CD44 is localized to the edge of SDF-1–induced cell protrusions in HPCs adhered to HA. Enriched CB CD34⁺ cells were plated on HA-coated coverslips, either untreated (top and second rows) or exposed to a uniform SDF-1 concentration of 200 ng/mL (third and bottom rows) following incubation with or without anti-CD44 (αCD44) mAb (- and +, respectively). After washing, the adherent cells were fixed, permeabilized, and indirectly labeled with antihuman CD44 mAb (red) and FITC-phalloidin (green) to detect polymerized actin. Bar = 10 μm. Insert “a” demonstrates a merged image (reduced 3-fold) of a polarized untreated cell with basal level of short filamentous structures, which are densely labeled by anti-CD44 mAb. Insert “b” shows the 2-fold enlarged region indicated by an asterisk. The arrow is pointing to the intense staining of CD44 at the edge of an SDF-1–induced protrusion.