Neither the innate nor adaptive immune system “responds” unless leukocytes cross blood
vessels. This process occurs through diapedesis, in which the leukocyte moves in an
ameboid fashion through tightly apposed endothelial borders and, in some cases, through
the endothelial cell itself. This review focuses on the active role of the endothelial cell in
diapedesis. Several mechanisms play a critical role in transendothelial migration, including
signals derived from clustering of apically disposed intercellular adhesion molecule 1 and …