Structural and functional properties of γ-globulins from a goiter with a fibrous variant of Hashimoto’s thyroiditis have been investigated in the present study. γ-Globulin concentration in the thyroid extract was found to be 8 mg/g, 10 times higher than in normal thyroid. Most were of the IgG class, whereas no IgM was detectable. Zonal electrophoresis showed that γ-globulin had a cathodic rather than anodic mobility as found in normal human γ-globulin. By isoelectrofocusing, it was shown that thyroid γ-globulin focused with a more basic pH and within a narrower range than human γ-globulin. Functional properties revealed that thyroid γ-globulins are composed mainly (50%) of antithyroglobulin antibodies of the IgG class. These antibodies precipitate in agar and in test tubes with human purified thyroglobulin giving a ‘horse-type’ profile of the precipitin curve. The molar ratio of antibodies to thyroglobulin was found to be 8. Antibodies isolated from the serum of the same patient showed similar properties. Studies on allotypes of γ-globulin showed that there are fewer genetic markers in thyroid and serum immunoglobulin than in patient’s serum γ-globulin. Part of the thyroid antibodies were bound to the 1 × 103, 3 × 104 and 1 × 105 g mins sediment. They were not eluted by acid pH but only by digesting the pellet with papain. In conclusion, in the thyroid of the fibrous variant of Hashimoto’s thyroiditis, there is a class of soluble and particulate thyroid antibodies produced in situ or concentrated in thyroid from the serum. Their structural homogeneity and allotype composition indicate that they are directed toward one or only a few antigenic determinants of the thyroglobulin molecule.
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Salabe et al. (2009) studied this question.