Localization of neural epitopes that bind to IgM monoclonal autoantibodies (M-proteins) from two patients with motor neuron disease.

We investigated IgM monoclonal antibodies (M-proteins) specific for the carbohydrate epitopes Gal(beta 1-3)GalNAc and Gal(beta 1-3)GlcNAc from two patients with motor neuron disease. The M-proteins from these patients immunostain central nervous system (CNS) and peripheral nervous system (PNS) tissue from human, monkey, dog and cat at greater dilutions than tissue from rabbit, guinea pig, rat and mouse, and immunostain gray matter at greater dilutions than white matter and nerve trunks. They also bind selectively to presynaptic structures at the motor endplate region, as denervation of muscle eliminates binding. Following in vivo injection of serum into the extracellular space of the spinal cord, the M-proteins appear to bind at the surface of cells and cell processes. These studies suggest that the M-proteins might act at any one of several anatomical sites in the nervous system. This information may be helpful in selecting an animal species for further investigation of the role of M-proteins in motor neuron disease.