Quantitative distribution of human thyroglobulin autoantibodies in different immunoglobulin classes.

The antigen-binding capacities of human sera containing thyroglobulin autoantibodies can be determined quantitatively by addition of excess radioactive antigen followed by co-precipitation of the complexes with an anti-immunoglobulin serum. Using a polyvalent anti-Ig serum it was shown that the antigen-binding capacity as measured by the radioactivity in the coprecipitate correlated well with the antibody content determined by precipitin curves. The distribution of antibodies among the major immunoglobulin classes could be estimated by co-precipitation with specific anti-Ig sera and the results obtained accorded with qualitative observations made by radioimmunoelectrophoresis. The specificity of the method was also checked on serum fractions obtained by preparative ultracentrifugation. In twenty-nine Hashimoto sera studied, the thyroglobulin antibodies were predominantly IgG. Sixteen of the sera contained appreciable concentrations of IgA antibodies representing up to 20% of the total antigen binding capacity; these antibodies sedimented with values intermediate between 7S and 19S. In only one serum were significant amounts of IgM antibodies detected by this method but they represented no more than 1% of the total activity. The method was shown to be valuable for following serial antibody levels in patients after operation or during thyroxine therapy.