Do I Really Need a Monoclonal Antibody?
It isn’t uncommon that we receive requests to generate custom monoclonal antibodies. And while there are applications for which monoclonal antibodies are the best tool, we’ve found that many researchers mistakenly believe that monoclonal antibodies are automatically superior to polyclonal antibodies in all situations. The truth is that polyclonal antibodies are better research tools in many situations and so it’s important to understand the fundamental differences between these two types of antibodies.
Monoclonal antibodies provide two particular advantages – 1) antibodies from the single clone are specific to a single epitope (a unit of 5-7 amino acids against which an individual antibody binds) and 2) large quantities of this identical epitope-specific antibody can be expressed. This ability to target a single epitope provides extremely high specificity in terms of targeting the antigen of interest. And, the ability to grow large quantities of antibody that are identical from batch to batch is critical for applications such as diagnostic kits and therapeutic drugs.
However, there are costs associated with this. Monoclonal antibodies are traditionally developed in mice, which provide a less robust immune response in comparison to larger mammalian species such as rabbits. The costs associated with developing monoclonal antibodies are also significantly higher than those for developing polyclonal antibodies. The time required to hybridize, screen and isolate the target lymphocyte is notably longer, after which the clone must be expressed and the resulting antibody purified. And, perhaps most important, a monoclonal antibody against a single epitope typically demonstrates lower affinity in binding with the target epitope on the native protein. In addition, if this single epitope isn’t accessible in a particular assay, or the protein conformation changes slightly, then the antibody will not be able to bind with the target protein.
Polyclonal antibodies, by definition, consist of antibodies against multiple epitopes. In the context of a full-length protein, this could lead to less specificity if domains or epitopes within the protein sequence are conserved. However, if we focus on a particular region of the protein and immunize with a small peptide (15 amino acids for example) corresponding to that region, then we end up with a very small pool of antibodies recognizing multiple epitopes within that peptide sequence. However, this ability to recognize multiple epitopes (compared to a monoclonal antibody that can only recognize a single epitope) in a targeted region provides superior affinity, quicker binding capability and more robustness in the event that denaturation, polymorphisms or conformational changes occur.
Next, by affinity purifying serum against the peptide sequence, we can isolate this small pool of antibodies against epitopes on the peptide sequence and thereby approach the specificity of a single monoclonal antibody. These highly specific polyclonal antibodies are typically known as monospecific antibodies and represent one of the most popular services that we offer.
Even better, polyclonal antibodies can be produced much quicker and for a fraction of the cost of a typical monoclonal project.