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Blood Groups
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The A, B O blood grouping system refer to the antigens on the surface of the red blood cells. Antigens are proteins. In blood there are chemicals called antibodies which attach themselves to proteins not normally found in the body (non-self) and cause them to agglutinate (stick together). These clumps of protein (or it may even be whole bacteria or viruses) can then be destroyed by white blood cells. Hence a person with the blood group A will have antigen A on the surface of their red blood cells and antibody b in their plasma (i.e. they carry the antibodies to the antigens they don't have themselves).
A person with the blood group O has no antigens on the surface of their red blood cells but both a and b antibodies in their plasma.
| Blood group |
A
|
B
|
AB
|
O
|
| antigens on red blood cells |
A
|
B
|
AB
|
-
|
| antibodies in plasma |
b
|
a
|
-
|
ab
|
This obviously has implications for blood transfusion. If blood carrying a particular antigen comes into contact with plasma containing the complementary antibody agluttination will take place. For example somebody with blood group B could not have blood group A blood transfused into them. The A antigens on the donors blood would react with the b antibodies in the recipents blood.
| recipient |
donor
|
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|
A
|
B
|
AB
|
O
|
||
|
A
|
safe
|
no
|
no
|
safe
|
|
|
B
|
no
|
safe
|
no
|
safe
|
|
|
AB
|
safe
|
safe
|
safe
|
safe
|
|
|
O
|
no
|
no
|
no
|
safe
|
|
The antibodies present in the donor blood are unimportant, they are soon get diluted.