Antibody affinity refers to the strength with which the epitope binds to an individual paratope (antigen-binding site) on the antibody. High affinity antibodies bind quickly to the antigen, permit greater sensitivity in assays and maintain this bond more readily under difficult conditions. Low affinity antibodies, by contrast, bind weakly to the antigen and often do not detect the antigen in-vivo or in assays.
Because antibodies can potentially be generated against millions of unique epitopes, the size of an organism’s genome would need to increase exponentially in order to code for every possible antigen-binding site. As a result, B-cells use a unique process called somatic hypermutation where the genes responsible for coding the antigen-binding site mutate rapidly in response to the antigen.
As successive generations of B cells mutate and are presented to the antigen, only those that recognize the antigen with high affinity will survive while B cells producing antibodies with low affinity will be eliminated. This process is known as affinity maturation.
From a custom antibody production perspective, this is critical because when the immune system is initially presented with a particular antigen, there will be a mix of low and high affinity antibody producing B cells (also known as clones). With time and continued exposure to the antigen, however, only the superior clones producing high affinity antibody will survive. It is for this reason that short or accelerated immunization protocols should be avoided.