Disassociation between the in vitro and in vivo effects of nitric oxide on a neurotropic murine coronavirus

Gaseous nitric oxide failed to inhibit the replication cycle of SARS-CoV-2 in vitro

Nitric oxide (NO) has been shown to have antimicrobial activity in vitro and in some in vivo models, while the virucidal activity of NO remains elusive. Some studies using NO donors have suggested that NO could be a potential candidate to treat SARS-CoV infection. The Covid-19 pandemic raised the hypothesis that NO gas might have an impact on Sars-CoV-2 replication cycle and might be considered as a candidate therapy to treat COVID-19. To our knowledge, there are no in vitro preclinical studies demonstrating a virucidal effect of gaseous NO on SARS-CoV-2. This study aims to determine whether gaseous NO has an impact on the replication cycle of SARS-CoV-2 in vitro. To that end, SARS-CoV-2 infected epithelial (VeroE6) and pulmonary (A549-hACE2) cells were treated with repeated doses of gaseous NO at different concentrations known to be efficient against bacteria. Our results show that exposing SARS-CoV-2 infected-cells to NO gas even at high doses (160 ppm, 6 h) does not influence the replication cycle of the virus in vitro. We report here that NO gas has no antiviral properties in vitro on SARS-COV-2. Therefore, there is no rationale for its usage in clinical settings to treat COVID-19 patients for direct antiviral purposes, which does not exclude other potential physiological benefits of this gas.

On the anti-correlation between COVID-19 infection rate and natural UV light in the UK

While it is well established that the rate of COVID-19 infections can be suppressed by social distancing, environmental effects may also affect it. We consider the hypothesis that natural Ultra-Violet (UV) light is reducing COVID-19 infections by enhancing human immunity through increasing levels of Vitamin-D and Nitric Oxide or by suppressing the virus itself. We focus on the United Kingdom (UK), by examining daily COVID-19 infections (F) and UV Index (UVI) data from 23 March 2020 to 10 March 2021. We find an intriguing empirical anti-correlation between log10(F) and log10(UVI) with a correlation coefficient of -0.934 from 11 May 2020 (when the first UK lockdown ended) to 10 March 2021. The anti-correlation may reflect causation with other factors which are correlated with the UVI. We advocate that UVI should be added as a parameter in modelling the pattern of COVID-19 infections and deaths. We started quantifying such correlations in other countries and regions.

Application Route and Immune Status of the Host Determine Safety and Oncolytic Activity of Oncolytic Coxsackievirus B3 Variant PD-H

The coxsackievirus B3 strain PD-0 has been proposed as a new oncolytic virus for the treatment of colorectal carcinoma. Here, we generated a cDNA clone of PD-0 and analyzed the virus PD-H, newly generated from this cDNA, in xenografted and syngenic models of colorectal cancer. Replication and cytotoxic assays revealed that PD-H replicated and lysed colorectal carcinoma cell lines in vitro as well as PD-0. Intratumoral injection of PD-H into subcutaneous DLD-1 tumors in nude mice resulted in strong inhibition of tumor growth and significantly prolonged the survival of the animals, but virus-induced systemic infection was observed in one of the six animals. In a syngenic mouse model of subcutaneously growing Colon-26 tumors, intratumoral administration of PD-H led to a significant reduction of tumor growth, the prolongation of animal survival, the prevention of tumor-induced cachexia, and the elevation of CD3+ and dendritic cells in the tumor microenvironment. No virus-induced side effects were observed. After intraperitoneal application, PD-H induced weak pancreatitis and myocarditis in immunocompetent mice. By equipping the virus with target sites of miR-375, which is specifically expressed in the pancreas, organ infections were prevented. Moreover, employment of this virus in a syngenic mouse model of CT-26 peritoneal carcinomatosis resulted in a significant reduction in tumor growth and an increase in animal survival. The results demonstrate that the immune status of the host, the route of virus application, and the engineering of the virus with target sites of suitable microRNAs are crucial for the use of PD-H as an oncolytic virus.

Nitric oxide for the prevention and treatment of viral, bacterial, protozoal and fungal infections

Although the antimicrobial potential of nitric oxide (NO) is widely published, it is little used clinically. NO is a key signalling molecule modulating vascular, neuronal, inflammatory and immune responses. Endogenous antimicrobial activity is largely mediated by high local NO concentrations produced by cellular inducible nitric oxide synthase, and by derivative reactive nitrogen oxide species including peroxynitrite and S-nitrosothiols. NO may be taken as dietary substrate (inorganic nitrate, L-arginine), and therapeutically as gaseous NO, and transdermal, sublingual, oral, intranasal and intravenous nitrite or nitrate. Numerous preclinical studies have demonstrated that NO has generic static and cidal activities against viruses (including β-coronaviruses such as SARS-CoV-2), bacteria, protozoa and fungi/yeasts  in vitro. Therapeutic effects have been seen in animal models  in vivo, and phase II trials have demonstrated that NO donors can reduce microbial infection. Nevertheless, excess NO, as occurs in septic shock, is associated with increased morbidity and mortality. In view of the dose-dependent positive and negative effects of NO, safety and efficacy trials of NO and its donors are needed for assessing their role in the prevention and treatment of infections. Trials should test dietary inorganic nitrate for pre- or post-exposure prophylaxis and gaseous NO or oral, topical or intravenous nitrite and nitrate for treatment of mild-to-severe infections, including due to SARS-CoV-2 (COVID-19). This review summarises the evidence base from  in vitro, in vivo and early phase clinical studies of NO activity in viral, bacterial, protozoal and fungal infections.

Nitric oxide for the prevention and treatment of viral, bacterial, protozoal and fungal infections

Although the antimicrobial potential of nitric oxide (NO) is widely published, it is little used clinically. NO is a key signalling molecule modulating vascular, neuronal, inflammatory and immune responses. Endogenous antimicrobial activity is largely mediated by high local NO concentrations produced by cellular inducible nitric oxide synthase, and by derivative reactive nitrogen oxide species including peroxynitrite and S-nitrosothiols. NO may be taken as dietary substrate (inorganic nitrate, L-arginine), and therapeutically as gaseous NO, and transdermal, sublingual, oral, intranasal and intravenous nitrite or nitrate. Numerous preclinical studies have demonstrated that NO has generic static and cidal activities against viruses (including β-coronaviruses such as SARS-CoV-2), bacteria, protozoa and fungi/yeasts  in vitro. Therapeutic effects have been seen in animal models  in vivo, and phase II trials have demonstrated that NO donors can reduce microbial infection. Nevertheless, excess NO, as occurs in septic shock, is associated with increased morbidity and mortality. In view of the dose-dependent positive and negative effects of NO, safety and efficacy trials of NO and its donors are needed for assessing their role in the prevention and treatment of infections. Trials should test dietary inorganic nitrate for pre- or post-exposure prophylaxis and gaseous NO or oral, topical or intravenous nitrite and nitrate for treatment of mild-to-severe infections, including due to SARS-CoV-2 (COVID-19). This review summarises the evidence base from  in vitro, in vivo and early phase clinical studies of NO activity in viral, bacterial, protozoal and fungal infections.

The recent outbreaks of human coronaviruses: A medicinal chemistry perspective

Coronaviruses (CoVs) infect both humans and animals. In humans, CoVs can cause respiratory, kidney, heart, brain, and intestinal infections that can range from mild to lethal. Since the start of the 21st century, three β-coronaviruses have crossed the species barrier to infect humans: severe-acute respiratory syndrome (SARS)-CoV-1, Middle East respiratory syndrome (MERS)-CoV, and SARS-CoV-2 (2019-nCoV). These viruses are dangerous and can easily be transmitted from human to human. Therefore, the development of anticoronaviral therapies is urgently needed. However, to date, no approved vaccines or drugs against CoV infections are available. In this review, we focus on the medicinal chemistry efforts toward the development of antiviral agents against SARS-CoV-1, MERS-CoV, SARS-CoV-2, targeting biochemical events important for viral replication and its life cycle. These targets include the spike glycoprotein and its host-receptors for viral entry, proteases that are essential for cleaving polyproteins to produce functional proteins, and RNA-dependent RNA polymerase for viral RNA replication.

Physical Exercise as a Multimodal Tool for COVID-19: Could It Be Used as a Preventive Strategy?

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or coronavirus disease 2019 (COVID-19) is a novel coronavirus not previously recognized in humans until late 2019. On 31 December 2019, a cluster of cases of pneumonia of unspecified etiology was reported to the World Health Organization in China. The availability of adequate SARS-CoV-2 drugs is also limited, and the efficacy and safety of these drugs for COVID-2019 pneumonia patients need to be assessed by further clinical trials. For these reasons, there is a need for other strategies against COVID-19 that are capable of prevention and treatment. Physical exercise has proven to be an effective therapy for most chronic diseases and microbial infections with preventive/therapeutic benefits, considering that exercise involves primary immunological mediators and/or anti-inflammatory properties. This review aimed to provide an insight into how the implementation of a physical exercise program against COVID-19 may be a useful complementary tool for prevention, which can also enhance recovery, improve quality of life, and provide immune protection against SARS-CoV-2 virus infection in the long term. In summary, physical exercise training exerts immunomodulatory effects, controls the viral gateway, modulates inflammation, stimulates nitric oxide synthesis pathways, and establishes control over oxidative stress.

Antiviral and Immunomodulatory Effects of Phytochemicals from Honey against COVID-19: Potential Mechanisms of Action and Future Directions

The new coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has recently put the world under stress, resulting in a global pandemic. Currently, there are no approved treatments or vaccines, and this severe respiratory illness has cost many lives. Despite the established antimicrobial and immune-boosting potency described for honey, to date there is still a lack of evidence about its potential role amid COVID-19 outbreak. Based on the previously explored antiviral effects and phytochemical components of honey, we review here evidence for its role as a potentially effective natural product against COVID-19. Although some bioactive compounds in honey have shown potential antiviral effects (i.e., methylglyoxal, chrysin, caffeic acid, galangin and hesperidinin) or enhancing antiviral immune responses (i.e., levan and ascorbic acid), the mechanisms of action for these compounds are still ambiguous. To the best of our knowledge, this is the first work exclusively summarizing all these bioactive compounds with their probable mechanisms of action as antiviral agents, specifically against SARS-CoV-2.

Potential Anti-SARS-CoV-2 Therapeutics That Target the Post-Entry Stages of the Viral Life Cycle: A Comprehensive Review

The coronavirus disease-2019 (COVID-19) pandemic continues to challenge health care systems around the world. Scientists and pharmaceutical companies have promptly responded by advancing potential therapeutics into clinical trials at an exponential rate. Initial encouraging results have been realized using remdesivir and dexamethasone. Yet, the research continues so as to identify better clinically relevant therapeutics that act either as prophylactics to prevent the infection or as treatments to limit the severity of COVID-19 and substantially decrease the mortality rate. Previously, we reviewed the potential therapeutics in clinical trials that block the early stage of the viral life cycle. In this review, we summarize potential anti-COVID-19 therapeutics that block/inhibit the post-entry stages of the viral life cycle. The review presents not only the chemical structures and mechanisms of the potential therapeutics under clinical investigation, i.e., listed in clinicaltrials.gov, but it also describes the relevant results of clinical trials. Their anti-inflammatory/immune-modulatory effects are also described. The reviewed therapeutics include small molecules, polypeptides, and monoclonal antibodies. At the molecular level, the therapeutics target viral proteins or processes that facilitate the post-entry stages of the viral infection. Frequent targets are the viral RNA-dependent RNA polymerase (RdRp) and the viral proteases such as papain-like protease (PLpro) and main protease (Mpro). Overall, we aim at presenting up-to-date details of anti-COVID-19 therapeutics so as to catalyze their potential effective use in fighting the pandemic.

Identification of Viruses in Patients With Postviral Olfactory Dysfunction by Multiplex Reverse-Transcription Polymerase Chain Reaction

Objectives/Hypothesis

To investigate causative viruses in patients with postviral olfactory disorders (PVOD).

Study Design

Case‐control study.

Methods

One hundred fifty‐one consecutive patients diagnosed with PVOD were enrolled, and samples from 38 patients who visited the doctor within 3 months of symptom onset were collected and analyzed. Thirty‐two individuals who underwent surgery for nasal septal deviation during the same time period were collected as the control group. The Sniffin' Sticks psychophysical olfactory test was used to evaluate olfactory function. Olfactory cleft specimens were collected using nasopharyngeal flocked swabs (COPAN FLOQSwabs). Eighteen viruses were tested for with the Luminex xTAG RVP FAST v2 Assay Kit.

Results

Out of the 38 patients with PVOD, rhinoviruses were detected in 13 patients, and coronavirus OC43 was detected in one patient. The frequency of positive virus detection in the patients with anosmia was higher than in those with hyposmia (58.8% vs. 19.0%, P = 0.018). In control group, rhinovirus was identified in one patient (3.1%). Nasal obstruction was the most common symptom and was experienced by 71.0% of patients.

Conclusions

Rhinovirus and coronavirus are more commonly identified in PVOD. Our methods represent an approach to screen for viruses that may be involved in PVOD.

Level of Evidence

4 Laryngoscope, 131:158–164, 2021

Role of cytotoxic T lymphocytes and interferon-γ in coronavirus infection: Lessons from murine coronavirus infections in mice

Murine coronavirus (CoV) is a beta-CoV that infects mice by binding to carcinoembryonic antigen-related cell adhesion molecule 1. Intraperitoneal infection with the murine CoV strain JHM (JHMV) induces acute mild hepatitis in mice. While both innate and acquired immune responses play a significant role in the protection against murine CoV infection in mice, CD8⁺ cytotoxic T lymphocytes (CTLs) and interferon-γ are essential for viral clearance in JHMV-induced hepatitis. In addition, CoVs are characterized by high diversity, caused by mutations, recombination, and gene gain/loss. 25V16G is an immune-escape JHMV variant, which lacks a dominant CTL epitope. By evading immune responses, 25V16G establishes persistent infections, leading to granulomatous serositis in interferon-γ-deficient mice. These examples of CoV-associated pathogenesis in mice might provide useful information on other CoV infections, including coronavirus disease 2019 (COVID-19).

SARS-CoV-2: An Update on Potential Antivirals in Light of SARS-CoV Antiviral Drug Discoveries

Coronaviruses (CoVs) are a group of RNA viruses that are associated with different diseases in animals, birds, and humans. Human CoVs (HCoVs) have long been known to be the causative agents of mild respiratory illnesses. However, two HCoVs associated with severe respiratory diseases are Severe Acute Respiratory Syndrome-CoV (SARS-CoV) and Middle East Respiratory Syndrome-CoV (MERS-CoV). Both viruses resulted in hundreds of deaths after spreading to several countries. Most recently, SARS-CoV-2 has emerged as the third HCoV causing severe respiratory distress syndrome and viral pneumonia (known as COVID-19) in patients from Wuhan, China, in December 2019. Soon after its discovery, SARS-CoV-2 spread to all countries, resulting in millions of cases and thousands of deaths. Since the emergence of SARS-CoV, many research groups have dedicated their resources to discovering effective antivirals that can treat such life-threatening infections. The rapid spread and high fatality rate of SARS-CoV-2 necessitate the quick discovery of effective antivirals to control this outbreak. Since SARS-CoV-2 shares 79% sequence identity with SARS-CoV, several anti-SARS-CoV drugs have shown promise in limiting SARS-CoV-2 replication in vitro and in vivo. In this review, we discuss antivirals described for SARS-CoV and provide an update on therapeutic strategies and antivirals against SARS-CoV-2. The control of the current outbreak will strongly depend on the discovery of effective and safe anti-SARS-CoV-2 drugs.

Anosmia in COVID-19: Mechanisms and Significance

The global pandemic of coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 remains a challenge for prevention due to asymptomatic or paucisymptomatic patients. Anecdotal and preliminary evidence from multiple institutions shows that these patients present with a sudden onset of anosmia without rhinitis. We aim to review the pathophysiology of anosmia related to viral upper respiratory infections and the prognostic implications. Current evidence suggests that SARS-CoV-2-related anosmia may be a new viral syndrome specific to COVID-19 and can be mediated by intranasal inoculation of SARS-CoV-2 into the olfactory neural circuitry. The clinical course of neuroinvasion of SARS-CoV-2 is yet unclear, however an extended follow up of these patients to assess for neurological sequelae including encephalitis, cerebrovascular accidents and long-term neurodegenerative risk may be indicated.

Drug Development and Medicinal Chemistry Efforts toward SARS-Coronavirus and Covid-19 Therapeutics

The COVID-19 pandemic caused by SARS-CoV-2 infection is spreading at an alarming rate and has created an unprecedented health emergency around the globe. There is no effective vaccine or approved drug treatment against COVID-19 and other pathogenic coronaviruses. The development of antiviral agents is an urgent priority. Biochemical events critical to the coronavirus replication cycle provided a number of attractive targets for drug development. These include, spike protein for binding to host cell-surface receptors, proteolytic enzymes that are essential for processing polyproteins into mature viruses, and RNA-dependent RNA polymerase for RNA replication. There has been a lot of ground work for drug discovery and development against these targets. Also, high-throughput screening efforts have led to the identification of diverse lead structures, including natural product-derived molecules. This review highlights past and present drug discovery and medicinal-chemistry approaches against SARS-CoV, MERS-CoV and COVID-19 targets. The review hopes to stimulate further research and will be a useful guide to the development of effective therapies against COVID-19 and other pathogenic coronaviruses.

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.

Porcine reproductive and respiratory syndrome virus induces interleukin-1β through MyD88/ERK/AP-1 and NLRP3 inflammasome in microglia

Porcine reproductive and respiratory syndrome virus (PRRSV) infection which caused severe reproductive failure and respiratory disorders in swine is accompanied with severe nervous symptoms. Our previous studies demonstrated that microglia, the resident innate immune cells in central nervous system (CNS), could support PRRSV infection and replication in vitro. And PRRSV infection led to the increased expressions of large amounts of proinflammatory cytokines and chemokines which contributed to neuropathogenesis of PRRSV. Interleukin-1β (IL-1β) is one of the increased proinflammatory cytokines, which possesses diverse functions in immune response upon virus infection, including activation of innate immune and modulation of adaptive immune responses. Importantly, considerable evidences indicated that 1L-1β is involved in neuronal injury. Here, we demonstrated that PRRSV infection up-regulated IL-1β expression at both the mRNA and protein levels in microglia in a dose-dependent manner. Myeloid differentiation primary response gene 88 (MyD88), extracellular signal-regulated kinase1/2 (ERK) and activator protein 1 (AP-1) were involved in PRRSV induced IL-1β production in microglia. Moreover, NOD-like receptor protein 3 (NLRP3) inflammasome is activated by PRRSV in microglia, which is required for IL-1β secretion. Taken together, our data indicated that PRRSV infection could induce IL-1β up-regulation, which was likely mediated by MyD88/ERK/AP-1 and NLRP3 inflammasome. These findings will provide new insights into the molecular mechanisms of IL-1β production and some implications for neuropathogenesis of PRRSV.

Activation of toll-like receptor signaling pathways leading to nitric oxide-mediated antiviral responses

Toll-like receptors (TLRs), well-characterized pattern-recognizing receptors of the innate arm of the immune system, are vital in detecting pathogen-associated molecular patterns (PAMPs). The TLR-PAMP interaction initiates an intracellular signaling cascade, predominantly culminating in upregulation of antiviral components, including inducible nitric oxide synthase (iNOS). After activation, various TLR pathways can promote iNOS production via the myeloid differentiation primary response-88 (MyD-88) adapter protein. Subsequently, iNOS facilitates production of nitric oxide (NO), a highly reactive and potent antiviral molecule that can inhibit replication of RNA and DNA viruses. Furthermore, NO can diffuse freely across cell membranes and elicit antiviral mechanisms in various ways, including direct and indirect damage to viral genomes. This review emphasizes current knowledge of NO-mediated antiviral responses elicited after activation of TLR signaling pathways.

Nitric oxide is elicited and inhibits viral replication in pigs infected with porcine respiratory coronavirus but not porcine reproductive and respiratory syndrome virus

There is little information on the role of nitric oxide (•NO) in innate immunity to respiratory coronavirus (CoV) infections. We examined •NO levels by Greiss assay in bronchoalveolar lavage (BAL) of pigs infected with either porcine respiratory coronavirus (PRCV) or porcine reproductive and respiratory syndrome virus (PRRSV), a member of Nidovirales, like CoV. The antiviral effects of •NO on these two viruses were tested in an in vitro system using a •NO donor, S-nitroso-N-acetylpenicillamine (SNAP). We detected a large increase in •NO levels in BAL fluids of PRCV-infected pigs, but not in PRRSV-infected pigs. Pulmonary epithelial cell necrosis induced by PRCV coincided with increased •NO. Moreover, •NO levels in cell culture medium of PRRSV-infected alveolar macrophages (AMs) did not differ from that of mock-infected AMs. Antiviral assays showed that •NO significantly inhibited PRCV replication in swine testicular (ST) cells, whereas PRRSV was not susceptible to •NO based on the conditions tested. Our study suggests that unlike PRRSV which induces apoptosis in AMs, respiratory CoVs such as PRCV that infect pulmonary epithelial cells and cause cytolysis, induce •NO production in the respiratory tract. Thus, •NO may play a role in innate immunity to respiratory CoV infections by inhibiting viral replication.

Nitric oxide inhibits the replication cycle of porcine parvovirus in vitro

This study investigated the inhibitory effect and mechanism of nitric oxide (NO) on porcine parvovirus (PPV) replication in PK-15 cells. The results showed that two NO-generating compounds, S-nitroso-l-acetylpenicillamine (SNAP) and l-arginine (LA), at a noncytotoxic concentration could reduce PPV replication in a dose-dependent manner and that this anti-PPV effect could be reversed by the NO synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (l-NAME). By assaying the steps of the PPV life cycle, we also show that NO inhibits viral DNA and protein synthesis. This experiment provides a frame of reference for the study of the anti-viral mechanism of NO.

Neurogliogenesis in the mature olfactory system: a possible protective role against infection and toxic dust

The outpost position of the olfactory bulb (OB) between the direct inputs from sensory neurons of the nasal epithelium and other parts of the brain suggests its highest vulnerability among all brain structures to penetration of exogenous agents. A number of neurotropic viruses have been found to invade the brain through the OB. There is growing evidence that microscopic particles of toxic dusts can propagate from the nasal epithelium to the OB and further into the brain. These harmful agents impair cellular elements of the brain. Apparently, cells in the OB are the most affected, as they are the first to encounter viral infections and toxic particles. It is well known that neuronal and glial progenitors are continuously generated from neuronal stem cells in the subventricular zone of the adult brain and then migrate predominantly into the OB. Therefore, it is feasible to suggest that substitution of injured or dead cells in the OB by new-born neurons, differentiating from progenitors, plays a role in protecting the OB neuronal microcircuits from destruction. Furthermore, some cytokines and chemokines released in response to infection and/or intoxication can modulate different stages of neurogenesis (proliferation, migration, and differentiation). We hypothesize that continuous neurogenesis in the olfactory system throughout adulthood evolved as a protective mechanism to prevent impairment of the most ancient but vitally important sensory system. In addition, differentiation of a substantial portion of progenitors to glial cells, including macrophages and microglia, may create an additional barrier to exogenous agents on their way deep to the brain.

PIN: a novel protein involved in IFN-gamma accumulation of NOS-1 in neurons

In this study we investigate the role of the protein inhibitor of NOS-1 (PIN) in the interferon-gamma (IFN-gamma)-mediated posttranscriptional accumulation of nitric oxide synthase-1 (NOS-1) and the anti-vesicular stomatitis virus response in neuronal cells. IFN-gamma-induced enhancement of NOS-1 activity is crucial for its antiviral activity in the central nervous system. IFN-gamma treatment of neuronal cells results in an increase of total NOS-1 and decrease of total PIN proteins without alteration in their respective mRNA levels. PIN/NOS-1 complexes decreased after IFN-gamma treatment. Transfection of cells with small interfering RNA (siRNA) for PIN results in a higher constitutive activity of NOS-1 and inhibition of viral replication. IFN-gamma treatment did not change the amount of NOS-1 detectable by Western blot, when PIN is diminished by RNAi treatment. Overexpression of PIN results in lower constitutive NOS-1 expression and activity, and diminishes activation of NOS-1 by IFN-gamma. Our findings indicate that in neurons, IFN-gamma upregulates NOS-1 through proteasomal degradation of PIN.

Chemokine expression during mouse-hepatitis-virus-induced encephalitis: contributions of the spike and background genes

Infection of mice with mouse hepatitis virus (MHV) strain JHM (RJHM) induces lethal encephalitis, with high macrophage and neutrophil, but minimal T-cell, infiltration into the brain when compared to the neuroattenuated strain RA59. To determine if chemokine expression corresponds with the cellular infiltrate, chemokine protein and RNA levels from the brains of infected mice were quantified. RJHM-infected mice had lower T-cell (CXCL9, CXCL10), but higher macrophage-attracting (CCL2), chemokine proteins compared to RA59. RJHM also induced significantly higher CXCL2 (a neutrophil chemoattractant) mRNA compared to RA59. The neurovirulent spike gene chimera SJHM/RA59 induces high levels of T cells and macrophages in the brain compared to the attenuated SA59/RJHM chimera. Accordingly, SJHM/RA59 induced higher levels of CXCL9, CXCL10, and CCL2 protein compared to SA59/RJHM. Chemokine mRNA patterns were in general agreement. Thus, chemokine patterns correspond with the cellular infiltrate, and the spike protein influences levels of macrophage, but not T-cell, chemokines.

Progress in Anti-SARS Coronavirus Chemistry, Biology and Chemotherapy

Proteolytic processing of the coronavirus replicase polyproteins is essential for ongoing viral ribonucleic acid (RNA) synthesis. Therefore, the severe acute respiratory syndrome (SARS)-coronaviruses (SARS-CoV) proteases are attractive targets for the development of antiviral drugs to reduce viral replication and pathogenicity. The structure and activity of the coronavirus 3C-like protease (3CLpro) has already been elucidated, and the design of inhibitors to 3CLpro as therapeutics has been proposed. The chapter discusses SARS-CoV 3CLpro inhibitors that include covalent inhibitors, noncovalent inhibitors, and inhibitors from screening. SARS-CoV papain-like protease (PLpro) is considered an equally viable target to 3CLpro for drug design because both are essential for viral replication. However, PLpro has likely not been pursued because of the paucity of structural information. Several compounds have been identified that have shown inhibitory activity against SARS-CoV. However, no information regarding their mechanism of action or the corresponding target is known. Glycyrrhizin showed inhibitory activity for SARS-CoV replication with EC50 = 300 mg/L after virus absorption in Vero cells. Some glycyrrhizin acid derivatives were found to inhibit SARS-CoV replication in vitro with EC50 values ranging from 5 to 50 μ M. Unfortunately, these compounds show high cytotoxity.

The role of the proteasome-ubiquitin pathway in regulation of the IFN-gamma mediated anti-VSV response in neurons

Pharmacologic inhibition of the proteasome resulted in increased NOS-1 protein levels and increased NO production by neuronal cells. This correlated with an increased antiviral effect of IFN-gamma against the replication of vesicular stomatitis virus (VSV) replication in vitro. We also observed that a regulatory protein, Protein Inhibitor of NOS-1 (PIN) was down-regulated by IFN-gamma treatment, and more ubiquitinated PIN accumulated in IFN-gamma treated neurons. In cells of the reticuloendothelial system, IFN-gamma treatment induces the expression of a set of low molecular weight MHC-encoded proteins (LMPs), which replace the beta-subunit of the proteasome complex during the proteasome neosynthesis, resulting in a complex termed the immunoproteasome. LMP2, -7, and -10 were induced and the immunoproteasome was generated by IFN-gamma treatment in neuronal cells. Importantly, we observed that IFN-gamma induced inhibition of VSV protein synthesis was not dependent on ubiquitination.

Gamma interferon plays a crucial early antiviral role in protection against West Nile virus infection

West Nile virus (WNV) causes a severe central nervous system (CNS) infection in humans, primarily in the elderly and immunocompromised. Prior studies have established an essential protective role of several innate immune response elements, including alpha/beta interferon (IFN-alpha/beta), immunoglobulin M, gammadelta T cells, and complement against WNV infection. In this study, we demonstrate that a lack of IFN-gamma production or signaling results in increased vulnerability to lethal WNV infection by a subcutaneous route in mice, with a rise in mortality from 30% (wild-type mice) to 90% (IFN-gamma(-/-) or IFN-gammaR(-/-) mice) and a decrease in the average survival time. This survival pattern in IFN-gamma(-/-) and IFN-gammaR(-/-) mice correlated with higher viremia and greater viral replication in lymphoid tissues. The increase in peripheral infection led to early CNS seeding since infectious WNV was detected several days earlier in the brains and spinal cords of IFN-gamma(-/-) or IFN-gammaR(-/-) mice. Bone marrow reconstitution experiments showed that gammadelta T cells require IFN-gamma to limit dissemination by WNV. Moreover, treatment of primary dendritic cells with IFN-gamma reduced WNV production by 130-fold. Collectively, our experiments suggest that the dominant protective role of IFN-gamma against WNV is antiviral in nature, occurs in peripheral lymphoid tissues, and prevents viral dissemination to the CNS.

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

Several viruses infect the mammalian central nervous system (CNS), some with devastating consequences, others resulting in chronic or persistent infections associated with little or no overt pathology. Coronavirus infection of the murine CNS illustrates the contributions of both the innate immune response and specific host effector mechanisms that control virus replication in distinct CNS cell types. Despite T-cell-mediated control of acute virus infection, host regulatory mechanisms, probably designed to protect CNS integrity, contribute to the failure to eliminate virus. Distinct from cytolytic effector mechanisms expressed during acute infection, non-lytic humoral immunity prevails in suppressing infectious virus during persistence.

LightUp probes in clinical diagnostics

The LightUp^® Probe technology has now matured and reached the phase where it has been implemented in commercial reagent kits, i.e. the ReSSQ^® product line. Several properties of the LightUp^® probes make them particularly suitable for clinical settings. For instance, extraordinary shelf life and a chemical stability that allows convenient fridge storage. The origin of the higher stability of LightUp^® probe kits compared to others, based on alternative probe technologies, is partly the relatively good stability of cyanine dyes but also the resistance towards nucleases and proteases of the synthetic DNA analogue peptide nucleic acid that is used as the sequence recognizing element in LightUp probes. It is clear from recent trends in the PCR amplification hardware technology that the instrumentation is becoming more flexible and less adapted for dedicated probe chemistries. This will pave the way for increased standardization in the field of DNA diagnostics and the development of cross-platform assays.

In the present review the LightUp technology will briefly be presented and discussed. The utility of the technology will be illustrated by examples from cytomegalovirus quantification and monitoring of the viral load of the SARS Coronavirus. An example of cancer diagnostics by detection of altered gene expression patterns will also be shown.

Role of nitric oxide (NO) in interferon-alpha therapy for hepatitis C

BACKGROUND AND AIM

The role of nitric oxide in infectious disease is gaining increased attention because antiviral effects of nitric oxide. In addition, there is evidence that nitric oxide synthase-2 expression was noted in chronic hepatitis C found within mononuclear cells.

METHODS

We studied serum levels of nitrite and nitrate before and during interferon alpha therapy in 66 patients with chronic hepatitis C.

RESULTS

There was no significant difference of their levels between the healthy control subjects and the patients before the treatment with interferon (55.9+/-21.8 microM vs. 60.9+/-30.0 microM). Their levels were determined at 2 weeks after the initiation of treatment with interferon and compared with those before the treatment in the patients with chronic hepatitis C. In the total patients treated, there was no significant difference between their levels before and at 2 weeks after the treatment (60.9+/-30.0 microM vs. 65.5+/-30.0 microM, P=0.14). However, when the levels were compared between sustained responders, in whom hepatitis C virus was eradicated, and non-responders, in whom the virus was not eradicated, the former had significantly higher levels of nitrite and nitrate than the latter at 2 weeks after the initiation of treatment (83.7+/-40.9 microM vs. 57.6+/-19.5 microM, P<0.01). The multivariate logistic regression analysis showed that the rise of nitrite and nitrate was an independent predictive factor for efficacy of interferon treatment.

CONCLUSIONS

Nitric oxide may be an important factor for antiviral therapy by interferon treatment for chronic hepatitis C, which suggests an additional therapeutic pathway for further study.

Development of antiviral therapy for severe acute respiratory syndrome

A new disease, the severe acute respiratory distress syndrome (SARS), caused by the SARS coronavirus (SARS-CoV), emerged at the beginning of 2003 and rapidly spread throughout the world. Although the disease had disappeared in June 2003 its re-emergence cannot be excluded. The development of vaccines against SARS-CoV may take years. Therefore, the availability of effective antiviral drugs against SARS-CoV may be crucial for the control of future SARS outbreaks. In this review, experimental and clinical data about potential anti-SARS drugs is summarised and discussed. Animal model studies will be needed to help to determine which interventions warrant controlled clinical testing.

The role of IL-12, IL-23 and IFN-gamma in immunity to viruses

IL-12, IL-23 and IFN-γ form a loop and have been thought to play a crucial role against infectious viruses, which are the prototype of “intracellular” pathogens. In the last 10 years, the generation of knock-out (KO) mice for genes that control IL-12/IL-23-dependent IFN-γ-dependent mediated immunity (STAT1, IFN-γR1, IFNγR2, IL-12p40 and IL-12Rβ1) and the identification of patients with spontaneous germline mutations in these genes has led to a re-examination of the role of these cytokines in anti-viral immunity. We here review viral infections in mice and humans with genetic defects in the IL-12/IL-23-IFN-γ axis. A comparison of the phenotypes observed in KO mice and deficient patients suggests that the human IL-12/IL-23-IFN-γ axis plays a redundant role in immunity to most viruses, whereas its mouse counterparts play a more important role against several viruses.

Nitric oxide inhibits the replication cycle of severe acute respiratory syndrome coronavirus

Nitric oxide (NO) is an important signaling molecule between cells which has been shown to have an inhibitory effect on some virus infections. The purpose of this study was to examine whether NO inhibits the replication cycle of the severe acute respiratory syndrome coronavirus (SARS CoV) in vitro. We found that an organic NO donor, S-nitroso-N-acetylpenicillamine, significantly inhibited the replication cycle of SARS CoV in a concentration-dependent manner. We also show here that NO inhibits viral protein and RNA synthesis. Furthermore, we demonstrate that NO generated by inducible nitric oxide synthase, an enzyme that produces NO, inhibits the SARS CoV replication cycle.

Modulatory effects of ammonia-N on the immune system of Penaeus japonicus to virulence of white spot syndrome virus

To study response to white spot syndrome virus (WSSV) under ammonia stress, Penaeus japonicus were exposed to 5 mg l^-1 ammonia-N and challenged orally with WSSV (NW). Controls consisted of an ammonia-N-exposed control group (N), a WSSV-challenged positive control group (W), and an untreated control group (control). Immune parameters measured were total haemocyte count (THC), haemocyte phagocytosis, plasma protein content and haemolymph enzymatic activities for prophenoloxidase (proPO), alkaline phosphatase (ALP), and nitric oxide synthase (NOS). THC and plasma protein had downward trends with time in all treatment groups (NW, N, and W) in contrast to the untreated control group (control). The percentage phagocytosis, NOS activity, and ALP and proPO activity of W and NW decreased initially then increased from 6 to 78 h (except for NOS and ALP, from 6 to 54 h) before declining thereafter until the end of the experiment. Compared with untreated controls (control), there was a downward trend for all measured parameters in the treatment groups (N, NW, and W), but the degree was W>NW>N. WSSV was detected at 78 h postchallenge in both W and NW. In conclusion, 5 mg l^-1 ammonia-N reduced the immunocompetence of P. japonicus and may have decreased the virulence of WSSV.

Inhibition of SARS-coronavirus infection in vitro by S-nitroso-N-acetylpenicillamine, a nitric oxide donor compound

INTRODUCTION

The recent outbreak of severe acute respiratory syndrome (SARS) warrants the search for effective antiviral agents to treat the disease. This study describes the assessment of the antiviral potential of nitric oxide (NO) against SARS coronavirus (SARS-CoV) strain Frankfurt-1 replicating in African Green Monkey (Vero E6) cells.

RESULTS

Two organic NO donor compounds, S-nitroso-N-acetylpenicillamine (SNAP) and sodium nitroprusside (SNP), were tested in a broad range of concentrations. The non-nitrosylated form of SNAP, N-acetylpenicillamine (NAP), was included as a control compound in the assay. Antiviral activity was estimated by the inhibition of the SARS-CoV cytopathic effect in Vero E6 cells, determined by a tetrazolium-based colorimetric method. Cytotoxicity of the compounds was tested in parallel.

CONCLUSION

The survival rate of SARS-CoV infected cells was greatly increased by the treatment with SNAP, and the concentration of this compound needed to inhibit the viral cytopathic effect to 50% was 222 microM, with a selectivity index of 3. No anti-SARS-CoV effect could be detected for SNP and NAP.

Early inhibition of nitric oxide production increases HSV-1 intranasal infection

Here, we studied the role of nitric oxide (NO) production during the first steps of the respiratory infection of BALB/c mice with herpes simplex virus type 1 (HSV-1), strain F. Nitric oxide synthase II (NOS-II) mRNA and protein were detected by reverse transcription (RT)-PCR and dot blot, respectively in samples of lungs and turbinates early post-infection (p.i.). Immunohistochemical analysis revealed pulmonar macrophages and PMN expressing NOS-II in the lungs of infected animals. Animals intranasally treated with aminoguanidine (AG), a NOS inhibitor, during the first steps of infection, showed a dose-dependent increase in pneumonitis compared to controls. Viral titres in turbinates, lungs, and brains were higher in AG treated mice. Finally, histopathology studies revealed a stronger inflammation in eyes, and lungs of these animals. Taken together, these results suggest a role of NO in controlling primary HSV intranasal infection.

Coronavirus neurovirulence correlates with the ability of the virus to induce proinflammatory cytokine signals from astrocytes and microglia

The molecular and cellular basis of coronavirus neurovirulence is poorly understood. Since neurovirulence may be determined at the early stages of infection of the central nervous system (CNS), we hypothesize that it may depend on the ability of the virus to induce proinflammatory signals from brain cells for the recruitment of blood-derived inflammatory cells. To test this hypothesis, we studied the interaction between coronaviruses (mouse hepatitis virus) of different neurovirulences with primary cell cultures of brain immune cells (astrocytes and microglia) and mouse tissues. We found that the level of neurovirulence of the virus correlates with its differential ability to induce proinflammatory cytokines (interleukin 12 [IL-12] p40, tumor necrosis factor alpha, IL-6, IL-15, and IL-1beta) in astrocytes and microglia and in mouse brains and spinal cords. These findings suggest that coronavirus neurovirulence may depend on a novel discriminatory ability of astrocytes and microglia to induce a proinflammatory response in the CNS.

Theiler's virus infection: a model for multiple sclerosis

Both genetic background and environmental factors, very probably viruses, appear to play a role in the etiology of multiple sclerosis (MS). Lessons from viral experimental models suggest that many different viruses may trigger inflammatory demyelinating diseases resembling MS. Theiler's virus, a picornavirus, induces in susceptible strains of mice early acute disease resembling encephalomyelitis followed by late chronic demyelinating disease, which is one of the best, if not the best, animal model for MS. During early acute disease the virus replicates in gray matter of the central nervous system but is eliminated to very low titers 2 weeks postinfection. Late chronic demyelinating disease becomes clinically apparent approximately 2 weeks later and is characterized by extensive demyelinating lesions and mononuclear cell infiltrates, progressive spinal cord atrophy, and axonal loss. Myelin damage is immunologically mediated, but it is not clear whether it is due to molecular mimicry or epitope spreading. Cytokines, nitric oxide/reactive nitrogen species, and costimulatory molecules are involved in the pathogenesis of both diseases. Close similarities between Theiler's virus-induced demyelinating disease in mice and MS in humans, include the following: major histocompatibility complex-dependent susceptibility; substantial similarities in neuropathology, including axonal damage and remyelination; and paucity of T-cell apoptosis in demyelinating disease. Both diseases are immunologically mediated. These common features emphasize the close similarities of Theiler's virus-induced demyelinating disease in mice and MS in humans.

CXC chemokine ligand 10 controls viral infection in the central nervous system: evidence for a role in innate immune response through recruitment and activation of natural killer cells

How chemokines shape the immune response to viral infection of the central nervous system (CNS) has largely been considered within the context of recruitment and activation of antigen-specific lymphocytes. However, chemokines are expressed early following viral infection, suggesting an important role in coordinating innate immune responses. Herein, we evaluated the contributions of CXC chemokine ligand 10 (CXCL10) in promoting innate defense mechanisms following coronavirus infection of the CNS. Intracerebral infection of RAG1(-/-) mice with a recombinant CXCL10-expressing murine coronavirus (mouse hepatitis virus) resulted in protection from disease and increased survival that correlated with a significant increase in recruitment and activation of natural killer (NK) cells within the CNS. Accumulation of NK cells resulted in a reduction in viral titers that was dependent on gamma interferon secretion. These results indicate that CXCL10 expression plays a pivotal role in defense following coronavirus infection of the CNS by enhancing innate immune responses.

IFN-gamma-producing gamma delta T cells help control murine West Nile virus infection

West Nile (WN) virus causes fatal meningoencephalitis in laboratory mice, thereby partially mimicking human disease. Using this model, we have demonstrated that mice deficient in gammadelta T cells are more susceptible to WN virus infection. TCRdelta(-/-) mice have elevated viral loads and greater dissemination of the pathogen to the CNS. In wild-type mice, gammadelta T cells expanded significantly during WN virus infection, produced IFN-gamma in ex vivo assays, and enhanced perforin expression by splenic T cells. Adoptive transfer of gammadelta T cells to TCRdelta(-/-) mice reduced the susceptibility of these mice to WN virus, and this effect was primarily due to IFN-gamma-producing gammadelta T cells. These data demonstrate a distinct role for gammadelta T cells in the control of and prevention of mortality from murine WN virus infection.

Nitric oxide and HSV vaginal infection in BALB/c mice

Here we study the role of nitric oxide in the vaginal infection of Balb/c mice with herpes simplex virus type 2. Inducible nitric oxide synthase (iNOS) mRNA was detected by RT-PCR in vaginal tissue and inguinal lymph nodes early postinfection. iNOS was also found to be activated in cells recovered from vaginal washings of infected animals. Animals treated with aminoguanidine (AG), an iNOS inhibitor, showed a dose-dependent increase in vaginal pathology after viral infection compared to controls. Viral titers in vaginal washings and vaginas were higher in AG-treated mice. Treated animals presented higher PMN counts in vaginal washings compared to controls. Histopathology studies revealed a profound inflammatory exudate in vaginal tissue of treated animals. Finally, RT-PCR analysis showed increased expression of the chemokines MIP-2 and RANTES in vaginal tissue and inguinal lymph nodes of these animals.

Virus demyelination

A number of viruses can initiate central nervous system (CNS) diseases that include demyelination as a major feature of neuropathology. In humans, the most prominent demyelinating diseases are progressive multifocal leukoencephalopathy, caused by JC papovirus destruction of oligodendrocytes, and subacute sclerosing panencephalitis, an invariably fatal childhood disease caused by persistent measles virus. The most common neurological disease of young adults in the developed world, multiple sclerosis, is also characterized by lesions of inflammatory demyelination; however, the etiology of this disease remains an enigma. A viral etiology is possible, because most demyelinating diseases of known etiology in both man and animals are viral. Understanding of the pathogenesis of virus-induced demyelination derives for the most part from the study of animal models. Studies with neurotropic strains of mouse hepatitis virus, Theiler's virus, and Semliki Forest virus have been at the forefront of this research. These models demonstrate how viruses enter the brain, spread, persist, and interact with immune responses. Common features are an ability to infect and persist in glial cells, generation of predominantly CD8(+) responses, which control and clear the early phase of virus replication but which fail to eradicate the infection, and lesions of inflammatory demyelination. In most cases demyelination is to a limited extent the result of direct virus destruction of oligodendrocytes, but for the most part is the consequence of immune and inflammatory responses. These models illustrate the roles of age and genetic susceptibility and establish the concept that persistent CNS infection can lead to the generation of CNS autoimmune responses.

Altering the expression kinetics of VP5 results in altered virulence and pathogenesis of herpes simplex virus type 1 in mice

While many herpes simplex virus (HSV) structural proteins are expressed with strict-late kinetics, the HSV virion protein 5 (VP5) is expressed as a "leaky-late" protein, such that appreciable amounts of VP5 are made prior to DNA replication. Our goal has been to determine if leaky-late expression of VP5 is a requirement for a normal HSV infection. It had been shown previously that recombinant viruses in which the VP5 promoter was replaced with promoters of other kinetic classes (including a strict late promoter) exhibited no alterations in replication kinetics or virus yields in vitro. In contrast, here we report that alterations in pathogenesis were observed when these recombinants were analyzed by experimental infection of mice. Following intracranial inoculation, a recombinant expressing VP5 from a strict-late promoter (U(L)38) exhibited an increased 50% lethal dose and a 10-fold decrease in virus yields in the central nervous system, while a recombinant expressing VP5 from an early (dUTPase) or another leaky-late (VP16) promoter exhibited wild-type neurovirulence. Moreover, following infection of the footpad, changing the expression kinetics of VP5 from leaky-late to strict-late resulted in 100-fold-less virus in the spinal ganglia during the acute infection than produced by either the parent virus or the rescued virus. These data indicate that the precise timing of appearance of the major capsid protein plays a role in the pathogenesis of HSV infections and that changing the expression kinetics has different effects in different cell types and tissues.

Murine hepatitis virus--a model for virus-induced CNS demyelination

Most murine hepatitis virus (MHV) strains, as their name suggests, infect the liver. However, several murine strains are tropic for the central nervous system (CNS) and cause encephalitis with subsequent CNS demyelination. The CNS demyelination shares pathological similarities with human CNS demyelinating diseases such as multiple sclerosis (MS). These viruses are, therefore, used to study the role of the immune system in viral clearance from the CNS, in CNS demyelination, and in remyelination. Nevertheless, it is still unclear exactly how MHV induces demyelination and to what extent the immune system plays a role in this pathology. Here we review this field in the context of the immune response to MHV in the liver and the CNS focusing on studies that have been published in the past 5 years.

Lack of nitric oxide synthase type 2 (NOS2) results in reduced neuronal apoptosis and mortality following mouse hepatitis virus infection of the central nervous system

The role of nitric oxide synthase type-2 (NOS2)-derived nitric oxide (NO) in the pathogenesis of mouse hepatitis virus (MHV)-induced central nervous system disease was examined. Infection of NOS2 knockout ((-/-)) and NOS2(+/+) mice with MHV resulted in similar kinetics of viral clearance from the brain and comparable levels of demyelination. MHV-infected NOS2(-/-) mice displayed a marked decrease in mortality as compared to infected NOS2(+/+) mice that correlated with a significant decrease (P < or = 0.001) in the number of apoptotic cells (determined by TUNEL staining) present in the brain. Confocal microscopy revealed that the majority of cells (>70%) undergoing apoptosis were neurons. These studies indicate that NOS2-generated NO contributes to apoptosis of neurons but not demyelination following MHV infection.

MHV infection of the CNS: mechanisms of immune-mediated control

Mice infected with neurotropic strains of mouse hepatitis virus (MHV) clear infectious virus; nevertheless, viral persistence in the central nervous system (CNS) is associated with ongoing primary demyelination. Acute infection induces a potent regional CD8+ T-cell response. The high prevalence of virus specific T cells correlates with ex vivo cytolytic activity, interferon-gamma (IFN-gamma) secretion and efficient reduction in virus. Viral clearance from most cell types is controlled by a perforin dependent mechanism. However, IFN-gamma is essential for controlling virus replication in oligodendrocytes. Furthermore, CD4+ T cells enhance CD8+ T-cell survival and effectiveness. Clearance of infectious virus is associated with a gradual decline of CNS T cells; nevertheless, activated T cells are retained within the CNS. The loss of cytolytic activity, but retention of IFN-gamma secretion during viral clearance suggests stringent regulation of CD8+ T-cell effector function, possibly as a means to minimize CNS damage. However, similar CD8+ T-cell responses to demyelinating and non demyelinating JHMV variants support the notion that CD8+ T cells do not contribute to the demyelinating process. Although T-cell retention is tightly linked to the presence of persisting virus, contributions to regulating the latent state are unknown. Studies in B-cell-deficient mice suggest that antibodies are required to prevent virus recrudescence. Although acute JHMV infection is thus primarily controlled by CD8+ T cells, both CD4+ T cells and B cells make significant contributions in maintaining the balance between viral replication and immune control, thus allowing host and pathogen survival.

Yellow fever virus encephalitis: properties of the brain-associated T-cell response during virus clearance in normal and gamma interferon-deficient mice and requirement for CD4+ lymphocytes

Viral encephalitis caused by neuroadapted yellow fever 17D virus (PYF) was studied in parental and gamma interferon (IFN-gamma)-deficient (IFN-gamma knockout [GKO]) C57BL/6 mice. The T-cell responses which enter the brain during acute fatal encephalitis of nonimmunized mice, as well as nonfatal encephalitis of immunized mice, were characterized for relative proportions of CD4+ and CD8+ cells, their proliferative responses, and antigen-specific expression of cytokines during stimulation in vitro. Unimmunized mice accumulated only low levels of T cells within the brain during fatal disease, whereas the brains of immunized mice contained higher levels of both T-cell subsets in response to challenge, with CD8+ cells increased relative to the CD4+ subset. The presence of T cells correlated with the time at which virus was cleared from the central nervous system in both parental and GKO mice. Lymphocytes isolated from the brains of challenged immunized mice failed to proliferate in vitro in response to T-cell mitogens or viral antigens; however, IFN-gamma, interleukin 4 (IL-4), and, to a lesser extent, IL-2 were detectable after stimulation. The levels of IFN-gamma, but not IL-2 or IL-4, were augmented in response to viral antigen, and this specificity was detectable in the CD4+ compartment. When tested for the ability to survive both immunization and challenge with PYF virus, GKO and CD8 knockout mice did not differ from parental mice (80 to 85% survival), although GKO mice exhibited a defect in virus clearance. In contrast, CD4 knockout and Igh-6 mice were unable to resist challenge. The data implicate antibody in conjunction with CD4+ lymphocytes bearing a Th1 phenotype as the critical factors involved in virus clearance in this model.

Expression of Mig (monokine induced by interferon-gamma) is important in T lymphocyte recruitment and host defense following viral infection of the central nervous system

Induction of a Th1 immune response against viral infection of the CNS is important in contributing to viral clearance. The present studies demonstrate a role for the T cell chemoattractant chemokine Mig (monokine induced by IFN-gamma) in contributing to a Th1 response against mouse hepatitis virus infection of the CNS. Analysis of the kinetics of Mig expression revealed mRNA transcripts present at days 7 and 12 postinfection (p.i.) but not early (day 2) or late (day 35) in the infection. To determine functional significance, mouse hepatitis virus-infected mice were treated with anti-Mig antisera, and the severity of disease was evaluated. Such treatment resulted in a marked increase in mortality that correlated with a >3 log increase in viral burden within the brains as compared with control mice treated with normal rabbit serum. Anti-Mig-treated mice displayed a significant decrease (p < 0.005) in CD4(+) and CD8(+) T cell recruitment into the CNS as compared with normal rabbit serum-treated mice. In addition, anti-Mig treatment resulted in a significant decrease (p < 0.05) in levels of IFN-gamma and IFN-beta that coincided with increased (p < 0.02) expression of the anti-inflammatory Th2 cytokine IL-10 within the CNS. Collectively, these data indicate that Mig is important in contributing to host defense by promoting a protective Th1 response against viral infection of the CNS.