Characterization of pathogenic monoclonal autoantibodies derived from muscle-specific kinase myasthenia gravis patients

Kazushiro Takata, Panos Stathopoulos, Michelangelo Cao, Marina Mane-Damas, Miriam L. Fichtner, Erik S. Benotti, Leslie Jacobson, Patrick Waters, Sarosh R. Irani, Pilar Martinez-Martinez, David Beeson, Mario Losen, Angela Vincent, Richard J. Nowak, Kevin C. O'Connor*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

25 Citations (Web of Science)

Abstract

Myasthenia gravis (MG) is a chronic autoimmune disorder characterized by muscle weakness and caused by pathogenic autoantibodies that bind to membrane proteins at the neuromuscular junction. Most patients have autoantibodies against the acetylcholine receptor (AChR), but a subset of patients have autoantibodies against muscle-specific tyrosine kinase (MuSK) instead. MuSK is an essential component of the pathway responsible for synaptic differentiation, which is activated by nerve-released agrin. Through binding MuSK, serum-derived autoantibodies inhibit agrin-induced MuSK autophosphorylation, impair clustering of AChRs, and block neuromuscular transmission. We sought to establish individual MuSK autoantibody clones so that the autoimmune mechanisms could be better understood. We isolated MuSK autoantibody-expressing B cells from 6 MuSK MG patients using a fluorescently tagged MuSK antigen multimer, then generated a panel of human monoclonal autoantibodies (mAbs) from these cells. Here we focused on 3 highly specific mAbs that bound quantitatively to MuSK in solution, to MuSK-expressing HEK cells, and at mouse neuromuscular junctions, where they colocalized with AChRs. These 3 IgG isotype mAbs (2 IgG4 and 1 IgG3 subclass) recognized the Ig-like domain 2 of MuSK. The mAbs inhibited AChR clustering, but intriguingly, they enhanced rather than inhibited MuSK phosphorylation, which suggests an alternative mechanism for inhibiting AChR clustering.

Original languageEnglish
Article number127167
Number of pages16
JournalJCI INSIGHT
Volume4
Issue number12
DOIs
Publication statusPublished - 20 Jun 2019

Keywords

  • B-CELLS
  • ACETYLCHOLINE-RECEPTORS
  • IGG4 AUTOANTIBODIES
  • CRYSTAL-STRUCTURE
  • ANTIGEN PRESENTATION
  • IMMUNOGLOBULIN G4
  • PASSIVE TRANSFER
  • MUSK ANTIBODIES
  • PLASMA-CELLS
  • PROTEIN 4

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