Antibodies, also called immunoglobulins, are typically secreted by plasma cells (B cells) to neutralize antigens like viruses and bacteria. An antibody’s classical representation is a Y-shaped molecule that comprises four polypeptides – two light chains and two heavy chains. Every tip of the Y-shaped molecule comprises a paratope specific to a single epitope on an antigen. In turn, this enables both of these structures to bind together accurately.

The capability to precisely bind antigens has resulted in their ubiquitous applications in various medicinal and life sciences. These antibodies can be divided into two main types – monoclonal antibodies and polyclonal antibodies – depending on how they were produced from lymphocytes. Every type plays a significant role in the body’s immune system and diagnostic exams and treatments.

This article will shed light on everything you need to know regarding polyclonal antibodies, including their synthesis and role in clinical therapeutics and diagnostics. Keep reading to find out more about polyclonal antibodies. You can also check out Biomatik to look at their extensive custom antibody collection available for research scientists.

Production of Polyclonal Antibodies

Polyclonal antibodies (pAbs) blend heterogeneous cells typically released by the B cell clones present in the body. These antibodies can recognize various epitopes on one antigen and successfully bind to them.

Polyclonal antibodies are secreted when you inject immunogens into animals. The reason for injecting these immunogens is to elicit the primary immune response of the animal. Consequently, the animal is offered secondary and even tertiary immunization to generate higher levels of antibodies against a specific antigen.

After the immunization process, polyclonal antibodies can be retrieved directly from the animal’s serum – blood in the absence of red blood cells and clotting proteins. The serum can also be further purified to get a solution that doesn’t contain other serum proteins.

Advantages and Disadvantages of Polyclonal Antibodies

Polyclonal antibodies have several advantages that make them ideal for their applications in science. Their advantages and disadvantages are determined by their multi-epitope specificity. Here are the pros and cons of polyclonal antibodies:

Advantages of polyclonal antibodies

• They are very stable and highly tolerant of buffer or pH changes

• They are cost-efficient and take a short time to produce

• They are tolerant of minor antigen changes – polyclonal antibodies tend to be less sensitive to changes in antigens, such as polymorphism, denaturation, and heterogeneity of glycosylation, as compared to monoclonal antibodies

• They have a high affinity – as antibodies can bind to more than a single epitope, they can amplify the target protein’s signal even with low expression levels. As a result, polyclonal antibodies are perfect for chromatin immunoprecipitation

Disadvantages of polyclonal antibodies

• They are susceptible to batch variability.

• If you’re dealing with several epitopes, you need to assess the immunogen sequence to establish whether there is cross-reactivity.

Diagnostic Studies

Polyclonal antibodies are the best reagents for use in hemagglutination reactions and diagnostic assays because of their capability to identify various epitopes of the target molecule. The best application of polyclonal antibodies is to recognize unknown antigens.

They can also be used as the secondary antibody during immunoassays, such as microarray assays, western blotting, ELISA, flow cytometry, and immunohistochemistry. Here, the objective is to bind together various epitopes and amplify that signal for better detection.

Treatment

There is plenty of research that shows polyclonal antibodies can be used to treat a wide range of diseases, and they can also be used as an immunosuppressant for patients undergoing a transplant procedure. However, they’re not very effective at treating cancerous cells. This is because they are not quite adept as compared to monoclonal antibodies. They also have a higher level of cross-reactivity and lack specificity.

Test Sensitivity, Test Specificity, and Cross-Reactivity

The accuracy of tests involving antibodies can be mainly described based on test specificity and test sensitivity. Test sensitivity is the likelihood of obtaining a positive result when a patient is infected. If a specific test has a high sensitivity, the chances of getting a false negative are low.

On the other hand, test specificity is the likelihood of obtaining negative results when a patient has not yet been infected. If a particular test has a high specificity, obtaining a false positive is low.

False positives are often caused by cross relativity. Cross relativity typically occurs when the epitopes of various pathogens are identical to the epitopes of the pathogens being tested for. Therefore, this explains why tests based on antibodies are mainly used as screening tests. When the results are confirmed to be positive, other confirmatory tests need to be carried out to ensure that the obtained results are not false positives.

For instance, a blood sample from a patient suspected to be suffering from Hepatitis C can undergo a screening test using the antibodies that bind themselves to Hepatitis C virus antigens. If that patient is infected with the Hepatitis C virus, then the antibodies will stick on the antigens, thus, producing a positive test result. If that patient is not infected with the Hepatitis C virus, the antibodies won’t bind themselves to anything; therefore, creating a negative result.

However, if that patient was infected previously with pathogens with antibodies that can cross-react with Hepatitis C virus pathogens.

The antibody tests for Hepatitis C have low specificity and high sensitivity. When a patient tests positive, they should undergo a confirmatory test to rule out the chances of a false positive. The confirmatory test directly determines whether the viral RNA of Hepatitis C is present. The patient can only be diagnosed definitively with Hepatitis C if the confirmatory test is also positive.

The Bottom Line

In summary, antibodies with high specificity usually bind themselves to antigens that challenge the immune system. However, they may show cross-reactivity when attaching themselves to antigens with the same chemical properties as the initial antigen.

When an antigen is injected into a particular animal, it results in a polyclonal antibody response. In this response, various antibodies are released to react with the epitopes of that specific antigen. Polyclonal antisera are mainly used to carry out specific laboratory assays, although other assays require a higher level of specificity. Diagnostic tests involving polyclonal antisera are used only for screening tests due to the likelihood of obtaining false-negative or false-positive results.