Reduced binding of soluble P-selectin on primitive neonatal HPCs (CD34+CD38lo/–). MNCs obtained from CB samples were stained for CD34 (using PE) and CD38 (using FITC) expression, and P-selectin–IgG chimera binding (using Cy5). (a) The gated regions represent CD34+ cells that bind (R2, green) or do not bind (R1, red) P-selectin–IgG. (b) CD38 expression on cells from R1 and R2 regions. The majority of cells that do not bind P-selectin–IgG are primitive CD34+CD38lo/– cells. Shown is one representative of eight replicates.