RT Journal Article SR Electronic T1 IgG-specific cell-based assay detects potentially pathogenic MuSK-Abs in seronegative MG JF Neurology - Neuroimmunology Neuroinflammation JO Neurol Neuroimmunol Neuroinflamm FD Lippincott Williams & Wilkins SP e357 DO 10.1212/NXI.0000000000000357 VO 4 IS 4 A1 Huda, Saif A1 Waters, Patrick A1 Woodhall, Mark A1 Leite, Maria Isabel A1 Jacobson, Leslie A1 De Rosa, Anna A1 Maestri, Michelangelo A1 Ricciardi, Roberta A1 Heckmann, Jeannine M. A1 Maniaol, Angelina A1 Evoli, Amelia A1 Cossins, Judy A1 Hilton-Jones, David A1 Vincent, Angela YR 2017 UL http://nn.neurology.org/content/4/4/e357.abstract AB Objective: To increase the detection of MuSK-Abs using a CBA and test their pathogenicity.Methods: Sera from 69 MuSK-RIA–positive patients with myasthenia gravis (MG) (Definite MuSK-MG), 169 patients negative for MuSK-RIA and AChR-RIA (seronegative MG, SNMG), 35 healthy individuals (healthy controls, HCs), and 16 NMDA receptor-Ab–positive (NMDAR-Ab) disease controls were tested for binding to MuSK on a CBA using different secondary antibodies.Results: Initially, in addition to 18% of SNMG sera, 11% of HC and 19% of NMDAR-Ab sera showed positive binding to MuSK-transfected cells; this low specificity was due to anti-IgG(H+L) detection of IgM bound nonspecifically to MuSK. Using an IgG Fc gamma-specific secondary antibody, MuSK-Abs were detected by CBA in 68/69 (99%) of Definite MuSK-MG, 0/35 HCs, 0/16 NMDAR-Ab, and 14/169 (8%) of SNMG sera, providing increased sensitivity with high specificity. The RIA-negative, CBA-positive MuSK-IgG sera, but not IgM-MuSK–binding sera, reduced agrin-induced AChR clustering in C2C12 myotubes, qualitatively similar to RIA-positive MuSK-Abs.Conclusions: An IgG-specific MuSK-CBA can reliably detect IgG MuSK-Abs and increase sensitivity. In the MuSK-CBA, IgG specificity is essential. The positive sera demonstrated pathogenic potential in the in vitro AChR-clustering assay, although less effective than Definite MuSK-MG sera, and the patients had less severe clinical disease. Use of IgG-specific secondary antibodies may improve the results of other antibody tests.Classification of evidence: This study provides Class III evidence that an IgG-specific MuSK-CBA identifies patients with MG.AChEI=acetylcholinesterase inhibitor; CBA=cell-based assay; CI=confidence interval; DMEM=Dulbecco Modified Eagle Medium; FCS=fetal calf serum; HC=healthy control; HEK=human embryonic kidney; MG=myasthenia gravis; MGFA=Myasthenia Gravis Foundation of America; PSA=Penicillin, Streptomycin, and Amphotericin; RT=room temperature; SNMG=seronegative MG