Characterization of primitive adherent BM cells. (A) Growth curve of cells derived from bone marrow (BM) of Rosa 26-LacZ mice; (B) their morphology under an inverted microscope (original magnification, 10×/0.3 NA Ph1), and (C) expression of surface markers at 39 cell doublings (≅ 100 days in culture). Histogram profiles are gated on forward and side scatters, and PI-negative (live) cells are shown in the first 2 panels. Plots show isotype control staining profile (thin line) versus specific antibody staining profile (thick line). Percentages represent the fraction of cells that express a given surface antigen.