Question

Universal donors have no antigens on the RBC’s but have both antibodies anti-A and anti-B. They belong to the group
(a) A
(b) B
(c) AB
(d) O

Answer 1

Universal donors are the ones whose blood doesn’t react with any other recipient’s blood during blood transfusion due to antigen-antibody reactions. It was discovered along with other blood groups by Karl Landsteiner.
Complete Step by Step Answer: There are certain molecules on the surface of all the cells in the body that can be recognized as foreign by the immune system of another individual and hence can induce the immune system of the latter. These molecules are called Antigens. As part of the immune response, particular lymphocytes, secrets a class of proteins called antibodies that bind to the specific antigens. Since in- group ‘O’ there are no antigens on the RBCs and have both antibodies anti-A and anti-B there will be no transfusion reaction to cause agglutination of the donor’s blood. Thus, it is known as ‘Universal Donor’ as it can be donated to other persons with any other blood group.
So, the correct answer is, '(d) O'.
Additional Information: There are many ways of blood grouping. The most common blood grouping systems are ABO Blood grouping and Rh grouping. Karl Landsteiner (1901) along with his co- workers recognized four types of blood groups in human beings, commonly known as ABO blood grouping. Abo grouping is predicated by the presence or absence of 2 surface antigens on the RBCs particularly A and B. Similarly, the plasma of different individuals also contains two natural antibodies called anti-A and anti-B.

BLOOD GROUP ACCORDING TO ABO GROUPING.	ANTIGENS	ANTIBODIES	DONOR’S GROUP ACCORDING TO ABO GROUPING.
GROUP A	ANTIGEN A	ANTI-B	GROUP A, O
GROUP B	ANTIGEN B	ANTI-A	GROUP B, O
GROUP O	NIL	ANTI-A, ANTI-B	GROUP O
GROUP AB	ANTIGEN A, B	NIL	GROUP AB, O, A, B

Note:
- According to Landsteiner’s law, if antibodies are present in the plasma, the corresponding antigen must be absent from the RBCs.
- It also states that if the antigen is absent on the RBCs, the corresponding antibody must be present in the plasma and vice- versa.
- The immune system exhibits tolerance to its red blood cell antigens.
- If the blood of a person containing an antibody is donated to a person having the corresponding antigen, the recipient’s immune system will attack the donor’s blood and will cause agglutination of the blood. Thus, thorough cross- matching is very important before blood transfusion.
- AB blood groups are the universal recipient because they lack antibodies in plasma but contain both A, B antigens.