Oral Presentation The Australasian Society for Immunology 2017 Annual Scientific Meeting

Exploring the importance of antigen conformation in human myelin oligodendrocyte glycoprotein autoantibody binding (#119)

Fiona Tea 1 , Sudarshini Ramanathan 1 , Vera Merheb 1 , Tina K Nguyen 1 , Alicia Zou 1 , Fiona Lee 1 , Joseph A Lopez 1 , Deepti Pilli 1 , Shekeeb Mohammad 1 , Victor Fung 2 , Owen White 3 , Simon Broadley 4 , Jeannette Lechner-Scott 5 , Steve Vucic 2 , Andrew Henderson 2 , Michael Barnett 6 , Stephen Reddel 6 , Russell C Dale 1 , Fabienne Brilot 1 , MOG Study Group 7
  1. Brain Autoimmunity Group, Kids Research Institute, Children's Hospital at Westmead, University of Sydney, Westmead, NSW, Australia
  2. Neurology Department, Westmead Hospital, Westmead, NSW, 2145
  3. Ocular Motor Research Laboratory, University of Melbourne, Melbourne, VIC, Australia
  4. Department of Neurology, Gold Coast University Hospital and Griffith University, Gold coast, QLD, Australia
  5. Neurology Department, Hunter Medical Research Institute and John Hunter Hospital, Newcastle, NSW, Australia
  6. Brain and Mind Centre, University of Sydney, Sydney, NSW, Australia
  7. MOG Study Group, Australia and New Zealand, Sydney, NSW, Australia

Autoantibodies which recognise myelin oligodendrocyte glycoprotein (MOG) have been recently associated with subsets of CNS demyelinating disorders, and are now used as a powerful diagnostic tool to identify patients with Neuromyelitis Optica Spectrum Disorders (NMOSD). Extensive literature has highlighted the need of rodent MOG autoantibodies to recognize conformational MOG in animal models, however data is scarce for human autoantibodies. This is greatly significant given 30 years of controversy on MOG autoantibody relevance in human disease, and the current commercialisation of MOG autoantibody detection systems using off-the-shelf chemically-preserved MOG-expressing cells. As fixation methods chemically alter protein structure, we examined the influence of widely used fixatives, and whether human MOG autoantibody binding was sensitive to its target native conformation. Using live MOG-expressing eukaryotic cells in a flow cytometry cell-based assay, we have identified 252 MOG autoantibody-positive patients, the largest cohort worldwide. We altered the conformation of human MOG on these cells using paraformaldehyde and methanol, and assessed the binding of sera from controls (n=28 children, n=32 adults), MOG autoantibody-negative (n=28 adults, n=28 children), and MOG autoantibody-positive patients (n=28 adults, n=27 children). Only 37% (10/27) of seropositive children and 32% (9/28) of seropositive adults could bind to paraformaldehyde-fixed MOG-expressing cells, whereas 7% (2/28) of MOG autoantibody-negative children bound and all control (60/60) and MOG autoantibody-negative adult sera (28/28) did not bind. When MOG-expressing cells were fixed with methanol, all adult control patients (32/32) and MOG autoantibody-negative sera (28/28) remained negative, whereas only 14% (4/28) of MOG autoantibody-positive adult sera bound to the cells. Modifying the conformation of human MOG significantly influences MOG autoantibody binding, and can lead to higher risk of false-positive and negative patient diagnosis. We shed critical light on the binding sensitivity of human autoantibodies, hence, antigen conformation must be carefully considered in diagnostic and pathogenic assays involving human autoantibodies.