The study of polyclonal antibodies brought many important insights to the field of immunology and helped in the development of different antibody drugs. Today, these antibodies remain an important research tool, while the production of biotherapeutics relies more on monoclonal antibodies due their specificity, with partners like evitria in recombinant antibody expression.
In this article, we will explain the role of polyclonal antibodies in the immune system and how they operate. Also, we will take a closer look at the history of their discovery. Furthermore, benefits and disadvantages will be explained and the differences between monoclonal bodies and polyclonal bodies investigated.
Polyclonal antibodies, short pAbs, are defined as a heterogeneous mix of antibodies usually secreted by different B-cell clones of an animal. They are a collection of immunoglobulin molecules reacting against specific antigens. Their heterogeneous binding provides them with a high sensitivity to antigens in many applications.
Polyclonal antibodies are used as secondary antibodies in immunoassays with the function to bind to the epitopes of primary antibodies and amplify the signal of these antibodies.
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In contrast to monoclonal antibodies (mAbs), which only recognize a single epitope, pAbs contain a heterogeneous combination of immunoglobulins, short IgGs, against the antigen. That means they are able to bind to more than one specific molecule on the antigen’s surface.
Once an antigen is detected, lymphocytes, namely t-cells and B-cells are activated. The B cell is then led to split and clone and releases the type of antibody into the circulation that reacts with the antigen.
The history and the discovery of polyclonal antibodies starts in 1890, with the discovery of Emil von Behring and Shibasabura Kitasato that animals suffering from diphtheria could be cured by injecting them with a serum from animals that had been immunized against it. Since then, research on the functions of amino acids and peptides became a field of interest.
One of the most important names in immunology is Paul Ehrlich, who found that side chain receptors on cells bind to specific pathogens and with that provided the first theory of antibody molecules and their binding. Immunohistochemistry uses antibodies to check for certain antigens in tissue.
1979, the Western Blotting method was invented, which made it possible to extract proteins and transfer them onto membranes in order to test immune reactions.
Polyclonal antibodies are a most valuable tool for research applications. In enzyme-linked immunosorbent assays (short ELISAs), pAbs have shown great sensitivity ranges due to their binding capabilities to different epitopes. As they detect multiple antigen epitopes present in the analyte, they are often used when observing variances in human samples.
Due to their multi-epitope binding capabilities, pAbs show similar qualities like that of the natural immune system, they are effective at viral and toxin neutralization. Especially in anti-tumour immunotherapy, the use of pAbs is valuable in mediating effector functions and inducing cancer cell apoptosis.
While mAbs can be produced in vitro, polyclonal antibodies are made by infusing an animal with a particular antigen. Commonly used animals in the process are rabbits, guinea pigs or sheep. Similar to the human immune system, the lab animal is led to a polyclonal antibody response after exposure to the antigen. After approximately two weeks, these antibodies are gathered in an antiserum. The antiserum contains a multitude of antibodies from different B cells. In the following the different steps will be explained.
One of the benefits of polyclonal antibodies is that production cost can be kept relatively low. The production time is shorter compared to most mAbs. Additionally, large quantities of an antibody can be isolated with one extraction.
Compared to monoclonal antibodies, PAbs show a better response to the antigen as the secondary antibody produced detects different epitopes on the antigen. They are also less likely to be affected by small changes in the epitopes of an antigen due to their heterogeneous quality and have shown to be very stable in different salt concentrations and pH values. This makes them an important tool in the studies of immunology and research on antibody production.1
Even though pAbs have the ability to bind to a wide range of antigenic epitopes, there are certain disadvantages that have led to a decrease of the use of pAbs in biotechnology. While their response to antigen is higher than in mAbs, they are more likely to show false positives and cross-reactions due to their lower antibody specificity to the target antigen.
As they have to be produced in vivo, the reproducibility of pAbs is limited to the lifespan of the host animal. Moreover, their affinity to antigens is at risk to change over time, providing different success rates. In contrast to monoclonal antibodies, pAbs provide lower concentration and purity levels of specific antibodies.
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One of the main challenges in connection with polyclonal antibodies is their limited supply. Due to the natural lifespan of the animal, the batch will be lost and a new immunization process has to be generated in a new host. As the immune response can be different from host to host, a variability in batches is most likely to occur. Moreover, batch variation can lead to cross reactivity and less binding affinity.
As polyclonal antibodies are less specific to the target protein, cross-reactivity and false positives lower the reliability of immunoassays.
To conclude, one must point out several differences between polyclonal and monoclonal antibodies. As the batch variability and limited expression time of polyclonal antibodies would be a big disadvantage in the research and production of biotherapeutics, monoclonal antibodies often the favored choice in biotechniques and the production of antibody drugs.
Monoclonal antibodies are less likely to contra-react with other proteins as they rely on one receptor. The big advantage is that they can be immortalized by fusion with hybridoma cells which allows for long term production.
Recombinant monoclonal antibodies are monoclonal antibodies that were generated in the laboratory without a living host. Synthetic genes and antibody fragments are combined in vitro, which makes it easy to culture cell lines under controlled circumstances. Evitria is specialized in the production of recombinant antibodies due to the enhanced reliability, efficiency and ethical improvement of the process.