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

Can Donate

Antibodies

Can Receive

Red Blood Cell

Blood To

in Serum

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

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.

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