The specificity and efficiency of leukocyte binding to endothelial cel
ls (ECs) depends on coordinated information transfer from the underlyi
ng tissue to endothelium and from there to the leukocyte. We address t
hree distinct information-transfer points in this system: 1. How does
the leukocyte read information from the EC? This process is best accou
nted for by the paradigm of a multi-step adhesion cascade optimized fo
r rapid information readout; it consists of primary adhesion (rolling/
tethering), triggering, and strong adhesion. Recent studies with T cel
ls, monocytes, and eosinophils confirm the generality of the paradigm.
The concept of primary adhesion has been expanded to involve not only
the selectins, but also certain integrins; furthermore, it depends on
receptor concentration on leukocyte microvilli. 2. What information f
rom the underlying tissue does the EC transform into signals for the l
eukocytes? And what rules govern that process ? We illustrate the prin
ciples with chemokines, believed to participate in the triggering step
. The endothelium displays chemokines either (a) directly by ''posting
'' them from other cells or (b) by integrating a variety of tissue and
environmental signals and ''relaying'' that information by producing
its own chemokines and surface adhesion molecules. The rules for this
endothelial transduction include specificity coupled with redundancy,
amplification, synergy, and coordinated induction of ensembles of mole
cules. Finally, 3. How does the relevant information reach the endothe
lium? Simple diffusion is sufficient to deliver signals from cells clo
se to the vessel. However, longer range soluble mediator transport app
ears to be facilitated by fiber bundles, particularly those ensheathed
by fibroblastic reticular cells in the lymph node.