CONFOCAL MICROSCOPIC LOCALIZATION OF ANTI-MYELIN-ASSOCIATED GLYCOPROTEIN AUTOANTIBODIES IN A PATIENT WITH PERIPHERAL NEUROPATHY INITIALLY LACKING A DETECTABLE IGM GAMMOPATHY

We report here on a patient with anti-myelin-associated glycoprotein ( MAG) neuropathy in whom examination of a sural nerve biopsy by multich annel confocal microscopy showed a partly overlapping distribution of MAG and IgM deposits in myelinated fibers. Our data demonstrate that M AG in Schmidt-Lanterman incisures and paranodal loops, as well as some additional HNK-1-positive components of the basal lamina, are the maj or targets of the anti-MAG monoclonal IgM autoantibodies in this neuro pathy in vivo. Perforation of the basal lamina can allow the penetrati on and binding of anti-MAG IgM inside myelinated fibers. Our results s upport and extend the notion that the production of monoclonal anti-MA G IgM may be antigenically driven by MAG molecules and that this proce ss may occur in the immunologically privileged environment of the nerv e prior to the appearance of a genuine gammopathy in serum.