Question

Please explain the antigen and antibody relationship in hemagglutination

Answer 1

Antigen react with specific antibodies to form antigen-antibody complex. When a particulate antigen react with corresponding antibody it leads to formation of a clump,this visible clumping is called agglutination.Haemoagglutination is routinely perform in blood group typing. The RBC is are mixed with antibodies to blood group antigen A and B on slide. If the antigens are present on RBC surface, they clump together and agglutinate.

Depending on the type of antigen present or absent, blood grouping is decided and matched. For example,if a person has 'A' blood group ,his RBCs have A antigen and will show following reaction:

The A antigen present on the RBC of the person with blood group A will react with antibodies 'A' and not 'B' because plasma of A blood group person have antibody B. So antigen A present on RBCs surface will agglutinate with antibody A and form clump .

Similarly,   B blood group antigen show agglutination with antibod' B'.

AB blood group agglutinate in presence of both antibody A and B because both antigen A and B are present on RBCs surface of AB blood group person.

O blood group does not aggulinate with neither of the two antibodies ie, A and B antibodies because O blood group person lack both antigen A and B on their RBCs surface.

Cross matching of blood groups  is done by mixing the blood of Donor and recipient. If there is clumping on mixing, the samples are mismatches. But if the group is same then both contain same antigen and antibodies and so no clumping is seen.For example, if both donor and recepient are A group then both have A antigen and B antibody and so no agglutination occurs.

Blood group	Antigen present on the RBCs surface .	Antibodies present in blood plasma	HaemoAgglutination antibody Reaction
A	A	antibody B	antigen A + A-antibody --> Ag -Ab clumping(haemoagglutination)
B	B	antibody A	antigenB + antibody A--->Ag-Ab clumping(haemoagglutination)
AB	A, B	both A and B antibodies are absent	Antigen A+ antibody A--->Ag-Ab Clumping Antigen B+ antibody B----> Ag-Ab clumping
O	Both A and B antigen are absent	Both A and B antibodies are present	No antigen hence no haematoagglutination reaction with neither of two Antibodies ie antibody A and B.