Theiler's virus infection in nude mice: viral RNA in vascular endothelial cells

Susceptibility of BALB/c-nu/nu mice and BALB/c mice to equine herpesvirus 9 infection

This study aimed to clarify the timing and infectivity of equine herpesvirus 9 (EHV-9) infection in BALB/c-nu/nu mice and their immunocompetent counterpart (BALB/c). Following intranasal inoculation with 10(5) PFU of EHV-9, specimens from 8 mice per group were collected at different times postinoculation (PI) and assessed using histopathology, immunohistochemistry for viral antigen, and quantitative real-time polymerase chain reaction for ORF30 gene expression. In BALB/c-nu/nu mice, EHV-9 antigen was abundant in olfactory epithelia of all inoculated animals, and in the olfactory bulb of 1 animal. In contrast, only 1 BALB/c mouse per time point had rhinitis, with mild to moderate immunopositivity starting from 12 to 48 h PI, followed by a gradual virus clearance at 72 h PI. Statistically, significant differences were noted in the immunohistochemistry reactions between the 2 mouse strains, indicating that BALB/c-nu/nu is more susceptible to infection. Relative expression levels of ORF30 gene in olfactory epithelia were significantly different between the 2 groups, with the exception of 12 h PI, when BALB/c-nu/nu animals showed dramatic increases in ORF30 gene expression level until 48 h PI, followed by a decline in expression level until the end of experiment. In contrast, the expression level in brains showed no differences between mouse strain except at 96 h PI. In both strains, the highest messenger RNA expression was detected at 48 h PI, followed by a decline in BALB/c mice, proving a rapid clearance of virus in BALB/c and a gradual slowing down of the increased expression levels in BALB/c-nu/nu.

In vivo tropisms and kinetics of rat theilovirus infection in immunocompetent and immunodeficient rats

Rat theilovirus (RTV) is a cardiovirus related to Theiler's murine encephalomyelitis virus. While RTV is a prevalent viral pathogen of rats used in biomedical research, the pathogenesis and characterization of RTV infections is not well understood. In the studies reported herein, we used immunohistochemistry to identify viral antigens in enterocytes of the small intestines of Sprague-Dawley (SD) rats. Fecal viral shedding in immunocompromised and immunocompetent rats following oral gavage with RTV1 was high for the first 2 weeks of infection with persistent shedding of high viral loads being observed in immunocompromised nude rats but not in immunocompetent rats. RTV was also detected in mesenteric lymph nodes and spleen of immunocompromised rats but not immunocompetent rats. In addition, the magnitude of serum antibody responses differed between immunocompetent rat strains with Brown Norway and SD rats having a significantly higher antibody response than CD or Fischer 344 rats. These data suggest that RTV1 has a tropism for the epithelial cells of the small intestine, immunocompetent rats have differing serum antibody responses to RTV infection, and sustained fecal shedding and extraintestinal dissemination of RTV1 occurs in rats deficient in T cell-dependent adaptive immunity. RTV infection in immunocompromised and immunocompetent rats has merit as a model for further studies of theilovirus pathogenesis following oral viral exposure.

Development of postinfection epilepsy after Theiler's virus infection of C57BL/6 mice

Viral infection of the central nervous system can lead to long-term neurologic defects, including increased risk for the development of epilepsy. We describe the development of the first mouse model of viral-induced epilepsy after intracerebral infection with Theiler's murine encephalomyelitis virus. Mice were monitored with long-term video-electroencephalogram at multiple time points after infection. Most mice exhibited short-term symptomatic seizures within 3 to 7 days of infection. This was followed by a distinct latent period in which no seizures were observed. Prolonged video-electroencephalogram recordings at 2, 4, and 7 months after the initial infection revealed that a significant proportion of the mice developed profound, spontaneous epileptic seizures. Neuropathologic examination revealed hippocampal sclerosis in animals with epilepsy. Theiler's murine encephalomyelitis virus-infected C57BL/6 mice represent a novel "hit-and-run" model to investigate mechanisms underlying viral-induced short-term symptomatic seizures, epileptogenesis, and epilepsy. Importantly, this model will also be useful to investigate novel therapies for the treatment and prevention of epilepsy.

Microbial induction of vascular pathology in the CNS

The central nervous system (CNS) is a finely tuned organ that participates in nearly every aspect of our day-to-day function. Neurons lie at the core of this functional unit and maintain an active dialogue with one another as well as their fellow CNS residents (e.g. astrocytes, oligodendrocytes, microglia). Because of this complex dialogue, it is essential that the CNS milieu be tightly regulated in order to permit uninterrupted and efficient neural chemistry. This is accomplished in part by anatomical barriers that segregate vascular components from the cerebral spinal fluid (CSF) and brain parenchyma. These barriers impede entry of noxious materials and enable the CNS to maintain requisite protein and ionic balances for constant electrochemical signaling. Under homeostatic conditions, the CNS is protected by the presence of specialized endothelium/epithelium, the blood brain barrier (BBB), and the blood-CSF barrier. However, following CNS infection these protective barriers can be comprised, sometimes resulting in severe neurological complications triggered by an imbalance or blockage of neural chemistry. In some instances, these disruptions are severe enough to be fatal. This review focuses on a selection of microbes (both viruses and parasites) that compromise vascular barriers and induce neurological complications upon gaining access to the CNS. Emphasis is placed on CNS diseases that result from a pathogenic interplay between host immune defenses and the invading microbe.

Innate host barriers to viral trafficking and population diversity: lessons learned from poliovirus

Poliovirus is an error-prone enteric virus spread by the fecal-oral route and rarely invades the central nervous system (CNS). However, in the rare instances when poliovirus invades the CNS, the resulting damage to motor neurons is striking and often permanent. In the prevaccine era, it is likely that most individuals within an epidemic community were infected; however, only 0.5% of infected individuals developed paralytic poliomyelitis. Paralytic poliomyelitis terrified the public and initiated a huge research effort, which was rewarded with two outstanding vaccines. During research to develop the vaccines, many questions were asked: Why did certain people develop paralysis? How does the virus move from the gut to the CNS? What limits viral trafficking to the CNS in the vast majority of infected individuals? Despite over 100 years of poliovirus research, many of these questions remain unanswered. The goal of this chapter is to review our knowledge of how poliovirus moves within and between hosts, how host barriers limit viral movement, how viral population dynamics impact viral fitness and virulence, and to offer hypotheses to explain the rare incidence of paralytic poliovirus disease.

Theiler's virus infection chronically alters seizure susceptibility

PURPOSE

Central nervous system infections greatly increase the risk for the development of seizures and epilepsy (recurrent unprovoked seizures). We have previously shown that Theiler's murine encephalomyelitis virus (Theiler's virus or TMEV) infection causes acute symptomatic seizures in C57BL/6 (B6) mice. The objective of the present study was threefold: (1) to assess pathologic changes associated with acute TMEV infection and infection-induced seizures, (2) to determine whether Theiler's virus infection and associated acute seizures lead to chronically altered seizure susceptibility, and (3) to determine whether genetic background influences seizure susceptibility following Theiler's virus infection.

METHODS

Immunohistochemical techniques were used to assess Theiler's virus antigen localization in the brain and associated neuronal cell death. A battery of electroconvulsive threshold (ECT) tests and corneal kindling studies were conducted to assess whether there were chronic alterations in seizure susceptibility and kindling development. Studies were conducted in both B6 and SJL/J mice to assess strain-dependent effects.

RESULTS

Histopathologic analyses indicate that TMEV has specific tropism for limbic structures and causes widespread cell death in these regions. Results from ECT studies demonstrate that B6 mice that displayed acute symptomatic seizures have significantly reduced seizure thresholds and kindle faster than either control mice or infected mice without acute seizures. Furthermore, these effects were mouse-strain dependent, since SJL/J mice displayed a different seizure threshold spectrum.

DISCUSSION

These findings indicate that Theiler's virus infection leads to chronically altered seizure susceptibility in mice. It is important to note that Theiler's virus infection of B6 mice represents a novel model to study postinfection hyperexcitability.

Contrasting roles for axonal degeneration in an autoimmune versus viral model of multiple sclerosis: When can axonal injury be beneficial?

Although demyelination is a cardinal feature in multiple sclerosis, axonal injury also occurs. We tested whether a delay in axonal degeneration could affect the disease severity in two models for multiple sclerosis: experimental autoimmune encephalomyelitis (EAE) and Theiler's murine encephalomyelitis virus (TMEV) infection. We compared wild-type C57BL/6 (B6) mice with C57BL/Wld(s) (Wld) mice, which carry a mutation that delays axonal degeneration. In EAE, both mouse strains were sensitized with myelin oligodendrocyte glycoprotein (MOG)(35-55) peptide and showed a similar disease onset, MOG-specific lymphoproliferative responses, and inflammation during the acute stage of EAE. However, during the chronic stage, B6 mice continued to show paralysis with a greater extent of axonal damage, demyelination, and MOG-specific lymphoproliferative responses compared with Wld mice, which showed complete recovery. In TMEV infection, only Wld mice were paralyzed and had increased inflammation, virus antigen-positive cells, and TMEV-specific lymphoproliferative responses versus infected B6 mice. Because TMEV can use axons to disseminate in the brain, axonal degeneration in B6 mice might be a beneficial mechanism that limits the virus spread, whereas slow axonal degeneration in Wld mice could favor virus spread. Therefore, axonal degeneration plays contrasting roles (beneficial versus detrimental) depending on the initiator driving the disease.

Restraint stress facilitates systemic dissemination of Theiler's virus and alters its pathogenecity

Theiler's murine encephalomyelitis virus (TMEV), a Picornavirus used as a viral model for multiple sclerosis (MS), causes an acute encephalomyelitis and chronic demyelination. The failure to clear the virus, which can result from stress, is a prerequisite for development of the later disease. Similarly, stressful life events have been associated with the development of MS. In the present study, a restraint stress (RS) model was used to investigate the effect of stress on the systemic dissemination of TMEV during the early stage of disease. Experimental data demonstrated that repeated RS remarkably facilitated the spread of virus from the CNS to such systemic organs as the spleen, lymph nodes, thymus, lungs and heart and compromised the ability of viral clearance within those tissues. RS also altered the pathogenecity of TMEV, enabling it to become cardiotropic, resulting in higher myocardial infectivity. These results demonstrate the profound impact that RS has upon both the tissue and organ dissemination of the virus, and the organ tropism of TMEV. An additional finding associated with stress was hepatic necrosis in the restrained animals, regardless of whether or not they were infected.

A comparison of the neurotropism of Theiler's virus and poliovirus in CBA mice

Theiler's murine encephalomyelitis virus (TMEV) and poliovirus infect the central nervous system (CNS) and cause neurological damage. The exact route by which TMEV and polioviruses enter the CNS remains, for the most part, unknown, although the neural and/or the hematogenous pathway have both been postulated. To explore these hypotheses, this research focuses on both the site of entry and the pathway used to invade the CNS. Following different inoculation sites of the GDVII strain of Theiler's virus or Lansing Type 2 poliovirus in CBA mice, the incidence of paralysis and/or encephalitis was evaluated on the basis of clinical signs and histopathology. The forms of paralysis displayed corresponded to the site of viral inoculation. Following intramuscular (i.m.), intraperitoneal (i.p.), and footpad routes of injection, bilateral and or contralateral paralyses were observed for both TMEV and poliovirus. In mice injected intratongue and in the hypoglossal nerve, tongue paralysis or paralysis of the forelimb, which progressed to bilateral forelimb paralysis, was observed, additionally the penis of most infected males was protruded. Intracranial (i.c.) injections with type II poliovirus strain resulted in forelimb paralysis. Intravenous (i.v.), injections with TMEV also resulted in forelimb paralysis. Thus Lansing Type II poliovirus and TMEV infections of CBA mice, result in similar incidence of paralysis and histopathological findings.

Exacerbation of viral and autoimmune animal models for multiple sclerosis by bacterial DNA

Theiler's murine encephalomyelitis virus (TMEV) infection and relapsing-remitting experimental allergic encephalomyelitis (R-EAE) have been used to investigate the viral and autoimmune etiology of multiple sclerosis (MS), a possible Th1-type mediated disease. DNA immunization is a novel vaccination strategy in which few harmful effects have been reported. Bacterial DNA and oligodeoxynucleotides, which contain CpG motifs, have been reported to enhance immunostimulation. Our objectives were two-fold: first, to ascertain whether plasmid DNA, pCMV, which is widely used as a vector in DNA immunization studies, could exert immunostimulation in vitro; and second, to test if pCMV injection could modulate animal models for MS in vivo. We demonstrated that this bacterially derived DNA could induce interleukin (IL)-12, interferon (IFN)gamma, (Th1-promoting cytokines), and IL-6 production as well as activate NK cells. Following pCMV injections, SJL/J mice were infected with TMEV or challenged with encephalitogenic myelin proteolipid protein (PLP) peptides. pCMV injection exacerbated TMEV-induced demyelinating disease in a dose-dependent manner. Exacerbation of the disease did not correlate with the number of TMEV-antigen positive cells but did with an increase in anti-TMEV antibody. pCMV injection also enhanced R-EAE with increased IFNgamma and IL-6 responses. These results caution the use of DNA vaccination in MS patients and other possible Th1-mediated diseases.

Axonal injury heralds virus-induced demyelination

Axonal pathology has been highlighted as a cause of neurological disability in multiple sclerosis. The Daniels (DA) strain of Theiler's murine encephalomyelitis virus infects the gray matter of the central nervous system of mice during the acute phase and persistently infects the white matter of the spinal cord during the chronic phase, leading to demyelination. This experimental infection has been used as an animal model for multiple sclerosis. The GDVII strain causes an acute fatal polioencephalomyelitis without demyelination. Injured axons were detected in normal appearing white matter at 1 week after infection with DA virus by immunohistochemistry using antibodies specific for neurofilament protein. The number of damaged axons increased throughout time. By 2 and 3 weeks after infection, injured axons were accompanied by parenchymal infiltration of Ricinus communis agglutinin I(+) microglia/macrophages, but never associated with perivascular T-cell infiltration or obvious demyelination until the chronic phase. GDVII virus infection resulted in severe axonal injury in normal appearing white matter at 1 week after infection, without the presence of macrophages, T cells, or viral antigen-positive cells. The distribution of axonal injury observed during the early phase corresponded to regions where subsequent demyelination occurs during the chronic phase. The results suggest that axonal injury might herald or trigger demyelination.

Altered cell growth and morphology in a BHK-21 cell mutant that lacks a receptor for Theiler's murine encephalomyelitis virus

The receptor for Theiler's murine encephalomyelitis virus (TMEV) remains unknown. In vitro, BHK-21 cells are permissive to infection by TMEV. Selecting mutants of BHK-21 cells produced a cell line (BHKR-) resistant to infection by TMEV. Viral persistence was ruled out by immunofluorescent staining for viral antigens. BHKR- cells were nonpermissive to infection even at high multiplicities of infection. In contrast, cells were able to support one round of virus replication when transfected with infectious TMEV RNA. Binding studies indicated that TMEV was unable to attach to these cells. These data are consistent with the BHKR- cells lacking a receptor for TMEV. Interestingly, BHKR- cells were larger in size and had a significant lag in growth after subculture versus BHK-21 cells. This suggests that the TMEV receptor on BHK-21 cells could play an important role in cell growth and morphology under physiologic conditions. BHKR- cells should facilitate the search for TMEV receptors.

Ovine IFN-tau modulates the expression of MHC antigens on murine cerebrovascular endothelial cells and inhibits replication of Theiler's virus

Interferon-beta (IFN-beta) has been used successfully to treat patients with relapsing-remitting multiple sclerosis (MS). IFN-tau is a new class of type I IFN that is secreted by the trophoblast and is the signal for maternal recognition of pregnancy in sheep. IFN-tau has potent immunosuppressive and antiviral activities similar to other type I IFN but is less cytotoxic than IFN-alpha/beta. The current investigation concerns the effect of recombinant ovine IFN-tau (rOvIFN-tau) on the modulation of MHC class I and II expression on cloned mouse cerebrovascular endothelial (CVE) cells. IFN-tau induced tyrosine phosphorylation of Stat1 and upregulated the expression of MHC class I on CVE. One proposed action by which type I IFN reduce the relapse rate in MS is via interference with IFN-gamma-induced MHC class II expression. IFN-tau was shown to downregulate IFN-gamma-induced MHC class II expression on CVE and, hence, may be of potential therapeutic value in downregulating inflammation in the central nervous system (CNS). IFN-tau did not upregulate the expression of MHC class II on CVE. IFN-tau also inhibited the replication of Theiler's virus in CVE. These in vitro results suggest that IFN-tau may be of therapeutic value in the treatment of virus-induced demyelinating disease.

Theiler's murine encephalomyelitis virus induces rapid necrosis and delayed apoptosis in myelinated mouse cerebellar explant cultures

Infection with the Daniel strain of Theiler's murine encephalomyelitis (TMEV-DA) virus induces persistent demyelinating lesions in mice and serves as a model for multiple sclerosis. During the acute phase of the disease, however, viral infection leads to cell death in vivo. Viral-induced death may result directly from viral infection of neural cells, or indirectly, by activation of the immune system. To examine the direct effects of TMEV infection on neural cells, myelinated explant cultures of the murine cerebellum were infected with 10(5) pfu of TMEV-DA for periods ranging from 1 to 72 h. Our results indicate that TMEV-DA replicates in cultured neural tissue. Initially, viral antigen is localized to a few isolated neural cells. However, within 72 h antigen was observed in multiple foci that included damaged cells and extracellular debris. Viral infection led to a rapid and cyclical induction of necrosis with a time period that was consistent with the lytic phase of the viral life-cycle. Simultaneously, we observed an increase in apoptosis 48 h post-infection. Electron micrographic analysis indicated that viral-infected cultures contained cells with fragmented nuclei and condensed cytoplasm, characteristic of apoptosis. The localization of apoptosis to the cerebellar granule cell layer, identified these cells as presumptive granule neurons. Viral infection, however, did not lead to myelin damage, though damaged axons were visible in TMEV-infected cultures. These results suggest that during the acute phase of infection, TMEV targets neural cells for apoptosis without directly disrupting myelin. Myelin damage may therefore result from the activation of the immune system.

Theiler's viruses with mutations in loop I of VP1 lead to altered tropism and pathogenesis

Theiler's murine encephalomyelitis viruses are picornaviruses that can infect the central nervous system. The DA strain produces an acute polioencephalomyelitis followed by a chronic demyelinating disease in its natural host, the mouse. The ability of DA virus to induce a demyelinating disease renders this virus infection a model for human demyelinating diseases such as multiple sclerosis. Here we describe the generation and characterization of DA virus mutants that contain specific mutations in the viral capsid protein VP1 at sites believed to be important contact regions for the cellular receptor(s). A mutant virus with a threonine-to-aspartate (T81D) substitution in VP1 loop I adjacent to the putative virus receptor binding site exhibited a large-plaque phenotype but had a slower replication cycle in vitro. When this mutant virus was injected into susceptible mice, an altered tropism was seen during the acute stage of the disease and the chronic demyelinating disease was not produced. A virus with a threonine-to-valine substitution (T81V) did not cause any changes in the pattern or extent of disease seen in mice, whereas a virus with a tryptophan substitution at this position (T81W) produced a similar acute disease but was attenuated for the development of the chronic disease. A change in amino acids in a hydrophobic patch located in the wall of the pit, VP1 position 91, to a hydrophilic threonine (V91T) resulted in a profound attenuation of the acute and chronic disease without persistence of virus. This report illustrates the importance of the loop I of VP1 and a site in the wall of the pit in pathogenesis and that amino acid substitutions at these sites result in altered virus-host interactions.

An attenuated variant of the GDVII strain of Theiler's virus does not persist and does not infect the white matter of the central nervous system

The DA strain of Theiler's virus causes a persistent and demyelinating infection of the white matter of spinal cord, whereas the GDVII strain causes a fatal gray-matter encephalomyelitis. Studies with recombinant viruses showed that this difference in phenotype is controlled mainly by the capsid. However, conflicting results regarding the existence of determinants of persistence in the capsid of the GDVII strain have been published. Here we show that a GDVII virus whose neurovirulence has been attenuated by an insertion in the 5' noncoding region does not persist in the central nervous systems of mice. Furthermore, this virus infects the gray matter efficiently, but not the white matter. These results confirm the absence of determinants of persistence in the GDVII capsid. They suggest that the DA capsid controls persistence by allowing the virus to infect cells in the white matter of the spinal cord.

Spontaneous demyelinating myelopathy in aging laboratory mice

Spontaneous demyelination has been observed to occur sporadically in the thoracic spinal cord of aging laboratory mice used in routine long-term chemical safety studies. Positive immunohistochemical reaction for VP-1 (virus protein) indicated that the demyelination was associated with Theiler's murine encephalomyelitis virus infection. Although this rare spontaneous lesion has no bearing on the quality of chemical safety studies, its knowledge is essential for the appropriate interpretation of study results.

The infection of mouse by Theiler's virus: from genetics to immunology

Theiler's virus is a picornavirus of mouse which causes an acute encephalomyelitis followed by a persistent infection of the white matter of the spinal cord with chronic inflammation and demyelination. This late disease is studied as a model for multiple sclerosis. Inbred strains of mice differ in their susceptibility to persistent infection and demyelination. Resistant strains clear the infection after the acute encephalomyelitis. This observation is the basis of genetic studies which we used as a thread for this review. The H-2D locus has a major effect on susceptibility. The H-2Db gene is involved in a fast and intense CTL response which confers resistance. The Tcrb locus is also implicated, although there is no proof that the susceptibility gene in this region codes for the T-cell receptor. A complete screen of the genome uncovered the role of the Ifng locus and led to the demonstration that IFN-gamma limits viral spread in the white matter. The roles of NK cells and B cells in limiting the infection are discussed. CD4+ T cells participate both in protection against the infection and in demyelination. Finally, the effect of non-immune factors in resistance is illustrated by mice with mutations in the MBP or PLP gene.

Apoptosis in acute and chronic central nervous system disease induced by Theiler's murine encephalomyelitis virus

Apoptosis has been observed in neural development and in various neurological diseases, including viral infection and multiple sclerosis. Theiler's murine encephalomyelitis virus is divided into two subgroups based on neurovirulence: the highly neurovirulent GDVII strain produces an acute fatal polioencephalomyelitis in mice, whereas the attenuated DA strain produces demyelination with virus persistence preceded by an acute infection. TUNEL combined with immunocytochemistry was used to detect apoptosis in the central nervous system and to characterize which cell types were involved during the acute stage in both GDVII and DA virus infection and during the chronic stage in DA virus infection. We found that during the acute stage, apoptosis was induced in neurons in both virus infections. However, the number of apoptotic neurons was much greater in GDVII virus-infected mice than in DA virus-infected mice (P < 0.01). During the chronic stage of DA virus infection, apoptotic cells were detected only in the spinal cord white matter. Some of these cells were dual labeled for fragmented DNA and carbonic anhydrase II, an oligodendrocyte marker. Our results indicate that apoptosis of neurons could be responsible for the fatal outcome in GDVII virus infection. In contrast, apoptosis of oligodendrocytes can contribute to the chronic demyelinating DA virus infection.

Infection of class II-deficient mice by the DA strain of Theiler's virus

The DA strain of Theiler's virus causes, in susceptible strains of mice, a persistent infection of the white matter of the spinal cord accompanied by chronic inflammation and primary demyelination. In resistant strains, including all H-2b strains, mice clear the infection after 1 to 2 weeks. We inoculated RHAbetao/o mice, an H-2b strain which does not express class II molecules. We found that they are susceptible to persistent infection and that they develop foci of chronic inflammation with demyelination. However, these foci are smaller and contain fewer demyelinated axons than those observed in susceptible SJL/J or beta2m-/- mice.

Characteristics of cloned cerebrovascular endothelial cells following infection with Theiler's virus. I. Acute infection

The present study describes the replication of Theiler's virus in cloned cerebrovascular endothelial cells (CVE) isolated from strains of mice that are either susceptible or resistant to Theiler's virus-induced demyelination (TVID). CVE isolated from all strains of mice were equally permissive to Theiler's virus infection. Interferon-gamma and tumor necrosis factor-alpha were found to inhibit the replication of Theiler's virus in CVE. A correlation between susceptibility to demyelination and the ability of Theiler's virus to induce MHC Class I on CVE was demonstrated.

Characteristics of cloned cerebrovascular endothelial cells following infection with Theiler's virus. II. Persistent infection

Cloned cerebrovascular endothelial cells (CVE) persistently infected with Theiler's virus (PI-CVE) have been established and characterized. The CVE were derived from strains of mice that are susceptible (SJL/J and CBA) and resistant (BALB/c) to Theiler's virus-induced demyelination (TVID). The cells were persistently infected with either the BeAn or GDVII strains of Theiler's virus in vitro and studied at various passage levels for infectious virus, viral antigen and the expression of major histocompatibility complex (MHC) Class I and II antigens. The virus replicated to lower titers than in acutely infected CVE and appeared to be more cell-associated. Flow cytometric analysis revealed that 18-39% of the PI-CVE contained viral antigen. Persistently infected CVE derived from SJL/J and CBA mice expressed high levels of MHC Class I, whereas BALB/c PI-CVE did not. MHC Class II was upregulated by IFN-gamma in SJL/J PI-CVE albeit at a slightly lower level than in uninfected CVE. In addition, the PI-CVE demonstrated increased levels of mRNA for IL-1 beta when compared to uninfected CVE.

Mode of spread to and within the central nervous system after oral infection of neonatal mice with the DA strain of Theiler's murine encephalomyelitis virus

Theiler's murine encephalomyelitis virus is a neurotropic enterovirus known to cause biphasic neural disease after intracerebral inoculation into adult mice. The present study characterizes a neonatal mouse model with a high disease incidence for the study of the acute phase of the pathogenesis of the DA strain of Theiler's murine encephalomyelitis virus after oral infection. The route of viral spread to and within the central nervous system (CNS) was determined by examining the kinetics of viral replication in various organs and by performing histopathological analysis. Viral antigen was detected widely in the neonatal CNS, mainly in the gray matter, and it was asymmetrical and multifocal in its distribution, with considerable variation in lesion distribution from animal to animal. Necrotizing lesions appeared to expand by direct extension from infected cells to their close neighbors, with a general disregard of neuroanatomical boundaries. The diencephalon showed particular susceptibility to viral infection. Other areas of the CNS, including the cerebellum and dentate gyrus of the hippocampus, were consistently spared. Neurons with axons extending peripherally to other organs or receiving direct input from the peripheral nervous system were not preferentially affected. The kinetics of viral replication in the liver, spleen, and CNS and the histopathological findings indicate that viral entry to the CNS is via a direct hematogenous route in orally infected neonatal mice and that the disease then progresses within the CNS mainly by direct extension from initial foci.

Immunology of Theiler's murine encephalomyelitis virus infection

Theiler's murine encephalomyelitis virus (TMEV) is a single-stranded RNA virus that belongs to the family of picornaviruses. Intracranial inoculation of susceptible mouse strains with TMEV results in biphasic disease, consisting of early acute disease that resembles poliomyelitis, followed by late chronic demyelinating disease that is characterized by the appearance of chronic inflammatory demyelinating lesions. Susceptibility to TMEV infection is genetically controlled by three loci: one that maps to the H-2D region of the major histocompatibility complex, one to the beta-chain constant region of the T-cell antigen receptor, and one located on chromosome 3. Both early acute and chronic late demyelinating diseases are immunologically mediated. T cells appear to play an important role in the pathogenesis of the disease. TMEV-induced demyelinating disease in mice has extensive similarities with multiple sclerosis, and it is considered one of the best experimental animal models for multiple sclerosis.

Semliki Forest virus infects mouse brain endothelial cells and causes blood-brain barrier damage

Induction of experimental allergic encephalomyelitis is facilitated in a genetically resistant BALB/c mouse strain by a nonpathogenic strain of a neurotropic alphavirus, Semliki Forest virus (SFV-A7). One possible explanation for this enhancement is virus infection of endothelial cells (EC), causing increased permeability of the blood-brain barrier. We have now sought evidence for virus infection of EC in vivo by immunocytochemistry and in situ hybridization. SFV-A7 antigens and RNA were detected in vascular EC and perivascular neurons in cerebellar and spinal cord white matter. Expression of viral antigens was followed by fibrinogen leakage from the blood vessels into brain parenchyma. This was shown by immunoperoxidase staining detecting fibrinogen extravascularly in central nervous system sections of infected mice. Simultaneously, expression of ICAM-1 (intercellular adhesion molecule 1) was induced on brain EC. SFV-A7 replicated in mouse brain microvascular EC in vitro and caused lysis of the cells. SFV-A7 did not induce ICAM-1 expression of mouse brain microvascular EC in vitro, while ICAM-1 was readily induced by gamma interferon and interleukin 1 beta. The observed increase of ICAM-1 expression on EC is immune mediated and not a direct effect of the virus infection. We conclude that SFV-A7 infection causes cerebral microvascular damage which contributes to the facilitation of experimental allergic encephalomyelitis in BALB/c mice.

Characterization of a murine central nervous system-derived cell line: infectability and presentation of viral antigen

The cerebral endothelial cell line, 33-Mse, was characterized for its MHC antigen expression, infectability with viruses and capacity to present antigen to immune spleen cells. The cell line had interferon-gamma inducible MHC antigen expression. Infection by Theiler's murine encephalomyelitis influenced the expression of MHC molecules on the cell surface of this line. These cells could not stimulate T splenocyte proliferation or act as targets for Theiler's murine encephalomyelitis cytolytic immune spleen cells. These cells were able to present viral antigen to vaccinia virus immune spleen cells and act as targets for cytotoxic T cells from vaccinia virus immune mice.

Importance of amino acid 101 within capsid protein VP1 for modulation of Theiler's virus-induced disease

We constructed a Theiler's virus mutant designated DA3304, in which the amino acid at position 101 of VP1 was changed from a threonine to an alanine. Because of this single amino acid change, DA3304 could still produce a biphasic central nervous system disease similar to that produced by the wild-type DA virus. However, DA3304 was significantly attenuated in both the acute and the chronic phases and induced smaller demyelinating lesions than the wild-type DA virus. The data are most compatible with the attenuated phenotype in DA3304 being due to the change of binding efficiency between the virus and receptor resulting from the physical alteration at the mutation site.

Viral infection and dissemination through the olfactory pathway and the limbic system by Theiler's virus

Theiler's murine encephalomyelitis virus (TMEV) infection of mice can produce a biphasic disease of the central nervous system (CNS). Most susceptible strains of mice survive the acute infection and develop a chronic demyelinating disease. In this report, we analyzed the routes of spread of TMEV within the CNS of nude mice and target sites eventually infected in the CNS. Compared to the immunocompetent mouse, in which an antiviral immune response is mounted but virus persists, the nude mouse develops a severe encephalomyelitis due to the lack of functional T lymphocytes and provides a useful model for the study of viral dissemination. We demonstrated, by immunohistochemistry, the presence of viral antigen in defined regions of the CNS, corresponding to various structures of the limbic system. In addition, we found a different time course for viral spread using two different sites of intracerebral inoculation, ie, via the olfactory bulb or the cortex. Limbic structures were rapidly infected following olfactory bulb infection and then showed a decrease in viral load, presumably due to loss of target neurons. Using either route of infection, the virus was able to disseminate to similar regions. These results indicate that limbic structures and their connections are very important for the spread of TMEV in the brain. In the spinal cord, not only neuronal but hematogenous pathways were suspected to be involved in the dissemination of Theiler's virus.

Theiler's virus infection of beta 2-microglobulin-deficient mice

Theiler's virus, a murine picornavirus, persists in the central nervous systems of susceptible mice and induces a chronic demyelinating disease. Susceptibility or resistance to this disease is controlled in part by the H2-D locus of the major histocompatibility complex (MHC). For this reason, it has been proposed that CD8+ class I-restricted cytotoxic T cells play a main role in the pathogenesis of this viral infection. We recently reported the existence of anti-virus CD8+ cytotoxic T cells in the course of Theiler's virus infection. In the present study, we examined the role of these effector cells in mice in which the beta 2-microglobulin gene had been disrupted. These mice fail to express class I MHC molecules and therefore lack CD8+ T cells. The mice are derived from a C57BL/6 x 129/Ola cross and are H-2b, a haplotype associated with resistance to Theiler's virus infection. beta 2-Microglobulin-deficient mice (beta 2m-/-mice) failed to clear the virus, developed demyelination, and, interestingly, did not succumb to early infection. These results demonstrate that CD8+ T cells are required to clear Theiler's virus infection. In contrast with a current hypothesis, they also demonstrate that CD8+ T cells are not major mediators of the demyelinating disease.

Vacuolar neuronal degeneration in the ventral horns of SCID mice in naturally occurring Theiler's encephalomyelitis

During a spontaneous outbreak of Theiler's encephalomyelitis severe combined immunodeficient mice developed high morbidity and high mortality. Histological lesions were localized in the ventral horns of the spinal cord and brain stem. The salient features were the severe vacuolar degeneration of neurones and glial cells and the absence of inflammatory cellular infiltrates. The clinical and pathological features of this outbreak indicate that the SCID mouse would be a much improved model for studying the mechanism of poliovirus infection and of virus-induced demyelinating diseases.

Viral susceptibility of an immortalized human microvascular endothelial cell line

CDC/EU.HMEC-1 is the first immortalized human microvascular endothelial cell line that retains morphologic, phenotypic, and functional characteristics of a normal human microvascular endothelial cell. This study evaluates a variety of viruses and their effects on this human endothelial cell line. The data indicate that adenoviruses, some herpesviruses, reoviruses and most picornaviruses grow well in HMEC-1, with distinctive cytopathic effects. The paramyxoviruses, however, do not appear to propagate, nor does HIV. The findings indicate that microvascular endothelial cells may act as a reservoir of these viruses; it also suggests the possibility that microvascular endothelium could be involved in the processing and presentation of antigen to immune cells.

Mouse hepatitis virus (MHV-4, JHM) blocks gamma-interferon-induced major histocompatibility complex class II antigen expression on murine cerebral endothelial cells

The regulation of gamma-interferon-induced major histocompatibility complex (MHC) class II antigen expression on mouse cerebral endothelial cells by the neurotropic mouse hepatitis virus (MHV-4, JHM) was studied in vitro. The results presented demonstrate that MHV-4 can selectively block gamma-interferon-induced class II antigen expression on cerebral endothelial cells. The blocking effect of class II expression occurs in a strain-dependent manner, and is limited to virus-susceptible mouse strains. Virus replication is not required to obtain the blocking effect since UV-inactivated MHV-4 produces the same result. MHV-4 blocking of gamma-interferon-induced class II antigen expression is observed at both the cell surface (flow cytometry) and transcriptional level (Northern analysis).

Role of the humoral immune response in resistance to Theiler's virus infection

Theiler's virus, a murine picornavirus, persists in the central nervous system of susceptible strains of mice, causing chronic inflammation and demyelination in the white matter of the spinal cord. Resistant strains, however, clear the virus and do not develop late disease. In this study, we compared the characteristics of T and B lymphocytes in C57BL/6 (resistant) and SJL/J (susceptible) mice 1 week after intracerebral infection. We detected a marked increase of the number of immunoglobulin M (IgM)-secreting cells in the spleens of C57BL/6 detected a marked increase of the number of immunoglobulin M (IgM)-secreting cells in the spleens of C57BL/6 mice (but not in those of SJL/J mice), which correlated with higher levels of serum IgM antiviral antibodies. The role of the humoral response in virus clearance and resistance was demonstrated by a marked decrease in the number of infected spinal cord cells in SJL/J mice after passive transfer of serum from infected C57BL/6 donors. The B-cell response was found to be partly T cell independent. These results suggest an important role of the early humoral immune response in resistance to Theiler's virus-induced disease.

Virological and pathological processes involved in Theiler's virus infection of the central nervous system

Theiler's virus strains GDVII and FA cause an acute encephalitis when injected intracerebrally into mice, whereas strains To, BeAn and DA establish a persistent infection and produce a chronic demyelinating disease. The chronic infection is also dependent on the mouse strain used, with susceptibility linked in part to the D locus of the MHC. The region of the virus genome associated with neurovirulence maps to the P1 region, encoding the capsid proteins, and to the 5′ non-coding region. There is evidence that BeAnDA virus persists in oligodendrocytes, where it reactivates to initiate demyelinating disease. Host factors are involved in the development of the lesion, including CD4⁺ T cell responses. These lymphocytes most probably mediate damage through activation of macrophages leading to local destruction of glial cells. Another possible pathological role for the immune system is the recognition of nerve cell antigens and the initiation of autoimmune disease. Such a virus-triggered phenomenon may well underlie human CNS diseases such as multiple sclerosis.

Nucleic acid detection systems for enteroviruses

The enteroviruses comprise nearly 70 human pathogens responsible for a wide array of diseases including poliomyelitis, meningitis, myocarditis, and neonatal sepsis. Current diagnostic tests for the enteroviruses are limited in their use by the slow growth, or failure to grow, of certain serotypes in culture, the antigenic diversity among the serotypes, and the low titer of virus in certain clinical specimens. Within the past 6 years, applications of molecular cloning techniques, in vitro transcription vectors, automated nucleic acid synthesis, and the polymerase chain reaction have resulted in significant progress toward nucleic acid-based detection systems for the enteroviruses that take advantage of conserved genomic sequences across many, if not all, serotypes. Similar approaches to the study of enteroviral pathogenesis have already produced dramatic advances in our understanding of how these important viruses cause their diverse clinical spectra.

Direct evidence of a role for amino acid 101 of VP-1 in central nervous system disease in Theiler's murine encephalomyelitis virus infection

The DA virus, a member of the TO subgroup of Theiler's virus, invokes a chronic demyelinating disease in its natural host, the mouse, RNA transcripts from a cDNA clone, pDAFL3, are infectious, and the resulting virus, DAFL3, produces in mice a disease indistinguishable from that caused by the DA virus. Using oligonucleotide-directed site-specific mutagenesis, a single nucleotide, cytosine at position 3305 (viral genome), was changed in this infectious cDNA to a thymine. The mutated nucleotide is located in an area coding for a neutralizing epitope on loop II of VP-1. Virus OSM101, produced from the mutagenized plasmid pDA101, had the same growth characteristics and plaque phenotype in vitro as the virus DAFL3 produced from clone pDAFL3. However, in vivo in the mouse, virus OSM101 was markedly less neurovirulent than DAFL3. Central nervous system tissues from mice infected 4 to 6 weeks previously with the OSM101 virus contained less infectious virus and fewer infected cells than central nervous system tissues from animals infected with the control virus, DAFL3. Thus, we demonstrated that the single nucleotide change resulting in an amino acid substitution at position 101 (threonine to isoleucine) of VP-1 determines one aspect of Theiler's virus persistence and disease in mice.

Restricted virus replication in the spinal cords of nude mice infected with a Theiler's virus variant

The Daniels strain of Theiler's murine encephalomyelitis produces a chronic disease which is an animal model for human demyelinating disorders. Previously, we selected a neutralization-resistant virus variant producing an altered and diminished central nervous system disease in immunocompetent mice which was evident during the later stage of infection (after 4 weeks) (A. Zurbriggen and R. S. Fujinami, J. Virol. 63:1505-1513, 1989). The exact epitope determining neurovirulence was precisely mapped to a capsid protein, VP-1, and represents a neutralizing region (A. Zurbriggen, J. M. Hogle, and R. S. Fujinami, J. Exp. Med. 170:2037-2049, 1989). Here, we present experiments with immunoincompetent animals to determine viral replication, spread, and targeting to the central nervous system in the absence of detectable antibodies or functional T cells. Nude mice were infected orally, and the virus was monitored by plaque assay, immunohistochemistry, and in situ hybridization. Early during the infection (1 week), the variant virus induced an acute disease comparable to that induced by the wild-type virus in these nude mice. Alterations in tropism in the central nervous system were not apparent when wild-type parental Daniels strain virus was compared with the variant virus. Moreover, variant virus replicated in tissue culture (BHK-21 cells) to similarly high titers in a time course identical to that of the wild-type virus (A. Zurbriggen and R. S. Fujinami, J. Virol. 63:1505-1513, 1989). However, replication of the variant virus versus the wild-type virus within the spinal cord of athymic nude mice infected per os was substantially restricted by 6 weeks postinfection. Therefore, the reduced neurovirulence in the later stage (6 weeks) of the disease is most likely due to a diminished growth rate or spread of the variant virus in the central nervous system rather than to marked differences in viral tropism.

Pathogenesis of Theiler's murine encephalomyelitis virus

Theiler's murine encephalomyelitis virus belongs to the family of picornaviridae. Picornaviruses are small ( “pico”), phylogenetically related RNA viruses. Based on different biochemical and biophysical characteristics picornaviruses are subdivided into four groups: enteroaphthovirus (foot-and-mouth disease virus), cardiovirus [encephalomyocarditis virus (EMCV), Mengo virus], and rhinovirus (human rhinovirus). Theiler's murine encephalomyelitis virus was originally classified among the picornaviridae as an enterovirus because of its biological similarities with poliovirus. Further comparison of the complete genome of TMEV BeAn 8386 strain identifies remarkable similarities at the level of nucleotides and predicted amino acids between BeAn and the cardioviruses EMCV and Mengo virus. Theiler's murine encephalomyelitis virus is a single-stranded nonenveloped RNA virus. The viral RNA is of positive sense, having the same polarity as mRNA. Viral mRNA lacks the cap structure found at the 5’ end of almost all eukaryotic mRNAs.

The relationship between viral RNA, myelin-specific mRNAs, and demyelination in central nervous system disease during Theiler's virus infection

The DA strain of Theiler's murine encephalomyelitis virus (DAV) causes a chronic demyelinating disease in susceptible mouse strains. To elucidate the pathogenesis of DAV-induced demyelination, the authors investigated the spatial and chronologic relationship between virus (antigen and RNA), myelin-specific mRNAs, and demyelination in DAV-infected mice using immunohistochemistry, in situ hybridization, and slot blot hybridization analyses. In spinal cord white matter, viral RNA was detected easily in ventral root entry zones 1 to 2 weeks after infection. Viral RNA increased to maximum levels by 4 weeks after infection, which was associated with inflammation and mild demyelination. At 8 to 12 weeks after infection, when demyelination became most extensive, viral RNA was significantly decreased. Demyelination did not chronologically or spatially parallel the presence of viral RNA within the spinal cord. Decrease of myelin-specific mRNAs, including myelin-basic protein and proteolipid protein mRNAs, was observed within the demyelinating lesions with or without detectable viral RNA. These results indicate that a viral infection of white matter in the early phase of the infection initiates spinal cord disease leading to demyelination, but later an ongoing immunopathologic process contributes to the presence of extensive demyelination.

Monoclonal antibody to Theiler's murine encephalomyelitis virus defines a determinant on myelin and oligodendrocytes, and augments demyelination in experimental allergic encephalomyelitis

Theiler's murine encephalomyelitis virus (TMEV) causes a chronic demyelinating disease in mice. The mechanisms underlying the demyelination have not been fully elucidated. We have raised a mAb to TMEV (DA strain), H8, that reacts both with TMEV VP-1 and galactocerebroside (GC). In mouse brain cultures, cells positive for the mAb H8 epitope were double labeled with antibody to myelin basic protein, indicating that those cells were oligodendrocytes. Further, mAb H8 could immunostain myelin structures in frozen sections from mouse brains. When injected intravenously into mice with acute allergic encephalomyelitis, mAb H8 increased by 10-fold the size of demyelinated areas within the spinal cords. This is the first report demonstrating that an antibody to virus can enhance demyelination of a central nervous system disease. Ig fractions from the sera of mice with chronic TMEV infection had antibody(s) to GC, as well as to TMEV, as determined by ELISA. Furthermore, a competition ELISA for TMEV or GC antigen revealed that sera from these infected mice contained antibody(s) with the same specificity as mAb H8. Our results indicate that antibodies generated by immune response to TMEV can react with myelin and oligodendrocytes, and contribute to demyelination through an immune process.

Poliovirus permissivity and specific receptor expression on human endothelial cells

To test the role of the endothelial cells (EC) in the poliomyelitis pathogenesis, their sensitivity to poliovirus infection was determined at different times after isolation from the human umbilical vein. While 80% of EC were permissive for poliovirus after 4 days of in vitro primary cultures, only 6% of freshly isolated EC were susceptible to poliovirus infection. A progressive development of this susceptibility was observed during the first 3 days of culture. In an attempt to explain the mechanism of the appearance of cell permissivity for poliovirus, the expression of the poliovirus receptor on EC was studied by cytofluorometric analysis using an anti-receptor monoclonal antibody. The number of poliovirus receptor molecules in the EC population was found to increase with time. This paralleled the increase of the poliovirus-binding capacity of EC cultures. In contrast, the efficiency of viral internalization did not appear to be dependent on the age of culture. These results indicate that the development of EC permissivity for poliovirus in vitro is mainly dependent on the expression of poliovirus receptor on the cell surface.

Survival of athymic (nu/nu) mice after Theiler's murine encephalomyelitis virus infection by passive administration of neutralizing monoclonal antibody

Little or no antiviral immune response is mounted in athymic nude mice infected with the Daniels strain of Theiler's murine encephalomyelitis virus. In these athymic mice, increasing levels of infectious virus could be detected in the central nervous system. Seventy-five percent (9 of 12) of the nude mice were moribund or dead by 4 weeks postinfection. In contrast, treatment of Theiler's virus-infected nude mice with a neutralizing monoclonal antibody (H7-2) against the viral protein VP-1 resulted in a dramatic reduction of infectious virus within the central nervous system. All antibody-treated nude animals survived beyond 4 weeks postinfection. Monoclonal antibody titers could be maintained by passive transfer in treated nude mice at levels comparable to those of polyclonal antibody titers found in heterozygous infected nu/+ littermates. Areas of demyelination were detected in the untreated animals as early as 7 days after infection with little or no remyelination present. In approximately one-half of the antibody-treated nude animals, no demyelinating lesions were found. However, the rest of these treated mice were found to have areas of both demyelination and remyelination. Thus, anti-Theiler's murine encephalomyelitis virus antibody against VP-1 can play a dramatic role in the survival of mice, clearance of virus, limiting viral spread, and altering the pattern of disease in the absence of a functional T-cell response.

A neutralization-resistant Theiler's virus variant produces an altered disease pattern in the mouse central nervous system

Theiler's murine encephalomyelitis virus infection of mice is an animal model for human demyelinating diseases. To further define the role of this virus in the disease process, we selected a virus variant resistant to neutralization by a monoclonal antibody to VP-1. This virus variant was then injected into SJL/J mice. Central nervous system tissue was compared between variant virus- and wild-type virus-infected mice. Within the brain, no large differences were observed between the two groups as to the distribution of inflammatory infiltrates around the injection site and the number of viral antigen-positive cells during the first weeks of the observation period. In contrast, in the spinal cord major differences were found between variant virus- and wild-type virus-infected mice regarding the number of inflammatory lesions, infected cells, and the size of the areas involved with time. By immunohistochemistry, equivalent numbers of infected cells could be found in the spinal cord 1 week postinfection (p.i.): however, after that time, the number of infected cells in the wild-type virus-infected mice continued to increase, whereas the virus-positive cells from the variant virus-infected mice gradually decreased. Thus, the number of viral antigen-containing cells peaked by 1 week p.i. in the variant virus-infected animals. Conversely, the number of infected cells in the spinal cords from mice inoculated with wild-type virus steadily increased until 8 weeks p.i. At this time (8 weeks p.i.), no more variant virus antigen-positive cells could be observed within the spinal cord. Plaque assay of central nervous system tissue confirmed these differences between the two groups observed by immunohistochemistry. No infectious variant virus could be isolated after 2 weeks p.i. from the brain and 4 weeks p.i. from the spinal cord, whereas infectious wild-type virus could be detected up to the end of the observation period (12 weeks p.i.). Virus which was isolated from variant virus-infected mice still retained the neutralization-resistant phenotype. These studies emphasize the important biological in vivo activity of Theiler's virus VP-1 in determining neurovirulence.

Is Theiler's murine encephalomyelitis virus infection of mice an autoimmune disease?

Viruses can initiate disease by many different means. Direct viral, immune mediated and host factors all play important parts. Molecular mimicry or having cross-reacting determinants that result in immune responses which have the potential to cause damage can be incorporated into this framework. Here, autoimmune responses generated by virus infection have been presented in relation to these other parameters. The cross-reacting immune response originally generated by virus would have to be directed toward or involve a disease inducing site such as an EAE (encephalitogenic), thyroiditis, or diabetogenic site. If the cross-reaction took place at a nondisease inducing site, the ensuring immune response may result in the production of autoantibodies, however no disease would occur. In other systems autoantibodies can potentiate an ongoing inflammatory response. This may be the case that is described here with Theiler's murine encephalomyelitis virus infection. Lastly, viruses having common determinants with MHC determinants may modify immune responses leading to immunosuppression and allowing virus to persist. In addition, similar determinants may lead to disease by an alternative route. For example, we have described a region of human cytomegalovirus that has a common determinant with HLA DR beta chain. This region is associated with diabetes in humans (Todd et al. 1988). Thus, many factors are involved in the outcome of disease induction by viruses of which autoimmunity is one.