Intravenous gamma-globulin inhibits binding of anti-GM1 to its target antigen.

In this study, we preincubated the sera of 3 patients with neuropathies associated with elevated titers of IgM anti-GM1 antibodies, with increasing concentrations of intravenous Ig (IVIg) and assayed the inhibitory effect of this mixture on antibody binding to immobilized GM1 by an enzyme-linked immunosorbent assay. Pharmacologic concentrations of IVIg, ranging from 0.1 microgram/ml to 100 mg/ml, inhibited anti-GM1 binding to its target antigen from 26 +/- 3 to 71 +/- 7%, respectively, in a dose-dependent manner. A similar inhibition of binding was also observed with IVIg F(ab')2 fragments. These findings provide a possible mechanism for the clinical efficacy of IVIg in motor neuropathies.