[Measurement of anti-acetylcholine receptor antibody using human rhabdomyosarcoma cell line]

We developed a radioimmunoassay for AChR Ab using AChR solubilized from membrane extracts of human rhabdomyosarcoma cell line (RD cell). The binding affinity of this AChR to the alpha-Bungarotoxin (alpha-BTX) was similar to that of AChR from cell surface. Lyophilized AChR was stable within two months at -20 degrees C. In our assay system, sera from patients with Myasthenia Gravis (MG) showed markedly high titers and frequency (94%) of anti-AChR Ab. On the other hand, almost all sera from normal and non-myasthenic patients such as rheumatoid arthritis and thyroid disease were negative (< 0.2nmol/l). Our assay using AChR from RD cells shows sufficient results in the intra- and inter-CV values, and recovery and dilution tests. AChR Ab titers of our assay showed good correlations with those measured by AChRs from both human ischemic muscles and TE671 cells (commercial kit). The radioimmunoassay for AChR Ab using the membrane extracts of RD cells has high sensitivity, specificity and stability. Therefore, the assay is valuable as the routine assay for the diagnosis of MG.