses triggered in the periphery. Using high-resolution microscopy, we investigated whether SARS-CoV-2 reaches the brain and how viral neurotropism can be modulated by aging in a non-human primate model of COVID-19. Seven days after infection, SARS-CoV-2 was detected in the olfactory cortex and interconnected regions, accompanied by robust neuroinflammation and neuronal damage exacerbated in aged diabetic animals. Our study provides an initial framework for identifying the molecular and cellular mechanisms underlying SARS-CoV-2 neurological complications, which will be essential to reducing both the short- and long-term burden of COVID-19.

A human coronavirus OC43-derived polypeptide causes neuropathic pain

Human coronaviruses have been recently implicated in neurological sequelae by insufficiently understood mechanisms. We here identify an amino acid sequence within the HCoV-OC43 p65-like protein homologous to the evolutionarily conserved motif of myelin basic protein (MBP). Because MBP-derived peptide exposure in the sciatic nerve produces pronociceptive activity in female rodents, we examined whether a synthetic peptide derived from the homologous region of HCoV-OC43 (OC43p) acts by molecular mimicry to promote neuropathic pain. OC43p, but not scrambled peptides, induces mechanical hypersensitivity in rats following intrasciatic injections. Transcriptome analyses of the corresponding spinal cords reveal upregulation of genes and signaling pathways with known nociception-, immune-, and cellular energy-related activities. Affinity capture shows the association of OC43p with an Na+ /K+ -transporting ATPase, providing a potential direct target and mechanistic insight into virus-induced effects on energy homeostasis and the sensory neuraxis. We propose that HCoV-OC43 polypeptides released during infection dysregulate normal nervous system functions through molecular mimicry of MBP, leading to mechanical hypersensitivity. Our findings might provide a new paradigm for virus-induced neuropathic pain.

Causes of Hypoxemia in COVID-19

The global pandemic of a new coronavirus disease (COVID-19) has posed challenges to public health specialists around the world associated with diagnosis, intensive study of epidemiological and clinical features of the coronavirus infection, development of preventive approaches, therapeutic strategies and rehabilitation measures. However, despite the successes achieved in the study of COVID-19 pathogenesis, many aspects that aggravate the severity of the disease and cause high mortality of patients remain unclear. The main clinical manifestation of the new variant of SARS-CoV-2 virus infection is pneumonia with massive parenchymal lesions of lung tissue, diffuse alveolar damage, thrombotic manifestations, disruption of ventilation-perfusion relationships, etc. However, symptoms in patients hospitalized with COVID pneumonia show a broad diversity: the majority has minimal manifestations, others develop severe respiratory failure complicated by acute respiratory distress syndrome (ARDS) with rapidly progressing hypoxemia that leads to high mortality. Numerous clinical data publications report that some COVID pneumonia patients without subjective signs of severe respiratory failure (dyspnea, “air hunger”) have an extremely low saturation level. As a result, there arises a paradoxical condition (called “silent hypoxia” or even “happy hypoxia”) contradicting the very basics of physiology, as it essentially represents a severe life-incompatible hypoxemia which lacks respiratory discomfort. All this raises numerous questions among professionals and has already ignited a discussion in scientific publications concerned with the pathogenesis of COVID-19. Respiratory failure is a complex clinical problem, many aspects of which remain controversial. However, according to the majority of authors, one of the first objective indicators of the clinical sign of respiratory failure are hypoxemia-associated changes in external respiration. This review addresses some possible causes of hypoxemia in COVID-19.

Genetic Engineering Systems to Study Human Viral Pathogens from the Coronaviridae Family

The COVID-19 pandemic caused by the previously unknown SARS-CoV-2 Betacoronavirus made it extremely important to develop simple and safe cellular systems which allow manipulation of the viral genome and high-throughput screening of its potential inhibitors. In this review, we made an attempt at summarizing the currently existing data on genetic engineering systems used to study not only SARS-CoV-2, but also other viruses from the Coronaviridae family. In addition, the review covers the basic knowledge about the structure and the life cycle of coronaviruses.

Neurological complications and infection mechanism of SARS-COV-2

Currently, SARS-CoV-2 has caused a global pandemic and threatened many lives. Although SARS-CoV-2 mainly causes respiratory diseases, growing data indicate that SARS-CoV-2 can also invade the central nervous system (CNS) and peripheral nervous system (PNS) causing multiple neurological diseases, such as encephalitis, encephalopathy, Guillain-Barré syndrome, meningitis, and skeletal muscular symptoms. Despite the increasing incidences of clinical neurological complications of SARS-CoV-2, the precise neuroinvasion mechanisms of SARS-CoV-2 have not been fully established. In this review, we primarily describe the clinical neurological complications associated with SARS-CoV-2 and discuss the potential mechanisms through which SARS-CoV-2 invades the brain based on the current evidence. Finally, we summarize the experimental models were used to study SARS-CoV-2 neuroinvasion. These data form the basis for studies on the significance of SARS-CoV-2 infection in the brain.

A Review on SARS-CoV-2-Induced Neuroinflammation, Neurodevelopmental Complications, and Recent Updates on the Vaccine Development

Coronavirus disease 2019 (COVID-19) is a devastating viral infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The incidence and mortality of COVID-19 patients have been increasing at an alarming rate. The mortality is much higher in older individuals, especially the ones suffering from respiratory distress, cardiac abnormalities, renal diseases, diabetes, and hypertension. Existing evidence demonstrated that SARS-CoV-2 makes its entry into human cells through angiotensin-converting enzyme 2 (ACE-2) followed by the uptake of virions through cathepsin L or transmembrane protease serine 2 (TMPRSS2). SARS-CoV-2-mediated abnormalities in particular cardiovascular and neurological ones and the damaged coagulation systems require extensive research to develop better therapeutic modalities. As SARS-CoV-2 uses its S-protein to enter into the host cells of several organs, the S-protein of the virus is considered as the ideal target to develop a potential vaccine. In this review, we have attempted to highlight the landmark discoveries that lead to the development of various vaccines that are currently under different stages of clinical progression. Besides, a brief account of various drug candidates that are being tested to mitigate the burden of COVID-19 was also covered. Further, in a dedicated section, the impact of SARS-CoV-2 infection on neuronal inflammation and neuronal disorders was discussed. In summary, it is expected that the content covered in this article help to understand the pathophysiology of COVID-19 and the impact on neuronal complications induced by SARS-CoV-2 infection while providing an update on the vaccine development.

Effects of COVID-19 on vital organs in patients infected with SARS-CoV-2

The world is now facing one of the most devastating public health concern where the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is spreading all over the world initiating from Wuhan, China, started from December, 2019. The World Health Organization (WHO) already announced the situation as pandemic all over the world. According to the webpage of WHO, this SARS-CoV-2 has been spreading all over the world (223 countries, areas or territories) with 126,890,643 confirmed cases of coronavirus disease 2019 (COVID-19) and 2,778,619 confirmed deaths (as of March 30, 2021). Accumulated published documents indicate that the SARS-CoV-2 virus primarily affects the lungs causing hypoxia, which is the leading cause of death. There are many reports describing that with the progress of this disease, many other organs (such as heart, kidney, liver, brain) of the affected person start to malfunction. Though SARS-CoV-2 uses the cell surface receptor angiotensin-converting enzyme 2 (ACE-2) expressed by lungs, cardiovascular system, and kidneys but it is still not clear except for lungs that all these other organs are directly affected by this virus or not. Therefore, the aim of this review is to gather informations about affected/damaged organs or tissues and consequences of this damage in COVID-19 patients.

Cellular and Molecular Effects of SARS-CoV-2 Linking Lung Infection to the Brain

In December 2019, a new viral disease emerged and quickly spread all around the world. In March 2020, the COVID-19 outbreak was classified as a global pandemic and by June 2021, the number of infected people grew to over 170 million. Along with the patients' mild-to-severe respiratory symptoms, reports on probable central nervous system (CNS) effects appeared shortly, raising concerns about the possible long-term detrimental effects on human cognition. It remains unresolved whether the neurological symptoms are caused directly by the SARS-CoV-2 infiltration in the brain, indirectly by secondary immune effects of a cytokine storm and antibody overproduction, or as a consequence of systemic hypoxia-mediated microglia activation. In severe COVID-19 cases with impaired lung capacity, hypoxia is an anticipated subsidiary event that can cause progressive and irreversible damage to neurons. To resolve this problem, intensive research is currently ongoing, which seeks to evaluate the SARS-CoV-2 virus' neuroinvasive potential and the examination of the antibody and autoantibody generation upon infection, as well as the effects of prolonged systemic hypoxia on the CNS. In this review, we summarize the current research on the possible interplay of the SARS-CoV-2 effects on the lung, especially on alveolar macrophages and direct and indirect effects on the brain, with special emphasis on microglia, as a possible culprit of neurological manifestation during COVID-19.

The impact of Parkinson's disease on manifestations and outcomes of Covid-19 patients: A systematic review and meta-analysis

Parkinson's disease (PD) patients who contracted Coronavirus disease 2019 (Covid‐19) had a decline in motor functions; nevertheless, there is limited evidence on whether PD patients have a higher risk for contracting Covid‐19 or have worse outcomes. This is the first systematic review and meta‐analysis to review the impact of PD on the prognosis of Covid‐19 patients. We performed a systematic search through seven electronic databases under the recommendations of the Preferred Reporting Items for Systematic Review and Meta‐analyses statement (PRISMA) guidelines. The R software version 4.0.2 was used to calculate pooled sample sizes and their associated confidence intervals (95%CI). Finally, we included 13 papers in this study. The pooled prevalence rate of Covid‐19 was 2.12% (95%CI: 0.75–5.98). Fever, cough, fatigue and anorexia were the most common symptoms with a rate of 72.72% (95% CI: 57.3 ‐ 92.29), 66.99% (95% CI: 49.08–91.42), 61.58% (95% CI: 46.69–81.21) and 52.55% (95% CI: 35.09–78.68), respectively. The pooled rates were 39.89% (95% CI: 27.09–58.73) for hospitalisation, 4.7% (95% CI: 1.56–14.16) for ICU admission and 25.1% (95%CI: 16.37–38.49) for mortality. On further comparison of hospitalisation and mortality rates among Covid‐19 patients with and without PD, there were no significant differences. In conclusion, the prevalence and prognosis of Covid‐19 patients seem comparable in patients with PD and those without it. The increased hospitalisation and mortality may be attributed to old age and co‐morbidities.

Coronavirus-induced autoimmunity

The pandemic of Coronavirus disease 2019 (COVID-19), caused by a new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spotlighted the link between viral infection and autoimmunity. In this review, we focus on coronavirus-induced autoimmunity based on evidence from experimental animal models, SARS-CoV infection with in vitro studies of molecular mimicry and COVID-19 with several clinical reports of autoimmune manifestations of this disease. Further studies will be needed to better characterize the role of SARS-CoV-2 in the development of autoimmunity.

Murine-β-coronavirus-induced neuropathogenesis sheds light on CNS pathobiology of SARS-CoV2

The pandemic caused by SARS-CoV-2 has caused widespread infection and significant mortality across the globe. Combined virology perspective of SARS-CoV-2 with a deep-rooted understanding of pathophysiological and immunological processes underlying the clinical manifestations of COVID-19 is of prime importance. The characteristic symptom of COVID-19 is respiratory distress with diffused alveolar damage, but emerging evidence suggests COVID-19 might also have neurologic consequences. Dysregulated homeostasis in the lungs has proven to be fatal, but one cannot ignore that the inability to breathe might be due to defects in the respiratory control center of the brainstem. While the mechanism of pulmonary distress has been documented in the literature, awareness of neurological features and their pathophysiology is still in the nascent state. This review makes references to the neuro-immune axis and neuro-invasive potential of SARS-CoV and SARS-CoV2, as well as the prototypic H-CoV strains in human brains. Simultaneously, considerable discussion on relevant experimental evidence of mild to severe neurological manifestations of fellow neurotropic murine-β-CoVs (m-CoVs) in the mouse model will help understand the underpinning mechanisms of Neuro-COVID. In this review, we have highlighted the neuroimmunopathological processes in murine CoVs. While MHV infection in mice and SARS-CoV-2 infection in humans share numerous parallels, there are critical differences in viral recognition and viral entry. These similarities are highlighted in this review, while differences have also been emphasized. Though CoV-2 Spike does not favorably interact with murine ACE2 receptor, modification of murine SARS-CoV2 binding domain or development of transgenic ACE-2 knock-in mice might help in mediating consequential infection and understanding human CoV2 pathogenesis in murine models. While a global animal model that can replicate all aspects of the human disease remains elusive, prior insights and further experiments with fellow m-β-CoV-induced cause-effect experimental models and current human COVID-19 patients data may help to mitigate the SARS-CoV-2-induced multifactorial multi-organ failure.

What HIV in the Brain Can Teach Us About SARS-CoV-2 Neurological Complications?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiologic agent of COVID-19, a disease that as of July 10, 2020, has infected >12 million people and killed >500,000. COVID-19 infection leads to acute respiratory distress syndrome in a subset of patients and is a primary driver of acute morbidity in infected persons. However, it is becoming increasingly clear that SARS-CoV-2 infection drives dysfunction and pathology outside the lungs, including reports of renal, cardiac, and neurological complications. In this study, we summarize the known incidence and evidence of neurological complications associated with SARS-CoV-2 infection and other pathogenic coronaviruses. These studies describe a poorly understood spectrum of COVID-19 central nervous system symptoms, ranging from common and subclinical issues such as anosmia and headache to more concerning reports of stroke and encephalopathy. We discuss potential mechanisms of pathogenesis, including a discussion of how the understanding of neurological complications known to occur in HIV-1 patients may provide insight into SARS-CoV-2-associated neurological manifestations. Specifically, three hypotheses are discussed that are informed by decades of knowledge about HIV pathogenesis in the brain, which include a potential direct viral effect, an indirect viral effect, and/or a neuroimmune axis effect. Individually or in combination these potential effects may contribute to COVID-19 neurological complications.

Infection Mechanism of SARS-COV-2 and Its Implication on the Nervous System

In late December 2019, multiple atypical pneumonia cases resulted in severe acute respiratory syndrome caused by a pathogen identified as a novel coronavirus SARS-CoV-2. The most common coronavirus disease 2019 (COVID-19) symptoms are pneumonia, fever, dry cough, and fatigue. However, some neurological complications following SARS-CoV-2 infection include confusion, cerebrovascular diseases, ataxia, hypogeusia, hyposmia, neuralgia, and seizures. Indeed, a growing literature demonstrates that neurotropism is a common feature of coronaviruses; therefore, the infection mechanisms already described in other coronaviruses may also be applicable for SARS-CoV-2. Understanding the underlying pathogenetic mechanisms in the nervous system infection and the neurological involvement is essential to assess possible long-term neurological alteration of COVID-19. Here, we provide an overview of associated literature regarding possible routes of COVID-19 neuroinvasion, such as the trans-synapse-connected route in the olfactory pathway and peripheral nerve terminals and its neurological implications in the central nervous system.

Evaluating the evidence for direct central nervous system invasion in patients infected with the nCOVID-19 virus

The current nCOVID-19 pandemic is raising several questions in the approximately 25% of patients who present with neurological symptoms. While secondary brain injury from the systemic manifestations of the disease account for the majority of non-specific neurological symptoms that include headache, nausea, and progressive confusion, the question that remains unanswered is does the nCOVID-19 virus use the olfactory mucosa as a portal to directly invade the brain? A second question is how common does direct CNS invasion complicate the classical cardiorespiratory severe form of the disease? We know from previous studies that almost all members of the Corona virus family have neurotropism. We also know from the current pandemic that deteriorating consciousness and cerebrovascular accidents are not uncommon. Several previous scattered case reports, and post-mortem examinations of brain tissue, demonstrated nCOVID-19 nucleic acid in the CSF, and brain tissue, of infected and deceased individuals. We performed a PubMed review of the literature to specifically assess the evidence for the direct CNS invasion by the nCOVID-19 virus. This phenomenon would explain the cerebral oedema and encephalitis, that does occur, and bring Neurosurgeons into the management of these patients by for example directed intra-cranial pressure management post insertion of an intra-cranial pressure monitor. Unfortunately, the answers to these questions were not definitively answered by the research reviewed. While suggestive that direct CNS invasion does occur, the exact scale and manifestations of the problem remains, to date, essentially unknown.

The nervous system-A new territory being explored of SARS-CoV-2

In December 2019, COVID-19 outbroke in Wuhan, then sweeping the mainland of China and the whole world rapidly. On March 4, Beijing Ditan Hospital confirmed the existence of SARS-CoV-2 in the cerebrospinal fluid by gene sequencing, indicating the neurotropic involvement of SARS-CoV-2. Meanwhile, neurological manifestations in the central nervous system, peripheral nervous system and skeletal muscular were also observed, indicating the potential neuroinvasion of SARS-CoV-2. In particular, we focused on its neurological manifestations and specific pathogenesis, as well as its comparison with other viral respiratory infections. Finally, we further summarized the significance of the neuroinvasion and the follow-up issues that need to be paid attention to by scientists, so as to help neurologists understand the influence of SARS-CoV-2 on nervous system better and promote the accurate diagnosis and efficient treatment of COVID-19.

Studying the neuropsychological sequelae of SARS-CoV-2: lessons learned from 35 years of neuroHIV research

The virology of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and the human immune response to the virus are under vigorous investigation. There are now several reports describing neurological symptoms in individuals who develop coronavirus disease 2019 (COVID-19), the syndrome associated with SARS-CoV-2 infection. The prevalence, incidence, and clinical course of these symptoms will become clearer in the coming months and years through epidemiological studies. However, the long-term neurological and cognitive consequence of SARS-CoV-2 infection will remain conjectural for some time and will likely require the creation of cohort studies that include uninfected individuals. Considering the early evidence for neurological involvement in COVID-19 it may prove helpful to compare SARS-CoV-2 with another endemic and neurovirulent virus, human immunodeficiency virus-1 (HIV-1), when designing such cohort studies and when making predictions about neuropsychological outcomes. In this paper, similarities and differences between SARS-CoV-2 and HIV-1 are reviewed, including routes of neuroinvasion, putative mechanisms of neurovirulence, and factors involved in possible long-term neuropsychological sequelae. Application of the knowledge gained from over three decades of neuroHIV research is discussed, with a focus on alerting researchers and clinicians to the challenges in determining the cause of neurocognitive deficits among long-term survivors.

A brief review of the neurological manifestations of the coronavirus disease

INTRODUCTION

It has been demonstrated experimentally that the coronavirus can enter the central nervous system through olfactory nerves and can even reach medulla. Neurological manifestations are observed more frequently in patients with coronavirus disease.

MAIN TEXT

The aim of the review is to seek evidence for infection of the nervous system by the human coronavirus and study the neurological manifestations of the coronavirus and its treatment. A search was done in PubMed, Google Scholar, CrossRef, and Scopus. There is evidence for the coronavirus infection of the nervous system from experimental studies, autopsy reports, and clinical studies. The virus can damage the nervous system either by direct viral damage to the neural cells or by immunopathology. Cerebral edema, neuronal degeneration, encephalitis, meningoencephalitis, acute disseminated encephalomyelitis, Guillain-Barré Syndrome, Bickerstaff's brainstem encephalitis, Miller Fisher syndrome, polyneuritis, toxic encephalopathy, and stroke can occur. The coronavirus has been demonstrated in the cerebrospinal fluid by polymerase chain reaction technique in infected patients. The abnormalities of the coagulation system increase the risk of cerebrovascular disease. Chloroquine analogs, lopinavir/ritonavir combination, remdesivir, dexamethasone, and immunoglobulin have been shown to be useful for the treatment.

CONCLUSION

There is substantial evidence for infection of the nervous system by the different strains of the human coronavirus. The coronavirus enters the nervous system either by the blood or from the olfactory nerves. The neurological diseases correlate with the severity of the coronavirus disease. The treatment is mainly supportive. The reports of patients with encephalitis, encephalomyelitis, and brainstem encephalitis show slow recovery. But a stroke has a high mortality.

Severe acute respiratory syndrome coronavirus 2 may be an underappreciated pathogen of the central nervous system

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a highly contagious respiratory disease referred to as COVID-19. However, emerging evidence indicates that a small but growing number of COVID-19 patients also manifest neurological symptoms, suggesting that SARS-CoV-2 may infect the nervous system under some circumstances. SARS-CoV-2 primarily enters the body through the epithelial lining of the respiratory and gastrointestinal tracts, but under certain conditions this pleiotropic virus may also infect peripheral nerves and gain entry into the central nervous system (CNS). The brain is shielded by various anatomical and physiological barriers, most notably the blood-brain barrier (BBB) which functions to prevent harmful substances, including pathogens and pro-inflammatory mediators, from entering the brain. The BBB is composed of highly specialized endothelial cells, pericytes, mast cells and astrocytes that form the neurovascular unit, which regulates BBB permeability and maintains the integrity of the CNS. In this review, potential routes of viral entry and the possible mechanisms utilized by SARS-CoV-2 to penetrate the CNS, either by disrupting the BBB or infecting the peripheral nerves and using the neuronal network to initiate neuroinflammation, are briefly discussed. Furthermore, the long-term effects of SARS-CoV-2 infection on the brain and in the progression of neurodegenerative diseases known to be associated with other human coronaviruses are considered. Although the mechanisms of SARS-CoV-2 entry into the CNS and neurovirulence are currently unknown, the potential pathways described here might pave the way for future research in this area and enable the development of better therapeutic strategies.

Neurological consequences of COVID-19: what have we learned and where do we go from here?

The coronavirus disease-19 (COVID-19) pandemic is an unprecedented worldwide health crisis. COVID-19 is caused by SARS-CoV-2, a highly infectious pathogen that is genetically similar to SARS-CoV. Similar to other recent coronavirus outbreaks, including SARS and MERS, SARS-CoV-2 infected patients typically present with fever, dry cough, fatigue, and lower respiratory system dysfunction, including high rates of pneumonia and acute respiratory distress syndrome (ARDS); however, a rapidly accumulating set of clinical studies revealed atypical symptoms of COVID-19 that involve neurological signs, including headaches, anosmia, nausea, dysgeusia, damage to respiratory centers, and cerebral infarction. These unexpected findings may provide important clues regarding the pathological sequela of SARS-CoV-2 infection. Moreover, no efficacious therapies or vaccines are currently available, complicating the clinical management of COVID-19 patients and emphasizing the public health need for controlled, hypothesis-driven experimental studies to provide a framework for therapeutic development. In this mini-review, we summarize the current body of literature regarding the central nervous system (CNS) effects of SARS-CoV-2 and discuss several potential targets for therapeutic development to reduce neurological consequences in COVID-19 patients.

SARS-CoV-2, immunosenescence and inflammaging: partners in the COVID-19 crime

Pneumonia outbreak in the city of Wuhan, China, prompted the finding of a novel strain of severe acute respiratory syndrome virus (SARS-CoV-2). Here, we discuss potential long-term consequences of SARS-CoV-2 infection, and its possibility to cause permanent damage to the immune system and the central nervous system. Advanced chronological age is one of the main risk factors for the adverse outcomes of COVID-19, presumably due to immunosenescence and chronic low-grade inflammation, both characteristic of the elderly. The combination of viral infection and chronic inflammation in advanced chronological age might cause multiple detrimental unforeseen consequences for the predisposition and severity of neurodegenerative diseases and needs to be considered so that we can be prepared to deal with future outcomes of the ongoing pandemic.

SAMHD1 as the Potential Link Between SARS-CoV-2 Infection and Neurological Complications

The recent pandemic of coronavirus infectious illness 2019 (COVID19) triggered by SARS-CoV-2 has rapidly spread around the globe, generating in severe events an acute, highly lethal pneumonia and death. In the past two hitherto similar CoVs, the severe acute respiratory syndrome CoV (SARS-CoV-1) and Middle East respiratory syndrome CoV (MERS-CoV) also gained universal attention as they produced clinical symptoms similar to those of SARS-CoV-2 utilizing angiotensin-converting enzyme 2 (ACE2) receptor and dipeptidyl peptidase 4 (DPP4) to go into the cells. COVID-19 may also present with overtly neurological symptoms. The proper understanding of the expression and dissemination of ACE2 in central and peripheral nerve systems is crucial to understand better the neurological morbidity caused by COVID-19. Using the STRING bioinformatic tool and references through text mining tools associated to Coronaviruses, we identified SAMHD1 as the probable link to neurological symptoms. Paralleled to the response to influenza A virus and, specifically, respiratory syncytial virus, SARS-CoV-2 evokes a response that needs robust induction of a subclass of cytokines, including the Type I and, obviously, Type III interferons as well as a few chemokines. We correlate ACE2 to the pathogenesis and neurologic complications of COVID-19 and found that SAMHD1 links to NF-κB pathway. No correlation was found with other molecules associated with Coronavirus infection, including ADAR, BST2, IRF3, IFITM3, ISG15, MX1, MX2, RNASEL, RSAD2, and VPRBP. We suggest that SAMHD1 is the molecule that may be behind the mechanisms of the neurological complications associated with COVID-19.

Experimental Models for the Study of Central Nervous System Infection by SARS-CoV-2

INTRODUCTION

The response to the SARS-CoV-2 coronavirus epidemic requires increased research efforts to expand our knowledge of the disease. Questions related to infection rates and mechanisms, the possibility of reinfection, and potential therapeutic approaches require us not only to use the experimental models previously employed for the SARS-CoV and MERS-CoV coronaviruses but also to generate new models to respond to urgent questions.

DEVELOPMENT

We reviewed the different experimental models used in the study of central nervous system (CNS) involvement in COVID-19 both in different cell lines that have enabled identification of the virus' action mechanisms and in animal models (mice, rats, hamsters, ferrets, and primates) inoculated with the virus. Specifically, we reviewed models used to assess the presence and effects of SARS-CoV-2 on the CNS, including neural cell lines, animal models such as mouse hepatitis virus CoV (especially the 59 strain), and the use of brain organoids.

CONCLUSION

Given the clear need to increase our understanding of SARS-CoV-2, as well as its potential effects on the CNS, we must endeavor to obtain new information with cellular or animal models, with an appropriate resemblance between models and human patients.

Post-traumatic stress disorder: A differential diagnostic consideration for COVID-19 survivors

Objective: SARS-CoV-2 infection and its oft-associated illness COVID-19 may lead to neuropsychological deficits, either through direct mechanisms (i.e., neurovirulance) or indirect mechanisms, most notably complications caused by the virus (e.g., stroke) or medical procedures (e.g., intubation). The history of past human coronavirus outbreaks resulting in similar health emergencies suggests there will be a substantial prevalence of post-traumatic stress disorder (PTSD) among COVID-19 survivors. To prepare neuropsychologists for the difficult task of differentiating PTSD-related from neuropathology-related deficits in the oncoming wave of COVID-19 survivors, we integrate research across a spectrum of related areas.Methods: Several areas of literature were reviewed: psychiatric, neurologic, and neuropathological outcomes of SARS and MERS patients; neurological outcomes in COVID-19 survivors; PTSD associated with procedures common to COVID-19 patients; and differentiating neuropsychological deficits due to PTSD from those due to acquired brain injuries in other patient groups.Conclusions: Heightened risk of PTSD occurred in MERS and SARS survivors. While data concerning COVID-19 is lacking, PTSD is known to occur in patient groups who undergo similar hospital courses, including ICU survivors, patients who are intubated and mechanically ventilated, and those that experience delirium. Research with patients who develop PTSD in the context of mild traumatic brain injury further suggests that PTSD may account for some or all of a patient's subjective cognitive complaints and neuropsychological test performance. Recommendations are provided for assessing PTSD in the context of COVID-19.

The potential role of the carotid body in COVID-19

The carotid body (CB) plays a contributory role in the pathogenesis of various respiratory, cardiovascular, renal, and metabolic diseases through reflex changes in ventilation and sympathetic output. On the basis of available data about peripheral arterial chemoreception and severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), a potential involvement in the coronavirus disease 2019 (COVID-19) may be hypothesized through different mechanisms. The CB could be a site of SARS-CoV-2 invasion, due to local expression of its receptor [angiotensin-converting enzyme (ACE) 2] and an alternative route of nervous system invasion, through retrograde transport along the carotid sinus nerve. The CB function could be affected by COVID-19-induced inflammatory/immune reactions and/or ACE1/ACE2 imbalance, both at local or systemic level. Increased peripheral arterial chemosensitivity and reflex sympatho-activation may contribute to the increased morbidity and mortality in COVID-19 patients with respiratory, cardiovascular, renal, or metabolic comorbidities.

Spectrum of neuropsychiatric manifestations in COVID-19

Corona Virus Disease 2019 (COVID-19) emerged in December 2019 from Wuhan, China. It typically presents with mild upper respiratory tract infection symptoms and may have life threatening complications, including acute respiratory distress syndrome, acute stroke, myocardial infarction, kidney failure, shock, and even death. Coronavirus infections are known to have neuroinvasive potential with consequent neuropsychiatric manifestations. We analyzed COVID-19 adult patients in the TriNetX database, which is a global health collaborative clinical research platform collecting real-time electronic medical records data from a network of health care organizations (HCOs) from January 20, 2020 to June 10th, 2020. 40,469 patients were diagnosed with COVID-19 among whom 9086 (22.5%) patients had neuropsychiatric manifestations. The most common neurologic manifestations included headache (3.7%) and sleep disorders (3.4%), Encephalopathy (2.3%), Stroke and transient ischemic attack (TIA) (1.0%) and 0.6% had seizures. Most common psychiatric manifestations included anxiety and other related disorders (4.6%), mood disorders (3.8%), while 0.2% patients had suicidal ideation. Early recognition and prompt management of neuropsychiatric manifestations in these patients have a potential to decrease overall morbidity and mortality.

Psychiatric face of COVID-19

The Coronavirus Disease 2019 (COVID-19) represents a severe multiorgan pathology which, besides cardio-respiratory manifestations, affects the function of the central nervous system (CNS). The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), similarly to other coronaviruses demonstrate neurotropism; the viral infection of the brain stem may complicate the course of the disease through damaging central cardio-respiratory control. The systemic inflammation as well as neuroinflammatory changes are associated with massive increase of the brain pro-inflammatory molecules, neuroglial reactivity, altered neurochemical landscape and pathological remodelling of neuronal networks. These organic changes, emerging in concert with environmental stress caused by experiences of intensive therapy wards, pandemic fears and social restrictions, promote neuropsychiatric pathologies including major depressive disorder, bipolar disorder (BD), various psychoses, obsessive-compulsive disorder and post-traumatic stress disorder. The neuropsychiatric sequelae of COVID-19 represent serious clinical challenge that has to be considered for future complex therapies.

COVID-19: A promising cure for the global panic

The novel Coronavirus disease 2019 (COVID-19) is caused by SARS-CoV-2, which is the causative agent of a potentially fatal disease that is of great global public health concern. The outbreak of COVID-19 is wreaking havoc worldwide due to inadequate risk assessment regarding the urgency of the situation. The COVID-19 pandemic has entered a dangerous new phase. When compared with SARS and MERS, COVID-19 has spread more rapidly, due to increased globalization and adaptation of the virus in every environment. Slowing the spread of the COVID-19 cases will significantly reduce the strain on the healthcare system of the country by limiting the number of people who are severely sick by COVID-19 and need hospital care. Hence, the recent outburst of COVID-19 highlights an urgent need for therapeutics targeting SARS-CoV-2. Here, we have discussed the structure of virus; varying symptoms among COVID-19, SARS, MERS and common flu; the probable mechanism behind the infection and its immune response. Further, the current treatment options, drugs available, ongoing trials and recent diagnostics for COVID-19 have been discussed. We suggest traditional Indian medicinal plants as possible novel therapeutic approaches, exclusively targeting SARS-CoV-2 and its pathways.

SARS-CoV-2 Shedding from Asymptomatic Patients: Contribution of Potential Extrapulmonary Tissue Reservoirs

The ongoing pandemic COVID-19, caused by SARS-CoV-2, has already resulted in more than 3 million cases and more than 200,000 deaths globally. Significant clinical presentations of COVID-19 include respiratory symptoms and pneumonia. In a minority of patients, extrapulmonary organs (central nervous system, eyes, heart, and gut) are affected, with detection of viral RNA in bodily secretions (stool, tears, and saliva). Infection of such extrapulmonary organs may serve as a reservoir for SARS-CoV-2, representing a potential source of viral shedding after the cessation of respiratory symptoms in recovered patients or in asymptomatic individuals. It is extremely important to understand this phenomenon, as individuals with intermittent virus shedding could be falsely identified as reinfected and may benefit from ongoing antiviral treatment. The potential of SARS-CoV-2 infection to rapidly disseminate and infect extrapulmonary organs is likely mediated through the nonstructural and accessory proteins of SARS-CoV-2, which act as ligands for host cells, and through evasion of host immune responses. The focus of this perspective is the extrapulmonary tissues affected by SARS-CoV-2 and the potential implications of their involvement for disease pathogenesis and the development of medical countermeasures.

COVID-19 Immunopathology and the Central Nervous System: Implication for Multiple Sclerosis and Other Autoimmune Diseases with Associated Demyelination

In the frame of the coronavirus disease 2019 (COVID-19) pandemic, recent reports on SARS-CoV-2 potential neuroinvasion placed neurologists on increased alertness in order to assess early neurological manifestations and their potentially prognostic value for the COVID-19 disease. Moreover, the management of chronic neurological diseases, such as Multiple Sclerosis (MS), underwent guided modifications, such as an Extended Interval Dose (EID) of Disease-Modifying Treatment (DMT) administration, in order to minimize patients' exposure to the health system, thus reducing the risk of SARS-CoV-2 infection. In this review, we summarize existing evidence of key immune pathways that the SARS-CoV-2 modifies during COVID-19 and the relevant implication for MS and other autoimmune diseases with associated demyelination (such as Systemic lupus erythematosus and Antiphospholipid syndrome), including the context of potential neuroinvasion by SARS-Cov-2 and the alterations that DMT induces to the immune system. Moreover we hereby aim to provide an overview of the possible consequences that COVID-19 may carry for the Central Nervous System (CNS) in People with MS (PwMS) and other demyelinating diseases, which are likely to pose challenges for treating Neurologists with respect to the long-term disease management of these diseases.

The neuroinvasive potential of SARS-CoV2 may play a role in the respiratory failure of COVID-19 patients

Following the severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), another highly pathogenic coronavirus named SARS-CoV-2 (previously known as 2019-nCoV) emerged in December 2019 in Wuhan, China, and rapidly spreads around the world. This virus shares highly homological sequence with SARS-CoV, and causes acute, highly lethal pneumonia coronavirus disease 2019 (COVID-19) with clinical symptoms similar to those reported for SARS-CoV and MERS-CoV. The most characteristic symptom of patients with COVID-19 is respiratory distress, and most of the patients admitted to the intensive care could not breathe spontaneously. Additionally, some patients with COVID-19 also showed neurologic signs, such as headache, nausea, and vomiting. Increasing evidence shows that coronaviruses are not always confined to the respiratory tract and that they may also invade the central nervous system inducing neurological diseases. The infection of SARS-CoV has been reported in the brains from both patients and experimental animals, where the brainstem was heavily infected. Furthermore, some coronaviruses have been demonstrated able to spread via a synapse-connected route to the medullary cardiorespiratory center from the mechanoreceptors and chemoreceptors in the lung and lower respiratory airways. Considering the high similarity between SARS-CoV and SARS-CoV2, it remains to make clear whether the potential invasion of SARS-CoV2 is partially responsible for the acute respiratory failure of patients with COVID-19. Awareness of this may have a guiding significance for the prevention and treatment of the SARS-CoV-2-induced respiratory failure.

The emergence of a novel coronavirus (SARS-CoV-2) disease and their neuroinvasive propensity may affect in COVID-19 patients

An outbreak of a novel coronavirus (SARS‐CoV‐2) infection has recently emerged and rapidly spreading in humans causing a significant threat to international health and the economy. Rapid assessment and warning are crucial for an outbreak analysis in response to serious public health. SARS‐CoV‐2 shares highly homological sequences with SARS‐CoVs causing highly lethal pneumonia with respiratory distress and clinical symptoms similar to those reported for SARS‐CoV and MERS‐CoV infections. Notably, some COVID‐19 patients also expressed neurologic signs like nausea, headache, and vomiting. Several studies have reported that coronaviruses are not only causing respiratory illness but also invade the central nervous system through a synapse‐connected route. SARS‐CoV infections are reported in both patients and experimental animals' brains. Interestingly, some COVID‐19 patients have shown the presence of SARS‐CoV‐2 virus in their cerebrospinal fluid. Considering the similarities between SARS‐CoV and SARS‐CoV‐2 in various aspects, it remains to clarify whether the potent invasion of SARS‐CoV‐2 may affect in COVID‐19 patients. All these indicate that more detailed criteria are needed for the treatment and the prevention of SARS‐CoV‐2 infected patients. In the absence of potential interventions for COVID‐19, there is an urgent need for an alternative strategy to control the spread of this disease.

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.

Titration of human coronaviruses, HcoV-229E and HCoV-OC43, by an indirect immunoperoxidase assay

Calculation of infectious viral titers represents a basic and essential experimental approach for virologists. Classical plaque assays cannot be used for viruses that do not cause significant cytopathic effects, which is the case for strains 229E and OC43 of human coronavirus (HCoV). An alternative indirect immunoperoxidase assay (IPA) is herein described for the detection and titration of these viruses. Susceptible cells are inoculated with serial logarithmic dilutions of samples in a 96-well plate. After viral growth, viral detection by IPA yields the infectious virus titer, expressed as "Tissue Culture Infectious Dose" (TCID50). This represents the dilution of a virus-containing sample at which half of a series of laboratory wells contain replicating virus. This technique is a reliable method for the titration of HCoV in biological samples (cells, tissues, or fluids).

Detection of antibodies against SARS-CoV in serum from SARS-infected donors with ELISA and Western blot

Recombinant fragments of S proteins from the Severe Acute Respiratory Syndrome (SARS) coronavirus (SARA-CoV) were generated and used in a Western blot (WB) assay that was compared to a commercial SARS ELISA method. In 85% of confirmed SARS cases (n = 20), the S2 recombinant fragment based WB was positive and this was comparable to the commercial ELISA using heat killed SARS-CoV. WB using the other four recombinant fragments in confirmed SARS cases generated lower rates of detection (S1--75%, S1-N--25%, S1-C--55%). Evaluation of sera from healthy controls (n = 60) resulted in two weakly positive ELISA results with the remainder being negative while the S2 protein WB demonstrated three positive results from the 20 controls with a history of SARS contact and no positive results in 40 noncontact controls. A discrepancy between the ELISA and S2 WB arose when evaluating per-2003 sera from individuals (n = 10) with SARS-like symptoms (ELISA--100% positive, S2 WB--30% positive). These data suggest that the S2 WB assay may be particularly useful in ELISA-negative SARS cases and in some ELISA-positive non-SARS cases.

T-cell epitopes in severe acute respiratory syndrome (SARS) coronavirus spike protein elicit a specific T-cell immune response in patients who recover from SARS

The immunogenicity of HLA-A2-restricted T-cell epitopes in the S protein of the Severe acute respiratory syndrome coronavirus (SARS-CoV) and of human coronavirus strain 229e (HCoV-229e) was analyzed for the elicitation of a T-cell immune response in donors who had fully recovered from SARS-CoV infection. We employed online database analysis to compare the differences in the amino acid sequences of the homologous T epitopes of HCoV-229e and SARS-CoV. The identified T-cell epitope peptides were synthesized, and their binding affinities for HLA-A2 were validated and compared in the T2 cell system. The immunogenicity of all these peptides was assessed by using T cells obtained from donors who had fully recovered from SARS-CoV infection and from healthy donors with no history of SARS-CoV infection. HLA-A2 typing by indirect immunofluorescent antibody staining showed that 51.6% of SARS-CoV-infected patients were HLA-A2 positive. Online database analysis and the T2 cell binding test disclosed that the number of HLA-A2-restricted immunogenic epitopes of the S protein of SARS-CoV was decreased or even lost in comparison with the homologous sequences of the S protein of HCoV-229e. Among the peptides used in the study, the affinity of peptides from HCoV-229e (H77 and H881) and peptides from SARS-CoV (S978 and S1203) for binding to HLA-A2 was higher than that of other sequences. The gamma interferon (IFN-gamma) release Elispot assay revealed that only SARS-CoV-specific peptides S1203 and S978 induced a high frequency of IFN-gamma-secreting T-cell response in HLA-A2(+) donors who had fully recovered from SARS-CoV infection; such a T-cell epitope-specific response was not observed in HLA-A2(+) healthy donors or in HLA-A2(-) donors who had been infected with SARS-CoV after full recovery. Thus, T-cell epitopes S1203 and S978 are immunogenic and elicit an overt specific T-cell response in HLA-A2(+) SARS-CoV-infected patients.

Infection of human oligodendroglioma cells by a recombinant measles virus expressing enhanced green fluorescent protein

One of the hallmarks of the human CNS disease subacute sclerosing panencephalitis (SSPE) is a high level of measles virus (MV) infection of oligodendrocytes. It is therefore surprising that there is only one previous report of MV infection of rat oligodendrocytes in culture and no reports of human oligodendrocyte infection in culture. In an attempt to develop a model system to study MV infection of oligodendrocytes, time-lapse confocal microscopy, immunocytochemistry, and electron microscopy (EM) were used to study infection of the human oligodendroglioma cell line, MO3.13. A rat oligodendrocyte cell line, OLN-93, was also studied as a control. MO3.13 cells were shown to be highly susceptible to MV infection and virus budding was observed from the surface of infected MO3.13 cells by EM. Analysis of the infection in real time and by immunocytochemistry revealed that virus spread occurred by cell-to-cell fusion and was also facilitated by virus transport in cell processes. MO3.13 cells were shown to express CD46, a MV receptor, but were negative for the recently discovered MV receptor, signaling leucocyte activation molecule (SLAM). Immunohistochemical studies on SSPE tissue sections demonstrated that CD46 was also expressed on populations of human oligodendrocytes. SLAM expression was not detected on oligodendrocytes. These studies, which are the first to show MV infection of human oligodendrocytes in culture, show that the cells are highly susceptible to MV infection and this model cell line has been used to further our understanding of MV spread in the CNS.

Molecular determinants of species specificity in the coronavirus receptor aminopeptidase N (CD13): influence of N-linked glycosylation

Aminopeptidase N (APN), a 150-kDa metalloprotease also called CD13, serves as a receptor for serologically related coronaviruses of humans (human coronavirus 229E [HCoV-229E]), pigs, and cats. These virus-receptor interactions can be highly species specific; for example, the human coronavirus can use human APN (hAPN) but not porcine APN (pAPN) as its cellular receptor, and porcine coronaviruses can use pAPN but not hAPN. Substitution of pAPN amino acids 283 to 290 into hAPN for the corresponding amino acids 288 to 295 introduced an N-glycosylation sequon at amino acids 291 to 293 that blocked HCoV-229E receptor activity of hAPN. Substitution of two amino acids that inserted an N-glycosylation site at amino acid 291 also resulted in a mutant hAPN that lacked receptor activity because it failed to bind HCoV-229E. Single amino acid revertants that removed this sequon at amino acids 291 to 293 but had one or five pAPN amino acid substitution(s) in this region all regained HCoV-229E binding and receptor activities. To determine if other N-linked glycosylation differences between hAPN, feline APN (fAPN), and pAPN account for receptor specificity of pig and cat coronaviruses, a mutant hAPN protein that, like fAPN and pAPN, lacked a glycosylation sequon at 818 to 820 was studied. This sequon is within the region that determines receptor activity for porcine and feline coronaviruses. Mutant hAPN lacking the sequon at amino acids 818 to 820 maintained HCoV-229E receptor activity but did not gain receptor activity for porcine or feline coronaviruses. Thus, certain differences in glycosylation between coronavirus receptors from different species are critical determinants in the species specificity of infection.

Analysis of gene expression in mutiple sclerosis lesions using cDNA microarrays

In multiple sclerosis (MS) patients, a coordinated attack of the immune system against the primary constituents of oligodendrocytes and/or the myelin sheath of oligodendrocytes results in the formation of lesions in the brain and spinal cord. Thus far, however, a limited number of genes that potentially contribute to lesion pathology have been identified. Using cDNA microarray technology, we have performed experiments on MS tissue monitoring the expression pattern of over 5,000 genes and compared the gene expression profile of normal white matter with that found in acute lesions from the brain of a single MS patient. Sixty-two differentially expressed genes were identified, including the Duffy chemokine receptor, interferon regulatory factor-2, and tumor necrosis factor alpha receptor-2 among others. Thus, cDNA microarray technology represents a powerful new tool for the identification of genes not previously associated with the MS disease process.

Persistent infection of human oligodendrocytic and neuroglial cell lines by human coronavirus 229E

Human coronaviruses (HuCV) cause common colds. Previous reports suggest that these infectious agents may be neurotropic in humans, as they are for some mammals. With the long-term aim of providing experimental evidence for the neurotropism of HuCV and the establishment of persistent infections in the nervous system, we have evaluated the susceptibility of various human neural cell lines to acute and persistent infection by HuCV-229E. Viral antigen, infectious virus progeny and viral RNA were monitored during both acute and persistent infections. The astrocytoma cell lines U-87 MG, U-373 MG, and GL-15, as well as neuroblastoma SK-N-SH, neuroglioma H4, and oligodendrocytic MO3.13 cell lines, were all susceptible to an acute infection by HuCV-229E. The CHME-5 immortalized fetal microglial cell line was not susceptible to infection by this virus. The MO3.13 and H4 cell lines also sustained a persistent viral infection, as monitored by detection of viral antigen and infectious virus progeny. Sequencing of the S1 gene from viral RNA after approximately 130 days of infection showed two point mutations, suggesting amino acid changes during persistent infection of MO3.13 cells but none for H4 cells. Thus, persistent in vitro infection did not generate important changes in the S1 portion of the viral spike protein, which was shown for murine coronaviruses to bear hypervariable domains and to interact with cellular receptor. These results are consistent with the potential persistence of HuCV-229E in cells of the human nervous system, such as oligodendrocytes and possibly neurons, and the virus's apparent genomic stability.

Persistent infection of neural cell lines by human coronaviruses

Human coronaviruses (HCV) have been associated mainly with infections of the respiratory tract. Accumulating evidence from in vitro and in vivo observations is consistent with the neurotropism of these viruses in humans. To verify the possibility of a persistent infection within the central nervous system (CNS), various human cell lines of neural origin were tested for their ability to maintain chronic infection by both known strains of HCV, OC43 and 229E. Production of infectious progeny virions was monitored by an immunoperoxydase assay on a susceptible cell line and viral RNA was observed after RT-PCR. Astrocytic cell lines U-373 MG and U-87 MG did not sustain a persistent HCV-229E infection, even though they were susceptible to an acute infection by this virus. On the other hand, these two cell lines could maintain a persistent infection by HCV-OC43 for as many as 25 cell passages (about 130 days of culture). Relatively stable titers of infectious viral particles, as well as apparently constant amounts of viral RNA were detected throughout the persistent infection of U-87 MG cells. However, persistent infection of U-373 MG cells was accompanied by the detection of infectious viral particles from passage 0 to passage 13 and then from passage 20 to the end of the experiment. This gap in the production of infectious virions was correlated by a drop in the apparent amount of viral RNA detected at passages 15 and 20. These results confirm the ability of HCV-OC43 to persistently infect cells of an astrocytic lineage and, together with our previous observations of HCV infection of primary cultures of human astrocytes and the detection of HCV RNA in human brains, are consistent with the possibility that this human coronavirus could persist in the human CNS by targeting astrocytes.

Involvement of aminopeptidase N (CD13) in infection of human neural cells by human coronavirus 229E

Attachment to a cell surface receptor can be a major determinant of virus tropism. Previous studies have shown that human respiratory coronavirus HCV-229E uses human aminopeptidase N (hAPN [CD13]) as its cellular receptor for infection of lung fibroblasts. Although human coronaviruses are recognized respiratory pathogens, occasional reports have suggested their possible neurotropism. We have previously shown that human neural cells, including glial cells in primary cultures, are susceptible to human coronavirus infection in vitro (A. Bonavia, N. Arbour, V. W. Yong, and P. J. Talbot, J. Virol. 71:800-806, 1997). However, the only reported expression of hAPN in the nervous system is at the level of nerve synapses. Therefore, we asked whether hAPN is utilized as a cellular receptor for infection of these human neural cell lines. Using flow cytometry, we were able to show the expression of hAPN on the surfaces of various human neuronal and glial cell lines that are susceptible to HCV-229E infection. An hAPN-specific monoclonal antibody (WM15), but not control antibody, inhibited the attachment of radiolabeled HCV-229E to astrocytic, neuronal, and oligodendrocytic cell lines. A correlation between the apparent amount of cell surface hAPN and the level of virus attachment was observed. Furthermore, the presence of WM15 inhibited virus infection of these cell lines, as detected by indirect immunofluorescence. These results indicate that hAPN (CD13) is expressed on neuronal and glial cell lines in vitro and serves as the receptor for infection by HCV-229E. This further strengthens the neurotropic potential of this human respiratory virus.

Infection of primary cultures of human neural cells by human coronaviruses 229E and OC43

We evaluated the ability of human coronaviruses to infect primary cultures of human neural cells. Double immunofluorescence with antibodies to virus and cell markers showed infection of fetal astrocytes and of adult microglia and astrocytes by strain OC43. RNA amplification revealed infection of fetal astrocytes, adult microglia, and a mixed culture of adult oligodendrocytes and astrocytes by strain 229E. Infectious virus was released only from fetal astrocytes, with higher titers for OC43. Human coronaviruses have the capacity to infect some cells of the central nervous system, although infection of adult cells appears abortive.

Myelin basic protein and human coronavirus 229E cross-reactive T cells in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating neurological disease in which autoreactive T lymphocytes sensitized to myelin components of the central nervous system are postulated to contribute to pathogenesis. The possible relevance of molecular mimicry between a human coronavirus and the myelin basic protein component of myelin in the generation of this autoimmune reaction was evaluated. Myelin basic protein- and virus-reactive T-cell lines were established from 16 MS patients and 14 healthy donors and shown to be mostly CD4+. In contrast to healthy donors, several T-cell lines isolated from MS patients showed cross-reactivity between myelin and coronavirus antigens. Overall, 29% of T-cell lines from MS patients (10 donors) but only 1.3% of T-cell lines from normal control subjects (2 donors) showed an HLA-DR-restricted cross-reactive pattern of antigen activation after in vitro selection with either myelin basic protein or human coronavirus strain 229E antigens. Moreover, reciprocal reactivities were only observed in MS patients (4 donors). This establishes molecular mimicry between a common viral pathogen, such as this human coronavirus, and myelin as a possible immunopathological mechanism in MS and is consistent with the possible involvement of more than one infectious pathogen as an environmental trigger of disease.