Selectin ligands on CB-CD34⁺ cells. (A) Structure of PSGL-1. PSGL-1 is homodimeric membrane mucin. A short N-terminal segment (residues 42-59; encircled) is critical for P-selectin binding. It includes 3 tyrosine residues that can be sulfated (underlined) and an important O-glycan (Thr57) that carries the tetrasaccharide sLex (shaded area). (B) Binding of P- and E-selectin on CB-CD34⁺ cells is heterogeneous. Dot plots depict CD34 staining and P- or E-selectin binding in CB- and mobilized peripheral blood (mPB) mononuclear cells (MNCs). Numbers indicate the percentage of CD34⁺ cells binding selectins (right quadrants) or not (left quadrants). Note that while all CD34⁺ cells from mPB bind P-selectin, a subset of CB-CD34⁺ cells does not bind P-selectin. Binding of E-selectin is heterogeneous in both CB and mPB CD34⁺ cells.