What is the Difference Between Affinity and Avidity?
🆚 Go to Comparative Table 🆚Affinity and avidity are terms used to describe the strength of the bond between an antibody and its antigen. Although they both involve binding strength, they have distinct meanings and should not be used interchangeably.
Affinity refers to the strength of the interaction between a single antigen-binding site on an antibody and an epitope of an antigen. It is the net result of attractive and repulsive forces between an antigen-antibody interaction and is usually measured by the dissociation constant (K_d), which is the rate of dissociation of the antibody from the antigen.
Avidity, also known as functional affinity, represents the overall strength of the antibody-antigen interaction and is influenced by three major parameters: binding affinity, valency, and the structural arrangement of the antibody and antigen. Avidity measures the total binding strength between a multivalent antibody and a multimeric antigen. It can define the strength of polyclonal antibody populations and takes into account the increase in binding strength resulting from the presence of multiple antigen-binding sites on an antibody.
In summary, affinity is the strength of the interaction between a single antigen-binding site on an antibody and an antigen, while avidity is the total strength of the interaction between a multimeric antigen and a multivalent antibody, taking into account multiple antigen-binding sites.
Comparative Table: Affinity vs Avidity
Affinity and avidity are terms used in immunology and microbiology to describe the binding strength between an antibody and an antigen. Although they are related concepts, they have distinct differences. Here is a table highlighting the key differences between affinity and avidity:
| Characteristic | Affinity | Avidity |
|---|---|---|
| Definition | Affinity is the strength of the interaction between a single antigen-binding site on an antibody and an antigen epitope. | Avidity is the total strength of the interaction between a multivalent antibody and a multimeric antigen. |
| Binding Site | Affinity describes the strength of a single binding site on a receptor. | Avidity describes the overall strength of the interaction between multiple receptors and multiple ligands. |
| Intrinsic/Extrinsic Property | Affinity is an intrinsic property, meaning it is inherent to the individual binding site. | Avidity is an extrinsic property that depends on the overall configuration of the receptor and the ligand, as well as their concentrations and valencies. |
| Applications | Affinity is used to measure the binding strength of individual antibodies to their target antigens. | Avidity is used to detect acute, recurrent, or past infections by checking the avidity of IgG antibodies for certain pathogens, such as rubella, HIV, hepatitis, and Epstein-Barr Virus (EBV). |
| Examples | IgE antibodies have two binding sites, and their affinity is the strength at just one of these binding sites. | The cumulative binding strength of an antibody like IgM, which has ten binding sites and recognizes the same epitope, is called avidity. |
In summary, affinity refers to the binding strength at a single binding site, while avidity measures the total binding strength in interactions involving multiple binding sites. Understanding these differences can help improve the interpretation of experimental results and the design of more effective therapeutic strategies.
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