Thyroglobulin epitope recognition in a post iodine-supplemented Sri Lankan population.

OBJECTIVE

We previously reported a high prevalence of raised thyroglobulin autoantibodies (TgAb) in apparently healthy Sri Lankan schoolgirls following salt iodination. To characterize these antibodies further we determined the epitopes on thyroglobulin (Tg) with which they react and compared these with serum obtained from both healthy subjects and established autoimmune thyroid disease (AITD) patients from the UK. To extend our study to a wider population within Sri Lanka, we in addition determined the epitopes recognized by a group of AITD patients selected from a thyroid clinic in Sri Lanka, as well as apparently healthy female Sri Lankan tea workers of distinct ethnicity from the schoolgirls and AITD patients.

DESIGN

Sri Lankan schoolgirls (n = 282) and adult female tea estate workers (n = 208) were examined for thyroid autoimmune markers. Sera with high TgAb (> 98 kIU/l) were selected from these two groups (n = 36 and 45, respectively) to study epitope-binding patterns. We also examined the sera from 16 AITD patients attending a thyroid clinic in Colombo, 16 patients with AITD from the thyroid clinic at the University Hospital of Wales and 16 sera from healthy control UK women with no evidence of thyroid disease. To determine the epitopes on Tg recognized by the subjects' TgAb, we employed a panel of Tg mouse monoclonal antibodies labelled with alkaline phosphatase in a competitive enzyme-linked immunosorbent assay reaction with the subjects' serum.

RESULTS AND CONCLUSIONS

A majority of the Sri Lankan schoolgirls did not react with the immunodominant epitopes and did not differ significantly from healthy subjects from the UK in their Tg epitope recognition pattern. On the other hand, tea estate workers and Sri Lankan AITD patients recognized typical autoimmune thyroid disease epitopes and, in addition, recognized a separate cluster not previously associated with either the autoimmune state or the healthy state. The significance of this cluster requires further clarification.