Nodal and paranodal auto-antibodies in immune-mediated peripheral neuropathies: clinical-serological characterisation and pathogenic mechanisms

The term inflammatory peripheral neuropathy, sometimes used interchangeably with immune-mediated peripheral neuropathy, encompasses a wide range of syndromes, broadly categorised into acute and chronic forms, most commonly Guillain Barré Syndrome (GBS) and Chronic Inflammatory Demyelinating Polyradiculoneuropathy (CIDP), respectively. Their clinical heterogeneity, likely reflecting diverse pathogenic mechanisms, can lead to a delay in diagnosis, in particular for the numerous atypical forms, unnecessary investigations, and trials of ineffective and potentially harmful treatments. This project focusses on a group of disorders within this category, which have recently been recognised to be pathologically and clinically distinct, and so recently renamed ‘Autoimmune Nodopathies’ (AIN). Crucially, these have been identified through the discovery of antibodies targeting the antigens Contactin-1 (CNTN1), Caspr1, Neurofascin-155 (NF155) and Neurofascin-186 (NF186) at the node of Ranvier, and adjacent paranodes ((para)nodal antibodies). These are one of a handful of existing serum biomarkers which are currently used in clinical practice with diagnostic and therapeutic impact for patients with immune-mediated peripheral neuropathies (Bellanti et al., 2024). The node of Ranvier is required for fast and efficient saltatory conduction along myelinated peripheral nerve fibres. This and adjacent perinodal regions are composed of a vast array of highly specialised molecules, involved in complex axoglial interactions, in order to facilitate the tightly regulated structural assembly and maintenance of these regions. Ganglioside antibody-mediated attack targeting the node and flanking regions has previously been reported in acute axonal neuropathies, though their identification is of limited clinical use in the majority of inflammatory and immune-mediated neuropathies. The (para)nodal antibodies discussed here have been shown to bind to the nodal regions, leading to structural dismantling and functional disruption. However, their individual mechanisms of pathogenicity are only beginning to be resolved. The overall aims of my doctoral research are to: 1. Clinically and serologically characterise patients with Autoimmune nodopathies (AIN) 2. Assess the utility of diagnostic assays used to detect (para)nodal antibodies 3. Investigate the mechanisms by which (para)nodal antibodies exert their pathogenic effect

Nodal-paranodal antibodies in HIV-immune mediated radiculo-neuropathies: clinical phenotypes and relevance

Background: The frequency of nodal–paranodal antibodies in HIV-infected patients with chronic immune-mediated radiculo-neuropathies (IMRN) has not been previously described. Methods: HIV-infected patients who met the inclusion criteria for chronic IMRN were screened for immunoglobulin G (IgG) antibodies directed against nodal (neurofascin (NF)186) and paranodal (NF155, contactin-1 (CNTN1) and contactin-associated protein(Caspr1)) cell adhesion molecules, using a live, cell-based assay. To explore potential pathogenicity, binding of human IgG to myelinated co-cultures was assessed by incubation with patients' sera positive for nodal or paranodal antibodies. Normal human serum was added as a source of complement to assess for complement activation as a mechanism for myelin injury. Results: Twenty-four HIV-infected patients with IMRN were included in the study, 15 with chronic inflammatory demyelinating polyneuropathy (CIDP), 4 with ventral root radiculopathies (VRR), and 5 with dorsal root ganglionopathies (DRG). Five patients with CIDP had combined central and peripheral demyelination (CCPD). Three patients (12.7%) tested positive for neurofascin IgG1 antibodies in the following categories: 1 patient with VRR was NF186 positive, and 2 patients were NF155 positive with DRG and mixed sensory-motor demyelinating neuropathy with optic neuritis, respectively. Conclusion: The frequency of nodal–paranodal antibodies is similar among IMRN regardless of HIV status. Interpretation of the results in the context of HIV is challenging as there is uncertainty regarding pathogenicity of the antibodies, especially at low titres. Larger prospective immune studies are required to delineate pathogenicity in the context of HIV, and to establish a panel of antibodies to predict for a particular clinical phenotype

Serum Contactin-1 in CIDP

To investigate whether serum levels of contactin-1, a paranodal protein, correlate with paranodal injury as seen in patients with CIDP with antibodies targeting the paranodal region. Serum contactin-1 levels were measured in 187 patients with CIDP and 222 healthy controls. Paranodal antibodies were investigated in all patients. Serum contactin-1 levels were lower in patients (N = 41) with paranodal antibodies compared with patients (N = 146) without paranodal antibodies (p < 0.01) and showed good discrimination between these groups (area under the curve 0.84; 95% CI: 0.76-0.93). These findings suggest that serum contactin-1 levels have the potential to serve as a possible diagnostic biomarker of paranodal injury in CIDP. This study provides class II evidence that serum contactin-1 levels can discriminate between patients with CIDP with or without paranodal antibodies with a sensitivity of 71% (95% CI: 56%-85%) and a specificity of 97% (95% CI: 83%-100%)

Inter‐laboratory validation of nodal/paranodal antibody testing

Background and Aims: Reliable detection of antibodies against nodal targets is vital for the diagnosis of autoimmune nodopathies. The performance characteristics of recently developed in-house assays are unknown. We compared testing at four centres. Methods: Each submitted 29–40 serum samples to a coordinating centre from one of three groups: (1) autoimmune nodopathy patients, with positive nodal/paranodal antibodies; (2) seronegative patients with other inflammatory neuropathies, and (3) healthy individuals or those with other neurological diseases. The coordinating centre recoded all samples and returned 160 identical aliquots to each testing centre for blinded testing. Once data from all centres had been received by the coordinating centre, unblinded results were returned for analysis. Sensitivity was defined by the proportion of group 1 samples returned as positive. Accuracy was defined as 0.075(sensitivity) + 0.925(specificity). Results: Centres performed various combinations of ELISA, cell-based (CBAs) and teased-nerve fibre assays. All labs produced highly accurate results (96%–100%) and concordance for the overall result across at least 3 or all 4 test centres was observed for 98% and 89% of the samples respectively. However, 10/30 individual assays (6/14 CBAs and 4/16 ELISAs) were less than 90% sensitive. Only 3 assays had more than 1 false positive result (2 ELISAs and 1 CBA). Combining different assay modalities to produce an overall result did not improve accuracy. Inter-laboratory consistency in the determination of antibody subclasses was poor. Interpretation: Although most samples were correctly categorised in all 4 centres, the use of a specific test modality or multiple tests did not guarantee accuracy. Early and repeated interlaboratory testing with sharing of samples is important to understand test performance and reproducibility, identify areas for improvement and maintain consistency. To aid this, we provide detailed methods for the best performing tests. Further standardisation of antibody subclass determination is required

Large-scale profiling of antibody reactivity to glycolipids in patients with Guillain-Barré syndrome

Guillain-Barré syndrome is an acute polyradiculoneuropathy in which preceding infections often elicit the production of antibodies that target peripheral nerve antigens, principally gangliosides. Anti-ganglioside antibodies are thought to play a key role in the clinical diversity of the disease and can be helpful in clinical practice. Extensive research into clinical associations of individual anti-ganglioside antibody specificities has been performed. Recent research has highlighted glycolipid complexes, glycolipid combinations that may alter antibody binding, as targets. In this study, we investigated antibody reactivity patterns to glycolipids and glycolipid complexes using combinatorial array, in relation to clinical features in Guillain-Barré syndrome. In total, 1413 patients from the observational International Guillain-Barré syndrome Outcome Study (0-91 years, 60.3% male) and 1061 controls (healthy, family, infectious, vaccination, other neurological disease) were included. Acute-phase sera from patients were screened for IgM, IgG, and IgA reactivity against 15 glycolipids and one phospholipid and their heteromeric complexes, similarly to archived control sera. Antibody specificities and reactivity patterns were analysed in relation to clinical features. Of all patients, 1309 (92.6%) were positive for at least one anti-glycolipid (complex) antibody. Anti-GM1 and anti-GQ1b (complex) antibodies best distinguished motor Guillain-Barré syndrome and Miller Fisher syndrome from controls, with antibodies to glycolipid complexes outperforming antibodies to single glycolipids. Three models consisting of anti-glycolipid (complex) antibodies distinguished patients with Guillain-Barré syndrome, the motor variant, and Miller Fisher syndrome from controls with high sensitivity and specificity, performing better than antibodies to single glycolipids used in clinical practice. Seven patient clusters with particular antibody reactivity patterns were identified. These clusters were distinguished by geographical region, clinical variants, preceding Campylobacter jejuni infection, electrophysiological subtypes, the Medical Research Council sum score at study entry, and the ability to walk 10 meters unaided at 26 weeks. Two patient clusters with distinct anti-GM1 (complex) reactivity (broad versus restricted) differed in frequency of the axonal subtype. In cumulative incidence analyses, 15 anti-glycolipid (complex) antibodies were associated with the time required to regain the ability to walk 10 meters unaided. After adjustment for known prognostic factors, IgG anti-GQ1b:GM4, GQ1b:PS, and GQ1b:Sulphatide remained associated with faster recovery. Addition of anti-glycolipid antibodies to clinical prognostic models slightly improved their discriminative capacity, though insufficiently to improve the models. Measurement of anti-glycolipid antibodies by combinatorial array increases the diagnostic yield compared to assaying single glycolipids, identifies clinically relevant antibody reactivity patterns to glycolipids and glycolipid complexes, and may be useful in outcome prediction in Guillain-Barré syndrome

Nodal and paranodal antibody-associated neuropathies

Within the last decade, antibodies targeting the node and paranode of myelinated peripheral nerves have been increasingly identified in patients with acquired immune-mediated neuropathies, commonly termed ‘nodo-paranodopathies’. Crucially, these patients often present with additional clinical features not usually seen with the most common immune-mediated neuropathies, Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy, and respond poorly to conventionally used immunomodulatory therapies. Emerging evidence that these are pathologically distinct diseases has further prompted the use of more targeted treatment, such as the B cell depleting monoclonal antibody rituximab, which has been reported to significantly improve functional outcomes in this subset of patients. We provide an overview of the emerging clinical and serological phenotypes in patients with specific nodal/paranodal antibodies, the practicalities of antibody testing and current evidence supporting the use of non-standard therapies.</jats:p

A rare case of Miller Fisher variant of Guillain-Barr<b>é</b> Syndrome (GBS) induced by a checkpoint inhibitor

With the recent development of novel, more potent cancer treatment, in particular, immune ‘checkpoint inhibitors’, cases of neurological immune-related adverse events are on the rise. Although rare, this includes Guillain-Barré Syndrome (GBS). We present the case of a 68-year-old male who was admitted with sudden onset of worsening neurological symptoms following immunotherapy treatment. These symptoms progressed quickly to respiratory failure requiring intubation and admission to the intensive care unit. He was thoroughly investigated and is believed to have an axonal neuropathy in the form of Miller Fisher Syndrome (MFS) variant of GBS, secondary to immunotherapy treatment. He was initially treated with intravenous immunoglobulin, and later, perhaps more effectively, with high dose steroids which significantly improved his symptoms. This case of checkpoint inhibitor-induced MFS is one of few in the literature and is an important reminder of the potential for new immunotherapeutic agents to cause significant neurotoxic effects. These should be promptly and thoroughly investigated, in particular, as the management of these patients can differ from standard treatments used in these conditions.</jats:p