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Contrasting effects of immunosuppression on herpes simplex virus type I (HSV I) induced central nervous system (CNS) demyelination in mice.

We previously reported that lip inoculation of Herpes simplex virus type I (HSV I) in specific strains of mice would induce multifocal brain demyelination (MBD). The mechanisms mediating the development of MBD are unknown. In this study, five inbred strains of mice (C57BL/6J, Balb/cByJ, A/J, SJL/J, PL/J) immunosuppressed with either irradiation (IR), cyclophosphamide (CY), or cyclosporin A (CP) along with three immune deficient strains (C57BL/6J nu/nu, Balb/cByJ nu/nu, C57BL/6J bg/bg) were lip inoculated with HSV I to determine the effect of immunosuppression on viral spread throughout the brain and the development of demyelination during the acute stage of infection. Mortality increased in all groups when compared with controls but was greatest in A/J, SJL/J, and PL/J strains, where all mice died before day 6 PI. In contrast with immunocompetent C57BL/6J mice where virus is restricted to the brainstem, virus spread throughout the brain of immunosuppressed C57BL/6J, C57BL/6J nu/nu, and C57BL/6J bg/bg mice. Despite viral spread throughout the brain of immunosuppressed C57BL/6J, C57BL/6J nu/nu, Balb/cByJ and Balb/cByJ nu/nu mice, MBD did not develop. MBD did develop however, in both HSV I infected C57BL/6J bg/bg and CP treated Balb/cByJ mice. Immunosuppression of HSV I infected Balb/cByJ mice prevents the development of demyelination at the trigeminal root entry zone (TREZ) of the brainstem while in Balb/cByJ nu/nu mice, the extent of demyelination at TREZ was reduced and delayed when compared with immunocompetent controls. These results suggest that the immune system plays an important role in limiting viral spread in the brain as well as in the development of demyelination at TREZ and of MBD throughout the brain during the acute phase of infection. Virus alone does not induce MBD in this animal model of virus induced CNS demyelination but is a prerequisite for its development.

Acute Disease↗

Lymphocyte responsiveness to lectin and myelin antigens in canine distemper infection in relation to the development of demyelinating lesions.

Eleven dogs were experimentally infected with canine distemper virus and studied for periods of up to 63 days post-inoculation. The responsiveness of lymphocytes in vitro toward phytohemagglutinin, myelin basic protein and galactocerebroside was tested at regular intervals during the course of infection by means of [3H]thymidine incorporation and flow cytometry. All dogs developed a marked decrease of lymphocyte responsiveness toward phytohemagglutinin. Four dogs recovered rapidly from the immunosuppression and did not develop demyelination or had only mild lesions, while two others failed to recover at all and developed severe non-inflammatory demyelinating lesions. The remaining dogs exhibited a slow or partial immune recovery and had various degrees of inflammatory demyelination. Lymphocytes from 2 dogs with demyelination and 2 dogs without myelin lesions responded to myelin antigens. The findings indicate that the degree of immunosuppression in canine distemper virus infection may determine the type of demyelination and autoimmune reactions that occur during the inflammatory stage of demyelination may be epiphenomena.

Animals↗

Morphology of demyelination in the human central nervous system.

The principles of the neuropathological classification of disorders of central nervous system myelin are recalled. They are illustrated by a few selected examples. Dysmyelination is characterized by the production of an abnormal and unstable myelin sheath; it is often associated with hypomyelination (paucity of myelin formation) and is due to metabolic disorders. It is the main process in leukodystrophies. Storage of different lipids (e.g. sulfatides, long-chain fatty acids) or associated pathology of various cell types (in Alexander's disease, for example) are used for classifying these disorders. Biochemical and genetic characterizations are presently ongoing. Demyelination is the destruction of apparently normal myelin. It is often followed by remyelination. Our present knowledge on the neuropathology of multiple sclerosis, the most common demyelinating disease, is summarized. Cell-mediated demyelination affects the myelin sheaths for an obscure reason. The causes of the multifocal and sharply demarcated plaques, and of the fading of the remyelination process at the edge of some plaques, are not clear. A few examples of demyelinating diseases of known etiology and of various mechanisms are given. The similarities between acute disseminated leukoencephalitis and experimental autoimmune encephalitis are stressed. In progressive multifocal leukoencephalopathy, chronic infection of oligodendrocytes by JC virus induces poorly defined areas of demyelination. In AIDS, the pathogenesis of the myelin change is unclear. Macrophages may be responsible. Toxic and vascular disorders provide also good models for the understanding of mechanisms of demyelination.

Central Nervous System Diseases↗

Primary demyelination induced by exposure to tellurium alters mRNA levels for nerve growth factor receptor, SCIP, 2',3'-cyclic nucleotide 3'-phosphodiesterase, and myelin proteolipid protein in rat sciatic nerve.

Weanling rats fed a diet containing tellurium develop a peripheral neuropathy characterized by a highly synchronous primary demyelination; this demyelination is followed closely by a period of rapid remyelination. The demyelination is related to the inhibition of squalene epoxidase activity, which results in a block in cholesterol synthesis. Expression of mRNA for the major structural proteins of PNS myelin, myelin basic protein and P0, is coordinately down-regulated during the demyelinating phase and then up-regulated during the remyelinating phase (Toews et al., J. Neurosci. Res., 26 (1990) 501-507). We now report tellurium-induced alterations in gene expression for several proteins which are not major structural components of myelin in the peripheral nervous system. Expression of mRNA for nerve growth factor receptor in sciatic nerve was very low in control animals, but was markedly up-regulated after 3-5 days of exposure to tellurium, a time corresponding to the beginning of demyelination. Levels remained elevated during the subsequent period of remyelination. Expression of mRNA for SCIP (a presumptive transcription factor) was also up-regulated in sciatic nerve following tellurium exposure, with a time course similar to that for nerve growth factor receptor. When examined as a fraction of total RNA, steady-state mRNA levels for 2',3'-cyclic nucleotide 3'-phosphodiesterase and the myelin proteolipid protein were decreased during the demyelinating phase; however, this decrease could be largely accounted for by increased levels of total RNA. When analyzed on a 'per nerve' basis, steady-state mRNA levels for these two proteins were actually increased about 2-fold by 9 days after beginning tellurium exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

2',3'-Cyclic-Nucleotide Phosphodiesterases↗

CD8+-dependent CNS demyelination following ocular infection of mice with a recombinant HSV-1 expressing murine IL-2.

Demyelinating diseases comprise a spectrum of immunopathologic syndromes in which myelin, the fatty covering of nerve cell fibers in the brain and spinal cord, is destroyed. In this study, we have shown for the first time that ocular infection of BALB/c mice with a recombinant herpes simplex virus type 1 (HSV-1) expressing IL-2 (HSV-IL-2) results in CNS demyelination as determined by light microscopy and EM. The demyelinated lesions involve periventricular white matter, brain stem, and spinal cord white matter. Demyelination was detected in the CNS of infected mice up to 75 days (the longest time point tested) post HSV-IL-2 infection. In contrast, mice infected with HSV-IFN-gamma or HSV-IL-4, which are identical to HSV-IL-2 but express IFN-gamma or IL-4 instead of IL-2, did not exhibit demyelination. Control mice infected with wild-type HSV-1 or parental virus also remained free of these symptoms. During early times (days 3-7), post-infection with HSV-IL-2 virus, a T(H)1 + T(H)2 pattern of cytokines was produced by lymphocytes of infected mice while mice infected with HSV-IFN-gamma or control viruses produced a T(H)1 pattern of cytokine. By day 21 post-infection, all infected groups exhibited a T(H)1 pattern of response. Immunohistochemistry and FACS analyses of infiltrates in the brains and spinal cords of HSV-IL-2-infected mice showed elevations in CD4+ and CD8+ T cells and macrophages. However, T cell depletion studies suggest that only central memory CD8+ T cells are directly involved in the demyelination process, with macrophages being involved through a bystander effect.

Animals↗

Early paranodal myelin swellings (tomacula) in an avian riboflavin deficiency model of demyelinating neuropathy.

INTRODUCTION: Disruption of the complex architectural and molecular organization of the paranodal region of myelinated peripheral nerve fiber may initiate the evolving time dependent process of segmental demyelination. In support of this notion was the finding of focal paranodal myelin swellings (tomacula) due to redundant folding of myelin sheaths, early in the time course of an avian riboflavin deficiency model of demyelinating neuropathy. METHODS: Newborn broiler meat chickens were maintained either on a routine diet containing 5.0 mg/kg riboflavin (control group) or a riboflavin-deficient diet containing 1.8 mg/kg riboflavin. Riboflavin concentrations in the liver were measured at postnatal day 11. Peripheral nerves were morphologically examined at days 6, 11, 16 and 21 using light and electron microscopy and teased nerve fiber techniques. RESULTS: Riboflavin-deficient chickens showed signs of a neuropathy from days 8 and pathological examination of peripheral nerves revealed a demyelinating neuropathy with paranodal tomacula formation starting on day 11. Paranodal tomacula consisted of redundant myelin infoldings or outfoldings, increased in size and frequency after day 11. After day 16, the paranodal swellings showed prominent degenerative changes accompanied by an increased frequency of myelinated fibers showing demyelination. CONCLUSION: Tomacula due to redundant myelin folds are generally considered a remyelination phenomenon, yet in this avian riboflavin deficiency model of demyelination, the paranodal tomacula occurred early in the course of demyelination.

Animals↗

In vivo visualization of focal demyelination in peripheral nerves by gadofluorine M-enhanced magnetic resonance imaging.

Magnetic resonance imaging (MRI) allows assessment of axonal nerve lesions, but detection of focal demyelination is still difficult. We have recently shown that the novel micellar magnetic resonance (MR) contrast agent gadofluorine M (Gf) accumulates in nerve fibers undergoing Wallerian degeneration. In the present study, we report on the in vivo visualization of focal demyelination induced by lysolecithin. Upon appropriate intraneural injection, lysolecithin focally dissolves myelin sheaths with sparing of axons. Conventional unenhanced and gadolinium-DTPA enhanced T1-w MRI did not show signal alterations or contrast enhancement. In contrast, application of Gf led to bright contrast enhancement on T1-w images at the site of focal demyelination, but spared distal nerve segments not affected by demyelination. Gf enhancement persisted until remyelination had occurred. Our study shows that areas of focal nerve demyelination can be detected in vivo by Gf-enhanced MRI. This finding opens up a broad spectrum of applications in experimental neurology, and, depending on further clinical development of Gf, may aid in the diagnostic work up of patients with patchy, multifocal demyelinative disorders in the future.

Animals↗

The role of cellular immune response in Theiler's virus-induced central nervous system demyelination.

Theiler's murine encephalomyelitis virus (TMEV) persists in spinal cord white matter of susceptible mice (e.g., SJL/J), resulting in chronic inflammation and demyelination. Reconstitution of severe combined immunodeficient (SCID) mice with CD4(+) T- or CD8(+) T-lymphocytes results in extensive TMEV-induced demyelination, and depletion of CD8(+) T-lymphocytes in the early or late phase of the disease decreases the extent of demyelination, indicating that the cellular immune response against the virus plays a key role in myelin destruction. In susceptible mice, the demyelinated lesions are characterized by infiltration of a large numbers of B- and T-lymphocytes; whereas in mice resistant to TMEV-induced demyelination (e.g., C57BL/6), virus clearance requires infiltration of between 2.9 x 10(5) and 5.7 x 10(5) CD8(+) T-lymphocytes and between 3.4 x 10(5) and 6.1 x 10(5) CD4(+) T-lymphocytes per mouse in the brain 5-9 days post infection. Transgenic expression of capsid proteins of TMEV abrogates resistance in C56BL/6 mice, rendering the mice susceptible to TMEV persistence and demyelination. Comparison of the kinetics of virus replication and B- and T-lymphocyte infiltration in mice lacking key adhesion molecules (L-selectin (L-sel(-/-)), P-selectin (P-sel(-/-)), intracellular adhesion molecule-1 (ICAM-1(-/-)), or leukocyte function-associated antigen-1 (LFA-1(-/-))) demonstrates a role for individual adhesion molecules in recruitment of immune cells into central nervous system (CNS), but the role is not significant to prevent eventual virus clearance.

Animals↗

Demyelination increases radial diffusivity in corpus callosum of mouse brain.

Myelin damage, as seen in multiple sclerosis (MS) and other demyelinating diseases, impairs axonal conduction and can also be associated with axonal degeneration. Accurate assessments of these conditions may be highly beneficial in evaluating and selecting therapeutic strategies for patient management. Recently, an analytical approach examining diffusion tensor imaging (DTI) derived parameters has been proposed to assess the extent of axonal damage, demyelination, or both. The current study uses the well-characterized cuprizone model of experimental demyelination and remyelination of corpus callosum in mouse brain to evaluate the ability of DTI parameters to detect the progression of myelin degeneration and regeneration. Our results demonstrate that the extent of increased radial diffusivity reflects the severity of demyelination in corpus callosum of mouse brain affected by cuprizone treatment. Subsequently, radial diffusivity decreases with the progression of remyelination. Furthermore, radial diffusivity changes were specific to the time course of changes in myelin integrity as distinct from axonal injury, which was detected by betaAPP immunostaining and shown to be most extensive prior to demyelination. Radial diffusivity offers a specific assessment of demyelination and remyelination, as distinct from acute axonal damage.

Algorithms↗

Injection of the sciatic nerve with TMEV: a new model for peripheral nerve demyelination.

Demyelination of the human peripheral nervous system (PNS) can be caused by diverse mechanisms including viral infection. Despite association of several viruses with the development of peripheral demyelination, animal models of the condition have been limited to disease that is either autoimmune or genetic in origin. We describe here a model of PNS demyelination based on direct injection of sciatic nerves of mice with the cardiovirus, Theiler's murine encephalomyelitis virus (TMEV). Sciatic nerves of FVB mice develop inflammatory cell infiltration following TMEV injection. Schwann cells and macrophages are infected with TMEV. Viral replication is observed initially in the sciatic nerves and subsequently the spinal cord. Sciatic nerves are demyelinated by day 5 post-inoculation (p.i.). Injecting sciatic nerves of scid mice resulted in increased levels of virus recovered from the sciatic nerve and spinal cord relative to FVB mice. Demyelination also occurred in scid mice and by 12 days p.i., hindlimbs were paralyzed. This new model of virus-induced peripheral demyelination may be used to dissect processes involved in protection of the PNS from viral insult and to study the early phases of lesion development.

Animals↗

Virus-induced demyelination in nude mice is mediated by gamma delta T cells.

Infection of mice with mouse hepatitis virus (MHV), strain JHM, results in acute and chronic demyelination with many similarities to the human disease multiple sclerosis. This pathological process is primarily T cell-mediated and MHV infection of mice lacking B and T cells does not result in demyelination. In apparent contradiction to these results, robust demyelination is detected in MHV-infected young nude (athymic) mice. Herein, we show that demyelination in nude mice was mediated by gamma delta T cells. These cells, but not conventional CD4 or CD8 alpha beta T cells, were detected in the central nervous system of MHV-infected nude mice and their depletion with neutralizing antibody resulted in an 80% reduction in demyelination. These results show, for the first time, that gamma delta T cells can substitute for alpha beta T cells in a virus model of demyelination and further support a pathological role for gamma delta T cells in patients with multiple sclerosis.

Animals↗

Rat sleep and eye movement density as biological markers of demyelinating disease.

Myelin mutants provide an opportunity to study neurophysiological and behavioral effects of demyelination. The taiep rats are myelin mutants with progressive demyelination of the central nervous system (CNS), resulting in five neurological symptoms: tremor, ataxia, immobility, epilepsy, and paralysis. The demyelination affects the brainstem, an important area in the control of sleep. This study compared eye movement density (EMD) in taiep vs. normal control rats during paradoxical sleep (PS). It was hypothesized that taiep rats would have significantly reduced EMD during PS in comparison to normal controls due to their demyelinating disease. In addition, demyelination of brainstem structures would suggest possible changes in sleep-wake structure. Hence, we compared sleep-wake stages in taiep vs. normal, control rats. The results confirmed significantly reduced EMD during PS in taiep rats compared to normal rats during the 12-h (light) recording period. In addition, analysis of EMD values across the 12-h light period revealed significant differences in EMD values as a function of time of day in the taeip rats only. Comparison of waking and sleep values across the 12-h light phase revealed an "immobility episode" in three taiep rats, which was not present in normal controls. In addition, PS percentage was significantly lower and low-voltage sleep was significantly higher in taiep rats. These results suggest that EMD, immobility episodes, and sleep architecture may be useful as measurable biological events in the study of demyelinating disease. The results were discussed in terms of possible mechanisms underlying these differences, as well as possible implications for future studies.

Animals↗

Bystander CD4 T cells do not mediate demyelination in mice infected with a neurotropic coronavirus.

Demyelination following infection of mice with the neurotropic coronavirus mouse hepatitis virus strain JHM (MHV) is immune-mediated. It has been demonstrated that MHV-specific CD4 and CD8 T cells are capable of causing demyelination independent of the other T cell subset. Recent work has also demonstrated that activated bystander CD8 T cells mediate significant demyelination. The ability of bystander CD4 T cells to mediate demyelination was investigated using CD4 T cell transgenic mice. The results indicated that bystander CD4 T cells were unable to cause demyelination in MHV-infected mice, despite being recruited into the central nervous system (CNS) and irrespective of activation status. These results suggest that CD4 T cells must recognize antigen in the CNS in order to cause demyelination.

Animals↗

Visual evoked potentials study in chronic idiopathic inflammatory demyelinating polyneuropathy.

BACKGROUND: The frequency of the association between chronic demyelinating inflammatory polyneuropathy (CIDP) and central nervous system (CNS) demyelinating lesions is probably underestimated. OBJECTIVE: To investigate the occurrence of combined central and peripheral demyelination in CIDP patients and to correlate visual evoked potential (VEP) abnormalities with CNS demyelinating lesions, observed on brain magnetic resonance imaging, and antibodies against glycolipids. METHODS: Nerve conduction studies, brain MRI and antibodies against glycolipids were prospectively studied in 17 patients who fulfilled the diagnostic criteria proposed for CIDP (Cornblath DR, Asbury AK, Albers JW, Feasby TE, Hahn AF, McLeod JG, Mendell JR, Parry GJ, Pollard JD, Thomas PK. Ad Hoc Subcommittee of the American Academy of Neurology AIDS Task Force. Research criteria for diagnosis of chronic inflammatory demyelinating polyneuropathy. Neurology, 1991;41:617-618). VEPs were performed in each case before and after 6 months treatment with either intravenous immunoglobulins (IVIG) or steroids. RESULTS: Eight patients (47%) had increased latencies in at least one eye or showed increased interocular latency difference. Four patients (23%) presented a significant high signal intensity on T2-weighted brain MRI images. Of these 4 patients, 3 had prolonged VEP latency. Two patients with delayed VEP latency had antibodies against GM1, and SGLPG and anti-sulfatides, respectively. One patient with normal VEPs also had antibodies to GM1. VEP results were not significantly modified after treatment, either with steroids or IVIG. CONCLUSION: This study confirmed the high frequency of abnormal VEPs in CIDP patients, and found that they are poorly correlated with CNS demyelinating lesions and antibodies against glycolipids. The VEP abnormalities of these patients may be explained by the susceptibility to immune-mediated damage of both the peripheral nervous system and the optic nerve.

Adolescent↗

Increased levels of myelin basic protein transcripts in virus-induced demyelination.

In multiple sclerosis, a demyelinating disease of young adults, there is a paucity of myelin repair in the central nervous system (CNS) which is necessary for the restoration of fast saltatory conduction in axons. Consequently, this relapsing disease often causes marked disability. In similar diseases of small rodents, however, remyelination can be quite extensive, as in the demyelinating disease caused by the A59 strain of mouse hepatitis virus (MHV-A59), a coronavirus of mice. To investigate when and where oligodendrocytes are first triggered to repair CNS myelin in such disease, we have used a complementary DNA probe specific for one major myelin protein gene, myelin basic protein (MBP), which hybridizes with the four forms of MBP messenger RNA in rodents. Using Northern blot and in situ hybridization techniques, we previously found that MBP mRNA is first detected at about 5 days after birth, peaks at 18 days and progressively decreases to 25% of the peak levels in the adult. We now report that in spinal cord sections of adult animals with active demyelination and inflammatory cells, in situ hybridization reveals a dramatic increase in probe binding to MBP-specific mRNA at 2-3 weeks after virus inoculation and before remyelination can be detected by morphological methods. This increase of MBP-specific mRNA is found at the edge of the demyelinating area and extends into surrounding areas of normal-appearing white matter. Thus, in situ hybridization with myelin-specific probes appears to be a useful method for detecting the timing, intensity and location of myelin protein gene reactivation preceding remyelination. This method could be used to elucidate whether such a reactivation occurs in multiple sclerosis brain tissue. Our results suggest that in mice, glial cells react to a demyelinating process with widespread MBP mRNA synthesis which may be triggered by a diffusible factor released in the demyelinated areas.

Animals↗

Inflammation and severe demyelination in the peripheral nervous system induced by the intraneural injection of recombinant mouse interleukin-12.

Inflammatory cytokines appear to be involved in damage to Schwann cells, myelin and axons, although the exact role of the different cytokines is uncertain. The direct injection model offers a new and simplified way of examining the mechanisms of early inflammation in the peripheral nervous system. The present study was performed to assess the direct effects of interleukin (IL)-12 on rat sciatic nerves injected with recombinant mouse IL-12. Histological and immunohistochemical examination 24 h after injection showed early inflammation as well as demyelination within the injected nerve fibres. By 4 days the inflammatory and demyelinating changes were significantly increased. Seven days after injection, the endoneurium still contained significant numbers of inflammatory cells and the demyelination was even more severe. Control rats injected with sterile phosphate-buffered saline exhibited no such inflammatory and demyelinating response. These changes are similar to those seen in inflammatory and demyelinating disorders of the peripheral nervous system and suggest that IL-12 could be relevant to the pathogenesis of demyelinating diseases such as Guillain-Barré syndrome.

Animals↗

The reaction of glial progenitor cells in remyelination following ethidium bromide-induced demyelination in the mouse spinal cord.

The present study investigated how glial progenitor cells participated in the process of remyelination following ethidium bromide (EBr)-induced demyelination in the adult mouse spinal cord. In situ hybridization techniques for detecting mRNA for platelet-derived growth factor alpha receptor (PDGFalphaR) and proteolipid protein (PLP) were employed to identify glial progenitor cells and mature oligodendrocytes, respectively. During the demyelination stage and early stage of remyelination, large cells strongly expressing PDGFalphaR mRNA were observed in the border of the demyelinating lesion, and with immunohistochemistry they exhibited positive labeling of the astrocytic marker glial fibrillary acidic protein (GFAP). Other glial progenitor cells expressing PDGFalphaR mRNA proliferated around the lesion during the demyelination stage. During the remyelination stage, some PDGFalphaR mRNA-positive cells partly expressed mRNA for PLP in the periphery of the demyelinating lesion. These results suggest that PDGFalphaR mRNA-positive glial progenitor cells may give rise to both astrocytes and oligodendrocytes, which participate in remyelination following demyelination.

Animals↗

Chronic inflammatory demyelinating polyneuropathy: immunopathological and ultrastructural study of peripheral nerve biopsy in 42 cases.

The authors recently reexamined the peripheral nerve biopsies from 42 patients with chronic inflammatory demyelinating polyneuropathy (CIDP). There were 27 males and 15 females, aged from 9 to 84 years, and 13 had relapses. No patient had vasculitis, monoclonal gammopathy, tumor, diabetes mellitus, Lyme disease, familial neuropathy, HIV, or any other immune deficiency. In the endoneurium, perivascular inflammatory cell infiltrates were present in only one case, but scattered histiocytes marked by KP1 on paraffin-embedded fragments were present in every case and there were no T-lymphocytes. At ultrastructural examination macrophage-associated demyelination was observed in 17 cases, of which 6 had relapses separated by intervals of several months or years. Axonal lesions without associated primary demyelination were observed in 4 cases and 3 of these had relapses. Thirty-two patients had mixed lesions of demyelination and axonal involvement. This study confirms other recent data indicating that in all cases of CIDP, macrophages are present in the endoneurium. Macrophage-associated demyelination is the characteristic feature of demyelinating forms. On the other hand, isolated primary axonal forms, which have been known since 1989, are relatively frequent and prone to relapses.

Adolescent↗