You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Most important for diapedesis? and explain in detail?
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.