Composition and characteristics of distinct macrophage subpopulations in the mouse thymus

The aim of the present study was to investigate the composition, morphology, characteristics, distribution and function of distinct macrophage subpopulations in the mouse thymus. Apoptosis of mouse thymocytes was induced by glucocorticoids and three monoclonal antibodies against Mac-2, F4/80 and ED1 were used for immunofluorescence staining and immunohistochemical analysis. The morphology of thymic macrophages was examined by transmission electron microscopy. Four subpopulations of mouse thymic macrophages were identified. Dendritic macrophages were identified using anti-Mac-2 and anti-F4/80 antibodies, and were demonstrated to be distributed in the entire thymus. Phagocytes were also observed. In addition, plate-shaped macrophages, identified using the anti-F4/80 antibody, were distributed under the thymic cortex capsule. Small oval macrophages, identified using the anti-Mac-2 antibody, were distributed in the thymic medulla and corticomedullary region (CMR), while phagocytes were not observed in these types of cell. ED1+ thymic macrophages with irregular forms were distributed in the CMR. All of the four subpopulations of mouse thymic macrophages described above exhibited acid phosphate activity. This study indicated the existence of macrophage subpopulations with different shapes, distribution and functions in the mouse thymus.