Dual implication of 2',3'-cyclic nucleotide 3' phosphodiesterase as major autoantigen and C3 complement-binding protein in the pathogenesis of multiple sclerosis

Correlation Between Anti-Myelin Proteolipid Protein (PLP) Antibodies and Disease Severity in Multiple Sclerosis Patients With PLP Response-Permissive HLA Types

The most prominent pathological features of multiple sclerosis (MS) are demyelination and neurodegeneration. The exact pathogenesis of MS is unknown, but it is generally regarded as a T cell-mediated autoimmune disease. Increasing evidence, however, suggests that other components of the immune system, particularly B cells and antibodies, contribute to the cumulative CNS damage and worsening disability that characterize the disease course in many patients. We have previously described strongly elevated T cell reactivity to an extracellular domain of the most abundant CNS myelin protein, myelin proteolipid protein (PLP) in people with MS. The current paper addresses the question of whether this region of PLP is also a target of autoantibodies in MS. Here we show that serum levels of isotype-switched anti-PLP_181-230 specific antibodies are significantly elevated in patients with MS compared to healthy individuals and patients with other neurological diseases. These anti-PLP_181-230 antibodies can also live-label PLP-transfected cells, confirming that they can recognize native PLP expressed at the cell surface. Importantly, the antibodies are only elevated in patients who carry HLA molecules that allow strong T cell responses to PLP. In that subgroup of patients, there is a positive correlation between the levels of anti-PLP_181-230 antibodies and the severity of MS. These results demonstrate that anti-PLP antibodies have potentially important roles to play in the pathogenesis of MS.

Endogenous protein and enzyme fragments induce immunoglobulin E-independent activation of mast cells via a G protein-coupled receptor, MRGPRX2

Mast cells play a central role in inflammatory and allergic reactions by releasing inflammatory mediators through 2 main pathways, immunoglobulin E-dependent and E-independent activation. In the latter pathway, mast cells are activated by a diverse range of basic molecules (collectively known as basic secretagogues) through Mas-related G protein-coupled receptors (MRGPRs). In addition to the known basic secretagogues, here, we discovered several endogenous protein and enzyme fragments (such as chaperonin-10 fragment) that act as bioactive peptides and induce immunoglobulin E-independent mast cell activation via MRGPRX2 (previously known as MrgX2), leading to the degranulation of mast cells. We discuss the possibility that MRGPRX2 responds various as-yet-unidentified endogenous ligands that have specific characteristics, and propose that MRGPRX2 plays an important role in regulating inflammatory responses to endogenous harmful stimuli, such as protein breakdown products released from damaged or dying cells.

Demyelinating strain of mouse hepatitis virus infection bridging innate and adaptive immune response in the induction of demyelination

The presence of immunoglobulin oligoclonal bands in the cerebrospinal fluid of Multiple Sclerosis (MS) patients supports the hypothesis of an infectious etiology, although the antigenic targets remain elusive. Neurotropic mouse hepatitis virus (MHV) infection in mice provides a useful tool for studying mechanisms of demyelination in a virus-induced experimental model of MS. This study uses Affymetrix microarray analysis to compare differential spinal cord mRNA levels between mice infected with demyelinating and non-demyelinating strains of MHV to identify host immune genes expressed in this demyelinating disease model. The study reveals that during the acute stage of infection, both strains induce inflammatory innate immune response genes, whereas upregulation of several immunoglobulin genes during chronic stage infection is unique to infection with the demyelinating strain. Results suggest that the demyelinating strain induced an innate-immune response during acute infection that may promote switching of Ig isotype genes during chronic infection, potentially playing a role in antibody-mediated progressive demyelination even after viral clearance.

Identification of biomarkers in cerebrospinal fluid and serum of multiple sclerosis patients by immunoproteomics approach

Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease of the central nervous system. At present, the molecular mechanisms causing the initiation, development and progression of MS are poorly understood, and no reliable proteinaceous disease markers are available. In this study, we used an immunoproteomics approach to identify autoreactive antibodies in the cerebrospinal fluid of MS patients to use as candidate markers with potential diagnostic value. We identified an autoreactive anti-transferrin antibody that may have a potential link with the development and progression of MS. We found this antibody at high levels also in the serum of MS patients and created an immunoenzymatic assay to detect it. Because of the complexity and heterogeneity of multiple sclerosis, it is difficult to find a single marker for all of the processes involved in the origin and progression of the disease, so the development of a panel of biomarkers is desirable, and anti-transferrin antibody could be one of these.

The myelin membrane-associated enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase: on a highway to structure and function

The membrane-anchored myelin enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) was discovered in the early 1960s and has since then troubled scientists with its peculiar catalytic activity and high expression levels in the central nervous system. Despite decades of research, the actual physiological relevance of CNPase has only recently begun to unravel. In addition to a role in myelination, CNPase is also involved in local adenosine production in traumatic brain injury and possibly has a regulatory function in mitochondrial membrane permeabilization. Although research focusing on the CNPase phosphodiesterase activity has been helpful, several open questions concerning the protein function in vivo remain unanswered. This review is focused on past research on CNPase, especially in the fields of structural biology and enzymology, and outlines the current understanding regarding the biochemical and physiological significance of CNPase, providing ideas and directions for future research.

Protein array-based profiling of CSF identifies RBPJ as an autoantigen in multiple sclerosis

OBJECTIVE

To profile the reactivity of CSF-derived immunoglobulin from patients with multiple sclerosis (MS) against a large panel of antigens, to identify disease-specific reactivities.

METHODS

CSF from subjects with MS with elevated immunoglobulin G and CSF from control subjects presenting with other inflammatory neurologic disease were screened against a protein array consisting of 9,393 proteins. Reactivity to a candidate protein identified using these arrays was confirmed with ELISA and immunocytochemistry.

RESULTS

Autoantibodies against one protein on the array, recombination signal binding protein for immunoglobulin kappa J region (RBPJ), discriminated between patients with MS and controls (p = 0.0052). Using a large validation cohort, we found a higher prevalence of autoantibodies against RBPJ in the CSF of patients with MS (12.5%) compared with the CSF of patients with other neurologic diseases (1.6%; p = 0.02) by ELISA. This difference in reactivity was restricted to the CSF as serum reactivity against RBPJ did not differ between patients and controls. The presence of CSF autoantibodies against RBPJ was further confirmed by immunocytochemistry.

CONCLUSIONS

These data indicate that RBPJ, a ubiquitous protein of the Notch signaling pathway that plays an important role in Epstein-Barr virus infection, is a novel MS autoantigen candidate that is recognized by CSF-derived immunoglobulin G in a subset of patients with MS.

Role of CNPase in the oligodendrocytic extracellular 2',3'-cAMP-adenosine pathway

Extracellular adenosine 3',5'-cyclic monophosphate (3',5'-cAMP) is an endogenous source of localized adenosine production in many organs. Recent studies suggest that extracellular 2',3'-cAMP (positional isomer of 3',5'-cAMP) is also a source of adenosine, particularly in the brain in vivo post-injury. Moreover, in vitro studies show that both microglia and astrocytes can convert extracellular 2',3'-cAMP to adenosine. Here, we examined the ability of primary mouse oligodendrocytes and neurons to metabolize extracellular 2',3'-cAMP and their respective adenosine monophosphates (2'-AMP and 3'-AMP). Cells were also isolated from mice deficient in 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase). Oligodendrocytes metabolized 2',3'-cAMP to 2'-AMP with 10-fold greater efficiency than did neurons (and also more than previously examined microglia and astrocytes); whereas, the production of 3'-AMP was minimal in both oligodendrocytes and neurons. The production of 2'-AMP from 2',3'-cAMP was reduced by 65% in CNPase -/- versus CNPase +/+ oligodendrocytes. Oligodendrocytes also converted 2'-AMP to adenosine, and this was also attenuated in CNPase -/- oligodendrocytes. Inhibition of classic 3',5'-cAMP-3'-phosphodiesterases with 3-isobutyl-1-methylxanthine did not block metabolism of 2',3'-cAMP to 2'-AMP and inhibition of classic ecto-5'-nucleotidase (CD73) with α,β-methylene-adenosine-5'-diphosphate did not attenuate the conversion of 2'-AMP to adenosine. These studies demonstrate that oligodendrocytes express the extracellular 2',3'-cAMP-adenosine pathway (2',3'-cAMP → 2'-AMP → adenosine). This pathway is more robustly expressed in oligodendrocytes than in all other CNS cell types because CNPase is the predominant enzyme that metabolizes 2',3'-cAMP to 2-AMP in CNS cells. By reducing levels of 2',3'-cAMP (a mitochondrial toxin) and increasing levels of adenosine (a neuroprotectant), oligodendrocytes may protect axons from injury.

Alpha actinin is specifically recognized by Multiple Sclerosis autoantibodies isolated using an N-glucosylated peptide epitope

Sophisticated approaches have recently led to the identification of novel autoantigens associated with Multiple Sclerosis (MuS), e.g. neurofascin, contactin, CNPase, and other T-cell receptor membrane anchored proteins. These putative antigens, although differing from the conventional myelin derivatives, are conceptually based on an animal model of experimental autoimmune encephalomyelitis. In this report we describe the identification of putative antigens based on their recognition by autoantibodies isolated from MuS patient serum. In a previous work from this laboratory we have shown that a peptide probe, named CSF114(Glc), specifically identifies serum autoantibodies in a subset of MuS patients, representing ∼30% of the patient population. The autoantibodies, purified from MuS patients' sera (six), through CSF114(Glc) affinity chromatography, detected three immunoreactive protein bands present in the rat brain. Proteomic analysis of the immunoreactive bands, involving MALDI and MS/MS techniques, revealed the presence of four proteins distinguishable by their mass: alpha fodrin, alpha actinin 1, creatine kinase, and CNPase. The immunoreactive profile of these rat brain proteins was compared with that of commercially available standard proteins by challenging against either CSF114(Glc) purified MuS autoantibodies, or monoclonal antibodies. Further discrimination among the rat brain proteins was provided by the following procedure: whereas monoclonal antibodies recognized all rat brain proteins, isolated MuS specific antibodies recognize only alpha actinin 1 as a putative antigen. In fact, alpha actinin 1 displayed a robust immunoreactive response against all MuS patients' sera examined, whereas the other three bands were not consistently detectable. Thus, alpha actinin 1, a cytoskeleton protein implicated in inflammatory/degenerative autoimmune diseases (lupus nephritis and autoimmune hepatitis) might be regarded as a novel MuS autoantigen, perhaps a prototypic biomarker for the inflammatory/degenerative process typical of the disease.

What do effective treatments for multiple sclerosis tell us about the molecular mechanisms involved in pathogenesis?

Multiple sclerosis is a potentially debilitating disease of the central nervous system. A concerted program of research by many centers around the world has consistently demonstrated the importance of the immune system in its pathogenesis. This knowledge has led to the formal testing of a number of therapeutic agents in both animal models and humans. These clinical trials have shed yet further light on the pathogenesis of MS through their sometimes unexpected effects and by their differential effects in terms of impact on relapses, progression of the disease, paraclinical parameters (MRI) and the adverse events that are experienced. Here we review the currently approved medications for the commonest form of multiple sclerosis (relapsing-remitting) and the emerging therapies for which preliminary results from phase II/III clinical trials are available. A detailed analysis of the molecular mechanisms responsible for the efficacy of these medications in multiple sclerosis indicates that blockade or modulation of both T- and B-cell activation and migration pathways in the periphery or CNS can lead to amelioration of the disease. It is hoped that further therapeutic trials will better delineate the pathogenesis of MS, ultimately leading to even better treatments with fewer adverse effects.

Neuronal antigens recognized by cerebrospinal fluid IgM in multiple sclerosis

Axonal injury is the major cause of disability in patients with multiple sclerosis (MS), but the mechanisms leading to axonal damage are poorly understood. Oligoclonal IgM against lipids predicts an aggressive disease course in MS; however, the antigen that elicits the immune response has not yet been identified. We screened the CSF of 12 patients with MS, 7 patients with neuromyelitis optica (NMO), and 5 controls with non-inflammatory neurological disease (NIND) for the presence of IgM-type antibodies (IgM-Ab) against neuronal surface antigens, and analyzed the relationship between IgM-Ab level and the extent of brain atrophy. The CSF of MS patients displayed significantly higher levels of IgM-Ab compared to NIND or NMO patients. Furthermore, we document for the first time that these IgM-Ab recognize neuronal surface antigens, and that the levels of neuronal-bound IgM-Ab were independent of the IgM concentration and correlate with brain atrophy. Our findings suggest a role for the CSF IgM-Ab in the development of MS pathophysiology.

B cells in MS: Why, where and how?

Multiple sclerosis (MS) is a chronic disease of the central nervous system (CNS), in which auto-aggressive lymphocytes participate in inflammation that causes myelin destruction. Although T lymphocytes have been viewed as important culprits in the inflammatory cascade that results in MS, clinical trial results and animal model data support a role for B lymphocytes in MS pathology. In spite of these encouraging results, the mechanism behind why B cell depletion might be effective for MS treatment remains unknown. Herein we summarize the state of our knowledge for how B cells and their antibody products may influence the initiation and or propagation of MS, drawing from human studies and animal model data.

Myelin 2',3'-cyclic nucleotide 3'-phosphodiesterase: active-site ligand binding and molecular conformation

The 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is a highly abundant membrane-associated enzyme in the myelin sheath of the vertebrate nervous system. CNPase is a member of the 2H phosphoesterase family and catalyzes the formation of 2'-nucleotide products from 2',3'-cyclic substrates; however, its physiological substrate and function remain unknown. It is likely that CNPase participates in RNA metabolism in the myelinating cell. We solved crystal structures of the phosphodiesterase domain of mouse CNPase, showing the binding mode of nucleotide ligands in the active site. The binding mode of the product 2'-AMP provides a detailed view of the reaction mechanism. Comparisons of CNPase crystal structures highlight flexible loops, which could play roles in substrate recognition; large differences in the active-site vicinity are observed when comparing more distant members of the 2H family. We also studied the full-length CNPase, showing its N-terminal domain is involved in RNA binding and dimerization. Our results provide a detailed picture of the CNPase active site during its catalytic cycle, and suggest a specific function for the previously uncharacterized N-terminal domain.

Investigation of autoantibody profiles for cerebrospinal fluid biomarker discovery in patients with relapsing-remitting multiple sclerosis

Using the UNIarray® marker technology platform, cerebrospinal fluid immunoglobulin G reactivities of 15 controls and 17 RRMS patients against human recombinant proteins were investigated. Patient cerebrospinal fluids were oligoclonal band positive and reactivities were compared to that of sex- and age-matched controls. We hereby aimed at the characterization of autoreactivity in patients with RRMS. Differences in autoreactivities between control and RRMS samples were identified comprising autoantigens identified in this study only and previously reported autoantigens as well. A combination of the 10-15 most significant proteins may be investigated further as autoantigens for diagnostic purposes. Additional investigations may include minimizing the number of proteins used in such diagnostic tests.

Serum autoantibody biomarkers for age-related macular degeneration and possible regulators of neovascularization

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in industrial counties. Its pathogenesis is at least partially mediated by immunological factors, including a possible autoimmune response. To date, only a few antibodies have been identified in sera from patients with AMD. In order to reveal an autoantibody profile for AMD and identify biomarkers for progression of this disease, we have performed an antigen microarray analysis of serum samples from patients with AMD and healthy controls. Sera from the AMD groups contained high levels of IgG and IgM autoantibodies to some systemic antigens when compared to the normal group. Targeted antigens included cyclic nucleotide phosphodiesterase, phosphatidylserine (PS) and proliferating cell nuclear antigen. The IgG/IgM ratio for antibodies to PS was notably elevated in the AMD group compared to the normal group, and this ratio correlated best with the stage of AMD patients with an anti-PS ratio greater than the cut-off value had a 44-fold risk for advanced AMD with choroidal neovascularization. PS immunoreactivity was also elevated in AMD retina. Moreover, IgG autoantibodies purified from sera of AMD patients induced more tube formation on choroidal-retinal endothelial cells compared to those of healthy donors. Hence, sera from patients with AMD contain specific autoantibodies which may be used as biomarkers for AMD, and the IgG/M ratio for autoantibodies to PS might allow better monitoring of AMD progression.

The experimental autoimmune encephalomyelitis model for proteomic biomarker studies: from rat to human

Multiple sclerosis (MScl) is defined by central nervous system (CNS) inflammation, demyelination and axonal damage. Some of the disease mechanisms are known but the cause of this complex disorder stays an enigma. Experimental autoimmune encephalomyelitis (EAE) is an animal model mimicking many aspects of MScl. This review aims to provide an overview over proteomic biomarker studies in the EAE model emphasizing the translational aspects with respect to MScl in humans.

Expression, purification, and initial characterization of different domains of recombinant mouse 2',3'-cyclic nucleotide 3'-phosphodiesterase, an enigmatic enzyme from the myelin sheath

Background

2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is an enigmatic enzyme specifically expressed at high levels in the vertebrate myelin sheath, whose function and physiological substrates are unknown. The protein consists of two domains: an uncharacterized N-terminal domain with little homology to other proteins, and a C-terminal phosphodiesterase domain.

Findings

In order to be able to fully characterize CNPase structurally and functionally, we have set up expression systems for different domains of CNPase, using a total of 18 different expression constructs. CNPase was expressed in E. coli with a TEV-cleavable His-tag. Enzymatic activity assays indicated that the purified proteins were active and correctly folded. The folding of both the full-length protein, as well as the N- and C-terminal domains, was also studied by synchrotron CD spectroscopy. A thermal shift assay was used to optimize buffer compositions to be used during purification and storage. The assay also indicated that CNPase was most stable at a pH of 5.5, and could be significantly stabilized by high salt concentrations.

Conclusions

We have been able to express and purify recombinantly several different domains of CNPase, including the isolated N-terminal domain, which is folded mainly into a β-sheet structure. The expression system can be used as an efficient tool to elucidate the role of CNPase in the myelin sheath.

Autoantibodies to the proteasome in monosymptomatic optic neuritis may predict progression to multiple sclerosis

OBJECTIVE

Proteasome autoantibodies (PAB) have been found in multiple sclerosis (MS) patient sera and cerebrospinal fluid (CSF). Presence of PAB could thus be a possible diagnostic marker for MS. We investigated whether PAB serum status in acute monosymptomatic optic neuritis (ON) and MS differed significantly from that of healthy controls, and whether or not PAB status is predictive of later MS development in patients with ON.

MATERIAL AND METHODS

Sera from ON patients, MS patients and healthy donors were analysed retrospectively using ELISA. Subsequently, a small group of PAB-positive samples were subjected to SDS-PAGE, immunoblotting and 2-D PAGE.

RESULTS

We found that 20 % (6/30) ON patients, 47 % (22/47) MS patients and 9 % (7/81) controls tested PAB positive using ELISA analysis. High PAB levels were found in 2 (4 %) MS patients, 1 (3 %) ON patient and 2 (3 %) controls. PAB positivity in ELISA was confirmed by immunoblotting. Separation of proteasome subunits by 2D PAGE followed by immunoblotting revealed no particular PAB subunit preference.

CONCLUSIONS

A retrospective search in available patient files revealed that 6 of 6 (100.0 %) PAB-positive ON patients developed MS over time. Eight of 24 (33 %) PAB-negative ON patients developed MS over time and 47 % (14/30) of all ON patients developed MS. A series of patient CSF was analysed by ELISA to assess the possible correlation between PAB status of concurrent serum and CSF samples, but no correlation was found. However, the results from the six PAB-positive ON patients could potentially be of prognostic value.

B-cells and humoral immunity in multiple sclerosis. Implications for therapy

B-cells and humoral immunity have been implicated in the pathogenesis of multiple sclerosis. The most common pattern of demyelinating pathology in multiple sclerosis is associated with the deposition of antibodies and the activation of complement, as well as T-cells and macrophages. Plasmapheresis has been found to be an efficient therapeutic approach in patients with this type of pathological lesion. Recent data have indicated that autoantibodies and complement C5b-9 may be involved in lesion formation and might also be beneficial for lesion repair. Thus, the role played by B-cells and humoral immunity is rather complex, and new strategies for targeting B-cell responses are continuing to emerge.

Systems biology approaches for the study of multiple sclerosis

Multiple sclerosis (MS) is a progressive neurological disease caused by an autoimmune attack to the central nervous system (CNS). MS is thought to result from a complex interaction between genetic and environmental factors. In this review we analyze the contribution of genomics, trancriptomics and proteomics in delineating these factors, as well as their utility for the monitoring of disease progression, the identification of new targets for therapeutic intervention and the early detection of individuals at risk.

Multiple sclerosis: Disease biomarkers as indicated by pathophysiology

Multiple sclerosis (MS), the most important human inflammatory demyelinating disease of the central nervous system, is characterized by heterogenous genetic backgrounds and immunopathogenetic subtypes, various clinical disease courses, and inhomogeneous and unpredictable therapeutic effects. Because of this heterogeneity, subtyping of our MS patients by genetical, clinical, neuroradiological, and neuroimmunological parameters will be an urgent need in the near future. Therefore the importance of identifying biological markers for MS has evolved over the past years. Evidence for a possible role of antibodies as biological markers for MS comes from several studies indicating that intrathecal antibody production and the dominance of B-cells are associated with a more progressive disease course. This review summarizes the current status and potential applicability of antibodies as biological markers for the diagnosis, classification, disease activity and prediction of clinical courses in MS. Antibodies (and other molecules) serving as biomarkers will help to establish a differential therapeutic concept in MS, which should allow to treat individuals selectively according to their pathogenetic subtype and disease status.

Preparation of potential cell-permeant nucleoside-2',3'-cyclic phosphate precursors

Uridine-3'-phosphorothiolate triesters bearing lipophilic moieties were prepared via Michaelis-Arbuzov chemistry. Subsequent deprotection of the S-cholesteryl phosphorothiolate triester afforded the corresponding diester which underwent spontaneous Cyclization to cleanly afford uridine 2',3'-cyclic phosphate. This transesterification reaction could be expedited by treatment with iodine under mild, neutral conditions.

Role of B Cells in Pathogenesis of Multiple Sclerosis

Despite the current limited understanding of the etiology of multiple sclerosis (MS), genetic susceptibility and environmental influences are known driving factors. MS is considered a T-cell-mediated disease given the prevalence of T cells in plaques. Plaque formation is characteristic of this disease attributable to immune mechanisms, triggered by an autoimmune attack aimed at antigens in the myelin sheath or oligodendrocyte proteins. The attack consists of the following: The role of the B cells is twofold: first, as autoreactive B cells they produce autoantibodies, secrete cytokines, clonally replicate memory B cells, and long-living plasma cells which serve to advance the diseased state by their constant production of autoantibodies. Second, as antigen-presenting cells they activate the autoreactive T cells. For this reason, the stipulation that T cell is the cornerstone of MS must be reevaluated. Various studies on pathogenesis of MS have indicated that B cells, as the humoral component of the adaptive immune system, are active participants in pathogenesis and lesion maintenance throughout the disease process. The active role of B cells and autoantibodies makes them an encouraging therapeutic target. Advances in the understanding of B-cell development and activity would allow for an enhanced strategy in the design of autoimmune treatment. For this reason, further investigation is necessary to determine whether depletion of B cells or antibodies may restore immune function.

The brain as a target of inflammation: common pathways link inflammatory and neurodegenerative diseases

Classical knowledge distinguishes between inflammatory and non-inflammatory diseases of the brain. Either the immune system acts on the CNS and initiates a damage cascade, as in autoimmune (e.g. multiple sclerosis) and infectious conditions, or the primary insult is not inflammation but ischemia or degeneration, as in stroke and Alzheimer's disease, respectively. However, as we review here, recent advances have blurred this distinction. On the one hand, the classical inflammatory diseases of the brain also exhibit profound and early neurodegenerative features - remarkably, it has been known for more than a century that neuronal damage is a key feature of multiple sclerosis pathology, yet this was neglected until very recently. On the other hand, immune mechanisms might set the pace of progressive CNS damage in primary neurodegeneration. Despite differing initial events, increasing evidence indicates that even in clinically heterogeneous diseases, there might be common immunological pathways that result in neurotoxicity and reveal targets for more efficient therapies.

Antibodies as biological markers for pathophysiological processes in MS

Multiple sclerosis (MS), the most important human inflammatory demyelinating disease of the central nervous system, is characterized by various clinical disease courses, inhomogeneous and unpredictable therapeutic effects, heterogenous genetic backgrounds and immunopathogenetic subtypes as demonstrated by neuropathology. Because of this heterogeneity of MS, a subtyping of our patients by genetical, clinical, neuroradiological, and neuroimmunological parameters will be necessary in the future. Therefore the importance of identifying biological markers for MS has evolved over the past years. Evidence for a possible role of antibodies as biological markers for MS comes from several studies indicating that intrathecal antibody production and the dominance of B cells are associated with a more progressive disease course. In this review we will give an overview on the current status and potential applicability of antibodies as biological markers for the diagnosis, classification, disease activity and prediction of clinical courses in MS. We will therefore summarize the findings on autoantibodies to myelin and nonmyelin antigens and on viral antigens in MS. We believe that antibodies serving as biomarkers will help to establish a differential therapeutic concept in MS, which will allow to treat individuals selectively according to their pathogenetic subtype and disease status.

Expression of 2',3'-cyclic nucleotide 3'-phosphodiesterase in the amoeboid microglial cells in the developing rat brain

Expression of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) in amoeboid microglial cells (AMC) in developing rat brain from prenatal day 18 (E18) to postnatal day 10 (P10) was demonstrated by immunohistochemistry/immunofluorescence and immunoelectron microscopy both in vivo and in vitro, respectively. Furthermore, real time-polymerase chain reaction (PCR) was performed to determine the expression of CNPase at mRNA level in cultured microglial cells in control conditions and following lipopolysaccharide stimulation. CNPase immunoreactive amoeboid microglia occurred in large numbers in the corpus callosum, subventricular zone and cavum septum pellucidum at P0 but were progressively reduced with age and were undetectable at P14. By immunoelectron microscopy, immunoreaction product was associated primarily with the plasma membrane, filopodial projections and mitochondria in AMC. Real time-PCR analysis revealed that CNPase mRNA was expressed by cultured amoeboid microglia and was significantly up-regulated in microglial activation induced in vitro by lipopolysaccharide. The functional role of CNPase in AMC remains speculative. Given its expression in AMC transiently occurring in the perinatal brain and that it is markedly elevated in activated microglia, it is suggested that the enzyme may be linked to the major functions of the cell type such as release of chemokines and cytokines. In relation to this, CNPase may play a key role associated with transportation of cytoplasmic materials.

Emergence of antibodies as biomarkers in multiple sclerosis

Rather than being a homogenous disease entity, multiple sclerosis (MS) represents a family of heterogenous inflammatory-demyelinating CNS diseases. The heterogeneity is demonstrated by various well known clinical disease courses and, more importantly, by inhomogenous and unpredictable therapeutic effects. Recent neuropathological evidence has initiated a process of re-evaluation of the immunopathogenetic concepts in MS. The heterogeneity of MS claims to subtype our patients more distinctively in the future by genetic, clinical, neuroradiological and neuroimmunological parameters. Therefore, the importance of identifiying biological markers in MS has evolved over the past few years. This review discusses the current status and potential applicability of antibodies as biological markers for the diagnosis, classification, disease activity and prediction of clinical courses in MS. Antibodies serving as biomarkers will create the future path for establishing a differential therapeutic concept in MS, which will allow the treatment of individuals selectively, according to their pathogenetic subtype and disease status.

Expansion of antibody reactivity in the cerebrospinal fluid of multiple sclerosis patients - follow-up and clinical implications

BACKGROUND

An intrathecal polyspecific antibody response is a well known finding in multiple sclerosis. However, little is known about the evolution of intrathecal antibodies over time and their impact on the disease progress. Therefore, we focused in this study on the intrathecal polyspecific antibody response in multiple sclerosis.

METHODS

Here we present a follow-up study of 70 patients with multiple sclerosis over 1 to 106 months. Serum and cerebrospinal fluid sample pairs were obtained from 1 to 5 consecutive lumbar punctures. CSF cell count, the IgG index, local IgG synthesis, oligoclonal bands and the antibody index for measles, rubella or varicella zoster were calculated. Results were analysed with regard to clinical characteristics of the patients.

RESULTS

Once an intrathecal antibody response was established, it persisted. De novo antibody response against measles virus developed in 7% of the patients between the first and the second spinal tap. In two of seven patients where 5 consecutive CSF samples were available, the intrathecal antibody response expanded from one to three antigens. Furthermore, an intrathecal measles antibody production was associated with a rapid progression of the disease.

CONCLUSION

These data stress the importance of activated B cells for the disease process and the clinical outcome in multiple sclerosis.

Activation of complement pathways after contusion-induced spinal cord injury

Previous studies have shown that a cellular inflammatory response is initiated, and inflammatory cytokines are synthesized, following experimental spinal cord injury (SCI). In the present study, we tested the hypothesis that the complement cascade, a major component of both the innate and adaptive immune response, is also activated following experimental SCI. We investigated the pathways, cellular localization, timecourse, and degree of complement activation in rat spinal cord following acute contusion-induced SCI using the New York University (NYU) weight drop impactor. Mild and severe injuries (12.5 and 50 mm drop heights) at 1, 7, and 42 days post injury time points were evaluated. Classical (C1q and C4), alternative (Factor B) and terminal (C5b-9) complement pathways were strongly activated within 1 day of SCI. Complement protein immunoreactivity was predominantly found in cell types vulnerable to degeneration, neurons and oligodendrocytes, and was not generally observed in inflammatory or astroglial cells. Surprisingly, immunoreactivity for complement proteins was also evident 6 weeks after injury, and complement activation was observed as far as 20 mm rostral to the site of injury. Axonal staining by C1q and Factor B was also observed, suggesting a potential role for the complement cascade in demyelination or axonal degeneration. These data support the hypothesis that complement activation plays a role in SCI.

Detection of ectopic B-cell follicles with germinal centers in the meninges of patients with secondary progressive multiple sclerosis

Multiple sclerosis (MS) is characterized by synthesis of oligoclonal immunoglobulins and the presence of B-cell clonal expansions in the central nervous system (CNS). Because ectopic lymphoid tissue generated at sites of chronic inflammation is thought to be important in sustaining immunopathological processes, we have investigated whether structures resembling lymphoid follicles could be identified in the CNS of MS patients. Sections from post-mortem MS brains and spinal cords were screened using immunohistochemistry for the presence of CD20+ B-cells, CD3+ T-cells, CD138+ plasma cells and CD21+, CD35+ follicular dendritic cells, and for the expression of lymphoid chemokines (CXCL 13, CCL21) and peripheral node addressin (PNAd). Lymphoid follicle-like structures containing B-cells, T-cells and plasma cells, and a network of follicular dendritic cells producing CXCL13 were observed in the cerebral meninges of 2 out of 3 patients with secondary progressive MS, but not in relapsing remitting and primary progressive MS. We also show that proliferating B-cells are present in intrameningeal follicles, a finding which is suggestive of germinal center formation. No follicle-like structures were detected in parenchymal lesions. The formation of ectopic lymphoid follicies in the meninges of patients with MS could represent a critical step in maintaining humoral autoimmunity and in disease exacerbation.

B cells in multiple sclerosis

The most common laboratory abnormality in multiple sclerosis (MS) is an increased amount of cerebrospinal fluid IgG and the presence of oligoclonal bands. Despite studies of the humoral response that suggest the involvement of an infectious agent or autoantigen in disease, the major targets of the oligoclonal response are still unknown. Identification of these targets will reveal valuable insights into the cause and pathogenesis of MS and is likely to lead to effective treatment.

Specificity of autoantibodies to epitopes of myelin proteins in multiple sclerosis

An autoimmune response to one or more myelin-protein components is thought to be part of the pathogenesis of multiple sclerosis (MS). The immunodominant-autoantibody epitope may be localized on a linear peptide segment, on a conformation-sensitive epitope, or on an epitope resulting from post-translational modifications. Primary, secondary, and tertiary structures of myelin proteins may determine the specific site for binding of autoantibodies. A myelin protein-specific autoantibody can bind to either a linear or conformational epitope, whereas all of the T cell epitopes are linear. At present, the conformational epitopes of myelin proteins have not been identified; most of the methods used to identify the myelin-protein epitopes corresponding to the pathogenesis of multiple sclerosis are involved in the linear epitope mapping. Polymorphism or mutations may cause inappropriate expression of the myelin proteins with alterations to their linear and/or conformational epitopes, and make them susceptible to autoantibody binding, especially if these changes occur at the surface of the protein. This review focuses on the specificity of autoantibodies to the epitopes of myelin proteins and correlates this to the structures of proteins. Factors that influence the expression of myelin-protein epitopes such as the alpha-helical or beta-sheet structure of the protein, the tri-proline site, and the post-translational modifications as well as physicochemical properties of amino acid changed are included.

The role of macrophage/microglia and astrocytes in the pathogenesis of three neurologic disorders: HIV-associated dementia, Alzheimer disease, and multiple sclerosis

Macrophage/microglia (M phi) are the principal immune cells in the central nervous system (CNS) concomitant with inflammatory brain disease and play a significant role in the host defense against invading microorganisms. Astrocytes, as a significant component of the blood-brain barrier, behave as one of the immune effector cells in the CNS as well. However, both cell types may play a dual role, amplifying the effects of inflammation and mediating cellular damage as well as protecting the CNS. Interactions of the immune system, M phi, and astrocytes result in altered production of neurotoxins and neurotrophins by these cells. These effects alter the neuronal structure and function during pathogenesis of HIV-1-associated dementia (HAD), Alzheimer disease (AD), and multiple sclerosis (MS). HAD primarily involves subcortical gray matter, and both HAD and MS affect sub-cortical white matter. AD is a cortical disease. The process of M phi and astrocytes activation leading to neurotoxicity share similarities among the three diseases. Human Immunodeficiency Virus (HIV)-1-infected M phi are involved in the pathogenesis of HAD and produce toxic molecules including cytokines, chemokines, and nitric oxide (NO). In AD, M phis produce these molecules and are activated by beta-amyloid proteins and related oligopeptides. Demyelination in MS involves M phi that become lipid laden, spurred by several possible antigens. In these three diseases, cytokine/chemokine communications between M phi and astrocytes occur and are involved in the balance of protective and destructive actions by these cells. This review describes the role of M phi and astrocytes in the pathogenesis of these three progressive neurological diseases, examining both beneficent and deleterious effects in each disease.

T cell response to 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) in multiple sclerosis patients

T cell responses targeting myelin antigens are possibly involved in the pathogenesis of demyelinating diseases, such as multiple sclerosis (MS). Little is known about human T cell responses to 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), the third most abundant myelin protein. We examined the primary peripheral T cell response to CNPase and characterized CNPase-specific CD4+ long-term T cell lines (TCL) from MS patients and healthy donors. The strongest primary responses were found in two MS patients with very active disease and were directed against CNP(343-373). We identified immunodominant epitope clusters in the regions CNP(343-373) and (356-388) that were recognized in the context of MS-associated HLA-DR2 and DR4 molecules. These data provide the immunological basis for further investigation of CNPase as a potential target self-antigen in MS.

Immunopathogenic and clinical relevance of antibodies against myelin oligodendrocyte glycoprotein (MOG) in Multiple Sclerosis

Recent neuropathological findings identified four distinct immunopathogenic pathways of demyelination and tissue destruction in the most common inflammatory demyelinating central nervous system disorder, Multiple Sclerosis. One of this neuropathological subtypes is characterised by features of antibody-mediated demyelination. A role of anti-myelin antibodies in the disease evolution of multiple sclerosis has been suggested already for a long time, however, their pathogenetic and clinical relevance is not understood yet. This present article will discuss recently published and some preliminary data on the immunopathogenic role of antibodies against myelin oligodendrocyte glycoprotein (MOG) and other myelin/nonmyelin targets in multiple sclerosis, as well as possible clinical implications for prognosis and therapy in the future.

Biology of oligodendrocyte and myelin in the mammalian central nervous system

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.

Anti-DNA antibodies are a major component of the intrathecal B cell response in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of unknown cause that afflicts the central nervous system. MS is typified by a highly clonally restricted antigen-driven antibody response that is confined largely to the central nervous system. The major antigenic targets of this response and the role of antibody in disease pathogenesis remain unclear. To help resolve these issues, we cloned the IgG repertoire directly from active plaque and periplaque regions in MS brain and from B cells recovered from the cerebrospinal fluid of a patient with MS with subacute disease. We found that high-affinity anti-DNA antibodies are a major component of the intrathecal IgG response in the patients with MS that we studied. Furthermore, we show DNA-specific monoclonal antibodies rescued from two subjects with MS as well as a DNA-specific antibody rescued from an individual suffering from systemic lupus erythematosus bound efficiently to the surface of neuronal cells and oligodendrocytes. For two of these antibodies, cell-surface recognition was DNA dependent. Our findings indicate that anti-DNA antibodies may promote important neuropathologic mechanisms in chronic inflammatory disorders, such as MS and systemic lupus erythematosus.

Anti-DNA antibodies are a major component of the intrathecal B cell response in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of unknown cause that afflicts the central nervous system. MS is typified by a highly clonally restricted antigen-driven antibody response that is confined largely to the central nervous system. The major antigenic targets of this response and the role of antibody in disease pathogenesis remain unclear. To help resolve these issues, we cloned the IgG repertoire directly from active plaque and periplaque regions in MS brain and from B cells recovered from the cerebrospinal fluid of a patient with MS with subacute disease. We found that high-affinity anti-DNA antibodies are a major component of the intrathecal IgG response in the patients with MS that we studied. Furthermore, we show DNA-specific monoclonal antibodies rescued from two subjects with MS as well as a DNA-specific antibody rescued from an individual suffering from systemic lupus erythematosus bound efficiently to the surface of neuronal cells and oligodendrocytes. For two of these antibodies, cell-surface recognition was DNA dependent. Our findings indicate that anti-DNA antibodies may promote important neuropathologic mechanisms in chronic inflammatory disorders, such as MS and systemic lupus erythematosus.

B cells and antibodies in CNS demyelinating disease

There is much evidence to implicate B cells, plasma cells, and their products in the pathogenesis of MS. Despite unequivocal evidence that the animal model for MS, EAE, is initiated by myelin-specific T cells, there is accumulating evidence of a role for B cells, plasma cells, and their products in EAE pathogenesis. The role(s) played by B cells, plasma cells, and antibodies in CNS inflammatory demyelinating diseases are likely to be multifactorial and complex, involving distinct and perhaps opposing roles for B cells versus antibody.

Complement C1q is dramatically up-regulated in brain microglia in response to transient global cerebral ischemia

Recent evidence suggests that the pathophysiology of neurodegenerative and inflammatory neurological diseases has a neuroimmunological component involving complement, an innate humoral immune defense system. The present study demonstrates the effects of experimentally induced global ischemia on the biosynthesis of C1q, the recognition subcomponent of the classical complement activation pathway, in the CNS. Using semiquantitative in situ hybridization, immunohistochemistry, and confocal laser scanning microscopy, a dramatic and widespread increase of C1q biosynthesis in rat brain microglia (but not in astrocytes or neurons) within 24 h after the ischemic insult was observed. A marked increase of C1q functional activity in cerebrospinal fluid taken 1, 24, and 72 h after the ischemic insult was determined by C1q-dependent hemolytic assay. In the light of the well-established role of complement and complement activation products in the initiation and maintenance of inflammation, the ischemia-induced increase of cerebral C1q biosynthesis and of C1q functional activity in the cerebrospinal fluid implies that the proinflammatory activities of locally produced complement are likely to contribute to the pathophysiology of cerebral ischemia. Pharmacological modulation of complement activation in the brain may be a therapeutic target in the treatment of stroke.

Molecular pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is best understood as an inflammatory disease of the central nervous system (CNS) white matter characterized by demyelination, focal T cell and macrophage infiltrates, axonal injury and loss of neurological function. Our current understanding invokes proinflammatory cells and mediators that may be triggered by environmental factors to mediate disease in a genetically susceptible host. Five major themes which have been associated with the pathogenesis of MS lesions will be discussed: (1) The differential activation states of myelin-reactive T cells from MS patients vs. normal individuals, (2) the selective expression of chemokines, adhesion molecules and matrix metalloproteinases, (3) the proposed roles of the B7 costimulatory pathway, (4) the proinflammatory cytokines and (5) the role of molecular mimicry.

Antibodies against the myelin oligodendrocyte glycoprotein and the myelin basic protein in multiple sclerosis and other neurological diseases: a comparative study

In experimental animal models of multiple sclerosis demyelinating antibody responses are directed against the myelin oligodendrocyte glycoprotein (MOG). We have investigated whether a similar antibody response is also present in multiple sclerosis patients. Using the recombinant human extracellular immunoglobulin domain of MOG (MOG-Ig) we have screened the sera and CSFs of 130 multiple sclerosis patients, 32 patients with other inflammatory neurological diseases (OIND), 30 patients with other non-inflammatory neurological diseases (ONND) and 10 patients with rheumatoid arthritis. We report that 38% of multiple sclerosis patients are seropositive for IgG antibodies to MOG-Ig compared with 28% seropositive for anti-myelin basic protein (MBP). In contrast, OIND are characterized by similar frequencies of serum IgG antibody responses to MOG-Ig (53%) and MBP (47%), whereas serum IgG responses to MOG-Ig are rare in ONND (3%) and rheumatoid arthritis (10%). Anti-MBP IgG antibodies, however, are a frequent finding in ONND (23%) and rheumatoid arthritis (60%). Our results provide clear evidence that anti-MOG-Ig antibodies are common in CNS inflammation. However, in OIND these antibody responses are transient, whereas they persist in multiple sclerosis. We demonstrate that the serum anti-MOG-Ig response is already established in early multiple sclerosis (multiple sclerosis-R0; 36%). In later multiple sclerosis stages frequencies and titres are comparable with early multiple sclerosis. In contrast, the frequency of anti-MBP antibodies is low in multiple sclerosis-R0 (12%) and increases during disease progression in relapsing-remitting (32%) and chronic progressive multiple sclerosis (40%), thus suggesting that anti-MBP responses accumulate over time. Finally we provide evidence for intrathecal synthesis of IgG antibodies to MOG-Ig in multiple sclerosis.