Rat thymus macrophages: an immunohistochemical study on fetal, neonatal and adult thymus.

The pre- and postnatal development of the macrophage population of rat thymus is investigated applying enzyme-histochemical and immunohistochemical techniques, both on tissue sections and cell suspensions. A set of three monoclonal antibodies (ED1, ED2 and ED3), each of which recognizes cells of the monocyte-macrophage lineage in the rat, enabled us to distinguish between macrophages in the various compartments of the thymus. The medulla is characterized by ED1-positive dendritic cells, the corticomedullary region comprises numerous monocyte-like ED1-positive macrophages and the cortex contains a particular subpopulation of branched ED2-positive macrophages. Both the medullary dendritic cells and the cortical branched cells show Ia-membrane staining. ED3-positive cells are only occasionally present. During fetal life ED1-positive monocyte-like macrophages and dendritic cells are present. Just after birth ED2-positive cortical macrophages start to develop. Their number increases strongly during the first week after birth. The role of the various subpopulations of thymic macrophages is discussed.