A POPULATION OF INTERSTITIAL-CELLS IN THE ANTERIOR-PITUITARY WITH A HEMATOPOIETIC ORIGIN AND A RAPID TURNOVER - A RELATIONSHIP WITH FOLLICULO-STELLATE CELLS

The non-hormone secreting folliculo-stellate (FS) cells in the anterio r pituitary (AP) appear heterogeneous. Some of these cells have been d escribed as having a neuroectodermal origin and being glial, while som e others have been suggested to be monocytic or dendritic cells (DC). We have analyzed here the hematopoietic origin of interstitial cell po pulations in the AP. In the rat AP, the relative densities of S100(+) FS cells and major histocompatibility complex (MHC) class IT-expressin g DC-like cells show a parallel increase in the postnatal period betwe en the age of 3 weeks to 2 months. We first looked for the presence of donor derived cells in the AP of lethally irradiated bone marrow (BM) -transplanted rats. Donor derived myeloid cells carrying the n haploty pe of the MHC class I antigen (RT1.A(n)) reacting with the OX27 moAb, could not be detected in the AP three months after transplantation. It appeared, however, that OX27(+) DC-like cells a-priori were virtually absent from the rat AP. Therefore this transplantation model was not suitable for our studies. We then turned to a model of transgenic mice expressing a suicide gene in subpopulations of dendritic cells. Mice were lethally irradiated and received a BM transplant from the transge nic animals, with or without a treatment with ganciclovir (GCV) that s pecifically kills the dividing cells expressing the suicide gene. This model has already been used to identify and delete mainly dendritic c ell populations, viz N418(+) and ER-BMDM1(+) dendritic cells in the ma rginal zones of the spleen and in the thymic medulla. We observed in t he AP a 30% reduction of the ER-BMDM1(+) FS-like cells and a 50-100% r eduction of interstitial cells expressing the F4/80, Mac-1 and MOMA-1 markers in the mice receiving the transgenic BM and treated with GCV, compared to control mice that were not treated with GCV or that receiv ed non-transgenic BM. When a treatment with granulocyte-macrophage col ony-stimulating factor (GM-CSF) was initiated during the GCV treatment , we observed an even stronger reduction of the above-mentioned inters titial cell populations. These data indicate that in the mouse AP a po pulation of stellate cells exists with a hematopoietic origin, that ex presses markers of myeloid cells, and that has a rapid turnover. (C) 1 997 Elsevier Science B.V.