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Title: Investigating the pathogenic effects of antibodies against the VGKC-complex and N-methyl-D-aspartate receptor in CNS disorders
Author: Pettingill, Philippa May
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2013
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Over the last few years, antibody-mediated disorders of the central nervous system (CNS) have been a rapidly expanding field in neurology. The antibodies bind to extracellular domains of proteins expressed in the CNS and impair neuronal function. Patients with limbic encephalitis, Morvan’s syndrome have antibodies that bind to the voltage gated potassium channel (VGKC)-complex proteins, LGI1 and CASPR2, while patients with antibodies to the NMDAR have more complex encephalopathies. Clinical evidence suggests that these antibodies are pathogenic as immunotherapy reduces antibody levels, which correlate closely with clinical improvement. Antibodies can be detected in patient sera using human embryonic kidney (HEK) cells transfected with CASPR2, LGI1 and NMDAR subunits, or by binding to rodent brain sections and primary neuronal cultures. In vitro NMDAR-antibodies have been shown to cross-link synaptic NMDARs and cause their subsequent internalisation from the cell membrane. It is not known if passive transfer of NMDAR-antibodies can recapitulate features of disease or if these pathogenic mechanisms occur with VGKC-complex antibodies. The characteristics of LGI1 and CASPR2 antibodies were explored in vitro. IgG1 and IgG4 were identified as the predominant antibody subclasses, with all CASPR2 sera containing IgG1 antibodies and all LGI1 sera containing IgG4. On transfected cells both LGI1 and CASPR2 antibodies activated the classical pathway of the complement cascade. Furthermore CASPR2 antibody binding to transfected HEK cells showed a reduction in intensity over time which was most likely a result of internalisation of the CASPR2-antibody bound complex. Both CASPR2 and LGI1 antibodies bound strongly to the surface of live hippocampal neurons in culture, and this staining was reduced 24 hours after the removal of IgG, corresponding to a loss of antigen expressed at the cell surface. Patients with NMDAR-encephalitis present with a psychotic disturbance, memory loss and seizures, usually progressing to a reduced level of consciousness and a marked movement disorder. A single injection of IgG, purified from patients with NMDAR-encephalitis was administered into the lateral ventricle of mice. Animals were observed for 40 days and showed significant behavioural changes, including a deficit in spontaneous alternation, dyskinetic hind-limb clasping and visual signs of spontaneous seizures, which are reminiscent to features of the disease. Behavioural changes were not observed in animals injected with IgG from healthy individuals. These behavioural alterations appeared to be reversible and were no longer present at day 40, which was supported by protein analysis showing equivalent levels of the NMDAR expressed in the hippocampus in animals receiving patient and control IgG. In summary, these findings provide further evidence that supports a direct role of autoantibodies in NMDAR-encephalitis, limbic encephalitis and Morvan’s syndrome.
Supervisor: Vincent, Angela Sponsor: Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Immunology ; Neurology