CXCR4 signaling regulates remyelination by endogenous oligodendrocyte progenitor cells in a viral model of demyelination

Following intracranial infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV), susceptible mice will develop widespread myelin destruction that results in pathological and clinical outcomes similar to those seen in humans with the demyelinating disease Multiple Sclerosis (MS). Partial remyelination and clinical recovery occurs during the chronic phase following control of viral replication yet the signaling mechanisms regulating these events remain enigmatic. Here we report the kinetics of proliferation and maturation of oligodendrocyte progenitor cells (OPCs) within the spinal cord following JHMV-induced demyelination and that CXCR4 signaling contributes to the maturation state of OPCs. Following treatment with AMD3100, a specific inhibitor of CXCR4, mice recovering from widespread demyelination exhibit a significant (P < 0.01) increase in the number of OPCs and fewer (P < 0.05) mature oligodendrocytes compared with HBSS-treated animals. These results suggest that CXCR4 signaling is required for OPCs to mature and contribute to remyelination in response to JHMV-induced demyelination. To assess if this effect is reversible and has potential therapeutic benefit, we pulsed mice with AMD3100 and then allowed them to recover. This treatment strategy resulted in increased numbers of mature oligodendrocytes, enhanced remyelination, and improved clinical outcome. These findings highlight the possibility to manipulate OPCs in order to increase the pool of remyelination-competent cells that can participate in recovery.     

In vivo and in vitro models of demyelinating diseases. III. JHM virus infection of rats

Suckling rats of three inbred and three outbred strains were inoculated intraperitoneally (P) or intracerebrally (IC) with the JHM strain of mouse hepatitis virus (JHMV) and were monitored for evidence of neurologic diseases. Consequences of varying age at inoculation, route of injection, and virus dose were ascertained. No disease was evident after IP injection but IC inoculation with at least 10(4) plaque-forming units at 2 days of age resulted in either a rapidly fatal encephalitis or a chronic, progressive, fatal neurologic disease in most rats, regardless of strain. Inoculation at 5 or 10 days of age predominantly caused the chronic neurologic disease, characterized by demyelinating lesions in the brain, spinal cord, or optic nerve, which sometimes were evident as late as several months postinoculation. Demyelination in the optic nerve proved to be concurrent with demyelinating lesions elsewhere in the CNS. Occasionally, clinical remissions were observed in rats in which posterior paralysis developed, suggesting that remyelination in the rat can occur. Demonstration of virus replication, by infectivity, in rats exhibiting neurologic disease and in rats without clinical symptoms was substantiated by electron microscopic observations of virus development and assembly in oligodendroglia of the optic nerve and spinal cord. In view of the protracted course of the disease in some rats, presence of demyelinating lesions confirmed by light and electron microscopy, and remissions of clinical symptoms, the JHMV-infected rat seems to be an appropriate animal model to study virus-mediated progressive demyelinating disease.     

Mouse hepatitis virus-induced recurrent demyelination. A preliminary report.

Four-week-old BALB/c mice inoculated intracerebrally with the JHM strain of mouse hepatitis virus developed an acute demyelinating disease followed by apparent recovery with remyelination. When surviving mice were examined 16 months later, small areas of active demyelination were still present. This is the first reported example, to our knowledge, of an experimental viral infection in which acute demyelination with recovery is followed by persisting or recurring demyelination.     

Effect of persistent mouse hepatitis virus infection on MHC Class I expression in murine astrocytes

Neurotropic strains of mouse hepatitis virus (MHV) have been used extensively for the study of viral pathogenesis in the central nervous system (CNS), serving as models for human neurological diseases such as multiple sclerosis (MS). MHV strains A59 and JHMV both cause acute and chronic encephalomyelitis and demyelination in susceptible strains of mice and rats. In acute disease, CNS damage is most likely the result of lytic infection in neurons and oligodendrocytes, and death can be prevented by the adoptive transfer of Class I-restricted CD8+ T cells. However, in later stages of the disease induced by some MHV strains, virus tends to be restricted to astrocytes in a nonlytic infection, and the immune response appears to contribute to CNS damage. These data lead us to suggest that the astrocyte may play a central role in the neuropathogenesis of MHV infection. Consistent with this possibility, A59 has been reported to induce the expression of Class I molecules of the major histocompatibility complex (MHC) in glial cells following infection in vivo and in vitro. In this communication, we have examined the influence of persistent infection by both A59 and JHMV on MHC Class I expression in primary murine astrocytes. Persistence was characterized by the presence of intracellular viral antigen and mRNA in the absence of detectable infectious virus particles. Under these conditions, JHMV, but not A59, inhibited constitutive expression of the H-2 K^b molecule, with the magnitude of inhibition increasing with postinfection time. A59 was not able to induce Class I during persistence, presumably due to the lack of infectious virus particles. Class I expression was restored by the addition of gamma-interferon (IFN-γ) to astrocytes persistently infected with either A59 or JHMV. Thus, Class I inhibition is not a permanent consequence of JHMV persistence, and persistence does not interfere with normal signalling pathways for Class I induction. © 1995 Wiley-Liss, Inc.     

Recurrent demyelination in chronic central nervous system infection produced by Theiler's murine encephalomyelitis virus

A morphologic study of demyelination produced by Theiler's encephalomyelitis virus (TMEV) infection in C3H/He mice was performed. Demyelination in this strain of mouse was less intense and had a milder gliomesodermal response than that observed in SJL mice. As early as 80 days after infection numerous remyelinated axons were present in C3H/He mice, and later, extensive remyelination was observed and was mainly by Schwann cells. About one-third of remyelinated plaques showed recurrent demyelinating activity at 200 days. The best evidence of recurrent demyelination was the loss of myelin by abons which had been previously remyelinated by Schwann cells. In addition, acute areas of demyelination were also seen in spinal cords which contained chronic or quiescent plaques. The demonstration of recurrent demyelination in TMEV infection is important for it increases the relevance of this model to multiple sclerosis (MS). In addition TMEV infection of C3H/He mice appears to be an excellent model for further studies of Schwann cell remyelination and recurrent demyelination in the central nervous system (CNS).     

Studies on the mechanism of protection from acute viral encephalomyelitis by delayed-type hypersensitivity inducer T cell clones

Previous studies have shown that mice can be protected from a lethal infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV) by the adoptive transfer of delayed-type hypersensitivity (DTH)-inducer T cell clones specific for the virus. Protection does not involve the suppression of virus replication in the central nervous system (CNS) or via augmentation of the antiviral antibody response. In the present report we have compared the CNS lesions induced by JHMV in lethally infected and T cell clone protected mice. The presence of virus-specific T cell clones induced a transient increase in mononuclear cell infiltration into the parenchyma of the brains of protected mice, consistent with previous data suggesting that a DTH response was responsible for protection. Immunohistochemical studies suggested further that virus was not replicating in the ependyma or cellular infiltrate, but that the presence of the T cell clone prevented neuronal infection. While the mechanism of effectively altering the in vivo cellular tropism is unknown, survival is accompanied by increased specific destruction of target tissues with fulminant CNS demyelination and an increased incidence of persistent infection.     

CD8-deficient SJL mice display enhanced susceptibility to Theiler's virus infection and increased demyelinating pathology

Theiler's murine encephalomyelitis virus (TMEV) infection of the central nervous system (CNS) induces a chronic, progressive demyelinating disease in susceptible mouse strains characterized by inflammatory mononuclear infiltrates and spastic hind limb paralysis. Our lab has previously demonstrated a critical role for TMEV- and myelin-specific CD4(+) T cells in initiating and perpetuating this pathology. It has however, also been shown that the MHC class I loci are associated with susceptibility/resistance to TMEV infection and persistence. For this reason, we investigated the contribution of CD8(+) T cells to the TMEV-induced demyelinating pathology in the highly susceptible SJL/J mouse strain. Here we show that beta2M-deficient SJL mice have similar disease incidence rates to wild-type controls, however beta2M-deficient mice demonstrated earlier onset of clinical disease, elevated in vitro responses to TMEV and myelin proteolipid (PLP) epitopes, and significantly higher levels of CNS demyelination and macrophage infiltration at 50 days post-infection. beta2M-deficient mice also displayed a significant elevation in persisting viral titers, as well as an increase in macrophage-derived pro-inflammatory cytokine mRNA expression in the spinal cord at this same time point. Taken together, these results indicate that CD8(+) T cells are not required for clinical or histologic disease initiation or progression in TMEV-infected SJL mice. Rather, these data stress the critical role of CD4(+) T cells in this capacity and further emphasize the potential for CD8(+) T cells to contribute to protection from TMEV-induced demyelination.     

Classification of demyelinating diseases at the interface between etiology and pathogenesis

The classical demyelinating diseases include the 'autoimmune' inflammatory demyelinating diseases, the inflammatory demyelinating diseases of infectious aetiology, and the demyelinating or dysmyelinating diseases of genetic/hereditary background. In addition, primary demyelination is present in other conditions, such as brain ischaemia and intoxication. Irrespective of the primary aetiology, selective demyelination can be mediated through various pathogenetic pathways: the immune-mediated inflammatory pathway; the metabolic pathway; and the ischaemic/excitotoxic pathway. These pathways are only partly segregated with distinct aetiologies of demyelinating diseases, but they also reflect the way in which the patient copes with the disease-inciting event in relation to their particular genetic background. For future therapeutic strategies it will be important to interfere with the specific pathogenetic pathways of demyelination, which may be common to various demyelinating diseases, but may differ in subgroups of patients who suffer from a particular clinical demyelinating disease entity.     

Effects of regional spinal X-irradiation on demyelinating disease caused by Theiler's virus, mouse hepatitis virus or experimental allergic encephalomyelitis

The effects of X-irradiation on the course of chronic demyelinating disease were examined in mice with experimental allergic encephalitis (EAE), mouse hepatitis virus (MHV) or Theiler's virus (DAV) infection. One month after the induction of EAE or 2-16 months after inoculation of DAV, exposure of the cervical spinal cord to 20 Gy X-rays caused local exacerbation of disease activity but spinal irradiation did not affect MHV-induced demyelination. In EAE, there was a significant increase in the number of inflammatory cells in the irradiated part of the cord. Mice infected with DAV showed locally increased demyelination and axonal degeneration but no change in the titer of infectious virus within the cord. Thus in DAV infection, as in EAE, the exacerbation of disease seemed to be due to vascular or immunological factors rather than viral reactivation.