Neuropathophysiological potential of Guillain-Barré syndrome anti-ganglioside-complex antibodies at mouse motor nerve terminals

[Guillain-Barré and Fisher syndromes: update on the pathophysiological role of antiganglioside antibodies]

There are growing experimental and clinical data on the pathophysiological roles of antiganglioside antibodies in Guillain-Barré syndrome (GBS) and Fisher syndrome (FS). Antibodies to a ganglioside complex (GSC) consisting of two different gangliosides are detected in some GBS and FS sera. Recently, anti-GM1/GalNAc-GD1a complex antibodies, anti-GA1/GQ1b antibodies with no reaction against GM1/GQ1b, and anti-GM1/LM1 antibodies have been detected in GBS or FS sera. The anti-GM1/GalNAc-GD1a antibodies correlated with pure motor GBS characterized by antecedent respiratory infection and early CBs at intermediate sites of motor nerves. Complement activation is considered to be a key process causing nerve damage in GBS and FS with antiganglioside antibodies. A recent ex vivo study indicates that antibodies to GM1/GD1a or GM1/GQ1b can induce complement-mediated functional and morphological injury at mouse motor nerve terminals. Complement-independent pathophysiology such as blockade of voltage-gated Ca channels, the apoptotic mechanism of neurons, and alteration of microdomains in the nerve cell membrane should also be considered. Complex glycolipid environments in the cell membrane may govern the accessibility and avidity of antiganglioside antibodies for target gangliosides. Thus, the pathogenic effect of antiganglioside antibodies may depend on the local glycolipid environment in the nerve membrane, as well as on the antibody specificity.

Update on Guillain-Barré syndrome

Understanding of Guillain-Barré syndrome (GBS) has progressed substantially since the seminal 1916 report by Guillain et al. Although Guillain, Barré, and Strohl summarised the syndrome based on observations of two French infantrymen, 2012 saw the beginning of an ambitious collaborative study designed to collect detailed data from at least 1,000 patients worldwide (IGOS, www.gbsstudies.org/about-igos). Progress has been made in many areas even since GBS was last reviewed in this journal in 2009. GBS subsequently received prominent attention in light of concerns regarding H1N1 influenza vaccinations, and several large-scale surveillance studies resulted. Despite these developments, and promising pre-clinical studies, disease-modifying therapies for GBS have not substantially altered since intravenous immunoglobulin was introduced over 20 years ago. In other areas, management has improved. Antibiotic prophylaxis in ventilated patients reduces respiratory tract infection, thromboprophylaxis has reduced the risk of venous thromboembolism, and there is increasing awareness of the benefit of high-intensity rehabilitation. This article highlights some of the interesting and thought-provoking developments of the last 3 years, and is based on a plenary lecture given at the 2012 Peripheral Nerve Society (PNS) meeting.

Antibodies to heteromeric glycolipid complexes in Guillain-Barré syndrome

Autoantibodies are infrequently detected in the sera of patients with the demyelinating form of Guillain-Barré syndrome most commonly encountered in the Western world, despite abundant circumstantial evidence suggesting their existence. We hypothesised that antibody specificities reliant on the cis interactions of neighbouring membrane glycolipids could explain this discrepancy, and would not have been detected by traditional serological assays using highly purified preparations of single gangliosides. To assess the frequency of glycolipid complex antibodies in a Western European cohort of patients GBS we used a newly developed combinatorial glycoarray methodology to screen against large range of antigens (11 gangliosides, 8 other single glycolipids and 162 heterodimeric glycolipid complexes). Serum samples of 181 patients from a geographically defined, Western European cohort of GBS cases were analysed, along with 161 control sera. Serum IgG binding to single gangliosides was observed in 80.0% of axonal GBS cases, but in only 11.8% of cases with demyelinating electrophysiology. The inclusion of glycolipid complexes increased the positivity rate in demyelinating disease to 62.4%. There were 40 antigens with statistically significantly increased binding intensities in GBS as compared to healthy control sera. Of these, 7 complex antigens and 1 single ganglioside also produced statistically significantly increased binding intensities in GBS versus neurological disease controls. The detection of antibodies against specific complexes was associated with particular clinical features including disease severity, requirement for mechanical ventilation, and axonal electrophysiology. This study demonstrates that while antibodies against single gangliosides are often found in cases with axonal-type electrophysiology, antibodies against glycolipid complexes predominate in cases with demyelinating electrophysiology, providing a more robust serum biomarker than has ever been previously available for such cases. This work confirms the activation of the humoral immune system in the dysimmune disease process in GBS, and correlates patterns of antigen recognition with different clinical features.

Autoantibodies in immune-mediated neuropathies

PURPOSE OF REVIEW

Over the past 25 years, many autoantibodies directed against peripheral nerve glycan and protein antigens have been described. Principally through this area of research, significant advances have been achieved in the understanding of the pathophysiology of inflammatory neuropathies. More evidence constantly continues to emerge supporting the role of antibodies in pathogenesis. This review reports the recent studies highlighting the complex association between autoantibodies directed against various peripheral nerve antigens and immune polyneuropathies.

RECENT FINDINGS

The discovery of serum antibodies directed against ganglioside and glycolipid complexes has generated huge interest in this area of research. The expectation that nodal proteins are important targets continues to be pursued in line with the improvements in detection methodology. Basic studies continue to support a direct role for autoantibodies in neuropathy pathogenesis.

SUMMARY

Discovery of new target epitopes has not only raised hopes for further improvement in our understanding of pathophysiology and availability of new diagnostic markers, but also for future targeted therapies. Further studies are required to elucidate the precise pathological and clinical significance of these new antibodies.