Evidence for an autocrine loop in the Axl/Gas6 pathway. CD34⁺ cells isolated from blood of 2 different donors were cultured for 3 days in the presence of IL-15. Harvested cells were fixed, permeabilized, and stained with antibodies against Gas6, Axl, and phospho-STAT5. Gating was on CD34⁺ cells, and numbers in the upper right quadrant indicate percentage of double-positive cell populations (Gas6⁺Axl⁺ or Gas6⁺ phospho-STAT5⁺).