Extracellular domains of the β γ and ε subunits of the human acetylcholine receptor as immunoadsorbents for myasthenic autoantibodies:: A combination of immunoadsorbents results in increased efficiency

Myasthenia gravis (MG) is usually caused by autoantibodies against the human muscle acetylcholine receptor (AChR). Plasmapheresis offers a therapeutic option, but, as well as removing the pathogenic anti-AChR autoantibodies, it non-specifically removes indispensable immunoglobulins. An attractive alternative to plasmapheresis would be the extracorporeal specific removal of the autoantibodics using AChR-based immunoadsorbents. Previously, we used the N-terminal extracellular domain (ECD) of the AChR alpha subunit to immunoadsorb anti-a subunit autoantibodies from MG sera. In this study, we immobilised the beta-,gamma-and epsilon-AChR ECDs on Sepharose and tested them as immunoadsorbents on 50 MG sera. A given ECD removed a different percentage of autoantibodies from different sera and different ECDs removed different percentages from the same serum;, on average. the beta-, gamma- and epsilon-ECDs removed 22%, 20% and 15.5% of the autoantibodies, respectively. Immunoadsorption was completed in 3 min, 1 mu g of ECD removed similar to 2 pmol of autoantibodies, and the immunoadsorbent could be recycled similar to 4 times. The combined use of two (alpha + gamma) or four (alpha+beta+gamma+epsilon) ECDs in a single immunoadsorbent resulted in much higher (often additive) immunoadsorption. These results show that MG sera have autoantibodies against several AChR subunits, and suggest that the combined use of all AChR ECDs could provide the basis for a novel, antigen-specific therapy for MG. (C) 2007 Elsevier B.V. All rights reserved.