Specificities of antibodies to acetylcholine receptors in sera from myasthenia gravis patients measured by monoclonal antibodies.

Abstract

The pattern of antibody specificities in sera from patients with myasthenia gravis (MG) was determined by the ability of monoclonal antibodies against defined determinants on the acetylcholine receptor molecule to inhibit binding of the serum antibodies to receptor from human muscle. We found that MG patients produce fundamentally the same pattern of specificities as that produced by animals immunized with receptor purified from fish electric organs or mammalian muscle. Most of the antibodies are directed at the "main immunogenic region" which is located on the extracellular surface of the a subunit and is distinct from the acetylcholine binding site. Regions on the P and y subunits near the main immunogenic region are also significantly immunogenic. In one patient the proportions of antibodies to various regions are constant over time despite changes in total antibody amount and clinical state. Between patients there is no obvious correlation between antibody specificities and clinical state. These data suggest that the autoimmune response in MG is stimulated by human receptor rather than a crossreacting (e.g., viral) antigen and that in both MG and experimental autoimmune MG the pattern of specificities produced is determined by the inherently immunogenic structural features ofthe receptor molecule. They also suggest that the wide differences in clinical state sometimes observed between patients with the same total concentration of antireceptor antibody are due primarily to differences in endogenous factors which affect the safety factor for neuromuscular transmission rather than to the presence of especially pathogenic antireceptor specificities.

The human medulloblastoma cell line TE671 expresses a muscle‐like acetylcholine receptor Cloning of the α‐subunit cDNA

“…The proteins in bacteria have been used to map the aBgt-binding site [36,37] and epitopes recognized by T cells in experimental autoimmune MG (EAMG) and MG (Melmes, A. et al, personal communication). Blount and Merlie [40] showed that the BC3Hl a-subunit expressed in quail fibroblast acquires the main immunogenic region (MIR), a highly conformation-dependent epitope against which the majority of antibodies in EAMG and MG are directed [41].…”

“…a-subunits are very important in the autoimmune response to AChR which occurs in MG because denatured u-subunit epitopes predominate in T lymphocyte recognition of AChRs [42,43], and because conformation-dependent a-subunit epitopes predominate in B lymphocyte recognition of AChRs ( [41] and review [44]). Although electric organ provides large amounts of AChR for studies of EAMG, human AChR for studies of speciesspecific autoimmune responses in MG has been available in only negligible amounts from extracts of amputated leg muscle.…”

Determination of amino acids critical to the main immunogenic region of intact acetylcholine receptors by in vitro mutagenesis

“…3, mutations in ~~68, a71 or (r68+71 eliminated the binding of MIR-specific mAbs raised against AChRs from human (mAb 198), rodent (mAb 210), Torpedo (mAb 6), and Electrophor~s (mAbs 22 and 47). mAb 35 is frequently used as the archetypic MIR mAb [5,7]. mAb 35 does not bind to synthetic peptides [12,14].…”

Isolation of potent human Fab fragments against a novel highly immunogenic region on human muscle acetylcholine receptor which protect the receptor from myasthenic autoantibodies

“…sh6.4 and the anti-MIR mAb 192 exhibited rather comparable inhibition of MG autoantibody binding to hAChR (33% and 40%, respectively), although the result for the latter was lower than the 50%-60% seen using other anti-MIR mAb [4,16]. sh6.4 and mAb 192 appeared to block the binding of overlapping populations of autoantibodies in the case of two sera, no 10119 and 9727, but it seems unlikely that this was the case for the other sera since the majority of them were inhibited by only one of the two competitors.…”

“…The Nterminal extracellular domains of the hAChR a-, b-, c-, and e-subunits were expressed in Pichia pastoris ( [10], and Kostelidou et al, manuscript in preparation). The rat antiAChR mAb used in this study have been previously described [11,16,23,24].…”