The endothelial adhesion molecule E-selectin pays critical roles in selecting specific cells from the vascular blood flow and is also involved in homing human haematopoietic progenitor cells (HPC) in bone marrow. In June 11 Journal of Cell Biology, Charles Dimitroff and colleagues from Harvard Medical School, Boston, report that glycosylated CD44 is a major E-selectin ligand expressed on HPCs and is essential for interactions with bone marrow endothelial cells.

Dimitroff et al used a shear-based adherence assay to analyze the E-selectin ligand activity of human HPC membrane proteins. They found that glycosilated CD44 is a new, more potent, and more specific E-selectin ligand than the previously known ligand PSGL-1. In addition, CD44 is only present on primitive human HPCs, not on more mature haematopoietic cells and is seen to promote human HPC rolling interactions with E-selectin expressed on human bone marrow endothelial cells (J Cell Biol 2001,...