Bispecific thyroglobulin and thyroperoxidase autoantibodies in patients with various thyroid and autoimmune diseases

Recent evidence indicates that thyroid autoimmune disorders are associated with the presence of circulating autoantibodies (aAb) with dual specificity for thyroglobulin (TG) and thyroperoxidase (TPO). The question of whether these aAb, called TGPO aAb, are of clinical relevance compared to TG and TPO aAb remains to be determined. The availability of purified preparations of human TG and TPO allowed the development of a specific and sensitive RIA for TGPO aAb in serum. In the present study, we compared levels of aAb that cross-react with both TG and TPO (TGPO aAb) and total TG and TPO aAb levels, respectively, in sera from 84 normal controls and 226 patients with various thyroid and autoimmune diseases, including nontoxic goiter (n = 50), toxic nodular goiter (n = 13), thyroid carcinoma (n = 20), primary idiopathic myxedema (n = 15), postpartum thyroiditis (n = 11), Hashimoto's thyroiditis (n = 38), pernicious anemia (n = 27), rheumatoid arthritis (n = 19), and insulin-dependent diabetes mellitus (n = 33). In addition, 16 patients with Hashimoto's thyroiditis were studied before therapy and after more than 3 months of treatment with L-T4. It was shown that TGPO aAb were generally, but not always, present in the serum of patients with Hashimoto's thyroiditis, which also contained TG and TPO aAb. In contrast, TGPO aAb were undetectable in normal controls (excepting a few cases reaching borderline levels) as well as in sera from the majority of the other patients tested. Selecting sera positive for TGPO and either TG or TPO aAb, a statistically significant correlation was found between TGPO and TG (n = 26; P < 0.005), but not TPO aAb. Interestingly, the TGPO aAb level significantly decreased in patients with Hashimoto's thyroiditis after hormonal therapy (P < 0.05), some of them shifting from TGPO aAb positive before treatment to negative after treatment. In conclusion, TGPO aAb determination distinguishes Hashimoto's patients from patients with either thyroid and/or autoimmune diseases. The specific presence of TGPO aAb in a subset of Hashimoto's patients and their variation during T4 therapy remain to be understood. This could give a clue to mechanisms of autoimmune thyroid disease.