Anti-GM2 gangliosides IgM paraprotein induces neuromuscular block without neuromuscular damage

We analyzed the effect on the mouse neuromuscular synapses of a human monoclonal IgM, which binds specifically to gangliosides with the common epitope [GalNAcβ1-4Gal(3-2αNeuAc)β1-]. We focused on the role of the complement. Evoked neurotransmission was partially blocked by IgM both acutely (1 h) and chronically (10 days). Transmission electron microscopy shows important nerve terminal growth and retraction remodelling though axonal injury can be ruled out. Synapses did not show mouse C5b-9 immunofluorescence and were only immunolabelled when human complement was added. Therefore, the IgM-induced synaptic changes occur without complement-mediated membrane attack.