Plasma membrane-ABO blood groups

The cell membrane is often described as a fluid mosaic. The cell membrane resembles a mosaic because of the many proteins that are embedded in a framework of phospholipids. The membrane is fluid which allows for the proteins to drift while the phospholipid bilayer remains intact.

The outside layer of the membrane is quite different to the internal layer. The outside surface has carbohydrates (chains of sugar molecules), shown in pink, bonded to proteins and to the phospholipids. A protein with sugars attached to it is called a glycoprotein, while a lipid with sugars attached is called a glycolipid. The sugar portion of glycolipids and glycoproteins differs from species to species and from individual to individual in a particular species.

Different cell types within the same individual have different sugar portions attached to the glycoproteins and glycolipids. We can therefore say that they function as tags identifying the individual, cell type and species. The immune system uses these to identify foreign cells such as bacteria and destroy them. Unfortunately the immune system also recognises beneficial transplanted cells as foreign and attacks them.
The glycolipids on the surface membrane of red blood cells are of particular importance as they play a critical role in life saving blood transfusions. These glycolipids form the ABO antigens and one red blood cells may have up to 800,000 antigen sites on its surface. These antigens are also present in other tissues as well as red blood cells which poses a problem in organ transplant.

In this unit we will take a simple view of the ABO blood grouping without looking at the Rh factor.

Two types of antigens are present on the surface of red blood cells and all of the red blood cells in an individual contain the same antigens. A person whose red blood cells have the "A antigen" has the blood type A. People whose red blood cells have the "B antigen" have the blood type B. Some people have red blood cells that contain both "A and B antigens" so they have the blood type AB. Other people have red blood cells with "neither A nor B antigens" so they have the blood type O.

Individuals with blood type O have no ABO antigens and therefore, their blood will not be rejected when it is given to to individuals with blood type A, B or O.  People with blood type O are known as universal donors but they themselves can receive blood type O only. 

Individuals with blood type AB do not make any A or B antibodies.  Their immune system does not reject blood types A, B or O.  Consequently, they are known as universal receivers. However, their blood will clot when given to people with every other type because they produce both A and B antigens.
The rules for blood transfusion were developed by a scientist by the name of Karl Landsteiner in 1900. These rules for the ABO Blood Group are:
- A person does not have antibody to his own antigens
- Each person has antibody to the antigen he lacks (only in the ABO system)
A summary is given in the table below.
Blood group
Antigen on the red cell membrane
Antibody found in the body
A
A
anti-B
B
B
anti-A
AB
A and B
neither A or B
O
neither A or B
anti-A and anti-B

Below is a table showing safe transfusions. (taken from http://www.mun.ca/biology/scarr/ABO_bloodgroup_transfusions.html 5/01/2015 10.11 AM)
Antibodies are proteins produced by white blood cells that have a specific shape for certain antigens and form part of the immune system. Now a person with blood type A will have antibodies in their blood that will act against the B antigen and a person with blood type B will have antibodies against the A antigen. A blood transfusion of the wrong type can be fatal for the antibodies will act against the foreign blood type, as shown on the right.

People who have the blood type AB produce antibodies against which antigens?

Those with blood type O produce antibodies against which antigens?

What antibodies does someone with the B Blood Type produce?

Can a person with Blood Type A give blood to a person with Blood Type O? Explain.

Which blood type is known as a universal receiver? Explain

Which blood type is known as a universal donor? Explain
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