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What is a polyclonal antibody?
A polyclonal antibody preparation consists of a mixture of different antibodies, also known as immunoglobulins, which bind to different parts of the same target. The target, also known as an antigen, is commonly a protein or small molecule. Each antibody binding site on the target is known as an epitope.
The advantage of polyclonal antibody preparations is that they are relatively quick, inexpensive and easy to produce in comparison to monoclonal antibodies. An animal is immunised with the target such as a protein. Blood is taken from the animal once the animal has had time to seroconvert, meaning the animal has produced an immune response specific to the target and antibodies against the target can be detected in its blood. The harvested blood is allowed to clot, by keeping it at room temperature for 15 - 30 minutes, and then centrifuged, for example at 2,000 x g for 10 minutes. The yellow coloured supernatant is the serum.
The serum contains a mixture of antibodies specific to the target, non-specific antibodies and other non-immunoglobulin proteins such as albumin. This is known as 'whole', 'crude' or 'unpurified' serum and is one form of a polyclonal antibody preparation.
Crude serum can be used for some applications, however, enrichment of the antibody component is often required for better performance in applications. This enrichment can be done using a number of antibody purification methods based on selecting antibodies by their size or affinity purification. Affinity purification is done by selecting antibodies based on their immunoglobulin class, for example IgG, using proteins that specifically bind to this class of antibody, this is known as 'class-specific affinity' purification. Alternatively, 'antigen-affinity' purification is done by incubating the serum with immobilised antigen, then washing, at this point only antigen specific antibodies are retained and these can be eluted off to produce a highly antigen specific polyclonal preparation.