Clinical and Laboratory Features in Anti-NF155 Autoimmune Nodopathy.

BACKGROUND AND OBJECTIVES: To study the clinical and laboratory features of antineurofascin-155 (NF155)-positive autoimmune nodopathy (AN). METHODS: Patients with anti-NF155 antibodies detected on routine immunologic testing were included. Clinical characteristics, treatment response, and functional scales (modified Rankin Scale [mRS] and Inflammatory Rasch-built Overall Disability Scale [I-RODS]) were retrospectively collected at baseline and at the follow-up. Autoantibody and neurofilament light (NfL) chain levels were analyzed at baseline and at the follow-up. RESULTS: Forty NF155+ patients with AN were included. Mean age at onset was 42.4 years. Patients presented with a progressive (75%), sensory motor (87.5%), and symmetric distal-predominant weakness in upper (97.2%) and lower extremities (94.5%), with tremor and ataxia (75%). Patients received a median of 3 (2-4) different treatments in 46 months of median follow-up. Response to IV immunoglobulin (86.8%) or steroids (72.2%) was poor in most patients, whereas 77.3% responded to rituximab. HLA-DRB1*15 was detected in 91.3% of patients. IgG4 anti-NF155 antibodies were predominant in all patients; anti-NF155 titers correlated with mRS within the same patient (r = 0.41, p = 0.004). Serum NfL (sNfL) levels were higher in anti-NF155+ AN than in healthy controls (36.47 vs 7.56 pg/mL, p < 0.001) and correlated with anti-NF155 titers (r = 0.43, p = 0.001), with I-RODS at baseline (r = -0.88, p < 0.001) and with maximum I-RODS achieved (r = -0.58, p = 0.01). Anti-NF155 titers and sNfL levels decreased in all rituximab-treated patients. DISCUSSION: Anti-NF155 AN presents a distinct clinical profile and good response to rituximab. Autoantibody titers and sNfL are useful to monitor disease status in these patients. The use of untagged-NF155 plasmids minimizes the detection of false anti-NF155+ cases. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that anti-NF155 antibodies associate with a specific phenotype and response to rituximab.

Anti-MAG neuropathy: From biology to clinical management.

The acquired chronic demyelinating neuropathies include a growing number of disease entities that have characteristic, often overlapping, clinical presentations, mediated by distinct immune mechanisms, and responding to different therapies. After the discovery in the early 1980s, that the myelin associated glycoprotein (MAG) is a target antigen in an autoimmune demyelinating neuropathy, assays to measure the presence of anti-MAG antibodies were used as the basis to diagnose the anti-MAG neuropathy. The route was open for describing the clinical characteristics of this new entity as a chronic distal large fiber sensorimotor neuropathy, for studying its pathogenesis and devising specific treatment strategies. The initial use of chemotherapeutic agents was replaced by the introduction in the late 1990s of rituximab, a monoclonal antibody against CD20+ B-cells. Since then, other anti-B cells agents have been introduced. Recently a novel antigen-specific immunotherapy neutralizing the anti-MAG antibodies with a carbohydrate-based ligand mimicking the natural HNK-1 glycoepitope has been described.

Antibodies against nodo-paranodal proteins are not present in genetic neuropathies.

OBJECTIVE: To study the presence of nodal and paranodal immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies in patients with genetic neuropathies. METHODS: A total of 108 patients with genetic neuropathies from 3 different centers were included. The presence of IgG and IgM antibodies against neurofascin-155 (NF155), nodal neurofascin (NF186 and NF140), and contactin-1 (CNTN1) were investigated with a cell-based assay (CBA) using immunocytochemistry in transfected HEK293 cells. Sera with positive or uncertain results were further tested by ELISA and immunohistochemistry in pig teased-nerve fibers. RESULTS: Six patients with Charcot-Marie-Tooth disease (CMT) had an uncertain staining pattern for IgM against nodal neurofascin that was not confirmed by ELISA. Two patients with CMT had an uncertain staining pattern for IgG against nodal neurofascin that was not confirmed by ELISA or immunohistochemistry. One patient with CMT with a confirmed GJB1 mutation tested positive for IgG against NF155 by CBA and ELISA (1/900), but was not confirmed by immunohistochemistry and was ultimately classified as negative. CONCLUSIONS: Antibodies against nodal or paranodal antigens were not detected in our cohort of patients with CMT, as previously reported. Some patients may falsely test positive for any of the techniques; confirmatory techniques should be incorporated into the routine testing.

Anti-neurofascin autoantibody and demyelination.

Demyelination diseases involving the central and peripheral nervous systems are etiologically heterogeneous with both cell-mediated and humoral immunities playing pathogenic roles. Recently, autoantibodies against nodal and paranodal proteins, such as neurofascin186 (NF186), neurofascin155 (NF155), contactin-1 (CNTN1), contactin-associated protein 1 (CASPR1) and gliomedin, have been discovered in not only chronic demyelinating conditions, such as multiple sclerosis (MS) and chronic inflammatory demyelinating polyradiculoneuropathy, but also in acute demyelinating conditions, such as Guillain-Barré syndrome. Only a minority of these patients harbor anti-nodal/paranodal protein antibodies; however, these autoantibodies, especially IgG4 subclass autoantibodies to paranodal proteins, are associated with unique features and these conditions are collectively termed nodopathy or paranodopathy. Establishing a concept of IgG4-related nodopathy/paranodopathy contributes to diagnosis and treatment strategy because IgG4 autoantibody-related neurological diseases are often refractory to conventional immunotherapies. IgG4 does not fix complements, or internalize the target antigens, because IgG4 exists in a monovalent bispecific form in vivo. IgG4 autoantibodies can bock protein-protein interaction. Thus, the primary role of IgG4 anti-paranodal protein antibodies may be blockade of interactions between NF155 and CNTN1/CASPR1, leading to conduction failure, which is consistent with the sural nerve pathology presenting paranodal terminal loop detachment from axons with intact internodes in the absence of inflammation. However, it still remains to be elucidated how these autoantibodies belonging to the same IgG4 subclass can cause each IgG4 autoantibody-specific manifestation. Another important issue is to clarify the mechanism by which IgG4 antibodies to nodal/paranodal proteins emerge. IgG4 antibodies develop on chronic antigenic stimulation and can block antibodies that alleviate allergic inflammation by interfering with the binding of allergen-specific IgE to allergens. Thus, environmental antigens cross-reacting with nodal and paranodal proteins may warrant future study.

Autoantibodies Against the Node of Ranvier in Seropositive Chronic Inflammatory Demyelinating Polyneuropathy: Diagnostic, Pathogenic, and Therapeutic Relevance.

Discovery of disease-associated autoantibodies has transformed the clinical management of a variety of neurological disorders. Detection of autoantibodies aids diagnosis and allows patient stratification resulting in treatment optimization. In the last years, a set of autoantibodies against proteins located at the node of Ranvier has been identified in patients with chronic inflammatory demyelinating polyneuropathy (CIDP). These antibodies target neurofascin, contactin1, or contactin-associated protein 1, and we propose to name CIDP patients with these antibodies collectively as seropositive. They have unique clinical characteristics that differ from seronegative CIDP. Moreover, there is compelling evidence that autoantibodies are relevant for the pathogenesis. In this article, we review the current knowledge on the characteristics of autoantibodies against the node of Ranvier proteins and their clinical relevance in CIDP. We start with a description of the structure of the node of Ranvier followed by a summary of assays used to identify seropositive patients; and then, we describe clinical features and characteristics linked to seropositivity. We review knowledge on the role of these autoantibodies for the pathogenesis with relevance for the emerging concept of nodopathy/paranodopathy and summarize the treatment implications.

Nodes, paranodes and neuropathies.

This review summarises recent evidence supporting the involvement of the specialised nodal and perinodal domains (the paranode and juxtaparanode) of myelinated axons in the pathology of acquired, inflammatory, peripheral neuropathies.The identification of new target antigens in the inflammatory neuropathies heralds a revolution in diagnosis, and has already begun to inform increasingly targeted and individualised therapies. Rapid progress in our basic understanding of the highly specialised nodal regions of peripheral nerves serves to strengthen the links between their unique microstructural identities, functions and pathologies. In this context, the detection of autoantibodies directed against nodal and perinodal targets is likely to be of increasing clinical importance. Antiganglioside antibodies have long been used in clinical practice as diagnostic serum biomarkers, and associate with specific clinical variants but not to the common forms of either acute or chronic demyelinating autoimmune neuropathy. It is now apparent that antibodies directed against several region-specific cell adhesion molecules, including neurofascin, contactin and contactin-associated protein, can be linked to phenotypically distinct peripheral neuropathies. Importantly, the immunological characteristics of these antibodies facilitate the prediction of treatment responsiveness.

ARTHUR ASBURY LECTURE: Chronic inflammatory demyelinating polyradiculoneuropathy: clinical aspects and new animal models of auto-immunity to nodal components.

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an autoimmune disorder of the peripheral nerves with clinical and immunological heterogeneity. Both cellular and humoral immune mechanisms against peripheral nerve antigens are considered to contribute to the pathogenesis of the disorder. Currently, the diagnosis of CIDP is based on clinical, laboratory and electrophysiological criteria. The field of CIDP recently underwent a major change with the identification of autoantibodies directed against paranodal (CNTN1, CASPR1 and NF155) and nodal (NF186/140) proteins. Over the last 5 years, correlations have been found between these autoantibodies and CIDP clinical subtypes including the likelihood of response to specific immunotherapies. Additionally, during this time a series of experimental studies have unraveled the underlying immunopathogenesis for CNTN1 and NF155 antibody associated CIDP. Although paranodal and nodal autoantibodies are only found in a small subset of patients with CIDP, the detection of these immune biomarkers should be incorporated in the evaluation of patients, considering the implications of their presence on prognosis, follow-up, and treatment decisions.

Autoantibodies in chronic inflammatory neuropathies: diagnostic and therapeutic implications.

The chronic inflammatory neuropathies (CINs) are rare, very disabling autoimmune disorders that generally respond well to immune therapies such as intravenous immunoglobulin (IVIg). The most common forms of CIN are chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), multifocal motor neuropathy, and polyneuropathy associated with monoclonal gammopathy of unknown significance. The field of CIN has undergone a major advance with the identification of IgG4 autoantibodies directed against paranodal proteins in patients with CIDP. Although these autoantibodies are only found in a small subset of patients with CIDP, they can be used to guide therapeutic decision-making, as these patients have a poor response to IVIg. These observations provide proof of concept that identifying the target antigens in tissue-specific antibody-mediated autoimmune diseases is important, not only to understand their underlying pathogenic mechanisms, but also to correctly diagnose and treat affected patients. This state-of-the-art Review focuses on the role of autoantibodies against nodes of Ranvier in CIDP, a clinically relevant emerging field of research. The role of autoantibodies in other immune-mediated neuropathies, including other forms of CIN, primary autoimmune neuropathies, neoplasms, and systemic diseases that resemble CIN, are also discussed.

Autoantibodies to nodal isoforms of neurofascin in chronic inflammatory demyelinating polyneuropathy.

Chronic inflammatory demyelination polyneuropathy is a heterogeneous and treatable immune-mediated disorder that lacks biomarkers to support diagnosis. Recent evidence indicates that paranodal proteins (contactin 1, contactin-associated protein 1, and neurofascin-155) are the targets of autoantibodies in subsets of patients showing distinct clinical presentations. Here, we identified neurofascin-186 and neurofascin-140 as the main targets of autoantibodies in five patients presenting IgG reactivity against the nodes of Ranvier. Four patients displayed predominantly IgG4 antibodies, and one patient presented IgG3 antibodies that activated the complement pathway in vitro. These patients present distinct clinical features compared to those with anti-neurofascin-155 IgG4. Most patients had a severe phenotype associated with conduction block or decreased distal motor amplitude. Four patients had a subacute-onset and sensory ataxia. Two patients presented with nephrotic syndromes and one patient with an IgG4-related retroperitoneal fibrosis. Intravenous immunoglobulin and corticosteroids were effective in three patients, and one patient remitted following rituximab treatment. Clinical remission was associated with autoantibody depletion and with recovery of conduction block and distal motor amplitude suggesting a nodo-paranodopathy. Our data demonstrate that the pathogenic mechanisms responsible for chronic inflammatory demyelination polyneuropathy are broad and may include dysfunctions at the nodes of Ranvier in a subgroup of patients.

Paranodal dissection in chronic inflammatory demyelinating polyneuropathy with anti-neurofascin-155 and anti-contactin-1 antibodies.

OBJECTIVE: To investigate the morphological features of chronic inflammatory demyelinating polyneuropathy (CIDP) with autoantibodies directed against paranodal junctional molecules, particularly focusing on the fine structures of the paranodes. METHODS: We assessed sural nerve biopsy specimens obtained from 9 patients with CIDP with anti-neurofascin-155 antibodies and 1 patient with anti-contactin-1 antibodies. 13 patients with CIDP without these antibodies were also examined to compare pathological findings. RESULTS: Characteristic light and electron microscopy findings in transverse sections from patients with anti-neurofascin-155 and anti-contactin-1 antibodies indicated a slight reduction in myelinated fibre density, with scattered myelin ovoids, and the absence of macrophage-mediated demyelination or onion bulbs. Teased-fibre preparations revealed that segmental demyelination tended to be found in patients with relatively higher frequencies of axonal degeneration and was tandemly found at consecutive nodes of Ranvier in a single fibre. Assessment of longitudinal sections by electron microscopy revealed that detachment of terminal myelin loops from the axolemma was frequently found at the paranode in patients with anti-neurofascin-155 and anti-contactin-1 antibody-positive CIDP compared with patients with antibody-negative CIDP. Patients with anti-neurofascin-155 antibodies showed a positive correlation between the frequencies of axo-glial detachment at the paranode and axonal degeneration, as assessed by teased-fibre preparations (p<0.05). CONCLUSIONS: Paranodal dissection without classical macrophage-mediated demyelination is the characteristic feature of patients with CIDP with autoantibodies to paranodal axo-glial junctional molecules.

Contactin-1 IgG4 antibodies cause paranode dismantling and conduction defects.

Paranodal axoglial junctions formed by the association of contactin-1, contactin-associated protein 1, and neurofascin-155, play important functions in nerve impulse propagation along myelinated axons. Autoantibodies to contactin-1 and neurofascin-155 define chronic inflammatory demyelinating polyradiculoneuropathy subsets of patients with specific clinical features. These autoantibodies are mostly of the IgG4 isotype, but their pathogenicity has not been proven. Here, we investigated the mechanisms how IgG subclasses to contactin-1 affect conduction. We show that purified anti-contactin-1 IgG1 and IgG4 bind to paranodes. To determine whether these isotypes can pass the paranodal barrier, we incubated isolated sciatic nerves with the purified antibody or performed intraneural injections. We found that IgG4 diffused into the paranodal regions in vitro or after intraneural injections. IgG4 infiltration was slow and progressive. In 24 h, IgG4 accessed the paranode borders near the nodal lumen, and completely fill the paranodal segments by 3 days. By contrast, control IgG, anti-contactin-1 IgG1, or even anti-contactin-associated-protein-2 IgG4 did not pass the paranodal barrier. To determine whether chronic exposure to these antibodies is pathogenic, we passively transferred anti-contactin-1 IgG1 and IgG4 into Lewis rats immunized with P2 peptide. IgG4 to contactin-1, but not IgG1, induced progressive clinical deteriorations combined with gait ataxia. No demyelination, axonal degeneration, or immune infiltration were observed. Instead, these animals presented a selective loss of the paranodal specialization in motor neurons characterized by the disappearance of the contactin-associated protein 1/contactin-1/neurofascin-155 complex at paranodes. Paranode destruction did not affect nodal specialization, but resulted in a moderate node lengthening. The sensory nerves and dorsal root ganglion were not affected in these animals. Electrophysiological examination further supported these results and revealed strong nerve activity loss affecting predominantly small diameter or slow conducting motor axons. These deficits partly matched with those found in patients: proximal motor involvement, gait ataxia, and a demyelinating neuropathy that showed early axonal features. The animal model thus seemed to replicate the early deteriorations in these patients and pointed out that paranodal loss in mature fibres results in conduction defects, but not conduction slowing. Our findings indicate that IgG4 directed against contactin-1 are pathogenic and are reliable biomarkers of a specific subset of chronic inflammatory demyelinating polyneuropathy patients. These antibodies appear to loosen the paranodal barrier, thereby favouring antibody progression and causing paranodal collapse.

Paranodal and other autoantibodies in chronic inflammatory neuropathies.

PURPOSE OF REVIEW: Autoimmune disorders of the peripheral nerves are diverse and heterogeneous. T cells, macrophages, and autoantibodies have been implicated in their pathogenesis. Autoantibodies to peripheral nerve molecules seem to play a role not only in the pathogenesis but provide diagnostic, prognostic, and therapeutic help. We review the state of the art and most relevant recent findings regarding autoantibodies in chronic inflammatory neuropathies, focusing on their clinical utility. RECENT FINDINGS: Research on autoantibodies in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) has received a recent boost with the description of antibodies against proteins of the node of Ranvier. Antibodies of the IgG4 isotype targeting the paranodal proteins contactin-1 (CNTN1) and neurofascin-155 (NF155) define specific CIDP subtypes and have diagnostic and prognostic implications. In multifocal motor neuropathy, anti-GM1 production is restricted to very few B-cell clones that could be the target of therapies aimed to remove or inactivate them. Moreover, novel ELISA and glycoarray techniques combining GM1 and galactocerebroside gangliosides improved the sensitivity of autoantibody detection. Detailed clinical and paraclinical features, including autoantibody reactivity patters, of autoimmune syndromes affecting simultaneously the central and peripheral nervous systems, are also described. SUMMARY: The heterogeneity of chronic inflammatory neuropathies is being unraveled with the description of specific autoantibodies and their association with small disease subtypes. The recently described paranodal autoantibodies anti-CNTN1 and NF155 have direct clinical value and seem to determine response to treatment. Further studies are needed to fully understand the primary contribution of the antibodies to the pathophysiology of the immune neuropathies.

Destruction of paranodal architecture in inflammatory neuropathy with anti-contactin-1 autoantibodies.

OBJECTIVE: Autoantibodies against paranodal proteins have been described in patients with inflammatory neuropathies, but their association with pathology of nodes of Ranvier is unclear. We describe the clinical phenotype and histopathological changes of paranodal architecture of patients with autoantibodies against contactin-1, identified from a cohort with chronic inflammatory demyelinating polyradiculoneuropathy (n=53) and Guillain-Barré syndrome (n=21). METHODS: We used ELISA to detect autoantibodies against contactin-1. Specificity of the autoantibodies was confirmed by immunoblot assay, binding to contactin-1-transfected human embryonic kidney cells, binding to paranodes of murine teased fibres and preabsorption experiments. Paranodal pathology was investigated by immunofluorescence labelling of dermal myelinated fibres. RESULTS: High reactivity to contactin-1 by ELISA was found in four patients with chronic inflammatory demyelinating polyradiculoneuropathy and in none of the patients with Guillain-Barré syndrome, which was confirmed by cell binding assays in all four patients. The four patients presented with a typical clinical picture, namely acute onset of disease and severe motor symptoms, with three patients manifesting action tremor. Immunofluorescence-labelling of paranodal proteins of dermal myelinated fibres revealed disruption of paranodal architecture. Semithin sections showed axonal damage but no classical signs of demyelination. INTERPRETATION: We conclude that anti-contactin-1-related neuropathy constitutes a presumably autoantibody-mediated form of inflammatory neuropathy with distinct clinical symptoms and disruption of paranodal architecture as a pathological correlate. Anti-contactin-1-associated neuropathy does not meet morphological criteria of demyelinating neuropathy and therefore, might rather be termed a 'paranodopathy' rather than a subtype of demyelinating inflammatory neuropathy.

The node of Ranvier in multifocal motor neuropathy.

Multifocal motor neuropathy affects myelinated motor axons in limb nerves at multifocal sites. It is characterized by weakness and muscle atrophy, motor conduction block, and antibodies against ganglioside GM1 which is expressed on the axolemma of nodes of Ranvier and perinodal Schwann cells. Treatment by regular IVIg courses results in temporary improvement but cannot prevent slowly progressing weakness due to axonal degeneration. This review discusses possible mechanisms of conduction block and the reasons why motor axons are selectively affected in this disorder.

Axonal Guillain-Barré syndrome: concepts and controversies.

Acute motor axonal neuropathy (AMAN) is a pure motor axonal subtype of Guillain-Barré syndrome (GBS) that was identified in the late 1990s. In Asia and Central and South America, it is the major subtype of GBS, seen in 30-65% of patients. AMAN progresses more rapidly and has an earlier peak than demyelinating GBS; tendon reflexes are relatively preserved or even exaggerated, and autonomic dysfunction is rare. One of the main causes is molecular mimicry of human gangliosides by Campylobacter jejuni lipo-oligosaccharides. In addition to axonal degeneration, electrophysiology shows rapidly reversible nerve conduction blockade or slowing, presumably due to pathological changes at the nodes or paranodes. Autoantibodies that bind to GM1 or GD1a gangliosides at the nodes of Ranvier activate complement and disrupt sodium-channel clusters and axoglial junctions, which leads to nerve conduction failure and muscle weakness. Improved understanding of the disease mechanism and pathophysiology might lead to new treatment options and improve the outlook for patients with AMAN.

Nodo-paranodopathy: beyond the demyelinating and axonal classification in anti-ganglioside antibody-mediated neuropathies.

In some anti-ganglioside antibody-mediated neuropathies, human and experimental data suggest a common pathogenic mechanism of dysfunction/disruption at the node of Ranvier resulting in a pathophysiologic continuum from transitory nerve conduction failure to axonal degeneration. The traditional classification of polyneuropathies into demyelinating or axonal may generate some confusion in the electrophysiological diagnosis of Guillain-Barré syndrome subtypes associated with anti-ganglioside antibodies. The axonal forms show, besides axonal degeneration, promptly reversible nerve conduction failure. This may be interpreted, by a single electrophysiological study, as demyelinating conduction block or distal axonal degeneration leading to errors in classification and in establishing prognosis. Moreover the term axonal may be misleading as it is commonly associated to axonal degeneration and not to a transitory, promptly reversible, dysfunction of the excitable axolemma. To focus on the site of nerve injury and overcome the classification difficulties, we propose the new category of nodo-paranodopathy which seems appropriate to various acute and chronic neuropathies associated with anti-ganglioside antibodies and we think better systematizes the neuropathies characterized by an autoimmune attack targeting the nodal region.

Antibodies to gliomedin cause peripheral demyelinating neuropathy and the dismantling of the nodes of Ranvier.

Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyneuropathy (CIDP) are conditions that affect peripheral nerves. The mechanisms that underlie demyelination in these neuropathies are unknown. Recently, we demonstrated that the node of Ranvier is the primary site of the immune attack in patients with GBS and CIDP. In particular, GBS patients have antibodies against gliomedin and neurofascin, two adhesion molecules that play a crucial role in the formation of nodes of Ranvier. We demonstrate that immunity toward gliomedin, but not neurofascin, induced a progressive neuropathy in Lewis rats characterized by conduction defects and demyelination in spinal nerves. The clinical symptoms closely followed the titers of anti-gliomedin IgG and were associated with an important deposition of IgG at nodes. Furthermore, passive transfer of antigliomedin IgG induced a severe demyelinating condition and conduction loss. In both active and passive models, the immune attack at nodes occasioned the loss of the nodal clusters for gliomedin, neurofascin-186, and voltage-gated sodium channels. These results indicate that primary immune reaction against gliomedin, a peripheral nervous system adhesion molecule, can be responsible for the initiation or progression of the demyelinating form of GBS. Furthermore, these autoantibodies affect saltatory propagation by dismantling nodal organization and sodium channel clusters. Antibodies reactive against nodal adhesion molecules thus likely participate in the pathologic process of GBS and CIDP.