Experimental demyelination of nerve induced by serum of patients with neuropathy and an anti-MAG IgM M-protein.

Demyelination of feline sciatic nerve was induced by intraneural injection of serum from three patients with neuropathy and an IgM M-protein that reacted with myelin-associated glycoprotein (MAG). Demyelination exceeded that induced by serum from 18 other individuals, including six IgM M-proteins unreactive with MAG. The myelinolytic effect required active human complement and was abolished by exposure of serum to homogenate of human peripheral nerve that removed 90% of the M-protein. Immunofluorescence studies demonstrated deposition of the injected M-protein and complement on the surface of myelin sheaths, implying that the M-protein reacted with epitopes of myelin exposed to the extracellular space.