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

Area of Science:

• Neurology
• Immunology
• Biochemistry

Background:

• Myasthenia gravis (MG) is an autoimmune disorder.
• Detection of anti-MuSK antibodies (MuSK-Abs) is crucial for diagnosing certain MG subtypes.
• Existing detection methods may lack optimal sensitivity or specificity.

Purpose of the Study:

• To enhance the detection of MuSK-Abs using a cell-binding assay (CBA).
• To evaluate the pathogenicity of detected MuSK-Abs.
• To assess the diagnostic utility of an IgG-specific MuSK-CBA.

Main Methods:

• Sera from definite MuSK-MG, seronegative MG (SNMG), healthy controls (HCs), and NMDAR-Ab disease controls were tested.
• A cell-binding assay (CBA) was employed using different secondary antibodies for MuSK-Ab detection.
• Pathogenicity was assessed via an in vitro acetylcholine receptor (AChR) clustering assay.

Main Results:

• An IgG-specific secondary antibody significantly improved MuSK-Ab detection by CBA, achieving 99% sensitivity in definite MuSK-MG patients with high specificity.
• The assay correctly identified MuSK-Abs in 99% of definite MuSK-MG patients, 0% of HCs, and 0% of NMDAR-Ab controls, with 8% in SNMG.
• MuSK-IgG positive sera from CBA demonstrated pathogenic potential in vitro, reducing AChR clustering.

Conclusions:

• An IgG-specific MuSK-CBA offers a sensitive and specific method for detecting IgG MuSK-Abs in myasthenia gravis.
• IgG specificity is critical for accurate MuSK-Ab detection in CBA.
• The identified antibodies possess pathogenic activity, contributing to MG, though potentially associated with less severe clinical disease.