DEVELOPMENT OF AN ASSAY FOR MODULATING ANTIACETYLCHOLINE RECEPTOR AUTOANTIBODIES USING HUMAN RHABDOMYOSARCOMA CELL-LINE

Three types of autoantibodies against the acetylcholine receptors (ACh R) of skeletal muscle are detectable in patients with myasthenia gravi s including binding, blocking, and modulating anti-AChR antibodies. Mo dulating autoantibodies correlate best with the severity of the diseas e. but are also technically most difficult to measure because the assa y generally requires fresh human muscle cells. We have developed an as say for the modulation of anti-AChR antibodies using a rhabdomyosarcom a (RD) cell line expressing AChR on the cell surface. By decreasing th e FetalClone III serum from 10% to 0.5% in Eagles Minimal Essential Me dium (EMEM) we were able to increase the number of AChR on RD cells to meet the need of sensitivity of the assay. The extent of modulation w as determined as the percent of AChR internalized in the presence or a bsence of modulating autoantibodies. Less than 6% modulation was found with the normal serum (n = 42). The CVs of both the intra- and day-to -day precision were less than 20%. When clinical samples (n = 105) wer e assayed in our laboratory and also at Nichols Institute, a correlati on coefficient of 0.816 was obtained. The selection of RD cell line, t he success of increasing the expression of the AChR on RD cells and th e use of I-125 alpha-bungarotoxin of high specific activity allowed th e establishment of an assay which can be used in routine clinical labo ratory for the measurement of modulating anti-AChR autoantibodies for the management of patients with myasthenia gravis. J. Clin. Lab. Anal. 12:315-319, 1998. (C) 1998 Wiley-Liss, Inc.