Figure 1.

Multistep leucocyte adhesion cascade. Endothelial selectins initiate tethering and rolling of leucocytes, including neutrophils as depicted here. Signals from engaged selectins and chemokines activate β2 integrins that mediate slow rolling and arrest. Integrins also direct spreading, intraluminal crawling, and migration between or through endothelial cells into perivascular tissues. Inset: Adherent neutrophils polarize to form a leading edge (lamellipodium) and a trailing edge (uropod). The selectin ligand PSGL-1 redistributes to the uropod and captures activated platelets by interacting with P-selectin. Platelet–neutrophil interactions transduce signals that facilitate intraluminal crawling.