Difference between Affinity and Avidity

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 and an antibody.

What is Avidity?

Avidity is the cumulative strength required for interaction between a multivalent antibody with a multivalent 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 antibody and an antigen epitope.

Avidity is the total strength required for interaction between a multivalent antigen with more than one antibody.

Measurement

It can be measured in thermodynamic terms.

It is measured in kinetic terms.

Occurrence

It is the strength between a single antibody and antigen.

It is the strength between multiple antibodies and antigens.

Value

It is a balance between attractive and repulsive forces.

It is larger than the sum of all affinities combined.

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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 multivalent antigen with more than one antibody.

Is avidity the sum of all affinities?

No, avidity is larger than the sum of all affinities.

What are the applications of avidity?

The avidity test for rubella, HIV, hepatitis and epstein-barr virus can be used to detect the acute, recurrent or past infections by checking the avidity of IgG.

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