Most important for diapedesis?

o Platelet endothelial cell adhesion molecule (PECAM or CD-31) is present on both endothelium and leukocytes. o It is the major adhesive molecule for diapedesis. Leukocyte and endothelial adhesion molecules o Leukocyte adhesion and transmigration are regulated largely by binding of complementary' adhesion molecules on the leukocyte & endothelial surface and by chemical mediators, o Cytokines affect these processes by modulating expression of adhesion molecules so that leukocytes can firmly adhere to endothelium. o There are four molecular families of adhesion receptors. 1. Selectin o Selectins function in the cell to cell interaction i.e., adhesion of leukocytes to endothelium, o E-selectin (CD-62 E) is present on endothelial cells and it binds to sialyl-lewis, (a sialylated form of oligosaccharide on leukocytes). o Endothelial cell expression of E-selection is a hallmark of acute cytokine-mediated inflammation, o P-selectin (CD-62 P) is present on endothelium and platelets and it binds to sialyl-Lewis on leukocytes, o L-selectin (CD-62 L) is present on leukocytes and it binds to mucin-like glycoprotein GlyCAM-1 on endothelium. 2. Immunoglobulin family o Present on endothelium o ICAM-l (intracellular adhesion molecule-1) binds to β2-integrins (VLA-4) of leukocytes, o Platelet endothelial cell adhesion molecule (PECAM or CD-31) is present on both endothelium and leukocytes. It is the major adhesive molecule for diapedesis. 3. Integrins o Integrins promote cell-cell or cell-matrix interaction ( in contrast to selectins that promote only cell-cell interaction) i.e., integrins helps in adhesion of leukocytes to endothelium and adhesion of leukocytes to an extracellular matrix such as fibronectin, vitronectin, activated complement, o Present on leukocytes o β1 - integrins (VLA-4) bind to VCAM-1 of endothelium, o β2 - integrins (LFA-1 and MAC-1) bind to ICAM-l of endothelium. 4. Mucin-like glycoprotein o These glycoproteins are present in the extracellular matrix and on the cell surface, o An example is Heparan sulfate, that serves as a ligand for the leukocyte adhesion molecule CD-44.