IgG-specific cell-based assay detects potentially pathogenic MuSK-Abs in seronegative MG.

Abstract

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.

• Authors: Saif Huda, Patrick Waters, Mark Woodhall, Maria Isabel Leite, Leslie Jacobson, Anna De Rosa, Michelangelo Maestri, Roberta Ricciardi, Jeannine M Heckmann, Angelina Maniaol, Amelia Evoli, Judy Cossins, David Hilton-Jones, Angela Vincent
• Journal: Neurology(R) neuroimmunology & neuroinflammation (Neurol Neuroimmunol Neuroinflamm) Vol. 4 Issue 4 Pg. e357 (Jul 2017) ISSN: 2332-7812 [Print] United States
• PMID: 28626780 (Publication Type: Journal Article)