Autoantibodies to thyroid peroxidase in patients with chronic thyroiditis: effect of antibody binding on enzyme activities.

Using thyroid peroxidase (TPO), which was purified from the thyroid of patients with Graves' disease, we attempted to determine whether sera from patients with chronic thyroiditis contained antibodies to the enzyme. When the binding was tested by ELISA, sera from patients with chronic thyroiditis revealed high binding activities to TPO. When TPO was incubated with IgG from sera followed by treatment with protein A-Sepharose and centrifugation, the remaining TPO activities in the supernatant fraction were lower in most of the patients, as compared to normal controls. Moreover, IgG purified by DEAE-cellulose chromatography from sera in patients interfered with the TPO activities. Titres of anti-TPO antibodies correlated well with those of anti-microsome antibodies. These results indicate the presence of autoantibodies to TPO in sera of most patients with chronic thyroiditis and that TPO may be one component of microsome antigen complexes recognized by the autoantibodies. Studies on the inhibition of TPO by IgG isolated from sera of patients using guaiacol and iodide assays revealed that at least three epitopes of TPO molecule were recognized by autoantibodies and that the antigenic determinants on TPO molecule recognized by autoantibodies could be heterogeneous in patients.