(Transcribed from Dr. Laville’s lecture, 11 Feb 2000 by Brian Buschman)
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If you centrifuge blood you get the section that is erythrocytes, the buffy coat which is leukocytes and the plasma. The plasma contains many proteins most of which are made in the liver. The notable exception to that rule are immunoglobulins (Igs) which are made by plasma and mast cells. Proteins are lost through passive diffusion into the renal glomeruli or intestinal walls. All plasma proteins play a different role in the body’s processes from maintenance of osmotic pressure of the blood to the immune response.
You can measure the total protein level but it only has a few uses. If the total protein is high it is probably a result of either:
1) Loss of protein free fluid.
2) A major increase in one of ore of the Ig’s.
A decrease in the total protein level is probably from:
1) Dilution of blood near an IV site.
2) Hypoalbuminemia.
3) Serious deficiency in an Ig level.
The more commonly used protein analysis involves using electrophoresis to separate the proteins. The proteins do no separate individually but into five major curves which are (in order) albumin, a1, a2, b, g. One can use raised or lowered levels of the curves as a diagnostic tool.
Albumin is the most abundant plasma protein and is responsible for maintaining the blood’s osmotic pressure so that the proper amount of fluid diffused into the intercellular space but the proper amount comes back into the blood vessels. Albumin has it’s own curve in the electrophoretic pattern.
a-fetoprotein is in the a1 curve. When it is elevated it is usually a sign of either liver cancer in the adult or neural tube defects in the fetus.
a1-antitrypsin is also in the a1 curve and inhibits leukocyte proliferation.
Thyroxine BG is in the a1 curve and binds thyroid hormones. To determine the thyroid hormone level one measures the level of thyroid BG rather then directly measuring the hormones.
Ceruloplasmin is in the a2 curve and functions to transport copper and to oxidize Fe2+ to Fe3+ in the mucosal cells. It can be measured to determine the amount of copper in the body.
Haptoglobin is found in the a2 curve and binds hemoglobin that has escaped from red blood cells.
a2-macroglobin is the largest plasma protein and almost never leaves the blood even if everything else does. This makes it’s rise a good indicator or renal disease. As it’s name implies it belongs to the a2 curve.
Hemopexin is in the b curve and transports escaped heme groups to the liver. It is elevated when heme is released from either Hb or Mb so the level can be up for problems associated with muscle or erythrocytes.
Fibrinogen is also in the b curve and is part of the common clotting pathway. There will be a shortage of fibrinogen if there is a shortage of vitamin K and it will be raised if there is tissue damage requiring blood clotting.
Transferrin is in the b curve and binds and carries iron through the blood stream. It will be elevated in the case of iron overload and decreased with iron shortage.
C-reactive protein is found in the g curve and is responsible for binding and removal of antigens.
Immunoglobulins are found in multiple curves but primarily in the g curve. As we will discuss in great detail in the immune pathways they play a large role in antigen binding and removal.
All the proteins belong to a fraction but when you read a fraction of a gel most of the curve is made up of only one or two proteins.
|
Fraction |
Proteins |
|
Albumin |
Albumin |
|
a1 |
a1-antitrypsin |
|
a2 |
a2-macroglobulin and haptoglobin |
|
b |
Transferrin |
|
g |
Igs |
When one suffers from an acute infection or problem that person will experience a rise in the acute phase proteins which include:
1) Haptoglobin
2) C-reactive protein
3) Ceruloplasmin
4) a1-antitrypsin
5) Fibrinogen
6) a2-macroglobulin
Notice that in an acute phase reaction the levels of the a1, a2 curves will go up right away. After studying the immune system this will make sense but after a little delay the g curve will go up (it takes time for the mechanisms that make Igs to begin to work).
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