Nerdy Science Blog

The terms “affinity” and “avidity” confuse many people. They are popular term use in immunology. Both of them mean the binding strength, but what is the difference between them?

“Affinity” is the strength of binding of one molecule to a ligand. For example, the strength of binding of an antibody to an antigen. Affinity is represented by dissociation constant (K_d). K_d is the value the concentration of ligands need to occupy half of the molecules in a solution. In the context of antibody and antigen, it is the concentration of antigens needed to occupy half of the antibody molecules. Smaller K_d indicates that affinity is stronger, hence less antigen is needed to occupy the antibody sites.

However “avidity” is different from “affinity” as avidity is the sum of total strength of binding of more than one molecules to ligands. The difference between them is that affinity is the binding strength of one molecule site to its ligand, but avidity and affinity are correlated. The strength of avidity depends on the affinity and the valency of interactions. For example, immunoglobulin M (IgM) (one type of antibodies, see figure on the right) has a pentameric shape and 10 antigen-binding sites. The multivalent IgM is able to bind to more antigens than other antibodies, such as IgG.

To simply things, affinity is just like how close you can be with a single person. Avidity represents how many friends you can have. For example, you might be attracted to a person in a party and you stick to her for the whole night, and that is the affinity. In the party, you might be able to talk with several people at the same time, and that is called avidity.

References:

Abbas, A.K., Lichtman, A.H. and Pillai, S. (2007), Cellular and Molecular Immunology (6th edn.), Saunders Elsevier.

Murphy, K., Travers, P. and Walport, M. (2008), Janeway’s Immunobiology (7th edn.), Garland Science.

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What is “cameltoe“?  From the word itself, you can guess that it’s the toe of the camel.  I first learnt about this word was from the movie “Weatherman”, and recently I heard it again from South Park.  Cameltoe is a slang refering to woman wearing tight fitting clothes and showing the outline of vulva.

Recently when I was in the immunology tutorial, my friends and I noticed that there was this guy wearing a really tight outfit, and showing the legendary cameltoe.  He was presenting the development of lymphocytes.  Then his cameltoe reminded us of “antibodies”.

As we know, the immunoglobulin molecules are composed of light chains and heavy chains, which formed the Y shape.  That looks exactly like a cameltoe!  Each immunoglobulin G (IgG) is consisted of two light chains and two heavy chains (like the picture on the left).  Using cameltoe to teach antibodies is really an interesting and memorable way, and that doesn’t make your lecture boring.

I just learn that “cameltoe” is not suitable to use on him, as that is for female.  “Moose knuckle” is the one what is used on males.

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Antibody & Beyond has collected links related to antibody, such as the knowledges, methods, applications, reviews and even where you can find these antibody. E-book in .pdf forms are also available for download on the web. There is also a forum for the global community to discuss about antibody.

Link: Antibody & Beyond: Methods and Techniques For Life Scientists

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