The immunopathogenesis of autoimmune neurological syndromes (AINS) with antibodies against the 65 kDa isoform of glutamic acid decarboxylase (anti-GAD65 AINS) remains poorly understood. To elucidate underlying disease mechanisms and identify relevant cell populations, we performed single-cell RNA and immune repertoire sequencing of cerebrospinal fluid (CSF) and peripheral blood mononuclear cells (PBMCs) of eight anti-GAD65 AINS individuals compared to eight noninflammatory controls. In addition, PBMCs from 19 anti-GAD65 AINS individuals and 20 healthy controls were analyzed by multidimensional flow cytometry, and brain tissue specimens from four anti-GAD65 AINS individuals were examined histologically. We detected higher frequencies of stem cell-like memory T cells (TSCM) within the PBMCs and a marked enrichment and clonal expansion of activated CD4+TSCM in the CSF of anti-GAD65 AINS individuals. Expanded T cells exhibited increased expression of proinflammatory genes. Histological analyses confirmed intraparenchymal CD8+ TSCM in three of four anti-GAD65 AINS individuals and rare meningeal/intraparenchymal CD4+ TSCM in one person. Although CSF B cell receptors (BCRs) displayed little to no clonal expansion, recombinant expression of 40 CSF BCRs revealed that 25% were GAD65-reactive with increased somatic hypermutations compared to non-GAD65-reactive BCRs. These findings further support the concept of an antigen-specific intrathecal immune response. In summary, we characterize the immune landscape of anti-GAD65 AINS at single-cell resolution and identify clonally expanded TSCM with cytotoxic properties as a hallmark of this disease.

Abstract Background Although significant progress has been made in identifying antigen targets in autoimmune encephalitis (AIE), in a substantial proportion of patients with presumed AIE no known autoantibodies can be detected. Herein, we describe a novel autoantibody reactivity, directed against copine-5 (CPNE5), in patients with AIE and melanoma. Methods Patients were identified through routine clinical testing for anti-neural autoantibodies by indirect immunofluorescence on neuronal tissue sections. The antigen was identified by immunoprecipitation and mass spectrometry and confirmed by recombinant protein assays. Results Serum and cerebrospinal fluid (CSF) immunoglobulin G (IgG) from four patients was found to exhibit distinct binding to cerebellar and hippocampal neurons. Copine-5 was identified as the target antigen. Clinical manifestations included cognitive decline, confusion/disorientation, psychosis, seizures and signs and symptoms compatible with basal ganglia involvement (movement disorders, including secondary parkinsonism, and/or abulia/akinetic mutism), alongside pain (including painful tonic spasms and focal allodynia), dysarthria, dysphagia, and abducens nerve palsy. Brain magnetic resonance imaging disclosed hyperintense lesions in the basal ganglia and the temporal lobe. CSF analysis revealed mild pleocytosis, intrathecal IgG synthesis, and blood/CSF barrier dysfunction. Of particular note, all four patients had melanoma, with an occult primary in three. In one patient, melanoma diagnosis and immunotherapy with the anti-PD-1 immune checkpoint inhibitor nivolumab preceded the onset of AIE by 9 months. Glucocorticoid treatment and/or intravenous immunoglobulins led to transient improvement in at least three patients; however, all relapsed and three progressed to hypoactive delirium or mutism. Plasma exchange and cyclophosphamide treatment were followed by clinical improvement and stabilization in one patient, but potentially contributed to fatal infectious complications. Copine-5-IgG belonged to the strongly complement-activating IgG1 subclass and was produced intrathecally. Serum titers ranged between 1:1000 and 1:100,000. Conclusions Copine-5 is a novel autoantibody target in AIE. Testing for anti-copine-5 autoantibodies should be included in the diagnostic workup of patients with AIE, especially, but not exclusively, if associated with melanoma or positive melanoma-associated tumor markers. Further studies investigating the immunopathogenesis of copine-5-related autoimmunity and the potential significance of anti-copine-5 as a novel paraneoplastic serological marker and of copine-5 as a histopathological tumor marker in patients with suspected melanoma are highly warranted.

Severe neuropathies with predominant involvement of motor fibres can resemble lower motor neuron disease (LMND) phenotypes. Given the fatal prognosis of LMND, identifying underlying autoimmune syndromes is crucial to provide treatment options to patients. We investigated a novel autoantibody binding pattern observed on murine teased sciatic nerve fibres. Target antigens were identified using immunoprecipitation combined with mass spectrometry. Target specificity of these autoantibodies was validated in cell-based assays, neutralization assays and knock-out models. A retrospective study cohort consisting of different neuropathies (chronic inflammatory demyelinating polyradiculopathy n = 86, Guillain-Barré syndrome n = 37, multifocal motor neuropathy n = 18, diabetic neuropathy n = 30, other inflammatory neuropathies n = 10), amyotrophic lateral sclerosis (n = 50), multiple sclerosis (n = 50) and healthy controls (n = 50) was negative for septin multimer autoantibodies. Histopathological analysis of skin and the sural nerve including electron microscopy was performed in one seropositive patient, and autoantibody binding was characterized in vitro. Extensive immunotherapy was initiated in one patient, with clinical and serological follow-up over 4 years. Among 3543 total samples tested, three patients (two male, one female)-diagnosed with the LMND variant of amyotrophic lateral sclerosis (aged 65, 72 and 79 years, respectively)-showed a novel and distinct autoantibody binding pattern of indirect immunofluorescence staining on peripheral nerves, targeting Schmidt-Lanterman incisures (SLIs), paranodes and the abaxonal myelin. Target identification and validation revealed septin multimers as autoantibody epitopes. Despite the primarily intracellular location of septins, autoantibody binding was evident in living myelinated dorsal root ganglia, primarily at SLIs ('incisuropathy'). Septin multimer autoantibodies further initiated complement deposition on fixed and permeabilized cell-based assays. Sural nerve and skin biopsies showed inflammation, myelin and axonal pathology. Extensive immunotherapy in one patient was followed by disease stabilization over 3 years. The other two patients died of rapid disease progression: one of them received no immunotherapy while the other had ineffective treatments with single administrations of intravenous immunoglobulin and rituximab. Our data suggest that septin multimer autoimmunity occurs in severe motor-predominant neuropathies which can clinically resemble a neurodegenerative LMND. Screening for septin multimer autoantibodies should be considered in patients presenting with this phenotype. Follow-up studies need to determine the direct pathogenicity of septin multimer autoantibodies, their potential as a biomarker of an autoimmune syndrome and responses to immunotherapy in larger cohorts.

Autoantibodies are important biomarkers for the diagnosis of autoimmune diseases that help to determine treatment strategies and to understand disease pathology. Despite the increasing numbers of neuronal autoantibody discoveries, there are still patients presenting with neurological autoimmune diseases and so far uncharacterized autoantibodies. Between 12/2016 and 06/2024, we collected sera of 314 patients with a distinct uncharacterized IgG pattern in neuronal tissue indirect immunofluorescence assay (IIFA). By immunoprecipitation and mass spectrometry we identified vesicular glutamate transporter 2 (VGLUT2) as the autoantibody target and confirmed it in sera of 285/314 patients by recombinant IIFA with VGLUT2-expressing HEK293 cells, competitive inhibition assays and colocalization studies with a commercial antibody. The main diagnoses available of 87/285 patients (mean age 58, range 1-92) were encephalitis 25/87, dementia/cognitive impairment 17/87 and polyneuropathy 16/87. Detailed clinical data of 18 patients were collected retrospectively. The major symptoms of those index patients (mean age 56, range 2-78) involved cognitive changes (10/18) including memory impairment, aphasia and disorientation as well as sensorimotor disturbances (9/18) and gait abnormalities (9/18), accompanied by visual impairments (8/18). (Poly)neuropathy was observed in 10/18 cases. The majority of the anti-VGLUT2 index patients had coexisting diabetes mellitus type 2 or other chronic multisystem disorders. In 8/12 index patients, immunotherapy had beneficial effects, although only slight improvements could be obtained in most of the cases. All 17 analyzed index patient sera recognized a cytoplasmic epitope between amino acid 520-564 of VGLUT2, determined by immunoblot with recombinant antigen fragments. Anti-VGLUT2 autoantibody-associated neurological diseases may represent a new type of autoimmune disorders that might benefit from immunomodulatory treatment and predominantly manifests with encephalitis, cognitive deficits and neuropathy.

Background Glutamic acid decarboxylase (GAD) antibody-associated autoimmune neurological syndromes (AINS) are a spectrum of autoimmune-mediated CNS disorders. While antibodies targeting the 65 kDa isoform of GAD are of high diagnostic value, T cell mediated cytotoxicity has been identified as a key component of disease pathogenesis. The precise pathophysiological mechanisms by which the disease is triggered and maintained, however, remain incompletely understood. Methods We performed single-cell transcriptome and immune repertoire sequencing (sc-seq) in CSF and blood of 8 anti-GAD65 AINS patients compared to 8 non-inflammatory controls. Monoclonal antibodies (mAbs) were synthesized from B cell receptor (BCR) data to evaluate the B cellular immune response. Findings We identified an increase and expansion of activated CD4+ stem cell-like memory T cells (TSCM) in the CSF of anti-GAD65 AINS patients. Expanded T cells showed increased expression of proinflammatory genes. The mAb analysis revealed a high frequency of GAD65-reactive BCRs in the CSF of anti-GAD65 AINS patients with increased somatic hypermutations compared to non-GAD-reactive BCRs and BCRs from controls. Conclusions Sc-seq identified clonally expanded CD4+ TSCM in the CSF of anti-GAD65 AINS patients harboring cytotoxic properties likely contributing to disease pathogenesis. GAD-reactive B cells circulate in the CSF of anti-GAD65 AINS patients further supporting the concept of an antigen-specific intrathecal immune response. Future studies need to clarify the actual pathogenicity of these immune cells and the link between T and B cellular immune mechanisms in the pathogenesis of anti-GAD65 AINS. Funding German Research Foundation (ERARE18-202 UltraAIE), German Federal Ministry of Education and Research (CONNECT GENERATE (2.0); 01GM1908A and 01GM2208A). ### Competing Interest Statement SB is affiliated with Novartis, Basel, Switzerland; SR received travel grants from Merck Healthcare Germany GmbH, Alexion Pharmaceuticals, Bristol Myers Squibb, the German Neurological Society, and the American Academy of Neurology. She served on a scientific advisory board from Merck Healthcare Germany GmbH and received honoraria for lecturing from Roche and Merck Healthcare Germany GmbH. Her research was supported by Novartis, "Stiftung zur Foerderung junger Neurowissenschaftler", and "Else Kroener-Fresenius-Stiftung"; KE was supported by the "Friedrich-Baur-Stiftung"; EK has received personal honoraria for lectures or advice from UCB, UNEEG, Medtronic, Desitin and Precisis and has participated in trials sponsored by Medtronic, UCB, Ergomed, and Precisis. Her research is supported by the Munich Clinican Scientist Program (MCSP); MR received lecture fees and/or served on advisory boards for AstraZeneca, Echosens, Eli Lilly, Madrigal, Merck-MSD, Novo Nordisk, Synlab and Target RWE and performed investigator-initiated research with support from Boehringer Ingelheim and Novo Nordisk to the German Diabetes Center (DDZ); HW received speaker honoraria from Alexion, Biogen, Bristol Myers Squibb, Genzyme, Merck, Neurodiem, Novartis, Ology, Roche, TEVA, and WebMD Global. He received honoraria for consulting services from Abbvie, Actelion, Argenx, BD, Bristol Myers Squibb, EMD Serono, Fondazione Cariplo, Gossamer Bio, Idorsia, Immunic, Immunovant, INmune Bio_Syneos Health, Janssen, Merck, NexGen, Novartis, Roche, Sanofi, Swiss MS Society, UCB and Worldwide Clinical Trials. His research is supported by the German Myasthenia Gravis Society; NHS declares financial ties to Menarini Silicon Biosystems (CellSearch Assay) in the form of third-party funding for research support, as well as to Illumina (NGS products) in the form of lecture fees; SGM receives honoraria for lecturing, and travel expenses for attending meetings from Academy 2, Argenx, Alexion, Almirall, Amicus Therapeutics Germany, Bayer Health Care, Biogen, BioNtech, BMS, Celgene, Datamed, Demecan, Desitin, Diamed, Diaplan, DIU Dresden, DPmed, Gen Medicine and Healthcare products, Genzyme, Hexal AG, IGES, Impulze GmbH, Janssen Cilag, KW Medipoint, MedDay Pharmaceuticals, Merck Serono, MICE, Mylan, Neuraxpharm, Neuropoint, Novartis, Novo Nordisk, ONO Pharma, Oxford PharmaGenesis, QuintilesIMS, Roche, Sanofi-Aventis, Springer Medizin Verlag, STADA, Chugai Pharma, Teva, UCB, Viatris, Wings for Life international and Xcenda, his research is funded by the German Ministry for Education and Research (BMBF), Bundesinstitut fuer Risikobewertung (BfR), Deutsche Forschungsgemeinschaft (DFG), Else Kroener Fresenius Foundation, Gemeinsamer Bundesausschuss (G-BA), German Academic Exchange Service, Hertie Foundation, Interdisciplinary Center for Clinical Studies (IZKF) Muenster, German Foundation Neurology and Alexion, Almirall, Amicus Therapeutics Germany, Biogen, Diamed, DGM e.v., Fresenius Medical Care, Genzyme, Gesellschaft von Freunden und Foerderern der Heinrich-Heine-Universitaet Duesseldorf e.V., HERZ Burgdorf, Merck Serono, Novartis, ONO Pharma, Roche, and Teva; MJT M.J. Titulaer has received funds for serving on a scientific advisory board of AmGen, ArgenX, Arialys and UCB, received funds from Dioraphte (2001 0403) EpilepsieNL (19-18), filed a patent for methods for typing neurologic disorders and cancer, and devices for use therein, received research funds for consultation at Guidepoint Global LLC, an unrestricted research grant from CSL Behring, and an unrestricted research grant from Euroimmun, was supported by an Interlaken Leadership Award and an E-RARE3 grant (Netherlands Medical Research Foundation [ZonMW], ERARE-JTC2018 202: UltraAIE).; FL is also supported by E-Rare Joint Transnational research support (ERA-Net, LE3064/2-1), Stiftung Pathobiochemie of the German Society for Laboratory Medicine and HORIZON MSCA 2022 Doctoral Network 101119457 - IgG4-TREAT and discloses speaker honoraria from Grifols, Teva, Biogen, Bayer, Roche, Novartis, Fresenius, travel funding from Merck, Grifols and Bayer and serving on advisory boards for Roche, Biogen and Alexion; GMzH received research support from Biogen and Merck Germany; he received honoraria from Alexion and LFB Pharma and participated in Data Safety Monitoring and/or Advisory Boards of LFB Pharma, Roche and Immunovant; FT received grant support from Novartis Pharma GmbH and speaker honoraria from Alexion Pharmaceuticals; NM received honoraria for lecturing and travel expenses for attending meetings from Biogen Idec, GlaxoSmithKline, Teva, Novartis Pharma, Bayer Healthcare, Genzyme, Alexion Pharmaceuticals, Fresenius Medical Care, Diamed, UCB Pharma, AngeliniPharma, BIAL and Sanofi-Aventis, received royalties for consulting from UCB Pharma, Alexion Pharmaceuticals and Sanofi, and received financial research support from Euroimmun, Fresenius Medical Care, Diamed, Alexion Pharmaceuticals, Novartis Pharma, and Sanofi. MS, RM, and LK are employees of EUROIMMUN. The remaining authors declare no conflict of interest. German Research Foundation, ERARE18-202 UltraAIE German Federal Ministry of Education and Research, CONNECT GENERATE (2.0); 01GM1908A and 01GM2208A

ObjectiveTo identify the target antigen of an anti-nuclear autoantibody (ANA) from a patient with a suspected systemic autoimmune disease and to study the autoantibody’s clinical association.MethodsThe index patient serum was screened for autoantibodies using indirect immunofluorescence assay (IFA) and line blots (membrane strips coated with parallel lines of different purified antigens). Immunoprecipitation with fixed HEp-2 cells followed by SDS-PAGE and MALDI-TOF mass spectrometry was used to identify the autoantigen, which was verified by competitive inhibition experiments, recombinant HEK293 cell-based IFA, and Western and line blots based on the recombinant antigen. The prevalence of autoantibodies against this antigen was studied in 693 patients with systemic autoimmune rheumatic diseases (SARD) and 150 healthy controls.ResultsThe index patient serum displayed a homogeneous nucleolar staining pattern on HEp-2 cells and monkey liver by IFA but did not react with 27 known nuclear antigens. Nuclear valosin-containing-protein-like (NVL) was identified as the ANA target antigen. Preincubation with recombinant NVL abolished the reactivity of the patient serum with HEp-2 cells in IFA. Additionally, the patient serum reacted with recombinant NVL in cell-based IFA and Western blot analysis, whereas sera from 15 healthy controls were nonreactive. Using line blots coated with recombinant NVL, anti-NVL autoantibodies were exclusively found in four out of 378 patients with systemic sclerosis, but neither in 315 patients with other SARD nor in 150 healthy controls.ConclusionThese findings indicate that autoantibodies against NVL may be a suitable marker to help narrowing the serological gap in systemic sclerosis.

OBJECTIVE:Here, we assess the performance of the new EUROLINE Neurologic Syndrome 15 Ag (IgG) which expands the EUROLINE Paraneoplastic Neurologic Syndrome 12 Ag by adding CDR2L (together with CDR2 targeted by anti-Yo), AK5, and Neurochondrin (NCDN). BACKGROUND:Many paraneoplastic as well as non-paraneoplastic autoantibodies (AAbs) have been described in neurological disorders in the last decade. By integrating the associated antigens into existing assays, the diagnostic work-up of patients is being improved and diagnostic gaps reduced. DESIGN/METHODS:Sensitivity of each AAb was analyzed using a total of 194 clinically and diagnostically pre-characterized samples (Table 1). Specificity of each AAb was investigated using a minimum of 100 sera from healthy blood donors. RESULTS:Using the EUROLINE Neurologic Syndrome 15 Ag, autoantibody positivity was confirmed in 89-100% of samples. In particular, all samples for which clinical and tissue-based indirect immunofluorescence assay pre-characterization indicated anti-Yo positivity were anti-CDR2 and -CDR2L double positive. Anti-AK5 was determined in serum and cerebrospinal fluid (CSF) with a sensitivity of 90 and 100%, respectively, and anti-NCDN with a sensitivity of 100%. The individual specificities were ≥99%. CONCLUSIONS:This kit is a tool for the qualitative in vitro determination of AAbs against a large panel of 15 different neuronal autoantigens to support the diagnosis of neurologic syndromes. The parallel detection of anti-CDR2 and anti-CDR2L (both anti-Yo) increases the diagnostic significance, as double positivity is strongly related to paraneoplastic cerebellar degeneration.[Table: see text].

BACKGROUND:We aimed to investigate the clinical, imaging and fluid biomarker characteristics in patients with antidiacylglycerol lipase alpha (DAGLA)-autoantibody-associated cerebellitis. METHODS:Serum and cerebrospinal fliud (CSF) samples from four index patients were subjected to comprehensive autoantibody screening by indirect immunofluorescence assay (IIFA). Immunoprecipitation, mass spectrometry and recombinant protein assays were used to identify the autoantigen. Sera from 101 patients with various neurological symptoms and a similar tissue staining pattern as the index patient samples, and 102 healthy donors were analysed in recombinant cell-based IIFA (RC-IIFA) with the identified protein. Epitope characterisation of all positive samples was performed via ELISA, immunoblot, immunoprecipitation and RC-IIFA using different DAGLA fragments. RESULTS:All index patients were relatively young (age: 18-34) and suffered from pronounced gait ataxia, dysarthria and visual impairments. Paraclinical hallmarks in early-stage disease were inflammatory CSF changes and cerebellar cortex hyperintensity in MRI. Severe cerebellar atrophy developed in three of four patients within 6 months. All patient samples showed the same unclassified IgG reactivity with the cerebellar molecular layer. DAGLA was identified as the target antigen and confirmed by competitive inhibition experiments and DAGLA-specific RC-IIFA. In RC-IIFA, serum reactivity against DAGLA was also found in 17/101 disease controls, including patients with different clinical phenotypes than the one of the index patients, and in 1/102 healthy donors. Epitope characterisation revealed that 17/18 anti-DAGLA-positive control sera reacted with a C-terminal intracellular DAGLA 583-1042 fragment, while the CSF samples of the index patients targeted a conformational epitope between amino acid 1 and 157. CONCLUSIONS:We propose that anti-DAGLA autoantibodies detected in CSF, with a characteristic tissue IIFA pattern, represent novel biomarkers for rapidly progressive cerebellitis.

Background Purkinje cytoplasmic autoantibody type 1 (PCA-1)/anti-Yo autoimmunity is a common high-risk paraneoplastic neurological disorder, traditionally attributed antigenically to cerebellar degeneration–related protein 2 (CDR2), predominantly affecting women with gynecologic or breast adenocarcinoma. Single-modality CDR2 testing may produce false-positive results. We assessed the performance characteristics of the more recently purported major PCA-1/Yo antigen, CDR2-like (CDR2L), side by side with CDR2, in a line blot format. Methods CDR2 and CDR2L were tested in six specimen groups (serum and cerebrospinal fluid (CSF)). Group 1, PCA-1/Yo mouse brain indirect immunofluorescence assay (IFA) positives; Group 2, PCA-1/Yo IFA mimics; Group 3, suspected CDR2 line blot false positives; Group 4, consecutive patient samples tested for neural antibodies over 1 year; Group 5, healthy subject serums; and Group 6, polyclonal (non-specific) immunoglobulin G (IgG)-positive serums. Results Group 1: Of 64 samples tested, all but two were CDR2 positive (both CSF samples) and all were CDR2L positive. In individual patients, CDR2L values were always higher than CDR2. The two “CDR2L-only” positives were CSF samples with low titer PCA-1/Yo by IFA with serum negativity but with typical clinical phenotype. Group 2: All 51 PCA-1/Yo mimics were CDR2/CDR2L negative. Group 3: Nine samples [six of 1289 (0.47%) serums and three of 700 CSF samples (0.43%) were PCA-1/Yo IFA negative/CDR2 positive; two of the six available (serums from the same patient) were also CDR2L positive; the other four CDR2L negative had low CDR2 values (17–22). Group 4: Twenty-two patients had unexpected CDR2 or CDR2L positivity; none had tissue IFA positivity. Eleven of the 2,132 serum (0.5%) and three of the 677 CSF (0.4%) samples were CDR2 positive; median value was 19 (range, 11–48). Seven of the 2,132 serum (0.3%) and three of the 677 CSF (0.4%) samples were CDR2L positive; median value was 18 (range, 11–96). Group 5: All 151 healthy serum samples were negative. Group 6: One of the 46 polyclonal serum samples was CDR2L positive. Optimum overall performance was accomplished by requiring both CDR2 and CDR2L positivity in serum (sensitivity, 100%; and specificity, 99.9%) and positivity for CDR2L in CSF (sensitivity, 100%; and specificity, 99.6%). Conclusion CDR2L provides additional PCA-1/anti-Yo sensitivity in CSF, and dual positivity with CDR2 provides additional specificity assurance in serum. Combining antigen-specific and tissue-based assays optimizes PCA-1/anti-Yo testing.

Ataxia with anti-regulator of G-protein signaling 8 autoantibodies (RGS8-Abs) is an autoimmune disease recently described in four patients. The present study aimed to identify other patients with RGS8-Abs, describe their clinical features, including the link between RGS8-related autoimmune cerebellar ataxia (ACA) and cancer. Patients with RGS8-Abs were identified retrospectively in the biological collections of the French Reference Center for Paraneoplastic Neurological Syndrome and the University of California San Francisco Center for Encephalitis and Meningitis. Clinical data were collected, and cerebrospinal fluid, serum, and tumor pathological samples were retrieved to characterize the autoantibodies and the associated malignancies. Only three patients with RGS8-Abs were identified. All of them presented with a pure cerebellar ataxia of mild to severe course, unresponsive to current immunotherapy regimens for ACA. Two patients presented with a Hodgkin lymphoma of the rare specific subtype called nodular lymphocyte-predominant Hodgkin lymphoma, with very mild extension. Autoantibodies detected in all patients enriched the same epitope on the RGS8 protein, which is an intracellular protein physiologically expressed in Purkinje cells but also ectopically expressed specifically in lymphoma cells of patients with RGS8-related ACA. The present results and those of the four cases previously described suggest that RGS8-Abs define a new paraneoplastic neurological syndrome of extreme rarity found mostly in middle-aged males that associates pure cerebellar ataxia and a particular lymphoma specifically expressing the RGS8 antigen. As in other paraneoplastic ACA with intracellular antigen, the disease course is severe, and patients tend to exhibit a poor response to immune therapy.

Introduction: The antibody repertoire from CSF-derived antibody-secreting cells and memory B-cells in patients with encephalitis contains a considerable number of antibodies that do not target the disease-defining autoantigen such as the GABA or NMDA receptors. This study focuses on the functional relevance of autoantibodies to brain blood vessels in patients with GABAA and NMDA receptor encephalitis.Methods: We tested 149 human monoclonal IgG antibodies from the cerebrospinal fluid of six patients with different forms of autoimmune encephalitis on murine brain sections for reactivity to blood vessels using immunohistochemistry. Positive candidates were tested for reactivity with purified brain blood vessels, effects on transendothelial electrical resistance (TEER), and expression of tight junction proteins as well as gene regulation using human brain microvascular endothelial hCMEC/D3 cells as in vitro blood-brain barrier model. One blood-vessel reactive antibody was infused intrathecally by pump injection in mice to study in vivo binding and effects on tight junction proteins such as Occludin. Target protein identification was addressed using transfected HEK293 cells.Results: Six antibodies reacted with brain blood vessels, three were from the same patient with GABAAR encephalitis, and the other three were from different patients with NMDAR encephalitis. One antibody from an NMDAR encephalitis patient, mAb 011-138, also reacted with cerebellar Purkinje cells. In this case, treatment of hCMEC/D3 cells resulted in decreased TEER, reduced Occludin expression, and mRNA levels. Functional relevance in vivo was confirmed as Occludin downregulation was observed in mAb 011-138-infused animals. Unconventional Myosin-X was identified as a novel autoimmune target for this antibody.Discussion: We conclude that autoantibodies to blood vessels occur in autoimmune encephalitis patients and might contribute to a disruption of the blood-brain barrier thereby suggesting a potential pathophysiological relevance of these antibodies.

Background Septins are cytoskeletal proteins with filament forming capabilities, which have multiple roles during cell division, cellular polarization, morphogenesis, and membrane trafficking. Autoantibodies against septin-5 are associated with non-paraneoplastic cerebellar ataxia, and autoantibodies against septin-7 with encephalopathy with prominent neuropsychiatric features. Here, we report on newly identified autoantibodies against septin-3 in patients with paraneoplastic cerebellar ataxia. We also propose a strategy for anti-septin autoantibody determination. Methods Sera from three patients producing similar immunofluorescence staining patterns on cerebellar and hippocampal sections were subjected to immunoprecipitation followed by mass spectrometry. The identified candidate antigens, all of which were septins, were expressed recombinantly in HEK293 cells either individually, as complexes, or combinations missing individual septins, for use in recombinant cell-based indirect immunofluorescence assays (RC-IIFA). Specificity for septin-3 was further confirmed by tissue IIFA neutralization experiments. Finally, tumor tissue sections were analyzed immunohistochemically for septin-3 expression. Results Immunoprecipitation with rat cerebellum lysate revealed septin-3, -5, -6, -7, and -11 as candidate target antigens. Sera of all three patients reacted with recombinant cells co-expressing septin-3/5/6/7/11, while none of 149 healthy control sera was similarly reactive. In RC-IIFAs the patient sera recognized only cells expressing septin-3, individually and in complexes. Incubation of patient sera with five different septin combinations, each missing one of the five septins, confirmed the autoantibodies’ specificity for septin-3. The tissue IIFA reactivity of patient serum was abolished by pre-incubation with HEK293 cell lysates overexpressing the septin-3/5/6/7/11 complex or septin-3 alone, but not with HEK293 cell lysates overexpressing septin-5 as control. All three patients had cancers (2 × melanoma, 1 × small cell lung cancer), presented with progressive cerebellar syndromes, and responded poorly to immunotherapy. Expression of septin-3 was demonstrated in resected tumor tissue available from one patient. Conclusions Septin-3 is a novel autoantibody target in patients with paraneoplastic cerebellar syndromes. Based on our findings, RC-IIFA with HEK293 cells expressing the septin-3/5/6/7/11 complex may serve as a screening tool to investigate anti-septin autoantibodies in serological samples with a characteristic staining pattern on neuronal tissue sections. Autoantibodies against individual septins can then be confirmed by RC-IIFA expressing single septins.

We report two novel cases of autoimmune cerebellar ataxia (ACA) associated with anti-glutamate receptor δ2 antibodies (Gluδ2-Abs). The first case was confirmed by indirect immunofluorescence and cell-based assays: a 29-year-old woman presented after 5 days of headache and vomiting, a pancerebellar syndrome, downbeat nystagmus, decreased visual acuity linked to bilateral retrobulbar optic neuritis (RON), and lymphocytic pleocytosis in the cerebrospinal fluid (CSF) without any abnormality detected using cerebral magnetic resonance imaging (MRI). Second-line immunotherapy allowed progressive clinical improvement, with full recovery achieved after a 4-year follow-up. Thereafter, we retrospectively tested Gluδ2-Abs in 350 patients with a suspicion of autoimmune encephalitis without characterized autoantibody. We identified a second case, a 12-year-old boy who developed 10 days after a respiratory infection, a static cerebellar syndrome with lymphocytosis in the CSF, and right cerebellum hyperintensity in MRI. Five days of corticosteroid treatment allowed a quick clinical improvement. No tumor was identified in both cases, whereas laboratory analyses revealed autoimmune stigma. The present cases suggested that ACA associated with Gluδ2-Abs is an extremely rare but treatable disease. Therefore, testing for Gluδ2-Abs might be considered in the setting of suspected ACA and no initial antibody identification. The visual deficits and ocular motility abnormalities observed in the first reported case might be part of the clinical spectrum of Gluδ2-Abs ACA. Young age, infectious prodromes, lymphocytic pleocytosis, and autoimmune background usually appear together with this syndrome and should lead to discuss the initiation of immunotherapy (after ruling out differential diagnosis, especially infectious causes).

Abstract Background Onconeuronal anti-Yo antibodies are key diagnostic markers for paraneoplastic cerebellar degeneration (PCD) and often associated with gynaecologic/breast cancer. Cerebellar degeneration-related protein 2-like (CDR2L), but not cerebellar degeneration-related protein 2 (CDR2), has recently been shown to be the major anti-Yo target (1, 2). This study investigated if inclusion of CDR2L in diagnostic tests results in increased specificity for PCD. Methods Three panels were examined for reactivity against CDR2L and CDR2 by line blot analysis (EUROLINE). Panel A comprised 14 preselected sera from women with Yo-specific reactivity by indirect immunofluorescence assay (IFA) on rat cerebellum, presenting with cerebellar ataxia (n = 13) or peripheral neuropathy (n = 1) and underlying gynaecologic/breast cancers (n = 14). Panel B included 2132 non-selected consecutive serum/CSF samples from patients with neurological symptoms. Panel C consisted of 150 samples from healthy blood donors. Results In Panel A, all samples (100%) from patients with typical clinical characteristics for Yo-associated PCD showed strong positive reactivity to both CDR2L and CDR2. In Panel B, seven (0.3%) sera were anti-CDR2 negative, but anti-CDR2L positive, all of them from patients (6M/1F) without PCD and two with cancer or pre-cancerous condition. Eleven (0.5%) patients (9M/2F) were found to be anti-CDR2 positive, but anti-CDR2L negative, including two with cerebellar ataxia and three with cancer or pre-cancerous condition. In all 18 cases, IFA on rat cerebellum was negative, suggesting non-specific line blot reactivity to CDR2L or CDR2. In Panel C, 0/150 sera were anti-CDR2L and 1/150 anti-CDR2 positive, corresponding to specificities of 100% and 99.3%, respectively. The anti-CDR2 positive blood donor was male with negative IFA result. Conclusion Using CDR2L in addition to CDR2 increases the specificity in diagnosing anti-Yo-associated PCD. Positive line blot reactivity against both parameters seems to confirm the diagnosis. In contrast, results showing isolated reactivity against either CDR2L or CDR2 have to be interpreted carefully as they may apply to non-PCD cases.