BMPC-rich elutriation fraction cultured on a sterile glass slide in DMEM-20% FCS and allowed to proliferate. (a) On day 7, the slide was washed and the cells were fixed and stained with anti-BMPR Type 1A antibody. In the background are many unstained, small, mononuclear cells. Two types of cell are stained: one looks like a fibroblast, and the other is a large, round cell with an adherent cytoplasm. (b) A similar culture on day 12, stained with anti-endoglin (CD105) antibody. The cytoplasm of almost all the large mesenchymal cells shows stippled staining with perinuclear accentuation.