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 Saif Huda
A1 Patrick Waters
A1 Mark Woodhall
A1 Maria Isabel Leite
A1 Leslie Jacobson
A1 Anna De Rosa
A1 Michelangelo Maestri
A1 Roberta Ricciardi
A1 Jeannine M. Heckmann
A1 Angelina Maniaol
A1 Amelia Evoli
A1 Judy Cossins
A1 David Hilton-Jones
A1 Angela Vincent
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