Remyelination by oligodendrocytes stimulated by antiserum to spinal cord

Antibody characterization using immunosignatures

Therapeutic monoclonal antibodies have the potential to work as biological therapeutics. OKT3, Herceptin, Keytruda and others have positively impacted healthcare. Antibodies evolved naturally to provide high specificity and high affinity once mature. These characteristics can make them useful as therapeutics. However, we may be missing characteristics that are not obvious. We present a means of measuring antibodies in an unbiased manner that may highlight therapeutic activity. We propose using a microarray of random peptides to assess antibody properties. We tested twenty-four different commercial antibodies to gain some perspective about how much information can be derived from binding antibodies to random peptide libraries. Some monoclonals preferred to bind shorter peptides, some longer, some preferred motifs closer to the C-term, some nearer the N-term. We tested some antibodies with clinical activity but whose function was blinded to us at the time. We were provided with twenty-one different monoclonal antibodies, thirteen mouse and eight human IgM. These antibodies produced a variety of binding patterns on the random peptide arrays. When unblinded, the antibodies with polyspecific binding were the ones with the greatest therapeutic activity. The protein target to these therapeutic monoclonals is still unknown but using common sequence motifs from the peptides we predicted several human and mouse proteins. The same five highest proteins appeared in both mouse and human lists.

Antibody-mediated Remyelination: Relevance to Multiple Sclerosis

Intravenous immunoglobulin (IVIG) is widely used for treatment of autoimmune neurological disorders and is currently in clinical trials as a therapy for multiple sclerosis. We have previously demonstrated that certain mouse monoclonal antibodies of the IgM isotype, promote significant remyelination when administered to mice with chronic Theiler's murine encephalomyelitis virus-induced demyelinating disease. These IgM antibodies bind to antigens expressed on oligodendrocytes. We now demonstrate that polyclonal human IgG (IVIG) and polyclonal human IgM also promote remyelination in this system. Although both polyclonal human IgG and IgM promote remyelination, IgM is more potent Polyclonal human IgM also differs from human IgG in its ability to bind strongly to antigens expressed in the CNS and by oligodendrocytes. We propose that polyclonal IgG and polyclonal IgM may function to promote remyelination by different mechanisms. IVIG may function based on its immunomodulatory activity, while the activity of IgM is critically dependent upon its reactivity with CNS antigens. This possibility has clear relevance to the use of antibodies as a therapy for multiple sclerosis, suggesting that combined treatment with antibodies exerting immunomodulatory activity, in concert with antibodies that function through direct binding to CNS antigens, may synergize to enhance the efficacy of the therapy.

N-methyl-D-aspartate receptor dysfunction by unmutated human antibodies against the NR1 subunit

Anti–N‐methyl‐D‐aspartate receptor (NMDAR) encephalitis is the most common autoimmune encephalitis related to autoantibody‐mediated synaptic dysfunction. Cerebrospinal fluid–derived human monoclonal NR1 autoantibodies showed low numbers of somatic hypermutations or were unmutated. These unexpected germline‐configured antibodies showed weaker binding to the NMDAR than matured antibodies from the same patient. In primary hippocampal neurons, germline NR1 autoantibodies strongly and specifically reduced total and synaptic NMDAR currents in a dose‐ and time‐dependent manner. The findings suggest that functional NMDAR antibodies are part of the human naïve B cell repertoire. Given their effects on synaptic function, they might contribute to a broad spectrum of neuropsychiatric symptoms. Ann Neurol 2019;85:771–776

IgM Natural Autoantibodies in Physiology and the Treatment of Disease

Antibodies are vital components of the adaptive immune system for the recognition and response to foreign antigens. However, some antibodies recognize self-antigens in healthy individuals. These autoreactive antibodies may modulate innate immune functions. IgM natural autoantibodies (IgM-NAAs) are a class of primarily polyreactive immunoglobulins encoded by germline V-gene segments which exhibit low affinity but broad specificity to both foreign and self-antigens. Historically, these autoantibodies were closely associated with autoimmune disease. Nevertheless, not all human autoantibodies are pathogenic and compelling evidence indicates that IgM-NAAs may exert a spectrum of effects from injurious to protective depending upon cellular and molecular context. In this chapter, we review the current state of knowledge regarding the potential physiological and therapeutic roles of IgM-NAAs in different disease conditions such as atherosclerosis, cancer, and autoimmune disease. We also describe the discovery of two reparative IgM-NAAs by our laboratory and delineate their proposed mechanisms of action in central nervous system (CNS) disease.

A comparison of human natural monoclonal antibodies and aptamer conjugates for promotion of CNS remyelination: where are we now and what comes next?

INTRODUCTION

Multiple sclerosis (MS) is a chronic and progressive inflammatory demyelinating disease of the human central nervous system (CNS) and is the most common disabling neurological condition in young adults, resulting in severe neurological defects. No curative or long-term progression-inhibiting therapy has yet been developed. However, recent investigation has revealed potential strategies that do not merely modulate potentially pathogenic autoimmune responses, but stimulate remyelination within CNS lesions.

AREAS COVERED

We discuss the history and development of natural human IgM-isotype immunoglobulins (HIgMs) and recently-identified aptamer-conjugates that have been shown to enhance endogenous myelin repair in animal models of demyelination by acting on myelin-producing oligodendrocytes (OLs) or oligodendrocyte progenitor cells (OPCs) within CNS lesions. We also discuss future development aims and applications for these important novel technologies.

EXPERT OPINION

Aptamer conjugate Myaptavin-3064 and recombinant human IgM-isotype antibody rHIgM22 regenerate CNS myelin, thereby reducing axonal degeneration and offering the potential of recovery from MS relapses, reversal of disability and prevention of disease progression. Advancement of these technologies into the clinic for MS treatment is therefore a top priority. It remains unclear to what extent the therapeutic modalities of remyelinating antibodies and aptamers may synergize with other currently-approved therapies to yield enhanced therapeutic effects.

Timing of Future Remyelination Therapies and Their Potential to Stop Multiple Sclerosis Progression

Prior to the onset of demyelination in multiple sclerosis (MS), early oligodendrocyte injury, axonal degeneration and astroglial scarring occur. The irreversible progressive phase of MS begins when the axonal loss threshold is reached. Progressive disease onset has the highest impact on a poor prognosis in MS. Conversion to progressive disease is essentially an age-dependent process independent of disease duration and initial disease course. Although prevention of relapses has been the primary approach in the disease management, incomplete recovery from even the first relapse correlates with the long-term neurodegenerative phenotype of progressive MS onset. Therefore, the provider should review each patient's potential for relapse-related disability and start DMDs with the goal of preventing relapses. Existing immunomodulatory medications used to prevent MS relapses do not prevent long-term disability, which requires agents focused on remyelination and axonal repair. If applied immediately after a relapse rather than during the progressive phase of MS, remyelination-stimulating strategies may result in full recovery and prevention of long-term neurodegeneration and progressive disease course.

Recruitment of endogenous CNS stem cells for regeneration in demyelinating disease

Demyelinating diseases, such as multiple sclerosis (MS), are responsible for a significant portion of the neurological disability burden worldwide, especially in young adults. Demyelination can be followed by a spontaneous regenerative process called remyelination, in which new myelin sheaths are restored to denuded axons. However, in chronic demyelinating disease such as MS, this process becomes progressively less efficient. This chapter reviews the biology of remyelination and the rationale and strategies by which it can be enhanced therapeutically in acquired demyelinating disease.

New perspectives on corpora amylacea in the human brain

Corpora amylacea are structures of unknown origin and function that appear with age in human brains and are profuse in selected brain areas in several neurodegenerative conditions. They are constituted of glucose polymers and may contain waste elements derived from different cell types. As we previously found on particular polyglucosan bodies in mouse brain, we report here that corpora amylacea present some neo-epitopes that can be recognized by natural antibodies, a certain kind of antibodies that are involved in tissue homeostasis. We hypothesize that corpora amylacea, and probably some other polyglucosan bodies, are waste containers in which deleterious or residual products are isolated to be later eliminated through the action of the innate immune system. In any case, the presence of neo-epitopes on these structures and the existence of natural antibodies directed against them could become a new focal point for the study of both age-related and degenerative brain processes.

Do Antibodies Stimulate Myelin Repair in Multiple Sclerosis?

One of the major goals in the study of multiple sclerosis (MS) is to identify a beneficial therapeutic intervention that mimics the intrinsic reparative process and results in long-term clinical improvement. As yet, the therapeutic strategies tested in MS have failed to accomplish this task. However, one potential therapy that has shown some promise in rodent models of demyelination involves the administration of antibodies. Studies in various models of demyelination (virus-induced, autoimmune, and toxic) indicate that a subset of autoantibodies with reactivity to CNS antigens promote remyelination. We have identified a prototypic germline IgMk monoclonal antibody, designated SCH 94.03, with reactivity to a surface antigen on oligodendrocytes that promotes CNS remyelination. This antibody has the phenotypic features of polyreactive physiological natural autoantibodies. Additionally, treatment of MS patients with intravenous immunoglobulin, which contains these natural autoantibodies, may be efficacious in a subset of patients. We propose three mechanisms (direct stimulation of oligodendrocytes, immunomodulation, and opsonization of debris) by which polyreactive natural autoantibodies directed against CNS antigen may promote remyelination. Remyelination has the potential to not only improve conduction velocity but also may protect axons from injury and improve neurological function.

Concomitant Use of Neuroprotective Drugs in Neuro Rehabilitation of Multiple Sclerosis

We provide an overview of rehabilitation in neurological diseases. A large amount of literature available on neurorehabilitation is based from the rehabilitative work on stroke and spinal cord injuries. After a brief description of rehabilitation, the potential application of neurorehabilitation in neurodegenerative diseases specifically multiple sclerosis (MS) is summarized. Since MS causes a wide variety of symptoms, the rehabilitation in MS patients may benefit from an interdisciplinary approach that encloses physiotherapy, cognitive rehabilitation, psychological therapy, occupational therapy, and other methods to improve fatigue. Neurorehabilitation helps patients to reach and maintain their optimal physical, psychological and intellectual, levels but it does not reverse long-term disabilities that arise from neurological disorders. This calls for the need of better neuroregenerative and neuroprotective treatment strategies in addition to neurorehabilitation. We discuss neuroprotective drugs aimed at preventing axonal, neuronal, myelin and oligodendrocyte damage and cell death that are approved and others that are currently in clinical trials, with an emphasis on human derived natural antibodies with remyleination potential. Our investigative group developed recombinant natural human IgM antibodies against oligodendrocytes and neurons with a potential for CNS repair and remyleination. One such recombinant antibody, rHIgM22 completed a phase 1 clinical trial with no toxicity and with an objective of promoting remyleination in multiple sclerosis. Inclusion of these drugs as a multifaceted approach may further enhance the efficacy of neurorehabilitation in neuroinflammatory and neurodegenerative disorders.

Lymphocytes and autoimmunity after spinal cord injury

Over the past 15 years an immense amount of data has accumulated regarding the infiltration and activation of lymphocytes in the traumatized spinal cord. Although the impact of the intraspinal accumulation of lymphocytes is still unclear, modulation of the adaptive immune response via active and passive vaccination is being evaluated for its preclinical efficacy in improving the outcome for spinal-injured individuals. The complexity of the interaction between the nervous and the immune systems is highlighted in the contradictions that appear in response to these modulations. Current evidence regarding augmentation and inhibition of the adaptive immune response to spinal cord injury is reviewed with an aim toward reconciling conflicting data and providing consensus issues that may be exploited in future therapies. Opportunities such an approach may provide are highlighted as well as the obstacles that must be overcome before such approaches can be translated into clinical trials.

Cellular targets and mechanistic strategies of remyelination-promoting IgMs as part of the naturally occurring autoantibody repertoire

Immunoglobulins with germline sequences occur in invertebrates and vertebrates and are named naturally occurring autoantibodies (NAbs). NAbs may target foreign antigens, self- or altered self-components and are part of the normal immunoglobulin repertoire. Accumulating evidence indicates that naturally occurring antibodies can act as systemic surveillance molecules, which tag, damaged or stressed cells, invading pathogens and toxic cellular debris for elimination by the immune system. In addition to acting as detecting molecules, certain types of NAbs actively signal in different cell types with a broad range of responses from induction of apoptosis in cancer cells to stimulation of remyelination in glial cells. This review emphasizes functions and characteristics of NAbs with focus on remyelination-promoting mouse and human antibodies. Human remyelination-promoting NAbs are potential therapeutics to combat a wide spectrum of disease processes including demyelinating diseases like multiple sclerosis. We will highlight the identified glycosphingolipid (SL) antigens of polyreactive remyelination-promoting antibodies and their proposed mechanism(s) of action. The nature of the identified antigens suggests a lipid raft-based mechanism for remyelination-promoting antibodies with SLs as most essential raft components. However, accumulating evidence also suggests involvement of other antigens in stimulation of remyelination, which will be discussed in the text.

Applications of SPR for the characterization of molecules important in the pathogenesis and treatment of neurodegenerative diseases

Characterization of binding kinetics and affinity between a potential drug and its receptor are key steps in the development of new drugs. Among the techniques available to determine binding affinities, surface plasmon resonance has emerged as the gold standard because it can measure binding and dissociation rates in real-time in a label-free fashion. Surface plasmon resonance is now finding applications in the characterization of molecules for treatment of neurodegenerative diseases, characterization of molecules associated with pathogenesis of neurodegenerative diseases and detection of neurodegenerative disease biomarkers. In addition it has been used in the characterization of a new class of natural autoantibodies that have therapeutic potential in a number of neurologic diseases. In this review we will introduce surface plasmon resonance and describe some applications of the technique that pertain to neurodegenerative disorders and their treatment.

Myelin recovery in multiple sclerosis: the challenge of remyelination

Multiple sclerosis (MS) is the most common demyelinating and an autoimmune disease of the central nervous system characterized by immune-mediated myelin and axonal damage, and chronic axonal loss attributable to the absence of myelin sheaths. T cell subsets (Th1, Th2, Th17, CD8⁺, NKT, CD4⁺CD25⁺ T regulatory cells) and B cells are involved in this disorder, thus new MS therapies seek damage prevention by resetting multiple components of the immune system. The currently approved therapies are immunoregulatory and reduce the number and rate of lesion formation but are only partially effective. This review summarizes current understanding of the processes at issue: myelination, demyelination and remyelination—with emphasis upon myelin composition/architecture and oligodendrocyte maturation and differentiation. The translational options target oligodendrocyte protection and myelin repair in animal models and assess their relevance in human. Remyelination may be enhanced by signals that promote myelin formation and repair. The crucial question of why remyelination fails is approached is several ways by examining the role in remyelination of available MS medications and avenues being actively pursued to promote remyelination including: (i) cytokine-based immune-intervention (targeting calpain inhibition), (ii) antigen-based immunomodulation (targeting glycolipid-reactive iNKT cells and sphingoid mediated inflammation) and (iii) recombinant monoclonal antibodies-induced remyelination.

The road to remyelination in demyelinating diseases: current status and prospects for clinical treatment

Within CNS disorders, demyelinating diseases are among the most devastating and cost intensive due to long-term disabilities affecting relatively young patients. Multiple sclerosis, a chronic inflammatory demyelinating disease in which the persistent inhibitory microenvironment of the resident oligodendrocyte precursor cells abrogates regeneration of myelin sheaths, is the most prominent disease in the spectrum of demyelinating diseases. The essential goal is to stimulate creation of new myelin sheaths on the demyelinated axons, leading to restoration of saltatory conduction and resolving functional deficits. The past few decades witnessed significant efforts to understand the cellular interactions at the lesion site with studies suggesting efficient remyelination as a prerequisite for functional repair. Despite its proven efficacy in experimental models, immunosuppression has not had profound clinical consequences in multiple sclerosis, which argued for a paradigm shift in the design of therapeutics aiming to achieve remyelination. For example, targeting oligodendrocytes themselves may drive remyelination in the CNS. This group and others have demonstrated that natural autoreactive antibodies directed at oligodendrocyte progenitors participate in remyelination. Accordingly, the authors developed a recombinant autoreactive natural human IgM antibody with therapeutic potential for remyelination.

Viral models of multiple sclerosis: neurodegeneration and demyelination in mice infected with Theiler's virus

Multiple sclerosis (MS) is a complex inflammatory disease of unknown etiology that affects the central nervous system (CNS) white matter, and for which no effective cure exists. Indeed, whether the primary event in MS pathology affects myelin or axons of the CNS remains unclear. Animal models are necessary to identify the immunopathological mechanisms involved in MS and to develop novel therapeutic and reparative approaches. Specifically, viral models of chronic demyelination and axonal damage have been used to study the contribution of viruses in human MS, and they have led to important breakthroughs in our understanding of MS pathology. The Theiler's murine encephalomyelitis virus (TMEV) model is one of the most commonly used MS models, although other viral models are also used, including neurotropic strains of mouse hepatitis virus (MHV) that induce chronic inflammatory demyelination with similar histological features to those observed in MS. This review will discuss the immunopathological mechanisms involved in TMEV-induced demyelinating disease (TMEV-IDD). The TMEV model reproduces a chronic progressive disease due to the persistence of the virus for the entire lifespan in susceptible mice. The evolution and significance of the axonal damage and neuroinflammation, the importance of epitope spread from viral to myelin epitopes, the presence of abortive remyelination and the existence of a brain pathology in addition to the classical spinal cord demyelination, are some of the findings that will be discussed in the context of this TMEV-IDD model. Despite their limitations, viral models remain an important tool to study the etiology of MS, and to understand the clinical and pathological variability associated with this disease.

Naturally occurring antibodies as therapeutics for neurologic disease: can human monoclonal IgMs replace the limited resource IVIG?

Naturally occurring autoantibodies (NAbs) are common in normal humans. The majority of NAbs are IgMs, but a small proportion are IgGs. Therefore a certain portion of pooled whole human IgG (IVIG) can be considered NAbs. While the applications of IVIG to modulate human disease have increased dramatically, the use of IgMs as drugs has lagged. In fact, much of the contaminating IgM component of IVIG is disposed of as waste. However, a number of model studies, including those targeting Alzheimer and multiple sclerosis (MS) suggest that IgMs may better modulate disease at much lower doses than IVIG. Our own studies in a model of MS show that polyclonal human IgM promotes better remyelination than IVIG and that monoclonal IgMs promote greater remyelination than monoclonal IgGs containing identical variable region sequences. We propose that this difference is due to the ability of IgM to cross link cell surface antigens better than IgGs and induce signals in nervous system cells. Monoclonal antibodies (mAbs) that promote remyelination induce a transient Ca(2+) influx in myelin forming cells, whereas IgGs with identical variable sequences do not. MAbs that promote remyelination were identified in human serum and in EBV-immortalized human B-cell lines obtained from normal adults, fetal cord blood, and rheumatoid arthritis and MS patients. Therefore therapeutic mAbs are present and common in normal circulation. All therapeutic mAbs were IgMs and bound to nervous system cells, however, the tissue binding patterns suggest that binding any one of multiple antigens induces repair. An expression vector was constructed that can manufacture gram quantities of recombinant monoclonal human IgM. Therefore the technology exists to determine whether human monoclonal NAbs can modulate human disease. IVIG can modulate neurologic disease, but using IVIG to treat these chronic diseases is unsustainable. A long-term solution is to identify the functional component of IVIG and test whether a recombinant human monoclonal can replicate its efficacy.

Therapeutics to promote CNS repair: a natural human neuron-binding IgM regulates membrane-raft dynamics and improves motility in a mouse model of multiple sclerosis

We have discovered a role for natural autoantibodies in central nervous system repair, remyelination and axon protection. These natural human antibodies are of the immunoglobulin M (IgM) isotype, and they bind to the surface of neural cells. The epitope of the antibody includes sialic acid because treatment with sialidase disrupts the binding. A fully human recombinant form of one of these IgMs, rHIgM12, has the same properties as the serum-derived IgM. rHIgM12 enhanced polarized axonal outgrowth from primary neurons when presented as a substrate in vitro and improved motor functions in chronically Theiler's virus-infected SJL mice, a model of MS. rHIgM12 bound to neuronal surfaces and induced cholesterol and ganglioside (GM1) clustering, indicating that rHIgM12 functions through a mechanism of axonal membrane stabilization. Our work demonstrates that a natural human neuron-binding IgM can regulate membrane domain dynamics. This antibody has the potential to improve neurologic disease.

Need for a paradigm shift in therapeutic approaches to CNS injury

Irreversible damage to the nervous system can result from many causes including trauma, disruption of blood supply, pathogen infection or neurodegenerative disease. Common features following CNS injury include a disruption of axons, neuron death and injury, local B-cell and microglial activation, and the synthesis of pathogenic autoantibodies. CNS injury results in a pervasive inhibitory microenvironment that hinders regeneration. Current approaches to eliminate the inhibitory environment have met with limited success. These results argue for a paradigm shift in therapeutic approaches to CNS injury. Targeting CNS cells (neurons, oligodendrocytes and astrocytes) themselves may drive CNS repair. For example, our group and others have demonstrated that autoreactive antibodies can participate in aspects of CNS regeneration, including remyelination. We have developed recombinant autoreactive natural human IgM antibodies with the therapeutic potential for CNS repair in several neurologic diseases.

Evidence for the role of B cells and immunoglobulins in the pathogenesis of multiple sclerosis

The pathogenesis of multiple sclerosis (MS) remains elusive. Recent reports advocate greater involvement of B cells and immunoglobulins in the initiation and propagation of MS lesions at different stages of their ontogeny. The key role of B cells and immunoglobulins in pathogenesis was initially identified by studies in which patients whose fulminant attacks of demyelination did not respond to steroids experienced remarkable functional improvement following plasma exchange. The positive response to Rituximab in Phase II clinical trials of relapsing-remitting MS confirms the role of B cells. The critical question is how B cells contribute to MS. In this paper, we discuss both the deleterious and the beneficial roles of B cells and immunoglobulins in MS lesions. We provide alternative hypotheses to explain both damaging and protective antibody responses.

Enhancing CNS repair in neurological disease: challenges arising from neurodegeneration and rewiring of the network

Repair of the central nervous system (CNS) constitutes an integral part of treating neurological disease and plays a crucial role in restoring CNS architecture and function. Distinct strategies have been developed to reconstruct the damaged neural tissue, with many tested preclinically in animal models. We review cell replacement-based repair strategies. By taking spinal cord injury, cerebral ischaemia and degenerative CNS disorders as examples for CNS repair, we discuss progress and potential problems in utilizing embryonic stem cells and adult neural/non-neural stem cells to repair cell loss in the CNS. Nevertheless, CNS repair is not simply a matter of cell transplantation. The major challenge is to induce regenerating neural cells to integrate into the neural network and compensate for damaged neural function. The neural cells confront an environment very different from that of the developmental stage in which these cells differentiate to form interwoven networks. During the repair process, one of the challenges is neurodegeneration, which can develop from interrupted innervations to/from the targets, chronic inflammation, ischaemia, aging or idiopathic neural toxicity. Neurodegeneration, which occurs on the basis of a characteristic vascular and neural web, usually presents as a chronically progressive process with unknown aetiology. Currently, there is no effective treatment to stop or slow down neurodegeneration. Pathological changes from patients with Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis indicate a broken homeostasis in the CNS. We discuss how the blood-brain barrier and neural networks are formed to maintain CNS homeostasis and their contribution to neurodegeneration in diseased conditions. Another challenge is that some inhibitors produced by CNS injury do not facilitate the regenerating neural cells to incorporate into a pre-existing network. We review glial responses to CNS injury. Of note, the reactive astrocytes not only encompass the lesions/pathogens but may also form glial scars to impede regenerating axons from traversing the lesions. In addition, myelin debris can prevent axon growth. Myelination enables saltatory transduction of electrical impulses along axonal calibers and actually provides trophic support to stabilize the axons. Therefore, repair strategies should be designed to promote axonal growth, myelination and modulate astrocytic responses. Finally, we discuss recent progress in developing human monoclonal IgMs that regulate CNS homeostasis and promote neural regeneration.

Method of identifying natural antibodies for remyelination

INTRODUCTION

Natural autoantibodies are part of the normal human immunoglobulin repertoire. These antibodies react to self-antigens, are usually polyreactive with relatively low affinity, and typically are of the IgM isotype. Natural IgMs in mice that stimulated remyelination in central nervous system (CNS) demyelinating disease all shared the characteristics of binding to the surface of live oligodendrocytes and myelinated tracts in living slices of CNS tissue.

METHODS

A screen for human IgMs with similar character resulted in two human natural antibodies, which when injected peripherally into animal models of demyelination induced remyelination. A recombinant human IgM (rHIgM22) that also promoted remyelination in vivo was constructed.

RESULTS

Very small doses of this IgM are required for the promotion of remyelination (EC50 is 460 ng per 20-g mouse). It is clear that after peripheral delivery, rHIgM22 enters the CNS and accumulates in CNS lesions. rHIgM22 was tracked in living mice using ferritin-labeled antihuman mu chain antibodies visualized by magnetic resonance imaging and traditional immunocytochemistry. Although the exact antigen recognized by rHIgM22 is not known, all mouse IgMs that promote remyelination bind to myelin membrane lipids, suggesting the antigen for rHIgM22 is similar.

CONCLUSIONS

We propose that the IgMs bind to CNS cells and reorganize the membrane, initiating a signal that results in oligodendrocyte proliferation and/or protection with an end result of increased myelin. Recombinant natural human antibodies are potentially important therapeutic molecules that may modulate a wide spectrum of human disease.

Natural antibodies, intravenous immunoglobulin and their role in autoimmunity, cancer and inflammation

Natural antibodies are produced by B lymphocytes in the absence of external antigen stimulation. With their ability to recognize self, altered self and foreign antigens, they comprise an important first-line defence against invading pathogens, but are also important for tissue homeostasis. By recognizing oligosaccharides expressed on tumour cells and modified cell surface structures accompanying necrosis, natural antibodies have an important anti-tumorigenic function. IVIg contains a wide spectrum of specificities presented in normal plasma including natural antibodies and has been shown to exert inhibitory effects on tumour cells through a subfraction of anti-vascular endothelial growth factor immunoglobulin (Ig)G antibodies with anti-angiogenic properties. IgA antibodies also have potent immunomodulatory properties, being able to both induce and suppress immune responses. IgA-mediated inhibitory function is able to inhibit several inflammatory diseases including asthma and glomerulonephritis. Autoantibodies of the IgM type, on the other hand, have shown promising results in the treatment of multiple sclerosis. These autoantibodies promote remyelination rather than modulating inflammation. Oxidation-specific epitopes, as found in atherosclerotic lesions and on apoptotic cells, comprise one important target of natural antibodies. By recognizing these epitopes, natural antibodies neutralize proinflammatory responses and mediate atheroprotection.

Molecular and immunogenic features of myelin lipids: incitants or modulators of multiple sclerosis?

Myelin lipids have long been thought to play intriguing roles in the pathogenesis of multiple sclerosis (MS). This review summarizes current understanding of the molecular basis of MS with emphasis on the: (i.) physico-chemical properties, organization and accessibility of the lipids and their distribution within the myelin multilayer; (ii.) characterization of myelin lipid structures, and structure-function relationships relevant to MS mechanisms, and; (iii.) immunogenic and other features of lipids in MS including molecular mimicry, lipid enzyme genetic knockouts, glycolipid-reactive NKT cells, and monoclonal antibody-induced remyelination. New findings associate anti-lipid antibodies with pathophysiological biomarkers and suggest clinical utility. The structure of CD1d-lipid complexed with the lipophilic invariant T cell receptor (iTCR) may be crucial to understanding MS pathogenesis, and design of lipid antigen-specific therapeutics. Novel immuno-modulatory tools for treatment of autoimmune diseases including MS in which there is both constraint of inflammation and stimulation of remyelination are now emerging.

Invited article: human natural autoantibodies in the treatment of neurologic disease

Naturally occurring autoantibodies are molecules that are part of the normal immunoglobulin repertoire. This review focuses on three distinct groups of human monoclonal antibodies (mAb). These are human natural autoantibodies that, when injected into an animal model of human disease, stimulate remyelination in CNS demyelinating diseases, protect neurons and extend neuronal processes in CNS axonal disorders, and activate immune dendritic cells to produce cytotoxic T cells to clear metastatic tumors. Natural autoantibodies react to self antigens and are of relatively low affinity. They are derived from germline immunoglobulin genes and are usually polyreactive. Our experiments demonstrated CNS entry by autoradiography of labeled mAb and by MRI. Remyelinating mAb rHIgM22 clusters beta-integrin and mouse mAb O4 recognizes sulfatide. Neuronal outgrowth mAbs sHIgM42 and sHIgM12 appear to target carbohydrates on the surface of neurons. The mAb sHIgM12 (B7-DC-Xab) also is promising as therapeutic against metastatic tumors. It functions by binding and cross-linking the antigen B7-DC on dendritic cells, inducing tumor-specific cytotoxic T cells. All these mAbs activate a transient increase in intracellular calcium, signal via NFkappab, and prevent apoptosis. The mAbs engage downstream signaling events that induce the primary function of the cell (that is, remyelination for oligodendrocytes, axonal preservation and neurite extension for neurons, or antigen presentation for dendritic cells). Natural human auto mAbs are a potentially important therapeutic technique in combating a wide spectrum of disease processes.

Remyelination in the CNS: from biology to therapy

Remyelination involves reinvesting demyelinated axons with new myelin sheaths. In stark contrast to the situation that follows loss of neurons or axonal damage, remyelination in the CNS can be a highly effective regenerative process. It is mediated by a population of precursor cells called oligodendrocyte precursor cells (OPCs), which are widely distributed throughout the adult CNS. However, despite its efficiency in experimental models and in some clinical diseases, remyelination is often inadequate in demyelinating diseases such as multiple sclerosis (MS), the most common demyelinating disease and a cause of neurological disability in young adults. The failure of remyelination has profound consequences for the health of axons, the progressive and irreversible loss of which accounts for the progressive nature of these diseases. The mechanisms of remyelination therefore provide critical clues for regeneration biologists that help them to determine why remyelination fails in MS and in other demyelinating diseases and how it might be enhanced therapeutically.

Immunization with recombinant Nogo-66 receptor (NgR) promotes axonal regeneration and recovery of function after spinal cord injury in rats

Nogo-66 receptor (NgR), a common receptor for the three known myelin-associated inhibitors, i.e., Nogo-A, myelin-associated glycoprotein (MAG), and oligodendrocyte myelin glycoprotein (OMgp), plays a key role in the failure of axonal regeneration in the adult mammalian central nervous system (CNS). Here we report a novel vaccine approach that stimulates the production of anti-NgR antibody to overcome NgR-mediated growth inhibition after spinal cord injury (SCI). We showed that adult rats immunized with recombinant NgR produced high titers of the anti-NgR antibody and that antisera obtained from the immunized rats promoted neurite outgrowth of rat cerebellar neurons on the inhibitory MAG substrate in vitro. In a spinal cord dorsal hemisection model, NgR immunization promoted regeneration of lesioned corticospinal tract (CST) axons, anterogradely labeled with biotin dextran amine (BDA), beyond the lesion site. In a contusive SCI model, NgR immunization markedly reduced the total lesion volume and improved Basso, Beattie, and Bresnahan (BBB) locomotor rating scale and grid walking performance. Thus, the NgR vaccine approach may represent a promising repair strategy to promote structural and functional recovery following SCI.

Mechanisms and implications of adaptive immune responses after traumatic spinal cord injury

Traumatic spinal cord injury (SCI) in mammals causes widespread glial activation and recruitment to the CNS of innate (e.g. neutrophils, monocytes) and adaptive (e.g. T and B lymphocytes) immune cells. To date, most studies have sought to understand or manipulate the post-traumatic functions of astrocytes, microglia, neutrophils or monocytes. Significantly less is known about the consequences of SCI-induced lymphocyte activation. Yet, emerging data suggest that T and B cells are activated by SCI and play significant roles in shaping post-traumatic inflammation and downstream cascades of neurodegeneration and repair. Here, we provide neurobiologists with a timely review of the mechanisms and implications of SCI-induced lymphocyte activation, including a discussion of different experimental strategies that have been designed to manipulate lymphocyte function for therapeutic gain.

Intravenous polyclonal human immunoglobulins in multiple sclerosis

Intravenous immunoglobulin (IVIG) is an established therapy for demyelinating diseases of the peripheral nervous system. IVIG exerts a number of effects that may be beneficial in multiple sclerosis (MS). Four double-blind IVIG trials have been performed in relapsing-remitting MS. A meta-analysis of the four trials has shown that IVIG reduces the relapse rate and, possibly, disease progression. In patients with a first episode of demyelinating disease, IVIG delays the time to the second relapse and thereby to the diagnosis of definite MS. In patients with an acute MS relapse, IVIG as add-on therapy to methylprednisolone does not make remission of symptoms faster or more complete. IVIG does not seem to be of any benefit to chronic visual or motor symptoms in MS. In secondary progressive MS, IVIG has not shown any effect on disease progression, relapses or new magnetic resonance imaging lesions. Experimental studies in the MS model experimental autoimmune encephalomyelitis in rats demonstrate that IVIG has to be administered at the time of induction of a relapse in order to be effective. In conclusion, IVIG can be considered as a second-line treatment to approved therapies for relapsing-remitting MS, but the ideal dosage of IVIG still needs to be determined. In order to be a first-line treatment for MS, the beneficial effect should be confirmed in a large-scale placebo-controlled survey, or in a study comparing the effect with approved therapies for relapsing-remitting MS using appropriate clinical and magnetic resonance imaging outcome measures.

Remyelination-promoting human IgMs: developing a therapeutic reagent for demyelinating disease

Promoting remyelination following injury to the central nervous system (CNS) promises to be an effective neuroprotective strategy to limit the loss of surviving axons and prevent disability. Studies confirm that multiple sclerosis (MS) and spinal cord injury lesions contain myelinating cells and their progenitors. Recruiting these endogenous cells to remyelinate may be of therapeutic value. This review addresses the use of antibodies reactive to CNS antigens to promote remyelination. Antibody-induced remyelination in a virus-mediated model of chronic spinal cord injury was initially observed in response to treatment with CNS reactive antisera. Monoclonal mouse and human IgMs, which bind to the surface of oligodendrocytes and myelin, were later identified that were functionally equivalent to antisera. A recombinant form of a human remyelination-promoting IgM (rHIgM22) targets areas of CNS injury and promotes maximal remyelination within 5 weeks after a single low dose (25 microg/kg). The IgM isoform of this reparative antibody is required for in vivo function. We hypothesize that the IgM clusters membrane domains and associated signaling molecules on the surface of target cells. Current therapies for MS are designed to modulate inflammation. In contrast, remyelination promoting IgMs are the first potential therapeutic molecules designed to induce tissue repair by acting within the CNS at sites of damage on the cells responsible for myelin synthesis.

Therapeutic vaccination for central nervous system repair

1. Vaccination against infectious agents has been heralded as a triumph in modern medicine and, more recently, cancer vaccines have risen in prominence. The present review looks towards the use of vaccine therapy to attenuate damage after injury to the central nervous system (CNS). 2. Significant debility is associated with brain injury, most commonly occurring as a result of physical trauma or stroke. This end result reflects the inability of neurons and axons to regenerate following injury to the CNS. This unconductive environment is due, in large part, to the presence of myelin and oligodendrocyte-related inhibitors of neurite outgrowth. 3. We review how a vaccine-based approach has been variably used to circumvent this issue and promote axonal regeneration and repair following traumatic injury and other neurodegenerative disorders. In addition, emerging evidence suggests that the immune response to injury in the CNS may be manipulated so as to reduce cellular damage. Vaccine-directed approaches using this concept are also outlined.

A recombinant human IgM promotes myelin repair after a single, very low dose

A recombinant human monoclonal IgM, rHIgM22, promotes the synthesis of new myelin when used to treat several animal models of demyelination. rHIgM22 binds to myelin and the surface of oligodendrocytes and accumulates at central nervous system lesions in vivo. The minimal dose of monoclonal IgM required to promote remyelination has a direct bearing on the proposed mechanism of action. A dose ranging study using rHIgM22 was performed in mice with chronic virus-induced demyelination, a model of chronic progressive multiple sclerosis. The lowest tested dose of rHIgM22 effective at promoting spinal cord remyelination was a single 500-ng intraperitoneal bolus injection. A time course study of spinal cord repair performed in chronically demyelinated mice revealed that remyelination plateaued by 5 weeks following treatment with rHIgM22. Two doses of rHIgM22 spaced 5 weeks apart did not increase the extent of remyelination over a single dose. The half-life of rHIgM22 in the mouse systemic circulation was determined to be 15 hr; the human IgM serum concentration was close to zero by 48 hr following antibody administration. We propose that the specificity of rHIgM22 for myelin on living tissue targets the antibody to demyelinated lesions, initiating a long-term reparative effect on the central nervous system.

Inflammation, demyelination, neurodegeneration and neuroprotection in the pathogenesis of multiple sclerosis

Although axonal loss has been observed in demyelinated multiple sclerosis (MS) lesions, there has been a major focus on understanding mechanisms of demyelination. However, identification of markers for axonal damage and development of new imaging techniques has enabled detection of subtle changes in axonal pathology and revived interest in the neurodegenerative component of MS. Axonal loss is generally accepted as the main determinant of permanent clinical disability. However, the role of axonal loss early in disease or during relapsing-remitting disease is still under investigation, as are the interactions and interdependency between inflammation, demyelination, neurodegeneration and neuroprotection in the pathogenesis of MS.

The neuroprotective role of inflammation in nervous system Injuries

The contribution of inflammation to the pathogenesis of several nervous system disorders has long been established. Other observations, however, indicate that both inflammatory cells and mediators may also have beneficial functions, assisting in repair and recovery processes. There is compelling evidence to indicate that in the injured nervous system, as in other tissues, macrophages are needed at an early stage after injury in order for healing to take place. Likewise, activated T cells of a particular specificity can reduce the spread of damage. This neuroprotective effect of T cells may be caused, at least in part, by the production of neurotrophic factors such as neurotrophin-3 or brain-derived neurotrophic factor. Interestingly, recent findings indicate that immune cells are able to produce a variety of neurotrophic factors which promote neuronal survival and may also mediate anti-inflammatory effects. Numerous cytokines are induced after nervous system injuries. Some cytokines, such as TNF-alpha, IL-1 and IFN-gamma, are well known for their promotion of inflammatory responses. However, these cytokines also have immunosuppressive functions and their subsequent expression also assists in repair or recovery processes, suggesting a dual role for some pro-inflammatory cytokines. This should be clarified, as it may be crucial in the design of therapeutic strategies to target specific cytokine(s). Finally, there is a growing body of evidence to show that autoreactive IgM antibodies may constitute an endogenous system of tissue repair, and therefore prove of value as a therapeutic strategy. Available evidence would appear to indicate that the inflammatory response observed in several neurological conditions is more complex than previously thought. Therefore, the design of more effective therapies depends on a clear delineation of the beneficial and detrimental effects of inflammation.

Cerebrospinal fluid immunoglobulin G promotes oligodendrocyte progenitor cell migration

Multiple sclerosis (MS) is characterized by demyelination of the CNS with associated neurological deficits. Remyelination can occur but is often incomplete. The process of myelin repair requires the proliferation and migration of oligodendrocyte progenitor cells (OPC) into the lesion from the neighboring areas. OPC migration is altered by several factors, including antibodies that bind to OPC surface proteins. We have previously reported elevated anti-OSP/claudin-11 antibodies in the cerebrospinal fluid (CSF) of MS patients and that anti-OSP/claudin-11 antibodies generated in rabbits can inhibit OPC migration. In the study presented here, we investigated the effect of CSF IgG from MS patients and controls on OPC migration in culture. Rat OPC cultured with CSF from MS patients tended to migrate more than those cultured with control CSF, but this did not reach statistical significance. To determine whether the IgG fraction in the CSF influenced migration, we removed it using protein-A sepharose. A dramatic decrease in OPC migration was found in both MS (45 +/- 24 vs.16 +/- 9) and control (40 +/- 19 vs. 22 +/- 13) samples after IgG was removed (P <.05). Anti-OSP/claudin-11 antibody concentration did not significantly correlate with OPC migration. These data demonstrate that CSF IgG promotes OPC migration. Identification of the specific IgG fraction responsible for this effect could lead to novel therapies to promote recovery in MS.

Neuron-binding human monoclonal antibodies support central nervous system neurite extension

Two human IgMs (sHIgM12 and sHIgM42) were identified that supported in vitro central nervous system (CNS) neurite extension equal to the potent neurite stimulatory molecule laminin. Both IgMs bound to multiple cell types in unfixed CNS tissue and to the surface of neurons in culture. Both monoclonal antibodies (mAbs) overrode the inhibitory effect of CNS mouse myelin on granule cell neurite extension. Neither mAb bound to the surface of mature oligodendrocytes or strictly colocalized with myelin proteins. Sialidase treatment eliminated the neuronal surface binding of both mAbs, whereas blocking sphingolipid synthesis with Fumonisin B1 or removing GPI-linked proteins with PIPLC did not. When used as substrates for mixed neuron/glia aggregates, sHIgM12 and sHIgM42 supported robust neurite extension while astrocytes remained in the aggregates. In contrast, laminin supported astrocyte migration and spreading. Human mAbs that support neurite extension are novel factors that may be of use in encouraging axon repair following injury while minimizing glial cell infiltration. Both human mAbs were isolated from individuals with monoclonal gammopathy. Each individual has carried high mAb titers in circulation for years without detriment. sHIgM12 and sHIgM42 are therefore unlikely to be systemically pathogenic.

Remyelination, axonal sparing, and locomotor recovery following transplantation of glial-committed progenitor cells into the MHV model of multiple sclerosis

The behavior and myelinogenic properties of glial cells have been well documented following transplantation into regions of focal experimental demyelination in animal models. However, the ability of glial cell preparations to remyelinate in such models does not necessarily indicate that their transplantation into demyelinated lesions in clinical disease will be successful. One of the precluding factors in this regard is a greater understanding of the environmental conditions that will support transplant-mediated remyelination. In this study, we determined whether the complex and reactive CNS environment of the mouse hepatitis virus (MHV) model of multiple sclerosis (MS) could support transplant-mediated remyelination. Striatal neural precursors derived from postnatal day 1 mice were committed to a glial cell lineage and labeled. Immunohistochemical staining indicated that this population generated >93% glial cells following differentiation in vitro. Transplantation of glial-committed progenitor cells into the T8 spinal cord of MHV-infected mice demonstrating complete hindlimb paralysis resulted in migration of cells up to 12 mm from the implantation site and remyelination of up to 67% of axons. Transplanted-remyelinated animals contained approximately 2× the number of axons within sampled regions of the ventral and lateral columns as compared to non-transplanted animals, suggesting that remyelination is associated with axonal sparing. Furthermore, transplantation resulted in behavioral improvement. This study demonstrates for the first time that transplant-mediated remyelination is possible in the pathogenic environment of the MHV demyelination model and that it is associated with locomotor improvement.

Molecular approaches to spinal cord repair

Axon growth inhibitors associated with myelin and the glial scar contribute to the failure of axon regeneration in the injured adult mammalian central nervous system (CNS). A number of these inhibitors, their receptors, and signaling pathways have been identified. These inhibitors can now be neutralized by a variety of approaches that point to the possibility of developing new therapeutic strategies to stimulate regeneration after spinal cord injury.

Immunization with myelin or recombinant Nogo-66/MAG in alum promotes axon regeneration and sprouting after corticospinal tract lesions in the spinal cord

We have shown previously that immunization with myelin in incomplete Freund's adjuvant (IFA) is able to promote robust regeneration of corticospinal tract fibers in adult mice. In the present study the effectiveness of such immunization with myelin was compared to that of a combination of two axon growth inhibitors in myelin, Nogo-66 (the 66-amino-acid inhibitory region of Nogo-A) and myelin-associated glycoprotein (MAG). The effectiveness of two adjuvants, IFA and aluminum hydroxide (Alum), was also compared, the latter being one that can be used in humans. In addition, larger dorsal overhemisections were made at the lower thoracic level, which resulted in a larger scar. These studies were carried out in SJL/J mice, a mouse strain that is susceptible to autoimmune experimental allergic encephalomyelitis (EAE). None of the immunized mice developed EAE. Long-distance axon regeneration and sprouting of the corticospinal tract was seen in myelin and Nogo-66/MAG immunized mice. Alum was as effective or better than IFA as the adjuvant. Overall, the robustness of axon growth and sprouting was greater in mice immunized with myelin. The abundance of this growth was less than in our earlier work in which smaller lesions were made, pointing to the possible influence of inhibitors in the scar. This work shows, however, that axon growth inhibitors in myelin can be selectively blocked using this immunization approach to promote long-distance axon regeneration in the spinal cord.

The role of intravenous immunoglobulin in the treatment of multiple sclerosis

Intravenous immunoglobulin (IVIG) has several effects on the immune system that could have a beneficial influence on disease processes in multiple sclerosis (MS). Owing to its anti-inflammatory properties, IVIG may be beneficial in the treatment of acute relapses and in prevention of new relapses. By promoting remyelination, IVIG could have a beneficial effect on disability and disease progression. Four double-blind trials in relapsing-remitting MS have demonstrated that IVIG reduces the relapse rate and the number of gadolinium enhancing lesions, and in this respect seems comparable to established therapies in relapsing-remitting MS, i.e. interferon-beta and glatiramer acetate. The doses of IVIG that have been used for treatment in relapsing-remitting have varied 10-fold, and the ideal dosage of IVIG for treating MS still needs to be determined. Three studies have been performed to assess the effect of IVIG on chronic visual impairment or established motor symptoms in MS. None of these trials could confirm that established symptoms in MS can be reversed by IVIG. In secondary progressive MS, a large randomized placebo-controlled trial has recently shown that IVIG is without beneficial effects in this phase of the disease. In conclusion, IVIG is a valuable alternative for treatment of relapsing-remitting MS in patients who do not tolerate or are unwilling to take the approved injectable medications, but additional studies are needed to establish the role of IVIG in the management of multiple sclerosis.

Intravenous immunoglobulins for multiple sclerosis

BACKGROUND

From animal experiments, there is evidence to suggest that intravenous immunoglobulins can reverse some of the disease process of central nervous system demyelination. Subsequently, clinical trials of intravenous immunoglobulins have been conducted in people with multiple sclerosis (MS).

OBJECTIVES

To identify and summarise the evidence that intravenous immunoglobulins are safe and beneficial for people with MS.

SEARCH STRATEGY

We searched the Cochrane Multiple Sclerosis Group trials Register( January 2003) The Cochrane Central Register of Controlled Trials (The Cochrane Library issue 4, 2002), MEDLINE (January 1966 to April 2001), EMBASE (January 1988 to April 2001) and reference lists of articles. We also contacted relevant pharmaceutical companies and authors of identified trials.

SELECTION CRITERIA

Randomised controlled trials of intravenous immunoglobulins for the secondary prevention of relapses and disease progression in MS.

DATA COLLECTION AND ANALYSIS

913 titles and abstracts were obtained from the literature search, and we eventually identified 10 clinical trials. All reviewers agreed on the final dataset for entry into RevMan 4.1, and summarised the results. Study authors were contacted for additional information but no response was obtained.

MAIN RESULTS

Of 913 potential studies, 10 trials were identified with a total of 918 participants, four of which are in progress or awaiting publication. The remaining six trials were suitable for consideration by this review (344 participants). Only two trials met our protocol's inclusion criteria. The four remaining trials were excluded as they did not use outcome measures specified in our review (2 trials, 122 participants), or were of insufficient methodological quality (2 trials, 34 participants). From the two included trials (168 participants) there was a reduction in relapse rate and increased time to first relapse during treatment with intravenous immunoglobulins, but reliable disease progression outcomes were not reported, nor were magnetic resonance imaging (MRI) data available to support clinical information. There may be as many as 574 participants in ongoing or yet to be published trials.

REVIEWER'S CONCLUSIONS

There is some evidence to support use of intravenous immunoglobulins as a preventative treatment for relapses in relapsing remitting MS, but further studies should be performed using MRI and disease progression endpoints. It may be possible to draw more robust conclusions when ongoing or recently completed trials make their data available for review. Two rigorously conducted trials with a total of 122 participants did not demonstrate a positive clinical benefit, but were excluded from this review as they employed outcome measures not specified in our protocol. Immunoglobulins were well tolerated with a less than 5% risk of adverse events in participants in included trials.

Cell transplantation, myelin repair, and multiple sclerosis

A decade ago, therapeutic strategies to remyelinate the CNS in diseases such as multiple sclerosis had much experimental appeal, but translation of laboratory success into clinical treatments appeared to be a long way off. Within the past 12 months, however, the first patients with multiple sclerosis have received intracerebral implants of autologous myelinating cells. Here we review the clinical and biological problems presented by multiple sclerosis disease processes, and the background to the development of myelin-repair strategies. We attempt to highlight those areas where difficulties have yet to be resolved, and draw on various experimental findings to speculate on how remyelinating therapies are likely to develop in the foreseeable future.

Human antibodies accelerate the rate of remyelination following lysolecithin-induced demyelination in mice

Immunoglobulin-based therapies are becoming increasingly common for the treatment of neurologic and autoimmune diseases in humans. In this study, we demonstrate that systemic administration of either polyclonal human immunoglobulins or specific human monoclonal antibodies can accelerate the rate of CNS remyelination following toxin-induced demyelination. Injection of lysolecithin directly into the spinal cord results in focal demyelinated lesions. In contrast to other murine models of demyelinating disease, the mechanism of demyelination following lysolecithin injection is independent of immune system activation, and chronic inflammation at the site of the lesion is minimal. Administration of polyclonal human IgM (pHIgM) or a serum-derived human monoclonal antibody (sHIgM22) resulted in approximately a twofold increase in remyelinating axons when compared to animals treated with saline or with antibodies that do not promote repair. Both pHIgM and sHIgM22 show strong binding to CNS white matter and oligodendrocytes, while antibodies that did not accelerate remyelination do not. This differential staining pattern suggests that enhanced remyelination may result from direct stimulation of oligodendrocyte remyelination by binding to surface receptors on oligodendrocytes or glial progenitor cells. We propose the use of human polyclonal IgM or specific human monoclonal IgM antibodies as potential therapies to enhance myelin repair following CNS injury and disease.

Recruiting the immune response to promote axon regeneration in the injured spinal cord

Myelin contains molecules that can inhibit the growth and regeneration of axons. Neutralizing the activity of these inhibitors can enhance axon regeneration in the adult mammalian central nervous system (CNS). The complexity of the CNS-immune system interactions after CNS trauma is now beginning to be better understood. Recent studies indicate that both cell-mediated and antibody-mediated immune responses can help in promoting axon regeneration after CNS injury. It is hoped that such advances will lead to the development of safe and effective vaccine and cytokine treatments for spinal cord injuries.

Humoral autoimmunity as a mediator of CNS repair

Autoimmune responses directed against the central nervous system (CNS) have generally been considered pathogenic in nature. Although there are several well understood conditions in which this is the case, there is also a growing body of experimental evidence to show that both the cellular and humoral immune responses can promote tissue repair following CNS injury and disease. Our laboratory has used a mouse model of chronic demyelinating disease to characterize a class of polyreactive IgM autoantibodies that react with oligodendrocyte surface antigens and promote myelin repair. By screening a large number of human monoclonal antibodies, we have found that IgM antibodies that react with CNS tissue are relatively common. Autoreactive IgM antibodies might constitute an endogenous system for tissue repair, and therefore these antibodies could be of value as therapeutic reagents.