Patterns of reactivity of human anti-GM1 antibodies with spinal cord and motor neurons.

Human anti-GM1 antibodies from patients with lower motor neuron disease or predominantly motor neuropathy recognize carbohydrate determinants shared by GM1 and related glycolipids and glycoproteins, but the identity of the antigens to which they bind in tissue is unknown. We examined the binding of anti-GM1 antibodies with differing fine specificities to spinal cord, isolated motor neurons, and dorsal root ganglia neurons in order to characterize the tissue antigens. All anti-GM1 antibodies tested bound to the surface of bovine spinal motor neurons and immunostained the gray matter of unfixed sections of spinal cord. The staining was blocked by cholera toxin, which is specific for GM1, indicating that GM1 itself was the target antigen. Binding to white matter was more variable and depended on fixation and the fine specificities of the antibodies. The anti-GM1 antibodies did not bind to dorsal root ganglia neurons in tissue sections or in culture. These studies suggest that the autoantibodies might exert their effect, in part, by binding to GM1 on the surface of motor neurons, and that the absence of binding to dorsal root ganglia neurons might explain the lack of sensory abnormalities in affected patients.