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Leukocyte Extravasation

When an inflammation develops as a response to a sickness or an imbalance in the body happens a number of cytokines as well as other mediators are produced. These cytokines and mediators produces a reaction on the endothelial cells of the local blood vessels that results in a state of activation of inflammation. Leukocytes, among them neutrophils, recognize that the endothelium is becoming inflamed and what results is that the leukocytes attempt to extravasate and migrate to the affected site (the site of infection) based on a sequential and overlapping four step process. These four steps are 1) rolling, 2) activation, 3) arrest of rolling and the adhesion to the endothelial cell surface, and 4) transendothelial migration.

Chemoattractants that include chemokines and other molecules (among them platelet activating factor) intervene in the activation of the process. By binding the said chemoattractants to receptors on the leukocyte membrane, a G protein mediated activation signal is triggered and this results in a larger increase in the attraction of the integrin molecules on the membrane of the leukocyte. This increased attraction, on the other hand, causes the leukocyte to adhere to the ICAM molecules that are located on the surface of the endothelial cells. By using the ICAM molecules as a point of adhesion, the leukocyte then tries to push in between the cells of the endothelium and try to enter the surrounding tissue. Once it has achieved this, the leukocyte increases the concentration of the chemoattractant molecules that are being produced in that particular site.

Web Resources On Leukocyte Extravasation

Leukocyte extravasation: chemokine transport and presentation by the endothelium
Leukocyte rolling and extravasation in surgical inflammation after mechanical and laser-induced trauma in human patients

Book Resources On Leukocyte Extravasation

Molecular Approaches to Cell-Cell Adhesion: From Leukocyte Extravasation to Embryo Implantation by Hans Werner Denker
Leukocyte Recruitment, Endothelial Cell Adhesion Molecules, and Transcriptional Control by Tucker Collins

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