Polyclonal Antibodies and COVID-19

As the Covid-19 virus turns another corner with the Omicron strain, guarding our immune systems is now more important than ever. Getting the first and second dose of the vaccine makes one fully vaccinated but as new strains are revealed booster shots become our next line of defense. Below we will use immunohistochemistry to shed some light on just how useful a booster shot can be in these times.

Polyclonal antibodies versus monoclonal antibodies

Immunohistochemistry (IHC) is a special staining process performed on fresh or frozen tissue, it detects antigens in tissue sections and cells using monoclonal or polyclonal antibodies. Antibodies are also known as immunoglobulins. A monoclonal antibody is an antibody produced by a single clone of cells or cell line with one parent cell. A monoclonal antibody is created by cloning a unique white blood cell. White blood cells are a part of the body’s immune system. They help the body fight infection and other diseases. Advantages of monoclonal antibodies are that they have a high homogeneity across batches, high specificity to a single epitope leading to lower cross-reactivity,  and low background noise. However, they are more expensive to produce, have a longer development process, and are more susceptible to binding changes when labeled.

In contrast, polyclonal antibodies are secreted by different B cell clones in the body and they recognize and bind to many different epitopes of a single antigen. The advantage of the polyclonal antibody is its versatility which allows for amplification of the signal; leading to better detection. Also, it is quite inexpensive and fast-producing. Some disadvantages may include batch to batch variability depending on the subject and time and cross-reactivity from binding to multiple epitopes of an antigen. An antigen on the other hand is a toxin or other foreign substance that when present triggers an alert for antibodies to be made to then fight off said antigen (i.e, bacteria, virus).

Fig. 1 Pictured to the left, polyclonal antibodies are binding to multiple epitopes of the antigen. To the right, the monoclonal antibody has one binding site on the antigen. (Credit: Adapted from nanoComposix| Fortis Life Sciences, January 26, 2022)

How are Polyclonal Antibodies Produced?

In the example given above, monoclonal antibodies are the kinds of antibodies that will occur naturally. However, polyclonal antibodies are produced by injecting an immunogen (an antigen that elicits an immune response) into an animal. After the first immune response, the animal is then given a second or even third dose of immunogen to build up higher-level polyclonal antibodies. After this process, the polyclonal antibodies needed to fight against the antigen can be obtained straight from the animal’s blood.

Fig. 2 Pictured here is the animal subject being injected with the immunogen to create polyclonal antibodies that are then collected via blood sample. (Credit: Adapted from MBL Life Science, January 26, 2022)

How does this relate to Covid-19 and the Booster?

As with the current pandemic, Covid-19 is the antigen (foreign virus), the Covid-19 vaccine is the immunogen and we are its subject. The Covid-19 vaccine is injected as an immunogen in 2 doses. After the first dose, one should have a primary immune response, and following some time after is the second dose of the vaccine. While we already have polyclonal antibodies at this stage, getting another dose of the immunogen (AKA the Covid Booster shot) will produce higher titers of polyclonal antibodies against the antigen, Covid-19. So as we go into this winter season, we can think of the power of polyclonal antibodies while we get the booster shot to build our immune system against the Covid-19 antigen. Lastly, with the current Omicron variant surge, the booster shot allows our immune system to fight against the antigen long-term as shown in figure 4.

Fig. 3 Displays the immune response after each dose of the Covid-19 immunogen. (Credit: Adapted from The Conversation, January 26, 2022)
Fig. 4 This diagram showcases the therapeutic benefits of the booster shot in response to the Omnicron Variant. (Credit: Adapted from Pfizer, January 26, 2022)

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