The original steps of the leukocyte adhesion cascade are shown in red: rolling, mediated by selectins, activation, mediated by chemokines, and arrest, mediated by integrins. This has been expanded to include additional steps: capture (or tethering), slow rolling, adhesion strengthening and spreading, intravascular crawling, and paracellular and transcellular transmigration. Crucial molecules involved are indicated in boxes. ESAM, endothelial cell-selective adhesion molecule; ICAM-1, intercellular adhesion molecule 1; JAM, junctional adhesion molecule; LFA-1, lymphocyte function-associated antigen 1 (also known as αLβ2-integrin); Mac-1, macrophage antigen 1; MAdCAM-1, mucosal vascular addressin cell-adhesion molecule 1; PSGL-1, P-selectin glycoprotein ligand 1; PECAM-1, platelet/endothelial-cell adhesion molecule 1; PI3Ki ases, phosphoinositide 3-kinases; VCAM-1, vascular cell-adhesion molecule 1; VLA-4, very late antigen 4 (also known as α4β1-integrin) .