Antibodies derived from multiple B-cell clones are known as polyclonal antibodies. Polyclonal antibodies are heterogeneous mixture of antibodies. Each Polyclonal antibodies recognising a different epitope on the same antigen.
• Polyclonal antibodies arise from many B-cell clones.
• Polyclonal antibodies have a heterogeneous collection of binding sites.
• Production of polyclonal antibodies in response to pathogens as an antigen has a very important advantage in vivo.
• These antibodies offer multiple ways to attack pathogens such as by facilitating phagocytosis, complement mediated Lysis etc.
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| Polyclonal Antibodies for different epitopes |
Antibody Production by B Lymphocytes
Origin and maturation of B-cells occuring in the bone marrow. These mature naive B-cells are released into the blood. They keep recirculating between lymph, blood and secondary lymphoid tissues.
These B-cells have specific receptors on their membrane for antigen recognition. These receptors are known as B-cell receptors. B-cell receptors are membrane bound immunoglobulins, their structure is similar to that of antibodies.
• Every day about 1 billion B-cells are produced in our body.
• The B-cell receptors present of these cells have pre-existing specificities.
• Therefore B-cells are able to recognise and react to any possible antigen which it encounters.
• Each B-cell can display about 100,000 B-cell receptors on its surface.
• All these B-cell receptors are specific for our only one particular epitope on an antigen.
• When a mateur B-cell encounters an antigen it gets activated and proliferate into a large clone of B-cells.
- Some of them differentiate into antibody producing plasma cells.
- Other become long-lived memory cells.
Both these plasma cells and memory cells will be specific to the antigen or more specifically the epitope which the maturer B sell encountered initially.
Polyclonal Antibodies
Microbes (Antigen) invade our body that microbial surface has many molecules that vary in their chemical nature. They may be proteins, carbohydrates and lipids.These microbial surface molecules are their portions are recognised by B-cell receptors. These are the epitopes to which B-cell receptor will bind.
• B-cells of diverse specificities are circulating in our body.
• Each of These B-cell is specific for a single epitope on an antigen. When there is an invasion by the antigens these B-cells recognise and bind to their specific epitopes and get activated.
• Each of these B-cells will proliferate and produce large clone of cells.
• Some of these cells in each case will get differentiated into plasma cell.
• Each of these plasma cell will secrete antibodies specific to the epitope which triggered their differentiation.
• As a result for this antigen our immune system produced different type of antibodies. Each specific for a different epitope on the same antigen.
• Antibodies derived from multiple B-cell clones are known as polyclonal antibodies.
Production of Polyclonal Antibodies
• Main source of polyclonal antibodies is human or animal blood.
• For the production of polyclonal antibodies, an organism for example, rabbit is immunized with the antigen against which we need polyclonal antibodies.
- Rabbit is injected with the antigen. This is done one or more times.
- Rabbits immune system will respond to these antigens by producing antibodies.
- After some time these antibodies are isolated and extracted from the rabbit's serum.
- By This way we get anti-serum containing polyclonal antibodies targeted against the desired antigen.
Importance of Antibodies
• Antibodies are a great tool in diagnostic immunology.
• This is because the antigen antibody interaction is highly specific.
• An antibody can detect one antigen molecule among 10⁸ other antigen molecules.
• Antibodies are used to locate and identify antigens to purify, characterize and quantitate antigens.
Polyclonal antibodies (In diagnostic immunology)
Polyclonal antibodies are useful in Agglutination and Immuno-precipitation based techniques.
• This is because these techniques involve large antigen antibody or immune complex formation.
• Polyclonal antibodies are efficient in this because they provide multiple ways of binding to the target antigens.
Disadvantages of Polyclonal Antibodies
Usage of polyclonal antibodies and diagnostic immunology has some disadvantages.
• For research and diagnostic usage we require antibodies in large quantity, but in a polyclonal mixture of antibodies desired antibody is present in low concentration.
• The polyclonal antibodies may have crossed reactivities. This will reduce their sensitivity and specificity.
• Moreover the isolation of desired antibody from a polyclonal mixture is expensive, time-consuming and less efficient.
Alternative solution to this was provided by Georges Kohler and Cesar Milstein. They developed Monoclonal Antibodies, These antibodies are Homogeneous and all recognise the same epitope.
