Research and diagnostic procedures use antibodies which are usually acquired from laboratory animals such as rabbit or a goat injected with a specific antigen. After a few weeks, the immune system of the laboratory animal will produce high amounts of antibodies specific for the antigen that was injected. The antibodies can be collected in an antiserum, a blood serum containing the antibodies specific to an antigen. The laboratory animal can produce multiple antibodies because most antigens have multiple epitopes. This response is called polyclonal antibody because it results in the production of multiple antibodies. Polyclonal antibody response is also the typical response by the human immune system during infection. Antiserum taken from an animal will carry antibodies from multiple clones of B cells. Each B cell will respond to the antigen’s specific epitope.
Laboratory animals usually receive antigen via injection at least twice when used for antiserum production. The second injection will activate the immune system specifically the memory cells that produce the IgG antibodies against the antigen. The memory cells also go through affinity maturation which results in the production of higher affinity antibodies. Affinity maturation occurs because of mutation in the variable regions of immunoglobulin gene which makes a slightly altered antigen-binding site in B cells. When B cells that can produce high affinity antibodies are re-exposed to the antigen, they will get stimulated to multiply and produce more antibody than their low affinity peers. A substance called adjuvant which enhances the immune system to an antigen, is often mixed together with the antigen before injecting into an animal.
Antiserum taken from animals will contain antibodies against the antigen that was injected and it will also contain antibodies against other antigens to which the animal has been exposed during its lifespan. Antisera are usually purified to remove unwanted antibodies before using for research and diagnostic procedures.
OpenStax Microbiology. Producing Polyclonal Antibodies. Accessed November 23, 2019