The binding of antigens and antibodies has been described in binding strength terms called affinity and avidity. The binding of antigen and antibody is a reversible process, and is known as agglutination.
What is Affinity?
Affinity is the binding strength between an antigen-binding site at the antibody and an antigen. It is the net result of attractive and repulsive forces between an antigen-antibody interaction. It is the degree of association between an antigen epitope and a paratope or antigen-binding site on an antibody.
What is Avidity?
Avidity is the cumulative strength required for the interaction between a multivalent antibody and a multimeric antigen. It is a collection of affinities but holds a larger value than all the affinities combined.
Affinity vs Avidity
|
Affinity |
Avidity |
| Definition | |
| Affinity is the strength required for an interaction between a site of antigen binding at an antibody and an antigen epitope. | Avidity is the total strength required for the interaction between a multivalent antibody and multiple antigenic epitopes. |
| Occurrence | |
| It is the strength between a single antigen-binding site on an antibody and an epitope of an antigen. | It is the total binding strength between multimeric antigen-antibody reactions. |
| Value | |
| It is a balance between attractive and repulsive forces. | It is larger than the sum of all affinities combined. |
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Also Read:
- What Are the 3 Antigen Presenting Cells?
- What is the difference between antigen and pathogen?
- Difference Between Antigen and Antibody
Frequently Asked Questions
What is the difference between antigen affinity and avidity?
Affinity is the interaction between a single antigen binding site at the antibody and an antigen epitope, whereas avidity is the total strength of interaction between a multimeric antigen and a multivalent antibody.
What are the applications of avidity?
The avidity test for rubella, HIV, hepatitis and Epstein-Barr Virus (EBV) can be used to detect acute, recurrent or past infections by checking the avidity of IgG.
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