Blood Type
Antigens And Antibodies
To understand blood typing, it is necessary to define antigen and antibody. An antigen is a substance, usually a protein or a glycoprotein, which, when injected into a human (or other organism) that does not have the antigen,
| RELATIONSHIPS BETWEEN BLOOD TYPES AND ANTIBODIES | ||||
| Blood Type | Antigens on Red Blood Cell | Can Donate Blood To | Antibodies in Serum | Can Receive Blood From |
| A | A | A, AB | Anti-B | A, O |
| B | B | B, AB | Anti-A | B, O |
| AB | A and B | AB | None | AB, O |
| O | None | A, B, AB, O | Anti-A and anti-B | O |
will cause an antibody to be produced. Antibodies are a specific type of immune-system proteins known as immunoglobulins, whose role is to fight infections by binding themselves to antigens. In the case of the ABO blood groups, the antigens are present on the surface of the red blood cell, while the antibodies are in the serum. These antibodies are unique to the ABO system and are termed "naturally occurring antibodies." The table shows the relationships between blood types and antibodies.
This aspect of the ABO blood group system is very important in transfusion. Blood group O individuals are said to be universal donors, because their blood can be used for transfusion in individuals who have any one of the four blood types. On the other hand, individuals with blood type A can only donate to either type A or type AB, and individuals with blood type B can only donate to B or AB types. AB individuals can only donate to type AB. However, before any transfusions, donor blood is mixed with serum from the recipient (a process called cross matching) to ensure that no agglutination will occur after transfusion.
Additional topics
Medicine EncyclopediaGenetics in Medicine - Part 1Blood Type - Antigens And Antibodies, Multiple Alleles, The Rh System