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Adhesion made simple by Dr. Mitch!

White blood cells travel through the bloodstream waiting for a signal to leave the blood and enter the tissues.  When that signal is received (probably via cytokines, but that's another lecture), the cells use two main types of adhesion molecules to exit the blood.

The first molecules involved are called....Selectins.

These molecules are involved in causing the white blood cells to slow down and roll along the lining of the vessel wall (the so called, endothelium).  The selectins may be expressed by the endothelium (eg E-selectin) or by the white blood cell (eg L-selectin).  They interact with special sugar-like molecules on other cells ("siayl Lewis-X").

Click here to see a pictoral representation!


The second class of adhesion molecules are called...Integrins!

Integrins are a class of molecules (composed of two chains) that are found on white blood cells.  They bind to certain cell surface molecules on endothelium (members of the immunoglobulin superfamily of proteins), cell-matrix proteins (eg fibrinogen), and complement fragments (eg iC3b).  The interaction between the integrin on the white blood cell and the counter-molecule on the endothelium is quite strong and causes the white blood cell to stick against the lining of the blood vessel.  Then, the white blood cell will crawl through a small opening between the cells lining the blood vessel wall and get into the tissue at the site of inflammation.

Click here to see a pictoral representation!


Well, that's enough for one day--make sure you have your homework done for next time.  And no excuses!!!

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Last update:  January 20, 2012.