The role of integrins in immune-mediated diseases of the nervous system

Simvastatin treatment does not protect retinal ganglion cells from degeneration in a rat model of autoimmune optic neuritis

In patients with multiple sclerosis (MS), non-remitting deficits are mainly caused by axonal and neuronal damage. We demonstrated previously that myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis in rats provokes severe axonal and neuronal injury even before clinical manifestation of the disease. In our present study, we investigated effects of simvastatin treatment on degeneration of retinal ganglion cell (RGC) bodies as well as their axons during MOG-induced optic neuritis. Electrophysiological functions of optic nerves and RGCs were analyzed in vivo. Although neuroprotective effects of simvastatin have been demonstrated before in other experimental settings, we did not observe an increase in RGC survival nor an improvement of visual functions. As we could not reproduce the anti-inflammatory effects that were observed under statin therapy in other EAE models, we hypothesize that patients suffering from optic neuritis might not take advantage of simvastatin applications.

An open-label safety and drug interaction study of natalizumab (Antegren) in combination with interferon-beta (Avonex) in patients with multiple sclerosis

In this open-label drug-interaction trial, we studied 38 patients with relapsing-remitting multiple sclerosis (MS) who received 3.0 or 6.0 mg/kg of natalizumab as a single intravenous (i.v.) infusion during stable treatment with intramuscular (i.m.) interferon beta-1a 30 microg (IFNbeta-1a; Avonex). To assess the pharmacokinetic (PK) interaction of natalizumab and IFNbeta-1a, serum concentration-time data for both agents were collected and analysed. Biologic response markers of IFNbeta-1a activity, beta2-microglobulin and neopterin, were also assessed to determine effects of natalizumab on IFNbeta-1a pharmacodynamics (PD). Further, safety and immunogenicity were evaluated. The combination of drug therapies was well tolerated. Although natalizumab serum concentrations (and corresponding PK exposure measures) appeared to be somewhat elevated in the presence of IFNbeta-1a, when compared to the same dose (6.0 mg/kg) administered alone in a concurrent comparator study, the differences were generally small and unlikely to be clinically relevant. In general, natalizumab had no apparent clinically relevant effects on the PK or PD properties of IFNbeta-1a. The presence of antibodies to IFNbeta-1a and natalizumab was relatively low. Overall, the study provided safety, immunogenicity, PK and PD data to support a combination strategy for the use of natalizumab and IFNbeta-1a in the treatment of patients with relapsing-remitting MS. A large clinical study is currently in progress to evaluate the efficacy and long-term safety of this combination drug therapy.

Combination therapy for multiple sclerosis: the treatment strategy of the future?

Multiple sclerosis (MS) is an inflammatory autoimmune disease characterised by demyelination and axonal loss in the CNS. Although new immunomodulatory therapies including interferon-beta and glatiramer acetate became available during the last decade, these therapies are only partially effective. There is a continuing need to develop more effective treatment strategies to combat the chronic and progressive aspects of the disease. In view of the complex pathophysiology underlying the MS disease process, combination therapy offers a rational therapeutic approach. Combining immunomodulatory agents with different mechanisms of action that promote synergistic or additive effects represents an important objective in MS therapeutic research. Ultimately, the optimal therapies will likely include strategies that promote repair and limit tissue destruction in combination with anti-inflammatory interventions.

Decreased integrin gene expression in patients with MS responding to interferon-beta treatment

Interferon-beta (IFN-beta) ameliorates disease course in a subset of patients with MS. The reasons for heterogeneity of clinical responses, however, are unclear. We assessed possible effects of IFN-beta on the gene expression of the leukocyte adhesion molecules VLA-4 and LFA-1 during the first year of treatment of 50 patients with relapsing-remitting MS who showed differential clinical responses. We observed a significant reduction of VLA-4 (P=0.002) and LFA-1 (P=0.03) mRNA expression compared to baseline in first-year clinical responders (n=22). In contrast, first-year IFN-beta non-responders (n=28) had unchanged levels of VLA-4 and LFA-1. In vitro treatment of PBMC with IFN-beta indicated a direct effect on transcription of the integrins' genes. Transcriptional downmodulation of adhesion molecules during IFN-beta treatment may contribute to its mode of action in MS.

Advances in understanding and treatment of immune-mediated disorders of the peripheral nervous system

During recent years, novel insights in basic immunology and advances in biotechnology have contributed to an increased understanding of the pathogenetic mechanisms of immune-mediated disorders of the peripheral nervous system. This increased knowledge has an impact on the management of patients with this class of disorders. Current advances are outlined and their implication for therapeutic approaches addressed. As a prototypic immune-mediated neuropathy, special emphasis is placed on the pathogenesis and treatment of the Guillain-Barré syndrome and its variants. Moreover, neuropathies of the chronic inflammatory demyelinating, multifocal motor, and nonsystemic vasculitic types are discussed. This review summarizes recent progress with currently available therapies and--on the basis of present immunopathogenetic concepts--outlines future treatment strategies.

Ultrastructural evidence of brain mast cell activation without degranulation in monkey experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is an animal model for the human demyelinating disease multiple sclerosis (MS). Increased permeability of the blood-brain barrier (BBB) precedes the development of clinical or pathologic findings in MS and may be induced by perivascular brain mast cells secreting vasoactive and proinflammatory molecules. Brain mast cells were investigated ultrastructurally in acute EAE of the non-human primate common marmoset Callithrix jacchus, which develops a mild neurologic relapsing-remitting course. Control diencephalic samples contained perivascular mast cells with mostly intact electron dense granules. In contrast, EAE samples had marked demyelination and mast cells with numerous altered secretory granules; their electron dense content varied in amount and texture with a "honeycomb" or "target" appearance, but without degranulation. These changes were evident even before the development of any clinical symptoms and suggest that brain mast cells may be involved in EAE, and possibly MS, through a unique process that may involve selective secretion of molecules able to disrupt the BBB.

Estrogen receptor-alpha mediates the brain antiinflammatory activity of estradiol

Beyond the key role in reproductive and cognitive functions, estrogens have been shown to protect against neurodegeneration associated with acute and chronic injuries of the adult brain. Current hypotheses reconcile this activity with a direct effect of 17beta-estradiol (E2) on neurons. Here we demonstrate that brain macrophages are also involved in E2 action on the brain. Systemic administration of hormone prevents, in a time- and dose-dependent manner, the activation of microglia and the recruitment of peripheral monocytes induced by intraventricular injection of lipopolysaccharide. This effect occurs by limiting the expression of neuroinflammatory mediators, such as the matrix metalloproteinase 9 and lysosomal enzymes and complement C3 receptor, as well as by preventing morphological changes occurring in microglia during the inflammatory response. By injecting lipopolysaccharide in estrogen receptor (ER)-null mouse brains, we demonstrate that hormone action is mediated by activation of ERalpha but not of ERbeta. The specific role of ERalpha is further confirmed by comparing the effects of ERs on the matrix metalloproteinase 9 promoter activity in transient transfection assays. Finally, we report that genetic ablation of ERalpha is associated with a spontaneous reactive phenotype of microglia in specific brain regions of adult ERalpha-null mice. Altogether, these results reveal a previously undescribed function for E2 in brain and provide a mechanism for its beneficial activity on neuroinflammatory pathologies. They also underline the key role of ERalpha in brain macrophage reactivity and hint toward the usefulness of ERalpha-specific drugs in hormone replacement therapy of inflammatory diseases.

CD49d overexpression and T cell autoimmunity

D10.G4.1 (D10) cells, a murine conalbumin-reactive Th2 cell line, made to overexpress the beta(2) integrin LFA-1 by pharmacological manipulation or by transfection become autoreactive and are capable of inducing in vivo autoimmunity. However, whether this is specific to LFA-1 and whether overexpression of other T cell integrin molecules has the same effect are unknown. We examined the functional consequences of T cell CD49d (alpha(4) integrin) overexpression by transfecting murine CD49d cDNA into D10 cells. Similar to the LFA-1-transfected cells, the CD49d-overexpressing T cells are autoreactive and proliferate in response to APCs in an MHC class II-dependent manner in the absence of nominal Ag. Additionally, CD49d overexpression is associated with increased in vitro adhesion to endothelial cells and increased in vivo splenic homing. However, in contrast to LFA-1 overexpression, increased T cell CD49d expression is not associated with autoreactive cytotoxicity or the ability to induce in vivo autoimmunity. In addition to the novel observation that CD49d overexpression is sufficient to induce T cell autoreactivity, our results also support the hypothesis that the ability to induce in vivo autoimmunity is related to T cell cytotoxicity and not to T cell proliferation function in the D10 murine adoptive transfer model of autoimmunity.

VLA-4 antagonists: potent inhibitors of lymphocyte migration

Circulating lymphocytes normally migrate through extravascular spaces in relatively low numbers as important members of the immunosurveillance process. That is until signals are received by endothelial cells that there is an underlying infection or inflammatory condition. These vascular surface cells in turn overexpress and present ligands to circulating lymphocyte adhesion molecules. Upon encountering this higher density of ligands, lymphocytes, which had been leisurely rolling along the vascular surface, now become more firmly attached, change shape, and migrate through tight junctions to the sites of infection or inflammation. If the initiating events are not resolved and the condition becomes chronic, there can be a sustained extravasation of lymphocytes that can exacerbate the inflammatory condition, which in turn will continue to recruit more inflammatory cells resulting in unwanted tissue destruction. It is for the attenuation of this cycle of sustained inflammatory cell recruitment that very late activating antigen-4 (VLA-4) antagonists are being developed. Most lymphocytes, except neutrophils, express VLA-4 on their surface and they interact with endothelial vascular cell adhesion molecule-1 (VCAM-1). It is this interaction that VLA-4 antagonists are intended to disrupt, thus, putting an end to the cycle of chronic inflammation, which is the hallmark of many diseases. This review will provide an update of VLA-4 antagonists that have appeared since early 2001 and will discuss some of the issues, both positive and negative, that may be encountered in their development.

Disease-modifying therapies in multiple sclerosis: an update on recent and ongoing trials and future strategies

Multiple sclerosis (MS) is the prototype inflammatory autoimmune disorder of the central nervous system and the most common cause of neurological disability in young adults exhibiting considerable clinical, radiological and pathological heterogeneity. Novel insights in the immunopathological processes, advances in biotechnology, development of powerful magnetic resonance imaging technologies together with improvements in clinical trial design led to a variety of evaluable therapeutic approaches. Therapy has changed dramatically over the past decade, yielding significant progress for the treatment of relapsing-remitting and secondary progressive MS. A substantial number of pivotal and preliminary reports continue to demonstrate encouraging new evidence that advances are being made in the care of MS patients. This review summarises recent progress with currently available disease-modifying therapies and - on the basis of present immunopathogenetic concepts - outlines ongoing studies as well as future treatment strategies.

Regulation of an inactivating potassium current (IA) by the extracellular matrix protein vitronectin in embryonic mouse hippocampal neurones

Integrins are a class of intrinsic membrane receptors for extracellular matrix ligands. In the central nervous system, integrins and their ligands influence neuronal growth and synaptic function, but relatively little is known about their potential to regulate intrinsic excitability. To explore this area, we examined the effects of matrix components on potassium currents in developing mouse hippocampal neurones, using electrophysiological and immunochemical approaches. We tested the effects of three integrin ligands present in the hippocampus, fibronectin, laminin and vitronectin, on electrogenesis in late embryonic hippocampal pyramidal neurones. Explants cultured in serum-free medium were exposed to ligands (fibronectin at 3 microg ml-1, laminin at 5 microg ml-1, vitronectin at 10 microg ml-1) for 3-4 days, and voltage-gated potassium currents were recorded from presumptive CA3 pyramidal neurones. Of the three matrix components, only vitronectin affected potassium currents, selectively increasing the amplitude of the inactivating potassium current (IA, or A-current) by about 75 % over control levels, and its density (current per unit area) by about 40 % (measured after 3 day exposures from embryonic day 15.5). Other potassium currents were spared, except to the extent that membrane area was increased. The actions of vitronectin were sensitive to RGD (Arg-Gly-Asp)-sequence-containing peptide, indicating the involvement of integrins as vitronectin receptors. The kinetic properties of IA, including the voltage-dependence of activation and inactivation, inactivation rate and the rate of recovery from inactivation, were minimally affected by vitronectin and were consistent with enhanced functional expression of Kv4-family subunits. Analyses of Kv4.2 and Kv1.4 immunoreactivity also suggested a preferential increase in Kv4.2 levels, with lesser effects on Kv1.4 levels. These results indicate that vitronectin can selectively regulate IA, and together with other observations suggest that modulation of neuronal excitability by integrins and their ligands occurs commonly.

Regional and temporal expression patterns of interleukin-10, interleukin-10 receptor and adhesion molecules in the rat spinal cord during chronic relapsing EAE

Adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) mediate leukocyte infiltration into the CNS, in experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis (MS). Because exogenous interleukin-10 (IL-10) inhibits ICAM-1 and VCAM-1 expression and clinical EAE, we hypothesize that endogenous IL-10 signaling may suppress expression of adhesion molecules. In a rat model of chronic relapsing EAE, expression levels of IL-10 and its receptor (IL-10R1), ICAM-1 and VCAM-1 mRNA in the spinal cord are markedly increased, whereas levels of IL-10 mRNA remain relatively low. The temporal pattern of mRNA and protein expression showed marked differences between spinal cord levels. During relapse, IL-10, IL-10R1, ICAM-1, VCAM-1 mRNA levels and neurological scores show positive correlations. We conclude that endogenous IL-10 is not a crucial factor inhibiting adhesion molecule expression in this model.

Immunomodulation in multiple sclerosis: from immunosuppression to neuroprotection

Multiple sclerosis (MS) is the most common disabling neurological disease of young adulthood. Following advances in the understanding of the immunological mechanisms that underlie the pathogenesis of MS, a growing arsenal of immunomodulatory agents is available. Two classes of immunomodulators are approved for long-term treatment of MS, the efficacy of several promising new concepts is being tested in clinical trials and classical immunosuppressive agents used in MS treatment have been shown to exert specific, immunomodulatory effects. Furthermore, two recent observations have changed our basic understanding of the pathogenesis of MS. First, immune cells in MS lesions have neuroprotective activity, which indicates a beneficial role of neuroinflammation. Second, there is evidence that axonal loss, rather than demyelination, underlies the progression of MS and, hence, constitutes a therapeutic target.

Integrins are involved in synaptogenesis, cell spreading, and adhesion in the postnatal brain

Integrins are a major family of heterodimeric surface glycoproteins that act as adhesion molecules, have a spectrum of extracellular matrix (ECM) molecules as their ligands, and regulate a variety of cellular functions. Integrins are known to be critical to embryonic brain development, and recent studies have indicated their essential role in adult brain function, although their role in postnatal brain development and function has not been examined. Here, we used the organotypic slice culture system to investigate the role of integrins in postnatal hippocampal development by exposing the tissue to either an integrin competitive antagonist, the peptide GRGDSP containing Arg-Gly-Asp (RGD) attachment site, or to function-blocking beta(1)-integrin antibodies to disrupt integrin interactions. These experiments revealed that beta(1)-integrin antibodies interfered with spreading of the culture, resulting in a rapid and marked diminution of slice area. beta(1)-integrin antibodies and RGD peptide disrupted cell adhesion, causing cell detachment and migration of glial cells from the explant. The majority of the detached cells were of macroglial origin and switched to expression of the intermediate filament proteins vimentin and nestin, suggesting a developmental regression. The organotypic organization of slice cultures was not affected, although exposure to either integrin antagonist or antibody resulted in a statistically significant reduction in the number of synapses measured in the apical dendrites of CA1 pyramidal neurons. The results demonstrate that integrins markedly affect postnatal CNS development, in both ultrastructural construction and organizational processes.

Vascular endothelial growth factor is expressed in multiple sclerosis plaques and can induce inflammatory lesions in experimental allergic encephalomyelitis rats

The active lesions in multiple sclerosis (MS) are characterized by blood-brain-barrier (BBB) breakdown, upregulation of adhesion molecules on capillary endothelial cells, and perivascular inflammation, suggesting that altered vessel permeability and activated endothelial cells are involved in the pathogenesis of the disease. Vascular endothelial growth factor (VEGF) mediates multiple aspects of blood vessel physiology, including regulation of growth, permeability, and inflammation. To investigate a possible relationship between VEGF expression and CNS autoimmune disease, we examined VEGF expression in MS plaques compared to normal white matter by immunohistochemistry and in situ hybridization. VEGF expression was consistently upregulated in both acute and chronic MS plaques. We also examined VEGF expression during the course of experimental allergic encephalomyelitis (EAE) in rats. VEGF-positive cells with astrocytic morphology increased in the spinal cord during the development of EAE and were found in association with inflammatory cells. Furthermore, intracerebral infusion of VEGF in animals previously immunized with myelin basic protein induced an inflammatory response in the brain, whereas infusion of vehicle, or infusion of VEGF in naive animals, did not. These results suggest that overexpression of VEGF may exacerbate the inflammatory response in autoimmune diseases of the CNS by inducing focal BBB breakdown and migration of inflammatory cells into the lesions.

Association of factor H of the alternative pathway of complement with agrin and complement receptor 3 in the Alzheimer's disease brain

Factor H, a regulatory protein of the alternative pathway of complement (APC), is present in amyloid-beta (Abeta) plaques in Alzheimer's disease (AD). Abeta plaques also contain significant amounts of heparan sulfate proteoglycans (HSPGs), such as agrin, as well as numerous activated microglia expressing increased levels complement receptor 3 (CR3). Here, we show the colocalization of each of these molecules in the AD brain and the functional capacity for these molecules to bind to one another in vitro. We propose that CR3 receptors expressed by microglia are used for ligand binding to factor H bound to HSPGs and Abeta in plaques in the AD brain.

The integrin family of cell adhesion molecules has multiple functions within the CNS

Integrins comprise a large family of cell adhesion molecules that mediate interactions between the extracellular environment and the cytoplasm. During the last decade, analysis of the expression and function of these molecules has revealed that integrins regulate many aspects of cell behavior including cell death, proliferation, migration, and differentiation. Within the central nervous system (CNS), most of the early studies focused on the role of integrins in mediating adhesive and migratory events in two distinct processes: neural development and CNS inflammation. Interestingly, recent analysis of transgenic mice has provided some surprising results regarding the role of integrins in neural development. Furthermore, a large body of evidence now supports the idea that in addition to these well-described functions, integrins play multiple roles in the CNS, both during development and in the adult in areas as diverse as synaptogenesis, activation of microglia, and stabilization of the endothelium and blood-brain barrier. Many excellent reviews have addressed the contribution of integrins in mediating leukocyte extravasation during CNS inflammation. This review will focus on recently emerging evidence of novel and diverse roles of integrins and their ligands in the CNS during development and in the adult, in health and disease.

Immune mechanisms in acquired demyelinating neuropathies: lessons from animal models

The peripheral nervous system (PNS) is the target for a heterogenous immune attack mediated by T-cells, B-cells, and macrophages. The interaction of the humoral and cellular immune system with the structural components in the peripheral nervous system may determine the extent of inflammation and possibly repair mechanisms. The animal model experimental autoimmune neuritis (EAN) allows detailed study of the various effector pathways and tests novel therapeutic strategies in vivo. Unexpectedly, involvement of the immune system is also found in animal models for inherited neuropathies and in its human counterpart Charcot-Marie-Tooth (CMT) disease, suggesting an autoimmune reaction triggered by the genetically determined demyelinating disorder. A better understanding of immune regulation and its failure in the peripheral nervous system may help to develop more specific and more effective immunotherapies.

Chemokines and chemokine receptors in inflammatory demyelinating neuropathies: a central role for IP-10

Inflammatory cell recruitment is an important step in the pathogenesis of autoimmune demyelinating diseases of the PNS. Chemokines might play a critical role in promoting leucocyte entry into the nervous system during immune-mediated inflammation. Here, we report the expression pattern of the chemokine receptors CCR-1, CCR-2, CCR-4, CCR-5 and CXCR-3 in sural nerve biopsies obtained from patients with classical Guillain-Barré syndrome (acute inflammatory demyelinating polyradiculoneuropathy), chronic inflammatory demyelinating polyradiculoneuropathy and various non-inflammatory neuropathies. A consistent chemokine receptor expression pattern was immunohistochemically detected in inflammatory demyelinating neuropathies and quantitation of labelled mononuclear cells revealed significantly elevated cell counts compared with controls. CCR-1 and CCR-5 were primarily expressed by endoneurial macrophages, whereas CCR-2, CCR-4 and CXCR-3 could be localized to invading T lymphocytes. Quantitative analysis revealed that CXCR-3 was expressed at highest numbers by infiltrating T cells compared with the other receptors. Thus, expression and distribution of CXCR-3 suggest a specific role of this receptor in chemokine-mediated lymphocyte traffic into the inflamed PNS tissue. Therefore, we further analysed the expression of its ligands interferon-gamma-inducible protein of 10 kDa (IP-10) and monokine induced by interferon-gamma (Mig). Significantly increased levels of IP-10 could be measured in the CSF of patients with inflammatory neuropathies, whereas no differences were observable for Mig. In situ hybridization for IP-10 mRNA mirrored the distribution of the cognate receptor within the inflamed PNS, and delineated endothelial cells as the primary cellular source of IP-10. Our results imply a pathogenic role for specific chemokine receptors and IP-10 in the genesis of inflammatory demyelinating neuropathies.

Nervous system pathology: the fibrin perspective

Studies of extracellular matrix (ECM) biology in the nervous system have mainly focused on laminin, fibronectin and tenascin-R, proteins that are present during nervous system development and normal function. However, during disease, fibrin, which physiologically is not present in the nervous tissue, is detected at nervous tissue lesions. This review summarizes evidence that correlates fibrin deposition with neuropathology and presents recent findings on cellular mechanisms and intracellular signaling pathways regulated by fibrin that might contribute to nervous system disease.

Factors modifying the migration of lymphocytes across the blood-brain barrier

Characterising the factors that control the entry of leucocytes into tissue in response to inflammatory or microbial insult continues to generate considerable interest. Of all the tissues studied it is probably that of the CNS which is the most fascinating because of the specialised properties of its blood vessel walls, which constitute the blood-brain barrier (BBB). In health, very few leucocytes penetrate the BBB but in disorders such as MS the barrier becomes compromised with the result that there is an intense infiltration of the CNS by T lymphocytes whose subsequent activity appears to underlie the onset and progression of disease. The purpose of this article is to summarise and assess recent literature pertaining to how lymphocytes bind to cerebral endothelial cells, migrate across the blood vessel walls and enter the CNS parenchyma. Particular emphasis is devoted to the cellular and molecular aspects of these events and addressing the questions of whether certain subsets of circulating T lymphocytes are more favourably disposed than others to CNS infiltration and whether entry is dependent upon the initial expression of distinct groups of adhesion molecules and upon the generation of chemotactic factors. This article also focuses upon identifying the key stages of lymphocyte migration across the BBB and their susceptibility to antagonism by therapeutic agents. It is intended that the review will provide a useful source of information and offer additional insights into the mechanisms controlling lymphocyte passage across the BBB during pathological disturbance.

The role of macrophages in immune-mediated damage to the peripheral nervous system

Macrophage-mediated segmental demyelination is the pathological hallmark of autoimmune demyelinating polyneuropathies, including the demyelinating form of Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy. Macrophages serve a multitude of functions throughout the entire pathogenetic process of autoimmune neuropathy. Resident endoneurial macrophages are likely to act as local antigen-presenting cells by their capability to express major histocompatibility complex antigens and costimulatory B7-molecules, and may thus be critical in triggering the autoimmune process. Hematogenous infiltrating macrophages then find their way into the peripheral nerve together with T-cells by the concerted action of adhesion molecules, matrix metalloproteases and chemotactic signals. Within the nerve, macrophages regulate inflammation by secreting several pro-inflammatory cytokines including IL-1, IL-6, IL-12 and TNF-alpha. Autoantibodies are likely to guide macrophages towards their myelin or primarily axonal targets, which then attack in a complement-dependent and receptor-mediated manner. In addition, non-specific tissue damage occurs through the secretion of toxic mediators and cytokines. Later, macrophages contribute to the termination of inflammation by promoting T-cell apoptosis and expressing anti-inflammatory cytokines including TGF-beta1 and IL-10. During recovery, they are tightly involved in allowing Schwann cell proliferation, remyelination and axonal regeneration to proceed. Macrophages, thus, play dual roles in autoimmune neuropathy, being detrimental in attacking nervous tissue but also salutary, when aiding in the termination of the inflammatory process and the promotion of recovery.

Multiple sclerosis: current pathophysiological concepts

Multiple sclerosis (MS) is an often disabling disease primarily affecting young adults that exhibits extraordinary clinical, radiological, and pathological heterogeneity. We review the following: (a) known environmental and genetic factors that contribute to MS susceptibility; (b) current knowledge regarding fundamental pathophysiological processes in MS, including immune cell recruitment and entry into the central nervous system (CNS), formation of the plaque, and orchestration of the immune response; (c) descriptive and qualitative distinct pathological patterns in MS and their implications; (d) the evidence supporting the causative role of direct toxins, cell-mediated and humorally mediated immune mechanisms, and the concept of a "primary oligodendrogliopathy" in demyelination and axonal injury; (e) the potential benefits of inflammation; (f) the prospects for remyelination; and (g) therapeutic implications and approaches suggested by putative pathophysiological mechanisms.

Sequential expression of chemokines in experimental autoimmune neuritis

Recruitment of inflammatory cells is of critical importance in the pathogenesis of immune-mediated demyelinating diseases in the peripheral nervous system (PNS). Evidence is increasing that chemokines might play a key role in this process, since they promote leukocyte entry into the nervous system during immune-mediated inflammation. In the present study we report the expression pattern of the chemokines interferon-gamma-inducible protein (IP)-10, monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, and regulated upon activation normal T cell expressed and secreted (RANTES) in sciatic nerves from animals with myelin-induced experimental autoimmune neuritis, using a semiquantitative reverse transcriptase-PCR dot-blot hybridization assay. The mRNAs for MIP-1alpha and MIP-1beta were found to be upregulated with peak values at day 13 post-immunization (p.i.), preceding maximum disease severity. In contrast, mRNAs for MCP-1, RANTES, and IP-10 exhibited peak levels coincident with peak of the disease at day 15 p.i. Increased mRNA expression was associated with enhanced protein levels, as demonstrated by immunoblotting for each chemokine investigated. Immunohistochemistry for IP-10 protein revealed immunoreactivity associated with perineurial endothelial cells. RANTES protein was localized immunohistologically to invading T lymphocytes. Our findings suggest that chemokines, which act towards T cells and mononuclear phagocytes, are sequentially upregulated during the clinical course of EAN and thus may contribute to the pathogenesis of inflammatory demyelinating diseases of the PNS.

T lymphocytes activated by persistent viral infection differentially modify the expression of metalloproteinases and their endogenous inhibitors, TIMPs, in human astrocytes: relevance to HTLV-I-induced neurological disease

Activation of T lymphocytes by human pathogens is a key step in the development of immune-mediated neurologic diseases. Because of their ability to invade the CNS and their increased secretion of proinflammatory cytokines, activated CD4+ T cells are thought to play a crucial role in pathogenesis. In the present study, we examined the expression of inflammatory mediators the cytokine-induced metalloproteinases (MMP-2, -3, and -9) and their endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMP-1, -2, and -3), in human astrocytes in response to activated T cells. We used a model system of CD4+ T lymphocytes activated by persistent viral infection (human T lymphotropic virus, HTLV-I) in transient contact with human astrocytes. Interaction with T cells resulted in increased production of MMP-3 and active MMP-9 in astrocytes despite increased expression of endogenous inhibitors, TIMP-1 and TIMP-3. These data suggest perturbation of the MMP/TIMP balance. These changes in MMP and TIMP expression were mediated, in part, by soluble factors (presumably cytokines) secreted by activated T cells. Integrin-mediated cell adhesion is also involved in the change in MMP level, since blockade of integrin subunits (alpha1, alpha3, alpha5, and beta1) on T cells resulted in less astrocytic MMP-9-induced expression. Interestingly, in CNS tissues from neurological HTLV-I-infected patients, MMP-9 was detected in neural cells within the perivascular space, which is infiltrated by mononuclear cells. Altogether, these data emphasize the importance of the MMP-TIMP axis in the complex interaction between the CNS and invading immune cells in the context of virally mediated T cell activation.

Bi-directional signal transduction by integrin receptors

The integrin family of cell surface glycoproteins functions primarily as receptors for extracellular matrix ligands. There are now many well characterized integrin-ligand interactions which are known to influence many aspects of cell behaviour including cell morphology, cell adhesion, cell migration as well as cellular proliferation and differentiation. However, in fulfilling these functions, integrins are not simple adhesion receptors that physically mediate connections across the plasma membrane. Rather, integrin function itself is highly regulated, largely through the formation of specific associations with both structural and regulatory components within cells. It is these intracellular interactions which allow integrin function to effect many biochemical signalling pathways and therefore to impinge upon complex cellular activities. Recently, much research has focused on elucidating the molecular mechanisms which control integrin function and the molecular processes which transduce integrin-mediated signalling events. In this review, we discuss progress in the field of integrin signal transduction including, where applicable, potential therapeutic applications arising from the research.

Chemokines and chemokine receptors in the pathogenesis of multiple sclerosis

In recent years we have seen growing evidence for the role of chemokines in the pathogenesis of several infectious and non-infectious inflammatory CNS disease states, including Multiple Sclerosis (MS) and its animal model, experimental allergic encephalomyelitis (EAE). An increase in proinflammatory chemokines has been associated with demyelinating lesions and clinical neurological dysfunction in patients with MS; these chemokines could be potential targets for MS therapy. Besides a clearly defined role in mediating leukocyte migration, these and other chemokines may act as immunoregulatory molecules in the driving to Th1/Th2 responses, switch of cytokine profiles, and the induction of tolerance. Since chemokine receptors have now been identified on macrophages, microglia, astrocytes, and endothelial cells as well as neurons in the CNS, chemokine/receptor interactions may mediate functional responses in a variety of CNS cell types during the course of inflammatory disease states. Therefore, clarification of the roles of chemokines and their receptors in the pathogenesis of EAE and MS will be useful in establishing immunotherapeutic strategies for these neurological autoimmune disorders.

Holers M, Campbell IL, Barnum SR. Central Nervous System-Targeted Expression of the Complement Inhibitor sCrry Prevents Experimental Allergic Encephalomyelitis

Although generally thought of as a T cell-driven autoimmune disease, recent studies in experimental allergic encephalomyelitis (EAE), the animal model of multiple sclerosis, suggest a significant role for innate immune mechanisms. To address the possibility that the complement system plays a central role in these diseases, we developed a transgenic mouse with astrocyte-targeted production of a soluble inhibitor of complement activation, complement receptor-related protein y (sCrry). Here, we show that sCrry transgenic mice are either fully protected against EAE or develop significantly delayed clinical signs. These results indicate that complement activation may have an essential role in the pathogenesis of the disease and that complement-mediated events may occur early during the effector phase of EAE. Furthermore, this work underscores the importance of humoral immunity in amplifying a T cell-initiated pathogenic process.

Pathogenesis of Guillain-Barré syndrome

Recent neurophysiological and pathological studies have led to a reclassification of the diseases that underlie Guillain-Barré syndrome (GBS) into acute inflammatory demyelinating polyradiculoneuropathy (AIDP), acute motor and sensory axonal neuropathy (AMSAN) and acute motor axonal neuropathy (AMAN). The Fisher syndrome of ophthalmoplegia, ataxia and areflexia is the most striking of several related conditions. Significant antecedent events include Campylobacter jejuni (4-66%), cytomegalovirus (5-15%), Epstein-Barr virus (2-10%), and Mycoplasma pneumoniae (1-5%) infections. These infections are not uniquely associated with any clinical subtype but severe axonal degeneration is more common following C. jejuni and severe sensory impairment following cytomegalovirus. Strong evidence supports an important role for antibodies to gangliosides in pathogenesis. In particular antibodies to ganglioside GM1 are present in 14-50% of patients with GBS, and are more common in cases with severe axonal degeneration associated with any subtype. Antibodies to ganglioside GQ1b are very closely associated with Fisher syndrome, its formes frustes and related syndromes. Ganglioside-like epitopes exist in the bacterial wall of C. jejuni. Infection by this and other organisms triggers an antibody response in patients with GBS but not in those with uncomplicated enteritis. The development of GBS is likely to be a consequence of special properties of the infecting organism, since some strains such as Penner 0:19 and 0:41 are particularly associated with GBS but not with enteritis. It is also likely to be a consequence of the immunogenetic background of the patient since few patients develop GBS after infection even with one of these strains. Attempts to match the subtypes of GBS to the fine specificity of anti-ganglioside antibodies and to functional effects in experimental models continue but have not yet fully explained the pathogenesis. T cells are also involved in the pathogenesis of most or perhaps all forms of GBS. T cell responses to any of three myelin proteins, P2, PO and PMP22, are sufficient to induce experimental autoimmune neuritis. Activated T cells are present in the circulation in the acute stage, up-regulate matrix metalloproteinases, cross the blood-nerve barrier and encounter their cognate antigens. Identification of the specificity of these T cell responses is still at a preliminary stage. The invasion of intact myelin sheaths by activated macrophages is difficult to explain according to a purely T cell mediated mechanism. The different patterns of GBS are probably due to the diverse interplay between antibodies and T cells of differing specificities.

Effector pathways in immune mediated central nervous system demyelination

Multiple sclerosis is generally regarded to be a primarily T-cell driven disease. Recent evidence has refocused interest on antibodies. Adhesion molecules, matrix metalloproteinases, chemokines and cytokines, and nitric oxide and oxygen metabolites all participate in the amplification and effector stages of the disease.