NA+ I- SYMPORTER DISTRIBUTION IN HUMAN THYROID TISSUES - AN IMMUNOHISTOCHEMICAL STUDY/

Antipeptide antibodies raised against the carboxyl-terminal region of the human sodium/iodide (Na+/I-) symporter (hNIS) were used to investi gate by immunohistochemistry the presence and distribution of the hNIS protein in normal thyroid tissues, in some pathological nonneoplastic thyroid tissues, and in different histotypes of thyroid neoplasms. In normal thyroid tissue, staining of hNIS protein was heterogeneous and limited to a minority of follicular cells that were in close contact with capillary vessels. In positive cells, immunostaining was Limited to the basolateral membrane. In contrast, in Graves' disease the major ity of follicular cells expressed the hNIS protein. In autoimmune thyr oiditis, the number of hNIS-positive cells, was similar to that found in normal tissue. These positive cells were found essentially close to lymphocytic infiltrates. This observation supports the concept of hNI S as an autoantigen. In diffuse nodular hyperplasia, hNIS staining was heterogeneous, but the number of hNIS-positive cells exceeded that fo und in normal tissue. In well differentiated follicular or papillary c arcinoma, the number of hNIS-positive cells was significantly lower th an in normal tissue. In poorly differentiated follicular carcinoma, th e number of hNIS-positive cells was less than that found in well diffe rentiated carcinoma, or there were no positive cells. Interestingly, i n all of these thyroid tissues, the number of follicular cells exhibit ing TSH receptor (TSHR) immunoreactivity was greater than the number o f hNIS-positive cells. As hNIS expression appears to be related to TSH R stimulation, the decreased number of TSHR-positive cells in cancers may contribute to the reduced capacity of neoplastic cells to concentr ate iodide. In one patient with a follicular cancer with an absence of hNIS immunostaining, the total body I-131 scan showed no uptake in me tastatic tissue. In three cancers with positive hNIS cells, the I-131 scan showed uptake in lymph node metastases. This suggests that immuno detection of hNIS could predict radioiodine uptake in thyroid cancers.