Polyclonal antibodies are characterized by their broad specificity. The ability to tackle several epitopes or antigens in the same sample makes them uniquely valuable for many applications. By themselves or in tandem with their monoclonal counterparts, polyclonal antibodies can be used to improve early diagnostic tools and generate better envenoming immunotherapies, among other applications. Check our frequently asked questions (FAQs) page focused on polyclonal antibodies to learn more about these invaluable reagents for research and diagnostics.
Main advantages and uses of polyclonal antibodies
Polyclonal antibodies are a mixture of monoclonal antibodies with distinct epitope-specificity and binding affinity. They are produced by immunizing animal hosts with a specific target (protein, peptide, DNA, etc.) and harvested by separation and purification of their serum after the development of a strong immune response.
Unlike monoclonal antibodies, prized for their high specificity and selectivity, polyclonal antibodies are known for their enhanced sensitivity. This property makes them invaluable tools for multiple applications including research (basic, medical, etc.), therapy, and diagnostics. They are particularly advantageous reagents to detect low abundance markers, toxins, among other substances. The detection of these rare markers is extremely useful for the design of early diagnostic tools, food monitoring applications, and for capturing rare targets and purifying them before further analysis.
From a therapeutic perspective, polyclonal antisera are invaluable to treat complex acute conditions like snakebite envenoming. Venoms cause acute reactions and are composed of a complex mixture of different proteins with key roles in pathogenesis. In this way, successful antivenom therapies need to be able to tackle several antigens and epitopes present in a single venom to block the pathogenic pathways and avoid adverse reactions.
From a technical point of view, polyclonal antibodies are cheaper to produce than their monoclonal counterparts. Plus, the timelines for polyclonal antibody production are significantly shorter than the lead time of monoclonal antibody production. In contrast, their most notable limitations are the difficulty in scaling up the process and high batch-to-batch variability. The impact of the latter can be mitigated by including proper controls (positive and negative) and standards in every assay.
Overcoming scale-up hurdles is more challenging, but recent breakthroughs have provided interesting solutions. One of the most interesting solutions is the purification of IgY antibodies present in egg yolk using ionic liquids. Due to the non-invasive methods of antibody harvesting and the cost-effective new purification methods, these molecules may soon gain ground over other polyclonal antibodies for a multitude of applications.
The advantages of pairing monoclonal and polyclonal antibodies
Polyclonal antibodies can be used by themselves or in tandem with their monoclonal counterparts in different assays. The most common application of polyclonal and monoclonal antibody pairs is the enzyme-linked immunosorbent assay (ELISA). In ELISA, monoclonal antibodies (also called primary antibodies) are typically used to bind a specific target, while polyclonal antibodies (secondary antibodies) are used to bind the primary antibodies.
In this configuration, the primary antibodies are “naked” (no tags) while the secondary antibodies carry the enzymatic tag. This format allows the amplification of the detection signal, lowering detection thresholds considerably. The signal amplification occurs because, while primary antibody binds to a single epitope on the target molecule, secondary antibodies bind to multiple regions of the primary antibodies. In this way, multiple secondary antibodies conjugated with an antibody can coat the surface of the primary antibody, dramatically enhancing the detection signal.
The enhanced sensitivity of these molecules comes with its own set of specific hurdles. For instance, polyclonal antibodies are notorious for their propensity for off-target binding, which may lead to false-positive results. To overcome this hurdle, polyclonal antibodies must be submitted to stricter purification processes (e.g. by performing antigen-specific antibody purification). Additionally, the inclusion of controls and standards can help researchers correctly identify thresholds of detection.
Due to their ability to target multiple epitopes, polyclonal antibodies are invaluable tools for the design of sensitive detection assays (i.e. ELISA, Western Blot, Immunohistochemistry, etc.) and therapies that help to curb acute reactions such as venomous bites and stings.
The sensitivity of polyclonal antibodies can make them useful for early diagnosis. Moreover, they can serve to capture low abundance markers from complex samples for further analysis using mass spectrometry, among other analytical methods.