Leukocyte Extravasation

Activated vascular endothelium cell express E-selectin and ICAM-1 and display chemokines on extracellular matix.leukocytes initiatly adhere by binding to selectins which recognise S-lex.these allows other molecules to bind,LFA-1 binds to ICAM-1,chemokine signalling converts this weak binding to tight adhesion.

• The tightly bound leukocytes now migrates across the endothelium squeezing between adjacent endothelial cells.
• Chemokine binding now signals leukocytes to migrate along the chemokine concentration gradient .
• The site of information is the source of chemokine gradient .hence leukocytes are attracted from the blood towards sites of infection.