blood would attack the A antigens on the RBCs in the donor blood, as shown inFigure
18.19. The antibodies would cause the RBCs to clump together, and the clumps could block
a blood vessel. Such a reaction could be fatal.
Figure 18.19: A person with type O blood has A and B antibodies in their plasma; if the
person was to get type A blood instead of type O, Their A antibodies would attach to the
antigens on the RBCs and cause them to clump together. ( 14 )
The Rhesus System
The second most important blood group system in human blood is the Rhesus (Rh) system.
The Rh blood group system currently consists of 50 blood group antigens, including the 5
antigensD, C, c, E, and e. The commonly used terms Rh factor, Rh positive and Rh negative
refer to the D antigen only. A person either has, or does not have the Rh(D) antigen on
the surface of their RBCs; written asRh(D) positive(does have the RhD antigen) orRh(D)
negative(does not have the antigen).
Blood Donors
Recall that people with type O blood do not have any antigens on their RBCs. As a result,
type O blood can be given to people with blood types A, B, or AB. If there are no antigens
on the RBCs, there cannot be an antibody reaction to the blood. People with type O blood
are often calleduniversal donors.
The blood plasma of AB blood does not contain any anti-A or anti-B antibodies. People
with type AB blood can receive any ABO blood type. People with type AB positive blood
are calleduniversal recipients. The antigens and antibodies that define blood type are
listed inTable(18.2).
In April 2007 researchers discovered a way to convert blood types A, B, and AB to O. The
researchers used enzymes to remove the antigens on the surface of the RBCs. This discovery
could lead to producing or modifying blood cells that can be used as donors to people with
all blood types.