Gangliosides GM₁ and GD(1b) are antigens for IgM M-protein in a patient with motor neuron disease

We studied a patient with an IgM M-protein and lower motor neuron disease to identify the antigens to which the M-protein bound. Gangliosides from peripheral nerve and spinal cord were separated by high-performance thin-layer chromatography and immunostained with the patient's serum. The serum IgM immunostained two gangliosides identified as GM₁ and GD(1b), and immunostaining was specific for the M-protein light chain type. IgM-binding to the two gangliosides was detectable by ELISA at serum dilutions of greater than 1:10,000, and the M-protein was selectively immunoabsorbed by liposomes containing GM₁ or GD(1b). The IgM M-protein also bound to asialo-GM₁, indicating reactivity to the galactosyl(β₁-3)N-acetylgalactosaminyl moiety shared by GM₁, GD(1b), and asialo-GM₁.