Abstract
Background and Objectives Autoantibodies against α3-subunit–containing nicotinic acetylcholine receptors (α3-nAChRs), usually measured by radioimmunoprecipitation assay (RIPA), are detected in patients with autoimmune autonomic ganglionopathy (AAG). However, low α3-nAChR antibody levels are frequently detected in other neurologic diseases with questionable significance. Our objective was to develop a method for the selective detection of the potentially pathogenic α3-nAChR antibodies, seemingly present only in patients with AAG.
Methods The study involved sera from 55 patients from Greece, suspected for autonomic failure, and 13 patients from Italy diagnosed with autonomic failure, positive for α3-nAChR antibodies by RIPA. In addition, sera from 52 patients with Ca2+ channel or Hu antibodies and from 2,628 controls with various neuroimmune diseases were included. A sensitive live cell-based assay (CBA) with α3-nAChR–transfected cells was developed to detect antibodies against the cell-exposed α3-nAChR domain.
Results Twenty-five patients were found α3-nAChR antibody positive by RIPA. Fifteen of 25 patients were also CBA positive. Of interest, all 15 CBA-positive patients had AAG, whereas all 10 CBA-negative patients had other neurologic diseases. RIPA antibody levels of the CBA-negative sera were low, although our CBA could detect dilutions of AAG sera corresponding to equally low RIPA antibody levels. No serum bound to control-transfected cells, and none of the 2,628 controls was α3-CBA positive.
Discussion This study showed that in contrast to the established RIPA for α3-nAChR antibodies, which at low levels is of moderate disease specificity, our CBA seems AAG specific, while at least equally sensitive with the RIPA. This study provides Class II evidence that α3-nAChR CBA is a specific assay for AAG.
Classification of Evidence This study provides Class II evidence that an α3-nAChR cell-based assay is a more specific assay for AAG than the standard RIPA.
Glossary
- AAG=
- autoimmune autonomic ganglionopathy;
- AQP4=
- aquaporin-4;
- CBA=
- cell-based assay;
- DMEM=
- Dulbecco's modified Eagle's medium;
- HEPES=
- 0.46% w/v N-(2-hydroxyethyl) piperazine-N’-(2-ethanesulfonic acid);
- LIPS=
- luciferase immunoprecipitation system;
- mAb=
- monoclonal antibody;
- nAChR=
- nicotinic acetylcholine receptor;
- POTS=
- postural orthostatic tachycardia syndrome;
- RIPA=
- radioimmunoprecipitation assay;
- RT=
- room temperature;
- VGCC=
- voltage-gated Ca++ channels P/Q-type;
- α3-nAChR=
- α3-subunit–containing nAChR
Footnotes
Go to Neurology.org/NN for full disclosures. Funding information is provided at the end of the article.
↵* These authors contributed equally to the study (co–first authors).
The Article Processing Charge was funded by the authors.
Class of Evidence: NPub.org/coe
- Received October 10, 2021.
- Accepted in final form February 10, 2022.
- Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.
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