Identification of thyroglobulin in orbital tissues of patients with thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is thought to have an autoimmune pa thogenesis because of its association with autoimmune thyroid disease, in p articular with Graves' disease. Nevertheless, the nature of the autoimmune reaction is unclear, and a target orbital autoantigen has not been conclusi vely identified. A widely discussed hypothesis is that antigens constitutiv ely shared by the thyroid and orbital tissues are targets of an autoimmune reaction. It has been also postulated that a thyroid-soluble antigen, namel y thyroglobulin (Tg), is transported to orbital tissues through the lymphat ics, where it accumulates and elicits autoimmune damages in susceptible ind ividuals. Here we have investigated whether Tg is present in orbital tissue s from patients with TAO. Retrobulbar tissue specimens were obtained from t hree patients with Graves' disease and TAO who underwent decompressive orbi totomy, and at autopsy from two patients with no thyroid or eye disease. Al l patients with TAO had been previously treated with radioiodine to control Graves' hyperthyroidism. Western blot analysis with a monoclonal anti-Tg a ntibody showed the presence of intact Tg, both in soluble and membrane-asso ciated fractions of orbital tissue extracts from the patients with TAO, in amounts estimated to range from similar to 320 to similar to 900 pg/mug Of tissue protein. In contrast, Tg was not detected in orbital tissue extracts from patients with no thyroid or eye disease. Tg was also demonstrated in orbital tissue extracts from two of three patients with TAO by enzyme-linke d immunosorbent assay (ELISA), in amounts estimated to range from similar t o 450 to similar to 1000 pg/mug of protein. In addition, Tg in orbital tiss ue extracts from patients with TAO was immunoprecipitated by a rabbit anti- Tg antibody, suggesting that it retained its native conformation. An anti-t hyroxine (T4) antibody captured in solid-phase Tg from orbital tissue extra cts, showing that it contained thyroid hormone residues and had therefore o riginated in the thyroid. Tg-anti-Tg immune complexes were not found in orb ital tissues, suggesting that if an autoimmune reaction to Tg occurs in TAO , it is likely to be cell mediated.