Affinity and Avidity of Antibodies
Antibody Affinity
antigen Affinity measures the strength of interaction between an epitope and an antibody’s binding site. It is defined by the same basic thermodynamic principles that govern any reversible biomolecular interaction:gta5线上模式
o K A = affinity constant工程部工作总结>一个微信号可以加多少好友
o[Ab] = molar concentration of unoccupied binding sites on the antibody
o[Ag] = molar concentration of unoccupied binding sites on the antigen
o[Ab-Ag] = molar concentration of the antibody-antigen complex
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In other words, K A describes how much antibody-antigen complex exists at the point when equilibrium is reached. The time taken for this to occur depends on rate of diffusion and is similar
for every antibody. However, high-affinity antibodies will bind a greater amount of antigen in a shorter p
新年卡片eriod of time than low-affinity antibodies. K A can therefore vary widely for antibodies from below 105 mol-1 to above 1012 mol-1, and can be influenced by factors including pH, temperature and buffer composition.
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The affinity of monoclonal antibodies can be measured accurately becau they are homogeneous and lective for a single epitope. Polyclonal antibodies are heterogeneous and will contain a mixture of antibodies of different affinities recognizing veral epitopes –therefore only an average affinity can be determined.
Antibody Avidity
Avidity gives a measure of the overall strength of an antibody-antigen complex. It is dependent
on three major parameters:
o Affinity of the antibody for the epitope (e above)
o Valency of both the antibody and antigen
o Structural arrangement of the parts that interact
All antibodies are IgGs are bivalent and and IgMs are decavalent. The greater an immunoglobulin’s valency (number of antigen binding sites), the greater the amount of antigen it can bind. Similarly, antigens can demonstrate multivalency becau they can bind to more than
one antibody. Multimeric interactions between an antibody and an antigen help their stabilization.
A favorable structural arrangement of antibody and antigen can also lead to a more stable antibody-antigen complex as illustrated in Figures 1 and 2.
Figure 1. An immobilized antigen (a high local concentration of available epitopes) provides more opportunity for the antibody-antigen complex to form than free antigen in solution over the same time period. Once the first antigen binding arm of an antibody attaches to an antigen on a solid support, the chances of a bivalent interaction are greatly improved. Many immunoassays like Western blotting and ELISA exploit this principle.播音稿
Figure 2. When an antigen is mixed with a polyclonal antibody, multivalent interactions may lead
to large, stable (high avidity) structures being formed. This is becau the antigen may be bound
by veral antibodies, each recognizing a different epitope. Polyclonal antibodies are therefore ideal
for immunoprecipitation experiments.
Further Uful Reading
o How we improve the affinity of our recombinant monoclonal antibodies generated using HuCAL? technology through affinity maturation
