FOLLICULO-STELLATE CELLS OF HUMAN PITUITARY-ADENOMAS - IMMUNOHISTOCHEMICAL STUDY OF THE MONOCYTE MACROPHAGE PHENOTYPE EXPRESSION/

Folliculo-stellate cells (FS) represent a small percentage of anterior pituitary elements of still undetermined embryological origin. They a re sparse among endocrine pituitary cells and are characterized by the lack of secretory granules and by the presence of few branching proce sses inserted between hormone-secreting cells. Although FS cell role i s still under discussion, recent reports showed that they produce mono cyte-derived cytokines able to influence the hormone production and mo dulate the immunoendocrine connections. In this study we applied three monocyte-macrophage markers (HAM56, KP1, HLA-DR) to 15 pituitary aden omas in order to ascertain whether FS cells belong to the macrophage l ineage. In this case FS cells could be considered the resident macroph ages of the pituitary. FS cells were identified according to the react ivity to S-100, GFAP and vimentin. We confirm that S-100 represents th e most useful marker for these cells that were detected scattered betw een tumor cells in more than half of the adenomas. GFAP stained only a percentage of FS cells, while vimentin recognized in addition to stel late cells endothelia, perivascular and infiltrating macrophages. We w ere unable to detect the expression of the macrophage markers on S-100 and GFAP reactive cells. Indeed, HAM56, KP1 and HLA-DR-positive cells were mostly round, small size and located in the perivascular and sep tal positions where FS cells were never detected. Lack of expression o f monocyte-macrophage lineage markers by FS cells in pituitary adenoma s suggests their preferential neuroectodermal origin. However, further studies on normal human pituitary will be needed before ruling out a possible role for FS cells as resident pituitary macrophages.