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Neuromuscular
Original research
Myasthenia gravis AChR antibodies inhibit function of rapsyn-clustered AChRs
  1. Hakan Cetin1,2,
  2. Richard Webster1,
  3. Wei Wei Liu1,
  4. Akiko Nagaishi1,
  5. Inga Koneczny3,
  6. Fritz Zimprich2,
  7. Susan Maxwell1,
  8. Judith Cossins1,
  9. David Beeson1,
  10. Angela Vincent1
  1. 1 Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, Oxfordshire, UK
  2. 2 Department of Neurology, Medical University of Vienna, Vienna, Austria
  3. 3 Institute of Neurology, Medical University of Vienna, Vienna, Austria
  1. Correspondence to Professor Angela Vincent, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, Oxfordshire OX1 2JD, UK; angela.vincent{at}ndcn.ox.ac.uk

Abstract

Objective Direct inhibition of acetylcholine receptor (AChR) function by autoantibodies (Abs) is considered a rare pathogenic mechanism in myasthenia gravis (MG), but is usually studied on AChRs expressed in cell lines, rather than tightly clustered by the intracellular scaffolding protein, rapsyn, as at the intact neuromuscular junction. We hypothesised that clustered AChRs would provide a better target for investigating the functional effects of AChR-Abs.

Methods Acetylcholine-induced currents were measured using whole-cell patch clamping and a fast perfusion system to assess fast (<2 min) functional effects of the serum samples. The sensitivity, specificity and rapidity of the system were first demonstrated by applying maternal AChR-Ab positive plasmas known to inhibit fetal AChR function in TE671 cells. Eleven previously untested AChR-Ab positive MG sera, 10 AChR-Ab negative MG sera and 5 healthy control sera were then applied to unclustered and rapsyn-clustered human adult AChRs in CN21 cells.

Results The maternal AChR-Ab positive plasmas reduced fetal AChR currents, but not adult AChR currents, by >80% within 100 s. Only 2/11 AChR-Ab positive sera inhibited AChR currents in unclustered AChRs, but 6/11 AChR-Ab positive sera compared with none of the 10 AChR-Ab negative sera (p=0.0020) inhibited rapsyn-clustered AChR currents, and current inhibition by the AChR-Ab positive sera was greater when the AChRs were clustered (p=0.0385). None of the sera had detectable effects on desensitisation or recovery from desensitisation.

Conclusion These results show that antibodies can inhibit AChR function rapidly and demonstrate the importance of clustering in exploring pathogenic disease mechanisms of MG Abs.

https://creativecommons.org/licenses/by/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution 4.0 Unported (CC BY 4.0) license, which permits others to copy, redistribute, remix, transform and build upon this work for any purpose, provided the original work is properly cited, a link to the licence is given, and indication of whether changes were made. See: https://creativecommons.org/licenses/by/4.0/.

https://doi.org/10.1136/jnnp-2019-322640

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    Footnotes

    • Contributors Study conception and design: HC, RW and AV. Acquisition of data: HC, WWL, AN, JC and SM. Collection of serum samples and clinical data: IK and FZ. Analysis and interpretation of data: HC, RW, DB and AV. Drafting the manuscript: HC and AV.

    • Funding This study was funded by Austrian Science Fund, Erwin Schrödinger Fellowship (J3589); Medical Research Council Program Grant (MR/M006824/1); Austrian Science Fund, Hertha Firnberg Fellowship (T996-B30).

    • Competing interests None declared.

    • Patient consent for publication Not required.

    • Ethics approval The study of these sera was approved by the ethical committee of the Medical University of Vienna (EK-Nr: 1442/2017).

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data availability statement Data are available upon reasonable request. The data sets of this study are available from the corresponding author on reasonable request.