Polyclonal Antibodies

What are polyclonal antibodies?

Polyclonal antibodies are antibodies (proteins that your body uses to fight infection) that come from different types (lineages) of plasma B cells. Each antibody recognizes different parts (epitopes) of the same antigen. An antigen is a type of label on the surface of substances in your body — like germs, pollen or proteins — that allows your immune system to recognize whether they’re part of your body (“self”) or not.

Humans and other animals naturally make polyclonal antibodies when fighting off infections. Polyclonal antibodies used in research and medicine usually come from mammals (like rabbits or sheep) or from people who’ve recovered from certain infections.

How do polyclonal antibodies work?

When you get infected with a virus, bacteria or other pathogen (germ), your immune system makes antibodies to fight it off. Antigens sit on the surface of pathogens where the antibodies recognize and attach (bind) to them. Each antibody only binds to one antigen and lets your immune system know to destroy that antigen (and the pathogen it’s attached to). You can think of each antibody like a key that looks for the specific lock (antigen) it can fit into.

But each antigen can have multiple epitopes, or the specific area that the antibody latches on to (the “keyhole”). Polyclonal antibodies in your blood, or in concentrated solutions (serums) used in medical treatments, have many different collections of antibodies, which can each recognize a different epitope. This means different antibodies can grab on to each part of the antigen. Multiple different kinds of antibodies — called lineages — give your immune system many chances to grab on to and recognize pathogens. In this way, you can think of some antigens as having multiple locks that each fit a slightly different kind of key.

What are polyclonal antibodies used for?

Polyclonal antibodies are made naturally in your body. In medicine, they’re used for:

• Diagnosing disease. Lab tests like ELISA and immunohistochemistry tests use polyclonal antibodies to help diagnose infectious diseases and cancer.
• Scientific research. Researchers use polyclonal antibodies to understand how our bodies work and how diseases affect us.
• Treating or preventing infectious diseases and certain health conditions. Some medication overdoses, venomous snake bites and blood conditions are treatable with polyclonal antibodies.

Polyclonal antibody treatments

Treatments that use polyclonal antibodies include:

• Polyclonal antibodies are used in some antivenoms for snake bites.
• Convalescent plasma. Healthcare providers sometimes use convalescent plasma during outbreaks of infectious diseases. Convalescent plasma comes from people who’ve recovered from the disease and contains the polyclonal antibodies their bodies made against it.
• Digoxin immune fab. This is an injection that treats digoxin.
• Rho(D) immune globulin. Rho(D) immune globulin — also written Rh₀(D) and Rh_o(D) — is given to pregnant people who have Rh- negative blood to prevent rhesus isoimmunization (rhesus incompatibility), a type of blood disorder in newborns. It’s also a treatment for chronic immune thrombocytopenia (immune thrombocytopenic purpura/ITP).

What’s the difference between monoclonal antibodies and polyclonal antibodies?

Polyclonal and monoclonal antibodies both target antigens. But polyclonal antibodies come from different immune cell lineages that recognize many different epitopes, and monoclonal antibodies are exact copies of the same antibody (they only recognize one epitope).

For medical purposes, polyclonal antibodies often come from the blood of mammals like rabbits, goats, sheep and sometimes humans. Monoclonal antibodies are taken from animal blood and reproduced in a lab. Healthcare providers use monoclonal antibodies more often than polyclonal antibodies in medical treatments.

What are the advantages of polyclonal antibodies?

Advantages of polyclonal antibodies include:

• They’re inexpensive to create.
• They’re good at detecting even low levels of antigens in a sample.
• They have better antigen recognition, as there are multiple antibodies that bind to different epitopes.

What are the disadvantages of polyclonal antibodies?

Disadvantages of polyclonal antibodies include:

• As they come from a natural source (human or animal blood), polyclonal antibodies aren’t consistent from batch to batch the way that medications or lab-made treatments are. So, their effectiveness can vary.
• There’s a higher chance of cross-reactivity (binding to a similar antigen) than with monoclonal antibodies. This can cause issues when using them in testing or research, like false positives. For instance, for very serious infectious diseases, providers might need to run multiple tests to confirm a positive diagnosis.
• Polyclonal antibodies that come from animals — rather than humans — have a higher risk of allergic reactions or other side effects when used in medical treatments.