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.