SJL bone marrow-derived macrophages do not have IRF3 mutations and are highly susceptible to Theiler's virus infection

Theiler's Murine Encephalomyelitis Virus Replicates in Primary Neuron Cultures and Impairs Spine Density Formation

In this study, we examined infection with the highly neurovirulent GDVII, the less neurovirulent DA strains, and with a mutant DA, which lacks the L* protein (L*-1) involved in viral persistence and demyelinating disease, to analyze the direct effects of Theiler's murine encephalomyelitis virus (TMEV) replication using primary cultures of mouse brain hippocampal neurons. All viruses replicate in cultured neurons, with GDVII having the highest titers and L*-1 the lowest. Accordingly, all were positive for viral antigen staining 3 days postinfection (dpi), and DA and L*-1 were also positive after 12 dpi. NeuN + immunostaining showed an early and almost complete absence of positive cells in cultures infected with GDVII, an approximately 50% reduction in cultures infected with DA, and fewer changes in L*-1 strains at 3 dpi. Accordingly, staining with chloromethyltetramethylrosamine orange (Mitotracker OrangeTM) as a parameter for cell viability showed similar results. Moreover, at 1 dpi, the strain DA induced higher transcript levels of neuroprotective genes such as IFN-Iβ, IRF7, and IRF8. At 3 dpi, strains GDVII and DA, but not the L*-1 mutant, showed lower PKR expression. In addition, confocal analysis showed that L*-1-infected neurons exhibited a decrease in spine density. Treatment with poly (I:C), which is structurally related to dsRNA and is known to trigger IFN type I synthesis, reduced spine density even more. These results confirmed the use of mouse hippocampal neuron cultures as a model to study neuronal responses after TMEV infection, particularly in the formation of spine density.

Virus-triggered spinal cord demyelination is followed by a peripheral neuropathy resembling features of Guillain-Barré Syndrome

Theiler’s murine encephalomyelitis virus (TMEV)-induces a demyelinating disease in the spinal cord (SC) of susceptible but not in resistant (B6) mouse strains. The aim of the present study was to induce SC demyelination and a peripheral neuropathy in resistant mice by switching the infection site from cerebrum to SC. B6 mice were intraspinally inoculated with TMEV. Infected mice showed clinical signs starting at 7 days post infection (dpi). Histopathology revealed a mononuclear myelitis, centred on the injection site at 3 dpi with subsequent antero- and retrograde spread, accompanied by demyelination and axonal damage within the SC. Virus protein was detected in the SC at all time points. SC inflammation decreased until the end of the investigation period (28 dpi). Concurrent with the amelioration of SC inflammation, the emergence of a peripheral neuropathy, characterized by axonal damage, demyelination and macrophage infiltration, contributing to persistent clinical sings, was observed. Intraspinal TMEV infection of resistant mice induced inflammation, demyelination and delayed viral clearance in the spinal cord and more interestingly, subsequent, virus-triggered inflammation and degeneration within the PN associated with dramatic and progressive clinical signs. The lesions observed in the PN resemble important features of Guillain-Barré syndrome, especially of acute motor/motor-sensory axonal forms.

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.