Polyclonal Antibodies

 Polyclonal antibodies

The B cells are synthesized and matured in the bone marrow. After maturation, the B cells scatter in the blood, lymph and lymphoid tissues. These B cells have specific receptors on their membranes for antigen recognition. These are known as B cell receptors. These receptors are membrane-bound immunoglobulin and are similar in structure to antibodies. Every day, about 1 billion B cells are synthesized in the bone marrow. The B cell receptors present on their surfaces have pre-existing specificities. Therefore, B cells can recognize and respond to any possible antigen that they encounter. Each B cell can represent about 100,000 on its surface, all specific for one epitope on an antigen.

When a mature B cell encounters an antigen, it gets activated and proliferates into a large clone of B cells. Some of them differentiate into antibody-producing plasma cells and others become long-lived memory cells. Both these plasma cells and memory cells are specific to the antigen and more specifically to the epitope that the mature B cell encountered initially.

What are polyclonal Antibodies?

Polyclonal antibodies refer to a diversified composition of immunoglobulin molecules that are released against particular antigens; each antibody recognizes a different epitope on the same antigen.

When an antigen enters the body, suppose a bacteria having different varieties of antigens on its surface. These antigens are the epitopes and may be proteins, lipids and carbohydrates which are identified by the B cell receptors.

When there is an invasion in the body by antigens, the B cells recognize and bind to their specific epitopes and get activated. Each of these B cells will proliferate to produce a large clone of cells. Some of these cells in each case will be differentiated into plasma cells and plasma cells will produce antibodies specific to the epitopes that triggered their differentiation. So, as a result of the entry of antigens into the body, the B cells produce antibodies which are known as polyclonal antibodies, specific to their epitopes.

Polyclonal Antibody Production

The main source of polyclonal antibody production is human or animal blood.  However, these can also be synthesized in the laboratory by artificial means. The most commonly used organisms for the production of polyclonal antibodies are rabbits, mice, sheep goats, etc.

For polyclonal antibody production, an organism such as a rabbit is immunized with the antigen against which the required antibodies are to be produced.

Procedure

1.  The antigen, for example, 2,4 dinitrophenol is injected into the blood of a mouse. Sometimes a conjugating material is also added to the antigen to increase its immunogenicity. This process is repeated after 3 weeks.
2. After 6 weeks, the blood containing antibodies against the injected antigen is dropped from the mouse.
3. These antibodies can be collected in an antiserum, which is whole serum harvested from animals following exposure to the antigen.
4. Antiserum derived from the animal will not only carry antibodies against the antigen, but it will also carry antibodies to any other antigens to which the animal has been exposed during its lifetime.
5. The polyclonal antibodies from the antiserum are purified by using most commonly used methos such as serum purification, salt precipitation and affinity purification.

Advantages of polyclonal antibodies

• Polyclonal antibodies are easy, fast and cheap to produce and can be easily stored.
• They are also firmly easy to produce on large scales.
• They can have high cross-reactivity.
• They can be usable for under four months after manufacturing.
• They have high stability and tolerance to pH and buffer changes.
• They have a high affinity as they can bind to more than one epitope.

Applications of Polyclonal Antibodies 

Biochemical Analysis

Polyclonal antibodies are used in western blotting, ELISA, immunohistochemistry and cytometry due to their ability to detect denatured proteins with high sensitivity, surface proteins and intracellular proteins, strong binding and signal amplification and powerful staining due to multi-epitope identification.

Diagnosis

Polyclonal antibodies have applications in clinical diagnostics such as pathogens and disease markers detection, rapid tests such as COVID-19 and pregnancy tests and allergen detection in food and biochemical samples.

Therapeutic applications

Polyclonal antibodies are utilized in neutralizing toxins and venoms from snakes and insects.

They are also used in passive immunization to give instant protection against some viral infections such as hepatitis B, rabies, measles, chickenpox, respiratory syncytial virus, etc. and bacterial infections such as diphtheria, tetanus and botulism.

Veterinary and Agriculture

Polyclonal antibodies are widely used in detecting pathogens in livestock and pets, protecting them against viral and bacterial infections and providing them with an immediate immune response by passive immunity.

In agriculture, polyclonal antibodies are used for monitoring the presence of herbicide and pesticide residues through immunoassays and for identifying fungal, bacterial and viral pathogens in crops.