Human monoclonal IgM anti-Gal(beta 1-3)GalNAc autoantibodies bind to the surface of bovine spinal motoneurons.

An IgM monoclonal autoantibody (M-protein) with anti-Gal(beta 1-3)GalNAc activity from a patient with lower motor neuron disease bound to the surface of motoneurons isolated from bovine spinal cord. The Gal(beta 1-3)GalNAc epitope is shared by the gangliosides GM1 and GD1b and by several glycoproteins in the nervous system, and binding was abolished by preabsorbing the patient's serum with GM1. Antibodies specific for GM1, however, which do not bind to GaL(beta 1-3)GalNAc, did not bind to the motoneurons. This suggests that Gal(beta 1-3)GalNAc bearing glycoproteins or glycolipids other than GM1 are expressed on the surface of motoneurons, while GM1 may be absent or shielded, and that antibody binding to the cell surface might contribute to the development of the motor neuron disease.