The binding of myelin basic protein to the Fc region of aggregated IgG and to immune complexes.

Bovine myelin basic protein was found to agglutinate polystyrene particles coated with human polyclonal IgG, monoclonal IgG1, or IgG Fc fragments, but not those coated with IgG F(ab')2 fragments, IgA, or IgM. The agglutination of Fc-coated particles was inhibited by heat-aggregated polyclonal IgG or monoclonal IgG2, IgG3 and IgG4, but not by native IgG. Reduction and alkylation of aggregated IgG did not affect their inhibitory activities. Soluble immune complexes displayed the highest inhibitory activity at a two-fold antigen excess. The interaction between myelin basic protein and aggregated IgG was confirmed by gel exclusion experiments on Sephadex G-200. The possible consequence of these findings could be significant in the interpretation of IgG deposits in brain plaques of multiple sclerosis patients and of the results of immunohistochemical studies, titration of anti-myelin basic protein antibodies and immunoassay of myelin basic protein.