Myasthenia gravis (MG) is a disease caused by pathogenic
autoantibodies against the neuromuscular junction and is characterized by
muscle weakness. Most MG patients produce
antibodies against the
acetylcholine receptor (AChR), but a subset of patients have been found to produce
autoantibodies against other components of the neuromuscular junction such as muscle specific
tyrosine kinase (
MuSK) and
low-density lipoprotein receptor-related
protein 4 (LRP4). The pathogenicity of these
autoantibodies has been studied using polyclonal
IgG or serum from MG patients; however, pathogenic B cells and
monoclonal antibodies from these patients have rarely been investigated because of the difficulty in isolating them. Recently, isolation of pathogenic B cells from
MuSK-MG patients and the subsequent generation of monoclonal pathogenic
antibodies from these cells, was reported. These data revealed the existence of pathogenic
IgG3 and
IgG4 antibodies and identified a pathogenic mechanism alternative to the inhibition of
MuSK phosphorylation. This review discusses research concerning pathogenic B cells in MG patients and
rituximab therapy specifically depleting B cells. Accumulating studies show
rituximab therapy is more effective in
MuSK-MG patients than in AChR-MG patients. Advances in molecular biology may lead to greater understanding of pathogenic B cells in MG patients and thus potentially lead to the development of novel
therapies for MG.