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!!!
Send Dr. Mitch some email!!....
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Grayson. All rights reserved.
Last update: January 20,
2012.