Molecular characteristics of the epitope in myelin-associated glycoprotein that is recognized by a monoclonal IgM in human neuropathy patients.

The antigen for the IgM monoclonal antibody from patients with IgM paraproteinemia and peripheral neuropathy is the myelin-associated glycoprotein (MAG), a minor protein component of both human PNS myelin and human CNS myelin. Sera from five patients were found to react with identical proteolytically derived fragments of MAG indicating that the monoclonal IgM from these patients is recognizing a common epitope. Furthermore, the lectin concanavalin A reacts with these fragments and deglycosylation of isolated MAG abolishes the recognition of MAG by the patient monoclonal IgM. Therefore, it appears that the monoclonal IgM from these five patients recognizes a common epitope which contains carbohydrate moieties. These data are consistent with the idea that the peripheral myelin sheath is involved in an autoimmune response directed against MAG.