Background and Objectives This study describes the human leukocyte antigen (HLA) Class II allele frequencies in patients with anti-CNTN1+ and anti-Caspr1+ autoimmune nodopathy (AN).Methods Forty-four AN patients and 50 seronegative CIDP patients from 19 different European hospitals were included in the study. Thirty AN patients had anti-contactin 1 (CNTN1) antibodies, 11 anti-contactin-associated protein 1 (Caspr1) antibodies, and 3 had antibodies against both proteins. HLA-DRB1 was genotyped at the 4-digit allele levels, and the percentage of individuals carrying each allele was compared with that of the general population, obtained from the Allele frequencies database.Results HLA-DRB1*11 alleles appeared in higher proportions in anti-CNTN1+ patients than in seronegative CIDP patients and in the general population (46.7% vs 18% vs 28.4%), with an odds ratio of 3.99 (CI = 1.44 to 11.03, p = 0.01) and 2.2 (CI = 1.07 to 4.53, p = 0.04), respectively. HLA-DRB1*03:01 alleles appeared in significantly higher proportions in anti-Caspr1+ patients than in CIDP patients and in the general population (64.3% vs 22% vs 24.2%), with an odds ratio of 6.38 (CI = 1.77 to 22.99, p = 0.007) and 5.64 (CI = 1.876 to 16.96, p = 0.002), respectively. In the anti-Caspr1+ group, we included 3 patients presenting with antibodies against both CNTN1 and Caspr1 proteins in the acute phase, in which the anti-CNTN1 antibodies disappeared in the chronic phase.Discussion HLA-DRB1*11 alleles are associated with the detection of anti-CNTN1 antibodies in AN patients, and HLA-DRB1*03:01 alleles associate with anti-Caspr1 antibodies. In addition, our study suggests that antiparanodal antibodies targeting both Caspr1 and CNTN1 are present in a small number of patients with AN. These data reinforce the idea that these patients represent specific subsets with clinical features and risk factors that differ from seronegative CIDP patients and from other AN patients. However, further studies should address the functional relevance of these associations and their pathophysiologic implications.

BACKGROUND AND AIMS:Intravenous immunoglobulin (IVIg) is the primary treatment for Guillain-Barré syndrome (GBS), yet its immunological mechanisms underlying variable clinical outcomes remain unclear. This study investigated the immunomodulatory effect of IVIg on regulatory T cells (Tregs), cytokines, and their association with treatment response and clinical outcomes. METHODS:In this prospective case-controlled study, 57 GBS patients and 57 age- and sex-matched healthy controls (HCs) were investigated. CD4+CD25+FoxP3+ Treg percentages, cytokine production (IL-10, TNF-α, IFN-γ, and IL-12), and serum C3 levels were measured using flow cytometry, Luminex assay, and turbidimetric methods, respectively. Treatment response was defined as ≥ 1-point GBS-disability score improvement during evaluation. RESULTS:GBS patients exhibited lower CD4+CD25+FoxP3+ Tregs frequencies compared to HCs (p = 0.006), which were inversely associated with serum C3 levels (p = 0.003) during the acute phase. At 4 weeks post-onset, patients with normal C3 levels (90-180 mg/dL) exhibited higher Treg frequencies (p = 0.005) compared to acute GBS, whereas patients with persistently elevated C3 levels showed reduced Treg percentage (p = 0.009). Among I VIg-treated patients, Tregs significantly increased at 2 and 4 weeks post-treatment, alongside significantly higher IL-10 and lower TNF-α, IFN-γ, and IL-12 levels at 4 weeks. However, patients with supportive care showed no such changes in Tregs and cytokine levels. Furthermore, Tregs elevated significantly in patients responsive to IVIg at 2 and 4 weeks (p < 0.05), but not in non-responsive or supportive care patients. INTERPRETATION:IVIg treatment modulates immune dysregulation in GBS by expanding CD4+CD25+FoxP3+ Tregs and altering cytokines and serum C3 levels, which are associated with clinical improvement. These findings indicate Tregs as potential biomarkers for monitoring initial clinical response to IVIg in GBS.

OBJECTIVES:Intravenous immunoglobulin (IVIg) is an effective treatment for Guillain-Barré syndrome (GBS), but recovery varies between patients. This study aims to evaluate the pharmacokinetics (PK) and pharmacodynamics (PD) of a single and a second IVIg dose (SID) in patients with GBS. METHODS:Data were analyzed from the SID-GBS trial, a double-blind, randomized, placebo-controlled study. Patients with poor prognosis (modified Erasmus GBS Outcome Score, mEGOS ≥6) after a standard course of IVIg (0.4 g/kg for 5 days) were randomized to receive either SID or placebo. Serum IgG levels were measured at standard serial time points and clinical outcomes were assessed using the GBS disability score and Medical Research Council sum score. PK modeling was performed to predict IVIg exposure and its association with clinical outcomes. RESULTS:Serum IgG concentration after a single and double course of IVIg was variable, but accurately described by the current PK model. Lower ΔIgG and IVIg exposure were associated with poorer clinical outcomes. SID increased the IgG concentration, but did not result in an improvement in clinical outcome. Serious adverse events, including thromboembolic events, occurred more frequently in the SID group and were associated with lower IVIg exposure. INTERPRETATION:SID increases serum IgG levels in GBS patients as predicted by the current PK model, but does not improve clinical outcomes and increases the risk of serious adverse events. Model-informed precision dosing may guide individualization of treatment.

BACKGROUND AND OBJECTIVES:Multifocal motor neuropathy (MMN) is an asymmetric motor neuropathy driven by IgM autoantibodies targeting gangliosides, particularly GM1. In this study, we investigated the relationship between IgM seropositivity, complement activation, and clinical parameters using an induced pluripotent stem cell (iPSC)-derived motor neuron (MN) model of MMN. METHODS:We used serum samples from 137 patients with MMN to assess IgM binding and subsequent C3 fixation to iPSC MNs and their correlation with clinical parameters, including muscle strength expressed as MRC sum scores, obtained from patient records. In addition, we tested the efficacy of IV immunoglobulin (IVIg) and specific complement inhibitors to prevent C3 fixation to MNs. RESULTS:We observed increased IgM binding to iPSC MNs using serum samples from patients with MMN compared with those from healthy controls, which correlated with IgM anti-ganglioside antibody titers. Higher antibody binding correlated with levels of C3 fixation, more severe weakness, and the need for higher IVIg doses. Complement activation, but not IgM binding, also correlated with vibration sense abnormalities, brachial plexus MRI abnormalities, and the degree of axonal damage. At therapeutic concentrations, IVIg moderately inhibited complement activation (34%-54%) while specific complement inhibitors were highly effective (89.1%-98.7%) in the iPSC MN model. DISCUSSION:This study demonstrates that IgM antibodies in serum samples from patients with MMN induce complement activation on iPSC MNs, which correlates significantly with clinical outcomes. In addition, our findings indicate that complement inhibitors offer a potentially targeted novel therapeutic strategy for MMN and that our iPSC MN model is a viable preclinical screening platform.

ABSTRACT 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.

Fc-gamma receptors (FcγRs) are important for the effector functions of immunoglobulin G (IgG) and are therefore expected to play a role in the pathophysiology of Guillain-Barré syndrome (GBS). The FCGR2/3 locus, which encodes low-to-medium-affinity FcγRs, contains extensive genetic variation. We hypothesized that genetic variation in the FCGR2/3 locus influences GBS susceptibility, muscle weakness, outcomes, and the pharmacokinetics of intravenous immunoglobulin (IVIg). Copy number variation and single nucleotide polymorphisms in the FCGR2/3 locus were studied using multiplex ligation-dependent probe amplification (MLPA). The study cohort consisted of 467 GBS patients and 919 healthy controls of European descent. Severe weakness was defined as an MRC sum score < 40 at nadir. The increase in serum IgG one or two weeks after start of IVIg treatment was determined. No significant associations were found between genetic variation in the FCGR2/3 locus and susceptibility to GBS. However, in patients with an antecedent Campylobacter jejuni infection, a higher frequency of three or more FCGR3A copies was observed compared to healthy controls (p = 0.023). FCGR3A copy numbers were also associated with more severe disease (OR = 2.02; 95

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 m 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 m unaided. After adjustment for known prognostic factors, IgG anti-GQ1b:GM4, GQ1b:PS and GQ1b:Sulfatide 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.

Background Several prognostic models predict clinical outcomes in Guillain-Barr & eacute; syndrome (GBS). Recently, neurofilament light chain (NfL) has emerged as a prognostic biomarker. We investigated the added prognostic value of NfL in serum (sNfL) and cerebrospinal fluid (cNfL) to models based on clinical factors predicting respiratory failure and inability to walk in GBS.Methods We included patients from a randomised placebo-controlled trial (second intravenous immunoglobulin dose in GBS). Serum was acquired at entry and week 1, 2, 4 and 12 and cerebrospinal fluid at entry. NfL levels were determined on a single molecule array. The additional prognostic value of NfL to the (modified) Erasmus GBS Outcome Score ((m)EGOS) and (modified) Erasmus GBS Respiratory Insufficiency Score was evaluated using logistic regression analyses.Results In total, 293 patients were included (74 (25%) mechanically ventilated, 38/275 (13%) unable to walk at 26 weeks). Higher sNfL at entry, week 1 and week 2 and cNfL at entry were associated with inability to walk at 4 and 26 weeks. Neither sNfL nor cNfL levels at entry were associated with respiratory failure. The EGOS and mEGOS improved after adding NfL (triangle C-statistic range: 0.01-0.11), especially the models predicting outcome at 26 weeks. A new model predicting inability to walk at 26 weeks consisting of sNfL at entry, GBS disability score at entry and Medical Research Council sum score at week 2 performed best (C-statistic: 0.88 (95% CI 0.83 to 0.94)).Conclusions Addition of NfL may improve clinical prognostic models for the prediction of inability to walk, but not of respiratory failure.Trial registration number NTR2224/NL2107.

A non-pathogenic Mycoplasma pneumoniae-based chassis is leading the development of live biotherapeutics (LBPs) for respiratory diseases. However, reports connecting Guillain-Barré syndrome (GBS) cases to prior M. pneumoniae infections represent a concern for exploiting such a chassis. Galactolipids, especially galactocerebroside (GalCer), are considered the most likely M. pneumoniae antigens triggering autoimmune responses associated with GBS development. In this work, we generated different strains lacking genes involved in galactolipids biosynthesis. Glycolipid profiling of the strains demonstrated that some mutants show a complete lack of galactolipids. Cross-reactivity assays with sera from GBS patients with prior M. pneumoniae infection showed that certain engineered strains exhibit reduced antibody recognition. However, correlation analyses of these results with the glycolipid profile of the engineered strains suggest that other factors different from GalCer contribute to sera recognition, including total ceramide levels, dihexosylceramide (DHCer), and diglycosyldiacylglycerol (DGDAG). Finally, we discuss the best candidate strains as potential GBS-free Mycoplasma chassis.

BACKGROUND:Multifocal motor neuropathy (MMN) is a rare, chronic immune-mediated polyneuropathy characterized by asymmetric distal limb weakness. An important feature of MMN is the presence of IgM antibodies against gangliosides, in particular GM1 and less often GM2. Antibodies against GM1 bind to motor neurons (MNs) and cause damage through complement activation. The involvement of Schwann cells (SCs), expressing GM1 and GM2, in the pathogenesis of MMN is unknown.METHODS:Combining the data of our 2007 and 2015 combined cross-sectional and follow-up studies in Dutch patients with MMN, we evaluated the presence of IgM antibodies against GM1 and GM2 in serum from 124 patients with MMN and investigated their binding to SCs and complement-activating properties. We also assessed the relation of IgM binding and complement deposition with clinical characteristics.RESULTS:Thirteen out of 124 patients (10%) had a positive ELISA titer for IgM anti-GM2. Age at onset of symptoms was significantly lower in MMN patients with anti-GM2 IgM. IgM binding to SCs correlated with IgM anti-GM2 titers. We found no correlation between IgM anti-GM2 titers and MN binding or with IgM anti-GM1 titers. IgM binding to SCs decreased upon pre-incubation of serum with soluble GM2, but not with soluble GM1. IgM anti-GM2 binding to SCs correlated with complement activation, as reflected by increased C3 fixation on SCs and C5a formation in the supernatant.CONCLUSION:Circulating IgM anti-GM2 antibodies define a subgroup of patients with MMN that has an earlier onset of disease. These antibodies probably target SCs specifically and activate complement, similarly as IgM anti-GM1 on MNs. Our data indicate that complement activation by IgM antibodies bound to SCs and MNs underlies MMN pathology.