Triggering of CD40 increases the expression of CD86 on CD34⁺ blood cells. Immunomagnetically separated CD34⁺ blood cells were stained with HPCA-2 (anti-CD34)–PE and anti–CD86-FITC MoAbs, or isotype control, immediately after isolation (0 hrs) and after 40 hours in liquid culture with B-B20 (anti-CD40) MoAb. CD34⁺ cells were gated for analysis and histograms represent staining with FITC-labeled isotype control (dashed line) and staining with CD86 FITC-labeled MoAb (solid line).