The pattern of antiganglioside antibody reactivities producing myelinated nerve conduction block in vitro

[Guillain-Barré syndrome after exposure to influenza]

Guillain-Barré Syndrome (GBS) is an acquired, monophasic inflammatory polyradiculoneuritis of autoimmune origin, which occurs after infection and occasionally also after vaccination. Seasonal and pandemic influenza vaccines have in particular been implicated as triggers for GBS. However, a number of recent studies indicate that infection with influenza virus may also cause GBS. This review summarizes the epidemiological and experimental data of the association of GBS with exposure to influenza antigens by immunization (including vaccines against A/H1N1/2009) and infection. Vaccination against influenza is associated with a very low risk for the occurrence of GBS. In contrast infection with influenza may play a more important role as a triggering factor for GBS than previously assumed.

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.

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.

Effect of anti-GM2 antibodies on rat sciatic nerve: electrophysiological and morphological study

We found that a monoclonal human IgM anti-GM2 was fixed in rat sciatic axons and Schwann cells and was able to activate human complement. The passive transfer of IgM and complement in sciatic nerves can induce an acute alteration in nerve conduction. When the transfer of IgM plus complement was repeated for 10 days, the compound action motor potential amplitude was very low and the morphological study showed axons and myelin damage. Without human complement, IgM can only slightly disorganize the myelin by separating some layers, probably by interfering with the functional role of gangliosides in the myelin package.

Chemical validation of molecular mimicry: interaction of cholera toxin with Campylobacter lipooligosaccharides

It is generally believed that molecular mimicry between bacterial lipooligosaccharide (LOS) and nerve glycolipids may play an important pathogenic role in immune-mediated peripheral neuropathy. One of the putative infectious agents is Campylobacter jejuni (C. jejuni). To elucidate the structural basis for the molecular mimicry, we investigated the structure of the lipooligosaccharide (LOS) fraction of C. jejuni, strain HS19, and found that it includes at least two components, characterized as fast-and slow-moving bands (LF and LS) by thin-layer chromatography as revealed by cholera toxin B subunit (Ctxb) overlay. Structural analysis of the oligosaccharide portion of LS established that it had the following structure: Gal-GalNAc-(NeuAc)Gal-Hep-(Glc;PO(3)H)Hep-Kdo. The GM1-like epitope was validated by a terminal tetrasaccharide unit within this structure. On the other hand, analysis of LF revealed an entirely different structure: 1, 4'-bisphosphoryl glucosamine disaccharide N, N'-acylated by 3-(2-hydroxytetracosanoyloxy)octadecanoic acid at 2- and 2'-positions, which is consistent with that of lipid A. No GM1-like epitope was observed in LF. Both LS and LF interacted with Ctxb as demonstrated by TLC-overlay and sucrose density gradient centrifugation. Surprisingly, LF does not have the basic GM1 structure for interacting with Ctxb. Instead, the affinity of LF to Ctxb required that one or both of the phosphate groups be present in the glucosamine disaccharide residue because after alkaline phosphatase treatment the dephosphorylated LF was unable to bind to Ctxb. We conclude that LS is likely the component contributing to GM1-mimicry in autoimmune peripheral neuropathy and that the role of LF is not clear but may be associated with the initial activation of autoreactive T cells.

Ca2+ Channel Currents Inhibited by Serum from Select Patients with Guillain-Barré Syndrome

We performed an electrophysiological study demonstrating inhibition of spontaneous muscle action potentials within a coculture of rat muscle and spinal cord by exposure to serum, as well as purified IgG, from patients with the acute motor axonal neuropathy (AMAN) variant of Guillain-Barré syndrome (GBS). However, exposure to serum from two patients with the acute inflammatory demyelinating polyneuropathy (AIDP) form of GBS had no effect. Using a whole-cell recording technique, we then investigated the effects of serum and purified IgG from patients with GBS on voltage-dependent calcium channel (VDCC) currents in nerve growth factor-differentiated PC12 cells. Serum from patients with GBS (AMAN) inhibited VDCC currents in PC12 cells, which was fully reversible by washing with the bath solution. Similarly, purified IgG from the serum of two patients with GBS (AMAN) also inhibited VDCC currents in PC12 cells. In contrast, sera from patients with AIDP and healthy volunteers did not affect VDCC currents in PC12 cells. These results suggest that muscle weakness in some patients with GBS might be induced by inhibition of Ca2+ channel currents within motor nerve terminals.

Molecular mimicry: sensitization of Lewis rats with Campylobacter jejuni lipopolysaccharides induces formation of antibody toward GD3 ganglioside

Recently we have reported cases of demyelinating inflammatory neuropathy showing elevated titers of anti-GD3 antibodies, which occurs rarely in Guillain-Barré syndrome. To examine the correlation between the anti-GD3 antibody titer and Campylobacter jejuni infection, we sensitized female Lewis rats with lipopolysaccharides (LPSs) from serotype HS19 of C. jejuni and examined changes in nerve conduction velocity and nerve conduction block (P/D ratio). After 16 weeks of sensitization, animals revealed decreases of nerve conduction velocity and conduction block (P/D ratio) and high titer of anti-GD3 antibodies. These anti-GD3 antibodies also blocked transmission in neuromuscular junctions of spinal cord-muscle cells cocultures. The GD3 epitope was verified to be located on the Schwann cell surface and nodes of Ranvier in rat sciatic nerve. To determine the target epitope for GD3 antibodies in causing nerve dysfunction, the LPS fraction containing the GD3 epitope was purified from the total LPS by using an anti-GD3 monoclonal antibody-immobilized affinity column. Subsequently, chemical analysis of the oligosaccharide portion was performed and confirmed the presence of a GD3-like epitope as having the following tetrasaccharide structure: NeuAcalpha2-8NeuAc2-3Galbeta1-4Hep. Our data thus support the possibility of a contribution of GD3 mimicry as a potential pathogenic mechanism of peripheral nerve dysfunction.

Antibodies induced by ganglioside-mimicking Campylobacter jejuni lipooligosaccharides recognise epitopes at the nodes of Ranvier

Molecular mimicry of gangliosides by Campylobacter jejuni lipooligosaccharides (LOSs) in the induction of anti-ganglioside antibodies has been hypothesised to contribute to GBS development. Rabbits were immunised with ganglioside-mimicking C. jejuni LOSs and anti-LOS responses were analysed using passive haemagglutination, and anti-ganglioside responses by enzyme-linked immunosorbent assay and thin-layer chromatography with immunostaining. High titres of anti-LOS antibodies were demonstrated in rabbit antisera that were cross-reactive with a panel of gangliosides. Non-ganglioside-mimicking C. jejuni HS:3 LOS induced a strong anti-LOS response, but no anti-ganglioside antibodies. Control rabbit antisera had no anti-LOS or -ganglioside responses. Moreover, IgG from a patient treated with parenteral gangliosides, who exhibited Guillain-Barré syndrome, had antibodies reactive with C. jejuni LOS. Biotinylated IgG fractions from the rabbit and the patient sera recognised epitopes at the nodes of Ranvier in sectioned human nerves, whereas fractions from controls did not. This study demonstrates that immunisation with ganglioside-mimicking C. jejuni LOS triggers the production of cross-reactive anti-ganglioside antibodies that recognise epitopes at the nodes of Ranvier.

Human Antiganglioside Autoantibodies: Validation of ELISA

Gangliosides have a hydrophilic sugar chain that contains antigenic determinants and a hydrophobic ceramide. In humans, gangliosides elicit a T-cell independent IgM response; antiganglioside IgM autoantibodies may be pentameric or polymeric. A correlation between specific neuropathies and antiganglioside autoantibodies has been confirmed. Although many neurologists attempt to lower titers of antiganglioside autoantibodies, oncologists are developing strategies to augment production of IgM antibodies that will remove immunosuppressive gangliosides from the circulation of patients and target gangliosides and kill tumor cells. Antiganglioside IgM antibodies can cause leakage of the blood-nerve barrier in a concentration-dependent and complement-independent manner, bind to neuronal gangliosides to create a neuromuscular block and serve as a marker of axonal damage in neuropathies such as multiple sclerosis. They are also a promising biomarker of early prostate cancer. There is a need to validate the protocol for enzyme-linked immunosorbent assay (ELISA) of antiganglioside IgM autoantibodies. This validation must consider the purity of gangliosides from different commercial sources, the coating of gangliosides onto a solid matrix in a manner that maximizes exposure of oligosaccharide epitopes to IgM paratopes, techniques to minimize background noise and eliminate nonspecific antibody binding, and carefully defined positive and negative controls. The validated protocol also must include a simple formula to estimate titers for several replicas. Finally, antibody titers must be converted to natural logs for statistical appraisal.

Effects on axonal conduction of anti-ganglioside sera and sera from patients with Guillain-Barré syndrome

The efficacy of plasma exchange as a therapy for Guillain-Barré syndrome (GBS) suggests that humoral factors might contribute to the axonal conduction block responsible for the major symptoms of the disease. To explore this possibility, we have applied sera to rat spinal roots in vitro while monitoring axonal conduction. Neither fresh sera from 12 patients with GBS or Miller-Fisher syndrome (MFS), nor serum from rabbits immunised with Campylobacter jejuni from patients with GBS, MFS or gastroenteritis were effective in causing acute conduction block, despite the presence of antibodies to gangliosides GD3, GM1, GQ1b and GT1a. Potential explanations are advanced.

Sialosyl-galactose: a common denominator of Guillain-Barré and related disorders?

The immune reactivity implicated in the pathogenesis of Guillain-Barré syndrome (GBS) and related diseases, which occur following infection with specific strains of Campylobacter jejuni bearing sialylated lipopolysaccharide structures that cross-react with specific gangliosides, is consistent with provocation of inflammation via molecular mimicry. In this review, we have focused upon microbial characteristics and structures, the fine structure of the essential carbohydrate determinants, and the application of our proposed criteria, modified from those of Koch for causation of infectious and of Witebsky for autoimmune diseases, to the circumstance of infectious induction of autoimmune disorder.

Guillain-Barré syndrome serum and anti-Campylobacter antibody do not exacerbate experimental autoimmune neuritis

To investigate whether antibodies are pathogenic in Guillain-Barré syndrome (GBS), we injected pre-treatment serum from 11 GBS patients intraperitoneally into rats in which the blood-nerve barrier had been opened by induction of mild adoptive transfer experimental autoimmune neuritis. There was no significant clinical, neurophysiological or pathological difference between rats receiving GBS serum compared with those receiving control serum, except that GBS serum caused minor excess weight loss. Murine monoclonal antibody to Campylobacter jejuni and gangliosides also did not exacerbate disease. This experiment failed to show antibody-mediated disease exacerbation and so does not support an antibody-mediated mechanism in GBS.

Recent studies on the roles of antiglycosphingolipids in the pathogenesis of neurological disorders

Evidence is mounting to suggest a causal role of humoral immunity arising from antiglycosphingolipid (GSL) antibodies in a variety of neurological disorders. These disorders include the demyelinating and axonal forms of Guillain-Barre syndrome, multifocal motor neuropathy, chronic inflammatory demyelinating polyradiculoneuropathy, and IgM paraproteinemia. Many claims have been made regarding other neurological disorders, which should be carefully scrutinized for their validity, based on several criteria proposed in this review. These criteria include 1) characterization of the causative antigens and immunoglobulins, 2) correlation of the pathological lesions and clinical manifestation of the antigens, 3) establishment of animal models using pure GSLs as the antigens, 4) immunopathogenic mechanisms of the neurodenerative process, 5) mechanisms for the malfunctioning of blood-nerve barrier and the ensuing leakage of circulating antibodies into peripheral nerve parenchyma, and 6) the roles of anti-GSL antibodies that may cause humorally mediated nerve dysfunction and injury as well as interference with ion channel function at the node of Ranvier, where carbohydrate epitopes are located. Finally, the origin of the anti-GSL antibodies is discussed in light of the recent circumstantial evidence pointing to a molecular mimicry mechanism with infectious agents. With a better understanding of the immunopathogenic mechanisms, it will then be possible to devise rational and effective diagnostic and therapeutic strategies for the treatment of these neurological disorders.

Factors directly affecting impulse transmission in inflammatory demyelinating disease: recent advances in our understanding

Demyelination and inflammation both contribute to the neurological deficits characteristic of multiple sclerosis and Guillain-Barré syndrome. Conduction deficits attributable to demyelination are well known, but it is becoming clear that factors such as nitric oxide, endocaine, cytokines, and antiganglioside antibodies also play significant roles. Demyelination directly affects conduction and also causes changes in both the distribution and repertoire of expressed axolemmal ion channels, which in turn affect impulse propagation and can promote hyperexcitability. In conducting axons, sustained trains of impulses can produce intermittent conduction failure, and, in the presence of nitric oxide exposure, can also cause axonal degeneration. Other factors impairing impulse transmission include nodal widening, glutamate toxicity, and disturbances of both the blood-brain barrier and synaptic transmission.

Molecular mimicry in Campylobacter jejuni and Helicobacter pylori lipopolysaccharides: contribution of gastrointestinal infections to autoimmunity

Molecular mimicry of host structures by the saccharide portion of lipopolysaccharides (LPS) of the gastrointestinal pathogens Campylobacter jejuni and Helicobacter pylori is thought to be associated with the development of autoimmune sequelae. C. jejuni, a leading cause of gastroenteritis, is the most common antecedent infection in Guillain-Barré syndrome (GBS), an inflammatory neuropathy. Chemical analyses of the core oligosaccharides of neuropathy-associated C. jejuni strains have revealed structural homology with human gangliosides. Serum antibodies against gangliosides are found in one third of GBS patients but are generally absent in enteritis cases. Collective data suggest that the antibodies are induced by antecedent infection with C. jejuni, and subsequently react with nerve tissue causing damage. The O-chains of most H. pylori strains express Lewis blood group antigens which are thought to have a role in camouflage of the bacterium as these antigens are also present on human gastric epithelial cells. In chronic H. pylori infections, bacterial expression of Lewis antigens is suggested to be involved in the induction of autoantibodies against the Lewis antigen-expressing gastric proton pump. Many aspects of the autoimmune mechanisms in C. jejuni -associated GBS and H. pylori -induced atrophic gastritis remain unclear, such as the involvement of T cells and the role of host factors.

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is a recently identified peripheral nerve disorder characterized by progressive, predominantly distal, asymmetric limb weakness mostly affecting upper limbs, minimal or no sensory impairment, and by the presence on nerve conduction studies of multifocal persistent partial conduction blocks on motor but not sensory nerves. The etiopathogenesis of MMN is not known, but there is some evidence, based mostly on the clinical improvement after immunological therapies, that the disease has an immunological basis. Antibodies, mostly IgM, to the gangliosides GM1, and though less frequently, GM2 and GD1a, are frequently detected in patients' sera, helping in the diagnosis of this disease. Even if there is some experimental evidence that these antibodies may be pathogenic in vitro, their role in the neuropathy remains to be established. Patients with MMN do not usually respond to steroids or plasma exchange, which may occasionally worsen the symptoms, while the efficacy of cyclophosphamide is limited by its relevant side effects. More than 80% of MMN patients rapidly improve with high dose intravenous immunoglobulin therapy (IVIg). The effect of this therapy is, however, transient and improvement has to be maintained with periodic infusions. A positive response to interferon-beta has been recently reported in a minority of patients, some of whom were resistant to IVIg. Even if many progresses have been made on the diagnosis and therapy of MMN, there are still several issues on the nosological position, etiopathogenesis and long-term treatment of this neuropathy that need to be clarified.

New concepts of Guillain-Barré syndrome

Guillain-Barré syndrome is an acute autoimmune polyradiculoneuropathy with a clinical presentation of flaccid paralysis with areflexia, variable sensory disturbance, and elevated cerebrospinal fluid protein without pleocytosis. Although Guillain-Barré syndrome previously had been viewed as a unitary disorder with variations, it currently is viewed as a group of syndromes with several distinctive subtypes. These include the principal subtype prevalent in the Western world (acute inflammatory demyelinating polyradiculoneuropathy, and others, each with distinctive electrodiagnostic and pathologic features, including acute motor axonal neuropathy), acute motor-sensory axonal neuropathy, Miller Fisher syndrome, and perhaps others. The clinical and pathologic features of these Guillain-Barré syndrome subtypes are reviewed, and the role of antecedent infections, particularly Campylobacter jejuni gastroenteritis, and the role of antiganglioside antibody responses are reviewed with respect to pathogenesis. Treatment of Guillain-Barré syndrome includes both important supportive measures and immunotherapies, specifically high-dose intravenous immunoglobulin and plasma exchange.

Pathogenesis of Guillain-Barré syndrome

Recent neurophysiological and pathological studies have led to a reclassification of the diseases that underlie Guillain-Barré syndrome (GBS) into acute inflammatory demyelinating polyradiculoneuropathy (AIDP), acute motor and sensory axonal neuropathy (AMSAN) and acute motor axonal neuropathy (AMAN). The Fisher syndrome of ophthalmoplegia, ataxia and areflexia is the most striking of several related conditions. Significant antecedent events include Campylobacter jejuni (4-66%), cytomegalovirus (5-15%), Epstein-Barr virus (2-10%), and Mycoplasma pneumoniae (1-5%) infections. These infections are not uniquely associated with any clinical subtype but severe axonal degeneration is more common following C. jejuni and severe sensory impairment following cytomegalovirus. Strong evidence supports an important role for antibodies to gangliosides in pathogenesis. In particular antibodies to ganglioside GM1 are present in 14-50% of patients with GBS, and are more common in cases with severe axonal degeneration associated with any subtype. Antibodies to ganglioside GQ1b are very closely associated with Fisher syndrome, its formes frustes and related syndromes. Ganglioside-like epitopes exist in the bacterial wall of C. jejuni. Infection by this and other organisms triggers an antibody response in patients with GBS but not in those with uncomplicated enteritis. The development of GBS is likely to be a consequence of special properties of the infecting organism, since some strains such as Penner 0:19 and 0:41 are particularly associated with GBS but not with enteritis. It is also likely to be a consequence of the immunogenetic background of the patient since few patients develop GBS after infection even with one of these strains. Attempts to match the subtypes of GBS to the fine specificity of anti-ganglioside antibodies and to functional effects in experimental models continue but have not yet fully explained the pathogenesis. T cells are also involved in the pathogenesis of most or perhaps all forms of GBS. T cell responses to any of three myelin proteins, P2, PO and PMP22, are sufficient to induce experimental autoimmune neuritis. Activated T cells are present in the circulation in the acute stage, up-regulate matrix metalloproteinases, cross the blood-nerve barrier and encounter their cognate antigens. Identification of the specificity of these T cell responses is still at a preliminary stage. The invasion of intact myelin sheaths by activated macrophages is difficult to explain according to a purely T cell mediated mechanism. The different patterns of GBS are probably due to the diverse interplay between antibodies and T cells of differing specificities.