Pattern of reactivity of IgM from the sera of eight patients with IgM monoclonal gammopathy and neuropathy with components of neural tissues: evidence for interaction with more than one epitope.

It has been postulated that binding of monoclonal IgM from the sera of some patients with IgM monoclonal gammopathy and neuropathy to components of peripheral nerve may play a key role in the pathogenesis of the neuropathy. Serum IgM from these patients has been shown to bind to antigenic determinants shared by the myelin-associated glycoprotein (MAG) and a polar glycolipid from peripheral nerve. Here we describe a study of sera from eight patients with IgM monoclonal gammopathy and neuropathy. Five of the patients had serum IgM directed both against MAG and one or two polar glycolipids from peripheral nerve. One of the patients had serum IgM that bound to a peripheral nerve glycolipid but not to MAG; no one had serum IgM that bound to MAG but not to a peripheral nerve glycolipid. The relative affinity of IgM from the sera of the patients for proteins in peripheral nerves of chickens, dogs, and humans varied from patient to patient. These data indicate that the epitope against which the serum IgM from these patients is directed is not necessarily the same in all of the cases.