Background: Inflammatory demyelinating polyradiculoneuropathies are rare disabling autoimmune diseases affecting the peripheral nervous system. These neuropathies can be acute, when signs and symptoms raise in less than 1 month (Guillain-Barr syndrome, GBS), or chronic, when deteriorations continue over more than 2 months from onset (CIDP). About half of GBS patients present with IgG1 or IgG3 anti-gangliosides antibodies. Gangliosides are glycolipidic structures mainly localized at the node and paranode areas. In CIDP patients, IgG4 auto-antibodies directed against nodal (Nfasc-186) or paranodal (Nfasc-155, CNTN1, Caspr-1) proteins are found in 5 to 10 %. In most GBS and CIDP patients, the antigenic target are unknown and clinical biomarkers are critically lacking to help diagnosis and treatment orientation. The aim of the present study is to identify new biomarkers in AIDP and CIDP patients.

Methods : The investigators conduct a national retrospective and prospective study to identify new antigenic targets in GBS and CIDP patients. Since 2015, the Institute for Neurosciences of Montpellier and the University Hospitals of Montpellier collect clinical, immulogical, electrophysiological, and histological data of GBS and CIDP patients. Each patient whose serum has already been collected gave written informed consent. GBS and CIDP are diagnosed according to the current criteria. Anti-gangliosides antibodies (by immunodot-blot) and anti-Nfasc155, -CNTN1, -Nfasc186, and -Caspr-1 antibodies (by ELISA and cell-binding assay) are assessed in GBS and CIDP patients, respectively. Among CIDP patients with monoclonal gammapathy, those presenting with anti-MAG antibodies, increasing VEGF, AL amyloidosis, and neurolymphomatosis are excluded. Patients' serum are also tested by immunohistochemical staining on wild-type and GalNacT -/- mouse sciatic nerve fibres.

Clinical and electrophysiological phenotypes are compared between patients with positive and negative immunostaining. Localization of the staining (i.e. node of Ranvier, paranodal region, and/or myelin sheath) as the subclass and isotype of the autoantibody are specified.

The search for a new antigenic target is performed in GBS and CIDP patients which are i) seronegatives for antiganglioside and anti-Nfasc155, -CNTN1, -Nfasc186, and -Caspr-1 antibodies, and presenting with ii) a postive immunostaining on wild-type and GalNacT-/- mouse sciatic nerve fibres. Then, serums of these selected patients are incubated with neuronal and glial cells in culture (spinal dorsal ganglia, motoneurons, Schwann cells, oligodendrocytes and neocortical neurons). In the case of positivity against cell culture, an immunoprecipitation is performed and the antigen/antibody complex is separated on SDS-PAGE 4-12% gel and electrophoretic bands are analyzed by mass spectrometry.

The aim of this study is to identify new antigenic targets in seronegative GBS and CIDP patients displaying immunoreactivity. The knowledge of these new targets may improve our diagnostic tools and could help to develop targeted therapies.