Class II MHC-expressing cells in the rat adrenal gland defined by monoclonal antibodies

The detailed distribution and heterogeneity of various immunocompetent cells were characterized in the normal adrenal gland of the rat, with special emphasis on major histocompatibility complex (MHC) class II-expressing cells and macrophages. All adrenals contained at least two different populations of cells reactive with the dendritic cell or the macrophage antibodies. These cells were clearly distinguished from adrenal parenchymal cells by their morphology and location. The majority of dendritic cells were immunoreactive for the MHC class II (Ia) antigen (MRC OX6) and/or the dendritic cell antibodies (MRC OX62), and negative for the macrophage antibodies (ED1, ED2, and/or MRC OX42), whereas the main population of macrophages was immunonegative for the former antibodies and positive for the latter. The OX62-positive cells and the OX42-labeled cells occurred exclusively throughout the medulla. The cellular density of dendritic cells in the adrenal cortex was significantly higher than that of macrophages. Double-immunoperoxidase staining for ED1 and OX6 revealed that positively stained cells could be classified into the following categories: ED1+OX6+, ED1+OX6-, and ED1-OX6+. More then 40% of OX6+ cells were immunoreactive for ED1 in the zona glomerulosa, while approximately 15%, 20%, and 30% of OX6+ cells were positive for ED1 in the zona fasciculata, zona reticularis and medulla, respectively. ED1+ED2- cells were more frequently detected in the zona glomerulosa than in other adrenal zones. Only a few ED1-ED2+ cells were located in the zona glomerulosa, whereas a large number of them were found in the zona fasciculata. In the zona reticularis and medulla, ED1+ED2+, ED1+ED2-, and ED1-ED2+ cells were detected in the ratio 2:1:3. Our rsults suggest that dendritic cells and macrophages mature during their migration within the adrenal gland. These immunocompetent cells may contribute to a paracrine regulation of adrenal function under physiological conditions.