Monoclonal IgM in two patients with motor neuron disease bind to the carbohydrate antigens Gal(beta 1-3)GalNAc and Gal(beta 1-3)GlcNAc.

We investigated the epitope specificity of monoclonal antibodies (M-proteins) from two patients with motor neuron disease and IgM monoclonal gammopathy. In previous studies, both M-proteins bound to gangliosides GM1 and GD1b which share Gal(beta 1-3)GalNAc as their terminal structure, and to lacto-N-tetraose-BSA which has the structure Gal(beta 1-3)GlcNAc(beta 1-3)Gal(beta 1-4)Glc-BSA. In this study we show that the serum IgM from both patients bind to bovine serum albumin (BSA) glycoconjugates of both Gal(beta 1-3)GalNAc and Gal(beta 1-3)GlcNAc. Binding was detected at serum dilutions of up to 1:100,000, and absorption with Gal(beta 1-3)GlcNAc-BSA completely removed the IgM binding to Gal(beta 1-3)-GalNAc-BSA, indicating that the same antibodies bound to both epitopes. Low levels of antibodies to Gal(beta 1-3)GlcNAc-BSA and to Gal(beta 1-3)GlcNAc-BSA were also detected in patients with amyotrophic lateral sclerosis (ALS) and in normal subjects at serum dilutions of up to 1:500, but these did not have the same specificity as the M-proteins, as binding to Gal(beta 1-3)GalNAc-BSA was not inhibited by absorption with Gal(beta 1-3)GlcNAc-BSA.