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Karl Landsteiner along with his coworkers recognized four types of blood groups in human beings, commonly called as ABO blood grouping.

Explanation:

The membrane of RBCs possess several antigens. Depending on the nature of antigens on the surface of RBCS various types of blood grouping has been done. Two such groupings are The ABO and Rh grouping and are widely used all over the world.  

ABO grouping:  

There are four types of blood groups in human beings. ABO grouping is based on the presence or absence of two surface antigens on the RBCs namely A and B. Similarly, the plasma of different individuals also contain two natural antibodies called anti-A and anti-B.

If an antigen is present on the surface of RBCs, the corresponding antibody must be absent from the plasma and if the antigen is absent on the RBCs, the corresponding antibody must be present in the plasma.  

Blood group A has A antigen on RBCs and anti-B antibody in plasma

Blood group B has B antigen on RBCs and anti-A antibody in plasma

Blood group AB has A and B antigen on RBCs and no antibody in plasma

Blood group O has no antigen on RBCs and both anti-A and anti-B antibody in plasma

Rh grouping:

Another group of antigens found on the RBCs of most people is the Rh factor. People who have this antigens are said to be Rh+ve whereas those who do not are called Rh-ve. Rh groups should also be matched before transfusion because A Rh-ve person if exposed to Rh+ve blood , will form specific antibodies against the Rh antigen.  

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