The roles of anti-GM1 complex antibodies in autoimmune neuropathies

Anti-ganglioside antibodies have been implicated in autoimmune neuropathies for several decades. They are thought to elicit injury through binding to sites in the peripheral nervous system, where they activate the complement pathway to induce cell death. Patient serum is therefore regularly screened for these antibodies to aid in the diagnosis of various conditions. Recent work has found that complexes composed of gangliosides and other glycolipids can improve the detection of these antibodies beyond the signals detected to the single ganglioside species. In MMN research, complexes comprised of GM1 and GalC have been found to significantly enhance antibody detection in patient sera. In certain patients, however, antibody binding was only detected against these complexes and not the single antigens. This led some researchers to hypothesise that an unidentified class of antibody may have arisen that binds specifically to a neoepitope formed by the combination of the two glycolipids. It has also been hypothesised that that this complex may be the true target of immune mediated attack in MMN. This thesis sought to address this hypothesis by either cloning these antibodies directly from patient serum or through active immunisations with mice. Analysis of previously generated human monoclonal antibodies indicated that their behaviours were modified by complexes containing particular gangliosides or glycolipids. Furthermore, the antibodies behaviours were found to diverge, when they were screened against complexes comprised of gangliosides and different concentrations of accessory lipids. These findings suggested that the accessory lipids were interacting with the ganglioside headgroups to modify the presentation of different binding epitopes. This indicated that conformational modulation, rather than neo-epitope formation, may be responsible for complex enhancement Cloning antibodies from patient sera was unsuccessful but examination of the screening techniques suggested that the appearance of complex-dependent antibodies may have been an artefact. Attempts to induce complex-specific responses in mice were similarly unsuccessful but several anti-ganglioside and anti-sulfatide antibodies were created. The subsequent chapters focused on the characterisation of these antibodies and indicated that most of them bound well to solid-phase assays, cells and tissue and may therefore be of use in future studies. Taken together, the data from this thesis suggests that complex-dependent antibodies may not exist but are merely low concentrations of anti-ganglioside antibodies that are cis-enhanced by particular lipids. Future work should therefore focus on assessing how the ganglioside microenvironment modifies epitope presentation and how this affects the binding capabilities of antiganglioside antibodies