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The bidirectional regulation between the gut microbiota and brain, known as gut-brain axis, has received significant attention. The myelin sheath, produced by oligodendrocytes or Schwann cells, is essential for efficient nervous signal transmission and the maintenance of brain function. Growing evidence shows that both oligodendrogenesis and myelination are modulated by gut microbiota and its metabolites, and when dysbiosis occurs, changes in the microbiota composition and/or associated metabolites may impact developmental myelination and the occurrence of neurodevelopmental disabilities. Although the link between the microbiota and demyelinating disease such as multiple sclerosis has been extensively studied, our knowledge about the role of the microbiota in other myelin-related disorders, such as neurodegenerative diseases, is limited. Mechanistically, the microbiota-oligodendrocyte axis is primarily mediated by factors such as inflammation, the vagus nerve, endocrine hormones, and microbiota metabolites as evidenced by metagenomics, metabolomics, vagotomy, and morphological and molecular approaches. Treatments targeting this axis include probiotics, prebiotics, microbial metabolites, herbal bioactive compounds, and specific dietary management. In addition to the commonly used approaches, viral vector-mediated tracing and gene manipulation, integrated multiomics and multicenter clinical trials will greatly promote the mechanistic and interventional studies and ultimately, the development of new preventive and therapeutic strategies against gut-oligodendrocyte axis-mediated brain impairments. Interestingly, recent findings showed that microbiota dysbiosis can be induced by hippocampal myelin damage and is reversible by myelin-targeted drugs, which provides new insights into understanding how hippocampus-based functional impairment (such as in neurodegenerative Alzheimer's disease) regulates the peripheral homeostasis of microbiota and associated systemic disorders., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Post-Infectious Neurological Syndromes (PINS) are heterogeneous neurological disorders with post or para-infectious onset. PINS diagnosis is complex, mainly related to the absence of any recognized guidelines and a univocal definition., Aim of the Study: To elaborate a diagnostic guide for PINS., Materials and Methods: We retrospectively analysed patients younger than 14 years old admitted to Bambino Gesù Children's Hospital in Rome for PINS from December 2005 to March 2018. Scientific literature using PubMed as research platform was analysed: the key words "Post-Infectious Neurological Syndromes" were used., Results: A polysymptomatic presentation occurred in a percentage of 88% of the children. Motor signs and visual disturbances the most observed symptoms/signs were the most detached, followed by fever, speech disturbances, sleepiness, headache and bradipsychism. Blood investigations are compatible with inflammation, as a prodromal illnesses was documented in most cases. Normal cerebral spinal fluid (CSF) characteristics has been found in the majority of the study population. Magnetic resonance imaging (MRI) was positive for demyelinating lesions. Antibiotics, acyclovir and steroids have been given as treatment., Discussion: We suggest diagnostic criteria for diagnosis of PINS, considering the following parameters: neurological symptoms, timing of disease onset, blood and CSF laboratory tests, MRI imaging., Conclusions: We propose criteria to guide clinician to diagnose PINS as definitive, probable or possible. Further studies are required to validate diagnostic criteria.

In contrast to gut, the oral microbiome of MS patients has not been characterized. Deep sequencing of saliva DNA from a pair of monozygotic twins (MSF1 with relapsing remitting MS; MSF2 with clinically isolated syndrome) identified 2036 bacterial species. Relative abundances of 3 phyla were higher, and 3 lower in MSF1 versus MSF2. Species diversity was greater in MSF2, and 20 abundant species differed at least 2-fold. Pathway analysis identified 116 functional hierarchies differing 50% or more. Although limited to one pair of twins, our data suggests that oral microbiome analysis may be useful for diagnosis or monitoring therapeutic efficacy., Competing Interests: Declaration of Competing Interest The authors declare they have no conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Young man with acute onset nausea, vomiting, joint pain, abdominal pain, fever and weight loss was found to have gait ataxia and positive B rucella titres. He deteriorated despite appropriate antibiotics and developed confusion and disorientation. Lumbar puncture revealed lymphocytosis with high protein and low glucose. MRI showed diffuse demyelination. Pulse steroids resulted in rapid clinical, biochemical and radiological recovery., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.)

Increasing evidence suggests a role of CD8 T cells in autoimmune demyelinating CNS disease, which, however, is still controversially discussed. Mice, which express ovalbumin (OVA) as cytosolic self-antigen in oligodendrocytes (ODC-OVA mice), respond to CNS infection induced by OVA-expressing attenuated Listeria with CD8 T cell-mediated inflammatory demyelination. This model is suitable to decipher the contribution of CD8 T cells and the pathogen in autoimmune CNS disease. Here, we show that both antigen and pathogen are required in the CNS for disease induction, though not in a physically linked fashion. Intracerebral challenge with combined toll like receptor (TLR) TLR2 and TLR9 as well as TLR7 and TLR9 agonists substituted for the bacterial stimulus, but not with individual TLR agonists (TLR2, TLR3,TLR5,TLR7, TLR9). Furthermore, MyD88 inactivation rendered ODC-OVA mice resistant to disease induction. Collectively, CD8 T cell-mediated destruction of oligodendrocytes is activated if (i) an antigen shared with an infectious agent is provided in the CNS microenvironment and (ii) innate immune signals inform the CNS microenvironment that pathogen removal warrants an immune attack by CD8 T cells, even at the expense of locally restricted demyelination., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Multiple sclerosis (MS) is an autoimmune disease characterized by multiple lesions in the brain and spinal cord. We used RNA sequencing to identify microbial sequences and characterize human gene expression patterns in 30 human brain biopsy specimens. RNAs which aligned to known microbial taxa, were significantly enriched in 10 of 12 primary demyelination (MS) brain specimens compared to a group of 15 epilepsy controls, leading to a list of 29 MS microbial candidate genera from 11 different phyla. Most of the candidate MS microbes are anaerobic bacteria. While there were some shared candidates, each of the 10 MS samples with significant microbial RNA enrichment had a distinct set microbial candidates. The fraction of microbial sequencing reads was greater for the MS group (128.8 PPM) compared to the controls (77.4 PPM, p = 0.016). Bacterial peptidoglycan was demonstrated in brain tissue sections from several MS subjects. Human gene expression analysis showed increased expression of inflammation-related pathways in the MS group. This data shows that demyelinating brain lesions are associated with the presence of microbial RNA sequences and bacterial antigen. This suggests that MS is triggered by the presence of a diverse set of microbes within a lesion.

Microbial communities reside in healthy tissues but are often disrupted during disease. Bacterial genomes and proteins are detected in brains from humans, nonhuman primates, rodents and other species in the absence of neurological disease. We investigated the composition and abundance of microbiota in frozen and fixed autopsied brain samples from patients with multiple sclerosis (MS) and age- and sex-matched nonMS patients as controls, using neuropathological, molecular and bioinformatics tools. 16s rRNA sequencing revealed Proteobacteria to be the dominant phylum with restricted diversity in cerebral white matter (WM) from MS compared to nonMS patients. Both clinical groups displayed 1,200-1,400 bacterial genomes/cm 3 and low bacterial rRNA:rDNA ratios in WM. RNAseq analyses showed a predominance of Proteobacteria in progressive MS patients' WM, associated with increased inflammatory gene expression, relative to a broader range of bacterial phyla in relapsing-remitting MS patients' WM. Although bacterial peptidoglycan (PGN) and RNA polymerase beta subunit immunoreactivities were observed in all patients, PGN immunodetection was correlated with demyelination and neuroinflammation in MS brains. Principal component analysis revealed that demyelination, PGN and inflammatory gene expression accounted for 86% of the observed variance. Thus, inflammatory demyelination is linked to an organ-specific dysbiosis in MS that could contribute to underlying disease mechanisms.

Autoantibodies against various components of host are known to occur in leprosy. Nerve damage is the primary cause of disability associated with leprosy. The aim of this study was to detect the level of autoantibodies and lympho-proliferative response against myelin basic protein (MBP) in leprosy patients (LPs) and their correlation with clinical phenotypes of LPs. Further, probable role of molecular mimicry in nerve damage of LPs was investigated. We observed significantly high level of anti-MBP antibodies in LPs across the spectrum and a positive significant correlation between the level of anti-MBP antibodies and the number of nerves involved in LPs. We report here that 4 B cell epitopes of myelin A1 and Mycobacterium leprae proteins, 50S ribosomal L2 and lysyl tRNA synthetase are cross-reactive. Further, M. leprae sonicated antigen hyperimmunization was responsible for induction of autoantibody response in mice which could be adoptively transferred to naive mice. For the first time our findings suggest the role of molecular mimicry in nerve damage in leprosy., (Copyright © 2015 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)

The fields of microbiology, immunology, neurology and nutrition are rapidly converging, as advanced sequencing and genomics-based methodologies have enabled the mapping out of the microbial diversity of humans for the first time. Bugs, guts, brains and behavior were once believed to be separate domains of clinical practice and research; however, recent observations in our understanding of the microbiome indicate that the boundaries between domains are becoming permeable. This permeability is multidirectional: Biological systems are operating simultaneously in a vastly complex and interconnected web. Understanding the microbiome-gut-brain axis will entail fleshing out the mechanisms by which transduction across each domain occurs, allowing us ultimately to appreciate the role of commensal organisms in shaping and modulating host immunity. This article will highlight animal and human research to date, as well as highlight directions for future research. We speculate that the gut microbiome is potentially the premier environmental risk factor mediating inflammatory central nervous system demyelination, in particular multiple sclerosis., (© The Author(s), 2014.)

There is increasing support for the importance of risk factors such as genetic makeup, obesity, smoking, vitamin D insufficiency, and antibiotic exposure contributing to the development of autoimmune diseases, including human multiple sclerosis (MS). Perhaps the greatest environmental risk factor associated with the development of immune-mediated conditions is the gut microbiome. Microbial and helminthic agents are active participants in shaping the immune systems of their hosts. This concept is continually reinforced by studies in the burgeoning area of commensal-mediated immunomodulation. The clinical importance of these findings for MS is suggested by both their participation in disease and, perhaps of greater clinical importance, attenuation of disease severity. Observations made in murine models of central nervous system demyelinating disease and a limited number of small studies in human MS suggest that immune homeostasis within the gut microbiome may be of paramount importance in maintaining a disease-free state. This review describes three immunological factors associated with the gut microbiome that are central to cytokine network activities in MS pathogenesis: T helper cell polarization, T regulatory cell function, and B cell activity. Comparisons are drawn between the regulatory mechanisms attributed to first-line therapies and those described in commensal-mediated amelioration of central nervous system demyelination.

The increasing prevalence of immune-related diseases, including multiple sclerosis, may be partly explained by reduced microbial burden during childhood. Within a multi-centre case-control study population, we examined: (i) the co-morbid immune diseases profile of adults with a first clinical diagnosis of central nervous system demyelination (FCD) and (ii) sibship structure in relation to an autoimmune (FCD) and an allergic (asthma) disease. FCD cases (n = 282) were aged 18-59 years; controls (n = 558) were matched on age, sex and region. Measures include: history of doctor-diagnosed asthma; sibling profile (number; dates of birth); and regular childcare attendance. FCD cases did not differ from controls with regard to personal or family history of allergy, but had a greater likelihood of chronic fatigue syndrome [odds ratio (OR) = 3·11; 95% confidence interval (CI) 1·11, 8·71]. Having any younger siblings showed reduced odds of FCD (OR = 0·68; 95% CI: 0·49, 0·95) but not asthma (OR = 1·47; 95% CI: 0·91, 2·38). In contrast, an increasing number of older siblings was associated with reduced risk of asthma (P trend = 0·04) but not FCD (P trend = 0·66). Allergies were not over-represented among people presenting with FCD. Sibship characteristics influence both FCD and asthma risk but the underlying mechanisms differ, possibly due to the timing of the putative 'sibling effect'., (© 2013 British Society for Immunology.)

Brucellosis is a public health problem in most countries in the Mediterranean. Involvement of the central nervous system is seen in 4-13% of patients with brucellosis. A 13-year-old girl was admitted because of gait disturbance, diplopia, and dizziness. Her complaints began about 1.5 years ago. The second symptomatic episode repeated about three months ago and the third two months ago. In total, attacks repeated 3 times over 1.5 years. The magnetic resonance imaging (MRI) and the clinical features mimicked multiple sclerosis. The patient was given pulse steroid treatments. After steroid treatment, her gait disturbance and diplopia improved over the short term. Following positive developments, her symptoms recurred. The tests were repeated; the MRI showed increasingly high signal abnormalities, and Brucella melitensis was grown in cerebrospinal fluid. The patient was started on an oral combination of rifampin, doxycycline, and ciprofloxacin. MRI findings improved markedly after nine months of treatment. Although neurobrucellosis is associated rarely with demyelination in adults, this finding has not been reported previously in children or adolescents. Additionally, this case is the first in terms of involvement of the corpus callosum in neurobrucellosis. In this article, we present an unusual case of neurobrucellosis.

The work describes three cases of patients at various ages, diagnosed for CNS demyelinating disease. The presence of specific antibodies to B. burgdorferi sensu lato, and findings of B. burgdorferi s.l. DNA, identified in one case as the genospecies B. garinii in the liquor, indicated previous experience with the infection. Presumably, persistence of borrelia in the organism could act as one of the autoimmune process triggers, resulting in the demyelinating disease.

Objective: To describe 2 patients presenting with severe neurological deficits and extensive lesions on brain magnetic resonance imaging after having experienced Legionella pneumonia., Design: Case reports., Setting: University hospital., Patients: Two patients who developed severe neurological symptoms, including encephalopathic signs, following Legionella infection, with widespread lesions on magnetic resonance imaging compatible with demyelination., Results: After extensive ancillary investigations, a diagnosis of acute disseminating encephalomyelitis was considered most likely. Steroid therapy was initiated in 1 of the patients, followed by plasmapheresis. In both patients, clinical and radiological signs gradually recovered, with only slight residual deficits., Conclusion: In patients presenting with neurological symptoms after an episode of pneumonia, Legionella infection and a subsequent immune-mediated process such as acute disseminating encephalomyelitis should be considered.

Although glial cells are recognized for their roles in maintaining neuronal function, there is growing appreciation of the ability of resident CNS cells to initiate and/or augment inflammation following trauma or infection. The tachykinin, substance P (SP), is well known to augment inflammatory responses at peripheral sites and its presence throughout the CNS raises the possibility that this neuropeptide might serve a similar function within the brain. In support of this hypothesis, we have recently demonstrated the expression of high affinity receptors for SP (Neurokinin-1 (NK-1) receptors) on microglia and shown that this tachykinin can significantly elevate bacterially induced inflammatory prostanoid production by isolated cultures of these cells. In the present study, we demonstrate that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation in vivo following exposure to two clinically relevant bacterial CNS pathogens, Neisseria meningitidis and Borrelia burgdorferi. We show that in vivo elevations in inflammatory cytokine production and decreases in the production of an immunosuppressive cytokine are markedly attenuated in mice genetically deficient in the expression of the NK-1R or in mice treated with a specific NK-1R antagonist. Furthermore, we have used isolated cultures of microglia and astrocytes to demonstrate that SP can augment inflammatory cytokine production by these resident CNS cell types following exposure to either of these bacterial pathogens. Taken together, these studies indicate a potentially important role for neurogenic exacerbation of resident glial immune responses in CNS inflammatory diseases, such as bacterial meningitis.

Inflammation is a prominent feature of several disorders characterized by primary demyelination, but it is not clear whether a relationship exists between inflammation and myelin damage. We have found that substantial demyelination results from the focal inflammatory lesion caused by the injection of lipopolysaccharide (LPS; 200 ng) directly into the rat dorsal funiculus. Within 24 h, such injections caused a focal inflammatory response consisting of a substantial number of polymorphonuclear cells and ED1-positive and inducible nitric oxide synthase (iNOS)-positive macrophages/microglia. The number of inflammatory cells was substantially reduced by day 7. OX-52-positive T-cells were less frequently observed but were present in the meninges at 8 h, reached a maximum in the dorsal funiculus at 7 days, and were rare at 14 days. The inflammation was followed by the appearance of a large lesion of primary demyelination that encompassed up to approximately 75% of the cross-sectional area of the dorsal funiculus. Treatment with dexamethasone significantly reduced the number of cells expressing iNOS, but did not prevent the demyelination. By 28 days the lesions were largely remyelinated, usually by Schwann cells. These changes were not observed in control, saline-injected animals. We conclude that the intraspinal injection of LPS results in inflammation and subsequently in prominent demyelination. The mechanisms underlying the demyelination are not clear, but it is notable that it typically begins with disruption of the adaxonal myelin. Indeed, there is an early loss of myelin-associated glycoprotein within the lesion, despite the persistence of proteolipid protein. This combination is a feature of the pattern III lesion recently described in multiple sclerosis (Lucchinetti et al., 2000), and we therefore suggest that LPS-induced demyelination may serve as the first experimental model available for the study of this type of multiple sclerosis lesion.

A 7-year-old female presented with Mycoplasma pneumoniae pneumonitis and a progressive ascending limb paralysis. She developed severe respiratory distress, requiring ventilation, and became apparently unresponsive with fixed dilated pupils. Peripheral nerves were inexcitable in nerve-conduction studies. Magnetic resonance imaging of the brain revealed evidence of extensive demyelination. Anti-GM1 immunoglobulin M antibody titers were raised. She improved after a second course of intravenous immunoglobulin and eventually made a full recovery.

Guillain-Barré syndrome (GBS), an acute, immune-mediated paralytic disorder affecting the peripheral nervous system, is the most common cause of acute flaccid paralysis in the post-polio era. GBS is classified into several subtypes based on clinical and pathologic criteria, with acute inflammatory demyelinating polyneuropathy (AIDP) and acute motor axonal neuropathy (AMAN) being the most common forms observed. To better understand the pathogenesis of GBS and host susceptibility to developing the disease, the distribution of HLA class II Ags along with the seroreactivity to Campylobacter jejuni were investigated in a population of GBS patients from northern China. Using DNA-based typing methods, 47 patients with AMAN, 25 patients with AIDP, and 97 healthy controls were studied for the distribution of class II alleles. We found that the DQ beta RLD(55-57)/ED(70-71) and DR beta E(9)V(11)H(13) epitopes were associated with susceptibility to AIDP (p = 0.009 and p = 0.004, respectively), and the DQ beta RPD(55-57) epitope was associated with protection (p = 0.05) from AIDP. These DQ beta/DR beta positional residues are a part of pockets 4 (DQ beta 70, 71, DR beta 13), 6 (DR beta 11), and 9 (DQ beta 56, 57, DR beta 9); have been demonstrated to be important in peptide binding and T cell recognition; and are associated with other diseases that have a pathoimmunological basis. Class II HLA associations were not identified with AMAN, suggesting a different immunological mechanism of disease induction in the two forms of GBS. These findings provide immunogenetic evidence for differentiating the two disease entities (AMAN and AIDP) and focuses our attention on particular DR beta/DQ beta residues that may be instrumental in understanding the pathophysiology of AIDP.

Demyelination results in severe disability in many neurodegenerative diseases and nervous system infections, and it is typically mediated by inflammatory responses. Mycobacterium leprae, the causative organism of leprosy, induced rapid demyelination by a contact-dependent mechanism in the absence of immune cells in an in vitro nerve tissue culture model and in Rag1-knockout (Rag1-/-) mice, which lack mature B and T lymphocytes. Myelinated Schwann cells were resistant to M. leprae invasion but undergo demyelination upon bacterial attachment, whereas nonmyelinated Schwann cells harbor intracellular M. leprae in large numbers. During M. leprae-induced demyelination, Schwann cells proliferate significantly both in vitro and in vivo and generate a more nonmyelinated phenotype, thereby securing the intracellular niche for M. leprae.

We addressed the contributions of persistent virus infection and immune cells to the pathogenesis of Theiler's virus-induced demyelination, a model for human multiple sclerosis. We developed a model involving the transfer of spleen cells into immunodeficient C.B-17-scid (SCID) mice, which normally die of overwhelming virus encephalitis without demyelination when infected with Theiler's virus. Adoptive transfer of nonimmune spleen cells from BALB/c mice into SCID mice resulted in the survival of all mice. However, these mice developed extensive demyelination and virus Ag/RNA persistence in the spinal cord white matter. The most demyelination was observed when mice received an intermediate number of spleen cells (1.8-7.5 x 10(6)), whereas too few cells (0.5 x 10(6)) did not ameliorate the SCID phenotype, and too many cells (30 x 10(6)) resulted in almost complete viral clearance with minimal demyelination. Adoptive transfer of spleen cells depleted of either CD4+ or CD8+ T cells produced vacuolar demyelination associated with virus persistence. In contrast, reconstitution with both CD4+ and CD8+ T cells produced less severe demyelination and partial clearance of virus. These experiments support the hypothesis that demyelination is the result of a balance between persistent virus infection and immune injury mediated by either CD4+ or CD8+ T cells.

Mouse hepatitis virus strain A59 causes a persistent productive, but nonlytic, infection of cultured glial cells. We have mutants isolated from persistently infected glial cell cultures which have been shown to be fusion-defective due to a histidine to aspartic acid mutation (H716D) near the cleavage site of the peplomer protein, S. Here, we examine the pathogenicity of these mutants and show differences in hepatotropism and virulence compared to wild-type virus (WT). Two mutants chosen for detailed study, B11 and C12, were impaired in their abilities to cause hepatitis and/or replicate in the liver of susceptible mice. Furthermore, B11 and C12 display two separate hepatotropic phenotypes. The ability of B11 to replicate in the liver was dependent on infectious dose and route of inoculation, while C12 consistently displayed decreased hepatotropism regardless of dose and route of inoculation. However, B11 and C12 were shown to replicate in the CNS of infected animals similarly to WT. Like WT, the mutants produced meningoencephalitis during acute infection, with viral antigen exhibiting a similar distribution in the brain, and demyelination during chronic infection. Sequence analysis of wild-type, mutant, and revertant S proteins indicates that (1) a mutation in the N terminal subunit of S (S1), resulting in a glutamine to leucine amino acid substitution (Q159L), may affect hepatotropism and (2) a cleavage site mutation which determines fusogenicity is not responsible for altered hepatotropism. Furthermore, since B11, C12, and a nonattenuated fusion mutant (B12) have identical S protein sequences, there must be additional mutations outside of S which influence both virulence and hepatotropism.

Infectious agents have been postulated as causes of multiple sclerosis for over a century. The possible role of a virus or viruses is supported by data that (1) a childhood exposure is involved and "viral" infections may precipitate exacerbations of disease, (2) experimental infections in animals and natural infections in humans can cause diseases with long incubation periods, remitting and relapsing courses, and demyelination, and (3) patients with multiple sclerosis have abnormal immune responses to viruses. The pathogenesis of three human demyelinating diseases of known viral etiology is discussed. In progressive multifocal leukoencephalopathy, a papovavirus selectively infects oligodendrocytes and causes focal areas of demyelination. In postmeasles encephalomyelitis, the virus is lymphotrophic and disrupts immune regulation that can result in an autoimmune perivenular demyelinating illness without evidence of infection of the central nervous system. In human immunodeficiency virus-encephalopathy and myelopathy virus is present in macrophages and microglia and the myelin abnormalities apparently are caused by soluble factors such as viral proteins, cytokines, or neurotoxins. These findings may have implications on how, when, and where to seek viruses in multiple sclerosis.

This case study documents a demyelinating process associated with atypical glial intranuclear inclusions. The patient, a 38-year-old woman, presented with acute onset of headaches and weakness. Magnetic resonance imaging revealed two discrete intrahemispheric lesions. Light microscopic examination showed small, homogeneous, eosinophilic inclusions chiefly in astroglial nuclei. By electron microscopy these inclusions were shown to be clusters of filamentous structures. Attempts to identify the particles with an antibody to measles virus and in situ hybridization to JC virus were negative. The morphologic appearance of the inclusions in this case is similar to that described in neuronal intranuclear inclusion disease.

Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), a model for multiple sclerosis, is a chronic T cell-mediated disease. Development of clinical symptoms in susceptible mouse strains generally correlates with TMEV-specific delayed-type hypersensitivity (DTH) responses. These responses, minimal or absent in resistant mouse strains, have been proposed as the pathogenic basis for the central nervous system inflammation and demyelination characterizing the disease. We demonstrate here that normally resistant (C57BL/6 x DBA/2)F1 hybrid mice develop clinical symptoms and DTH responses against TMEV after low doses of gamma-irradiation. Parental C57BL/6 animals remain resistant after similar pretreatment. Thus low-dose irradiation elicits a "latent" susceptibility to TMEV-IDD in some, but not all, resistant mice. Adoptively transferred spleen cells from syngeneic, unirradiated donors reconfer resistance on irradiated, infected B6D2F1 hybrids and reduce DTH responsiveness against TMEV, suggesting a protective role for a radiation-sensitive splenic population(s). The closely related C57BL/6 and C57BL/10 strains differ with respect to intrinsic and latent susceptibility.

The neurotropic murine coronavirus, MHV-JHM (JHMV) causes encephalitis and paralytic-demyelinating disease in susceptible strains of mice and rats, serving as a model for human demyelinating diseases such as multiple sclerosis. In this communication, we report that a single intracerebral administration of the naturally occurring neuropeptide, beta-endorphin, reduced the incidence of JHMV-induced paralytic-demyelinating disease 40-50% in C57Bl/6 mice. Protection from disease was accompanied by significantly reduced virus replication in the brain as early as 3 days post-infection and did not occur in irradiated, or immunoincompetent mice. The data suggest that beta-endorphin engages immune mechanisms of host resistance to JHMV infection to protect the mice from disease.

We utilized the polymerase chain reaction (PCR) to examine for preferential expression of T cell receptor (TcR) V beta s in T cells infiltrating the central nervous system (CNS) of mice infected with Theiler's virus. Infection of susceptible strains of mice with Theiler's virus results in demyelinating disease similar to multiple sclerosis. At 7 days following infection, no difference was observed in TcR V beta usage in lymphocytes infiltrating the CNS between resistant (B10.K) and susceptible (B10.Q or SJL/J) mice. In susceptible mice with prominent demyelination (day 45 and 238 following infection), no preferential expression of TcR V beta s was observed in the CNS. There is strong evidence that T cells play a major role in pathogenesis of TMEV-induced demyelination. There is increasing evidence using recombinant inbred strain mice with TcR V beta deletions that T cells expressing certain TcR V beta genes may be critical in the disease process. Yet, analysis of TcR V beta expression on T cells in CNS using PCR technology did not provide a way to dissect which antigen-specific T cells play a role in disease. These results confirm that during active demyelination specific as well as non-specific T cells are recruited to the CNS. Even though the pathogenesis of TMEV-induced disease may not be identical to that in multiple sclerosis, it is unlikely that similar approaches utilizing polymerase chain reaction will provide insights to the role of T cell receptors in the pathogenesis of multiple sclerosis.

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.

Inbred strains of mice vary in their susceptibility to the chronic inflammatory and demyelinating disease caused by Theiler's virus. The severity of this disease depends on the extent of demyelination but also on the occurrence of remyelination. We studied the extent of demyelination and remyelination in mice with different genetic backgrounds. To estimate the extent of demyelination, we analyzed the abundance of proteolipid protein (PLP) transcripts in the spinal cord 45 days after inoculation. RNA transcripts were quantitated at the single cell level using in situ hybridization. We observed a correlation between the reduction of PLP mRNA and the extent of inflammation in the SJL/J, C3H, F1 SJL x C3H and C3H.Q strains. Remyelination by Schwann cells was estimated by the detection of P0 mRNA and was observed in C3H mice only. It is likely that intense inflammation in highly susceptible strains prevents the migration of Schwann cells into the central nervous system (CNS).

Theiler's murine encephalomyelitis virus (TMEV) induces immune-mediated demyelination in susceptible strains of mice, providing an excellent model for multiple sclerosis. Class I genes within the major histocompatibility complex locus (H-2D region) play a major role in determining whether strains of mice develop chronic demyelination and TMEV persistence. B10.D2dml mice with deletion in the 3' end of Dd and the 5' end of Ld genes develop the most prominent demyelination in comparison with resistant B10.D2 mice with normal complementation of H-2D region genes. We tested whether expression of a class I human transgene (HLA-B27) would modulate virus-induced demyelination in mutant B10.D2dml mice. Transgenic B10.D2dml (HLA-B27+) mice infected with virus showed dramatic decrease in the extent of demyelination (p < 0.0001) and virus antigen expression in spinal cord compared with littermate controls without the human class I transgene. These experiments demonstrate that transgenic expression of a human class I major histocompatibility complex locus molecule can prevent demyelination induced by a virus in mutant mice.

Two separate studies are described in this report. First, 5 Owl monkeys were inoculated intracerebrally (IC) with coronavirus JHM OMP1; this virus isolate was cultured from the brain of an animal inoculated with uncloned MHV JHM. Two of the animals became neurological impaired and were sacrificed; these animals had developed severe encephalomyelitis as previously described. Two of the remaining 3 healthy animals were inoculated IC again at 90 days post-inoculation (DPI) and all 3 were sacrificed approximately 5 months after the first virus inoculation. Despite the lack of detectable infectious virus, viral RNA and antigen, all 3 animals had significant white matter inflammation and areas of demyelination in the spinal cord. In the second study 4 Owl monkeys were inoculated intranasally (IN) and ocularly and 4 inoculated intravenously (i.v.) with JHM OMP1. The animals were sacrificed between 16 and 215 DPI with 2 IN and 2 i.v. animals receiving a second i.v. inoculum at 152 DPI. Viral RNA and/or antigen was detected in the brains of all animals and the distribution corresponded to areas of inflammation and edema. One of the animals that received the second inoculum developed neurological impairment and subsequent analysis of tissues showed viral antigen in both brain and spinal cord. Viral products were predominantly found in blood vessels suggesting hematogenous spread with entry into the central nervous system (CNS) through endothelium.

It has previously been shown that passive immunization with antibodies specific for the hemagglutinin-esterase (HE) protein of mouse hepatitis virus (MHV) prevents acute lethal encephalitis, resulting in a subacute and chronic demyelination in mice infected with JHM(2), an isolate of the neurotropic JHM strain of MHV. To determine possible genetic changes occurring during infection, viruses were isolated from the brain of infected mice at various time points after infection and examined for the patterns of their structural proteins. The results showed that the sizes and expression levels of the viral spike, membrane, and nucleocapsid proteins were constant among 161 virus isolates throughout the infection. In contrast, most of the viruses isolated later in infection did not synthesize HE protein. This finding suggests that the HE gene expression is extremely variable and is preferentially lost during prolonged viral infections. In contrast, when viruses were passaged in tissue culture, no significant accumulation of HE protein-defective mutants was observed, suggesting that the accumulation of HE protein-defective mutants in infected animals was most likely the result of the positive selection for these mutants during the subacute and chronic infection. The genetic defects of HE gene in these mutants were characterized by cloning, sequencing, and in vitro translation of HE genes. Most of the mutations in the HE protein-defective mutants consisted of deletions of various lengths at different sites within the HE-coding region, resulting in the change of the reading frame and early termination. However, most of the truncated HE proteins were not detected in the infected cells. Since viruses from different mice exhibited different types of defects, the HE mutations probably occurred de novo in the brain. These results demonstrated the exceptionally rapid selection of HE-defective mutants during viral infection of mice and suggest that their selection may be related to the neuropathogenicity or persistence of MHV.

Most studies suggest that the pathogenesis of Multiple Sclerosis (MS) is based on immune mechanisms of myelin injury. In addition, a viral infection, possibly established in the first few years of the patient's life, may be crucial in setting the stage for such immune mediated injury when acting on the appropriate genetic background. Of the several models of virus-induced demyelination described in the last two decades, Theiler's murine encephalomyelitis virus (TMEV) infection has emerged as one of the best models for MS.

We examined the cerebrospinal fluid findings, including the activity of the myelin-associated enzyme 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP), and virus serology in patients with Bell's palsy. Eighty-nine of 164 patients showed hematological and/or serological evidence of an inflammatory reaction. Examinations of the CSF disclosed an elevated total protein level and pleocytosis in 33% and 10% of the 91 patients, respectively. The activity of CNP was significantly elevated in the patient group (15.5 +/- 3.8 nmol/h/ml) as compared with the control (13.2 +/- 1.3 nmol/h/ml) (p < 0.01), suggesting the presence of intrathecal myelin breakdown. Furthermore, there was an association between antibodies against herpes simplex virus (HSV) and elevated CNP activity. The inflammatory alterations and accompanying spinal fluid abnormalities, together with the high frequency of HSV antibodies suggest that HSV-associated demyelination may play a pathogenetic role in Bell's palsy.

Chronic infection of susceptible strains of mice with Theiler's murine encephalomyelitis virus (TMEV) results in central nervous system (CNS) demyelination similar to multiple sclerosis. Demyelination induced by TMEV is mediated, in part, by class I-restricted CD8+ T lymphocytes. For these T cells to function, they must recognize virus-infected CNS targets in the presence of class I major histocompatibility complex (MHC) antigen. Therefore, we studied in vivo expression of class I MHC antigen and viral antigen-RNA in prototypic mouse strains that are susceptible (SJL/J) or resistant (C57BL/10SNJ) to TMEV-induced demyelination. In brains of resistant mice, viral antigen-RNA expression peaked on day 3 after infection and was effectively diminished by day 5 such that few virus-infected cells were ever detected in the spinal cord. In contrast, susceptible mice demonstrated delay in clearance of TMEV from the brain and a subsequent increase and persistence of viral antigen-RNA in the spinal cord for as long as 277 days. Viral infection resulted in "upregulation" of class I MHC expression in the CNS. Class I MHC antigens were expressed as early as 1 day after infection in the choroid plexus of both strains of mice before detection of viral antigen or inflammation. In resistant mice, class I MHC expression predominated in the gray matter of the brain and spinal cord on day 7 after infection but returned to undetectable levels by day 28. In susceptible mice, class I MHC expression in the CNS persisted and was intense in the white matter of the spinal cord throughout chronic infection and demyelination. No class I MHC expression was detected in the CNS of uninfected mice. Coexpression of viral RNA and class I MHC antigen was demonstrated in CNS cells by using simultaneous in situ hybridization and immunoperoxidase technique. These results support the hypothesis that a class I-restricted immune response directed against virus-infected cells may be important in the mechanism of demyelination.

Multifocal central nervous system (CNS) demyelination develops in the brains of SJL/J, PL/J, and A/J mice following lip inoculation with a specific strain of herpes simplex virus I (HSV I). The lesions in all three inbred strains of mice share similar characteristics including demyelination, relative preservation of axons, and a mononuclear cell (MNC) infiltrate. The lesions, developing during the early phase of demyelination, also appear sequentially in the CNS (trigeminal root entry zone of the brainstem greater than cerebellum greater than cerebral hemispheres) of all three strains of mice but differ in the time of their initial appearance following infection as well as their morphology. In SJL/J mice, new areas of demyelination are observed for only 24 days following lip inoculation with virus. Late stage multifocal CNS demyelination persists throughout 28 weeks postinoculation (pi) in PL/J mice while in A/J mice the development of new areas of demyelination are restricted to 8 weeks pi. Although mononuclear inflammatory cells are present in the new areas of demyelination in either PL/J or A/J mice, viral antigens are not detected in the CNS beyond 12 days pi. In contrast, in situ hybridization studies using 35S-cDNA HSV probes and performed beyond day 12 pi identify probe-positive cells central to a number of the multifocal CNS demyelinating lesions in A/J mice. Results from studies with inbred and congenic strains of mice indicate that the major histocompatibility complex (H-2) does not determine the development of multifocal CNS demyelination following lip inoculation with HSV I but does influence the morphological appearance of the lesions that do develop.

An antigenic variant of the neurotropic murine coronavirus JHMV, designated 2.2-V-1, causes marked demyelination in the relative absence of encephalitis. It is thus useful for the study of the pathogenesis of demyelinating lesions. To better understand the sequential events leading to demyelination, we have examined murine brain and spinal cord tissue at daily intervals after intracerebral inoculation, evaluating them for the distribution of viral antigen, leukocyte infiltration, and demyelination. Immunohistochemical staining indicated that virus established primary infection in the ependymal cells in both brain and spinal cord before spreading into nearby structures and along white matter tracts by cell-to-cell contact. Spread from brain to spinal cord appeared to occur via cerebrospinal fluid. Viral replication was focally cytocidal for ependymal cells, and essentially noncytocidal for other neural cells including glia. In brain, viral antigen and inflammation reached a peak at day 5 postinfection, and rapidly subsided by day 10 postinfection. In spinal cord, viral antigen was less abundant than in brain and was maximal between days 7 and 9 postinfection. The inflammatory response and demyelination, however, were more severe persisting from day 7 through day 19. In the spinal cord, demyelinating lesions developed initially in areas closer to the central canal and were detected most prominently in the anterior funiculi. This finding suggests that the permissiveness of the ependymal cell is crucial to viral entry and that sequential infection of glial cells leads to the characteristic distribution of demyelination.

Two species of primates, Owl and African green monkeys, were inoculated intracerebrally with either the neurotropic mouse hepatitis virus JHM or the putative multiple sclerosis brain coronavirus isolate SD. These viruses caused an acute to subacute panencephalitis and/or demyelination in the infected animals. The course of pathogenesis and sites of detected viral RNA and antigen was dependent both on animal species and virus strain but the results clearly showed that these viruses replicated and disseminated in the central nervous system (CNS) of these primates. This study suggests that human CNS may be susceptible to coronavirus infection.

Epidemiologists have long worked at the limit of their powers to invoke an infectious agent to explain some of the epidemiological features of multiple sclerosis (MS). No virus has yet been definitively assigned a causal role in the pathogenesis of MS. Many viruses, however, have been incriminated, but it has not been possible to reproduce every single observation. Nevertheless, important lessons have been learned from the quest to identify such agents. Other kinds of demyelinating disease within the central nervous system (CNS) have been clearly linked to direct or indirect effects of viral infection. An understanding of the pathogenesis of these models affords possible insights into the mechanisms by which viruses or other agents might be operative in MS and other chronic diseases of the nervous system.

Intracerebral infection of certain strains of mice with Theiler's virus results in chronic immune-mediated demyelination in spinal cord. We used mouse mutants with deletion of the V beta class of TCR genes to examine the role of TCR genes in this demyelinating disease which is similar to multiple sclerosis. Quantitative analysis of spinal cord lesions demonstrated a markedly increased number and extent of demyelinated lesions in persistently infected RIII S/J mice which have a massive deletion of the TCR V beta-chain (V beta 5.2, V beta 8.3, V beta 5.1, V beta 8.2, V beta 5.3, V beta 8.1, V beta 13, V beta 12, V beta 11, V beta 9, V beta 6, V beta 15, V beta 17) compared with B10.RIII mice which are of identical MHC haplotype (H-2r) but have normal complement of V beta TCR genes. In contrast, infection of C57L (H-2b) or C57BR (H-2k) mice which have deletion of the V beta TCR genes (V beta 5.2, V beta 8.3, V beta 5.1, V beta 8.2, V beta 5.3, V beta 8.1, V beta 13, V beta 12, V beta 11, and V beta 9) resulted in few demyelinating lesions. Genetic segregation analysis of (B10.RIII x RIII S/J) x RIII S/J backcrossed mice and (B10.RIII x RIII S/J) F2 mice demonstrated correlation of increased susceptibility to demyelination with deletion of TCR V beta genes. The increase in number of demyelinating lesions correlated with increase in number of virus-Ag+ cells in spinal cord. These experiments provide strong evidence that the structural diversity at the TCR beta-complex can influence susceptibility to virus-induced demyelination.

Immunosuppression using cyclophosphamide or anti-T cell monoclonal antibodies (mAbs) directed at CD4 or CD8 promoted remyelination of CNS axons in the spinal cords of mice infected chronically with Theiler's virus. Treatment with a mAb directed at class II major histocompatibility gene products did not increase the extent of CNS remyelination. Following immunosuppressive treatment, quantitative morphometry revealed a five- to sevenfold increase in new myelin synthesis. Proliferating nervous system cells were identified at the edges of remyelinated lesions by their incorporation of [3H]thymidine. CNS remyelination occurred in mice depleted of selected subsets of T lymphocytes despite the local persistence of viral antigen. These findings indicate that CNS remyelination occurs as a normal consequence of primary myelin injury, but factors associated with immune T cells somehow impair remyelination. Interference with the function of immune T cells enhances CNS remyelination by oligodendrocytes. Similar depletion of immune T cells may allow for enhanced remyelination in the CNS of patients with chronic multiple sclerosis.

We describe a 33-year-old homosexual man with a steroid-responsive, remitting and relapsing leukoencephalopathy associated with recent human immunodeficiency virus type 1 (HIV-1) seroconversion. Biopsy of a parieto-occipital lesion revealed demyelination and astrogliosis with focal necrosis. Detailed investigations demonstrated no pathogens in the brain other than HIV-1. This patient illustrates that a neurological disorder clinically indistinguishable from multiple sclerosis may be the presenting manifestation of HIV-1 infection and may occur in the absence of clinically significant immunosuppression.

Coronavirus MHV-JHM infection of rodents can result in demyelinating encephalomyelitis. We analysed histological changes induced by coronavirus MHV-JHM infection in Lewis rats. Besides an acute disease (AE), chronic panencephalitis (CPE) and subacute demyelinating encephalomyelitis (SDE) were induced. These disease types were differentiated by the incubation period, the localization of lesions, the type of tissue damage and distribution of virus antigen. In AE and CPE, virus antigen was detected in neurons, astrocytes and oligodendrocytes, whereas in SDE neurons lacked virus antigen. Viral nucleocapsid protein (N) was present in the cytoplasm and the spike protein (S) was displayed on the surface of infected neural cells. However, expression of S protein relative to N protein was severely impaired in SDE lesions. Quantitative analysis of infiltrating inflammatory cells revealed that the number of macrophages and T cells were similar in lesions of AE, CPE and SDE. In contrast to that, SDE lesions contained a significantly higher number of IgG + B cells and plasma cells. In addition active demyelinating SDE lesions displayed an enhanced IgG content and deposits of complement C9. These results indicate that virus induced primary demyelination could be a consequence of antibody mediated cytotoxicity. Furthermore, a reduction in the number of cells producing spike protein in the chronic forms of the disease indicates down-regulation of this protein, possibly mediated by anti-S antibodies.