What is antibody affinity?

Antibody affinity refers to the strength of the binding force between an antibody and an antigen. More specifically, it is the measure of how well an epitope on the antigen binds to a single paratope on the antibody. Antibody affinity is influenced by several factors. One factor is that the binding strength relies on the degree of how well the binding site of the antibody matches the shape and chemical properties (stereochemical fit) of the target antigen (epitope). Other factors are size of the region of contact between the antibody and antigen, and the arrangement of charged and hydrophobic components at their interaction site. High affinity antibodies are able to rapidly bind to the antigen, and allow more sensitivity in assays. In contrast, low affinity antibodies bind weakly to the antigen and usually do not detect the antigen in assays or in vivo.