Leukocyte extravasation

Leukocyte extravasation is a process that occurs during the body's immune response to tissue damage or infection. It involves the movement of leukocytes (white blood cells) from the bloodstream into the surrounding tissues. This process is crucial for the body's defense against pathogens and for the healing of damaged tissues.

Process

Leukocyte extravasation involves several steps:

1. Margination and rolling: Leukocytes move to the periphery of the blood vessel due to changes in blood flow and vessel architecture. They then begin to roll along the vessel wall, which is facilitated by selectins, a type of cell adhesion molecule.
2. Activation and adhesion: The leukocytes are activated by chemokines, which are released by cells at the site of infection or injury. This activation leads to the expression of integrins, which allow the leukocytes to firmly adhere to the endothelial cells of the blood vessel wall.
3. Transmigration: The leukocytes move through the endothelial cell layer and underlying basement membrane, a process known as diapedesis. This is facilitated by molecules such as PECAM-1 and CD99.
4. Migration: After exiting the blood vessel, the leukocytes migrate through the extracellular matrix towards the site of infection or injury, guided by chemotactic signals.

Role in disease

While leukocyte extravasation is a crucial part of the immune response, it can also contribute to disease. For example, in inflammatory diseases such as rheumatoid arthritis and atherosclerosis, excessive or inappropriate leukocyte extravasation can lead to tissue damage. In addition, some cancer cells can hijack the process to spread to other parts of the body, a process known as metastasis.

See also

• Leukocyte
• Inflammation
• Immune response
• Chemotaxis

References

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