Autoantobodies activate small GTPase RhoA to modulate neurite outgrowth

This review illustrates an example of adaptive immune responses (auto-antibodies) modulating growth/repair behavior of neurons in the disease context of Guillain-Barré syndrome (GBS), which is a prototypic autoimmune, acute monophasic disorder of the peripheral nerves that is the commonest cause of acute flaccid paralysis worldwide. Anti-ganglioside antibodies (Abs) are the most commonly recognized autoimmune markers in all forms of GBS and these Abs are associated with poor recovery. Extent of axonal injury and failure of axonal regeneration are critical determinants of recovery after GBS. In this clinical context, our group examined the hypothesis that anti-ganglioside Abs adversely affect axon regeneration after peripheral nerve injury. We show that anti-ganglioside Abs inhibit axon regeneration in preclinical cell culture and animal models. This inhibition is mediated by activation of small GTPase RhoA and its downstream effector Rho kinase (ROCK) by modulation of growth cone extension and associated neurite elongation in neuronal cultures. Our studies suggest that RhoA and ROCK are potential targets for development of novel therapeutic strategies to enhance nerve repair.

The role of molecular mimicry in the etiology of Guillain Barré Syndrome

Molecular mimicry between host tissue structures and microbial components has been proposed as the pathogenic mechanism for triggering of autoimmune diseases by preceding infection. Recent studies stated that molecular mimicry as the causative mechanism remains unproven for most of the human diseases. Still, in the case of the peripheral neuropathy Guillain-Barré syndrome (GBS) this hypothesis is supported by abundant experimental evidence. GBS is the most frequent cause of acute neuromuscular paralysis and in some cases occurs after infection with Campylobacter jejuni (C. jejuni). Epidemiological studies, showed that more than one third of GBS patients had antecedent C. jejuni infection and that only specific C. jejuni serotypes are associated with development of GBS. The molecular mimicry between the human gangliosides and the core oligosaccharides of bacterial lipopolysaccharides (LPSs) presumably results in production of antiganglioside cross-reactive antibodies which are likely to be a contributory factor in the induction and pathogenesis of GBS. Antiganglioside antibodies were found in the sera from patients with GBS and by sensitization of rabbits with gangliosides and C. jejuni LPSs animal disease models of GBS were established. GBS as prototype of post-infection immune-mediated disease probably will provide the first verification that an autoimmune disease can be triggered by molecular mimicry.

Guillain-barré syndrome animal model: the first proof of molecular mimicry in human autoimmune disorder

Molecular mimicry between self and microbial components has been proposed as the pathogenic mechanism of autoimmune diseases, and this hypothesis is proven in Guillain-Barré syndrome. Guillain-Barré syndrome, the most frequent cause of acute neuromuscular paralysis, sometimes occurs after Campylobacter jejuni enteritis. Gangliosides are predominantly cell-surface glycolipids highly expressed in nervous tissue, whilst lipo-oligosaccharides are major components of the Gram-negative bacterium C. jejuni outer membrane. IgG autoantibodies to GM1 ganglioside were found in the sera from patients with Guillain-Barré syndrome. Molecular mimicry was demonstrated between GM1 and lipo-oligosaccharide of C. jejuni isolated from the patients. Disease models by sensitization of rabbits with GM1 and C. jejuni lipo-oligosaccharide were established. Guillain-Barré syndrome provided the first verification that an autoimmune disease is triggered by molecular mimicry. Its disease models are helpful to further understand the molecular pathogenesis as well as to develop new treatments in Guillain-Barré syndrome.

Plasma exchange and intravenous immunoglobulins: mechanism of action in immune-mediated neuropathies

Immune-mediated neuropathies are a heterogeneous group of peripheral nerve disorders, which are classified by time course, clinical pattern, affected nerves and pathological features. Plasma exchange (PE) and intravenous immunoglobulins (IVIg) are mainstays in the treatment of immune-mediated neuropathies. Of all treatments currently used, IVIg has probably the widest application range in immune-mediated neuropathies and efficacy has been well documented in several randomized controlled trials for Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy (CIDP). Beneficial effects of IVIg have also been proven for multifocal motor neuropathy (MMN). Likewise, PE is an established treatment for GBS and CIDP, whereas it is considered to be ineffective in MMN. Different mechanisms of action are sought to be responsible for the immunemodulatory effect of PE and IVIg in autoimmune disorders. Some of those might be important for immune-mediated neuropathies, while others are probably negligible. The aim of this review is to summarize the recent advances in elucidating disease-specific mechanisms of actions of PE and IVIg in the treatment of immune-mediated neuropathies.

Transient immunosuppression: a bridge between infection and the atypical autoimmunity of Guillain-Barré syndrome?

Guillain-Barré syndrome (GBS) is an acute, usually monophasic, disorder of the peripheral nervous system that is assumed to be of immune-mediated pathogenesis. However, several clinical features and experimental findings of GBS are uncharacteristic for an immune-mediated disorder and set this condition apart from other disorders with a putative immune-mediated pathogenesis. These features include, among others, the monophasic nature of GBS, the lack of response to immunosuppressive (unlike immunomodulatory) therapy, the absence of a typical association with immunogenetic background and the inability to establish a valid and relevant animal model. We suggest a comprehensive hypothesis for the pathogenesis of GBS that is based on the assumption that the condition is due to a transient (or occasionally chronic) immune deficiency, as in most cases GBS follows an infection with pathogens known to induce immunosuppression. Such infections may be followed by breakdown of immune tolerance and induction of an immune attack on peripheral nerves. Mounting of the immune-mediated assault might be triggered either by the same infective pathogen or by secondary infection. Clearance of the infection and resumption of a normal immune response and tolerance eventually terminate the immune-mediated damage to the peripheral nerves and enable recovery. This hypothesis assumes that the entire sequence of events that culminates in GBS is due to transient exogenous factors and excludes a significant role for inherent host susceptibility, which explains the monophasic nature of the disorder.

Guillain-Barré syndrome after exposure to influenza virus

Guillain-Barré syndrome (GBS) is an acute, acquired, monophasic autoimmune disorder of peripheral nerves that develops in susceptible individuals after infection and, in rare cases, after immunisation. Exposure to influenza via infection or vaccination has been associated with GBS. We review the relation between GBS and these routes of exposure. Epidemiological studies have shown that, except for the 1976 US national immunisation programme against swine-origin influenza A H1N1 subtype A/NJ/76, influenza vaccine has probably not caused GBS or, if it has, rates have been extremely low (less than one case per million vaccine recipients). By contrast, influenza-like illnesses seem to be relevant triggering events for GBS. The concerns about the risk of inducing GBS in mass immunisation programmes against H1N1 2009 do not, therefore, seem justified by the available epidemiological data. However, the experiences from the 1976 swine flu vaccination programme emphasise the importance for active and passive surveillance to monitor vaccine safety.

The neonatal Fc receptor as therapeutic target in IgG-mediated autoimmune diseases

Therapy approaches based on lowering levels of pathogenic autoantibodies represent rational, effective, and safe treatment modalities of autoimmune diseases. The neonatal Fc receptor (FcRn) is a major factor regulating the serum levels of IgG antibodies. While FcRn-mediated half-life extension is beneficial for IgG antibody responses against pathogens, it also prolongs the serum half-life of IgG autoantibodies and thus promotes tissue damage in autoimmune diseases. In the present review article, we examine current evidence on the relevance of FcRn in maintaining high autoantibody levels and discuss FcRn-targeted therapeutic approaches. Further investigation of the FcRn-IgG interaction will not only provide mechanistic insights into the receptor function, but should also greatly facilitate the design of therapeutics combining optimal pharmacokinetic properties with the appropriate antibody effector functions in autoimmune diseases.

Monospecific high-affinity and complement activating anti-GM1 antibodies are determinants in experimental axonal neuropathy

It has been difficult to replicate consistently the experimental model of axonal Guillain-Barré syndrome (GBS). We immunized rabbits with two lipo-oligosaccharides (LOS1 and LOS2) derived from the same C. jejuni strain and purified in a slightly different way. LOS1 did not contain proteins whereas several proteins were present in LOS2. In spite of a robust anti-GM1 antibody response in all animals the neuropathy developed only in rabbits immunized with LOS1. To explain this discrepancy we investigated fine specificity, affinity and ability to activate the complement of anti-GM1 antibodies. Only rabbits immunized with LOS1 showed monospecific high-affinity antibodies which activated more effectively the complement. Although it is not well understood how monospecific high-affinity antibodies are induced these are crucial for the induction of experimental axonal neuropathy. Only a strict adherence to the protocols demonstrated to be successful may guarantee the reproducibility and increase the confidence in the animal model as a reliable tool for the study of the human axonal GBS.

Enteritis caused by Campylobacter jejuni followed by acute motor axonal neuropathy: a case report

Introduction

Campylobacter species represent the main cause of bacterial diarrhea in developed countries and one of the most frequent causes of enterocolitis in developing ones. In some patients, Campylobacter jejuni infection of the gastrointestinal tract has been observed as an antecedent illness of acute motor axonal neuropathy, a variant of Guillain-Barré syndrome.

Case presentation

We present a case of acute motor axonal neuropathy following infection with Campylobacter jejuni subspecies jejuni, biotype II, heat stable serotype O:19. A 46-year-old Caucasian man developed acute motor neuropathy 10 days after mild intestinal infection. The proximal and distal muscle weakness of his upper and lower extremities was associated with serum antibodies to Campylobacter jejuni and antibodies to ganglioside GM1. The electromyographic signs of neuropathic muscle action potentials with almost normal nerve conduction velocities indicated axonal neuropathy. Our patient's clinical and electrophysiological features fulfilled criteria for the diagnosis of an acute motor axonal neuropathy, a subtype of Guillain-Barré syndrome.

Conclusion

As this is the first case of acute motor axonal neuropathy following infection with Campylobacter jejuni subspecies jejuni reported from the Balkan area, the present findings indicate the need for systematic studies and further clinical, epidemiological and microbiological investigations on the prevalence of Campylobacter jejuni and its heat stable serotypes in the etiology of Guillain-Barré syndrome and other post-infectious sequelae.

Antibodies to gangliosides and ganglioside complexes in Guillain-Barré syndrome and Fisher syndrome: mini-review

Antiganglioside antibodies play a pathogenic role in the pathophysiology of Guillain-Barré syndrome (GBS) and Fisher syndrome (FS). Antiganglioside antibody-mediated nerve injury is likely to result from nerve damage through complement activation or dysfunction of molecules such as voltage-gated sodium and calcium channels. Clustered epitopes of complexes of two gangliosides in the cell membrane can be targeted by serum antibodies in GBS and FS and may regulate the accessibility and avidity of antiganglioside antibodies. The glycolipid environment or the specific distribution of target gangliosides in the peripheral nervous system may also influence the pathogenic effect of antiganglioside antibodies in GBS and FS. Structural and functional analyses of glycoepitopes of ganglioside complexes in membranes will provide new vistas on antibody-antigen interaction in GBS and shed light on microdomain function mediated by carbohydrate-carbohydrate interactions, which may lead to novel treatments for GBS and FS.

Human gangliosides and bacterial lipo-oligosaccharides in the development of autoimmune neuropathies

Guillain-Barré syndrome (GBS), the most frequent cause of acute flaccid paralysis, can develop after infection by Campylobacter jejuni. The condition is often associated with serum anti-GM1 or anti-GD1a IgG antibodies. Gangliosides contribute to stability of paranodal junctions and ion channel clusters in myelinated nerve fibers. Autoantibodies to GM1 and GD1a disrupt lipid rafts, paranodal or nodal structures, and ion channel clusters in peripheral motor nerves. Molecular mimicry exists between GM1 and GD1a gangliosides and lipo-oligosaccharides of C. jejuni isolates from GBS patients. Sensitization of rabbits with GM1 or C. jejuni lipo-oligosaccharide produces replica of GBS. These findings provide strong evidence for carbohydrate mimicry being a cause of GBS and show the role of gangliosides in peripheral nerves.

The role of endotoxin in infection: Helicobacter pylori and Campylobacter jejuni

Both Helicobacter pylori and Campylobacter jejuni are highly prevalent Gram-negative microaerophilic bacteria which are gastrointestinal pathogens of humans; H. pylori colonizes the gastroduodenal compartment and C. jejuni the intestinal mucosa. Although H. pylori causes chronic gastric infection leading to gastritis, peptic ulcers and eventually gastric cancer while C. jejuni causes acute infection inducing diarrhoeal disease, the endotoxin molecules of both bacterial species contrastingly contribute to their pathogenesis and the autoimmune sequelae each induces. Compared with enterobacterial endotoxin, that of H. pylori has significantly lower endotoxic and immuno-activities, the molecular basis for which is the underphosphorylation and underacylation of the lipid A component that interacts with immune receptors. This induction of low immunological responsiveness by endotoxin may aid the prolongation of H. pylori infection and therefore infection chronicity. On the other hand, this contrasts with acute infection-causing C. jejuni where overt inflammation contributes to pathology and diarrhoea production, and whose endotoxin is immunologically and endotoxically active. Futhermore, both H. pylori and C. jejuni exhibit molecular mimicry in the saccharide components of their endotoxins which can induce autoreactive antibodies; H. pylori expresses mimicry of Lewis and some ABO blood group antigens, C. jejuni mimicry of gangliosides. The former has been implicated in influencing the development of inflammation and gastric atrophy (a precursor of gastic cancer), the latter is central to the development of the neurological disorder Guillain-Barré syndrome. Both diseases raise important questions concerning infection-induced autoimmunity awaiting to be addressed.

[The significance of intravenous immunoglobulin in treatment of immune-mediated polyneuropathies]

Long-term treatment of immune-mediated polyneuropathies remains difficult. For acute polyneuritis, or Guillain-Barré syndrome, the established standard therapy utilizes high doses of polyvalent intravenous immunoglobulins (IVIG). A recently published randomized placebo-controlled study of patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) showed IVIG to be clinically effective also for this disorder in both short and long term. This survey presents data of this so-called ICE study ("Intravenous immune globulin for the treatment of chronic inflammatory demyelinating polyradiculoneuropathy"). It also discusses the value of IVIG in the treatment of immune-mediated polyneuropathies.

The neuropathic potential of anti-GM1 autoantibodies is regulated by the local glycolipid environment in mice

Anti-GM1 ganglioside autoantibodies are used as diagnostic markers for motor axonal peripheral neuropathies and are believed to be the primary mediators of such diseases. However, their ability to bind and exert pathogenic effects at neuronal membranes is highly inconsistent. Using human and mouse monoclonal anti-GM1 antibodies to probe the GM1-rich motor nerve terminal membrane in mice, we here show that the antigenic oligosaccharide of GM1 in the live plasma membrane is cryptic, hidden on surface domains that become buried for a proportion of anti-GM1 antibodies due to a masking effect of neighboring gangliosides. The cryptic GM1 binding domain was exposed by sialidase treatment that liberated sialic acid from masking gangliosides including GD1a or by disruption of the live membrane by freezing or fixation. This cryptic behavior was also recapitulated in solid-phase immunoassays. These data show that certain anti-GM1 antibodies exert potent complement activation-mediated neuropathogenic effects, including morphological damage at living terminal motor axons, leading to a block of synaptic transmission. This occurred only when GM1 was topologically available for antibody binding, but not when GM1 was cryptic. This revised understanding of the complexities in ganglioside membrane topology provides a mechanistic account for wide variations in the neuropathic potential of anti-GM1 antibodies.

Antiganglioside antibodies and their pathophysiological effects on Guillain-Barré syndrome and related disorders--a review

Guillain-Barré syndrome (GBS) is an acute immune-mediated polyradiculoneuropathy which can cause acute quadriplegia. Infection with micro-organisms, including Campylobacter jejuni (C. jejuni), Haemophilus influenzae, and Cytomegalovirus (CMV), is recognized as a main triggering event for the disease. Lipooligosaccharide (LOS) genes are responsible for the formation of human ganglioside-like LOS structures in infectious micro-organisms that can induce GBS. Molecular mimicry of LOSs on the surface of infectious agents and of ganglioside antigens on neural cells is thought to induce cross-reactive humoral and cellular immune responses. Patients with GBS develop antibodies against those gangliosides, resulting in autoimmune targeting of peripheral nerve sites, leading to neural damage. Heterogeneity of ganglioside expression in the peripheral nervous system (PNS) may underlie the differential clinical manifestation of the GBS variants. Recent studies demonstrate that some GBS sera react with ganglioside complexes consisting of two different gangliosides, such as GD1a and GD1b, or GM1 and GD1a, but not with each constituent ganglioside alone. The discovery of antiganglioside complex antibodies not only improves the detection rate of autoantibodies in GBS, but also provides a new concept in the antibody-antigen interaction through clustered carbohydrate epitopes. Although ganglioside mimicry is one of the possible etiological causes of GBS, unidentified factors may also contribute to the pathogenesis of GBS. While GBS is not considered a genetic disease, host factors, particularly human lymphocyte antigen type, appear to have a role in the pathogenesis of GBS following C. jejuni infection.

Clinical features, pathogenesis, and treatment of Guillain-Barré syndrome

Guillain-Barré syndrome (GBS) is an important cause of acute neuromuscular paralysis. Molecular mimicry and a cross-reactive immune response play a crucial part in its pathogenesis, at least in those cases with a preceding Campylobacter jejuni infection and with antibodies to gangliosides. The type of preceding infection and patient-related host factors seem to determine the form and severity of the disease. Intravenous immunoglobulin (IVIg) and plasma exchange are effective treatments in GBS; mainly for practical reasons, IVIg is the preferred treatment. Whether mildly affected patients or patients with Miller Fisher syndrome also benefit from IVIg is unclear. Despite medical treatment, GBS often remains a severe disease; 3-10% of patients die and 20% are still unable to walk after 6 months. In addition, many patients have pain and fatigue that can persist for months or years. Advances in prognostic modelling have resulted in the development of a new and simple prognostic outcome scale that might also help to guide new treatment options, particularly in patients with GBS who have a poor prognosis.

Complement inhibitor prevents disruption of sodium channel clusters in a rabbit model of Guillain-Barré syndrome

Complement-mediated disruption of voltage-gated sodium channels at the nodes of Ranvier acts in the development of acute motor axonal neuropathy. Nafamostat mesilate, a synthetic serine protease inhibitor, used in clinical practice for more than 20 years, has anti-complement activity. Acute motor axonal neuropathy rabbits obtained by GM1 ganglioside sensitization were or were not given nafamostat mesilate intravenously. Complement deposition and sodium channel disruption in the spinal anterior roots were significantly less frequent in the treated rabbits than in the controls. Nafamostat mesilate inhibited complement deposition and prevented sodium channel disruption. This provided the rationale for a clinical trial.

Intravenous immunoglobulins in the treatment of immune neuropathies

PURPOSE OF REVIEW

The aim of this review is to describe the value of high-dose polyclonal intravenous immunoglobulins as a treatment option in autoimmune disorders affecting the peripheral nervous system.

RECENT FINDINGS

A randomized placebo-controlled trial in patients with chronic inflammatory demyelinating polyradiculoneuropathy revealed short-term and long-term efficacy and safety of intravenous immunoglobulins as a treatment option for the chronically inflamed peripheral nervous system. Case reports suggest that the subcutaneous administration of immunoglobulins may represent a convenient alternative.

SUMMARY

Intravenous immunoglobulin represents an effective and safe treatment option in patients with autoimmune-mediated diseases affecting the peripheral nerves.

Anti-ganglioside antibody induction by swine (A/NJ/1976/H1N1) and other influenza vaccines: insights into vaccine-associated Guillain-Barré syndrome

BACKGROUND

Receipt of an A/NJ/1976/H1N1 "swine flu" vaccine in 1976, unlike receipt of influenza vaccines used in subsequent years, was strongly associated with the development of the neurologic disorder Guillain-Barré syndrome (GBS). Anti-ganglioside antibodies (e.g., anti-GM(1)) are associated with the development of GBS, and we hypothesized that the swine flu vaccine contained contaminating moieties (such as Campylobacter jejuni antigens that mimic human gangliosides or other vaccine components) that elicited an anti-GM(1) antibody response in susceptible recipients.

METHODS

Surviving samples of monovalent and bivalent 1976 vaccine, comprising those from 3 manufacturers and 11 lot numbers, along with several contemporary vaccines were tested for hemagglutinin (HA) activity, the presence of Campylobacter DNA, and the ability to induce anti-Campylobacter and anti-GM(1) antibodies after inoculation into C3H/HeN mice.

RESULTS

We found that, although C. jejuni was not detected in 1976 swine flu vaccines, these vaccines induced anti-GM(1) antibodies in mice, as did vaccines from 1991-1992 and 2004-2005. Preliminary studies suggest that the influenza HA induces anti-GM(1) antibodies.

CONCLUSIONS

Influenza vaccines contain structures that can induce anti-GM(1) antibodies after inoculation into mice. Further research into influenza vaccine components that elicit anti-ganglioside responses and the role played by these antibodies (if any) in vaccine-associated GBS is warranted.

Serologic marker of acute motor axonal neuropathy in childhood

Guillain-Barré syndrome is divided into two subtypes: acute inflammatory demyelinating polyneuropathy, and acute motor axonal neuropathy. Autoantibodies to gangliosides GM1, GM1b, GD1a, or GalNAc-GD1a were proposed as serologic markers of acute motor axonal neuropathy in adults. In a previous study of Japanese children with Guillain-Barré syndrome, acute motor axonal neuropathy was associated with anti-GM1 immunoglobulin G antibodies. Larger, comprehensive studies are required to confirm this finding. The present study revealed that immunoglobulin G antibodies were against GM1 (34%), GM1b (22%), GD1a (25%), GalNAc-GD1a (13%), and any of these (44%) in 32 Japanese children with Guillain-Barré syndrome. Patients who had the autoantibodies more often manifested previous diarrhea (71% vs 11%, P = 0.001), acute motor axonal neuropathy (64% vs 11%, P = 0.003), and slower recovery (healthy at final follow-up: 29% vs 78%, P = 0.011; able to run with minor signs, 64% vs 11%, P = 0.003) than patients who did not. The clinical features were consistent with those in adults carrying anti-ganglioside antibodies. Anti-ganglioside antibody testing may help predict outcomes in pediatric patients with Guillain-Barré syndrome who prefer not to undergo repeated nerve-conduction studies.

Structural requirements of anti-GD1a antibodies determine their target specificity

The acute motor axonal neuropathy (AMAN) variant of Guillain-Barré syndrome (GBS) is associated with anti-GD1a and anti-GM1 IgG antibodies. The basis of preferential motor nerve injury in this disease is not clear, however, because biochemical studies demonstrate that sensory and motor nerves express similar quantities of GD1a and GM1 gangliosides. To elucidate the pathophysiology of AMAN, we have developed several monoclonal antibodies (mAbs) with GD1a reactivity and reported that one mAb, GD1a-1, preferentially stained motor axons in human and rodent nerves. To understand the basis of this preferential motor axon staining, several derivatives of GD1a were generated by various chemical modifications of N-acetylneuraminic (sialic) acid residues (GD1a NeuAc 1-amide, GD1a NeuAc ethyl ester, GD1a NeuAc 1-alcohol, GD1a NeuAc 1-methyl ester, GD1a NeuAc 7-alcohol, GD1a NeuAc 7-aldehyde) on this ganglioside. Binding of anti-GD1a mAbs and AMAN sera with anti-GD1a Abs to these derivatives was examined. Our results indicate that mAbs with selective motor axon staining had a distinct pattern of reactivity with GD1a-derivatives compared to mAbs that stain both motor and sensory axons. The fine specificity of the anti-GD1a antibodies determines their motor selectivity, which was validated by cloning a new mAb (GD1a-E6) with a chemical and immunocytochemical binding pattern similar to that of GD1a-1 but with two orders of magnitude higher affinity. Control studies indicate that selective binding of mAbs to motor nerves is not due to differences in antibody affinity or ceramide structural specificity. Since GD1a-reactive mAb with preferential motor axon staining showed similar binding to sensory- and motor nerve-derived GD1a in a solid phase assay, we generated computer models of GD1a based on binding patterns of different GD1a-reactive mAbs to different GD1a-derivatives. These modelling studies suggest that critical GD1a epitopes recognized by mAbs are differentially expressed in motor and sensory nerves. The GD1a-derivative binding patterns of AMAN sera resembled those with motor-specific mAbs. On the basis of these findings we postulate that both the fine specificity and ganglioside orientation/exposure in the tissues contribute to target recognition by anti-ganglioside antibodies and this observation provides one explanation for preferential motor axon injury in AMAN.

The clinical value of therapeutic plasma exchange in multifocal motor neuropathy

OBJECTIVE

Although there is evidence for a pathogenic role of humoral factors in multifocal motor neuropathy (MMN), plasma exchange (PE) is assumed to be an ineffective treatment. We set out to elucidate possible reasons for this apparent contradiction.

METHODS

A retrospective analysis of seven patients with MMN, who underwent 4 to 18 sessions of PE. Clinical response, electrophysiological parameter and anti-ganglioside antibody titers were reviewed.

RESULTS

Two patients, who had anti-ganglioside antibodies, exhibited transient clinical responses to PE, manifested by improved neurological function. Whereas electrophysiological parameters continued to worsen in all patients, anti-ganglioside antibody titers declined during PE, but increased after PE.

CONCLUSION

PE is of limited therapeutic value in patients with MMN, who do not respond to established treatment options. It may only be useful as an adjunctive treatment in a subset of patients. The transient decrease of anti-ganglioside-antibodies titers suggests that pathogenic humoral factors in MMN are only temporarily reduced. Further, PE treatment alone is insufficient to prevent axons from continuing degeneration, which may explain the failure of PE to substantially influence the disease course of patients with MMN.

Cutting edge: Guillain-Barre syndrome-associated IgG responses to gangliosides are generated independently of CD1 function in mice

CD1 molecules present a variety of microbial glycolipids and self-glycolipids to T cells, but their potential role in humoral responses to glycolipid Ags remains to be established. To address this issue directly, we used GM1/GD1a-deficient mice, which, upon immunization with heat-killed Campylobacter jejuni, develop Guillain-Barré syndrome-associated IgG Abs against the GM1/GD1a sugar chain epitopes of bacterial lipo-oligosaccharides (LOS). Our results showed that anti-ganglioside Abs of the IgG1, IgG2b, and IgG3 isotypes were produced in the absence of group 2 CD1 (CD1d) expression. Unlike mouse and human group 2 CD1 molecules that specifically bound LOS, none of the group 1 CD1 molecules (CD1a, CD1b, and CD1c in humans) were capable of interacting with LOS. Thus, these results indicate CD1-independent pathways for anti-ganglioside Ab production.

Autoantibodies in celiac disease

Autoantibody production is an important feature of many autoimmune disorders, signifying a breakdown of immune tolerance to self-antigens. In celiac disease, an autoimmune enteropathy with multiple extra-intestinal manifestations, autoantibody reactivity to transglutaminase 2 (TG2) has been shown to closely correlate with the acute phase of the disease. It serves as a specific and sensitive marker of celiac disease, and is highly useful in aiding diagnosis and follow-up. Immune reactivity to other autoantigens, including transglutaminase 3, actin, ganglioside, collagen, calreticulin and zonulin, among others, has also been reported in celiac disease. The clinical significance of these antibodies is not known, although some may be associated with specific clinical presentations or extra-intestinal manifestations of celiac disease. This review examines the presence of anti-TG2 and other autoantibodies in celiac disease, discussing their diagnostic value, their potential role in disease pathogenesis and current hypotheses that explain how their release may be triggered.

Resistance is futile: antineuronal autoimmunity in multiple sclerosis

For many years, loss of myelin was considered to be the major cause of neurological dysfunction in multiple sclerosis (MS), a chronic inflammatory, demyelinating disease of the central nervous system. This 'myelinocentric' view of MS was revised recently, after recognition that axonal damage, rather than demyelination, provides a better correlate to clinical symptoms. Nonetheless, current views of MS pathogenesis remain focused on the role of myelin-specific autoimmunity, and the potential contribution of autoimmune responses to axonal and neuronal antigens is ignored. Drawing on experience gained from work with other neurodegenerative diseases, we hypothesize that autoimmunity, particularly pathogenic antibodies to neuronal and axonal antigens, plays a significant role in the development of axonal pathology in MS. This concept offers a new perspective of disease pathogenesis and therapeutic approaches to prevent irreversible axonal loss and chronic disability in MS.

Anti-GM1 antibodies as a model of the immune response to self-glycans

Glycans are a class of molecules with high structural variability, frequently found in the plasma membrane facing the extracellular space. Because of these characteristics, glycans are often considered as recognition molecules involved in cell social functions, and as targets of pathogenic factors. Induction of anti-glycan antibodies is one of the early events in immunological defense against bacteria that colonize the body. Because of this natural infection, antibodies recognizing a variety of bacterial glycans are found in sera of adult humans and animals. The immune response to glycans is restricted by self-tolerance, and no antibodies to self-glycans should exist in normal subjects. However, antibodies recognizing structures closely related to self-glycans do exist, and can lead to production of harmful anti-self antibodies. Normal human sera contain low-affinity anti-GM1 IgM-antibodies. Similar antibodies with higher affinity or different isotype are found in some neuropathy patients. Two hypotheses have been developed to explain the origin of disease-associated anti-GM1 antibodies. According to the "molecular mimicry" hypothesis, similarity between GM1 and Campylobacter jejuni lipopolysaccharide carrying a GM1-like glycan is the cause of Guillain-Barré syndrome associated with anti-GM1 IgG-antibodies. According to the "binding site drift" hypothesis, IgM-antibodies associated with disease originate through changes in the binding site of normally occurring anti-GM1 antibodies. We now present an "integrated" hypothesis, combining the "mimicry" and "drift" concepts, which satisfactorily explains most of the published data on anti-GM1 antibodies.

The immunocompetence of Schwann cells

Schwann cells are the myelinating glial cells of the peripheral nervous system that support and ensheath axons with myelin to enable rapid saltatory signal propagation in the axon. Immunocompetence, however, has only recently been recognized as an important feature of Schwann cells. An autoimmune response against components of the peripheral nervous system triggers disabling inflammatory neuropathies in patients and corresponding animal models. The immune system participates in nerve damage and disease manifestation even in non-inflammatory hereditary neuropathies. A growing body of evidence suggests that Schwann cells may modulate local immune responses by recognizing and presenting antigens and may also influence and terminate nerve inflammation by secreting cytokines. This review summarizes current knowledge on the interaction of Schwann cells with the immune system, which is involved in diseases of the peripheral nervous system.

Anti-ganglioside antibodies alter presynaptic release and calcium influx

Acute motor axonal neuropathy (AMAN) variant of Guillain-Barré syndrome is often associated with IgG anti-GM1 and -GD1a antibodies. The pathophysiological basis of antibody-mediated selective motor nerve dysfunction remains unclear. We investigated the effects of IgG anti-GM1 and -GD1a monoclonal antibodies (mAbs) on neuromuscular transmission and calcium influx in hemidiaphragm preparations and in cultured neurons, respectively, to elucidate mechanisms of Ab-mediated muscle weakness. Anti-GM1 and -GD1a mAbs depressed evoked quantal release to a significant yet different extent, without affecting postsynaptic currents. At equivalent concentrations, anti-GD1b, -GT1b, or sham mAbs did not affect neuromuscular transmission. At fourfold higher concentration, an anti-GD1b mAb (specificity described in immune sensory neuropathies) induced completely reversible blockade. In neuronal cultures, anti-GM1 and -GD1a mAbs significantly reduced depolarization-induced calcium influx. In conclusion, different anti-ganglioside mAbs induce distinct effects on presynaptic transmitter release by reducing calcium influx, suggesting that this is one mechanism of antibody-mediated muscle weakness in AMAN.

Lewis rats immunized with GM1 ganglioside do not develop peripheral neuropathy

Elevated levels of anti-GM1 antibodies are associated with motor nerve syndromes. Although there is a lot of circumstantial evidence that anti-GM1 antibodies may be causing the disease, their precise role remains unclear. In order to study the role of anti-GM1 antibodies in the pathogenesis of peripheral neuropathy, eight Lewis rats were injected with GM1 ganglioside mixed with keyhole limpet hemocyanin (KLH) and emulsified with Freund's adjuvant and three rats were immunized with GM1 in liposomes. Although IgM class anti-GM1 antibodies were detected in all animals immunized with GM1, none of the animals exhibited overt signs of neuropathy during 6 months after initial immunization. IgG antibody to GM1 was not produced in any of the animals. There was no pathological evidence of nerve damage. These studies suggest that elevated levels of IgM anti-GM1 antibodies by themselves do not cause nerve damage in rats.

Antibody testing in peripheral neuropathies

Many autoantibodies have been described in association with peripheral neuropathy, but the use of antibody testing in clinical practice remains a matter of some debate. Serum autoantibodies to gangliosides or glycoproteins are implicated in a variety of sensory and motor neuropathy syndromes. Paraneoplastic antibodies help identify patients who have a neuropathy related to an underlying malignancy. Detection of an autoantibody in the right clinical setting provides some evidence that the peripheral nerve disturbance is immune mediated and that immunomodulatory therapy may be of benefit.

From bench to bedside--experimental rationale for immune-specific therapies in the inflamed peripheral nerve

Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy are autoimmune-mediated inflammatory diseases of the PNS. In recent years, substantial progress has been made towards understanding the immune mechanisms that underlie these conditions, in large part through the study of experimental models. Here, we review the available animal models that partially mimic human Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy, and discuss the wide range of therapeutic approaches that have been successfully established in these models of inflammatory neuropathies. Transfer of this preclinical knowledge to patients has been far less successful, and inflammatory neuropathies are still associated with significant morbidity and mortality. We will summarize successful therapeutic trials in human autoimmune neuropathies to provide a vantage point for the transfer of experimental treatment strategies to clinical practice in immune-mediated diseases of the peripheral nerve.

Guillain-Barré syndrome

Guillain-Barré syndrome (GBS) is currently divided into the two major subtypes: acute inflammatory demyelinating polyneuropathy (AIDP) and acute motor axonal neuropathy (AMAN). This review highlights relevant recent publications, particularly on the pathophysiology of AMAN. Molecular mimicry of the bacterial lipo-oligosaccharide by the human gangliosides is now considered an important cause of AMAN. Gangliosides GM1, GM1b, GD1a, and GalNAc-GD1a expressed on the motor axolemma are likely to be the epitopes for antibodies in AMAN. At the nodes or paranodes, deposition of antiganglioside antibodies initially cause reversible conduction block followed by axonal degeneration. Electrodiagnostic findings support this process. Disruption of glycolipids, which are important to maintain ion channel clustering at the nodes and paranode, may impair nerve conduction. Genetic polymorphisms of Campylobacter jejuni determine the expression of the gangliosides on the bacterial wall. In contrast, target molecules in AIDP have not yet been identified. Meta-analyses show efficacy of plasmapheresis and immunoglobulin therapy, but not corticosteroids, in hastening recovery.

Immune circuitry in the peripheral nervous system

PURPOSE OF REVIEW

The aim of this review is to describe the local immune circuitry in the peripheral nervous system and its dialogue with systemic immunity under pathological conditions. Specifically, interactions of the immune system with cellular and extracellular components within peripheral nerve and immune functions of tissue-resident endoneurial macrophages and Schwann cells will be discussed.

RECENT FINDINGS

New insights into the elements involved in the pathogenesis of immune-mediated disorders of the peripheral nervous system provide a better understanding of the complex interplay of these cellular and molecular components in the immunology of the peripheral nervous system.

SUMMARY

The application of innovative and cutting-edge technologies to the study of immunoinflammatory disorders of the peripheral nervous system provides a better understanding of underlying principles of the organization of the immune network present in the peripheral nerve and its dialogue with the systemic immune system. This may foster the development of specific and highly effective therapies for immune-mediated disorders of the peripheral nerve.

Guillain-Barré syndrome and its treatment

Guillain-Barré syndrome typically presents with an acute ascending areflexic weakness, progressing over 4 weeks or less. The most common form of the disease is an acute inflammatory demyelinating polyneuropathy, but other forms with primarily axonal pathologies are well documented. The association of Guillain-Barré syndrome with a range of antecedent infections, particularly Campylobacter jejuni enteritis, is also established. A range of serological and neurophysiological investigations can assist in making an accurate diagnosis. Background information about the syndrome and the evidence base for such treatments are discussed herein.

Leukocyte and complement activation by GM1-specific antibodies is associated with acute motor axonal neuropathy in rabbits

Acute motor axonal neuropathy (AMAN) in humans is associated with the presence of GM1-specific antibodies. Immunization of rabbits with GM1-containing ganglioside mixtures, purified GM1, or Campylobacter jejuni lipo-oligosaccharide exhibiting a GM1-like structure elicits GM1-specific antibodies, but axonal polyneuropathy only occurs in a subset of animals. This study aimed to dissect the molecular basis for the variable induction of AMAN in rabbits. Therefore, we analyzed the pro-inflammatory characteristics of GM1-specific antibodies in plasma samples from ganglioside-immunized rabbits with and without neurological deficits. GM1-specific plasma samples from all rabbits with AMAN were capable of activating both complement and leukocytes, in contrast to none of the plasma samples from rabbits without paralysis. Furthermore, GM1-specific IgG-mediated activation of leukocytes was detected before the onset of clinical signs. These data suggest that AMAN only occurs in rabbits that develop GM1-specific antibodies with pro-inflammatory properties.