The biology of blood groups

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The biology of blood groups

The blood groups refer to the presence in the erythrocyte membrane of certain antigens, “the blood group substances”. Chemically, they are glycolipids and are inherited as Mendelian dominants.

The most widely studied blood group is the ABO system. Besides, the other well-known blood group systems are the Rh system, the MN, Kell, Lutheran, Duffy, Diego, and Kidd system.



BLOOD GROUP ANTIBODIES

Antibodies are generated primarily in the bone marrow, spleen, liver and lymph nodes. The blood group antibodies are associated with the serum globulins. It can be divided into two types:

(I) Immune and (ii) Naturally Occurring.

(i) Immune Antibodies

During transfusion of blood, if the blood of the person containing Rh antigen is transfused into a person who lacks this antigen, the recipient is immunized and the corresponding antibody appears in his blood. In the case of a pregnant female, a fetus can carry Rh antigen into a Rh‾ mother, and produce immune antibodies which can be fatal for the next child.

These Immune blood antibodies of γG globulins (IgG) having molecular between 150,000 to 160,000. They are minute enough to cross the placenta.

(ii) Naturally Occurring Antibodies

Anti-A and Anti-B immune globulins are two naturally occurring antibodies found in the blood of human beings who is never immunized by any blood antigen. They are present in the new-born babies of both animals and humans

These antibodies are γM globulins (IgM) having a molecular weight approximately 900,000. They are large and cannot cross the placenta.

THE ABO SYSTEM

Karl Landsteiner (1900) discovered two different antigens in the red blood cells of man. For convenience, he termed them as ‘A’ and ‘B’. He observed that the cells could either contain 'A' or 'B' or both 'A' and 'B' together as 'AB' or contain none of them. De Castello and Sturli (1902) discovered ‘O’ type blood group. Karl Landsteiner observed that the serum of human beings contains antibodies which can react with the antigen not present in the erythrocytes. 

IMPORTANCE IN BLOOD TRANSFUSIONS

The blood of the same group has to be transfused into the recipient or else due to the presence of antibodies in the plasma of the recipient transfused blood cells can agglutinate. The figure given below gives the clear chart of the donor and the recipient:


THE RHESUS SYSTEM (Rh)

In 1940 Landsteiner and Weiner discovered a different antigen in the blood of rhesus monkey also present in the red blood cells of about 85% human beings. Persons having Rh antigen in their red cells are called Rh positive (Rh⁺). About 15% people do not possess Rh antigen are called as Rh negative (Rh‾). No person has found to contain natural anti-Rh bodies but Rh‾ person can develop these antibodies if exposed to Rh antigen, for example, in blood transfusion with Rh⁺ blood, or Rh‾ woman who had borne Rh⁺ children.

TRANSFUSION OF RH BLOOD

The following chart gives a clear picture of the combinations of ABO system and Rhesus System in humans and their transfusion:



If the blood of Rh⁺ is transfused into Rh‾, the recipient may not show any sign of incompatibility but if similar transfusion is done after 15 days or years later a serious or even fatal reaction may occur due to the formation of antibodies in the recipient’s red cells.

The blood groups refer to the presence in the erythrocyte membrane of certain antigens, “the blood group substances”. Chemically, they are glycolipids and are inherited as Mendelian dominants. The most widely studied blood group is the ABO system.

Rh system, the MN, Kell, Lutheran, Duffy, Diego and Kidd system are some other blood group systems.

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