Polyclonal antibodies are a mixture of antibodies with different epitope or antigen specificity. Given their ability to bind a broad range of targets, these antibodies are especially useful to detect and capture low abundance molecules. The specific applications of polyclonal antibodies are discussed in this article. Check our frequently asked questions (FAQs) page focused on polyclonal antibodies to learn more about these invaluable reagents for research and diagnostics.
What are polyclonal antibodies?
Polyclonal antibodies consist of a mixture of monoclonal antibodies produced by distinct B cell clones. Consequently, antibodies within this mixture have different specificity, selectivity, and antigen-binding affinity. Unlike their monoclonal counterparts, polyclonal antibodies can recognize different epitopes of a specific target molecule, making them invaluable for multiple applications including research and in vitro diagnostics (i.e. basic, medical, environmental, etc.).
Given their multi-epitope specificity, polyclonal antibodies are characterized by a better sensitivity in comparison to their monoclonal counterparts. Thus, they are particularly useful to detect or capture low abundance targets. Moreover, these reagents are often used in tandem with monoclonal antibodies providing the amplification of detection signals.
When monoclonal and polyclonal antibodies are used in tandem, they are classified according to their role in the assay. The most typical configuration involves the use of monoclonal antibodies as primary antibodies (designed to bind to the main target) and polyclonal antibodies as secondary antibodies (designed to bind to the primary antibodies). In this way, if several polyclonal molecules carrying tags (e.g. enzymatic or fluorescent) bind to the mAb-antigen complex, the detection signal becomes stronger and clearer.
What are the main applications of polyclonal antibodies?
In general, polyclonal antibodies are easier and cheaper to produce than their monoclonal counterparts. Provided these reagents are corrected produced (using the adequate antigen and host species) and purified, they can serve a multitude of purposes.
Polyclonal antibodies have found broad applicability as reagents for:
- Immunoassays in research and diagnostics – immunohisto- and immunocytochemistry, ELISA, Western Blot, Flow Cytometry, Immunoprecipitation, among others.
- Immunotherapy – polyclonal antisera has been widely used to treat complex diseases such as snakebite envenoming and to provide temporary protection against infectious diseases (e.g. use of convalescent plasma to treat COVID-19 infections).
- Enrichment and purification applications – polyclonal antibodies can serve to enrich specific antigens for a complex sample and thus significantly lower detection limits. Moreover, they can serve to purify other molecules (including antibodies) after the production stage.
- Oligotherapy discovery – for a long time, polyclonal antibody sequencing has been considered challenging; however, techniques for sequencing these complex mixtures are evolving at a fast pace. For this reason, many experts believe that soon, polyclonal antibodies will be sequenced with great accuracy (at least the dominant forms) thus serving as frameworks for the design of effective oligoclonal antibodies for therapeutic, research, and diagnostic applications.
In sum, polyclonal antibodies have found greater applicability for in vitro diagnostics and research. Given their enhanced sensitivity in comparison to their monoclonal counterparts, polyclonal antibodies are especially useful for early detection of cancer or autoimmunity markers, among others. Thus, they are deemed essential to prevent unfavorable disease outcomes. Plus, given the lack of more effective treatments, polyclonal antiserum (or convalescent plasma) is still widely used as anti-venom and anti-toxin treatments.
Nevertheless, working with these reagents still poses some important challenges. Given they are produced in animal hosts, production yields depend on the size of the animal and the method used for immunization. Moreover, as no two immune responses are alike, polyclonal preparations are characterized by a great variability regarding antigen selectivity, specificity, and binding affinity. For this reason, all applications that employ polyclonal antibodies for detection should take these limitations into account. This translates into including proper control samples in every immunoassay.
Despite these limitations, these reagents continue to find a broad use for many applications. Particularly when used in tandem with monoclonal antibodies.