Immunogenic functions of folliculo-stellate cells of the normal human pituitary?

Folliculo-stellate cells in pituitary adenomas of patients with acromegaly

Pituitary adenoma tissue from patients with acromegaly (n = 286) was obtained by surgery and examined for folliculo-stellate cells by immunostaining for S100 protein. The number of immunostained cells varied from one adenoma to another. A hundred and ninety-eight pituitary adenomas (69%) contained S100 protein positive cells corresponding to folliculo-stellate cells (FSC): in 100 cases (35%), only few sparse FSC were found, in 43 cases (15%) FSC were scattered throughout the adenoma, and in 55 cases (19%) there was an abundance of FSC. There were no significant differences regarding sex or age of the patients. The relative amount of FSC vaired among different adenoma types. Plurihormonal adenomas showed the highest FSC density, whereas the majority of monohormonal adenomas contained only few or no FSC. Patients with pituitary adenomas containing scattered FSC had a significantly higher preoperative mean GH level than patients with pituitary adenomas not having FSC. There was a negative correlation between the FSC density in adenoma tissue and the preoperative mean PRL level. There was no correlation between the tumour size and the amount of FSC. Our data indicate no effect of the duration of symptoms on the FSC density and do not suggest a correlation between FSC density and the percentage of a certain hormone-secreting cell type.

Amyloid Deposits in Pituitaries and Pituitary Adenomas: Immunohistochemistry and In Situ Hybridization

The patterns of deposition and immunoreactivity of interstitial amyloid were studied in 11 pituitary glands obtained at autopsy and 9 surgically resected pituitary adenomas using Congo red staining and a panel of antisera directed against 5 major amyloid fibril proteins and all pituitary hormones. The deposition pattern of amyloid in pituitary glands differed from that in adenomas but all amyloid deposits showed an immunostaining with anti-amyloid X-light chain. The remaining antisera were immunonegative. In situ hybridization using an oligodeoxyribonucleotide-probe complementary to the mRNA coding for the constant region of human X-light chain yielded no hybridization signals in the pituitaries or pituitary adenomas, excluding local synthesis and secretion of immunoglobulins. Since no case studied suffered from generalized AX-amyloidosis and adsorption of immunoglobulins to the unknown amyloid fribril protein of the pituitary seems to be unlikely, crossreaction of the polyclonal antisera with an undefined antigen is probable. The similar immunostaining properties of amyloid deposits in "normal" pituitaries and pituitary adenomas suggest they both originate from the same precursor protein.

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.

Folliculostellate cells of the pituitary

In addition to the hormone-producing granulated cells, the so-called folliculostellate (FS) cells of the adenohypophysis represent a population of nongranulated cells extensively described in a large number of species. They show distinctive morphological features including a star shape with thin cytoplasmic projections extending between granulated cells and well-developed junctional complexes. FS cells are joined together surrounding irregular microcavities and project microvilli into the lumina. The immunocytochemical localization of S-100 protein, glial fibrillary acidic protein, and vimentin constitutes a reliable and easy method for investigating their presence and distribution in the normal pituitary gland and in pituitary adenomas. Although the expression of glial cell markers raised the hypothesis of a neuroectodermal origin of FS cells, most evidence supports that they derive from the epithelium of the Rathke's pouch, as do granulated adenohypophyseal cells. Morphological studies indicate that FS cells are involved in phagocytosis and possess sustentacular functions. Investigations using cell cultures show that FS cells play important roles in the paracrine regulation of adenohypophy-seal secretion by their ability to liberate several growth factors and regulate the ionic composition of the extracellular fluid. Further research using novel immunocytochemical markers and ceil culture techniques may clarify the origin and the role of this enigmatic cell type in the normal and pathological pituitary gland.