Reactivity with the peripheral myelin glycoprotein P_o in serum from patients with monoclonal IgM gammopathy and polyneuropathy

The major glycoprotein P_o from human and bovine peripheral nerves carries the L2/HNK-1 and L3 carbohydrate epitopes and is recognized by serum from patients with IgM gammopathy and polyneuropathy. Only serum from patients with reactivity toward the myelin-associated glycoprotein (MAG) was reactive with P_o, while serum that did not react with MAG also did not recognize P_o Furthermore, the neural adhesion molecules L1, N-CAM, and J1 were also recognized by the serum that reacted with MAG, while the L3 carbohydrate-carrying cell adhesion molecule AMOG was not recognized. These observations indicate a restricted specificity in carbohydrate reactivity of IgM paraproteins and implicate yet another and, for the first time, peripheral myelin-specific glycoprotein in the pathogenesis of demyelinating neuropathy.