Expression of CD9 on cord blood CD34⁺ cells and regulation by SDF-1. (A) Cell-surface expression of CD9 and CXCR4 on CD34⁺CD38^hi and the more primitive CD34⁺CD38^−/lo cells were analyzed by flow cytometry (n = 41). Right panel, gating strategy of cord blood CD34⁺ subsets based on CD38 expression and dot plots of CD9 and CXCR4 expression of a representative experiment. Quadrants were set on the basis of staining with respective isotypic antibodies, and the percentage of cells in each quadrant is depicted. (B) Expressions of CD9 and CXCR4 on total cord blood CD34⁺, CD34⁺CD38^hi, and CD34⁺CD38^−/lo cells after 4 hours of culture in medium alone (CTRL) or in the presence of SDF-1 (100 ng/mL). A representative of 4 independent experiments is shown. (C) Kinetics of SDF-1–regulated CD9 and CXCR4 expression in cord blood CD34⁺ cells at the (i,iii) protein (n = 3-5) and (ii,iv) mRNA levels (n = 3-4). Results in subpanels ii and iv are gene expression levels relative to GAPDH (glyceraldehyde 3-phosphate dehydrogenase) expression. *P < .05; **P < .01. Data are means ± SEM.