Human cerebrospinal fluid monoclonal CASPR2 autoantibodies induce changes in electrophysiology, functional MRI, and behavior in rodent models.

Anti-contactin associated protein receptor 2 (CASPR2) encephalitis is a severe autoimmune encephalitis with a variable clinical phenotype including behavioral abnormalities, cognitive decline, epileptic seizures, peripheral nerve hyperexcitability and neuropathic pain. The detailed mechanisms of how CASPR2 autoantibodies lead to synaptic dysfunction and clinical symptoms are largely unknown. Aiming for analyses from the molecular to the clinical level, we isolated antibody-secreting cells from the cerebrospinal fluid of two patients with CASPR2 encephalitis. From these we cloned four anti-CASPR2 human monoclonal autoantibodies (mAbs) with strong binding to brain and peripheral nerves. All were highly hypermutated and mainly of the IgG4 subclass. Mutagenesis studies determined selective binding to the discoidin domain of CASPR2. Surface plasmon resonance revealed affinities with dissociation constants KD in the pico- to nanomolar range. CASPR2 mAbs interrupted the interaction of CASPR2 with its binding partner contactin 2 in vitro and were internalized after binding to CASPR2-expressing cells. Electrophysiological recordings of rat hippocampal slices after stereotactic injection of CASPR2 mAbs showed characteristic afterpotentials following electrical stimulation. In vivo experiments with intracerebroventricular administration of human CASPR2 mAbs into mice and rats showed EEG-recorded brain hyperexcitability but no spontaneous recurrent seizures. Behavioral assessment of infused mice showed a subtle clinical phenotype, mainly affecting sociability. Mouse brain MRI exhibited markedly reduced resting-state functional connectivity without short-term structural changes. Together, the experimental data support the direct pathogenicity of CASPR2 autoantibodies. The minimally invasive EEG and MRI techniques applied here may serve as novel objective, quantifiable tools for improved animal models, in particular for subtle neuropsychiatric phenotypes or repeated measurements.

Acquired hyperexcitable peripheral nerve disorders: Clinical and laboratory features, therapeutic responses, and long-term follow-up.

INTRODUCTION/AIMS: Hyperexcitable peripheral nerve disorders (HPNDs) are rare. Although their clinical and laboratory features have been well studied, information on treatment and follow-up is limited. The aim of this study is to explore the long-term clinical, investigative, and therapeutic profile of patients with acquired HPNDs. METHODS: This study retrospectively analyzed patients from a single tertiary care center with HPND (January 2012 to January 2022). Patients were recruited according to published inclusion and exclusion criteria. Details of clinical features, diagnostic tests, therapeutic interventions, and follow-up were recorded. This study included patients with follow-up of 2 or more years. RESULTS: A total of 32 patients (M = 26, F = 6) were studied. The common clinical features included myokymia, neuropathic or shock-like pain, cramps, sleep disturbances, encephalopathy, cerebellar ataxia, and seizures. A total of 81.25% of patients responded favorably to corticosteroids and membrane stabilizers. Among the nonresponders, five received intravenous immunoglobulin (IVIG), and one received plasma exchange (PLEX). Two patients required rituximab due to poor responses to the above treatments. The mean duration of response was 6 weeks (4-24 weeks) from the initiation of treatment. All patients had favorable outcomes, reaching clinical remission within 1-5 years from the initiation of treatment. Only two patients had relapses. Immunotherapy could be stopped in 78% of patients within 3 years and 100% by 5 years. DISCUSSION: Chronic immunosuppression starting with corticosteroids is required for satisfactory outcomes of HPNDs. These disorders usually run a monophasic course, and relapses are uncommon.

Distinct movement disorders in contactin-associated-protein-like-2 antibody-associated autoimmune encephalitis.

Autoimmune encephalitis can be classified into antibody-defined subtypes, which can manifest with immunotherapy-responsive movement disorders sometimes mimicking non-inflammatory aetiologies. In the elderly, anti-LGI1 and contactin associated protein like 2 (CASPR2) antibody-associated diseases compose a relevant fraction of autoimmune encephalitis. Patients with LGI1 autoantibodies are known to present with limbic encephalitis and additionally faciobrachial dystonic seizures may occur. However, the clinical spectrum of CASPR2 autoantibody-associated disorders is more diverse including limbic encephalitis, Morvan's syndrome, peripheral nerve hyperexcitability syndrome, ataxia, pain and sleep disorders. Reports on unusual, sometimes isolated and immunotherapy-responsive movement disorders in CASPR2 autoantibody-associated syndromes have caused substantial concern regarding necessity of autoantibody testing in patients with movement disorders. Therefore, we aimed to systematically assess their prevalence and manifestation in patients with CASPR2 autoimmunity. This international, retrospective cohort study included patients with CASPR2 autoimmunity from participating expert centres in Europe. Patients with ataxia and/or movement disorders were analysed in detail using questionnaires and video recordings. We recruited a comparator group with anti-LGI1 encephalitis from the GENERATE network. Characteristics were compared according to serostatus. We identified 164 patients with CASPR2 autoantibodies. Of these, 149 (90.8%) had only CASPR2 and 15 (9.1%) both CASPR2 and LGI1 autoantibodies. Compared to 105 patients with LGI1 encephalitis, patients with CASPR2 autoantibodies more often had movement disorders and/or ataxia (35.6 versus 3.8%; P < 0.001). This was evident in all subgroups: ataxia 22.6 versus 0.0%, myoclonus 14.6 versus 0.0%, tremor 11.0 versus 1.9%, or combinations thereof 9.8 versus 0.0% (all P < 0.001). The small group of patients double-positive for LGI1/CASPR2 autoantibodies (15/164) significantly more frequently had myoclonus, tremor, 'mixed movement disorders', Morvan's syndrome and underlying tumours. We observed distinct movement disorders in CASPR2 autoimmunity (14.6%): episodic ataxia (6.7%), paroxysmal orthostatic segmental myoclonus of the legs (3.7%) and continuous segmental spinal myoclonus (4.3%). These occurred together with further associated symptoms or signs suggestive of CASPR2 autoimmunity. However, 2/164 patients (1.2%) had isolated segmental spinal myoclonus. Movement disorders and ataxia are highly prevalent in CASPR2 autoimmunity. Paroxysmal orthostatic segmental myoclonus of the legs is a novel albeit rare manifestation. Further distinct movement disorders include isolated and combined segmental spinal myoclonus and autoimmune episodic ataxia.

The neurobiology and immunology of CASPR2-associated neurological disorders.

CASPR2-associated neurological disorders encompass a wide clinical spectrum broadly divided into overlapping three autoimmune syndromes: CASPR2 limbic encephalitis, Morvan syndrome, and Isaacs syndrome. CASPR2 is a neuronal protein expressed at different sites in the central and peripheral nervous system and has a variety of roles and functions regarding neuronal excitability, synaptic plasticity, and homeostasis of inhibitory networks, most of which are only partially understood. CASPR2 antibodies have various pathogenic effects including internalization of CASPR2, disruption of protein-protein interactions, and, possibly, complement activation. Their pathogenic effect is well demonstrated in the limbic encephalitis phenotype, but the role of pathogenic antibodies in the development of other clinical manifestations is less clear. CASPR2 limbic encephalitis also differ from the other CASPR2-associated disorders in regard to HLA allele and paraneoplastic associations, suggesting it has immunological mechanisms distinct from the other clinical forms. Future studies are needed to better understand how the immunological alterations lead to the different phenotypes associated with CASPR2 antibodies.

Functional changes in neuronal circuits due to antibody-driven autoimmune response.

Autoimmune-mediated encephalitis syndromes are increasingly being recognized as important clinical entities. They need to be thought of as differential diagnosis in any patient presenting with fast-onset psychosis or psychiatric problems, memory deficits or other cognitive problems, including aphasias, as well as seizures or motor automatisms, but also rigidity, paresis, ataxia or dystonic / parkinsonian symptoms. Diagnosis including imaging and CSF search for antibodies needs to be fast, as progression of these inflammatory processes is often causing scarring of brain tissue, with hypergliosis and atrophy. As these symptoms show, the autoantibodies present in these cases appear to act within the CNS. Several of such antibodies have by now been identified such as IgG directed against NMDA-receptors, AMPA receptors, GABAA and GABAB receptors, and voltage gated potassium channels and proteins of the potassium channel complex (i.e. LGI1 and CASPR2). These are neuropil / surface antigens where antibody interaction can well be envisaged to cause dysfunction of the target protein, including internalization. Others, such as antibodies directed against GAD65 (an intracellular enzyme responsible for GABA-synthesis from glutamate), are discussed to constitute epiphenomena, but not causal agents in disease progression. This review will focus on the current knowledge of antibody interaction mechanisms, especially discussing cellular excitability changes and synaptic interactions in hippocampal and other brain networks. One challenge in this context is to find viable hypotheses for the emergence of both, hyperexcitability and seizures, and presumably reduced synaptic plasticity and underlying cognitive dysfunction.

A case of herpes simplex virus induced peripheral neuropathy and encephalitis with positive GM3 and CASPR2 antibody.

BACKGROUND: We reported on a case involving an older patient with HSV-1 encephalitis who simultaneously experienced the onset of peripheral nerve symptoms associated with the presence of anti-GM3 immunoglobulin G (IgG). CASE PRESENTATION: A 77-year-old male was admitted to hospital with high fever, weakness of both lower limbs, and an unstable gait. A CSF test revealed a strikingly increased protein level (1,002 mg/L, normative values: 150-450 mg/L) and MRI revealed hyper-signal lesions in the right temporal lobe, right hippocampus, right insula, and right cingulate gyrus. The CSF was positive for HSV PCR (HSV-1,17870). In addition, the serum samples were positive for CASPR2 antibodies (antibody titer: 1/10) and anti-GM3 immunoglobulin G (IgG) (+). The patient was diagnosed with HSV-1-induced peripheral nerve symptoms that were associated with encephalitis and the presence of anti-GM3 IgG and anti-CASPR2 antibodies. The patient had received included intravenous immunoglobulin, intravenous acyclovir, and corticosteroids therapy. At the one-year follow-up examination, he had regained the necessary skills associated with daily life. CONCLUSIONS: Herpes simplex virus infection often induces encephalitis, and reaction to the virus may trigger an autoimmune response. Early diagnosis and treatment can avoid the progression of the disease to include autoimmune encephalitis.

Hyperexcitable and immature-like neuronal activity in the auditory cortex of adult rats lacking the language-linked CNTNAP2 gene.

The contactin-associated protein-like 2 gene, CNTNAP2, is a highly penetrant risk gene thought to play a role in the genetic etiology of language-related disorders, such as autism spectrum disorder and developmental language disorder. Despite its candidacy for influencing language development, few preclinical studies have examined the role of CNTNAP2 in auditory processing. Using in vivo and in vitro electrophysiological recordings in a rat model with translational validity, we report that a loss of the Cntnap2 gene function caused immature-like cortical evoked potentials, delayed multiunit response latencies to acoustic stimuli, impaired temporal processing, and led to a pattern of hyperexcitability in both multiunit and single cell recordings in adulthood. These collective results provide direct evidence that a constitutive loss of Cntnap2 gene function in rats can cause auditory processing impairments similar to those seen in language-related human disorders, indicating that its contribution in maintaining cortical neuron excitability may underlie the cortical activity alterations observed in Cntnap2-/- rats.

Anti-CASPR2 encephalitis in a liver posttransplant patient receiving immune-suppression and lenvatinib: a case report and literature review.

It has been assumed that patients with strict immunosuppressive treatment after solid organ transplantation have only marginal risk in developing autoimmune encephalitis. We reported a woman in her late 40 s who presented with generalized convulsions and loss of consciousness. After detailed history review, neuropsychological tests, metagenomic next-generation sequencing of serum and cerebrospinal fluid (CSF), magnetic resonance imaging (MRI) brain, and electroencephalogram, she was diagnosed as anti-CASPR2 encephalitis based on the positive anti-CASPR2 auto-antibody in serum and CSF. The patient underwent liver transplantation and has taken lenvatinib for 2 months, in addition to tacrolimus, mycophenotale mofetil, and entecavir administered for half a year. This case was the first report of anti-CASPR2 encephalitis in post-organ transplantation patients. Together with the reports of other encephalitis cases in organ transplantation, it warns the possibility of developing immune-oriented encephalitis in patients undergoing immunosuppression, especially in combination with other treatments of immunomodulatory activity.

Novelties in Autoimmune and Paraneoplastic Cerebellar Ataxias: Twenty Years of Progresses.

Major advances in our knowledge concerning autoimmune and paraneoplastic cerebellar ataxias have occurred in the last 20 years. The discovery of several neural antibodies represents an undeniable contribution to this field, especially those serving as good biomarkers of paraneoplastic neurological syndromes and those showing direct pathogenic effects. Yet, many patients still lack detectable or known antibodies, and also many antibodies have only been reported in few patients, which makes it difficult to define in detail their clinical value. Nevertheless, a notable progress has additionally been made in the clinical characterization of patients with the main neural antibodies, which, although typically present with a subacute pancerebellar syndrome, may also show either hyperacute or chronic onsets that complicate the differential diagnoses. However, prodromal and transient features could be useful clues for an early recognition, and extracerebellar involvement may also be highly indicative of the associated antibody. Moreover, important advances in our understanding of the pathogenesis of cerebellar ataxias include the description of antibody effects, especially those targeting cell-surface antigens, and first attempts to isolate antigen-specific T-cells. Furthermore, genetic predisposition seems relevant, although differently involved according to cancer association, with particular HLA observed in non-paraneoplastic cases and genetic abnormalities in the tumor cells in paraneoplastic ones. Finally, immune checkpoint inhibitors used as cancer immunotherapy may rarely induce cerebellar ataxias, but even this undesirable effect may in turn serve to shed some light on their physiopathology. Herein, we review the principal novelties of the last 20 years regarding autoimmune and paraneoplastic cerebellar ataxias.

Seizure underreporting in LGI1 and CASPR2 antibody encephalitis.

Patients with anti-leucine-rich glioma-inactivated 1 protein (LGI1) or anti-contactin-associated protein 2 (CASPR2) antibody encephalitis typically present with frequent epileptic seizures. The seizures generally respond well to immunosuppressive therapy, and the long-term seizure outcome seems to be favorable. Consequentially, diagnosing acute symptomatic seizures secondary to autoimmune encephalitis instead of autoimmune epilepsy was proposed. However, published data on long-term seizure outcomes in CASPR2 and LGI1 antibody encephalitis are mostly based on patient reports, and seizure underreporting is a recognized issue. Clinical records from our tertiary epilepsy center were screened retrospectively for patients with LGI1 and CASPR2 antibody encephalitis who reported seizure freedom for at least 3 months and received video-electroencephalography (EEG) for >24 h at follow-up visits. Twenty (LGI1, n = 15; CASPR2, n = 5) of 32 patients with LGI1 (n = 24) and CASPR2 (n = 8) antibody encephalitis fulfilled these criteria. We recorded focal aware and impaired awareness seizures in four of these patients (20%) with reported seizure-free intervals ranging from 3 to 27 months. Our results question the favorable seizure outcome in patients with CASPR2 and LGI1 antibody encephalitis and suggest that the proportion of patients who have persistent seizures may be greater. Our findings underline the importance of prolonged video-EEG telemetry in this population.

Long-term seizure outcomes in patients with autoimmune encephalitis: A prospective observational registry study update.

OBJECTIVE: This study was undertaken to update and evaluate long-term seizure outcomes in patients with autoimmune encephalitis (AE) based on a large cohort study with long follow-up. METHODS: In this prospective observational registry study, we analyzed data from patients with AE mediated by common types of neuronal surface antibodies (anti-N-methyl-d-aspartate receptor [NMDAR], anti-leucine-rich glioma-inactivated 1 [LGI1]/contactin-associated protein-like 2 [Caspr2], anti-γ-aminobutyric acid type B receptor [GABAB R]). All patients were recruited from the Department of Neurology at West China Hospital between October 2011 and June 2019, and data were collected prospectively on their demographic and clinical characteristics, treatment strategy, and seizure outcomes, with a median follow-up of 42 months (range = 6-93 months). Potential risk factors associated with seizure recurrence were also assessed. RESULTS: Of 320 AE patients, 75.9% had acute seizures, among whom >90% of patients had their last seizure within 12 months of disease onset. During our follow-up, 21 (9.3%) patients experienced seizure recurrence. Patients with anti-GABAB R encephalitis had a higher cumulative incidence of seizure recurrence than those with anti-NMDAR (log-rank p = .03) or anti-LGI1/Caspr2 encephalitis (log-rank p = .04). Among patients with anti-NMDAR encephalitis, women had a significantly higher cumulative incidence of seizure recurrence than men (log-rank p = .01). Interictal epileptiform discharges (IEDs) or seizures captured on continuous electroencephalogram (EEG) in the acute phase were identified as potential risk factors for seizure recurrence (p = .04, p = .007). Among 163 patients with ≥24 months of follow-up, five (3.1%) showed persistent seizures and required ongoing antiseizure medications despite aggressive immunotherapy. SIGNIFICANCE: Seizure recurrence occurred in a small number of patients and chronic epilepsy occurred in 3.1% of patients during prolonged follow-up. Across all types of AE, risk factors for seizure recurrence were IEDs or seizures captured on EEG in the acute phase; for anti-NMDAR encephalitis, female sex was also a risk factor.

Caspr2 antibodies in herpes simplex encephalitis: an extension of the spectrum of virus induced autoimmunity? - A case report.

BACKGROUND: Post herpes simplex virus (HSV) autoimmune encephalitis has been reported mainly in association with NMDA receptor antibodies, however, never with Caspr2 antibodies. CASE PRESENTATION: We report an 82-year old female patient with encephalitis who presented with aphasia, left temporo-mesial hyperintense lesion on MRI, epileptiform discharges on spot electroencephalography, cerebrospinal fluid (CSF) lymphocytic pleocytosis and who showed positive HSV polymerase chain reaction in CSF as well as antibodies against contactin-associated protein-like 2 (Caspr2). CONCLUSION: This is the first report of a patient with encephalitis who tested positive for HSV as well as for Caspr2 antibodies.

Isaacs' syndrome as the initial presentation of malignant thymoma and associated with double-positive voltage-gated potassium channel complex antibodies, a case report.

BACKGROUND: Isaacs' syndrome is a peripheral nerve hyperexcitability (PNH) syndrome due to peripheral motor nerve instability. Acquired Isaacs' syndrome is recognized as a paraneoplastic autoimmune disease with possible pathogenic voltage-gated potassium channel (VGKC) complex antibodies. However, the longitudinal correlation between clinical symptoms, VGKC antibodies level, and drug response is still unclear. CASE PRESENTATION: A 45-year-old man had progressive four limbs soreness, muscle twitching, cramps, and pain 4 months before admission. Electromyography (EMG) studies showed myokymic discharges, neuromyotonia, and an incremental response in the high-rate (50 Hz) repetitive nerve stimulation (RNS) test. Isaacs' syndrome was diagnosed based on clinical presentations and EMG reports. Serum studies showed positive VGKC complex antibodies, including leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (CASPR2) antibodies. The acetylcholine receptor antibody was negative. Whole-body computed tomography (CT) and positron emission tomography revealed a mediastinal tumor with the great vessels encasement, right pleura, and diaphragm seeding. Biopsy confirmed a World Health Organization type B2 thymoma, with Masaoka stage IVa. His symptoms gradually improved and both LGI1 and CASPR2 antibodies titer became undetectable after concurrent chemoradiotherapy (CCRT) and high dose steroid treatment. However, his Isaacs' syndrome recurred after the steroid was reduced 5 months later. Follow-up chest CT showed probable thymoma progression. LGI1 antibody turned positive again while CASPR2 antibody remained undetectable. CONCLUSIONS: Our patient demonstrates that Isaacs' syndrome could be the initial and only neuromuscular manifestation of malignant thymoma. His Isaacs' syndrome is correlated well with the LGI1 antibody level. With an unresectable thymoma, long-term immunosuppressant therapy may be necessary for the management of Isaacs' syndrome in addition to CCRT for thymoma.

Caspr2 interacts with type 1 inositol 1,4,5-trisphosphate receptor in the developing cerebellum and regulates Purkinje cell morphology.

Contactin-associated protein-like 2 (Caspr2) is a neurexin-like protein that has been associated with numerous neurological conditions. However, the specific functional roles that Caspr2 plays in the central nervous system and their underlying mechanisms remain incompletely understood. Here, we report on a functional role for Caspr2 in the developing cerebellum. Using a combination of confocal microscopy, biochemical analyses, and behavioral testing, we show that loss of Caspr2 in the Cntnap2-/- knockout mouse results in impaired Purkinje cell dendritic development, altered intracellular signaling, and motor coordination deficits. We also find that Caspr2 is highly enriched at synaptic specializations in the cerebellum. Using a proteomics approach, we identify type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) as a specific synaptic interaction partner of the Caspr2 extracellular domain in the molecular layer of the developing cerebellum. The interaction of the Caspr2 extracellular domain with IP3R1 inhibits IP3R1-mediated changes in cellular morphology. Together, our work defines a mechanism by which Caspr2 controls the development and function of the cerebellum and advances our understanding of how Caspr2 dysfunction might lead to specific brain disorders.

Peripheral nerve hyperexcitability syndrome: A clinical, electrophysiological, and immunological study.

INTRODUCTION: Peripheral nerve hyperexcitability syndrome (PNHS) is characterized by muscle fasciculations and spasms. Nerve hyperexcitability and after-discharges can be observed in electrophysiological studies. Autoimmune mechanisms play a major role in the pathophysiology of primary PNHS. METHODS: We retrospectively conducted a case-control study recruiting patients with clinical and electrophysiological features of PNHS. Control patients were diagnosed with other neuronal or muscular diseases. Contactin-associated protein2 (CASPR2) and leucine-rich glioma-inactivated1 (LGI1) antibodies were examined. RESULTS: A total of 19 primary PNHS patients and 39 control patients were analyzed. The most common symptoms for the case group were fasciculations (11/19) and muscle spasms (13/19). Case group patients were likely to demonstrate electrodiagnostic findings of nerve hyperexcitability (17/19) and after-discharges in the tibial nerve (19/19). We found high prevalence of CASPR2 (9/19) and LGI1 (6/19) antibodies in the case group. DISCUSSION: Primary PNHS patients were likely to show after-discharges in the tibial nerve. The pathogenesis of PNHS is autoimmune CASPR2 and LGI1 antibodies are possible pathogenic antibodies for primary PNHS.

Morvan syndrome associated with LGI1 antibody: a case report.

BACKGROUND: Morvan syndrome (MoS) is a rare autoimmune syndrome associated with antibodies against two kinds of potassium channel proteins, contactin associated protein-like 2 (CASPR2) and leucine-rich glioma inactivated protein 1 (LGI1). MoS patients with only LGI1-antibody seropositivity have rarely been reported. Here, we describe a 64-year-old male MoS patient with only LGI1-antibody seropositivity. CASE PRESENTATION: A 64-year-old male patient was referred to our hospital due to limb pain, widespread myokymia, insomnia, constipation, and hyperhidrosis for 1 month. The patient was diagnosed with MoS based on the clinical symptoms and positive LGI1-antibody in serum. He was treated with intravenous immunoglobulin (IVIG), intravenous methylprednisolone followed by oral prednisone, and other drugs for symptomatic relief. Several days later, myokymia and insomnia symptoms improved. After 60 days of follow-up, all the drugs had been stopped for 2 weeks, and the patient achieved complete remission without any medical side effects. CONCLUSION: We report the clinical characteristics of a Chinese MoS patient with only LGI1-antibody seropositivity, and further support the view that non-neoplasm MoS patients respond well to immunotherapy.

Serum and CSF cytokine levels mirror different neuroimmunological mechanisms in patients with LGI1 and Caspr2 encephalitis.

Changes in levels of cytokines or soluble receptors in biological fluids may provide information on immunological pathomechanisms underlying the respective diseases. Here, we studied cytokine patterns of patients with autoimmune encephalitis (AE) before and after immunosuppressive treatment in order to identify possible biomarker candidates and to look for putatively involved pathomechanisms. We performed measurements in Cerebrospinal fluid (CSF) and serum of 7 patients suffering from AE with antibodies (ab) against Leucine-rich glioma-inactivated-protein 1 (LGI1) and 9 AE patients with Contactin-associated protein-like 2 (Caspr2) ab recruited from two tertiary AE centers in Magdeburg and Berlin, Germany. In the Magdeburg samples before and after treatment were available for the measurements and in the Berlin cohort samples were collected after treatment was initiated. First, we used a human cytokine array comprising 36 cytokines or soluble receptors to screen for biomarkers in CSF samples of 8 AE (before and after treatment), 4 herpes-simplex virus meningoencephalitis patients and 4 controls without neuroinflammation. Next, CCL2, CXCl10, CXCl13, Il -6 and sICAM1 were chosen as candidates and measured in CSF and serum with specific ELISA systems in all 16 AE patients, 14 controls without neuroinflammation and 7 herpes-simplex virus meningitis patients. Clinical outcome was assessed via modified Rankin scale. LGI1 and Caspr2 abs from the Magdeburg cohort were purified by chromatography. IgG subclasses of these LGI1 or Caspr2 abs were identified by immunoblot analysis. The levels of most candidate parameters were higher in the CSF of Caspr2 than of LGI1 AE patients and controls, but there were no significant changes of cytokine concentrations before and after initiating treatment. Thus, these parameters seem unsuited as surrogate biomarkers of disease. Significantly higher levels were observed in the CSFs of Caspr2 AE patients (CXCL13 and sICAM1) as well as in the serum of Caspr2 (CXCL10) and LGI1 AE patients (CXCL13) in comparison to control samples. These results suggest that neuro-immunological pathomechanisms may differ between Caspr2 and LGI1 AE patients. Caspr2 AE seems to elicit a higher immune response than LGI1 AE, which has no correlation to the respective IgG subclass combination of AE specific abs involved in each type of disease.

Anti-CASPR2 clinical phenotypes correlate with HLA and immunological features.

OBJECTIVE: Antibodies against contactin-associated protein-like 2 (CASPR2-Abs) have been described in acquired neuromyotonia, limbic encephalitis (LE) and Morvan syndrome (MoS). However, it is unknown whether these constitute one sole spectrum of diseases with the same immunopathogenesis or three distinct entities with different mechanisms. METHODS: A cluster analysis of neurological symptoms was performed in a retrospective cohort of 56 CASPR2-Abs patients. In parallel, immunological features and human leucocyte antigen (HLA) were studied. RESULTS: Cluster analysis distinguished patients with predominant limbic symptoms (n=29/56) from those with peripheral nerve hyperexcitability (PNH; n=27/56). In the limbic-prominent group, limbic features were either isolated (LE/-; 18/56, 32.1%), or combined with extralimbic symptoms (LE/+; 11/56, 19.6%). Those with PNH were separated in one group with severe PNH and extralimbic involvement (PNH/+; 16/56, 28.6%), resembling historical MoS descriptions; and one group with milder and usually isolated PNH (PNH/-; 11/56, 19.6%). LE/- and LE/+ patients shared immunogenetic characteristics demonstrating a homogeneous entity. HLA-DRB1*11:01 was carried more frequently than in healthy controls only by patients with LE (94.1% vs 18.3%; p=1.3×10-10). Patients with LE also had serum titres (median 1:40 960) and rates of cerebrospinal fluid positivity (93.1%) higher than the other groups (p<0.05). Conversely, DRB1*11:01 association was absent in PNH/+ patients, but only they had malignant thymoma (87.5%), serum antibodies against leucine-rich glioma-inactivated 1 protein (66.7%) and against netrin-1 receptor deleted in colorectal carcinoma (53.8%), and myasthenia gravis (50.0%). INTERPRETATION: Symptoms' distribution supports specific clinical phenotypes without overlap between LE and MoS. The distinct immunogenetic characteristics shared by all patients with LE and the particular oncological and autoimmune associations of MoS suggest two very different aetiopathogenesis.

Cytokine changes during treatment of anti-Caspr2 encephalitis: a case report.

BACKGROUND: Cytokines are effective molecules of immune reactions. They work in inflammatory sites as well as circulate in the blood. Cytokines in the cerebrospinal fluid have been suggested to be markers of autoimmune encephalitis and reflect disease progression. However, studies on blood cytokines in autoimmune encephalitis are scarce. We report a case presenting with serial changes in blood cytokine levels in a male patient with anti-contactin-associated protein 2 (Caspr2) encephalitis. CASE PRESENTATION: A 61-year-old man without systemic disease presented with ataxia and speech disturbance 1 week. After admission, he further developed visual hallucinations, psychosis, and consciousness deterioration. Brain magnetic resonance imaging and infection and tumor surveillances were negative. 18F-fluorodeoxyglucose positron emission tomography of brain revealed frontal and occipital hypometabolism and anterior cingulate gyrus and mesial temporal hypermetabolism. Autoimmune studies confirmed Caspr2 antibodies in his blood. After receiving a diagnosis of anti-Caspr2 encephalitis, the patient received steroids, plasmapheresis, and zonisamide. He recovered well and was totally independent 6 months after disease onset. A cytokine profiler array kit was used to investigate neuroimmune mechanisms during the disease course. Several cytokines showed significant changes in plasma levels, such as B cell activating factor for B cell proliferation; thymus and activation-regulated chemokine for T cell chemoattraction; soluble CD40 ligand for Th2 cell mediation; C5/C5a for complement activation; brain-derived neurotrophic factor for neuronal survival response; and dipeptidyl peptidase 4, retinol binding protein, dickkopf-related protein, and epidermal growth factor for response to environmental provocation. The concentration of cytokines was verified using Luminex multiplexing assay. CONCLUSIONS: Due to their easy accessibility, blood cytokines are potential biomarkers of autoimmune encephalitis. Based on the investigating platform of this single case study, future larger scale studies are warranted.

Behaviour and neuropathology in mice injected with human contactin-associated protein 2 antibodies.

Serum antibodies that bind to the surface of neurons or glia are associated with a wide range of rare but treatable CNS diseases. In many, if not most instances, the serum levels are higher than CSF levels yet most of the reported attempts to reproduce the human disease in mice have used infusion of antibodies into the mouse cerebral ventricle(s) or intrathecal space. We used the intraperitoneal route and injected purified plasma IgG from either a CASPR2-antibody-positive patient (n = 10 mice) or healthy individual (n = 9 mice) daily for 8 days. Lipopolysaccharide was injected intraperitoneally on Day 3 to cause a temporary breach in the blood brain barrier. A wide range of baseline behaviours, including tests of locomotion, coordination, memory, anxiety and social interactions, were established before the injections and tested from Day 5 until Day 11. At termination, brain tissue was analysed for human IgG, CASPR2 and c-fos expression, lymphocyte infiltration, and neuronal, astrocytic and microglial markers. Mice exposed to CASPR2-IgG, compared with control-IgG injected mice, displayed reduced working memory during the continuous spontaneous alternation test with trends towards reduced short-term and long-term memories. In the open field tests, activities were not different from controls, but in the reciprocal social interaction test, CASPR2-IgG injected mice showed longer latency to start interacting, associated with more freezing behaviour and reduced non-social activities of rearing and grooming. At termination, neuropathology showed more IgG deposited in the brains of CASPR2-IgG injected mice, but a trend towards increased CASPR2 expression; these results were mirrored in short-term in vitro experiments where CASPR2-IgG binding to hippocampal neurons and to CASPR2-transfected HEK cells led to some internalization of the IgG, but with a trend towards higher surface CASPR2 expression. Despite these limited results, in the CASPR2-IgG injected mouse brains there was increased c-fos expression in the piriform-entorhinal cortex and hypothalamus, and a modest loss of Purkinje cells. There was also increased microglia density, morphological changes in both microglia and astrocytes and raised complement C3 expression on astrocytes, all consistent with glial activation. Patients with CASPR2 antibodies can present with a range of clinical features reflecting central, autonomic and peripheral dysfunction. Although the behavioural changes in mice were limited to social interactions and mild working-memory defects, the neuropathological features indicate potentially widespread effects of the antibodies on different brain regions.