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Abstract
Anti-GM2 IgM antibodies have been reported in some patients with dysimmune neuropathy
or lower motor neuron syndrome. To determine whether these antibodies can induce complement-dependent
cytolysis we performed a cytotoxicity assay on neuroblastoma cells with sera from
seven patients with demyelinating dysimmune neuropathies and high titers of anti-GM2
IgM. As controls we used sera from seven patients with other anti-neural reactivities,
six with the same neuropathies but no anti-GM2 or other anti-neural reactivity and
from eight normal subjects. Of the seven positive sera tested, six induced complement-mediated
cytotoxicity, while none of the controls had any relevant effect on neuroblastoma
cells. Preincubation of positive sera with purified GM2 removed cytotoxic activity.
Affinity purified anti-GM2 IgM had the same cytotoxic anti-GM2 effect of whole serum
while serum or complement alone did not have any effect. In four anti-GM2-positive
patients the percentage of cell lysis correlated with anti-GM2 titers and with IgM
staining of neuroblastoma cells while in two the cytotoxic effect was higher than
expected from antibody titers. Complement-mediated cell lysis induced by anti-GM2
IgM antibodies may be a possible mechanism of neural damage in patients with dysimmune
neuropathy and high titers of anti-GM2 IgM antibodies.