Lesion development in Marburg's type of acute multiple sclerosis: from inflammation to demyelination

Oxygen treatment reduces neurological deficits and demyelination in two animal models of multiple sclerosis

AIMS

The objective of the study is to explore the importance of tissue hypoxia in causing neurological deficits and demyelination in the inflamed CNS, and the value of inspiratory oxygen treatment, using both active and passive experimental autoimmune encephalomyelitis (EAE).

METHODS

Normobaric oxygen treatment was administered to Dark Agouti rats with either active or passive EAE, compared with room air-treated, and naïve, controls.

RESULTS

Severe neurological deficits in active EAE were significantly improved after just 1 h of breathing approximately 95% oxygen. The improvement was greater and more persistent when oxygen was applied either prophylactically (from immunisation for 23 days), or therapeutically from the onset of neurological deficits for 24, 48, or 72 h. Therapeutic oxygen for 72 h significantly reduced demyelination and the integrated stress response in oligodendrocytes at the peak of disease, and protected from oligodendrocyte loss, without evidence of increased oxidative damage. T-cell infiltration and cytokine expression in the spinal cord remained similar to that in untreated animals. The severe neurological deficit of animals with passive EAE occurred in conjunction with spinal hypoxia and was significantly reduced by oxygen treatment initiated before their onset.

CONCLUSIONS

Severe neurological deficits in both active and passive EAE can be caused by hypoxia and reduced by oxygen treatment. Oxygen treatment also reduces demyelination in active EAE, despite the autoimmune origin of the disease.

Conserved spinal cord bioenergetics in experimental autoimmune encephalomyelitis in C57BL6 mice, measured using phosphorescence oxygen analyzer

Background

We have previously reported that spinal cord respiration (cellular mitochondrial oxygen consumption) and ATP content are conserved in the studied model of experimental autoimmune encephalomyelitis (EAE), foreseeing a recovery of the diseased rats. This exemplary lesion of multiple sclerosis is used here to measure spinal cord bioenergetics in C57BL6 mice. Our hypothesis is that, despite the well-known focal axonal mitochondrial pathology, bioenergetics of the CNS is reasonably preserved in this disease.

Methods

EAE was induced with an immunodominant myelin oligodendrocyte glycoprotein epitope in complete Freund's adjuvant, appended by injections of pertussis toxin. A low- and high-dose of the encephalitogen, administered into base of tail or hind-flank, were investigated. Control mice received only the incomplete adjuvant into tail. Oxygen measurements were based on quenching the phosphorescence of Pd(II) meso-tetra (sulfophenyl) tetrabenzoporphyrin by molecular oxygen. Cellular ATP was measured using the luciferin/luciferase system.

Results

The kinetics of spinal cord oxygen consumption was zero-order (linear with time) and inhibited by cyanide, confirming oxygen was reduced by cytochrome oxidase. The rate of respiration (in μM O₂.min⁻¹.mg⁻¹; measured on Days 13–28) in control mice was (mean ± SD) 0.086 ± 0.024 (n = 8) and in immunized mice was 0.079 ± 0.020 (n = 15, P = 0.265, Mann-Whitney test). Consistently, cellular ATP (in μmol mg⁻¹ dry pellet weight; measured on Days 13–28) in control mice was 0.068 ± 0.079 (n = 11) and in immunized mice was 0.063 ± 0.061 (n = 24, P = 0.887, Mann-Whitney U test).

Conclusions

In vitro measurements of spinal cord bioenergetics show conservation of the mitochondrial function in mice with EAE. These results suggest the previously documented reduced mitochondrial electrochemical potential in this disease is alterable, and likely reflects the adverse events of neuroinflammation.

Microglial process convergence on axonal segments in health and disease

Microglia dynamically interact with neurons influencing the development, structure, and function of neuronal networks. Recent studies suggest microglia may also influence neuronal activity by physically interacting with axonal domains responsible for action potential initiation and propagation. However, the nature of these microglial process interactions is not well understood. Microglial-axonal contacts are present early in development and persist through adulthood, implicating microglial interactions in the regulation of axonal integrity in both the developing and mature central nervous system. Moreover, changes in microglial-axonal contact have been described in disease states such as multiple sclerosis (MS) and traumatic brain injury (TBI). Depending on the disease state, there are increased associations with specific axonal segments. In MS, there is enhanced contact with the axon initial segment and node of Ranvier, while, in TBI, microglia alter interactions with axons at the site of injury, as well as at the axon initial segment. In this article, we review the interactions of microglial processes with axonal segments, analyzing their associations with various axonal domains and how these interactions may differ between MS and TBI. Furthermore, we discuss potential functional consequences and molecular mechanisms of these interactions and how these may differ among various types of microglial-axonal interactions.

Multiple sclerosis pathogenesis: missing pieces of an old puzzle

Traditionally, multiple sclerosis (MS) was considered to be a CD4 T cell-mediated CNS autoimmunity, compatible with experimental autoimmune encephalitis model, which can be characterized by focal lesions in the white matter. However, studies of recent decades revealed several missing pieces of MS puzzle and showed that MS pathogenesis is more complex than the traditional view and may include the following: a primary degenerative process (e.g. oligodendroglial pathology), generalized abnormality of normal-appearing brain tissue, pronounced gray matter pathology, involvement of innate immunity, and CD8 T cells and B cells. Here, we review these findings and discuss their implications in MS pathogenesis.

Spatiotemporal evolution of venous narrowing in acute MS lesions

Objective

To investigate the spatiotemporal evolution of venous narrowing in newly developing MS lesions in a longitudinal MRI study including susceptibility-weighted images (SWIs).

Methods

We retrospectively investigated serial MR examinations of 18 patients with MS acquired on a 3T MRI system including SWI for acute contrast-enhancing lesions with at least 1 MRI examination before contrast enhancement. The mean diameter of veins at the time point of contrast enhancement was compared with the mean diameter of veins before and after contrast enhancement.

Results

A total of 40 acute contrast-enhancing lesions with a corresponding intralesional central vein were included in the study. The mean diameter of intralesional veins at the time of contrast enhancement (0.80 ± 0.12 mm) was smaller than that at before (1.16 ± 0.19 mm) and after contrast enhancement (1.07 ± 0.15 mm; p < 0.001 for all comparisons).

Conclusions

Our findings contribute to the increasing database of plaque development and evolution. The smaller diameter of intralesional veins on SWI at the time of blood-brain barrier breakdown may reflect morphologic changes because of perivascular inflammation and/or decreased levels of deoxygenated hemoglobin.

Inhibition of neurogenesis in a case of Marburg variant multiple sclerosis

INTRODUCTION

Neural stem cells (NSC) are located essentially in the subventricular zone (SVZ), subgranular zone (SGZ), and along the central canal of the spinal cord. These cells can proliferate in vitro and differentiate into neurons, oligodendrocytes, and astroglia, thus contributing to repair in multiple sclerosis (MS). We conducted a pathological study to analyse neurogenic response in a patient with Marburg variant MS.

METHODS

We present the case of a 27-year-old immunocompetent patient with Marburg variant MS, a fulminant form of the disease. The condition lasted 20 days. Diagnosis was based on clinical symptoms and MRI showed demyelinating lesions located in subependymal areas and histopathological findings. Neurogenic niches (SVZ and dentate gyrus) were analysed by confocal microscopy using markers of proliferation (Ki-67, PCNA), neuroblasts (PSA-NCAM, DCX, Tuj1), stem cells (Nestin, GFAPδ, SOX2, PAX6, Musashi), astrocytes (GFAP, AQ4), oligodendrocytes (NG2, Olig), microglia and cell infiltrates (IBA-1, CD68, MHCII), and cell death (TUNEL).

RESULTS

Expression of the markers GFAPδ, SOX2, and PAX6 in NSC was found to be very low. Likewise, markers of proliferation (Ki-67) and intermediate precursors (NG2) were also reduced. This lack of markers of the first stages of cell differentiation means that neurogenesis is inhibited even in very early stages of the disease.

CONCLUSION

Inhibition of neurogenesis in our patient, which cannot be explained by the fulminant nature of his symptoms, may be related to inflammation and immune response. This finding may further our knowledge of repair mechanisms in MS.

Mitochondrial dysfunction is an important cause of neurological deficits in an inflammatory model of multiple sclerosis

Neuroinflammation can cause major neurological dysfunction, without demyelination, in both multiple sclerosis (MS) and a mouse model of the disease (experimental autoimmune encephalomyelitis; EAE), but the mechanisms remain obscure. Confocal in vivo imaging of the mouse EAE spinal cord reveals that impaired neurological function correlates with the depolarisation of both the axonal mitochondria and the axons themselves. Indeed, the depolarisation parallels the expression of neurological deficit at the onset of disease, and during relapse, improving during remission in conjunction with the deficit. Mitochondrial dysfunction, fragmentation and impaired trafficking were most severe in regions of extravasated perivascular inflammatory cells. The dysfunction at disease onset was accompanied by increased expression of the rate-limiting glycolytic enzyme phosphofructokinase-2 in activated astrocytes, and by selective reduction in spinal mitochondrial complex I activity. The metabolic changes preceded any demyelination or axonal degeneration. We conclude that mitochondrial dysfunction is a major cause of reversible neurological deficits in neuroinflammatory disease, such as MS.

Autologous stem cell transplantation as rescue therapy in malignant forms of multiple sclerosis

Malignant forms of multiple sclerosis (MS) represent a limited group of very aggressive demyelinating diseases, which rapidly progress to severe disability leading often to life-threatening conditions. On these clinical entities, currently available therapies for MS are not very effective. Recently, it has been demonstrated that intense immunosuppression followed by autologous stem cell transplantation (ASCT) can affect the clinical course of individuals with severe MS and completely abrogate the inflammatory activity detected by magnetic resonance imaging (MRI). We report on the treatment with intense immune ablation followed by ASCT of three patients with malignant MS whose clinical course indicated a dramatically poor prognosis. This procedure succeeded in halting the rapidly worsening course of disease. The effect was long lasting, as demonstrated by a sustained efficacy over a two-year period in two subjects and 12 months in the third case. In addition, a striking effect on inflammation-related MRI findings was obtained. These results support a role for intense immunosuppression followed by ASCT as treatment in rapidly evolving malignant MS cases unresponsive to conventional therapies.

The most fulminant course of the Marburg variant of multiple sclerosis-autopsy findings

Multiple sclerosis (MS) is usually a chronic and disabling inflammatory disease. Marburg's type of MS is characterized by rapid progression and severe disease course that leads to death within one year after the onset of clinical signs. We describe a fulminant clinical presentation of this malignant subtype of MS and discuss the neuropathological hallmarks as well as differential diagnoses of other fulminant demyelinating diseases. To the best of our knowledge, this is the most fulminant course of this MS variant reported in the literature.

Multiple sclerosis: molecular mechanisms and therapeutic opportunities

The pathophysiology of multiple sclerosis (MS) involves several components: redox, inflammatory/autoimmune, vascular, and neurodegenerative. All of them are supported by the intertwined lines of evidence, and none of them should be written off. However, the exact mechanisms of MS initiation, its development, and progression are still elusive, despite the impressive pace by which the data on MS are accumulating. In this review, we will try to integrate the current facts and concepts, focusing on the role of redox changes and various reactive species in MS. Knowing the schedule of initial changes in pathogenic factors and the key turning points, as well as understanding the redox processes involved in MS pathogenesis is the way to enable MS prevention, early treatment, and the development of therapies that target specific pathophysiological components of the heterogeneous mechanisms of MS, which could alleviate the symptoms and hopefully stop MS. Pertinent to this, we will outline (i) redox processes involved in MS initiation; (ii) the role of reactive species in inflammation; (iii) prooxidative changes responsible for neurodegeneration; and (iv) the potential of antioxidative therapy.

Neurological deficits caused by tissue hypoxia in neuroinflammatory disease

OBJECTIVE

To explore the presence and consequences of tissue hypoxia in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS).

METHODS

EAE was induced in Dark Agouti rats by immunization with recombinant myelin oligodendrocyte glycoprotein and adjuvant. Tissue hypoxia was assessed in vivo using 2 independent methods: an immunohistochemical probe administered intravenously, and insertion of a physical, oxygen-sensitive probe into the spinal cord. Indirect markers of tissue hypoxia (eg, expression of hypoxia-inducible factor-1α [HIF-1α], vessel diameter, and number of vessels) were also assessed. The effects of brief (1 hour) and continued (7 days) normobaric oxygen treatment on function were evaluated in conjunction with other treatments, namely administration of a mitochondrially targeted antioxidant (MitoQ) and inhibition of inducible nitric oxide synthase (1400W).

RESULTS

Observed neurological deficits were quantitatively, temporally, and spatially correlated with spinal white and gray matter hypoxia. The tissue expression of HIF-1α also correlated with loss of function. Spinal microvessels became enlarged during the hypoxic period, and their number increased at relapse. Notably, oxygen administration significantly restored function within 1 hour, with improvement persisting at least 1 week with continuous oxygen treatment. MitoQ and 1400W also caused a small but significant improvement.

INTERPRETATION

We present chemical, physical, immunohistochemical, and therapeutic evidence that functional deficits caused by neuroinflammation can arise from tissue hypoxia, consistent with an energy crisis in inflamed central nervous system tissue. The neurological deficit was closely correlated with spinal white and gray matter hypoxia. This realization may indicate new avenues for therapy of neuroinflammatory diseases such as MS.

Oligodendrocytes and the early multiple sclerosis lesion

There is little agreement among neuropathologists regarding the timing and nature of oligodendrocyte loss in multiple sclerosis (MS). This review describes changes that accompany acute oligodendrocyte loss in new lesions. Included is a description of the immunopathology of new lesions in 23 severe early cases selected from a bank of 300 MS autopsies. Oligodendrocytes in prephagocytic lesions exhibit cytopathic changes that include apoptosis of oligodendrocytes immunoreactive for caspase 3, phagocytosis of apoptotic oligodendrocytes, swelling of cells with abnormal nuclei, complement deposition, and lysis. These are nonspecific changes that provide no clue as to the cause of oligodendrocyte injury. Associated changes include the presence of enlarged immunoglobulin (IgG)(+) microglia and early macrophages, the presence nearby of a focus of inflammatory demyelination, an open blood-brain barrier, and the presence of rare CD8 T cells. Myelin contacted by IgG(+) macrophages is immunoreactive for complement but not for IgG. It is likely that macrophage activity in evolving white and gray matter plaques is scavenging activity directed at nonvital myelin secondary to oligodendrocytes loss. One feature of MS that is not understood is the extraordinarily close resemblance the disease shows pathologically to neuromyelitis optica (NMO), including that demyelination in both is secondary to a loss of caspase 3-positive apoptotic oligodendrocytes. These similarities raise the possibility that like NMO, MS is an autoimmune disease in which oligodendrocyte apoptosis is determined by injury to some other glial or mesenchymal component.

A second case of Marburg’s variant of multiple sclerosis with vasculitis and extensive demyelination

Marburg’s variant of multiple sclerosis is a rapidly progressive and malignant form of multiple sclerosis (MS) that usually leads to severe disability or death within weeks to months without remission. Few cases have been described in the literature since the original description by Marburg. The classic pathological findings usually include highly destructive zones of extensive demyelination, necrosis with dense cellular infiltrate, and giant reactive astrocytes. We report a case of a 31-year-old woman with Marburg’s variant of MS who, over a period of eight months, became totally disabled, blind, and quadriplegic, with vocal cord paralysis, requiring a tracheostomy. The patient underwent diagnostic stereotactic brain biopsy. Clinical findings, magnetic resonance imaging (MRI), serologic and cerebrospinal fluid (CSF) findings, and neuropathology are discussed. MRI showed extensive white matter involvement in the brain and spinal cord that continuously progressed over time. A diagnostic stereotactic brain biopsy revealed extensive active demyelination with unexpected finding of active vasculitis and fibrinoid necrosis with a vascular inflammatory cell infiltrate, including polymorphonuclear neutrophils and rare eosinophils. Serologic work-up for vasculitis and neuromyelitis optica was unremarkable and the CSF showed only one oligoclonal band (OCB) not present in serum. This is the second case of Marburg’s variant of MS that demonstrated both demyelination and vasculitis. In our case these features were demonstrated simultaneously, even though the demyelination was the predominant pathological finding. Since vasculitis is not a feature of classic MS, these findings pose the question as to whether Marburg’s variant of MS is a true variant or different entity altogether.

Importance of oligodendrocyte protection, BBB breakdown and inflammation for remyelination

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the CNS. A better understanding of why remyelination fails in MS is necessary to improve remyelination strategies. Remyelination is mediated by oligodendrocyte precursor cells (OPCs), which are widely distributed throughout the adult CNS. However, it is still unclear whether OPCs detectable in MS lesions survive the inflammatory response but are unable to myelinate or whether OPC and oligodendrocyte death is primarily responsible for remyelination failure and detectable OPCs enter demyelinated areas from adjacent tissue as the lesion evolves. Remyelination strategies should, therefore, focus on stimulation of differentiation or prevention of apoptosis, as well as establishment of a supportive environment for OPC-mediated remyelination, which may be especially important in chronically demyelinated lesions.

Multiple sclerosis on steroids

A 57-year-old man developed acute bilateral vision loss clinically consistent with bilateral optic neuritis. Within 1 month of diagnosis, he developed progressive and severe neurologic dysfunction, and repeat MRI demonstrated enhancement of the optic chiasm and optic tracts, as well as a large enhancing lesion within the right parieto-occipital lobe. Stereotactic-guided brain biopsy demonstrated demyelination consistent with multiple sclerosis. A diagnosis of fulminant multiple sclerosis was made. The patient died within 2 months of diagnosis. Multiple sclerosis and a fulminant subtype known as Marburg disease are discussed.

Multiple sclerosis: distribution of inflammatory cells in newly forming lesions

OBJECTIVE

CD4 T-cell-dependent macrophage activation directed against a myelin or oligodendrocyte antigen is generally thought to be the mechanism causing myelin destruction in multiple sclerosis (MS). However, areas within expanding MS lesions may exhibit prominent oligodendrocyte loss and apoptosis in the absence of infiltrating lymphocytes. The present study was designed to further investigate the inflammatory profile of different regions within rapidly expanding MS lesions.

METHODS

Twenty-six active lesions from 11 patients with early MS were serially sectioned and immunostained for T and B cells, plasma cells, ramified microglia, macrophages, monocytes, and CD209-positive dendritic cells. Cell counts were compared in prephagocytic, phagocytic, and immediately postphagocytic areas.

RESULTS

Parenchymal T and B cells were largely absent in areas of initial oligodendrocyte loss and in areas of degenerate and dead myelin infiltrated by myelin phagocytes. In contrast, trailing areas of complete demyelination packed with lipid macrophages, and, in some lesions, regenerating oligodendrocytes, showed large numbers of T cells, B cells, and immunoglobulin G (IgG)-positive plasma cells. Lesions in 2 exceptionally early cases contained relatively few T and B cells, and no IgG-positive plasma cells.

INTERPRETATION

Early loss of oligodendrocytes is a prominent feature in tissue bordering rapidly expanding MS lesions. Macrophage activity is largely an innate scavenging response to the presence of degenerate and dead myelin. Adaptive immune activity involving T and B cells is conspicuous chiefly in recently demyelinated tissue, which may show signs of oligodendrocyte regeneration. The findings suggest that plaque formation has some basis other than destructive cell-mediated immunity directed against a myelin or oligodendrocyte antigen.

MRI characteristics of atypical idiopathic inflammatory demyelinating lesions of the brain : A review of reported findings

BACKGROUND

Idiopathic inflammatory demyelinating lesions (IIDL) of the brain usually present with a morphologic pattern characteristic of multiple sclerosis (MS). Atypical appearances of IIDLs also exist, however, and can pose significant diagnostic problems and uncertainty regarding prognosis and adequate therapy. We attempted to improve upon this situation by reviewing the literature.

METHODS

We performed a PubMed search from January 1984 through December 2004 for articles in English reporting on IIDLs which had been considered as morphologically atypical (66 articles; 270 cases reported). From these publications 69 individual patient reports allowed the extraction of adequate information on magnetic resonance imaging (MRI) and associated disease characteristics.

RESULTS

Reported atypical IIDLs most frequently manifested as large ring-like lesions (n = 27) which are now considered quite suggestive of an antibodymediated form of MS. Truly atypical IIDLs were less common and exhibited appearances which we termed megacystic (n = 8), Balolike (n = 11) and diffusely infiltrating (n = 11). Despite limitations imposed by the absence of original data the inter-rater agreement in defining these subtypes of atypical IIDLs was moderate to substantial (kappa 0.48-0.68) and we noted trends for their association with certain demographic, clinical and paraclinical variables.

INTERPRETATION

We suggest that IIDLs reported as atypical in the literature can be segregated into several distinct subtypes based on their MRI appearance. The recognition of these patterns may be useful for the differential diagnosis and for a future classification. Because of the limitations inherent in our review this will have to be confirmed by a prospective registry.

Lesion genesis in a subset of patients with multiple sclerosis: a role for innate immunity?

Lesions obtained early in the course of multiple sclerosis (MS) have been studied immunocytochemically, and compared with the early stages of the experimental lesion induced in rats by the intraspinal injection of lipopolysaccharide. Large hemispheric or double hemispheric sections were examined from patients who had died in the course of acute or early relapsing multiple sclerosis. In MS patients exhibiting hypoxia-like lesions [Pattern III; Lucchinetti et al. Ann Neurol (2000) 47: 707-17], focal areas in the white matter showed mild oedema, microglial activation and mild axonal injury in the absence of overt demyelination. In such lesions T-cell infiltration was mild and restricted to the perivascular space. Myeloperoxidase and the inducible form of nitric oxide synthase were expressed primarily by microglia, and the activated form of these cells was associated with extracellular deposition of precipitated fibrin. In addition, these lesions showed up-regulation of proteins involved in tissue preconditioning. When active demyelination started, lesions were associated with massive T-cell infiltration and microglia and macrophages expressed all activation markers studied. Similar tissue alterations were found in rats in the pre-demyelinating stage of lesions induced by the focal injection of bacterial lipopolysaccharide into the spinal white matter. We suggest that the areas of microglial activation represent an early stage of tissue injury, which precedes the formation of hypoxia-like demyelinated plaques. The findings indicate that mechanisms associated with innate immunity may play a role in the formation of hypoxia-like demyelinating lesions in MS.

Sodium channels and multiple sclerosis: roles in symptom production, damage and therapy

Our understanding of the potential role of sodium channels in multiple sclerosis (MS) has grown substantially in recent years. The channels have long had a recognized role in the symptomatology of the disease, but now also have suspected roles in causing permanent axonal destruction, and a potential role in modulating the intensity of immune activity. Sodium channels might also provide an avenue to achieve axonal and neuronal protection in MS, thereby impeding the otherwise relentless advance of permanent neurological deficit. The symptoms of MS are largely determined by the conduction properties of axons and these, in turn, are largely determined by sodium channels. The number, subtype and distribution of the sodium channels are all important, together with the way that channel function is modified by local factors, such as those resulting from inflammation (eg, nitric oxide). Suspicion is growing that sodium channels may also contribute to the axonal degeneration primarily responsible for permanent neurological deficits. The proposed mechanism involves intra-axonal sodium accumulation which promotes reverse action of the sodium/calcium exchanger and thereby a lethal rise in intra-axonal calcium. Partial blockade of sodium channels protects axons from degeneration in experimental models of MS, and therapy based on this approach is currently under investigation in clinical trials. Some recent findings suggest that such systemic inhibition of sodium channels may also promote axonal protection by suppressing inflammation within the brain.

The immunopathology of multiple sclerosis: an overview

Multiple sclerosis (MS) is traditionally seen as an inflammatory demyelinating disease, characterized by the formation of focal demyelinated plaques in the white matter of the central nervous system. In this review we describe recent evidence that the spectrum of MS pathology is much broader. This includes demyelination in the cortex and deep gray matter nuclei, as well as diffuse injury of the normal-appearing white matter. The mechanisms responsible for the formation of focal lesions in different patients and in different stages of the disease as well as those involved in the induction of diffuse brain damage are complex and heterogeneous. This heterogeneity is reflected by different clinical manifestations of the disease, such as relapsing or progressive MS, and also explains at least in part the relation of MS to other inflammatory demyelinating diseases.

Multiple sclerosis: is there neurodegeneration independent from inflammation?

Clinical and magnetic resonance imaging studies in multiple sclerosis have recently suggested that neurodegenerative events may take place in multiple sclerosis brains, which occur independently from inflammation. Here we summarize the results from recent pathological studies, which show, that inflammation is invariably present at all stages and in all forms of the disease. However, the patterns of inflammation differ between different disease stages. This may in part explain, why anti-inflammatory or immunosuppressive treatments fail in progressive multiple sclerosis.

Idiopathic inflammatory-demyelinating diseases of the central nervous system

Idiopathic inflammatory-demyelinating diseases (IIDDs) include a broad spectrum of central nervous system disorders that can usually be differentiated on the basis of clinical, imaging, laboratory and pathological findings. However, there can be a considerable overlap between at least some of these disorders, leading to misdiagnoses or diagnostic uncertainty. The relapsing-remitting and secondary progressive forms of multiple sclerosis (MS) are the most common IIDDs. Other MS phenotypes include those with a progressive course from onset (primary progressive and progressive relapsing) or with a benign course continuing for years after onset (benign MS). Uncommon forms of IIDDs can be classified clinically into: (1) fulminant or acute IIDDs, such as the Marburg variant of MS, Baló's concentric sclerosis, Schilder's disease, and acute disseminated encephalomyelitis; (2) monosymptomatic IIDDs, such as those involving the spinal cord (transverse myelitis), optic nerve (optic neuritis) or brainstem and cerebellum; and (3) IIDDs with a restricted topographical distribution, including Devic's neuromyelitis optica, recurrent optic neuritis and relapsing transverse myelitis. Other forms of IIDD, which are classified clinically and radiologically as pseudotumoral, can have different forms of presentation and clinical courses. Although some of these uncommon IIDDs are variants of MS, others probably correspond to different entities. MR imaging of the brain and spine is the imaging technique of choice for diagnosing these disorders, and together with the clinical and laboratory findings can accurately classify them. Precise classification of these disorders may have relevant prognostic and treatment implications, and might be helpful in distinguishing them from tumoral or infectious lesions, avoiding unnecessary aggressive diagnostic or therapeutic procedures.

Abnormal endothelial tight junctions in active lesions and normal-appearing white matter in multiple sclerosis

Blood-brain barrier (BBB) breakdown, demonstrable in vivo by enhanced MRI is characteristic of new and expanding inflammatory lesions in relapsing-remitting and chronic progressive multiple sclerosis (MS). Subtle leakage may also occur in primary progressive MS. However, the anatomical route(s) of BBB leakage have not been demonstrated. We investigated the possible involvement of interendothelial tight junctions (TJ) by examining the expression of TJ proteins (occludin and ZO-1 ) in blood vessels in active MS lesions from 8 cases of MS and in normal-appearing white (NAWM) matter from 6 cases. Blood vessels (10-50 per frozen section) were scanned using confocal laser scanning microscopy to acquire datasets for analysis. TJ abnormalities manifested as beading, interruption, absence or diffuse cytoplasmic localization of fluorescence, or separation of junctions (putative opening) were frequent (affecting 40% of vessels) in oil-red-O-positive active plaques but less frequent in NAWM (15%), and in normal (< 2%) and neurological controls (6%). Putatively "open" junctions were seen in vessels in active lesions and in microscopically inflamed vessels in NAWM. Dual fluorescence revealed abnormal TJs in vessels with pre-mortem serum protein leakage. Abnormal or open TJs, associated with inflammation may contribute to BBB leakage in enhancing MRI lesions and may also be involved in subtle leakage in non-enhancing focal and diffuse lesions in NAWM. BBB disruption due to tight junctional pathology should be regarded as a significant form of tissue injury in MS, alongside demyelination and axonopathy.

Theiler's virus infection: a model for multiple sclerosis

Both genetic background and environmental factors, very probably viruses, appear to play a role in the etiology of multiple sclerosis (MS). Lessons from viral experimental models suggest that many different viruses may trigger inflammatory demyelinating diseases resembling MS. Theiler's virus, a picornavirus, induces in susceptible strains of mice early acute disease resembling encephalomyelitis followed by late chronic demyelinating disease, which is one of the best, if not the best, animal model for MS. During early acute disease the virus replicates in gray matter of the central nervous system but is eliminated to very low titers 2 weeks postinfection. Late chronic demyelinating disease becomes clinically apparent approximately 2 weeks later and is characterized by extensive demyelinating lesions and mononuclear cell infiltrates, progressive spinal cord atrophy, and axonal loss. Myelin damage is immunologically mediated, but it is not clear whether it is due to molecular mimicry or epitope spreading. Cytokines, nitric oxide/reactive nitrogen species, and costimulatory molecules are involved in the pathogenesis of both diseases. Close similarities between Theiler's virus-induced demyelinating disease in mice and MS in humans, include the following: major histocompatibility complex-dependent susceptibility; substantial similarities in neuropathology, including axonal damage and remyelination; and paucity of T-cell apoptosis in demyelinating disease. Both diseases are immunologically mediated. These common features emphasize the close similarities of Theiler's virus-induced demyelinating disease in mice and MS in humans.

Hypoxia-like tissue injury as a component of multiple sclerosis lesions

Recent data suggest that the mechanisms of demyelination and tissue damage in multiple sclerosis (MS) are heterogenous. In this review, evidence is discussed, which show that in a subset of multiple sclerosis patients the central nervous system (CNS) lesions show profound similarities to tissue alterations found in acute white matter stroke, thus suggesting that a hypoxia-like metabolic injury is a pathogenetic component in a subset of inflammatory brain lesions. Both, vascular pathology as well as metabolic disturbances induced by toxins of activated macrophages and microglia may be responsible for such lesions in multiple sclerosis.

Preferential loss of myelin-associated glycoprotein reflects hypoxia-like white matter damage in stroke and inflammatory brain diseases

Destruction of myelin and oligodendrocytes leading to the formation of large demyelinated plaques is the hallmark of multiple sclerosis (MS) pathology. In a subset of MS patients termed pattern III, actively demyelinating lesions show preferential loss of myelin-associated glycoprotein (MAG) and apoptotic-like oligodendrocyte destruction, whereas other myelin proteins remain well preserved. MAG is located in the most distal periaxonal oligodendrocyte processes and primary "dying back" oligodendrogliopathy may be the initial step of myelin degeneration in pattern III lesions. In the present study, various human white matter pathologies, including acute and chronic white matter stroke, virus encephalitis, metabolic encephalopathy, and MS were studied. In addition to a subset of MS cases, a similar pattern of demyelination was found in some cases of virus encephalitis as well as in all lesions of acute white matter stroke. Brain white matter lesions presenting with MAG loss and apoptotic-like oligodendrocyte destruction, irrespective of their primary disease cause, revealed a prominent nuclear expression of hypoxia inducible factor-1alpha in various cell types, including oligodendrocytes. Our data suggest that a hypoxia-like tissue injury may play a pathogenetic role in a subset of inflammatory demyelinating brain lesions.

T-cells in the cerebrospinal fluid express a similar repertoire of inflammatory chemokine receptors in the absence or presence of CNS inflammation: implications for CNS trafficking

It is believed that chemokines and their receptors are involved in trafficking of T-cells to the central nervous system (CNS). The aim of the current study was to define the expression on cerebrospinal fluid (CSF) T-cells of six chemokine receptors associated with trafficking to sites of inflammation. Flow cytometry was used to detect chemokine receptor expression. We observed that CD3+T-cells in the CSF express a restricted array of inflammatory chemokine receptors, specifically CXCR3, CCR5 and CCR6, but little CCR1-3. This repertoire was independent of the presence of CNS inflammation, since comparable findings were obtained in patients with multiple sclerosis (MS) and individuals with non-inflammatory neurological diseases. The enrichment of CCR5+T-cells in the CSF could largely be explained by higher frequency of CD4+/CD45RO+T-cells in this compartment. In contrast, CD4+/CD45RO+T-cells expressing CXCR3 were significantly enriched in CSF as compared with blood. Similar levels of CCR6+/CD3+T-cells were observed in blood and CSF, while levels of CCR2+/CD3+T-cells were lower in CSF than in blood. The CSF was virtually devoid of CCR5+/CXCR3- T-cells, suggesting that the expression of CCR5 alone is not sufficient for the trafficking of CD3+T-cells to the CSF. We hypothesize that CXCR3 is the principal inflammatory chemokine receptor involved in intrathecal accumulation of T-cells in MS. Through interactions with its ligands, CXCR3 is proposed to mediate retention of T-cells in the inflamed CNS.

The role of nitric oxide in multiple sclerosis

Nitric oxide (NO) is a free radical found at higher than normal concentrations within inflammatory multiple sclerosis (MS) lesions. These high concentrations are due to the appearance of the inducible form of nitric oxide synthase (iNOS) in cells such as macrophages and astrocytes. Indeed, the concentrations of markers of NO production (eg, nitrate and nitrite) are raised in the CSF, blood, and urine of patients with MS. Circumstantial evidence suggests that NO has a role in several features of the disease, including disruption of the blood-brain barrier, oligodendrocyte injury and demyelination, axonal degeneration, and that it contributes to the loss of function by impairment of axonal conduction. However, despite these considerations, the net effect of NO production in MS is not necessarily deleterious because it also has several beneficial immunomodulatory effects. These dual effects may help to explain why iNOS inhibition has not provided reliable and encouraging results in animal models of MS, but alternative approaches based on the inhibition of superoxide production, partial sodium-channel blockade, or the replacement of lost immunomodulatory function, may prove beneficial.

CCR1+/CCR5+ mononuclear phagocytes accumulate in the central nervous system of patients with multiple sclerosis

Mononuclear phagocytes (monocytes, macrophages, and microglia) are considered central to multiple sclerosis (MS) pathogenesis. Molecular cues that mediate mononuclear phagocyte accumulation and activation in the central nervous system (CNS) of MS patients may include chemokines RANTES/CCL5 and macrophage inflammatory protein-1alpha/CCL3. We analyzed expression of CCR1 and CCR5, the monocyte receptors for these chemokines, on circulating and cerebrospinal fluid CD14+ cells, and in MS brain lesions. Approximately 70% of cerebrospinal fluid monocytes were CCR1+/CCR5+, regardless of the presence of CNS pathology, compared to less than 20% of circulating monocytes. In active MS lesions CCR1+/CCR5+ monocytes were found in perivascular cell cuffs and at the demyelinating edges of evolving lesions. Mononuclear phagocytes in early demyelinating stages comprised CCR1+/CCR5+ hematogenous monocytes and CCR1-/CCR5- resident microglial cells. In later stages, phagocytic macrophages were uniformly CCR1-/CCR5+. Cultured in vitro, adherent monocytes/macrophages up-regulated CCR5 and down-regulated CCR1 expression, compared to freshly-isolated monocytes. Taken together, these findings suggest that monocytes competent to enter the CNS compartment derive from a minority CCR1+/CCR5+ population in the circulating pool. In the presence of ligand, these cells will be retained in the CNS. During further activation in lesions, infiltrating monocytes down-regulate CCR1 but not CCR5, whereas microglia up-regulate CCR5.

IVIG-pools: regulatory gifts--transiting from harmony toward harmonious immunoglobulins: why? and why not?

Based on 'initial conditions' which depend on each donors' exposure to a unique environment, a pooled intravenous immunoglobulin (IVIG) product transfers its immunoglobulin molecule repertoire, unchanged, to the altered host. The relay function of the cell-bound receptors, especially that of the inhibitory Fc(gamma)RIIB, may then allow sufficient amplification to make regulatory activity possible. To the clinician, IVIG may be considered a tool to promote reversal of the dysregulation causing autoimmune disease. Generically, IVIG may be seen as a promoter allowing a progression from harm by an inflammatory/fibrotic reaction, then down-regulating toward restitutio ad integrum. By modifying natural processes, IVIG may play minor roles in promoting defense against spontaneous bleeding and, perhaps, stimulating remyelination. The wide spectrum of IVIG specificities, by reflecting evolutionary epitope selection, may not further destabilize cell/molecule disarray in the affected host. Benefit to the patient by IVIG treatment cannot be predicted nor can potentially severe or even fatal accidents entirely be excluded. Important aspects of IVIG treatment still await clarification including dosage, timing and the isotype form. In the foreseeable future it does not seem that biotechnological advances will match the physiologic harmony of IVIG, leaving antibody characteristics aside.

Tumour necrosis factor alpha mRNA expression in early multiple sclerosis lesions: correlation with demyelinating activity and oligodendrocyte pathology

The precise role of tumour necrosis factor alpha (TNFalpha) in multiple sclerosis (MS) is still controversial. Most findings from the animal model experimental allergic encephalomyelitis have yet to be confirmed in multiple sclerosis. The aim of this study was to define the significance of TNFalpha with respect to the hallmark of MS, that is demyelination. Therefore, 78 lesion areas from diagnostic brain biopsies of 32 patients were analysed. Lesion demyelinating activity was classified by the presence of myelin degradation products in macrophages and macrophage activation markers. Non-radioactive in situ hybridisation was carried out to detect TNFalpha mRNA expressing cells. DNA fragmentation was visualised by TdT-mediated X-dUTP nick end labeling. A significantly higher number of cells expressed TNFalpha mRNA in active demyelinating lesions than in inactive or remyelinating lesions irrespective of the extent of the inflammatory infiltrate. TNFalpha mRNA expression correlated with the appearance of DNA fragmentation in T lymphocytes and oligodendrocytes within the lesions. In the periplaque white matter, expression of TNFalpha mRNA negatively correlated with oligodendrocyte numbers. These data support previous findings from animal models and in vitro experiments. Although not proving, the current study strongly suggests a pathogenic role of TNFalpha in demyelination in human multiple sclerosis and gives further support for TNFalpha-directed therapeutic strategies.