Glucocorticoid exposure alters the pathogenesis of Theiler's murine encephalomyelitis virus during acute infection

Previous research has shown that chronic restraint stress exacerbates Theiler's virus infection, a murine model for CNS inflammation and multiple sclerosis. The current set of experiments was designed to evaluate the potential role of glucocorticoids in the deleterious effects of restraint stress on acute CNS inflammatory disease. Exposure to chronic restraint stress resulted in elevated levels of corticosterone as well as increased clinical scores and weight loss (Experiment 1). In addition, corticosterone administration alone exacerbated behavioral signs of TMEV-induced sickness (i.e. decreased body weight, increased symptoms of encephalitis, and increased mortality) and reduced inflammation in the CNS (Experiment 2). Infected subjects receiving exogenous corticosterone showed exacerbation of acute phase measures of sickness and severe mortality as well as decreased viral clearance from CNS (Experiment 3). These findings indicate that corticosterone exposure alone is sufficient to exacerbate acute CNS inflammatory disease.     

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: Pathophysiology of demyelination and neurodegeneration

Multiple sclerosis (MS) has been suggested to be an autoimmune demyelinating disease of the central nervous system (CNS), whose primary target is either myelin itself, or myelin-forming cells, the oligodendrocytes. Although axonal damage occurs in MS, it is regarded as a secondary event to the myelin damage. Here, the lesion develops from the myelin (outside) to the axons (inside) “Outside-In model”. The Outside-In model has been supported by an autoimmune model for MS, experimental autoimmune (allergic) encephalomyelitis (EAE). However, recently, (1) EAE-like disease has also been shown to be induced by immune responses against axons, and (2) immune responses against axons and neurons as well as neurodegeneration independent of inflammatory demyelination have been reported in MS, which can not be explained by the Outside-In model. Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) is a viral model for MS. In TMEV infection, axonal injury precedes demyelination, where the lesion develops from the axons (inside) to the myelin (outside) “Inside-Out model”. The initial axonal damage could result in the release of neuroantigens, inducing autoimmune responses against myelin antigens, which potentially attack the myelin from outside the nerve fiber. Thus, the Inside-Out and Outside-In models can make a “vicious” immunological cycle or initiate an immune cascade.     

Silencing of NbXrn4 facilitates the systemic infection of Tobacco mosaic virus in Nicotiana benthamiana

The 5'-3' exoribonucleases (Xrns) play key roles in degradation and processing pathways of several classes of RNAs including mRNA, rRNA, miRNA and other small RNAs. Recent work revealed that the cytoplasmic Xrn (Xrn1p in yeast and Xrn4 in plants) affected the stability of the viral RNA of tombusviruses in yeast and plants, which indicates that the cytoplasmic Xrn might be involved in plant defense against virus by degrading viral RNA. Here, we demonstrated that silencing of Nicotiana benthamiana cytoplasmic Xrn4 facilitated both local and systemic infection of Tobacco mosaic virus (TMV) in N. benthamiana. The results support the suggestion that cytoplasmic Xrn4 participates in the viral defense system of plants.     

Susceptibility of peritoneal macrophages to infection by Theiler's virus

Theiler's murine encephalomyelitis virus (TMEV) strains fall into two groups: high-neurovirulence GDVII virus results in rapidly fatal encephalitis, while low-neurovirulence BeAn and DA viruses produce persistent central nervous system (CNS) infection and inflammatory demyelinating disease. Because macrophages (Mphis) are key components in BeAn virus-induced demyelinating disease, we examined the susceptibility of primary peritoneal macrophages (pMphis) to BeAn infection in vitro. Freshly isolated, thioglycollate-elicited pMphis were resistant to BeAn virus infection even at high multiplicity of infection. In contrast, after incubation of thioglycollate-elicited pMphis at 37 degrees C for 4 days before infection, approximately half of the cells expressed virus antigen(s) and contained nicked DNA indicative of apoptosis. However, BeAn virus RNA replication and virus yields were highly restricted. Interestingly, about one-third of the cells were apoptotic but negative for virus RNA and antigen(s). Tumor necrosis factor-alpha (TNF-alpha) and interferon-alpha (IFN-alpha) were elevated in BeAn-infected pMphi cultures suggesting that bystander killing may be responsible for the apoptosis seen in BeAn virus antigen-negative cells. These data show for the first time that pMphis are susceptible to BeAn virus infection, although the infection is highly restricted and most of these cells undergo BeAn-induced apoptosis.     

Yersinia enterocolitica invasin-dependent and invasin-independent mechanisms of systemic dissemination

We report here invasin-dependent and invasin-independent mechanisms in which the enteropathogen Yersinia enterocolitica is able to disseminate from the lumen of the small intestine to the spleen. The invasin-dependent route is clearly discernible in mice devoid of intestinal Peyer's patches and mesenteric lymph nodes.     

Ultrastructural immunohistochemical localization of virus in acute and chronic demyelinating Theiler's virus infection.

Mice experimentally infected with Theiler's murine encephalomyelitis virus (TMEV) develop a persistent infection of the central nervous system (CNS). The most striking feature of this infection is the occurrence of inflammatory primary demyelination in the spinal cord white matter. The pathogenesis of myelin degeneration in this model has not been clarified, but morphologic and immunologic data suggest that the host immune response plays a major role in the production of myelin injury. Because of low virus titers in infected adult mice and of the small size of TMEV, virus particles have never been observed in this demyelinating model. Yet elucidation of the types of cells in the CNS supporting virus replication would be important for a better understanding of both virus persistence and virus-induced demyelinating pathology. The present paper is a sequential study of the localization of TMEV in the spinal cord in infected mice by ultrastructural immunohistochemical techniques. Results indicate that virus replication is mainly in neurons during the acute phase of the disease, while in the chronic phase viral inclusions are mainly found in macrophages in and around demyelinating lesions. Other cells are also infected, but to a lesser degree. In the neuronal system both axoplasmic and dendritic flow appear to facilitate the spread of virus in the CNS. In macrophages, the presence of virus particles and the association of virus with altered components of the cytoskeleton support active virus production rather than simple internalization. The macrophage appears to play an important role in both the establishment of virus persistence and in the process of demyelination in this animal model.     

新型冠状病毒SARS-CoV-2:高致病性及其防治

冠状病毒曾被认为是一类在人群中不致病的或仅引起轻微自愈性疾病的病原体。但是,在人类在进入21世纪的前20年中,却经历了2002—2003年的SARS-CoV、2012年的MERS-CoV和2019—2020年的SARS-CoV-2三次冠状病毒的世界范围的流行。其中尤以最近这次大流行最为严重。截至2020年3月12日,已造成全球逾12.6万人感染,其中死亡超过4600人。与前两次冠状病毒暴发相似,SARS-CoV-2也是经过跨物种传播由蝙蝠传给人类的,但中间宿主未知。与前两种冠状病毒相同,SARS-CoV-2也属于下呼吸道病原体,易感染有基础性疾病(如糖尿病、高血压等)的年长男性。重症以上患者除表现不同程度的呼吸障碍外,还可伴有消化道症状,甚至发生心脏及肾脏功能改变。病理检测发现,危重症患者肺脏常呈实质性改变,大量黏稠液体充斥气道导致呼吸困难。此外,淋巴细胞减少,C反应蛋白水平升高,大量炎性反应因子分泌导致细胞因子风暴,多脏器衰竭也是病情恶化重要指标。新冠肺炎患者间症状差别较大,需要根据患者的具体情况辨证施治;避免因治疗方法不当加重病情的进展,甚至导致患者死亡。本文将从新冠病毒的结构特点出发,对该病毒的来源、复制周期、致病性、发病特点及临床防治进行初步的回顾性综述。     

Neuronal and oligodendroglial infection by the WW strain of Theiler's virus.

Newborn ICR mice were infected by intracerebral inoculation of 10(5.3) LD50 of the WW strain of Theiler's virus and examined serially by virologic and ultrastructural methods. Maximal titers of 10(6) LD50 developed in the brain by day 8 when 90 per cent of the animals were dead or moribund. The virus first appeared and was most prominent in the thalamus, basal ganglia, and midbrain. It spread from these areas throughout the cortex, brainstem, and spinal cord but spared the cerebellar cortex. Both neurons and oligodendroglia were infected. Infected cells first showed dispersion of polyribosomes, accumulation of vesicles, and widening of perinuclear cisternae. Normal cytoplasmic organelles and the nucleus were displaced by an accumulation of viral crystals, membranous profiles, and fibrillar material. Within degenerating cells the nuclear chromatin became clumped and marginated and the cytoplasm was filled either with vesicles or masses of paracrystalline viral arrays. These changes were accompanied by a vigorous inflammatory response of lymphocytes, plasma cells, macrophages, neutrophils, and eosinophils. Lysis of oligodendroglia during acute infection with the WW strain of Theiler's virus may provide a stimulus for the late autoimmune demyelination that has been described in animals that survive the acute encephalitis.     

Theiler's murine encephalomyelitis: a model of demyelination and persistence of virus

Theiler's murine encephalomyelitis virus (TMEV) causes immune-mediated demyelination in susceptible mice which is similar to human demyelinating disorders such as multiple sclerosis. In addition, the picornavirus persists within the central nervous system throughout the course of the chronic demyelinating disease. This article reviews the neuropathology, virology, immunology, and molecular biology of the model system. We analyze the possible mechanisms by which this virus induces demyelination and persists in the nervous system. Finally, we provide a hypothesis that the specificity of primary white matter destruction in the TMEV model depends on immune-sensitized cells which interact with viral antigen plus major histocompatibility complex (MHC) antigens on the surfaces of oligodendrocytes or myelin sheaths.     

Neonatal infection with the Daniels strain of Theiler's murine encephalomyelitis virus

The clinical and pathologic manifestation of Theiler's murine encephalomyelitis are age related. Animals infected during the first week of life die of a fulminant encephalitis analogous to human poliomyelitis. By contrast, animals infected within 2 and 4 weeks of age survive but develop chronic relapsing demyelination and persistent infection of the central nervous system. The neonatal infection results in widespread necrosis beginning with neuronal vacuolar degeneration followed by inflammatory infiltrates. Electron microscopy reveals paracrystalline arrays of 27-nm viral particles characteristic of picornaviruses within neurons and macrophages. In addition, oligodendrocytes show reactive changes and intracytoplasmic vacuoles. Immunoperoxidase studies show viral antigen primarily localized within neurons of the cerebral cortex, basal ganglia, hippocampus, and anterior horn cells. Viral antigen is found within the apical dendrites and axonal projections of hippocampal pyramidal cells suggesting that Theiler's murine encephalomyelitis may travel intraaxonally.     

Role of T cells in resistance to Theiler's virus infection.

Intracerebral infection of C57BL/10SNJ mice with Theiler's virus results in acute encephalitis with subsequent virus clearance and absence of spinal cord demyelination. In contrast, infection of SJL/J mice results in acute encephalitis, virus persistence, and immune-mediated demyelination. These experiments examined the role of T-cell subsets in the in vivo immune response to Theiler's virus in resistant C57BL/10SNJ mice. Depletion of T-cell subsets with monoclonal antibodies (mAbs) directed at CD3 (pan-T-cell marker), CD4+ (class II-restricted) or CD8+ (class I-restricted) T cells resulted in increased frequency of paralysis and death as a result of acute encephalitis. Neuropathologic studies 10 days after infection demonstrated prominent necrosis, primarily in the pyramidal layer of hippocampus and in the thalamus of mice depleted of T-cell subsets. In immunosuppressed and infected C57BL/10SNJ mice, analysis of spinal cord sections 35 days after infection demonstrated small demyelinated lesions relatively devoid of inflammatory cells even though virus antigen could be detected by immunocytochemistry. Both CD4+ and CD8+ T cells are important in the resistance to infection with Theiler's virus in C57BL/10SNJ mice. However, subsequent spinal cord demyelination, to the extent observed in susceptible mice, depends on the presence of virus antigen persistence and a competent cellular immune response.     

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.     

Neutralization of chemokines RANTES and MIG increases virus antigen expression and spinal cord pathology during Theiler's virus infection

The role of chemokines during some viral infections is unpredictable because the inflammatory response regulated by these molecules can have two, contrasting effects-viral immunity and immunopathologic injury to host tissues. Using Theiler's virus infection of SJL mice as a model of this type of disease, we have investigated the roles of two chemokines-regulated on activation, normal T cell-expressed and secreted (RANTES) chemokine and monokine induced by IFN-gamma (MIG)-by treating mice with antisera that block lymphocyte migration. Control, infected mice showed virus persistence, mild inflammation and a small degree of demyelination in the white matter of the spinal cord at 6 weeks post-infection. Treatment of mice with RANTES antiserum starting at 2 weeks post-infection increased both viral antigen expression and the severity of inflammatory demyelination at 6 weeks post-infection. MIG antiserum increased the spread of virus and the proportion of spinal cord white matter with demyelination. Overall, viral antigen levels correlated strongly with the extent of pathology. At the RNA level, high virus expression was associated with low IL-2 and high IL-10 levels, and RANTES antiserum decreased the IL-2/IL-10 ratio. Our results suggest that RANTES and MIG participate in an immune response that attempts to restrict viral expression while limiting immunopathology and that anti-chemokine treatment poses the risk of exacerbating both conditions in the long term.     

Location and distribution of virus antigen in the central nervous system of mice persistently infected with Theiler's virus

The present study has shown that virus can be readily detected by immunofluorescent staining in the central nervous system (CNS) of SJL mice persistently infected with Theiler's murine encephalomyelitis virus (TMEV). Considering the low CNS virus content, large amounts of virus antigen were found in the white matter, the site of demyelinating lesions. Virus antigen was detected in all animals killed after post-infection (PI) Day 21, a time which can be considered as the beginning of the persistent phase of this infection, and the appearance of virus antigen in white matter corresponded closely in time with the onset of demyelination. The pathogensis of this persistent infection can now be reasonably well reconstructed from the temporal observations made in this study. It would appear that between the second and third week PI, virus replication largely shifts from neurons in spinal cord gray matter to other cell types located in white matter. While a lower-grade persistent infection (in terms of the relative number of cells containing virus antigen) is established and maintained in cells in the gray matter and inflammatory and leptomeningeal infiltrates, cells in white matter appear to be mainly responsible for perpetuating the infection. Why these cells should supplant neurons as the most susceptible host cell during the chronic phase of the infection is discussed.     

Restraint theory and its implications for obesity treatment

Restraint theory was developed to evaluate both causes and consequences of attempts to restrict food intake for the purpose of weight maintenance. Research suggests that restraint has many negative consequences including lowered mood and overeating behaviour and that restrained eating is best characterized as an intention which is only occasionally realized. The present paper reviews the restraint literature and examines the implications of restraint theory for obesity treatment. It assesses the role of restraint in both traditional and contemporary behavioural treatment packages for obesity and concludes that if restraint is detrimental to both the physical and psychological health of the normal weight individual, it should not be recommended as a solution to the physical and psychological problems of the obese.