Thyroglobulin autoantibodies of patients with subacute thyroiditis are restricted to a major B cell epitope

Background: Thyroglobulin autoantibodies (TgAb) can develop in patients with subacute thyroiditis (SAT). Aim: Comparison of the epitope pattern of TgAb of patients with SAT, Hashimoto’s thyroiditis (HT) [autoimmune thyroid disease (AITD)] and non-toxic multinodular goiter (NTMG) (non-AITD). Subjects and methods: Serum TgAb from 10 patients with SAT, 45 with HT, and 19 with NTMG were evaluated. Serum TgAb binding to Tg was inhibited by 4 recombinant human TgAb-Fab, recognizing Tg epi tope regions A, B, C, and D. The ability of single TgAb-Fab to inhibit the binding of serum TgAb to Tg was evaluated in enzyme-linked immunosorbent assay. Results: Levels of inhibition were different for all TgAb-Fab in the 3 groups of patients. Inhibition by region A TgAb-Fab in SAT [50.5 (30.3–62.5)%] (median and 25 th to 75 th percentiles) was similar to HT [49.0 (38.0–69.5)%] and sig nificantly higher than in NTMG [25.0 (14.0–37.0)%]; by region B TgAb-Fab in SAT [0.0 (0.0–12.5)%] was significantly lower than in HT [28.0 (9.5–48.0)%] and similar to NTMG [9.0 (4.8–20.5)%]; by region C TgAb-Fab in SAT [9.5 (0.0–25.8)%] were similar to HT [23.0 (9.5–41)%] and NTMG [6.5 (1.7–21.5)%]; and by region D TgAb-Fab in SAT [0.0 (0.0–8.0)%] were lower than in HT [12.0 (1.0–28.5)%] and similar to NTMG [1.0 (0.0–5.0)%]. Conclusions: The epitope pattern of TgAb of SAT is restricted to the A region that is immunodominant in AITD and non-AITD. In the majority of patients with SAT, the autoimmune phenomena represent a non-specific and transient response to the release of thyroid antigens, rather than the expression of thyroid autoimmunity.