(A) Expression of c-mpl of murine fetal liver stem cell populations. Fetal liver stem cells were enriched for AA4 and stained with MoAbs to murine Sca, c-kit, and c-mpl as described in Materials and Methods. Fetal liver cells positive for both Sca and c-kit were gated and the resultant c-mpl positive cells are shown. Analysis was done a minimum of four times. (B) Expression of c-kit, Sca, and c-mpl on murine BM hematopoietic progenitors. The mononuclear fraction from BM was isolated by a density gradient and stained with a Lin cocktail of antibodies (see Materials and Methods). Lin stained cells were then removed by magnetic bead depletion. The lineage-depleted cells were then stained using directly conjugated MoAbs against Sca (R-PE), c-kit (FITC), c-mpl (biotin), and the Lin cocktail (Cascade Blue). The biotinylated c-mpl was detected using Streptavidin Red-670. Analysis was repeated three times. (C) Expression of CD34, CD38, and c-mpl on enriched human BM progenitor cells. CD34 cells were isolated as described. The enriched cells were then stained with MoAbs to CD34 (FITC), CD38 (R-PE), and c-mpl (Red -670). Cells were then analyzed on a Coulter Epics Elite flow cytometer as described. BM cells were enriched for CD34 using an immunomagnetic column. Analysis was repeated six times.