Variability in the binding of anti-MAG and anti-SGPG antibodies to target antigens in demyelinating neuropathy and IgM paraproteinemia

Waldenström Macroglobulinemia - A State-of-the-Art Review: Part 1: Epidemiology, Pathogenesis, Clinicopathologic Characteristics, Differential Diagnosis, Risk Stratification, and Clinical Problems

Waldenström macroglobulinemia (WM) is an infrequent variant of lymphoma, classified as a B-cell malignancy identified by the presence of IgM paraprotein, infiltration of clonal, small lymphoplasmacytic B cells in the bone marrow, and the MYD88 L265P mutation, which is observed in over 90% of cases. The direct invasion of the malignant cells into tissues like lymph nodes and spleen, along with the immune response related to IgM, can also lead to various health complications, such as cytopenias, hyperviscosity, peripheral neuropathy, amyloidosis, and Bing-Neel syndrome. Chemoimmunotherapy has historically been considered the preferred treatment for WM, wherein the combination of rituximab and nucleoside analogs, alkylating drugs, or proteasome inhibitors has exhibited notable efficacy in inhibiting tumor growth. Recent studies have provided evidence that Bruton Tyrosine Kinase inhibitors (BTKI), either used independently or in conjunction with other drugs, have been shown to be effective and safe in the treatment of WM. The disease is considered to be non-curable, with a median life expectancy of 10 to 12 years.

Update on Intravenous Immunoglobulin in Neurology: Modulating Neuro-autoimmunity, Evolving Factors on Efficacy and Dosing and Challenges on Stopping Chronic IVIg Therapy

In the last 25 years, intravenous immunoglobulin (IVIg) has had a major impact in the successful treatment of previously untreatable or poorly controlled autoimmune neurological disorders. Derived from thousands of healthy donors, IVIg contains IgG1 isotypes of idiotypic antibodies that have the potential to bind pathogenic autoantibodies or cross-react with various antigenic peptides, including proteins conserved among the "common cold"-pre-pandemic coronaviruses; as a result, after IVIg infusions, some of the patients' sera may transiently become positive for various neuronal antibodies, even for anti-SARS-CoV-2, necessitating caution in separating antibodies derived from the infused IVIg or acquired humoral immunity. IVIg exerts multiple effects on the immunoregulatory network by variably affecting autoantibodies, complement activation, FcRn saturation, FcγRIIb receptors, cytokines, and inflammatory mediators. Based on randomized controlled trials, IVIg is approved for the treatment of GBS, CIDP, MMN and dermatomyositis; has been effective in, myasthenia gravis exacerbations, and stiff-person syndrome; and exhibits convincing efficacy in autoimmune epilepsy, neuromyelitis, and autoimmune encephalitis. Recent evidence suggests that polymorphisms in the genes encoding FcRn and FcγRIIB may influence the catabolism of infused IgG or its anti-inflammatory effects, impacting on individualized dosing or efficacy. For chronic maintenance therapy, IVIg and subcutaneous IgG are effective in controlled studies only in CIDP and MMN preventing relapses and axonal loss up to 48 weeks; in practice, however, IVIg is continuously used for years in all the aforementioned neurological conditions, like is a "forever necessary therapy" for maintaining stability, generating challenges on when and how to stop it. Because about 35-40% of patients on chronic therapy do not exhibit objective neurological signs of worsening after stopping IVIg but express subjective symptoms of fatigue, pains, spasms, or a feeling of generalized weakness, a conditioning effect combined with fear that discontinuing chronic therapy may destabilize a multi-year stability status is likely. The dilemmas of continuing chronic therapy, the importance of adjusting dosing and scheduling or periodically stopping IVIg to objectively assess necessity, and concerns in accurately interpreting IVIg-dependency are discussed. Finally, the merit of subcutaneous IgG, the ineffectiveness of IVIg in IgG4-neurological autoimmunities, and genetic factors affecting IVIg dosing and efficacy are addressed.

Antibody testing in neuropathy associated with anti-Myelin-Associated Glycoprotein antibodies: where we are after 40 years

PURPOSE OF REVIEW

The diagnosis of Myelin-Associated Glycoprotein (MAG) neuropathy is based on the presence of elevated titers of IgM anti-MAG antibodies, which are typically associated with IgM monoclonal gammopathy, and a slowly progressive, distal demyelinating phenotype. The condition, however, can be under or over diagnosed in patients with mildly elevated antibody titers, absent monoclonal gammopathy, or an atypical presentation. The purpose of this paper is to examine recent advances in our understanding of the currently available anti-MAG antibody assays, their reliability, and their use in deciding treatment or monitoring the response to therapy.

RECENT FINDINGS

Higher titers of anti-MAG antibodies are more likely to be associated with the typical MAG phenotype or response to therapy. Mildly elevated antibody levels can occur in patients with chronic inflammatory demyelinating polyneuropathy. Testing for cross-reactivity with HNK1 can add to the specificity of the antibody assays. Patients with MAG neuropathy can present with an atypical phenotype and in the absence of a detectable monoclonal gammopathy.

SUMMARY

Assays for anti-MAG antibodies by Enzyme-Linked Immunosorbent Assay can be improved by testing for antibody binding at multiple serum dilutions, the inclusion of antigen-negative microwells as internal controls for each sample, testing for cross-reactivity with HNK1, and formal validation. The diagnosis needs to be considered in patients with demyelinating neuropathy, even in the absence of a monoclonal gammopathy or typical phenotype. The change in antibody levels needs to be considered in evaluating the response to therapy with B-cell depleting agents.

Complement in neurological disorders and emerging complement-targeted therapeutics

The complement system consists of a network of plasma and membrane proteins that modulate tissue homeostasis and contribute to immune surveillance by interacting with the innate and adaptive immune systems. Dysregulation, impairment or inadvertent activation of complement components contribute to the pathogenesis of some autoimmune neurological disorders and could even contribute to neurodegenerative diseases. In this Review, we summarize current knowledge about the main functions of the complement pathways and the involvement of complement in neurological disorders. We describe the complex network of complement proteins that target muscle, the neuromuscular junction, peripheral nerves, the spinal cord or the brain and discuss the autoimmune mechanisms of complement-mediated myopathies, myasthenia, peripheral neuropathies, neuromyelitis and other CNS disorders. We also consider the emerging role of complement in some neurodegenerative diseases, such as Alzheimer disease, amyotrophic lateral sclerosis and even schizophrenia. Finally, we provide an overview of the latest complement-targeted immunotherapies including monoclonal antibodies, fusion proteins and peptidomimetics that have been approved, that are undergoing phase I–III clinical trials or that show promise for the treatment of neurological conditions that respond poorly to existing immunotherapies.

In this Review, Dalakas et al. discuss the complement system, the role it plays in autoimmune neurological disease and neurodegenerative disease, and provide an overview of the latest therapeutics that target complement and that can be used for or have potential in neurological disorders.

Complement has an important physiological role in host immune defences and tissue remodelling.

The physiological role of complement extends to the regulation of synaptic development.

Complement has a key pathophysiological role in autoimmune neurological diseases and mediates the actions of pathogenic autoantibodies, such as acetylcholine receptor antibodies and aquaporin 4 antibodies.

For some autoimmune neurological diseases, such as myasthenia gravis and neuromyelitis optica spectrum disorders, approved complement-targeted treatments are now available.

Complement also seems to be of pathogenic relevance in neurodegenerative diseases such as Alzheimer disease, in which innate immune-driven inflammation is receiving increasing attention.

The field of complement-targeted therapeutics is rapidly expanding, with several FDA-approved agents and others currently in phase II and phase III clinical trials.

Association of variability in antibody binding affinity with a clinical course of anti-MAG neuropathy

Anti-myelin-associated glycoprotein (MAG) neuropathy is mediated by the binding of IgM M-proteins to the human natural killer-1 epitope of several glycoconjugates, including MAG and phosphacan. We recently reported that IgM M-proteins with a higher ratio of anti-phosphacan titer to anti-MAG titer (P/M ratio) were associated with a progressive clinical course. Herein, we investigated the temporal variability of the P/M ratio. The results showed that P/M ratios in worsened cases were significantly increased relative to stable or improved cases. Thus, temporal variability in the specificity of IgM M-proteins may be related to the disease course of anti-MAG neuropathy.

Native versus deglycosylated IgM in anti-MAG neuropathy: Correlation with clinical status - Study of 10 cases

BACKGROUND/PURPOSE

In anti-myelin associated glycoprotein (anti-MAG) neuropathies, there is evidence that anti-MAG antibodies are pathogenic but numerous studies report the absence or a weak correlation between the titers of these antibodies and disease course. In this study we assessed the relationships between MAG and glycosylated moieties located on Fc fragment of IgM anti-MAG.

MATERIAL AND METHODS

IgM were extracted from the serum of 8 patients with anti-MAG neuropathy and in 2 patients with anti-MAG antibodies without anti-MAG neuropathy. Anti-MAG activity was performed with pre- and post-deglycosylated IgM extracts using indirect immunofluorescence (IIF) and ELISA. Sera from 49 patients with IgM monoclonal gammopathy without neurological disease were tested as control group (CG). Results were compared to clinical scores. For 4 patients the affinity constant of IgM with MAG was analyzed pre- and post-deglycosylated, using surface plasmon resonance technology (SPR).

RESULTS

The relationships between MAG and glycosylated moieties of IgM anti-MAG were confirmed by kinetic and immunological assays. Deglycosylation resulted in a decrease in anti-MAG titers. Post-deglycosylation anti-MAG titers trended with changes in IgM titers and allowed quantifying anti-MAG antibodies without a saturation of the testing method. After deglycosylation, the titers better represented pathogenic activity and help to follow a given patient's clinical status prospectively. Six patients from CG (12.2%) had anti-MAG antibody titers over positive threshold: 1000 Bühlmann-Titer-Units (BTU) supporting the hypothesis of neutral intermolecular interactions between IgM and MAG. Deglycosylation allowed distinguishing infra clinical forms from neutral relationships forms, when the titers are weak but this assay remains essentially a diagnostic tool.

Waldenstrom-associated anti-MAG paraprotein polyneuropathy with neurogenic tremor

A 71-year-old female patient presented with a 14-year history of slowly progressive distal limb numbness, paraesthesia and reduced vibration perception, ataxic gait and intentional tremor. Examination revealed with a length-dependent sensory neuropathy. Nerve conduction studies showed a chronic sensorimotor inflammatory demyelinating polyneuropathy. Intravenous immunoglobulin treatment (on two occasions) proved ineffective. Serum electrophoresis showed increased monoclonal IgM with kappa light chains. Anti-myelin-associated glycoprotein (MAG) levels were extremely elevated, >70 000 BTU. Bone marrow biopsy revealed 15%-20% small B cells and positive MYD88 mutation, indicative of Waldenstrom macroglobulinaemia. A diagnosis of Waldenstrom-associated anti-MAG paraprotein neuropathy with intentional (neurogenic) tremor was made. Repeat nerve conduction study showed a severe sensory demyelinating neuropathy with no axonal lesion. Treatment with rituximab was given for 1 month with minimal improvement. Repeat anti-MAG levels dropped to 53 670 BTU, with minimal clinical improvement.

Advances in the diagnosis, immunopathogenesis and therapies of IgM-anti-MAG antibody-mediated neuropathies

Polyneuropathy with immunoglobulin M (IgM) monoclonal gammopathy is the most common paraproteinemic neuropathy, comprising a clinicopathologically and immunologically distinct entity. The clinical spectrum spans from distal paresthesias and mild gait imbalance to more severe sensory ataxia, with falls and a varying degree of distal sensorimotor deficits. In approximately 75% of patients, the monoclonal IgM immunoreacts with myelin-associated glycoprotein (MAG) and sulfoglucuronyl glycosphingolipid (SGPG), or other peripheral nerve glycolipids that serve as antigens. These antibodies are considered pathogenic because IgM and complement are deposited on the myelin sheath, splitting the myelin lamellae, while adoptive transfer of patients’ IgM into susceptible host animals causes sensory ataxia and reproduces the human pathology. In spite of the apparently convincing pathogenicity of these antibodies, the response to immunotherapies remains suboptimal. Clorambuscil, cladibrine, cyclophospamide and intravenous immunoglobulin may help some patients but the benefits are minimal and transient. Open-label studies in >200 patients indicate that rituximab is helpful in 30–50% of these patients, even with long-term benefits, probably by suppressing IgM anti-MAG antibodies or inducing immunoregulatory T cells. Two controlled studies with rituximab did not however meet the primary endpoint, mostly because of the poor sensitivity of the scales used; they did however show statistical improvement in secondary endpoints and improved clinical functions in several patients. This review provides an overview of the clinical phenotypes and immunoreactivity of IgM to glycolipids or glycoproteins of peripheral nerve myelin, summarizes the progress on treatment with rituximab as a promising therapy, discusses the pitfalls of scales used, identifies possible biomarkers of response to therapy and highlights the promising new anti-B cell or target-specific immunotherapies.

The role of human natural killer-1 (HNK-1) carbohydrate in neuronal plasticity and disease

BACKGROUND

The human natural killer-1 (HNK-1) carbohydrate, a unique trisaccharide possessing sulfated glucuronic acid in a non-reducing terminus (HSO₃-3GlcAß1-3Galß1-4GlcNAc-), is highly expressed in the nervous system and its spatiotemporal expression is strictly regulated. Mice deficient in the gene encoding a key enzyme, GlcAT-P, of the HNK-1 biosynthetic pathway exhibit almost complete disappearance of the HNK-1 epitope in the brain, significant reduction of long-term potentiation, and aberration of spatial learning and memory formation. In addition to its physiological roles in higher brain function, the HNK-1 carbohydrate has attracted considerable attention as an autoantigen associated with peripheral demyelinative neuropathy, which relates to IgM paraproteinemia, because of high immunogenicity. It has been suggested, however, that serum autoantibodies in IgM anti-myelin-associated glycoprotein (MAG) antibody-associated neuropathy patients show heterogeneous reactivity to the HNK-1 epitope.

SCOPE OF REVIEW

We have found that structurally distinct HNK-1 epitopes are expressed in specific proteins in the nervous system. Here, we overview the current knowledge of the involvement of these HNK-1 epitopes in the regulation of neural plasticity and discuss the impact of different HNK-1 antigens of anti-MAG neuropathy patients.

MAJOR CONCLUSIONS

We identified the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptor subunit GluA2 and aggrecan as HNK-1 carrier proteins. The HNK-1 epitope on GluA2 and aggrecan regulates neural plasticity in different ways. Furthermore, we found the clinical relationship between reactivity of autoantibodies to the different HNK-1 epitopes and progression of anti-MAG neuropathy.

GENERAL SIGNIFICANCE

The HNK-1 epitope is indispensable for the acquisition of normal neuronal function and can be a good target for the establishment of diagnostic criteria for anti-MAG neuropathy.

Diagnosis and treatment of chronic acquired demyelinating polyneuropathies

Chronic neuropathies are operationally classified as primarily demyelinating or axonal, on the basis of electrodiagnostic or pathological criteria. Demyelinating neuropathies are further classified as hereditary or acquired-this distinction is important, because the acquired neuropathies are immune-mediated and, thus, amenable to treatment. The acquired chronic demyelinating neuropathies include chronic inflammatory demyelinating polyneuropathy (CIDP), neuropathy associated with monoclonal IgM antibodies to myelin-associated glycoprotein (MAG; anti-MAG neuropathy), multifocal motor neuropathy (MMN), and POEMS syndrome. They have characteristic--though overlapping--clinical presentations, are mediated by distinct immune mechanisms, and respond to different therapies. CIDP is the default diagnosis if the neuropathy is demyelinating and no other cause is found. Anti-MAG neuropathy is diagnosed on the basis of the presence of anti-MAG antibodies, MMN is characterized by multifocal weakness and motor conduction blocks, and POEMS syndrome is associated with IgG or IgA λ-type monoclonal gammopathy and osteosclerotic myeloma. The correct diagnosis, however, can be difficult to make in patients with atypical or overlapping presentations, or nondefinitive laboratory studies. First-line treatments include intravenous immunoglobulin (IVIg), corticosteroids or plasmapheresis for CIDP; IVIg for MMN; rituximab for anti-MAG neuropathy; and irradiation or chemotherapy for POEMS syndrome. A correct diagnosis is required for choosing the appropriate treatment, with the aim of preventing progressive neuropathy.

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.

Rituximab in the treatment of peripheral neuropathy associated with monoclonal gammopathy

Peripheral neuropathy associated with immunoglobulin (Ig)M gammopathy and anti-myelin-associated glycoprotein antibodies is frequently treatment-resistant and different treatment regimens carry substantial toxicity and side effects. More recently, the chimeric anti-CD20 monoclonal antibody rituximab has shown benefits in the treatment of peripheral neuropathy associated with IgM gammopathy with a favorable side-effect profile. There are no published reports of its use in the treatment of neuropathy associated with IgG and IgA gammopathies. Rituximab is usually given at 375 mg/m(2) intravenously with four weekly doses that may be repeated after 6-12 months. Large controlled studies are still pending but rituximab is an exciting and promising treatment offering another option in the treatment of peripheral neuropathy associated with IgM monoclonal gammopathy.

Antibody testing in peripheral nerve disorders

The identification of autoantibodies associated with dysimmune neuropathies was a major contribution to the characterization of peripheral nerve disorders, the understanding of their pathophysiology, and the clinical diagnosis of neuropathies. Antibodies directed to GM1, GQ1b, and disyalilated gangliosides, and anti-MAG antibodies are very useful in the diagnosis of acute or chronic motor or sensory-motor neuropathies with or without monoclonal IgM. Anti-onconeural anti-Hu and anti-CV2/CRMP antibodies allow when they are detected the diagnosis of paraneoplastic neuropathies. This chapter focuses on the description of these antibodies as diagnostic markers and on their immunopathogenesis. We give a background overview on the origin of these antibodies, their detection, and review those studies, which clearly show that these antibodies are capable of binding to the target tissues in peripheral nerve and thereby can exert a variety of pathophysiological effects. The corresponding electrophysiological and histological changes observed both in human and animal models are exemplified in order to get a better understanding of the immune mechanisms of these antibody-mediated neuropathies.

The role of sulfoglucuronosyl glycosphingolipids in the pathogenesis of monoclonal IgM paraproteinemia and peripheral neuropathy

In IgM paraproteinemia and peripheral neuropathy, IgM M-protein secretion by B cells leads to a T helper cell response, suggesting that it is antibody-mediated autoimmune disease involving carbohydrate epitopes in myelin sheaths. An immune response against sulfoglucuronosyl glycosphingolipids (SGGLs) is presumed to participate in demyelination or axonal degeneration in the peripheral nervous system (PNS). SGGLs contain a 3-sulfoglucuronic acid residue that interacts with anti-myelin-associated glycoprotein (MAG) and the monoclonal antibody anti-HNK-1. Immunization of animals with sulfoglucuronosyl paragloboside (SGPG) induced anti-SGPG antibodies and sensory neuropathy, which closely resembles the human disease. These animal models might help to understand the disease mechanism and lead to more specific therapeutic strategies. In an in vitro study, destruction or malfunction of the blood-nerve barrier (BNB) was found, resulting in the leakage of circulating antibodies into the PNS parenchyma, which may be considered as the initial key step for development of disease.

Further comparisons of assays for detecting MAG IgM autoantibodies

Anti-MAG antibodies are commonly found in the sera of patients with demyelinating sensorimotor neuropathy and IgM paraproteinemia. Our objective here was to compare MAG results obtained by two different laboratories using similar methods (Western blot, EIA, IFA). Western blot (WB) employing MAG from monkey was less sensitive (72.5%) than myelin IFA (92.5%; monkey nerve) and EIA (97.5%; human MAG) when compared to WB using human MAG and is most likely due to methodology (not antigen source). EIA detected low titers of MAG IgM antibodies in suspected patient sera (negative by other methods) that were also SGPG IgM-positive. Patients having low titers by EIA, but negative by WB may have other autoimmune neuropathies without demyelination.

Myelin-associated glycoprotein (MAG): past, present and beyond

The myelin-associated glycoprotein (MAG) is a type I transmembrane glycoprotein localized in periaxonal Schwann cell and oligodendroglial membranes of myelin sheaths where it functions in glia-axon interactions. It contains five immunoglobulin (Ig)-like domains and is in the sialic acid-binding subgroup of the Ig superfamily. It appears to function both as a ligand for an axonal receptor that is needed for the maintenance of myelinated axons and as a receptor for an axonal signal that promotes the differentiation, maintenance and survival of oligodendrocytes. Its function in the maintenance of myelinated axons may be related to its role as one of the white matter inhibitors of neurite outgrowth acting through a receptor complex involving the Nogo receptor and/or gangliosides containing 2,3-linked sialic acid. MAG is expressed as two developmentally regulated isoforms with different cytoplasmic domains that may activate different signal transduction pathways in myelin-forming cells. MAG contains a carbohydrate epitope shared with other glycoconjugates that is a target antigen in autoimmune peripheral neuropathy associated with IgM gammopathy and has been implicated in a dying back oligodendrogliopathy in multiple sclerosis.

Terminal latency index in neuropathy with antibodies against myelin-associated glycoproteins

Neuropathy with antibodies against myelin-associated glycoproteins (MAG/SGPG-N) and hereditary sensorimotor neuropathy type 1 (HMSN1) are characterized by chronic demyelination with little conduction block. Electrodiagnostic studies suggest that in HMSN1 conduction slowing occurs uniformly along the nerve, whereas in MAG/SGPG-N it is predominantly distal. Some but not all previous reports have shown that the terminal latency index (TLI) was useful to distinguish MAG/SGPG-N from chronic idiopathic demyelinating polyneuropathy. We compared median TLI from 21 patients with MAG/SGPG-N with those obtained from 26 patients with HMSN1, 20 with HMSN2, and 12 healthy volunteers. All patients with TLI <0.26 had MAG/SGPG-N, and all patients with TLI > or =0.32 had HMSN1. In the remaining patients with intermediate TLI values, ulnar distal motor latency (DML) aided in differentiation between MAG/SGPG-N and HMSN1 with an overall sensitivity of 100% and specificity of 98%. In conclusion, median TLI in combination with ulnar DML can further guide the demyelinating neuropathy evaluation toward hereditary or autoimmune causes.

Immunodetection of anti-MAG IgM antibody by cross-reactivity to LA-N-1 neuroblastoma cells

Demyelinating polyneuropathiy associated with IgM paraproteinemia and high titers of anti-MAG IgM antibodies (MAG-PN) is considered different from chronic inflammatory demyelinating polyneuropathy, particularly because of the poorer response to treatment of MAG-PN patients. Therefore, anti-MAG anitbodies may have relevant prognostic value. Available anti-MAG antibody assays require central nervous system myelin proteins from autopsied human brains. This study investigated the feasibility of detecting anti-MAG antibody by immunofluorescence and flow cytometry using a panel of human neuroblastoma cell lines as targets. We report here on the evaluation of the LA-N-1 cell line as an appropriate substrate for the detection of anti-MAG antibody by indirect immunoflourescence.

The use of intravenous immunoglobulin in the treatment of autoimmune neuromuscular diseases: evidence-based indications and safety profile

Intravenous immunoglobulin (i.v.Ig) has multiple actions on the immunoregulatory network that operate in concert with each other. For each autoimmune neuromuscular disease, however, there is a predominant mechanism of action that relates to the underlying immunopathogenetic cause of the respective disorder. The best understood actions of i.v.Ig include the following: (a) modulation of pathogenic autoantibodies, an effect relevant in myasthenia gravis (MG), Lambert-Eaton myasthenic syndrome (LEMS), Guillain-Barré syndrome (GBS), chronic inflammatory demyelinating polyneuropathy (CIDP), and stiff-person syndrome (SPS); (b) inhibition of complement activation and interception of membranolytic attack complex (MAC) formation, an action relevant to the complement-mediated mechanisms involved in GBS, CIDP, MG, and dermatomyositis (DM); (c) modulation of the inhibitory or activation Fc receptors on macrophages invading targeted tissues in nerve and muscle, as seen in CIDP, GBS, and inflammatory myopathies; (d) down-regulation of pathogenic cytokines and adhesion molecules; (e) suppression of T-cell functions; and (f) interference with antigen recognition. Controlled clinical trials have shown that i.v.Ig is effective as first-line therapy in patients with GBS, CIDP, and multifocal motor neuropathy (MMN), and as second-line therapy in DM, MG, LEMS, and SPS. In paraproteinemic IgM anti-MAG (myelin-associated glycoprotein) demyelinating polyneuropathies and inclusion body myositis (IBM), the benefit is variable, marginal, and not statistically significant. i.v.Ig has a remarkably good safety record for long-term administration, however, the following side effects have been observed: mild, infusion-rate-related reactions, such as headaches, myalgia, or fever; moderate but inconsequential events, such as aseptic meningitis and skin rash; and severe, but rare, complications, such as thromboembolic events and renal tubular necrosis. Future studies are needed to (a) find the appropriate dose and frequency of infusions that maintain a response; (b) address pharmacoeconomics, comparing the high cost of i.v.Ig to the cost of the other therapies, which, although less expensive, cause significantly more long-term side effects; (c) determine why some patients respond better than others; and (d) examine the merits of combining i.v.Ig with other immunosuppressive drugs.

Clinical features and pathophysiological basis of sensory neuronopathies (ganglionopathies)

Sensory ganglionopathies have a frequent association with neoplastic disorders (paraneoplastic subacute sensory neuronopathy, or SSN) or dysimmune disorders (Sjögren's syndrome, SS; Miller Fisher syndrome; and Bickerstaff's brainstem encephalitis, BBE), with drugs, such as cisplatin or pyridoxine, and with inherited disorders with degeneration of dorsal root ganglion cells. Unsteady gait and pseudoathetoid movements of the hand are the distinctive signs encountered in these disorders. The chronic disorders are characterized by non-length-dependent abnormalities of sensory nerve action potentials (SNAPs) and differ from other sensory neuropathies in showing a global, rather than distal, decrease in SNAP amplitudes. This review focuses on recent advances in defining the mechanisms involved in sensory ganglionopathies. Specific topics include a summary of their clinical features, pathological findings, and immunopathology. In SSN, early diagnosis by the detection of anti-Hu antibodies and early treatment of the cancer gives the best chance of stabilizing the disorder. In SS sensory ganglionitis, response to treatment has been disappointing, but immunomodulating treatments are emerging. The immunological profile common to BBE and Fisher syndrome supports a common pathogenesis. In toxic sensory neuronopathy, no treatment is available. The differential diagnosis involves separating sensory ganglionopathies from other ataxic polyneuropathies, such as infectious neuropathies, sensory neuropathies with various autoantibodies, and the neuropathies seen in celiac disease.

Different clinical, electrophysiological and immunological features of CIDP associated with paraproteinaemia

Chronic inflammatory demyelinating polyneuropathy (CIDP) is frequently associated with monoclonal gammopathies of undetermined significance (MGUS), Waldenström disease and osteosclerotic myeloma. There are still controversies about the role of these paraproteinaemias in determining the clinical features and the response to treatment of CIDP. We review the clinical, electrophysiological and immunological features and the response to treatment of patients with CIDP associated with paraproteinaemias. The available literature suggest some conclusions: presence of antimyelin-associated glycoprotein (MAG) antibody (Ab) identifies patients with mainly sensory CIDP and low response to treatment; CIDP associated with IgM-paraproteinaemia without anti-MAG Ab probably are similar to CIDP not associated with paraproteinaemia as well as CIDP with IgG- or IgA-MGUS; however, some patients with IgA-MGUS can show features similar to CIDP with IgM paraproteinaemia and anti-MAG Ab. Low response to immunomodulating treatment in patients with mainly motor CIDP should prompt a careful research of an underlying osteosclerotic myeloma.

Serum IgG antibodies to P0 dimer and 35 kDa P0 related protein in neuropathy associated with monoclonal gammopathy

BACKGROUND

Peripheral neuropathies (PN) associated with monoclonal gammopathy (MG) are widely considered as autoimmune disorders, but the putative role of incriminated antigens is still not understood.

OBJECTIVE

Fifty five patients with PN associated with MG were studied to investigate whether new antigens could be found, and to evaluate their relation to clinical manifestations.

METHODS

An immunological study was conducted on patient sera to identify autoreactivities against nerve proteins by western blotting. Antigen proteins were purified and analysed by proteomic tools. Correlation with ultrastrucural and clinical features was then studied.

RESULTS

Of the 55 patients suffering from PN associated with MG, 17 exhibited IgG autoantibodies directed against peripheral nerve proteins of 35, 58, and 60 kDa. N-terminal microsequencing and mass spectrometry analyses of the 35 kDa protein revealed perfect peptidic matching with 47% of the amino acid sequence of P0, whereas the 58 and 60 kDa proteins were identified as the reduced and non-reduced forms of a P0 dimer. Deglycosylation did not affect IgG binding to the 35 kDa P0 related protein, suggesting a peptidic epitope. In contrast, deglycosylation abolished IgG recognition of the P0 dimer protein, so that a carbohydrate moiety may be implicated in the epitope formation. This confirmed the existence of two different types of IgG, one recognising the 58 and 60 kDa proteins and one directed against the 35 kDa protein.

CONCLUSIONS

This is the first report of antibody activity directed against the dimeric association of P0. Although P0 oligomerisation and adhesion properties play a crucial part in the myelin sheath compaction, the pathogenic significance of these autoantibodies needs further investigations to be elucidated.

Microheterogeneity of anti-myelin-associated glycoprotein antibodies

Antibodies to the myelin-associated glycoprotein (MAG) are implicated in the pathogenesis of an acquired demyelinating polyneuropathy. We studied IgM affinity to MAG in 18 patients with anti-MAG antibodies. Binding of sera was tested for anti-MAG immunoreactivity in central nervous system (CNS) by ELISA and in CNS and peripheral nervous system (PNS) by Western blot analysis. Furthermore, immunohistochemical characterization of IgM binding on sural nerve tissue was investigated using the indirect peroxidase method. Western blot analysis revealed that all sera detected MAG in central myelin, but only eight in peripheral myelin. Anti-MAG-IgM-ELISA-titers correlated significantly (p<0.0001) with PNS-Western blot results. By indirect immunoperoxidase immunohistochemistry, 12 sera stained myelin sheaths, while 6 sera showed no staining. These results demonstrate considerable variations in antibody binding strength to MAG between PNS myelin and CNS myelin. The relevance of these differences for the pathogenesis of the neuropathy and clinical impairment remains to be demonstrated.

Antibodies to L-periaxin in sera of patients with peripheral neuropathy produce experimental sensory nerve conduction deficits

L-Periaxin is a PDZ-domain protein localized to the plasma membrane of myelinating Schwann cells and plays a key role in the stabilization of mature myelin in peripheral nerves. Mutations in L-periaxin have recently been described in some patients with demyelinating peripheral neuropathy, suggesting that disruption of L-periaxin function may result in nerve injury. In this study, we report the presence of autoantibodies to L-periaxin in sera from two of 12 patients with diabetes mellitus (type 2)-associated neuropathy and three of 17 patients with IgG monoclonal gammopathy of undetermined significance (MGUS) neuropathy, an autoimmune peripheral nerve disorder. By comparison, anti-L-periaxin antibodies were not present in sera from nine patients with IgM MGUS neuropathy or in sera from 10 healthy control subjects. The effect of anti-L-periaxin serum antibody on peripheral nerve function was tested in vivo by intraneural injection. Sera containing anti-L-periaxin antibody, but not sera from age-matched control subjects, injected into the endoneurium of rat sciatic nerve significantly (p < 0.005, n = 3) attenuated sensory-evoked compound muscle action potential (CMAP) amplitudes in the absence of temporal dispersion. In contrast, motor-evoked CMAP amplitudes and latencies were not affected by intraneural injection of sera containing anti-L-periaxin antibody. Light and electron microscopy of anti-L-periaxin serum-injected nerves showed morphologic evidence of demyelination and axon enlargement. Depleting sera of anti-L-periaxin antibodies neutralized the serum-mediated effects on nerve function and nerve morphology. Together, these data support anti-L-periaxin antibody as the pathologic agent in these serum samples. We suggest that anti-L-periaxin antibodies, when present in sera of patients with IgG MGUS- or diabetes-associated peripheral neuropathy, may elicit sensory nerve conduction deficits.

Elevated serum titers of proinflammatory cytokines and CNS autoantibodies in patients with chronic spinal cord injury

This study characterized the proinflammatory cytokines, interleukin-2 (IL-2) and tumor necrosis factor alpha (TNFalpha), the antiinflammatory cytokines, IL-4 and IL-10, autoantibodies specific for GM1 ganglioside (anti-GM1), IgG and IgM, and myelin-associated glycoprotein (anti-MAG), in the sera of infection-free, chronic (>12 months), traumatically injured SCI patients (n = 24). Healthy able-bodied subjects (n = 26) served as controls. The proinflammatory cytokines and anti-GM1 antibodies were of particular interest as they have been implicated in an autoimmune "channelopathy" component to central and peripheral conduction deficits in various chronic neuroinflammatory diseases. Antibody and cytokine titers were established using enzyme-linked immunosorbent assays (ELISA). The mean anti-GM(1) (IgM) titer value for the SCI group was significantly higher (p < 0.05) than controls. The SCI group also demonstrated significantly higher titers (p < 0.05) of IL-2 and TNF alpha than controls. No differences were found between the SCI group and control group mean levels of IL-4 or IL-10. Overall, the serum of 57% of SCI patients contained increased levels of autoantibodies or proinflammatory cytokines relative to control values. These results provide preliminary support for the hypothesis that chronic immunological activation in the periphery occurs in a subpopulation of chronic SCI patients. It remains to be established whether elevated serum titers of proinflammatory cytokines and autoantibodies against GM1 are beneficial to the patients or whether they are surrogate markers of a channelopathy that compounds the neurological impairment associated with traumatic axonopathy or myelinopathy.

Anti-myelin associated glycoprotein antibodies: variability in patterns of IgM binding to peripheral nerve

We previously found that serums with anti-sulfatide antibodies have several different patterns of binding to neural tissue. In this study, we asked whether serums with anti-myelin associated glycoprotein (MAG) antibodies also have similar variations in patterns of tissue binding. We examined binding to peripheral nerve in 49 serums with IgM anti-MAG antibodies and 13 serums with IgM anti-sulfoglucuronyl paragloboside (SGPG) antibodies but no MAG binding. We correlated patterns of binding with titers of IgM binding to MAG and SGPG measured by ELISA methods. Our results show that IgM in most anti-MAG serums stained areas of non-compact myelin, including the periaxonal and outer myelin membranes and Schmidt-Lanterman incisures. However, other patterns included IgM binding to areas of compact myelin and to non-myelin structures including axons and endoneurial macrophages. IgM in anti-SGPG serums bound to axons or macrophages, but rarely to myelin-related structures. A total of 11/62 (18%) of serums had IgM binding to axons, six with anti-MAG antibodies and five with anti-SGPG antibodies. The majority of these serums (73%) had SGPG titers greater than MAG titers when measured by ELISA. We conclude that anti-MAG serums have several different binding patterns to neural tissue, including axonal binding, especially when anti-MAG antibodies cross-react with SGPG. These different binding patterns may relate to the ability of anti-MAG serum IgM to bind both MAG and SGPG or to other molecules with a sulfated glucuronic acid epitope that are present in peripheral nerve.

Variability in immunohistochemistries of IgM M-proteins binding to sulfated glucuronyl paragloboside

Serum IgMs from 4 of 12 patients with polyneuropathy and IgM M-proteins that bind to sulfated glucuronyl paragloboside (SGPG) strongly immunostained the human peripheral nerve myelin (group A), whereas those from the other eight patients strongly immunostained the cytoplasm of the Schwann cells surrounding the myelin sheath with only weak staining of the myelin (group B). Strong immunostaining of peripheral myelin by IgMs from group A patients may be due to the strong cross-reactivities against P0 and peripheral myelin protein-22 (PMP-22), which are localized in compact myelin. Only three patients (all in group B) showed some response to the immunotherapies. Weak reactivities to P0 and and PMP-22 might indicate the possibility of improvement after the immunotherapies.

Treatment experience in patients with anti-myelin-associated glycoprotein neuropathy

We report our experience with 24 consecutively treated patients (15 men and 9 women, median age 64 years) with anti-myelin-associated glycoprotein (anti-MAG) neuropathy. The rates of response to plasma exchange (40%), immune globulin (16%), and cyclophosphamide-based therapy (36%) were similar. Five (24%) responded to the first treatment modality, 32% to a second, alternative modality, and 31% to a third. Only 4 of 12 responders had sustained improvement; the others relapsed after a median of 7 months. In those 4 patients, the median immunoglobulin M (IgM) level dropped by 25% compared to an increase of 24% in the nonresponders (P = 0.04). Thus, most patients with anti-MAG neuropathy failed to have sustained improvement after treatment, and none of the therapies emerged as superior. Disability improved transiently after therapy in approximately 50% of cases. A 25% reduction of the IgM level predicted sustained improvement, but was difficult to achieve. There were no clinical or electrodiagnostic features associated with a treatment response, nor did a reduction of the anti-MAG antibody titer correlate with clinical improvement.

EFNS task force report: a questionnaire-based survey on the service provision and quality assurance for determination of diagnostic autoantibody tests in European neuroimmunology centres. European Federation of Neurological Societies

Autoantibodies to a wide variety of neural components are frequently sought in the sera of patients with neurological diseases suspected to have an antibody-associated autoimmune basis. Variations in assay methodology and availability are likely to exist throughout European diagnostic immunology centres, and interlaboratory discrepancies in performance for some assays have been reported. The availability of quality assurance is largely unknown. In this questionnaire-based EFNS task force, all 18 national representatives of the Neuroimmunology Panel within the EFNS were invited to estimate the service provision within their country; 12 panel members responded. From these responses, it emerged that a range of assays are being performed throughout European centres, involving over 20 separate antigens, using a broad array of immunodetection techniques. With the exception of the estimation of anti-AChR antibodies for the diagnosis of myasthenia gravis, no systematic quality assurance schemes are available, this being conducted on an ad hoc basis, or not at all. Since quality is a central component of assay sensitivity and specificity, we conclude that there is an urgent need to introduce pan-European quality assurance schemes, based on provision of positive and negative test sera from a central source, and in which all neuroimmunology laboratories should participate.

The role of antiglycolipid antibodies in peripheral neuropathies

The role of antiglycolipid antibodies in peripheral neuropathy continues to be defined in terms of clinical-serological associations and innovative experimental work establishing the role of these antibodies in pathogenesis. The present review focuses on the major developments in this field over the past 12 months.

Structure of a major oligosaccharide of PASII/PMP22 glycoprotein in bovine peripheral nerve myelin

The amino acid sequence of the glycopeptide obtained from bovine PASII/PMP22 protein in the PNS myelin was determined to be Gln-Asn-Cys-Ser-Thr, where the asparagine was glycosylated. To eliminate all the contaminated P(o) glycopeptides from the PASII/PMP22 glycopeptide preparation, we used a fluorescent probe, N-[2-(2-pyridylamino)ethyl]maleimide, which reacts with the cysteine of the PASII/PMP22 glycopeptides. The labeled PASII/PMP22 glycopeptides were isolated by HPLC and were digested further with glycopeptidase A. The resultant oligosaccharides were conjugated with 2-aminopyridine (PA) as a fluorescent tag. One major PA-oligosaccharide, OPPE1, was purified by HPLC. The structure of OPPE1 was elucidated by fast atom bombardment mass spectrometry and (1)H-NMR studies and comparing the derivatives of PA-OPPE1 and PA-oligosaccharides of gamma-globulin on HPLC. The structure, SO(4)-3GlcAbeta1-3Galbeta1-4GlcNAcbeta1-2Manalpha1+ ++-6(GlcNAcbeta1-4) (GlcNAcbeta1-2Manalpha1-3)Manbeta1-4GlcNAcbeta1- 4(Fucalpha1-6)GlcNAc- PA, was identical to the pyridylaminated form of the major oligosaccharide D8 of bovine P(o) previously reported.

Intravenous immunoglobulin in the treatment of autoimmune neuromuscular diseases: present status and practical therapeutic guidelines

This review summarizes the current status of intravenous immunoglobulin (IVIg) in the treatment of autoimmune neuromuscular disorders and the possible mechanisms of action of the drug based on work in vivo, in vitro, and in animal models. Supply of idiotypic antibodies, suppression of antibody production, or acceleration of catabolism of immunoglobulin G (IgG) are relevant in explaining the efficacy of IVIg in myasthenia gravis (MG), Lambert-Eaton myasthenic syndrome (LEMS), and antibody-mediated neuropathies. Suppression of pathogenic cytokines has putative relevance in inflammatory myopathies and demyelinating neuropathies. Inhibition of complement binding and prevention of membranolytic attack complex (MAC) formation are relevant in dermatomyositis (DM), Guillain-Barré syndrome (GBS), and MG. Modulation of Fc receptors or T-cell function is relevant in chronic inflammatory demyelinating polyneuropathy (CIDP), GBS, and inflammatory myopathies. The clinical efficacy of IVIg, based on controlled clinical trials conducted in patients with GBS, CIDP, multifocal motor neuropathy (MMN), DM, MG, LEMS, paraproteinemic IgM anti-myelin-associated glycoprotein (anti-MAG) demyelinating polyneuropathies, and inclusion body myositis is summarized and practical issues related to each disorder are addressed. The present role of IVIg therapy in other disorders based on small controlled or uncontrolled trials is also summarized. Finally, safety issues, risk factors, adverse reactions, spurious results or serological tests, and practical guidelines associated with the administration of IVIg in the treatment of neuromuscular disorders are presented.

Autoantibodies associated with peripheral neuropathy

High titers of serum antibodies to neural antigens occur in several forms of neuropathy. These include neuropathies associated with monoclonal gammopathy, inflammatory polyneuropathies, and paraneoplastic neuropathies. The antibodies frequently react with glycosylated cell surface molecules, including glycolipids, glycoproteins, and glycosaminoglycans, but antibodies to intracellular proteins have also been described. There are several correlations between antibody specificity and clinical symptoms, such as anti-MAG antibodies with demyelinating sensory or sensorimotor neuropathy, anti-GM1 ganglioside antibodies with motor nerve disorders, antibodies to gangliosides containing disialosyl moieties with sensory ataxic neuropathy and Miller-Fisher syndrome, and antibodies to the neuronal nuclear Hu antigens with paraneoplastic sensory neuronopathy. These correlations suggest that the neuropathies may be caused by the antibodies, but evidence for a causal relationship is stronger in some examples than others. In this review, we discuss the origins of the antibodies, evidence for and against their involvement in pathogenic mechanisms, and the implications of these findings for therapy.