Modification of ligand specificity by sulfation on sugar chains is an interesting subject in the field of glycobiology. It was originally discovered on neutrophils, but it is now known to be expressed on essentially all types of leukocytes. Rapid and transient binding and dissociation between selectin and its ligand make leukocyte slow down at post capillary venules at the site of inflammation or at high endothlial venules in the lymphoid tissue. Basically, leukocytes roll on vascular endothelial cells based on the interaction between selectins and their ligands in vivo. Secondary rolling phenomenon has also been reported in which leukocytes roll on other leukocytes that have already adhered to endothelial cells.
Leukocytes slow down by rolling, then receive signals.
Thus, selectins and their ligands not only contribute to the leukocyte extravasation as cell adhesion molecules but may also play some role in the signaling process. J. Cell Biol.