Objective: The human sodium iodide symporter (hNIS) is a candidate autoantigen in autoimmune thyroid diseases. To investigate the possible existence of autoantibodies able to interfere with the biological activity of hNIS, an assay was developed using a cell line stably expressing hNIS. Methods: hNIS complementary cDNA cloned in pcDNA3 and a neomycin resistance gene vector were co-transfected into CHO cells. After selection with geneticin, a cell line termed PA4, showing the highest level of Na125 I uptake, was characterized. The time course of iodide uptake was evaluated by incubating PA4 cells with 10 μmol/I NaI and 0.1 μCi Na125I for a period up to 90 min. The accumulation of iodide increased linearly between 2 and 10 min, reaching a plateau at 45 min. The curve of iodide efflux mirrored that of iodide influx. Both perchlorate and thiocyanate inhibited iodide uptake in PA4 cells in a dose-dependent manner starting from concentrations as low as 0.01 and 0.1 μmol/I respectively and complete inhibition was obtained at concentrations of 100 μmol/I perchlorate and 1000 μmol/l thiocyanate. The sensitivity of the inhibition assay was further improved using both inhibitors after 5 min incubation and in the absence of cold NaI. Results: Included in the study were 42 patients with Grave's disease (25 had active hyperthyroidism, ten were euthyroid and seven had hypothyroidism); 34 patients with Hashimoto's thyroiditis (one was euthyroid, four had subclinical hypothyroidism and 29 were overtly hypothyroid); and 19 with atrophic thyroiditis (all hypothyroid). Four out of eight whole sera from patients with Hashimoto's thyroiditis, and 8 out of 25 whole sera from patients with Graves' disease caused an inhibition of iodide uptake in PA4 cells greater tha 20% but also in 4 out of 15 sera from normal subjects. This inhibition activity exerted by sera from patients and controls was lost after dialyzing against buffer. Accordingly, IgGs purified from sera of all patients with Graves' disease and with Hashimoto's thyroiditis or atrophic thyroiditis were devoid of any effect on iodide uptake. Conclusions: In conclusion, we believe that autoantibodies able to block the function of hNIS are very rare.
|Number of pages||8|
|Journal||European Journal of Endocrinology|
|Publication status||Published - 2001|
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