Leukocyte Extravasation

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