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

Double-edged effects of tamoxifen-in-oil-gavage on an infectious murine model for multiple sclerosis

Tamoxifen gavage is a commonly used method to induce genetic modifications in cre-loxP systems. As a selective estrogen receptor modulator (SERM), the compound is known to have immunomodulatory and neuroprotective properties in non-infectious central nervous system (CNS) disorders. It can even cause complete prevention of lesion development as seen in experimental autoimmune encephalitis (EAE). The effect on infectious brain disorders is scarcely investigated. In this study, susceptible SJL mice were infected intracerebrally with Theiler's murine encephalomyelitis virus (TMEV) and treated three times with a tamoxifen-in-oil-gavage (TOG), resembling an application scheme for genetically modified mice, starting at 0, 18, or 38 days post infection (dpi). All mice developed 'TMEV-induced demyelinating disease' (TMEV-IDD) resulting in inflammation, axonal loss, and demyelination of the spinal cord. TOG had a positive effect on the numbers of oligodendrocytes and oligodendrocyte progenitor cells, irrespective of the time point of application, whereas late application (starting 38 dpi) was associated with increased demyelination of the spinal cord white matter 85 dpi. Furthermore, TOG had differential effects on the CD4+ and CD8+ T cell infiltration into the CNS, especially a long lasting increase of CD8+ cells was detected in the inflamed spinal cord, depending of the time point of TOG application. Number of TMEV-positive cells, astrogliosis, astrocyte phenotype, apoptosis, clinical score, and motor function were not measurably affected. These data indicate that tamoxifen gavage has a double-edged effect on TMEV-IDD with the promotion of oligodendrocyte differentiation and proliferation, but also increased demyelination, depending on the time point of application. The data of this study suggest that tamoxifen has also partially protective functions in infectious CNS disease. These effects should be considered in experimental studies using the cre-loxP system, especially in models investigating neuropathologies.

Facets of Theiler's Murine Encephalomyelitis Virus-Induced Diseases: An Update

Theiler’s murine encephalomyelitis virus (TMEV), a naturally occurring, enteric pathogen of mice is a Cardiovirus of the Picornaviridae family. Low neurovirulent TMEV strains such as BeAn cause a severe demyelinating disease in susceptible SJL mice following intracerebral infection. Furthermore, TMEV infections of C57BL/6 mice cause acute polioencephalitis initiating a process of epileptogenesis that results in spontaneous recurrent epileptic seizures in approximately 50% of affected mice. Moreover, C3H mice develop cardiac lesions after an intraperitoneal high-dose application of TMEV. Consequently, TMEV-induced diseases are widely used as animal models for multiple sclerosis, epilepsy, and myocarditis. The present review summarizes morphological lesions and pathogenic mechanisms triggered by TMEV with a special focus on the development of hippocampal degeneration and seizures in C57BL/6 mice as well as demyelination in the spinal cord in SJL mice. Furthermore, a detailed description of innate and adaptive immune responses is given. TMEV studies provide novel insights into the complexity of organ- and mouse strain-specific immunopathology and help to identify factors critical for virus persistence.

Organ-specific protective role of NKT cells in virus-induced inflammatory demyelination and myocarditis depends on mouse strain

Theiler's murine encephalomyelitis virus (TMEV) can induce demyelination or myocarditis in susceptible mouse strains. A deficiency of NKT cells exacerbated TMEV-induced demyelinating disease (TMEV-IDD) in SJL/J and BALB/c mice. In C57BL/6 background, however, NKT-cell-deficient Jα18 KO mice remained as resistant to TMEV-IDD as wild-type mice. Echocardiography and histology showed that Jα18 KO mice developed more severe myocarditis (greater T cell infiltration and fibrosis) than wild-type mice, suggesting a protective role of NKT cells in myocarditis in C57BL/6 mice. Jα18 KO mice had higher cardiac viral RNA and anti-viral antibody titers, but had lower lymphoproliferation and IL-4 and IL-10 production.

Distinct kinetics of viral replication, T cell infiltration, and fibrosis in three phases of myocarditis following Theiler's virus infection

We established a novel model of myocarditis induced with Theiler’s murine encephalomyelitis virus (TMEV), which has been used as a viral model for multiple sclerosis and seizure/epilepsy. Following TMEV infection, C3H mice developed severe myocarditis with T cell infiltration, while C57BL/6 mice had mild lesions and SJL/J mice had no inflammation in the heart. In C3H mice, myocarditis was divided into three phases: acute viral, subacute immune, and chronic fibrotic phases. Using toll-like receptor (TLR) 4-deficient C3H mice, we found that interleukin (IL)-6, IL-17, TLR4, and anti-viral immune responses were associated with myocarditis susceptibility.

Neonatal experience interacts with adult social stress to alter acute and chronic Theiler's virus infection

Previous research has shown that neonatal handling has prolonged protective effects associated with stress resilience and aging, yet little is known about its effect on stress-induced modulation of infectious disease. We have previously demonstrated that social disruption stress exacerbates the acute and chronic phases of the disease when applied prior to Theiler's virus infection (PRE-SDR) whereas it attenuates disease severity when applied concurrently with infection (CON-SDR). Here, we asked whether neonatal handling would protect adult mice from the detrimental effects of PRE-SDR and attenuate the protective effects of CON-SDR on Theiler's virus infection. As expected, handling alone decreased IL-6 and corticosterone levels, protected the non-stressed adult mice from motor impairment throughout infection and reduced antibodies to myelin components (PLP, MBP) during the autoimmune phase of disease. In contrast, neonatal handling X PRE/CON-SDR elevated IL-6 and reduced corticosterone as well as increased motor impairment during the acute phase of the infection. Neonatal handling X PRE/CON-SDR continued to exacerbate motor impairment during the chronic phase, whereas only neonatal handling X PRE-SDR increased in antibodies to PLP, MOG, MBP and TMEV. Together, these results imply that while handling reduced the severity of later Theiler's virus infection in non-stressed mice, brief handling may not be protective when paired with later social stress.

Chronic restraint stress during early Theiler's virus infection exacerbates the subsequent demyelinating disease in SJL mice: II. CNS disease severity

Theiler's murine encephalomyelitis virus (TMEV) infection is a well-characterized model of multiple sclerosis (MS). Previous research has shown that chronic restraint stress (RS) during early TMEV infection exacerbates behavioral signs of the disease. The present data suggest that RS-induced increases in CNS inflammation, demyelination, and axonal degeneration may underlie this exacerbation. In addition, we report that males exhibit greater CNS inflammation and higher numbers of demyelinating lesions while females show greater susceptibility to RS-induced exacerbation. These findings indicate that RS during early TMEV infection increases CNS lesion formation during the late phase and suggest that the effects of RS are sex-dependent.

Neonatal maternal separation alters immune, endocrine, and behavioral responses to acute Theiler's virus infection in adult mice

Previous studies have established a link between adverse early life events and subsequent disease vulnerability. The present study assessed the long-term effects of neonatal maternal separation on the response to Theiler's murine encephalomyelitis virus infection, a model of multiple sclerosis. Balb/cJ mouse pups were separated from their dam for 180-min/day (180-min MS), 15-min/day (15-min MS), or left undisturbed from postnatal days 2-14. During adolescence, mice were infected with Theiler's virus and sacrificed at days 14, 21, or 35 post-infection. Prolonged 180-min MS increased viral load and delayed viral clearance in the spinal cords of males and females, whereas brief 15-min MS increased the rate of viral clearance in females. The 15-min and 180-min MS mice exhibited blunted corticosterone responses during infection, suggesting that reduced HPA sensitivity may have altered the immune response to infection. These findings demonstrate that early life events alter vulnerability to CNS infection later in life. Therefore, this model could be used to study gene-environment interactions that contribute to individual differences in susceptibility to infectious and autoimmune diseases of the CNS.

Restraint stress fails to render C57BL/6 mice susceptible to Theiler's virus-induced demyelination

OBJECTIVES

Multiple sclerosis is a degenerative disease of the CNS with a pathology consistent with immunological mediation. Although its cause is unknown, multiple factors are thought to influence both the onset and exacerbation of the disease, including both genetic background as well as environmental factors.

METHODS

We are interested in the effect of psychological stress on the onset and exacerbation of Theiler's virus-induced demyelinating disease (TVID), a murine model of MS in which viral persistence facilitates demyelination. In the current study, we determined whether chronic restraint stress (RS)-induced immunosuppression could result in the establishment of a persistent CNS infection in the normally TVID-resistant C57BL/6 mouse strain, resulting in demyelination.

RESULTS

Our data indicated that RS repeated over the course of 7 days was not sufficient to cause decreases in virus-specific adaptive immunity, and did not significantly alter CNS viral levels. Furthermore, chronic repeated RS lasting until 4 weeks after infection altered neither the development of virus-specific IgG nor motor function determined by Rotarod analysis. In addition, histological analysis of the CNS of stressed mice indicated no inflammation or demyelination on day 193 after infection.

CONCLUSION

These results suggest that stress alone is not sufficient to overcome genetic resistance to TVID in the C57BL/6 mouse strain.

TH, Meagher MW. Effects of stress on the immune response to Theiler's virus--implications for virus-induced autoimmunity

Psychological stress is an important factor in susceptibility to many diseases. Our laboratory has been investigating the impact of stress on the susceptibility to Theiler's virus-induced demyelination (TVID), a mouse model of multiple sclerosis. Using immunodominant viral peptides specific for identification of either CD4(+) or CD8(+) T cells, stress reduced IFN-gamma-producing virus-specific CD4(+) and CD8(+) T cells in the spleen and CD8(+) T cells in the CNS. Expression of mRNA for the Th1 transcription factor T-bet and the Th2 transcription factor GATA-3 were decreased in spleen cells isolated from stressed mice. Cytokine production by cells isolated from the CNS or spleens following stimulation with virus indicated that stress decreased both type 1 and type 2 responses. The adverse effects of stress were partially reversed by concurrent RU486 administration but mimicked by dexamethasone, indicating a major role for glucocorticoids. Global stress-induced immunosuppression resulted in higher levels of virus replication and dissemination. The higher viral load subsequently led to an earlier disease onset and more severe clinical and histological signs of demyelinating disease. Our results have important implications for understanding the pathogenesis of MS, and suggest that stressful events during early infection with an agent capable of inducing demyelination may result in immunosuppression and failure to eliminate the pathogen, which in turn may lead to the development of MS.

Restraint stress modulates virus specific adaptive immunity during acute Theiler's virus infection

Multiple sclerosis (MS) is a devastating CNS disease of unknown origin. Multiple factors including genetic background, infection, and psychological stress affect the onset or progression of MS. Theiler's murine encephalomyelitis virus (TMEV) infection is an animal model of MS in which aberrant immunity leads to viral persistence and subsequently results in demyelination that resembles MS. Here, we examined how stress during acute TMEV infection altered virus-specific cell mediated responses. Using immunodominant viral peptides specific for either CD4(+) or CD8(+) T cells, we found that stress reduced IFN-gamma producing virus-specific CD4(+) and CD8(+) T cells in the spleen and CD8(+) T cells CNS. Cytokine production by cells isolated from the CNS or spleens following stimulation with virus or viral peptides, indicated that stress decreased both type 1 and type 2 responses. Glucocorticoids were implicated in the decreased T cell function as the effects of stress were partially reversed by concurrent RU486 administration but mimicked by dexamethasone. As T cells mediate viral clearance in this model, our data support the hypothesis that stress-induced immunosuppression may provide a mechanism for enhanced viral persistence within the CNS.

Neuroimmune interactions in a model of multiple sclerosis

Psychological stress has been implicated in both the onset and exacerbation of multiple sclerosis (MS). Our research has focused on the role of stress at the onset of MS, using the mouse model Theiler's murine encephalomyelitis virus-induced demyelination. Theiler's virus is a natural pathogen of mice that causes a persistent infection of the central nervous system (CNS) and inflammatory immune-mediated demyelination that is very similar to MS. Our research has shown that restraint stress sufficiently increases corticosterone secretion to cause immunosuppression. Stressed mice develop decreased innate and adaptive immune responses, including decreased chemokine and cytokine responses, to virus, which leads to increased viral replication within the CNS. Higher levels of virus then cause increased later demyelinating disease. These findings may have important implications in our understanding of the interactions between stress and the development of autoimmune diseases induced by infectious agents.

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.