Leucocyte extravasation
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Leucocyte extravasation can be thought to occur in 4 stages:
Chemoattraction and rolling
Macrophages in the affected tissue release cytokines such as IL-1, TNF-α. This both attracts circulating leucocytes and causes the endothelium to express cellular adhesion molecules such as selectins.
Leucocytes express integrins in response to the cytokines. These bind to ICAM proteins on endothelial cells.
PECAM proteins on both endothelial cells and leucocytes interact and facilitate the migration of the leucocytes through the endothelium.
- 1. Chemoattraction
- 2. Rolling
- 3. Tight adhesion
- 4. Transmigration
Chemoattraction and rolling
Macrophages in the affected tissue release cytokines such as IL-1, TNF-α. This both attracts circulating leucocytes and causes the endothelium to express cellular adhesion molecules such as selectins.
Tight adhesion
Leucocytes express integrins in response to the cytokines. These bind to ICAM proteins on endothelial cells.
Transmigration
PECAM proteins on both endothelial cells and leucocytes interact and facilitate the migration of the leucocytes through the endothelium.