Hemagglutination/Blood Typing (an agglutination reaction): ( Prescott, et. al., page 650)
Human red blood cells (erythrocytes) have many glycoprotein and glycolipid components on their cell membrane surfaces that have antigenic properties. The surface antigens are genetically determined, and a person's blood type is inherited. Although many different types of glycoproteins and glycolipids may be unique to an individual, there are some antigens that appear to be common to most people. Two major classifications of human red blood cells are ABO grouping and the Rh system.
ABO Blood Grouping
ABO blood grouping is based on differences in the type of glycoprotein (protein with carbohydrates attached) present on the surface of red blood cells. Type A individuals have type A glycoproteins; Type B individuals have type B glycoproteins; Type AB individuals have both; and Type O individuals have neither. An individual's ABO blood type is commonly determined by using antibodies specific for type A and type B glycoproteins. Antibody-A (Anti-A) and Antibody-B (Anti-B) combine with A and B antigens, respectively. The binding of these antibodies to the surface antigens of red blood cells will result in clumping, or hemagglutination.
ABO typing of a blood sample:
Blood sample mixed with type A specific antibody -------> hemagglutination is observed.
*This result indicates that type A glycoproteins are present on the red blood cells.
Blood sample is mixed with type B specific antibody -------> NO hemagglutination
*This result indicates that type B glycoproteins are NOT present.
This blood sample would be Type A.
Humans normally do not produce antibodies to a particular antigen until they are exposed to it; however, the ABO system is an exception. Antibodies to the ABO blood group antigens that are NOT present on their own erythrocytes are commonly produced in humans without ever being directly exposed to them. It is thought that these antibodies are formed in response to antigens of the intestinal normal flora that are similar to the blood group substances. The antibodies could then cross-react with antigens on the appropriate red blood cell. Type A people have the anti-B antibody in their plasma; type B people have anti-A antibody; type AB people have neither of these antibodies (universal acceptor); and Type O people have both antibodies (universal donor). It is for this reason that blood is typed before being transfused from one person to another. Donor and recipient must be compatible, or a severe hemagglutination reaction may occur in the recipient causing blockage of blood vessels and serious circulation problems.
Rh System
The second major classification of human blood types is the Rh system. Rh stands for rhesus; this factor was first identified in the blood of rhesus monkeys. Rh classification is based on the presence or absence of the RhD antigen on red blood cells. RhD positive people have the RhD antigen; RhD negative people do not. About 85% of all the people in the United States are RhD+. Similar to the ABO system, the presence of the RhD factor on red blood cells is determined by using anti-RhD antibody in a hemagglutination reaction.
In contrast to the ABO system, RhD (-) people do not have RhD antibodies in their plasma. They must be exposed to the RhD antigen to develop the antibodies. For example, anti-RhD antibodies develop in an RhD- person over a period of several months following an accidental transfusion of RhD(+) blood. Once this has happened, a second transfusion can result in a severe hemagglutination reaction.
A serious problem may also occur when an RhD(-) mother and an RhD(+) father have and RhD(+) child. The child produces red blood cells with the RhD antigen, which gains access to the mother's circulation when the placenta ruptures during childbirth. Responding to the foreign RhD antigens, the mother produces anti-RhD antibodies that are able to cross the placenta. During any subsequent pregnancy, the RhD(-) mother may produce enough anti-RhD antibodies to agglutinate and destroy the red blood cells of the RhD (+) child, producing hemolytic disease of the newborn. Hemolytic disease causes liver and spleen enlargement resulting in decreased function, fluid accumulation, congestive heart failure and possibly death. This disease can be prevented by injecting the RhD(-) mother with Anti-RhD antibodies (RhoGam) within 72 hours after delivery of the first child. These passively administered antibodies prevent the mother from developing antibodies against the RhD antigen of the RhD(+) red blood cells that have entered her circulation.
In today's lab we will determine the ABO and Rh blood type of two different samples using a simulated human blood typing kit.