ANTI-MAG ANTIBODIES - MAJOR EFFECTS OF ANTIGEN PURITY AND ANTIBODY CROSS-REACTIVITY ON ELISA RESULTS AND CLINICAL CORRELATION

There is controversy regarding the relationship of polyneuropathy synd romes to the presence of serum antibody binding to myelin-associated g lycoprotein (MAG), Using standard ELISA methodology, we identified 74 sera that appeared to have high titers of IgM binding to MAG and found that only 34% of these sera stained MAG using Western blot methodolog y. Follow-up studies showed that two factors greatly influence concord ance between ELISA and Western blot testing for anti-MAG antibodies. S era with high titers of binding to both MAG and histone H3 identified by ELISA rarely stain MAG on Western blot. In addition, sera analyzed by ELISA often bind to impurities in the semipure MAG that is frequent ly used in ELISA assays. Further purifications to separate MAG from ot her contaminants improved concordance between ELISA and Western blot r esults to 85% to 90% in a retrospective analysis, as well as in a pros pective study of 49 additional sera. Patients with a polyneuropathy an d serum IgM binding to MAG preparations by ELISA but not by Western bl ot methodology had several different clinical syndromes, including gai t disorders and asymmetric motor neuropathies. Patients with IgM bindi ng to MAG by both assay methods usually had a distal, sensory-motor, s ymmetric polyneuropathy with some features of demyelination on electro diagnostic testing.