Overview Introduction Leukocytes play an important role in eliminating offending agents neutrophils and macrophages are capable of destroying microbes, necrotic tissue, and foreign substances The process of leukocytes migrating from the blood vessel to tissue involves multiple steps and are mediated by adhesion molecules and chemokines margination leukocytes become redistributed closer to the vessel wall rolling leukocytes transiently attach to endothelium and then detach these cells therefore "roll" on the vessel wall the endothelium possesses E-selectin and P-selectin cytokines from the inflamed tissue regulate selectin expression Sialyl-Lewis X protein binds to E-selectin and P-selectin found on leukocytes firm endothelial adhesion mediated by integrin proteins vascular cell adhesion molecule 1 (VCAM1) and intercellular adhesion molecule-1 (ICAM-1) are found on the endothelium low affinity integrin are found on leukocytes migration through the vessel wall migration to tissue StepMolecule on Vasculature/StromaMolecule on Leukocyte1. Loose adhesion, rolling E-selection, P-selectinSialyl Lewis2. Tight adhesion ICAM-1LFA-1 (integrin)3. Diapedesis PECAM-1PECAM-14. Migration through ECMBacterial products, C5a, IL-8, LTB4, KallikreinVarious