Regulation of Tie-2 receptor expression on cord blood CD34⁺ cells. (A) Two-color flow cytometric analysis of cord blood CD34⁺ cells showing expression of Tie-2 in freshly isolated cells (day 0) and after 2 days of culture (day 2). (B) Three-color flow cytometric analysis of cord blood CD34⁺ cells stained for CD34, CD11b, and Tie-2. Middle panels show the staining for CD34 and CD11b relative to isotype control antibodies in freshly isolated cells (day 0) and after 2 days of culture (day 2). Gating on the CD34⁺CD11b⁺ (B, upper panels) and CD34⁺CD11b^– (B, lower panels) populations demonstrate the selective up-regulation of Tie-2 in the CD34⁺CD11b⁺ subset at 2 days of culture. Percentages of CD34⁺Tie-2⁺ cells and CD34⁺CD11b⁺ are indicated in dot-plot quadrants. Data are representative of 5 independent experiments.