White Blood Cell Extravasation: How Leukocytes Leave Vessels to Fight Infection

White blood cells (leukocytes) can exit blood vessels and enter tissues—a process called extravasation or diapedesis. Steps:

1. Margination: cells slow and roll along endothelium.
2. Adhesion: selectins/integrins bind endothelial ligands, firm attachment.
3. Transmigration: cells squeeze between endothelial cells, creating temporary gaps.
4. Chemotaxis: follow chemical gradients to infection/injury site.

Once in tissue, they perform phagocytosis, release antimicrobial substances, and activate other immune cells. This ability is crucial for host defense and tissue homeostasis.