CHARACTERIZATION OF A 58-KD AND A 78-KD MONOCYTIC MEMBRANE-PROTEIN WITH AFFINITY TO THE ACETYLCHOLINE-RECEPTOR IN MYASTHENIA-GRAVIS PATIENTS

The autoimmune disease myasthenia gravis (MG), caused by the effect of specific antibodies, directed towards the nicotinic acetylcholine rec eptor, is triggered by autoantigen-specific T cells. In order to inves tigate cellular parts of the immune response in MG, the authors invest igated the binding of the nicotinic acetylcholine receptor (AChR) to p eripheral blood mononuclear cells (PBMC) from MG patients. AChR bindin g cells were identified by resetting experiments using AChR-coated flu oresceine beads. Applying this technique, a significant percentage of PBMC (21.2 +/- 7.65%) from MG patients formed rosettes with AChR-coate d beads. Membrane preparations of nycodenz- or percoll-separated monoc ytes from MG patients or T-cell depleted monocytic subpopulations were applied to SDS-PAGE under reducing conditions. Ligand-blotting studie s with biotinylated AChRs revealed two cell-membrane proteins with mol ecular weights of 58- and 78-kD. In parallel the same results were obt ained by affinity chromatography of monocytic membrane proteins using AChR-sepharose. A possible interference of anti-AChR IgG was excluded. The 58- and the 78-kD proteins are detectable under reducing conditio ns by ligand blotting with AChR-biotin, while under non-reducing condi tions only the 58-kD protein can be detected. Furthermore, in experime nts using Endoglycosidase-H, the 58-kD protein appears to be non-glyco sylated, while the 78-kD protein bears carbohydrates. These findings s uggest that monocytes which bind the AChR via specific membrane protei ns on their surface might act as antigen-presenting cells and may lead to an induction of the T-cell response, in the early phase of the dis ease.