Question

Explain the concept of specificity in the immune system using blood type interactions as an example. Define specificity in the context of immunity and relate this to interactions between different blood types during transfusions. Your answer should define and discuss antigens and antibodies in the ABO blood type system.

Answer 1

SPECIFICITY AND ABO BLOOD GROUP

The specificity of the immune system refers to the  immune system's ability to target a specific antigenic determinant.

In ABO blood group system; there are A and B antigens on the surface of the RBCs and there are antibodies against A and B antigens in the serum. A person with a particular antigen on RBC surface will lack antibody to that specific antigen.

For example, a person with blood group 'A', he has 'A' antigen on RBC surface, but lacks the anti-A antibody in serum. Instead he has Anti-B antibodies. The different blood groups, depending on this are : -

Here, the Anti-A or Anti-B antibodies are 'specific' to the corresponding antigens 'A' or 'B' respectively. When the Anti-A antibody detects an antigen 'A', an immune response is generated. Also, when the Anti-B antibody detects an antigen 'B', an immune response is generated

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BLOOD TRANSFUSION

During transfusion of blood, the donor blood should not have an antigen (say X), against which an antibody is present in the recepiet blood (anti-X)

So, if a person with blood group O recieves tranfusion of blood with group 'A' : then, A and B antibodies present in the recepients blood [group O] and 'A' antigen is present in the donor blood [group A]

Here, the recepient A antibody will detect the A antigen in the donor blood resulting in transfusion reaction. So, this transfusion is not safe.

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Now, if a person with blood group A recieves tranfusion of blood with group O' : then,  B antibodies are present in the recepients blood [group A] and no antigen is present in the donor blood [group O]

Here, the recepient B antibody cannot detect a B antigen in the donor blood. So, there is no transfusion reaction. This transfusion is safe.