DISTINCT MOUSE BONE-MARROW MACROPHAGE PRECURSORS IDENTIFIED BY DIFFERENTIAL EXPRESSION OF ER-MP12 AND ER-MP20 ANTIGENS

The characterization of early branch points in the differentiation of leukocytes requires identification of precursor cells in the bone marr ow. Recently, we produced two monoclonal antibodies, ER-MP12 and ER-MP 20, which in two-color flow-cytometric analysis divide the murine bone marrow into six defined subsets. Here we show, using fluorescence-act ivated cell sorting followed by macrophage colony-stimulating factor-s timulated culture in soft agar, that precursors of the mononuclear pha gocyte system reside only within the ER-MP12(hi)20(-), ER-MP12(+)20(+) and ER-MP12(-)20(hi) bone marrow subsets. Together, these subsets com prise 15% of nucleated bone marrow cells. Furthermore, we provide evid ence that the macrophage precursors present in these subsets represent successive stages in a maturation sequence where the most immature ER -MP12(hi)20(-) cells develop via the ER-MP12(+)20(+) stage into ER-MP1 2(-)20(hi) monocytes.