Binding of soluble P-selectin and PSGL-1 expression on CB and mPB CD34⁺ cells. (a) MNCs obtained from CB or mPB samples were stained for CD34 and P-selectin–IgG binding in the presence or absence of 5 mM EDTA. Data represent geometric mean of fluorescence ± SEM of P-selectin–IgG binding on gated CD34⁺ cells. n = 8 separate experiments from different donors. *P = 0.008. (b) Scattergram profiles of CB and mPB MNCs stained for CD34⁺ cells and P-selectin–IgG in the presence or absence of 5 mM EDTA. In the presence of divalent cations, virtually all mPB CD34⁺ cells bind P-selectin–IgG, whereas two distinct subpopulations are present among CB CD34⁺ cells: one that binds P-selectin–IgG normally (∼70%) and one that does not bind soluble P-selectin (∼30%). (c) Expression of PSGL-1 in CB and mPB CD34⁺ cells. (d) PSGL-1 is the sole P-selectin ligand on CB and mPB CD34⁺ cells. MNCs were preincubated with 2 μg of function-blocking (KPL1) or non-blocking (PSL-275) anti–PSGL-1 before staining to detect P-selectin–IgG chimera binding and CD34. The numbers indicate the percentage of CD34⁺ cells in each quadrant. The scattergrams represent one of at least five replicates.