Analysis of human sodium iodide symporter immunoreactivity in human exocrine glands

The human sodium iodide symporter (hNIS) is an intrinsic transmembrane prot ein that mediates the active transport of iodide across the basolateral mem brane of thyroid follicular cells. In addition to normally functioning thyr oid tissue, various extrathyroidal tissues, including salivary gland, lacri mal gland, gastric mucosa, choroid plexus, and lactating mammary gland, hav e been demonstrated to accumulate iodide. After cloning and molecular chara cterization of the sodium iodide symporter, expression of hNIS messenger ri bonucleic acid has been detected in a broad range of extrathyroidal tissues using Northern blot analysis and RT-PCR. In this study we used both monocl onal and polyclonal antibodies directed against different portions of hNIS protein together with a highly sensitive immunostaining technique to assess hNIS protein expression in tissue sections derived from normal human saliv ary and lacrimal glands, pancreas, as well as gastric and colonic mucosa. I mmunohistochemical analysis of normal human salivary and lacrimal glands re vealed marked hNIS immunoreactivity in ductal cells and less intense staini ng of acinar cells. Further, immunostaining of gastric and colonic mucosa s howed marked hNIS immunoreactivity confined to chief and parietal cells in gastric mucosa and to epithelial cells lining mucosal crypts in colonic muc osa In normal human pancreas, hNIS immunoreactivity was located in ductal c ells, exocrine parenchymal cells, and Langerhans islet cells. In conclusion , our study demonstrates the expression of hNIS protein by several human ex ocrine glands, suggesting that iodide transport in these glands is a specif ic property conferred by the expression of hNIS protein, which may serve im portant functions by concentrating iodine in glandular secretions.