S-100 protein immunopositivity in human nontumorous hypophyses and pituitary adenomas

The presence, distribution, and morphological appearance of S-100 protein-immunoreactive cells in the human hypophysis were studied by immunocytochemistry. One hundred and twelve nonadenomatous pituitaries from fetuses to adults and pituitaries affected by several lesions including metastases, acute infarcts, and lymphocytic hypophysitis, as well as 115 pituitary adenomas were examined.S-100 protein immunoreactivity was detected in neurohy-pophyseal pituicytes and stellate cells of the pars distalis from 5 months following birth. In adults, S-100 protein-immunopositive cells displayed a preferential topographical association with growth hormone-, follicle-stimulating hormone-, luteinizing hormone-, and alpha-sub-unit-immunoreactive cells and with capillary walls. Colloid-containing follicles were mainly lined by hormone-containing cells, although scattered S-100 protein-immunoreactive processes or cell bodies were also observed forming their walls.No major changes in S-100 protein-immunoreactive cells were observed in the pituitary parenchyma bordering metastatic, inflammatory, necrotic, or adenomatous tissues. Eighteen of 115 pituitary adenomas contained a variable number of S-100 protein-immunoreactive cells. No preferential association of these cells with any type of pituitary adenoma was found.We propose that S-100 protein expression in the nontumorous adenohypophysis and pituitary adenomas may constitute a dynamic process and that S-100 protein-positive cells may constitute a heterogeneous cell population composed of pure, fully differentiated stellate cells and of transdifferentiated follicular cells.