'Moonlighting' surface antigens: a paradigm for autoantibody pathogenicity in neurology?

Paraneoplastic neuropathies and peripheral nerve hyperexcitability disorders

Peripheral neuropathy is a common referral for patients to the neurologic clinics. Paraneoplastic neuropathies account for a small but high morbidity and mortality subgroup. Symptoms include weakness, sensory loss, sweating irregularity, blood pressure instability, severe constipation, and neuropathic pain. Neuropathy is the first presenting symptom of malignancy among many patients. The molecular and cellular oncogenic immune targets reside within cell bodies, axons, cytoplasms, or surface membranes of neural tissues. A more favorable immune treatment outcome occurs in those where the targets reside on the cell surface. Patients with antibodies binding cell surface antigens commonly have neural hyperexcitability with pain, cramps, fasciculations, and hyperhidrotic attacks (CASPR2, LGI1, and others). The antigenic targets are also commonly expressed in the central nervous system, with presenting symptoms being myelopathy, encephalopathy, and seizures with neuropathy, often masked. Pain and autonomic components typically relate to small nerve fiber involvement (nociceptive, adrenergic, enteric, and sudomotor), sometimes without nerve fiber loss but rather hyperexcitability. The specific antibodies discovered help direct cancer investigations. Among the primary axonal paraneoplastic neuropathies, pathognomonic clinical features do not exist, and testing for multiple antibodies simultaneously provides the best sensitivity in testing (AGNA1-SOX1; amphiphysin; ANNA-1-HU; ANNA-3-DACH1; CASPR2; CRMP5; LGI1; PCA2-MAP1B, and others). Performing confirmatory antibody testing using adjunct methods improves specificity. Antibody-mediated demyelinating paraneoplastic neuropathies are limited to MAG-IgM (IgM-MGUS, Waldenström's, and myeloma), with the others associated with cytokine elevations (VEGF, IL6) caused by osteosclerotic myeloma, plasmacytoma (POEMS), and rarely angiofollicular lymphoma (Castleman's). Paraneoplastic disorders have clinical overlap with other idiopathic antibody disorders, including IgG4 demyelinating nodopathies (NF155 and Contactin-1). This review summarizes the paraneoplastic neuropathies, including those with peripheral nerve hyperexcitability.

General features, pathogenesis, and laboratory diagnostics of autoimmune encephalitis

Autoimmune encephalitis (AE) is a group of inflammatory conditions that can associate with the presence of antibodies directed to neuronal intracellular, or cell surface antigens. These disorders are increasingly recognized as an important differential diagnosis of infectious encephalitis and of other common neuropsychiatric conditions. Autoantibody diagnostics plays a pivotal role for accurate diagnosis of AE, which is of utmost importance for the prompt recognition and early treatment. Several AE subgroups can be identified, either according to the prominent clinical phenotype, presence of a concomitant tumor, or type of neuronal autoantibody, and recent diagnostic criteria have provided important insights into AE classification. Antibodies to neuronal intracellular antigens typically associate with paraneoplastic neurological syndromes and poor prognosis, whereas antibodies to synaptic/neuronal cell surface antigens characterize many AE subtypes that associate with tumors less frequently, and that are often immunotherapy-responsive. In addition to the general features of AE, we review current knowledge on the pathogenic mechanisms underlying these disorders, focusing mainly on the potential role of neuronal antibodies in the most frequent conditions, and highlight current theories and controversies. Then, we dissect the crucial aspects of the laboratory diagnostics of neuronal antibodies, which represents an actual challenge for both pathologists and neurologists. Indeed, this diagnostics entails technical difficulties, along with particularly interesting novel features and pitfalls. The novelties especially apply to the wide range of assays used, including specific tissue-based and cell-based assays. These assays can be developed in-house, usually in specialized laboratories, or are commercially available. They are widely used in clinical immunology and in clinical chemistry laboratories, with relevant differences in analytic performance. Indeed, several data indicate that in-house assays could perform better than commercial kits, notwithstanding that the former are based on non-standardized protocols. Moreover, they need expertise and laboratory facilities usually unavailable in clinical chemistry laboratories. Together with the data of the literature, we critically evaluate the analytical performance of the in-house vs commercial kit-based approach. Finally, we propose an algorithm aimed at integrating the present strategies of the laboratory diagnostics in AE for the best clinical management of patients with these disorders.

Pathophysiological Effects of Autoantibodies in Autoimmune Encephalitides

The heterogeneity of autoantibody targets in autoimmune encephalitides presents a challenge for understanding cellular and humoral pathophysiology, and the development of new treatment strategies. Thus, current treatment aims at autoantibody removal and immunosuppression, and is primarily based on data generated from other autoimmune neurological diseases and expert consensus. There are many subtypes of autoimmune encephalitides, which now entails both diseases with autoantibodies targeting extracellular antigens and classical paraneoplastic syndromes with autoantibodies targeting intracellular antigens. Here, we review the current knowledge of molecular and cellular effects of autoantibodies associated with autoimmune encephalitis, and evaluate the evidence behind the proposed pathophysiological mechanisms of autoantibodies in autoimmune encephalitis.

Neurological Manifestations of Glutamic Acid Decarboxylase Autoimmunity in Indian Patients

Objective

To study the neurological manifestations of glutamic acid decarboxylase (GAD 65) autoimmunity in Indian patients.

Methods

Retrospective study conducted in a tertiary care referral hospital in South India. Patients who tested positive for GAD 65 antibodies from February 2013 to July 2019 were included.

Results

We identified 922 patients who underwent GAD 65 testing, of which 81 tested positive (8.78%) [mean age 55.42 years (SD 17.39, range 9-86 years, median age 57 years)]. Males (n = 47) outnumbered the females (n = 34). All the GAD values measured were <5000 IU/ml. There were 34 cases (42%) of atypical parkinsonism (16/34, 47% fulfilled the diagnostic criteria for autoimmune atypical parkinsonism) in our series forming the most common group with GAD 65 positivity, followed by autoimmune encephalitis (8 cases, 9.88%). Men were more affected with atypical parkinsonism (22/34; 64.70%), stiff person syndrome (2/3; 66.66%), and neuropathy (4/7; 57.1%) while women were more with autoimmune encephalitis (6/8; 75%). Eighteen (22.6%) had underlying autoimmunity (three had type 1 diabetes mellitus). Six (7.4%) had underlying neoplasm. Thirty-three out of 43 patients responded to immunotherapy (76.74%). Five had spontaneous improvement.

Conclusion

Glutamic acid decarboxylase65 antibody values were much lower in our study population. Male-dominant autoimmunity was seen unlike that in Western literature. The most striking was the high preponderance of atypical parkinsonism in GAD 65-positive patients. We also found that GAD 65 positivity is a useful marker for a positive response to immunotherapy in suspected autoimmune neurological syndromes irrespective of their titers.

Autoimmune movement disorders with neuronal antibodies - an update

PURPOSE OF REVIEW

The rapid developments in neuroimmunology reflect also on the field of movement disorders, where there is an ever expanding spectrum of new antibodies. This review focuses on the new neuronal antibodies, their clinical spectrum and recent pathophysiological insights. It gives an update on previous work about neuronal antibody-related movement disorders.

RECENT FINDINGS

Phosphodiesterase 10A antibodies are a new marker of paraneoplastic chorea. Seizure-related 6 homolog like 2 antibodies are a differential diagnosis in atypical parkinsonism with cerebellar ataxia and cognitive impairment. mGluR5-antibodies cause various hyperkinetic movement disorders with Ophelia syndrome. Most new antibodies were described in the context of cerebellar ataxia: Kelch-like protein 11 antibodies are a comparatively frequent marker of paraneoplastic cerebellar ataxia with germ cell tumours. Nonparaneoplastic cerebellar ataxia occurs with Septin-5 and neurochondrin antibodies. Studies into the mechanisms of neuronal surface antibodies have shown that there is much pathophysiological heterogeneity, ranging from immediate antagonistic effect to induction of neurodegeneration after weeks.

SUMMARY

The new markers of autoimmune movement disorders are key to identify those patients that may benefit from immunotherapy, and tumour therapy, where appropriate. Insights into the underlying pathophysiology might guide treatment decisions and help tailoring more targeted approaches in the future.

Structural Analysis of Anti-Hapten Antibodies to Identify Long-Range Structural Movements Induced by Hapten Binding

Antibodies are well known for their high specificity that has enabled them to be of significant use in both therapeutic and diagnostic applications. Antibodies can recognize different antigens, including proteins, carbohydrates, peptides, nucleic acids, lipids, and small molecular weight haptens that are abundantly available as hormones, pharmaceuticals, and pesticides. Here we focus on a structural analysis of hapten-antibody couples and identify potential structural movements originating from the hapten binding by comparison with unbound antibody, utilizing 40 crystal structures from the Protein Data Bank. Our analysis reveals three binding surface trends; S1 where a pocket forms to accommodate the hapten, S2 where a pocket is removed when the hapten binds, and S3 where no pockets changes are found. S1 and S2 are expected for induced-fit binding, whereas S3 indicates that a pre-existing population of optimal binding antibody conformation exists. The structural analysis reveals four classifications of structural reorganization, some of which correlate to S2 but not to the other binding surface changes. These observations demonstrate the complexity of the antibody-antigen interaction, where structural changes can be restricted to the binding sites, or extend through the constant domains to propagate structural changes. This highlights the importance of structural analysis to ensure successful and compatible transformation of small antibody fragments at the early discovery stage into full antibodies during the subsequent development stages, where long-range structural changes are required for an Fc effector response.

Paraneoplastic neurological syndromes: clinical presentations and management

We provide an overview of the varied presentations of paraneoplastic neurological syndromes. We also review the onconeural antibodies and their particular oncological and neurological associations. Recognition of these syndromes and their oncological associations is crucial, as early diagnosis and management has been associated with better patient outcomes. Specific management strategies and prognosis vary widely depending on the underlying etiology. An understanding of the relevant clinical details, imaging findings, and other diagnostic information can help tailor treatment approaches. We provide an outline of the diagnostic evaluation and treatment of various paraneoplastic neurological disorders, presenting with central and/or peripheral nervous system involvement. We briefly discuss neurologic immune checkpoint inhibitor-related adverse events, which can occasionally present with paraneoplastic neurological syndrome phenotypes.

Involuntary movement in stiff-person syndrome with amphiphysin antibodies: A case report

RATIONALE

Stiff-person syndrome (SPS) is a rare neurological immune disorder characterized by progressive axial and proximal limb muscle rigidity, stiffness, and painful muscle spasms. Amphiphysin antibodies are positive in approximately 5% of SPS patients. To date, there have been no relevant reports on involuntary movement in cases of SPS with amphiphysin antibodies.

PATIENT CONCERNS

We describe the case of a 69-year-old man with a 2-year history of progressive stiffness in the neck, bilateral shoulders, and chest muscles, and a more-than-a-year history of dyspnea accompanied by mandibular involuntary movement. The patient was a vegetarian and had good health in the past. The family's medical history was unremarkable.

DIAGNOSES

He was diagnosed with SPS based on the progressive muscle stiffness, the amphiphysin antibody seropositivity, the continuous motor activity on electromyography, and the effective treatment with benzodiazepines.

INTERVENTIONS

The patient was orally administered clonazepam and baclofen, and corticosteroid IV followed by prednisone orally.

OUTCOMES

In the hospital, after treatment with methylprednisolone, clonazepam, and baclofen, the patient's rigidity, stiffness, and dyspnea significantly improved. The involuntary movement of the mandible persisted throughout the treatment process. Currently, under oral treatment with baclofen and clonazepam, the patient's symptoms of muscle stiffness and dyspnea exist, and follow-up is continued.

LESSONS

We report a rare and novel case of involuntary movement in SPS with amphiphysin antibodies. The present report explores the relationship between SPS and involuntary movement and expands the spectrum of clinical manifestations of SPS.

Biotherapeutic Antibodies for the Treatment of Head and Neck Cancer: Current Approaches and Future Considerations of Photothermal Therapies

Head and neck cancer (HNC) is a heterogeneous disease that includes a variety of tumors originating in the hypopharynx, oropharynx, lip, oral cavity, nasopharynx, or larynx. HNC is the sixth most common malignancy worldwide and affects thousands of people in terms of incidence and mortality. Various factors can trigger the development of the disease such as smoking, alcohol consumption, and repetitive viral infections. HNC is currently treated by single or multimodality approaches, which are based on surgery, radiotherapy, chemotherapy, and biotherapeutic antibodies. The latter approach will be the focus of this article. There are currently three approved antibodies against HNCs (cetuximab, nivolumab, and pembrolizumab), and 48 antibodies under development. The majority of these antibodies are of humanized (23 antibodies) or human (19 antibodies) origins, and subclass IgG1 represents a total of 32 antibodies. In addition, three antibody drug conjugates (ADCs: telisotuzumab-vedotin, indatuximab-ravtansine, and W0101) and two bispecific antibodies (GBR 1372 and ABL001) have been under development. Despite the remarkable success of antibodies in treating different tumors, success was limited in HNCs. This limitation is attributed to efficacy, resistance, and the appearance of various side effects. However, the efficacy of these antibodies could be enhanced through conjugation to gold nanoparticles (GNPs). These conjugates combine the high specificity of antibodies with unique spectral properties of GNPs to generate a treatment approach known as photothermal therapy. This approach can provide promising outcomes due to the ability of GNPs to convert light into heat, which can specifically destroy cancer cells and treat HNC in an effective manner.

Autoimmune encephalitis and epilepsy: evolving definition and clinical spectrum

Advances in autoimmune encephalitis studies in the past 10 years have led to the identification of new syndromes and biomarkers that have transformed the diagnostic approach to the disorder. The disorder or syndrome has been linked to a wide variety of pathologic processes associated with the neuron-specific autoantibodies targeting intracellular and plasma membrane antigens. However, current criteria for autoimmune encephalitis are quite dependent on antibody testing and responses to immunotherapy, which might delay the diagnosis. This form of encephalitis can involve the multifaceted presentation of seizures and unexpected behavioral changes. The spectrum of neuropsychiatric symptoms in children is less definitive than that in adults, and the incorporation of clinical, immunological, electrophysiological, and neuroradiological results is critical to the diagnostic approach. In this review, we document the clinical and immunologic characteristics of autoimmune encephalitis known to date, with the goal of helping clinicians in differential diagnosis and to provide prompt and effective treatment.

Treatment of Movement Disorder Emergencies in Autoimmune Encephalitis in the Neurosciences ICU

Immune response against neuronal and glial cell surface and cytosolic antigens is an important cause of encephalitis. It may be triggered by activation of the immune system in response to an infection (para-infectious), cancer (paraneoplastic), or due to a patient's tendency toward autoimmunity. Antibodies directed toward neuronal cell surface antigens are directly pathogenic, whereas antibodies with intracellular targets may become pathogenic if the antigen is transiently exposed to the cell surface or via activation of cytotoxic T cells. Immune-mediated encephalitis is well recognized and may require intensive care due to status epilepticus, need for invasive ventilation, or dysautonomia. Patients with immune-mediated encephalitis may become critically ill and display clinically complex and challenging to treat movement disorders in over 80% of the cases (Zhang et al. in Neurocrit Care 29(2):264-272, 2018). Treatment options include immunotherapy and symptomatic agents affecting dopamine or acetylcholine neurotransmission. There has been no prior published guidance for management of these movement disorders for the intensivist. Herein, we discuss the immune-mediated encephalitis most likely to cause critical illness, clinical features and mechanisms of movement disorders and propose a management algorithm.

Autoantibodies in SLE: prediction and the p value matrix

Autoantibodies (AA) and antinuclear antibodies (ANA) serve as key diagnostic and classification criteria for systemic lupus erythematosus (SLE). More than 200 different AA have been reported in SLE, although only a handful (<20) are considered "mainstream" because they are widely and routinely used in diagnostic, research and clinical medicine. Although the vast majority of AA have been relegated to the diminished status of "orphan" AA, some serve as predictors of SLE because they first appear in very early or subclinical SLE. Some AA are pathogenic, whereas others are thought to protect against or ameliorate disease progression and, hence, taken together can be used as predictive biomarkers of prognosis. Although studies have shown that specific AA are detected in the preclinical phase of SLE and are biomarkers of increased risk of developing the disease, AA are currently not widely used to predict very early SLE in individuals who have low pretest probability of disease. With the advent of multianalyte arrays with analytic algorithms, emerging evidence indicates that when certain combinations of biomarkers, such as the interferon signature and stem cell factor accompany AA and ANA, the predictive power for SLE is markedly increased.

An evolving redefinition of autoimmune encephalitis

Autoimmune encephalitis encompasses a wide variety of protean pathologic processes associated with the presence of antibodies against neuronal intracellular proteins, synaptic receptors, ion channels and/or neuronal surface proteins. This type of encephalitis can also involve children with complex patterns of seizures and unexpected behavioural changes, which jeopardize their prompt recognition and treatment. Many epidemiological studies have shown that numerous immune-based forms of encephalitis can be encountered, almost surpassing the rate of postinfectious encephalitides. However, the overall exact prevalence of autoimmune encephalopathies remains underestimated, and the definition of diagnostic algorithms results muddled. The spectrum of neuropsychiatric manifestations in the pediatric population with autoimmune encephalitis is less clear than in adults, but the integration of clinical, immunological, electrophysiological and neuroradiological data is essential for a general approach to patients. In this review we report the most relevant data about both immunologic and clinical characteristics of the main autoimmune encephalitides recognized so far, with the aim of assisting clinicians in the differential diagnosis and favouring an early effective treatment. Correlations between phenotype and autoantibodies involved in the neurological damage of autoimmune encephalitis are largely unknown in the first years of life, because of the relatively small number of pediatric patients adequately studied. Future multicenter collaborative studies are needed to improve the diagnostic approach and tailor personalized therapies in the long-term.

The clinical features, underlying immunology, and treatment of autoantibody-mediated movement disorders

An increasing number of movement disorders are associated with autoantibodies. Many of these autoantibodies target the extracellular domain of neuronal surface proteins and associate with highly specific phenotypes, suggesting they have pathogenic potential. Below, we describe the phenotypes associated with some of these commoner autoantibody‐mediated movement disorders, and outline increasingly well‐established mechanisms of autoantibody pathogenicity which include antigen downregulation and complement fixation. Despite these advances, and the increasingly robust evidence for improved clinical outcomes with early escalation of immunotherapies, the underlying cellular immunology of these conditions has received little attention. Therefore, here, we outline the likely roles of T cells and B cells in the generation of autoantibodies, and reflect on how these may guide both current immunotherapy regimes and our future understanding of precision medicine in the field. In addition, we summarise potential mechanisms by which these peripherally‐driven immune responses may reach the central nervous system. We integrate this with the immunologically‐relevant clinical observations of preceding infections, tumours and human leucocyte antigen‐associations to provide an overview of the therapeutically‐relevant underlying adaptive immunology in the autoantibody‐mediated movement disorders. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Movement disorders with neuronal antibodies: syndromic approach, genetic parallels and pathophysiology

Movement disorders are a prominent and common feature in many autoantibody-associated neurological diseases, a group of potentially treatable conditions that can mimic infectious, metabolic or neurodegenerative disease. Certain movement disorders are likely to associate with certain autoantibodies; for example, the characteristic dyskinesias, chorea and dystonia associated with NMDAR antibodies, stiff person spectrum disorders with GAD, glycine receptor, amphiphysin or DPPX antibodies, specific paroxysmal dystonias with LGI1 antibodies, and cerebellar ataxia with various anti-neuronal antibodies. There are also less-recognized movement disorder presentations of antibody-related disease, and a considerable overlap between the clinical phenotypes and the associated antibody spectra. In this review, we first describe the antibodies associated with each syndrome, highlight distinctive clinical or radiological 'red flags', and suggest a syndromic approach based on the predominant movement disorder presentation, age, and associated features. We then examine the underlying immunopathophysiology, which may guide treatment decisions in these neuroimmunological disorders, and highlight the exceptional interface between neuronal antibodies and neurodegeneration, such as the tauopathy associated with IgLON5 antibodies. Moreover, we elaborate the emerging pathophysiological parallels between genetic movement disorders and immunological conditions, with proteins being either affected by mutations or targeted by autoantibodies. Hereditary hyperekplexia, for example, is caused by mutations of the alpha subunit of the glycine receptor leading to an infantile-onset disorder with exaggerated startle and stiffness, whereas antibodies targeting glycine receptors can induce acquired hyperekplexia. The spectrum of such immunological and genetic analogies also includes cerebellar ataxias and some encephalopathies. Lastly, we discuss how these pathophysiological considerations could reflect on possible future directions regarding antigen-specific immunotherapies or targeting the pathophysiological cascades downstream of the antibody effects.

Diagnostic utility of cortactin antibodies in myasthenia gravis

Patients with myasthenia gravis (MG) without antibodies to the acetylcholine receptor (AChR) or muscle-specific tyrosine kinase (MuSK) have been classified as having double-seronegative myasthenia gravis (dSNMG). We used the sera from six dSNMG patients with positive immunohistochemistry assays in a protein array to screen reactivity with 9000 human proteins. We identified cortactin, an intracellular protein that interacts with agrin/MuSK favoring AChR aggregation, as a new antigen in dSNMG. We then designed an in-house enzyme-linked immunosorbent assay as a screening assay and confirmed these results by western blot. We found that 19.7% of dSNMG patients had anti-cortactin antibodies. In contrast, patients with AChR⁺ MG or other autoimmune disorders and healthy controls were positive at significantly lower rates. Five percent of healthy controls were positive. In a recent study, we screened sera from 250 patients (AChR⁺ MG, MuSK⁺ MG, dSNMG) and 29 healthy controls. Cortactin antibodies were identified in 23.7% of dSNMG and 9.5% AChR⁺ MG patients (P = 0.02). None of the MuSK⁺ MG patients, patients with other autoimmune disorders, or healthy controls had antibodies against cortactin. Patients with dSNMG cortactin⁺ MG were negative for anti-striated muscle and anti-LRP4 antibodies. Patients with dSNMG cortactin⁺ MG presented ocular or mild generalized MG without bulbar symptoms. We conclude that cortactin autoantibodies are biomarkers of MG that, when present, suggest that the disease will be mild.

Autoantibodies to Synaptic Receptors and Neuronal Cell Surface Proteins in Autoimmune Diseases of the Central Nervous System

Investigations in the last 10 years have revealed a new category of neurological diseases mediated by antibodies against cell surface and synaptic proteins. There are currently 16 such diseases all characterized by autoantibodies against neuronal proteins involved in synaptic signaling and plasticity. In clinical practice these findings have changed the diagnostic and treatment approach to potentially lethal, but now treatable, neurological and psychiatric syndromes previously considered idiopathic or not even suspected to be immune-mediated. Studies show that patients' antibodies can impair the surface dynamics of the target receptors eliminating them from synapses (e.g., NMDA receptor), block the function of the antigens without changing their synaptic density (e.g., GABAb receptor), interfere with synaptic protein-protein interactions (LGI1, Caspr2), alter synapse formation (e.g., neurexin-3α), or by unclear mechanisms associate to a new form of tauopathy (IgLON5). Here we first trace the process of discovery of these diseases, describing the triggers and symptoms related to each autoantigen, and then review in detail the structural and functional alterations caused by the autoantibodies with special emphasis in those (NMDA receptor, amphiphysin) that have been modeled in animals.

Single-Molecule Localization Microscopy in Eukaryotes

Super-resolution fluorescence imaging by photoactivation or photoswitching of single fluorophores and position determination (single-molecule localization microscopy, SMLM) provides microscopic images with subdiffraction spatial resolution. This technology has enabled new insights into how proteins are organized in a cellular context, with a spatial resolution approaching virtually the molecular level. A unique strength of SMLM is that it delivers molecule-resolved information, along with super-resolved images of cellular structures. This allows quantitative access to cellular structures, for example, how proteins are distributed and organized and how they interact with other biomolecules. Ultimately, it is even possible to determine protein numbers in cells and the number of subunits in a protein complex. SMLM thus has the potential to pave the way toward a better understanding of how cells function at the molecular level. In this review, we describe how SMLM has contributed new knowledge in eukaryotic biology, and we specifically focus on quantitative biological data extracted from SMLM images.