Campylobacter jejuni virulence factors: update on emerging issues and trends

Campylobacter jejuni is a very common cause of gastroenteritis, and is frequently transmitted to humans through contaminated food products or water. Importantly, C. jejuni infections have a range of short- and long-term sequelae such as irritable bowel syndrome and Guillain Barre syndrome. C. jejuni triggers disease by employing a range of molecular strategies which enable it to colonise the gut, invade the epithelium, persist intracellularly and avoid detection by the host immune response. The objective of this review is to explore and summarise recent advances in the understanding of the C. jejuni molecular factors involved in colonisation, invasion of cells, collective quorum sensing-mediated behaviours and persistence. Understanding the mechanisms that underpin the pathogenicity of C. jejuni will enable future development of effective preventative approaches and vaccines against this pathogen.

Current status of Guillain-Barré syndrome (GBS) in China: a 10-year comprehensive overview

Guillain-Barré syndrome (GBS) is an acute inflammatory polyradiculoneuropathy; a disease involving the peripheral nervous system which is the most common cause of acute flaccid paralysis worldwide. So far, it is still lack of a comprehensive overview and understanding of the national epidemiological, clinical characteristics, and the risk factors of GBS in China, as well as differences between China and other countries and regions in these respects. With the global outbreak of the coronavirus disease 2019 (COVID-19), an epidemiological or phenotypic association between severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and GBS has attracted great attention. In this review, we outlined the current clinical data of GBS in China by retrieving literature, extracting and synthesizing the data of GBS in China from 2010 to 2021. Besides, we compared the characteristics of epidemiology, preceding events and clinical profiles of GBS between China and other countries and regions. Furthermore, in addition to conventional intravenous immunoglobulin (IVIG) and plasma exchange (PE) therapy, the potential therapeutic effects with novel medications in GBS, such as complement inhibitors, etc., have become the research focus in treatments. We found that epidemiological and clinical findings of GBS in China are approximately consistent with those in the International GBS Outcome Study (IGOS) cohort. We provided an overall picture of the present clinical status of GBS in China and summarized the global research progress of GBS, aiming to further understand the characteristics of GBS and improve the future work of GBS worldwide, especially in countries with the middle and low incomes.

Macrophages are scavengers for injured myelin in a rabbit model of acute inflammatory demyelinating polyneuropathy

In acute inflammatory demyelinating polyneuropathy (AIDP), myelin vesiculation mediated by complement activation contributes to nerve injury. Macrophage infiltration of the spinal roots has been demonstrated in AIDP, but its pathological significance remains uncertain. The present study aimed to investigate the role of macrophages in the pathogenic sequence of AIDP. A rabbit model of AIDP was induced by immunization with galactocerebroside. Immunostaining was performed to localize the macrophages and myelin injury. The rabbit developed tetraparesis with electrophysiological and pathological features of peripheral nerve demyelination. Immunostaining demonstrated colocalization of IgG antibodies, complement deposition and myelin injury apart from macrophages. Immunostaining and electron microscopy showed myelin injury preceded macrophage infiltration. There was significant disruption of voltage-gated sodium channel clusters at the nodes of Ranvier in the spinal roots. Macrophages acted may as scavengers to remove myelin debris following complement activation-mediated demyelination in the AIDP rabbit. Lesions at the node of Ranvier contribute to conduction failure and muscle weakness.

Sex differences in Guillain Barré syndrome, chronic inflammatory demyelinating polyradiculoneuropathy and experimental autoimmune neuritis

Guillain Barré syndrome (GBS) and its variants, and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP and its variants, are regarded as immune mediated neuropathies. Unlike in many autoimmune disorders, GBS and CIDP are more common in males than females. Sex is not a clear predictor of outcome. Experimental autoimmune neuritis (EAN) is an animal model of these diseases, but there are no studies of the effects of sex in EAN. The pathogenesis of GBS and CIDP involves immune response to non-protein antigens, antigen presentation through non-conventional T cells and, in CIDP with nodopathy, IgG4 antibody responses to antigens. There are some reported sex differences in some of these elements of the immune system and we speculate that these sex differences could contribute to the male predominance of these diseases, and suggest that sex differences in peripheral nerves is a topic worthy of further study.

Campylobacter jejuni Infection, Anti-Ganglioside Antibodies, and Neuropathy

Preceding infection with Campylobacter jejuni (Cj) occurs in approximately 30% of patients with Guillain–Barre syndrome (GBS), and the risk of GBS following Cj infection is increased by 77 to 100-fold. GBS is most often of the axonal subtype and is thought to be mediated by IgG antibodies to peripheral nerve gangliosides that are cross reactive with oligosaccharides in the Cj lipopolysaccharides (LPS). The antibodies are thought to be induced by molecular mimicry, where immune reactivity to a cross reactive epitope in the infectious organism and normal tissue can cause autoimmune disease. Clonally restricted IgM antibodies that react with the same oligosaccharides in gangliosides and Cj-LPS are associated with chronic neuropathies of otherwise similar phenotypes. The anti-ganglioside antibodies in GBS are of the IgG1 and IgG3 subclasses, indicating T-cell reactivity to the same antigens that could help disrupt the blood–nerve barrier. Cj infection can activate multiple innate and adoptive pro-inflammatory pathways that can overcome immune tolerance and induce autoimmunity. Elucidation of the specific immune mechanisms involved in the development of the autoantibodies and neuropathy would help our understanding of the relation between infection and autoimmunity and aid in the development of more effective preventive interventions and therapies.

Risk Factors for Mechanical Ventilation in Patients with Guillain-Barré Syndrome

BACKGROUND

Respiratory support is required in 20-30% of patients with Guillain-Barré syndrome (GBS). We investigated clinical and biological risk factors for mechanical ventilation (MV) in northeast China through a retrospective GBS study. The Erasmus GBS Respiratory Insufficiency Score (EGRIS) is a prognostic model for MV in patients with GBS, and its usefulness has been validated in several countries but not in China. Therefore, we intended to validate the EGRIS model in our GBS cohort.

METHODS

A total of 252 patients with GBS were included in this study from January 2013 to October 2017. Risk factors for MV were identified via multivariate logistic regression analysis. The prognostic value of the EGRIS was validated via receiver operating characteristic curve analysis.

RESULTS

Thirty-one patients (12.3%) required MV (mean age 54.19 years), with a majority being male (77.4%). The risk factors for MV were male sex [odds ratio (OR) 3.720, 95% confidence interval (CI) 1.155-11.985, p < 0.05], shorter interval from onset to admission (OR 0.830, 95% CI 0.711-0.970, p < 0.05), lower Medical Research Council sum score at admission (OR 0.942, 95% CI 0.911-0.973, p < 0.001), neutrophil-to-lymphocyte ratio at admission (OR 1.174, 95% CI 1.049-1.315, p < 0.01), and cranial nerve deficit (OR 3.805, 95% CI 1.373-10.541, p < 0.05). The EGRIS had a good predictive ability for MV (area under the receiver operating curve 0.861) in patients with GBS, and a high EGRIS was a predictor for MV (OR 8.778, 95% CI 3.432-22.448, p < 0.001). However, there was no significant difference in ganglioside administration between ventilated and nonventilated patients.

CONCLUSIONS

An elevated neutrophil-to-lymphocyte ratio at admission and a high EGRIS could serve as predictors for MV in our GBS cohort.

Immune mechanisms, the role of complement, and related therapies in autoimmune neuropathies

INTRODUCTION

Autoimmune neuropathies have diverse presentations and underlying immune mechanisms. Demonstration of efficacy of therapeutic agents that inhibit the complement cascade would confirm the role of complement activation.

AREAS COVERED

A review of the pathophysiology of the autoimmune neuropathies, to identify those that are likely to be complement mediated.

EXPERT OPINION

Complement mediated mechanisms are implicated in the acute and chronic neuropathies associated with IgG or IgM antibodies that target the Myelin Associated Glycoprotein (MAG) or gangliosides in the peripheral nerves. Antibody and complement mechanisms are also suspected in the Guillain-Barré syndrome and chronic inflammatory demyelinating neuropathy, given the therapeutic response to plasmapheresis or intravenous immunoglobulins, even in the absence of an identifiable target antigen. Complement is unlikely to play a role in paraneoplastic sensory neuropathy associated with antibodies to HU/ANNA-1 given its intracellular localization. In chronic demyelinating neuropathy with anti-nodal/paranodal CNTN1, NFS-155, and CASPR1 antibodies, myotonia with anti-VGKC LGI1 or CASPR2 antibodies, or autoimmune autonomic neuropathy with anti-gAChR antibodies, the response to complement inhibitory agents would depend on the extent to which the antibodies exert their effects through complement dependent or independent mechanisms. Complement is also likely to play a role in Sjogren's, vasculitic, and cryoglobulinemic neuropathies.

Protective Effect of Hyperbaric Oxygen Treatment on Axon Degeneration after Acute Motor Axonal Neuropathy

OBJECTIVES

Acute motor axonal neuropathy (AMAN) is a disease that leads to acute flaccid paralysis and may result from the binding of antibody and antigen to the spinal cord. The objective of this study is to evaluate the protective effect of hyperbaric oxygen treatment (HBOT) on axon degeneration of the spinal cord and sciatic nerve of the AMAN model rabbit. Axonal degeneration was assessed by evaluating glutathione (GSH) activity, interleukin-1β (IL-1β) expression, and clinical and histopathological features.

METHODS

Twenty-one New Zealand rabbits were divided into three groups. The treatment group was exposed to 100% oxygen at 2.4 ATA 90 minutes for 10 days at a decompression rate of 2.9 pounds per square inch/minute. GSH level was evaluated using an enzyme-linked immune-sorbent assay. An expression of IL-1β in the spinal cord was determined by immunohistochemistry. Clinical appearances were done by motor scale and body weight. Histological features observed neuronal swelling and inflammatory infiltration in the sagittal lumbar region and the undulation of the longitudinal sciatic nerve.

RESULTS

Rabbits exposed to HBO had high GSH activity levels (p < 0.05) but unexpectedly had high IL1β expression (p > 0.05). In addition, the HBO-exposed rabbits had a better degree of undulation, the size of neuronal swelling was smaller, the number of macrophages was higher, and motor function was better than the AMAN model rabbits (p < 0.05).

CONCLUSIONS

These findings indicate that HBO therapy can decrease axon degeneration by triggering GSH activity, increasing IL-1β level, and restoring tissues and motor status. In conclusion, HBO has a protective effect on axon degeneration of the spinal cord and sciatic nerve of the AMAN model rabbit.

Novel Immunological and Therapeutic Insights in Guillain-Barré Syndrome and CIDP

Inflammatory neuropathies are a heterogeneous group of rare diseases of the peripheral nervous system that include acute and chronic diseases, such as Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). The etiology and pathophysiological mechanisms of inflammatory neuropathies are only partly known, but are considered autoimmune disorders in which an aberrant immune response, including cellular and humoral components, is directed towards components of the peripheral nerve causing demyelination and axonal damage. Therapy of these disorders includes broad-spectrum immunomodulatory and immunosuppressive treatments, such as intravenous immunoglobulin, corticosteroids, or plasma exchange. However, a significant proportion of patients do not respond to any of these therapies, and treatment selection is not optimized according to disease pathophysiology. Therefore, research on disease pathophysiology aiming to reveal clinically and functionally relevant disease mechanisms and the development of new treatment approaches are needed to optimize disease outcomes in CIDP and GBS. This topical review describes immunological progress that may help guide therapeutic strategies in the future in these two disorders.

Guillain-Barré syndrome

Guillain-Barré syndrome is the most common cause of acute flaccid paralysis worldwide. Most patients present with an antecedent illness, most commonly upper respiratory tract infection, before the onset of progressive motor weakness. Several microorganisms have been associated with Guillain-Barré syndrome, most notably Campylobacter jejuni, Zika virus, and in 2020, the severe acute respiratory syndrome coronavirus 2. In C jejuni-related Guillain-Barré syndrome, there is good evidence to support an autoantibody-mediated immune process that is triggered by molecular mimicry between structural components of peripheral nerves and the microorganism. Making a diagnosis of so-called classical Guillain-Barré syndrome is straightforward; however, the existing diagnostic criteria have limitations and can result in some variants of the syndrome being missed. Most patients with Guillain-Barré syndrome do well with immunotherapy, but a substantial proportion are left with disability, and death can occur. Results from the International Guillain-Barré Syndrome Outcome Study suggest that geographical variations exist in Guillain-Barré syndrome, including insufficient access to immunotherapy in low-income countries. There is a need to provide improved access to treatment for all patients with Guillain-Barré syndrome, and to develop effective disease-modifying therapies that can limit the extent of nerve injury. Clinical trials are currently underway to investigate some of the potential therapeutic candidates, including complement inhibitors, which, together with emerging data from large international collaborative studies on the syndrome, will contribute substantially to understanding the many facets of this disease.

Antiglycolipid antibodies in Guillain-Barré and Fisher syndromes: discovery, current status and future perspective

Guillain-Barré syndrome (GBS) and Fisher syndrome (FS) are acute autoimmune neuropathies, often preceded by an infection. Antiglycolipid antibody titres are frequently elevated in sera from the acute-phase patients. Particularly, IgG anti-GQ1b antibodies are positive in as high as 90% of FS cases and thus useful for diagnosis. The development of animal models of antiglycolipid antibody-mediated neuropathies proved that some of these antibodies are directly involved in the pathogenetic mechanisms by binding to the regions where the respective target glycolipid is specifically localised. Discovery of the presence of the antibodies that specifically recognise a new conformational epitope formed by two different gangliosides (ganglioside complex) in the acute-phase sera of some patients with GBS suggested the carbohydrate-carbohydrate interaction between glycolipids. This finding indicated the need for further research in basic glycobiological science. Antiglycolipid antibodies, in particular antigangliosides antibodies, are mostly detected in acute motor axonal neuropathy type of GBS and in FS, and less frequently in the acute inflammatory demyelinating polyneuropathy (AIDP) type of GBS or in central nervous system (CNS) diseases. In the future, the search for the putative antibodies in AIDP and those that might be present in CNS diseases should continue. In addition, more efficient standardisation of antiglycolipid antibody detection methods and use as biomarkers in daily clinical practice in neurology is needed.

The Neuroimmunology of Guillain-Barré Syndrome and the Potential Role of an Aging Immune System

Guillain-Barré syndrome (GBS) is a paralyzing autoimmune condition affecting the peripheral nervous system (PNS). Within GBS there are several variants affecting different aspects of the peripheral nerve. In general, there appears to be a role for T cells, macrophages, B cells, and complement in initiating and perpetuating attacks on gangliosides of Schwann cells and axons. Of note, GBS has an increased prevalence and severity with increasing age. In addition, there are alterations in immune cell functioning that may play a role in differences in GBS with age alongside general age-related declines in reparative processes (e.g., delayed de-differentiation of Schwann cells and decline in phagocytic ability of macrophages). The present review will explore the immune response in GBS as well as in animal models of several variants of the disorder. In addition, the potential involvement of an aging immune system in contributing to the increased prevalence and severity of GBS with age will be theorized.

Neutrophil–lymphocyte ratio and response to plasmapheresis in Guillain–Barré syndrome: a prospective observational study

Background

Guillain–Barré Syndrome (GBS) is one of the most severe neurological diseases that causes marked disability and even death.

Aim

The aim of this study is to investigate the role of the neutrophil–lymphocyte ratio (NLR) as a prognostic marker for GBS and response to treatment with plasmapheresis.

Methods

Seventy-five subjects (35 GBS patients and 40 healthy controls) were recruited. Complete general and neurological examinations were performed and Hughes disability scale score was evaluated for assessing functional motor deficits in GBS patients. In addition, NLR, erythrocyte sedimentation rate, and C-reactive protein level were calculated.

Results

NLR was significantly higher in GBS patients than in controls (p < 0.001) and was significantly higher in axonal form than other demyelinating and mixed subtypes (p < 0.02). Patients with a poor outcome had a significantly high NLR than patients with a good outcome (p = 0.006). NLR was also positively correlated with Hughes disability scale score (p < 0.001). The cut-off value for NLR to predict a good response of patients to plasmapheresis was ≤ 4.4.

Interpretation

NLR may be a rapid, simple, inexpensive biomarker for predicting the severity of GBS, outcome of patients, and their response to plasmapheresis.

Finger drop sign as a new variant of acute motor axonal neuropathy

We propose the finger drop sign as a new clinical variant of acute motor axonal neuropathy (AMAN) defined by immunological and radiological evidence. We identified eight consecutive patients who had AMAN. All of them developed prominent involvement of the finger extensors. We performed magnetic resonance imaging (MRI) of the extremity muscles and serological assays for antiganglioside antibodies and Campylobacter jejuni. Patients with AMAN showed characteristic and a markedly sustained weakness of the finger extensors with a distinctive pattern of the finger drop sign. Limb MRI revealed unevenly distributed abnormal signals in the muscles mainly innervated by the posterior interosseous nerve. All tested patients showed positivity for immunoglobulin G antibody against ganglioside complex of GM1 and phosphatidic acid. A pathophysiological understanding of this unique syndrome can provide further insight into antiganglioside-antibody-mediated axonal injury in Guillain-Barré syndrome.

Toxemia in Human Naturally Acquired Botulism

Human botulism is a severe disease characterized by flaccid paralysis and inhibition of certain gland secretions, notably salivary secretions, caused by inhibition of neurotransmitter release. Naturally acquired botulism occurs in three main forms: food-borne botulism by ingestion of preformed botulinum neurotoxin (BoNT) in food, botulism by intestinal colonization (infant botulism and intestinal toxemia botulism in infants above one year and adults), and wound botulism. A rapid laboratory confirmation of botulism is required for the appropriate management of patients. Detection of BoNT in the patient's sera is the most direct way to address the diagnosis of botulism. Based on previous published reports, botulinum toxemia was identified in about 70% of food-borne and wound botulism cases, and only in about 28% of infant botulism cases, in which the diagnosis is mainly confirmed from stool sample investigation. The presence of BoNT in serum depends on the BoNT amount ingested with contaminated food or produced locally in the intestine or wound, and the timeframe between serum sampling and disease onset. BoNT levels in patient's sera are most frequently low, requiring a highly sensitive method of detection. Mouse bioassay is still the most used method of botulism identification from serum samples. However, in vitro methods based on BoNT endopeptidase activity with detection by mass spectrometry or immunoassay have been developed and depending on BoNT type, are more sensitive than the mouse bioassay. These new assays show high specificity for individual BoNT types and allow more accurate differentiation between positive toxin sera from botulism and autoimmune neuropathy patients.

Facing acute neuromuscular diseases during COVID-19 pandemic: focus on Guillain-Barré syndrome

In December 2019, a cluster of cases with 2019 Novel Coronavirus pneumonia from Wuhan, China, aroused worldwide concern due to an escalating outbreak in all the countries in the world. Coronavirus belongs to a family of single-stranded RNA viruses, which includes severe acute respiratory syndrome (SARS-CoV) and Middle East respiratory syndrome (MERS-CoV), that have caused human epidemics with high fatality. The spectrum of the novel coronavirus disease (SARS-Co-2 or COVID-19) ranges from asymptomatic infections to fatal pneumonia, and differs from other viral pulmonary infections. MERS-CoV is known to be potentially neuroinvasive. Extensive reports from China documented central and peripheral nervous system involvement in patients with COVID-19, and identified in angiotensin converting enzyme2 (ACE2), which is present in multiple human organs, the functional receptor for this virus. Guillain-Barré syndrome (GBS) has recently been associated to COVID-19 rising concern among physicians. This review summarizes the current state of knowledge on GBS during or after COVID-19 infection, attempting to clarify the pathophysiology of the associated respiratory dysfunction and failure.

Post-infectious neurological disorders

A multitude of environmental factors can result in breakdown of immune tolerance in susceptible hosts. Infectious pathogens are among the most important environmental triggers in the pathogenesis of autoimmunity. Certain autoimmune disorders have a strong association with specific infections. Several neurological autoimmune disorders are thought to occur through post-infectious mechanisms. In this review, we discuss the proposed mechanisms underlying pathogen-induced autoimmunity, and highlight the clinical presentation and treatment of several post-infectious autoimmune neurological disorders. We also highlight post-infectious neurological disorders in the setting of recent outbreaks.

The electrophysiology of axonal neuropathies: More than just evidence of axonal loss

It is common belief that axonal neuropathies are characterized by simple axonal degeneration and loss and that the electrophysiological correlates are just reduced compound muscle action potential and sensory nerve action potential amplitudes with normal or slightly slow conduction velocity. However, axonal autoimmune neuropathies with involvement of the nodal region and axonal neuropathies due to energy restriction such as occurring in nerve ischemia, thiamine deficiency, critical illness, and mitochondrial disorders present conduction failure that can be either reversible with prompt recovery or progress to axonal degeneration with poor outcome. Moreover autoimmune axonal neuropathies due to nodal voltage gated sodium channels dysfunction/disruption may show slowing of conduction velocity, even in the demyelinating range, possibly due to prolongation of the depolarization time required to reach the threshold for action potential regeneration at subsequent nodes. These observations widen the spectrum of the electrophysiological features in some axonal neuropathies, should be taken into account to avoid misdiagnoses and for correct prognostication, and should stimulate the quest of timely targeted treatments that can eventually halt the progression from conduction failure to axonal degeneration.

Do Vaccines Have a Role as a Cause of Autoimmune Neurological Syndromes?

Vaccines are the most important preventive measure against infectious diseases presently available. Although they have led to the eradication or the elimination of some infectious diseases, concerns about safety are among the main reasons for vaccine hesitancy. In some cases, the biological plausibility of a given damage in association with the temporal association between vaccine administration and disease development makes it difficult to define causality and can justify hesitancy. Only well-conducted epidemiological studies with adequate evaluation of results can clarify whether a true association between vaccines and adverse event development truly exists. Autoimmune neurological syndromes that follow vaccine use are among these. In this narrative review, the potential association between vaccines and the development of these syndromes are discussed. Literature analysis showed that most of the associations between vaccines and nervous system autoimmune syndromes that have been reported as severe adverse events following immunization are no longer evidenced when well-conducted epidemiological studies are carried out. Although the rarity of autoimmune diseases makes it difficult to strictly exclude that, albeit exceptionally, some vaccines may induce an autoimmune neurological disease, no definitive demonstration of a potential role of vaccines in causing autoimmune neurological syndromes is presently available. Consequently, the fear of neurological autoimmune disease cannot limit the use of the most important preventive measure presently available against infectious diseases.

Axonal degeneration in Guillain-Barré syndrome: a reappraisal

The aim of this review was to analyse the pathophysiology of axonal degeneration in Guillain-Barré syndrome (GBS) with emphasis on early stages (≤ 10 days after onset). An overview of experimental autoimmune neuritis (EAN) models is provided. Originally GBS and acute inflammatory demyelinating polyneuropathy were equated, presence of axonal degeneration being attributed to a "bystander" effect. Afterwards, primary axonal GBS forms were reported, designated as acute motor axonal neuropathy/acute motor-sensory axonal neuropathy. Revision of the first pathological description of axonal GBS indicates the coexistence of active axonal degeneration and demyelination in spinal roots, and pure Wallerian-like degeneration in peripheral nerve trunks. Nerve conduction studies are essential for syndrome subtyping, though their sensitivity is scanty in early GBS. Serum markers of axonal degeneration include increased levels of neurofilament light chain and presence of anti-ganglioside reactivity. According to nerve ultrasonographic features and autopsy studies, ventral rami of spinal nerves are a hotspot in early GBS. In P₂-induced EAN models, the initial pathogenic change is inflammatory oedema of spinal roots and sciatic nerve, which is followed by demyelination, and Wallerian-like degeneration in nerve trunks possessing epi-perineurium; a critical elevation of endoneurial fluid pressure is a pre-requisite for inducing ischemic axonal degeneration. Similar lesion topography may occur in GBS. The repairing role of adaxonal Schwann cytoplasm in axonal degeneration is analysed. A novel pathophysiological mechanism for nerve trunk pain in GBS, including pure motor forms, is provided. The potential therapeutic role of intravenous boluses of methylprednisolone for early severe GBS and intractable pain is argued.

Perisynaptic Schwann cells phagocytose nerve terminal debris in a mouse model of Guillain-Barré syndrome

In mouse models of acute motor axonal neuropathy, anti-ganglioside antibodies (AGAbs) bind to motor axons, notably the distal nerve, and activate the complement cascade. While complement activation is well studied in this model, the role of inflammatory cells is unknown. Herein we aimed to investigate the contribution of phagocytic cells including macrophages, neutrophils and perisynaptic Schwann cells (pSCs) to distal nerve pathology. To observe this, we first created a subacute injury model of sufficient duration to allow inflammatory cell recruitment. Mice were injected intraperitoneally with an anti-GD1b monoclonal antibody that binds strongly to mouse motor nerve axons. Subsequently, mice received normal human serum as a source of complement. Dosing was titrated to allow humane survival of mice over a period of 3 days, yet still induce the characteristic neurological impairment. Behaviour and pathology were assessed in vivo using whole-body plethysmography and post-sacrifice by immunofluorescence and flow cytometry. ex vivo nerve-muscle preparations were used to investigate the acute phagocytic role of pSCs following distal nerve injury. Following complement activation at distal intramuscular nerve sites in the diaphragm macrophage localisation or numbers are not altered, nor do they shift to a pro- or anti-inflammatory phenotype. Similarly, neutrophils are not significantly recruited. Instead, ex vivo nerve-muscle preparations exposed to AGAb plus complement reveal that pSCs rapidly become phagocytic and engulf axonal debris. These data suggest that pSCs, rather than inflammatory cells, are the major cellular vehicle for axonal debris clearance following distal nerve injury, in contrast to larger nerve bundles where macrophage-mediated clearance predominates.

Physiology of gangliosides and the role of antiganglioside antibodies in human diseases

Gangliosides are structurally and functionally polymorphic sialic acid containing glycosphingolipids that are widely distributed in the human body. They play important roles in protecting us against immune attacks, yet they can become targets for autoimmunity and act as receptors for microbes, like the influenza viruses, and toxins, such as the cholera toxin. The expression patterns of gangliosides vary in different tissues, during different life periods, as well as in different animals. Antibodies against gangliosides (AGA) can target immune attack e.g., against neuronal cells and neutralize their complement inhibitory activity. AGAs are important especially in acquired demyelinating immune-mediated neuropathies, like Guillain-Barré syndrome (GBS) and its variant, the Miller-Fisher syndrome (MFS). They can emerge in response to different microbial agents and immunological insults. Thereby, they can be involved in a variety of diseases. In addition, antibodies against GM3 were found in the sera of patients vaccinated with Pandemrix®, who developed secondary narcolepsy, strongly supporting the autoimmune etiology of the disease.

Axonal variants of Guillain-Barré syndrome: an update

Axonal variants of Guillain-Barré syndrome (GBS) mainly include acute motor axonal neuropathy, acute motor and sensory axonal neuropathy, and pharyngeal-cervical-brachial weakness. Molecular mimicry of human gangliosides by a pathogen's lipooligosaccharides is a well-established mechanism for Campylobacter jejuni-associated GBS. New triggers of the axonal variants of GBS (axonal GBS), such as Zika virus, hepatitis viruses, intravenous administration of ganglioside, vaccination, and surgery, are being identified. However, the pathogenetic mechanisms of axonal GBS related to antecedent bacterial or viral infections other than Campylobacter jejuni remain unknown. Currently, autoantibody classification and serial electrophysiology are cardinal approaches to differentiate axonal GBS from the prototype of GBS, acute inflammatory demyelinating polyneuropathy. Newly developed technologies, including metabolite analysis, peripheral nerve ultrasound, and feature selection via artificial intelligence are facilitating more accurate diagnosis of axonal GBS. Nevertheless, some key issues, such as genetic susceptibilities, remain unanswered and moreover, current therapies bear limitations. Although several therapies have shown considerable benefits to experimental animals, randomized controlled trials are still needed to validate their efficacy.

Simulating perinodal changes observed in immune-mediated neuropathies: impact on conduction in a model of myelinated motor and sensory axons

Immune-mediated neuropathies affect myelinated axons, resulting in conduction slowing or block that may affect motor and sensory axons differently. The underlying mechanisms of these neuropathies are not well understood. Using a myelinated axon model, we studied the impact of perinodal changes on conduction. We extended a longitudinal axon model (41 nodes of Ranvier) with biophysical properties unique to human myelinated motor and sensory axons. We simulated effects of temperature and axonal diameter on conduction and strength-duration properties. We then studied effects of impaired nodal sodium channel conductance and paranodal myelin detachment by reducing periaxonal resistance, as well as their interaction, on conduction in the 9 middle nodes and enclosed paranodes. Finally, we assessed the impact of reducing the affected region (5 nodes) and adding nodal widening. Physiological motor and sensory conduction velocities and changes to axonal diameter and temperature were observed. The sensory axon had a longer strength-duration time constant. Reducing sodium channel conductance and paranodal periaxonal resistance induced progressive conduction slowing. In motor axons, conduction block occurred with a 4-fold drop in sodium channel conductance or a 7.7-fold drop in periaxonal resistance. In sensory axons, block arose with a 4.8-fold drop in sodium channel conductance or a 9-fold drop in periaxonal resistance. This indicated that motor axons are more vulnerable to developing block. A boundary of block emerged when the two mechanisms interacted. This boundary shifted in opposite directions for a smaller affected region and nodal widening. These differences may contribute to the predominance of motor deficits observed in some immune-mediated neuropathies.NEW & NOTEWORTHY Immune-mediated neuropathies may affect myelinated motor and sensory axons differently. By the development of a computational model, we quantitatively studied the impact of perinodal changes on conduction in motor and sensory axons. Simulations of increasing nodal sodium channel dysfunction and paranodal myelin detachment induced progressive conduction slowing. Sensory axons were more resistant to block than motor axons. This could explain the greater predisposition of motor axons to functional deficits observed in some immune-mediated neuropathies.

Clinical Characteristics of Intravenous Injection of Monosialotetrahexosyl Ganglioside Sodium-Related Guillain-Barre Syndrome

Introduction: Guillain Barre Syndrome (GBS) is an acute inflammatory immune-mediated multiple nerve root neuropathy. GBS primarily damages the spinal nerve root and peripheral nerves, but can also affect the cranial nerves and cause acute demyelination. This study analyzed the clinical features of intravenous injection of monosialotetrahexosyl ganglioside sodium-related Guillain-Barre syndrome (GRD-GBS). Methods: We retrospectively studied 12 patients who developed GRD-GBS after receiving monosialotetrahexosyl ganglioside sodium treatment in association with recent trauma, surgery, acute cerebrovascular disease, or chronic peripheral neuropathy. Clinical characteristics, electrophysiological examinations, serum-specific antibodies, and prognosis were assessed. As controls, we selected 12 patients hospitalized with non-ganglioside-related (NGRD)-GBS. Results: The positive rate of the ganglioside antibody test was significantly higher in the GRD-GBS group (66.67%) than in the NGRD-GBS group (8.33%). CSF protein levels were similar between the groups, but the incidence of blood-nerve-barrier (BNB) disruption was higher in the GRD-GBS group. Patient scores for the Hughes Functional Grading Scale (HFGS), a disability scale, were higher (more severe disability) in the GRD-GBS group than in the NGRD-GBS group. The HFGS scores of the GRD-GBS group did not change between peak onset and 30 days after discharge, but did change significantly by 90 days after discharge, while scores were significantly lower at both 30 and 90 days after discharge in the NGRD-GBS group. Conclusions: GRD-GBS patients showed more severe clinical manifestations, poorer prognosis, and slower recovery than patients with NGRD-GBS. Ganglioside treatment should be used with extreme caution in patients with trauma that damages the BNB.

Anti-ganglioside Antibodies in Peripheral Nerve Pathology

Anti-ganglioside antibodies are principally associated with autoimmune peripheral neuropathies. In these disorders, immune attack is inadvertently directed at peripheral nerve by autoantibodies that target glycan structures borne by glycolipids, particularly gangliosides concentrated in nerve myelin and axons. The most thoroughly studied disorder is the acute paralytic disease, Guillain-Barré syndrome (GBS) in which IgG autoantibodies against gangliosides arise following acute infections, notably Campylobacter jejuni enteritis. Additionally, chronic autoimmune neuropathies are associated with IgM antibodies directed against many glycolipids including gangliosides. This introductory chapter briefly summarizes the immunological and pathological features of these disorders, focusing on the methodological development of antibody measurement and of animal models.

Clinical electrophysiology of axonal polyneuropathies

Axonal neuropathies encompass a wide range of acquired and inherited disorders with electrophysiologic characteristics that arise from the unique neurophysiology of the axon. Accurate interpretation of nerve conduction studies and electromyography requires an in-depth understanding of the pathophysiology of the axon. Here we review the unique neurophysiologic properties of the axon and how they relate to clinical electrodiagnostic features. We review the length-dependent Wallerian or "dying-back" processes as well as the emerging body of literature from acquired axonal neuropathies that highlights the importance of axonal disease at the nodes of Ranvier. Neurophysiologic features of individual inherited and acquired axonal diseases, including primary nerve disease as well as systemic immune mediated, metabolic, and toxic diseases involving the peripheral nerve, are reviewed. This comprehensive review of electrodiagnostic findings coupled with the current understanding of pathophysiology will aid the clinician in the evaluation of axonal polyneuropathies.

Subacute Sensorimotor Neuropathy Accompanied by Anti-ganglioside GM1 Antibody in a Patient with Lung Cancer

A 66-year-old man presented with subacute sensorimotor neuropathy in association with small cell lung cancer. Tests for the anti-ganglioside antibody GM1-IgM were positive. Chemotherapy and intravenous immunoglobulin treatment led to a slight improvement in neurological symptoms. Four additional cases of neuropathy accompanied by anti-ganglioside antibody and lung cancer have been reported. The most commonly reported pattern was subacute sensorimotor neuropathy. Patients died from cancer progression after 5 to 18 months. There is evidence that anti-ganglioside antibody inhibits tumor progression, prolonging the patient survival. However, severe neurological disturbance may offset the survival benefit of anti-ganglioside antibody in patients with paraneoplastic neurological syndrome.

Vaccine-preventable diseases, vaccines and Guillain-Barre' syndrome

Guillain-Barré syndrome (GBS) is an acute, immune-mediated polyradiculoneuropathy. Infections and vaccines have been hypothesized to play a role in triggering GBS development. These beliefs can play a role in reducing vaccination coverage. In this report, data concerning this hypothesis are discussed. It is shown that an association between vaccine administration and GBS has never been proven for most of debated vaccines, although it cannot be definitively excluded. The only exception is the influenza vaccine, at least for the preparation used in 1976. For some vaccines, such as measles/mumps/rubella, human papillomavirus, tetravalent conjugated meningococcal vaccine, and influenza, the debate between supporters and opponents of vaccination remains robust and perception of vaccines' low safety remains a barrier to achieving adequate vaccination coverage. Less than 1 case of GBS per million immunized persons might occur for these vaccines. However, in some casesimmunization actually reduces the risk of GBS development. In addition, the benefits of vaccination are clearly demonstrated by the eradication or enormous decline in the incidence of many vaccine-preventable diseases. These data highlight that the hypothesized risks of adverse events, such as GBS, cannot be considered a valid reason to avoid the administration of currently recommended vaccines.

Autoimmune nodo-paranodopathies of peripheral nerve: the concept is gaining ground

Peripheral neuropathies are classified as primarily demyelinating or axonal. Microstructural alterations of the nodal region are the key to understand the pathophysiology of neuropathies with antibodies to gangliosides and the new category of nodo-paranodopathy has been proposed to better characterise these disorders and overcome some inadequacies of the dichotomous classification. Recently, the research in autoimmune neuropathies has been boosted by reports of patients carrying immunoglobulin G4 antibodies against paranodal axo-glial proteins with distinct phenotypes and showing loss of transverse bands, terminal myelin loop detachment, nodal widening and axonal loss. These patients have been classified up to now as chronic inflammatory demyelinating polyradiculoneuropathy but, in our opinion, better fit into the nodo-paranodopathy category because nerve injury is due to dismantling of the paranode, segmental de-remyelination is absent and the pathogenic mechanism is not inflammatory. Evidence from nerve conductions and electron microscopy studies in patients and mutant animal models can reconcile the apparent contrast between the electrophysiological 'demyelinating' features, explainable just by the paranodal involvement and the axonal pathology. These patients broaden the autoimmune nodo-paranodopathy category and re-emphasise the usage of the term that pointing to the site of nerve injury reminds specific pathophysiological mechanisms, reconciles contrasting electrophysiological and pathological findings, and avoids misdiagnosis and taxonomic confusion. In our opinion, the nodo-paranodopathy term more adequately classifies the peripheral nerve disorders due to an autoimmune attack directed and limited to the nodal region integrating the traditional classification of peripheral neuropathies.

Inhibition of complement in Guillain-Barré syndrome: the ICA-GBS study

The outcome of Guillain-Barré syndrome (GBS) remains unchanged since plasma exchange and intravenous immunoglobulin (IVIg) were introduced over 20 years ago. Pathogenesis studies on GBS have identified the terminal component of complement cascade as a key disease mediator and therapeutic target. We report the first use of terminal complement pathway inhibition with eculizumab in humans with GBS. In a randomised, double-blind, placebo-controlled trial, 28 subjects eligible on the basis of GBS disability grade of at least 3 were screened, of whom 8 (29%) were randomised. Five received eculizumab for 4 weeks, alongside standard IVIg treatment. The safety outcomes, monitored via adverse events capture, showed eculizumab to be well-tolerated and safe when administered in conjunction with IVIg. Primary and secondary efficacy outcomes in the form of GBS disability scores (GBS DS), MRC sum scores, Rasch overall disability scores, and overall neuropathy limitation scores are reported descriptively. For the primary efficacy outcome at 4 weeks after recruitment, two of two placebo- and two of five eculizumab-treated subjects had improved by one or more grades on the GBS DS. Although the small sample size precludes a statistically meaningful analysis, these pilot data indicate further studies on complement inhibition in GBS are warranted.

Tissue resident macrophages are sufficient for demyelination during peripheral nerve myelin induced experimental autoimmune neuritis?

The contribution of resident endoneurial tissue macrophages versus recruited monocyte derived macrophages to demyelination and disease during Experimental Autoimmune Neuritis (EAN) was investigated using passive transfer of peripheral nerve myelin (PNM) specific serum antibodies or adoptive co-transfer of PNM specific T and B cells from EAN donors to leukopenic and normal hosts. Passive transfer of PNM specific serum antibodies or adoptive co-transfer of myelin specific T and B cells into leukopenic recipients resulted in a moderate reduction in nerve conduction block or in the disease severity compared to the normal recipients. This was despite at least a 95% decrease in the number of circulating mononuclear cells during the development of nerve conduction block and disease and a 50% reduction in the number of infiltrating endoneurial macrophages in the nerve lesions of the leukopenic recipients. These observations suggest that during EAN in Lewis rats actively induced by immunization with peripheral nerve myelin, phagocytic macrophages originating from the resident endoneurial population may be sufficient to engage in demyelination initiated by anti-myelin antibodies in this model.

Novel pathomechanisms in inflammatory neuropathies

Inflammatory neuropathies are rare autoimmune-mediated disorders affecting the peripheral nervous system. Considerable progress has recently been made in understanding pathomechanisms of these disorders which will be essential for developing novel diagnostic and therapeutic strategies in the future. Here, we summarize our current understanding of antigenic targets and the relevance of new immunological concepts for inflammatory neuropathies. In addition, we provide an overview of available animal models of acute and chronic variants and how new diagnostic tools such as magnetic resonance imaging and novel therapeutic candidates will benefit patients with inflammatory neuropathies in the future. This review thus illustrates the gap between pre-clinical and clinical findings and aims to outline future directions of development.

Experimental Guillain-Barre syndrome induced by immunization with gangliosides: Keyhole limpet hemocyanin is required for disease triggering

An experimental model of Guillain-Barré Syndrome has been established in recent years. Rabbits develop disease upon immunization with a single dose of an emulsion containing bovine brain gangliosides, KLH and complete Freund's adjuvant. Within a period of four to ten weeks after immunization, they began to produce anti-ganglioside IgG-antibodies first, and to show clinical signs of neuropathy afterwards. In addition to gangliosides, KLH is a requirement for antibody production and disease triggering. Although KLH is commonly used as an immunological carrier protein, an anti-KLH-specific immune response was necessary for induction of both events. KLH is a glycoprotein carrying most of the immunogenicity in its glycan moiety. Between 20% to 80% of anti-ganglioside IgG-antibodies present in sick rabbit sera cross-reacted with KLH, indicating that both immune responses are related. The terminal Gal-ß(1,3)-GalNAc glycan (present in gangliosides and KLH) is proposed as "key" antigenic determinant involved in inducing the anti-ganglioside immune response. These results are discussed in the context of the "binding site drift" hypothesis.

Guillain-Barré syndrome: What have we learnt during one century? A personal historical perspective

We are approaching the centenary of the first description of Guillain-Barré syndrome. The past 30 years had witnessed an amazing progress in the understanding of the immunological and pathological mechanisms of this disorder. We now recognize that Guillain-Barré syndrome is remarkably heterogeneous and under this umbrella term are several variants and subtypes with distinct clinical, electrophysiological and immunopathological features. This review is a historical journey, through a personal perspective, following the milestones that led to the current substantial knowledge of Guillain-Barré syndrome.

Mapping autoantigen epitopes: molecular insights into autoantibody-associated disorders of the nervous system

Background

Our knowledge of autoantibody-associated diseases of the central (CNS) and peripheral (PNS) nervous systems has expanded greatly over the recent years. A number of extracellular and intracellular autoantigens have been identified, and there is no doubt that this field will continue to expand as more autoantigens are discovered as a result of improved clinical awareness and methodological practice. In recent years, interest has shifted to uncover the target epitopes of these autoantibodies.

Main body

The purpose of this review is to discuss the mapping of the epitope targets of autoantibodies in CNS and PNS antibody-mediated disorders, such as N-methyl-D-aspartate receptor (NMDAR), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), leucine-rich glioma-inactivated protein 1 (Lgi1), contactin-associated protein-like 2 (Caspr2), myelin oligodendrocyte glycoprotein (MOG), aquaporin-4 (AQP4), 65 kDa glutamic acid decarboxylase (GAD65), acetylcholine receptor (AChR), muscle-specific kinase (MuSK), voltage-gated calcium channel (VGCC), neurofascin (NF), and contactin. We also address the methods used to analyze these epitopes, the relevance of their determination, and how this knowledge can inform studies on autoantibody pathogenicity. Furthermore, we discuss triggers of autoimmunity, such as molecular mimicry, ectopic antigen expression, epitope spreading, and potential mechanisms for the rising number of double autoantibody-positive patients.

Conclusions

Molecular insights into specificity and role of autoantibodies will likely improve diagnosis and treatment of CNS and PNS neuroimmune diseases.

Guillain-Barré syndrome: causes, immunopathogenic mechanisms and treatment

INTRODUCTION

Guillain-Barré syndrome is a rare disease representing the most frequent cause of acute flaccid symmetrical weakness of the limbs and areflexia usually reaching its peak within a month. The etiology and pathogenesis remain largely enigmatic and the syndrome results in death or severe disability in 9-17% of cases despite immunotherapy. Areas covered: In terms of etiology, Guillain-Barré syndrome is linked to Campylobacter infection but less than 0.1% of infections result in the syndrome. In terms of pathogenesis, activated macrophages and T cells and serum antibodies against gangliosides are observed but their significance is unclear. Expert commentary: Guillain-Barré syndrome is a heterogeneous condition with numerous subtypes and recent data point towards the role of ganglioside epitopes by immunohistochemical methods. Ultimately, the syndrome results from a permissive genetic background on which environmental factors, including infections, vaccination and the influence of aging, lead to disease.

Sialylated intravenous immunoglobulin suppress anti-ganglioside antibody mediated nerve injury

The precise mechanisms underlying the efficacy of intravenous immunoglobulin (IVIg) in autoimmune neurological disorders including Guillain-Barré syndrome (GBS) are not known. Anti-ganglioside antibodies have been reported to be pathogenic in some variants of GBS, and we have developed passive transfer animal models to study anti-ganglioside antibody mediated-endoneurial inflammation and associated neuropathological effects and to evaluate the efficacy of new therapeutic approaches. Some studies indicate that IVIg's anti-inflammatory activity resides in a minor sialylated IVIg (sIVIg) fractions and is dependent on an innate Th2 response via binding to a specific ICAM3-grabbing nonintegrin related 1 receptor (SIGN-R1). Therefore the efficacy of IVIg, IVIg fractions with various IgG Fc sialylation status, and the involvement of Th2 pathway were examined in one of our animal model of antibody-mediated inhibition of axonal regeneration. We demonstrate that both IVIg and sIVIg ameliorated anti-glycan antibody mediated-pathological effect, whereas, the unsialylated fractions of IVIg were not beneficial in our model. Tenfold lower doses of sIVIg compared to whole IVIg provided equivalent efficacy in our studies. Moreover, we found that whole IVIg and sIVIg significantly upregulates the gene expression of IL-33, which itself can provide protection from antibody-mediated nerve injury in our model. Our results support that the SIGN-R1-Th2 pathway is involved in the anti-inflammatory effects of IVIg on endoneurium in our model and elements of this pathway including IL-33 can provide novel therapeutics in inflammatory neuropathies.

Neurologic autoimmunity: mechanisms revealed by animal models

Over the last decade, neurologic autoimmunity has become a major consideration in the diagnosis and management of patients with many neurologic presentations. The nature of the associated antibodies and their targets has led to appreciation of the importance of the accessibility of the target antigen to antibodies, and a partial understanding of the different mechanisms that can follow antibody binding. This chapter will first describe the basic principles of autoimmune inflammation and tissue damage in the central and peripheral nervous system, and will then demonstrate what has been learnt about neurologic autoimmunity from circumstantial clinical evidence and from passive, active, and occasionally spontaneous or genetic animal models. It will cover neurologic autoimmune diseases ranging from disorders of neuromuscular transmission, peripheral and ganglionic neuropathy, to diseases of the central nervous system, where autoantibodies are either pathogenic and cause destruction or changes in function of their targets, where they are harmless bystanders of T-cell-mediated tissue damage, or are not involved at all. Finally, this chapter will summarize the relevance of current animal models for studying the different neurologic autoimmune diseases, and it will identify aspects where future animal models need to be improved to better reflect the disease reality experienced by affected patients, e.g., the chronicity or the relapsing/remitting nature of their disease.

Myelin and macrophages in the PNS: An intimate relationship in trauma and disease

Macrophages of the peripheral nervous system belong to the so-called tissue macrophages, with multiple functions during injury and disease. Their origin during ontogeny has not yet been completely resolved, but it is clear that upon injury and disease conditions, they are supplemented by hematopoietic derivatives. In the peripheral nervous system, the most abundantly investigated scenario in which resident and infiltrating macrophages are involved is the so-called "Wallerian degeneration", a complex degenerative process where macrophages exhibit mostly beneficial functions by phagocytosing myelin and axonal remnants. Of special interest is the implication of macrophages in inflammatory nerve diseases, like acute Guillain-Barré syndromes and its permanent variant, chronic inflammatory demyelinating polyneuropathy, where macrophages are supposed to be substantial (co-)mediators of the diseases. In inherited peripheral neuropathies nerve macrophages possess a clear disease-amplifying function. In the corresponding animal models, a coordinated interplay between mutant Schwann cells, macrophages, endoneurial fibroblasts and the target structure, myelin, emerged. Along this process, a newly discovered disease mechanism mediated by macrophages is the dedifferentiation of myelinating Schwann cells. As macrophages are amplifiers of the genetically-mediated, non-curable diseases, targeting the mechanisms of their activation might be a promising strategy to treat these disorders. This article is part of a Special Issue entitled SI: Myelin Evolution.