Leukocyte emigration into lymphatic tissues or inflammatory sites is regulated by the
expression of adhesion and signaling molecules (1). Binding of selectins to cell-surface
carbohydrate ligands allows flowing leukocytes to attach and then roll on the vessel wall.
These transient attachments expose the leukocytes to locally expressed signaling
molecules. The activated leukocy~ es then adhere firmly through binding of activated
integrins to Ig-hke ligands on the endothelium. In response to chemoattractant gradients, the …