Expression of integrins on human CD34⁺cells. (A) UCB MNC were stained with MoAbs specific for human integrin α3, α4, α5, αv, or β1 subunit and FITC-conjugated goat anti-mouse IgG, and then with PE-conjugated anti-human CD34 MoAb. The stained cells were analyzed by flow cytometry. Quadrants are indicated to show levels of background staining observed with appropriate irrelevant control antibodies. (B) Purified CD34⁺ cells were stained with anti–CD34-PE, anti–α4-FITC or anti–α5-FITC (shaded histograms). The levels of background staining with negative control antibodies (open histograms) are shown in each panel for direct comparison.