BIOC 212 Lecture Notes - Lecture 29: Glycosylphosphatidylinositol, Cysteine, Cnidaria
29 May 2018
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Cell Junctions & Cell Adhesion IX
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Function of Selectins
• When have inflammation, WBCs (lymphocytes) crawl out of the bloodstream at the
site of inflammation
o Clear the wound and take care of bacteria
• How do they come out of fast flowing bloodstream into target tissue?
o Must be slowed down
o Do this with help of selectins
• Inflamed endothelial cells express selectins that bind weakly to lectins on WBCs
(oligosaccharides)
o Binding & release interaction slows down the cells
o Start rolling along endothelial cell lining
o Then other cell adhesion molecules help them anchor firmly on the
endothelial cell
• Integrins
• Then can start extravasation; get out of bloodstream into tissue
• How selectins and integrins mediate the cell–cell adhesions required for a white
blood cell to migrate out of the bloodstream into a tissue:
o Binding white blood cells to endothelial cell linings
• Migrate out of the bloodstream into the tissue.
o In lymphoid organ, endothelial cell express oligosaccharides recognized by
L-selectin on lymphocytes
• Cells become trapped
o Conversely at the inflammation site, EC express selectins which recognize
the oligosaccharides on lymphocytes
• Flag the lymphocytes to help
• Selectins act in combination with integrins which strengthen the binding of blood
cells to the endothelium.
• Cell-cell adhesion mediated by selectins and integrins are of the heterophilic type
o Selectins bind to specific oligosaccharides on glycoproteins and glycolipids,
while integrins bind to specific proteins.
• Selectins and integrins act in sequence
1. The selectins mediate a weak adhesion = rolling
2. Rolling continues until the blood cell activates its integrins = stronger binding
to the EC
3. Crawl out of the blood vessel between adjacent EC.
Ig-like Cell Adhesion Proteins (N-CAM)
• Cadherins, selectin & integrins depend on Ca2+
