Autoimmunity involving the human sodium/iodide symporter: Fact or fiction?

Presence, functional activity and clinical relevance of autoantibodies dire cted against the human sodium iodide symporter (NIS) in thyroid autoimmune diseases have become the subject of much controversy in recent years. Earli er reports have claimed that NIS may represent a major thyroid autoantigen that elicits formation of functionally relevant autoantibodies in a signifi cant proportion of patients with Graves' disease (GD) and Hashimoto's thyro iditis (HT). Moreover, a recent study has extended this notion by reporting detection of NIS-autoantibodies in 22% and 24% of a small number of patien ts with GD and HT, respectively, but not in patients with other autoimmune diseases. However, in striking contrast to these reports, two independent g roups of investigators have now presented convincing evidence that NIS-dire cted autoantibodies occur with low frequency among a large sample of patien ts with autoimmune thyroid diseases. Moreover, no evidence of specific iodi de uptake inhibiting activity was obtained once sera had been subjected to dialysis and/or IgG extraction. Thus, although the controversy has not been definitively resolved, hNIS does not appear to be a major functionally rel evant antigen in autoimmune thyroid diseases. Moreover, when detected in ad dition to TPO and TSH receptor autoantibodies, NIS-directed autoantibodies do not appear to contribute any diagnostic power for GD and HT.