Intranasally administered alpha/beta interferon prevents extension of mouse hepatitis virus, strain JHM, into the brains of BALB/cByJ mice

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

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

Chemokine CXCL10 and Coronavirus-Induced Neurologic Disease

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

Microglia are required for protection against lethal coronavirus encephalitis in mice

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

Promoting remyelination: utilizing a viral model of demyelination to assess cell-based therapies

Multiple sclerosis (MS) is a chronic inflammatory disease of the CNS. While a broad range of therapeutics effectively reduce the incidence of focal white matter inflammation and plaque formation for patients with relapse-remitting forms of MS, a challenge within the field is to develop therapies that allow for axonal protection and remyelination. In the last decade, growing interest has focused on utilizing neural precursor cells (NPCs) to promote remyelination. To understand how NPCs function in chronic demyelinating environments, several excellent pre-clinical mouse models have been developed. One well accepted model is infection of susceptible mice with neurotropic variants of mouse hepatitis virus (MHV) that undergo chronic demyelination exhibiting clinical and histopathologic similarities to MS patients. Combined with the possibility that an environmental agent such as a virus could trigger MS, the MHV model of demyelination presents a relevant mouse model to assess the therapeutic potential of NPCs transplanted into an environment in which inflammatory-mediated demyelination is established.

The chemokine receptor CXCR2 and coronavirus-induced neurologic disease

Inoculation with the neurotropic JHM strain of mouse hepatitis virus (MHV) into the central nervous system (CNS) of susceptible strains of mice results in an acute encephalomyelitis in which virus preferentially replicates within glial cells while excluding neurons. Control of viral replication during acute disease is mediated by infiltrating virus-specific T cells via cytokine secretion and cytolytic activity, however sterile immunity is not achieved and virus persists resulting in chronic neuroinflammation associated with demyelination. CXCR2 is a chemokine receptor that upon binding to specific ligands promotes host defense through recruitment of myeloid cells to the CNS as well as protecting oligodendroglia from cytokine-mediated death in response to MHV infection. These findings highlight growing evidence of the diverse and important role of CXCR2 in regulating neuroinflammatory diseases.

CXCR2 signaling and host defense following coronavirus-induced encephalomyelitis

Inoculation of the neurotropic JHM strain of mouse hepatitis virus (JHMV) into the central nervous system (CNS) of susceptible strains of mice results in wide-spread replication within glial cells accompanied by infiltration of virus-specific T lymphocytes that control virus through cytokine secretion and cytolytic activity. Virus persists within white matter tracts of surviving mice resulting in demyelination that is amplified by inflammatory T cells and macrophages. In response to infection, numerous cytokines/chemokines are secreted by resident cells of the CNS and inflammatory leukocytes that participate in both host defense and disease. Among these are the ELR-positive chemokines that are able to signal through CXC chemokine receptors including CXCR2. Early following JHMV infection, ELR-positive chemokines contribute to host defense by attracting CXCR2-expressing cells including polymorphonuclear cells to the CNS that aid in host defense through increasing the permeability the blood-brain-barrier (BBB). During chronic disease, CXCR2 signaling on oligodendroglia protects these cells from apoptosis and restricts the severity of demyelination. This review covers aspects related to host defense and disease in response to JHMV infection and highlights the different roles of CXCR2 signaling in these processes.

The pathogenesis of murine coronavirus infection of the central nervous system

Mouse hepatitis virus (MHV) is a positive-strand RNA virus that causes an acute encephalomyelitis that later resolves into a chronic fulminating demyelinating disease. Cytokine production, chemokine secretion, and immune cell infiltration into the central nervous system are critical to control viral replication during acute infection. Despite potent antiviral T-lymphocyte activity, sterile immunity is not achieved, and MHV chronically persists within oligodendrocytes. Continued infiltration and activation of the immune system, a result of the lingering viral antigen and RNA within oligodendrocytes, lead directly to the development of an immune-mediated demyelination that bears remarkable similarities, both clinically and histologically, to the human demyelinating disease multiple sclerosis. MHV offers a unique model system for studying host defense during acute viral infection and immune-mediated demyelination during chronic infection.

IFN-gamma-mediated suppression of coronavirus replication in glial-committed progenitor cells

The neurotropic JHM strain of mouse hepatitis virus (JHMV) replicates primarily within glial cells following intracranial inoculation of susceptible mice, with relative sparing of neurons. This study demonstrates that glial cells derived from neural progenitor cells are susceptible to JHMV infection and that treatment of infected cells with IFN-γ inhibits viral replication in a dose-dependent manner. Although type I IFN production is muted in JHMV-infected glial cultures, IFN-β is produced following IFN-γ-treatment of JHMV-infected cells. Also, direct treatment of infected glial cultures with recombinant mouse IFN-α or IFN-β inhibits viral replication. IFN-γ-mediated control of JHMV replication is dampened in glial cultures derived from the neural progenitor cells of type I receptor knock-out mice. These data indicate that JHMV is capable of infecting glial cells generated from neural progenitor cells and that IFN-γ-mediated control of viral replication is dependent, in part, on type I IFN secretion.

Mouse hepatitis virus infection of the CNS: a model for defense, disease, and repair

Viral infection of the central nervous system (CNS) results in varied outcomes ranging from encephalitis, paralytic poliomyelitis or other serious consequences. One of the principal factors that directs the outcome of infection is the localized innate immune response, which is proceeded by the adaptive immune response against the invading viral pathogen. The role of the immune system is to contain and control the spread of virus within the CNS, and paradoxically, this response may also be pathological. Studies with a neurotropic murine coronavirus, mouse hepatitis virus (MHV) have provided important insights into how the immune system combats neuroinvasive viruses, and have identified molecular and cellular mechanisms contributing to chronic disease in persistently infected mice.

Type I interferons are essential in controlling neurotropic coronavirus infection irrespective of functional CD8 T cells

Neurotropic coronavirus infection induces expression of both beta interferon (IFN-beta) RNA and protein in the infected rodent central nervous system (CNS). However, the relative contributions of type I IFN (IFN-I) to direct, cell-type-specific virus control or CD8 T-cell-mediated effectors in the CNS are unclear. IFN-I receptor-deficient (IFNAR(-/-)) mice infected with a sublethal and demyelinating neurotropic virus variant and those infected with a nonpathogenic neurotropic virus variant both succumbed to infection within 9 days. Compared to wild-type (wt) mice, replication was prominently increased in all glial cell types and spread to neurons, demonstrating expanded cell tropism. Furthermore, increased pathogenesis was associated with significantly enhanced accumulation of neutrophils, tumor necrosis factor alpha, interleukin-6, chemokine (C-C motif) ligand 2, and IFN-gamma within the CNS. The absence of IFN-I signaling did not impair induction or recruitment of virus-specific CD8 T cells, the primary adaptive mediators of virus clearance in wt mice. Despite similar IFN-gamma-mediated major histocompatibility complex class II upregulation on microglia in infected IFNAR(-/-) mice, class I expression was reduced compared to that on microglia in wt mice, suggesting a synergistic role of IFN-I and IFN-gamma in optimizing class I antigen presentation. These data demonstrate a critical direct antiviral role of IFN-I in controlling virus dissemination within the CNS, even in the presence of potent cellular immune responses. By limiting early viral replication and tropism, IFN-I controls the balance of viral replication and immune control in favor of CD8 T-cell-mediated protective functions.

Inhibition of the alpha/beta interferon response by mouse hepatitis virus at multiple levels

Mouse hepatitis virus (MHV) was used as a model to study the interaction of coronaviruses with the alpha/beta interferon (IFN-alpha/beta) response. While MHV strain A59 appeared to induce IFN-beta gene transcription and low levels of nuclear translocation of the IFN-beta transcription factor interferon regulatory factor 3 (IRF-3), MHV did not induce IFN-beta protein production during the course of infection in L2 mouse fibroblast cells. In addition, MHV was able to significantly decrease the level of IFN-beta protein induced by both Newcastle disease virus (NDV) and Sendai virus infections, without targeting it for proteasomal degradation and without altering the nuclear translocation of IRF-3 or IFN-beta mRNA production or stability. These results indicate that MHV infection causes an inhibition of IFN-beta production at a posttranscriptional level, without altering RNA or protein stability. In contrast, MHV induced IFN-beta mRNA and protein production in the brains of infected animals, suggesting that the inhibitory mechanisms observed in vitro are not enough to prevent IFN-alpha/beta production in vivo. Furthermore, MHV replication is highly resistant to IFN-alpha/beta action, as indicated by unimpaired MHV replication in L2 cells pretreated with IFN-beta. However, when L2 cells were coinfected with MHV and NDV in the presence of IFN-beta, NDV, but not MHV, replication was inhibited. Thus, rather than disarming the antiviral activity induced by IFN-beta pretreatment completely, MHV may be inherently resistant to some aspects of the antiviral state induced by IFN-beta. These findings show that MHV employs unique strategies to circumvent the IFN-alpha/beta response at multiple steps.

Coronaviruses and their therapy

Coronaviruses may cause respiratory, enteric and central nervous system diseases in many species, including humans. Until recently, the relatively low burden of disease in humans caused by few of these viruses hampered development of coronavirus specific therapeutics. However, the emergence of severe acute respiratory syndrome coronavirus (SARS-CoV) has prompted the discovery of such drugs. Subsequent studies in animal models demonstrated the efficacy of SARS-CoV specific monoclonal antibodies, pegylated-interferon-alpha and siRNAs against SARS-CoV. Furthermore, several antivirals shown to be effective against other viruses were tested in vitro. Because of availability and shown efficacy, the use of interferons may be considered should SARS-CoV or a related coronavirus (re)-emerge. The more recent design of wide-spectrum inhibitors targeting the coronavirus main proteases may lead to the discovery of new antivirals against multiple coronavirus induced diseases.

Pegylated interferon-alpha protects type 1 pneumocytes against SARS coronavirus infection in macaques

The primary cause of severe acute respiratory syndrome (SARS) is a newly discovered coronavirus. Replication of this SARS coronavirus (SCV) occurs mainly in the lower respiratory tract, and causes diffuse alveolar damage. Lack of understanding of the pathogenesis of SARS has prevented the rational development of a therapy against this disease. Here we show extensive SCV antigen expression in type 1 pneumocytes of experimentally infected cynomolgus macaques (Macaca fascicularis) at 4 d postinfection (d.p.i.), indicating that this cell type is the primary target for SCV infection early in the disease, and explaining the subsequent pulmonary damage. We also show that prophylactic treatment of SCV-infected macaques with the antiviral agent pegylated interferon-alpha (IFN-alpha) significantly reduces viral replication and excretion, viral antigen expression by type 1 pneumocytes and pulmonary damage, compared with untreated macaques. Postexposure treatment with pegylated IFN-alpha yielded intermediate results. We therefore suggest that pegylated IFN-alpha protects type 1 pneumocytes from SCV infection, and should be considered a candidate drug for SARS therapy.

The glycosylation status of the murine hepatitis coronavirus M protein affects the interferogenic capacity of the virus in vitro and its ability to replicate in the liver but not the brain

The coronavirus M protein, the most abundant coronaviral envelope component, is invariably glycosylated, which provides the virion with a diffuse, hydrophilic cover on its outer surface. Remarkably, while the group 1 and group 3 coronaviruses all have M proteins with N-linked sugars, the M proteins of the group 2 coronaviruses [e.g., mouse hepatitis virus (MHV)] are O-glycosylated. The conservation of the N- and O-glycosylation motifs suggests that each of these types of carbohydrate modifications is beneficial to their respective virus. Since glycosylation of the M protein is not required for virus assembly, the oligosaccharides are likely to be involved in the virus-host interaction. In order to investigate the role of the M protein glycosylation in the host, two genetically modified MHVs were generated by using targeted RNA recombination. The recombinant viruses carried M proteins that were either N-glycosylated or not glycosylated at all, and these were compared with the parental, O-glycosylated, virus. The M protein glycosylation state did not influence the tissue culture growth characteristics of the recombinant viruses. However, it affected their interferogenic capacity as measured using fixed, virus-infected cells. Viruses containing M proteins with N-linked sugars induced type I interferons to higher levels than viruses carrying M proteins with O-linked sugars. MHV with unglycosylated M proteins appeared to be a poor interferon inducer. In mice, the recombinant viruses differed in their ability to replicate in the liver, but not in the brain, whereas their in vivo interferogenic capacity did not appear to be affected by their glycosylation status. Strikingly, their abilities to replicate in the liver correlated with their in vitro interferogenic capacity. This apparent correlation might be explained by the functioning of lectins, such as the mannose receptor, which are abundantly expressed in the liver but also play a role in the induction of interferon-alpha by dendritic cells.

Feasibility of aerosol vaccination in humans

The feasibility of using aerosol vaccines to achieve mass and rapid immunization, especially in developing countries and disaster areas, is being assessed on the basis of current available information. The aerosol mode of vaccine introduction, which best follows the natural route of many infections, may first lead to development of immunity at the portal of entry, and may also induce a more generalized defense. The recommended optimal way of introducing an aerosol vaccine is nasal breathing, which is more suitable for geriatric and pediatric populations, permits use of greater antigen volumes, and allows easier monitoring of results. Technical requirements for ideal aerosol vaccines and delivery systems, possible adverse effects, and cost-effectiveness are other issues addressed. Several thousand human subjects have been aerosol-vaccinated over a period of many years in Russia with live-attenuated strains against many diseases. Extensive field trials in South America with aerosolized live-attenuated measles vaccine have also been successful, and excellent results have been reported with pilot projects employing inactivated or live-attenuated aerosol influenza A vaccine. We conclude that aerosol immunization seems a promising method of vaccination. Although some basic information is still lacking, this method has already been used successfully in large populations and has therefore passed the phase of initial feasibility evaluation.

Protective effects of murine recombinant interferon-beta administered by intravenous, intramuscular or subcutaneous route on mouse hepatitis virus infection

The significance of the route for administration of murine recombinant interferon-beta (IFN-beta) for inducing its therapeutic effects has been studied. BALB/c mice were daily injected intravenously, intramuscularly or subcutaneously with 1.5x10(3), 1. 5x10(4), or 1.5x10(5) IU of IFN-beta, from one day before to 8th day after mouse hepatitis virus (MHV-2) challenge. All mice received IFN-beta survived significantly longer than those without IFN. In the liver of those IFN-treated mice, viral growth and the histopathological damages were extremely alleviated. These results suggest that, irrespective of the differences in the route of administration, IFN-beta markedly suppressed viral activity when its administration was started prior to viral infection. For clinical use, however, further studies are needed on the optimal route for administration if IFN-beta is given after viral infection.

Systemic effects of orally administered interferons and interleukin-2

Orally administered interferons (IFN-alpha, IFN-beta, and IFN-gamma) have been shown to exert a number of systemic effects. Orally administered IFNs exert dose-dependent suppressive effects on the peripheral white blood cell (WBC) count. The suppression of the peripheral WBC count is mediated by a suppression of the function of the bone marrow, as measured in an in vitro bone marrow colony-forming assay. The peripheral WBC and bone marrow suppressive effects of orally administered IFNs are at least as potent as those occurring with parenterally administered IFNs. However, the mechanism by which orally administered IFNs exert these peripheral WBC suppressive and bone marrow suppressive effects differs significantly from that of parenterally administered IFNs: orally administered IFN is not detectable in the serum, the effect of orally administered IFN is not blocked by circulating antibody, the effect of orally administered IFN can be adoptively transferred by injection with peripheral white blood cells from donor mice, and the effect of orally administered IFN develops more slowly than that of parenterally administered interferon. Orally administered IFN-alpha employed alone and in synergistic combination with intraperitoneally administered IFN-gamma can exert an antitumor effect. Finally, orally administered interleukin-2 can exert a suppressive effect on both the peripheral white blood cell count and on the bone marrow. These observations suggest that the oral route may be an effective and novel mechanism for the efficacious administration of IFNs and other lymphokines/cytokines.

Oral application of cytokines

A number of different laboratories reported on studies with orally administered interferons and cytokines. Their observations extend previous observations which showed that orally administered interferons and cytokines can exert both local and systemic effects. As difficult as it may be to understand how orally administered interferons and cytokines may exert both effects, the increasing number of laboratories that demonstrate biological effects with orally administered cytokines suggests that serious consideration be given to the possibility that orally administered interferons and cytokines can indeed exert effects. They also raise the possibility that these effects may have biological relevance for the treatment of human disease. Moreover, they may indicate that the nasal/oral region is a window on the environment. It is most important, however, to assure that these experiments are performed with special care to avoid presenting preliminary data that is not properly controlled. It is essential to carry out these studies with sufficient animals or patients to ascertain their significance; and to plan the studies as double-blind evaluations to avoid misinterpretations when subjective tests are used. Nevertheless, the overall data presented give one the impression of an area that should be pursued.

Modulation of peripheral leukocyte counts and bone marrow function in mice by oral administration of interleukin-2

Interferons alpha, beta, and gamma have been shown to exert systemic effects following their oral administration to mice. It was of importance to determine whether oral administration of another biologic response modifier, interleukin-2 (IL-2), could also exert systemic effects in mice. Two systemic effects, peripheral WBC suppression and bone marrow suppression, were evaluated. Oral administration of IL-2 was found to suppress the peripheral WBC count in a dose-dependent manner. Oral administration of IL-2 was also found to suppress the bone marrow proliferative activity. The levels of suppression of both peripheral WBC and myelopoietic progenitor cell numbers observed with orally administered IL-2 were comparable to those seen with subcutaneously administered IL-2. The results demonstrate that orally administered IL-2 can exert systemic effects. Further, the results raise the possibility that oral administration of IL-2 may have therapeutic potential.

T-cell-mediated clearance of mouse hepatitis virus strain JHM from the central nervous system

Clearance of the neurotropic JHM strain of mouse hepatitis virus from the central nervous system was examined by the transfer of spleen cells from immunized donors. A T cell with the surface phenotype of Thy1.2+ CD4+ CD8- asialo-GM1+ Mac-1- was found to be necessary for viral clearance. The surface phenotype and adherence to nylon wool suggest that these cells are activated helper-inducer T cells. Adoptive transfer to congenic histocompatibility strains demonstrated the necessity for compatibility at the D locus of the major histocompatibility complex. The expression of the CD4 surface marker and the requirement for major histocompatibility complex class I were further studied by the transfer of cells to recipients treated with anti-CD4 or anti-CD8 monoclonal antibodies. Treatment of recipients with either the anti-CD8 or the anti-CD4 antibodies inhibited virus clearance from the central nervous system. This suggests that the CD4+ cell acts as a helper and that virus is cleared from the central nervous system. This suggests that the CD4+ cell acts as a helper and that virus is cleared from the central nervous system by CD8+ cells that recognize viral antigen in the context of the H-2Db gene product.

Virus strain specificity of challenge immunity to coronavirus

The resistance of immunized mice to challenge with the same or a different strain of mouse hepatitis virus (MHV) was examined as a model of challenge immunity to coronavirus infection. Genetically susceptible BALB/cByJ mice were given an intranasal immunizing infection of respiratory-type MHV-JHM, MHV-S, or enterotropic MHV-Y. Control mice were sham-immunized with sterile tissue culture fluid. Recovered mice were challenged intranasally with MHV-JHM, MHV-S or sterile tissue culture fluid at 30 days after immunization. Resistance to challenge inoculation was evaluated in groups of mice at 4 and 30 days after challenge. At 4 days, the prevalence of MHV lesions in nose and liver was tabulated and MHV titers in liver were determined. At 30 days, the prevalence of residual brainstem spongiform lesions was tabulated and serum antibody to MHV-JHM and MVH-S was quantified by enzyme immunoassay. Mice immunized with MHV-JHM or MHV-S resisted challenge with the MHV homotype, but MHV-S-immunized mice were fully susceptible to challenge with MVH-JHM. Mice immunized with enterotropic MHV-Y were only partially protected against challenge with antigenically related, but biologically different MHV-S. Serum antibody responses to MHV supported these observations. These data indicate that challenge immunity to coronaviruses is strong, but highly virus strain-specific.