Axonal neuropathy in a patient with IgM M-protein reactive with nerve endoneurium

IgM M-proteins have been found in patients with axonal neuropathies, but it is not known whether these M-proteins bind to nerve components or actually cause the neuropathy. In one patient with axonal neuropathy studied, the IgM M-protein bound to chondroitin sulfate, and there were deposits of IgM in the endoneurium of the patient's nerve. A monoclonal anti-idiotype antibody generated against that M-protein was used to study the binding of the M-protein to normal nerve and to distinguish it from binding of other IgM species that might be present in the patient's serum. In immunofluorescence studies, the M-protein bound to the endoneurium in normal nerve and to connective tissue in other organs. In immunoblot studies, the M-protein bound to several protein bands in nerve and other tissues. The data suggest that the M-protein bound to mucopolysaccharides in nerve endoneurium and connective tissue.