Peripheral blood T cell activation after radioiodine treatment for Graves' disease

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Abstract
Radioiodine therapy for Graves'' thyrotoxicosis produces a rise in thyroid autoantibodies in the first three months after treatment, but little is known of its efects on T cells. We have therefore followed the changes in T cell subsets in sequential samples from 23 patients with Graves'' disease treated with radioiodine, using dual-color flow cytometry. In the first month after treatment there was a significant rise in activated T cells, identified by the markers HLA-DR (la) and CDw26/Tal (p < 0.025 in both cases). CD45RO-positive T cells, which are the primed population containing memory cells, also increased (p < 0.025), but there was no change in CD45R positive, resting T cells or in the CD4 to CD8 (helper to cytotoxic/suppressor) ratio. Vicia villosa-binding T cells, containing the contrasuppressor population, showed a more variable response, but the trend was to an overall increase from pre-treatment values (p < 0.025). The changes did not appear to be related to antithyroid drug treatment, since they were seen irrespective of whether patients continued such therapy. These results suggest that T cell activation and enhanced contrasuppressor activity may in part be responsible for the rise in autoantibodies after radioiodine. The T cell changes could also contribute to the worsening of ophthalmopathy seen in some radioiodine-treated patients.