Fetal liver HSCs are CD41^–. (A) CD150⁺CD48^– cells accounted for 0.068% ± 0.01% of E14.5 fetal liver cells (note that these gates used for the analysis of HSC frequency were somewhat tighter than those used in Figure 1D for the analysis of colony-forming progenitors), and (B) 51% ± 7% of the cells in this population were CD41⁺. In the analysis shown in panel B, CD41, CD48, and CD150 staining were detected in the FITC, PE, and APC channels, respectively. (C) Three-and-one-fifth percent of fetal liver cells expressed CD41. (D) CD41 expression was detected on only 2.7% of cells within the ThylowSca-1⁺lineage^–Mac-1⁺ HSC population. In this analysis CD41, Thy-1, Sca-1, lineage marker, and Mac-1 staining were detected in the FITC, PE-Cy5, APC-Cy7 (PR), PE, and APC channels, respectively. (E) Irradiated recipient mice received transplants of 1620 CD41⁺ fetal liver cells (blue lines) or 48 380 CD41^– fetal liver cells (red lines). Most mice that received transplants of CD41^– cells became long-term multilineage reconstituted (4 of 5; the other mouse was transiently multilineage reconstituted), but none of the mice that received transplants of CD41⁺ cells showed convincing reconstitution (0 of 8 mice).