Affinity vs Avidity: Difference and Comparison

Affinity and Avidity are the terms that are connected with the study of the immune system that is immunology. The term is linked with the antibodies produced by the body’s immune system against the foreign bodies that enter the body.


Science Quiz

Test your knowledge about topics related to science

1 / 10

What is the function of root hair cells?

2 / 10

The first link in all food chains is-

3 / 10

Chemical formula for water is

4 / 10

Name the veins that carry oxygenated blood from the heart to other parts of the body?

5 / 10

Washing soda is the common name for

6 / 10

Which among the following is not a synthetic fiber?

7 / 10

Which of the following organism breathes from skin?

8 / 10

Which is the type of food having maximum energy?

9 / 10

Non-stick cooking utensils are coated with

10 / 10

Acid turns blue litmus paper into which color?

Your score is


Key Takeaways

  1. Affinity measures the strength of a single binding site between a ligand and a receptor; avidity refers to the overall binding strength between a multivalent ligand and its target.
  2. Affinity measures the binding strength of one binding site; avidity considers the cumulative strength of multiple binding sites.
  3. Avidity is more relevant for evaluating the functional strength of interactions involving multivalent ligands and receptors.

Affinity vs Avidity

Affinity is measured by the equilibrium dissociation constant (Kd), which is the concentration of antigen required to dissociate 50% of antibody-antigen complexes. Avidity is the strength of the interaction between a multivalent antibody and a multivalent antigen, determined by the affinity of the individual binding sites.

Affinity vs Avidity

Affinity, in simple words, can be stated as the bond strength between the antigen and the antibody. The only point that must be considered is that affinity is determined for a single antibody and antigen relationship molecule.

The three main factors for determining avidity are – valency, the arrangement of the structure, and binding strength. The antibody IgM is a very good example of Avidity. 

 Comparison Table

Parameters of ComparisonAffinityAvidity
DefinitionThe attraction between the antibody and its specific antigenAttraction or the strength between the multiple affinities
SignificanceBetween the epitope and the paratopeProduced by multiple affinities
Antigen-Binding Number Monovalent or DivalentMultivalent
ExampleIgD, IgE, IgG, and ABO antibodiesIgM
Expressed InThermodynamic termsKinetic terms
Terms of calculationSingleMultiple

What is Affinity?

The affinity of a molecule can be stated as the force of attraction between the antibody having its paratope and the antigen having an epitope specific to the binding site.

Four different types of interactions help in participating at the binding site – hydrogen bonds, hydrophobic bonds, van der Waal forces, and electrostatic bonds.

Even the term is measured or expressed in the form of thermodynamic terms. Examples of affinity are the antibodies IgG, IgE, IgD, and ABO antibodies.  

What is Avidity?

Antibodies tend to have multiple binding sites on their surface that may be up to 2 to 10 in number. Thus avidity is the sum of the strength of the multiple affinities given for the multiple antibodies with multiple binding sites.

There are three different factors that affect or influence avidity, and they are – the structure of the arrangement, the binding strength, and the valency.

In simple words, avidity can be explained as the individual sum of the affinity of the multiple paratopes with its specific binding antigen or epitope. The capacity of the IgM antibody is five times more than that of IgE, and it is the best example of avidity. 

Main Differences Between Affinity and Avidity

  1. The affinity of a molecule can be expressed through thermodynamical terms, whereas comparatively, on the other hand, the avidity of a molecule can be expressed only through kinetic terms. 
  2. The terms of calculation of affinity are based on a single molecule of antibody to its specific binding antigen, whereas comparatively, on the other hand, the terms of calculation of avidity are based on antibody with multiple sites to antigen with multiple sites.  
One request?

I’ve put so much effort writing this blog post to provide value to you. It’ll be very helpful for me, if you consider sharing it on social media or with your friends/family. SHARING IS ♥️

Leave a Comment

Your email address will not be published. Required fields are marked *

Want to save this article for later? Click the heart in the bottom right corner to save to your own articles box!

Ads Blocker Image Powered by Code Help Pro

Ads Blocker Detected!!!

We have detected that you are using extensions to block ads. Please support us by disabling these ads blocker.