Macrophage subpopulations in the mouse spleen renewed by local proliferation

A dual origin, by both immigration of blood monocytes and local proliferation has been reported for macrophages, which are heterogeneous in several aspects. Until now few studies have focussed on renewal of macrophages. Therefore, in this study macrophage renewal by local proliferation has been studied in the spleen. Spleen tissue of mice which had received BrdU intravenously was investigated immunohistochemically to detect BrdU incorporated by macrophages. BrdU incorporation by splenic macrophages was studied under steady state conditions as well as during repopulation after experimental macrophage depletion. Under steady state conditions, BrdU incorporation was found in 3.0 +/- 0.5% of the white pulp macrophages and in approximately 1% of the metallophilic macrophages only. Comparable results were found during repopulation after experimental macrophage depletion. The data suggest that renewal of macrophages by local proliferation is restricted to certain subsets in the spleen and that the macrophage subsets of the spleen are renewed by different mechanisms, or belong to different lineages of macrophage differentiation.