There are two classes of antibodies: monoclonal and polyclonal. Though they are both antibodies that are derived from B cells, there are important differences between the two.

Monoclonal Antibodies

Monoclonal antibodies only bind to a specific epitope on a target antigen and therefore have a high degree of specificity for its antigen or epitope. They are derived from the same clone of plasma B cells and are ultimately a homogenous population of antibodies. They are created by injecting an immunogen into a host animal, then harvesting B-cells from the spleen after an immune response has occurred. The extracted B-cells are fused with myeloma cells to create a hybridoma cell line. These cells excrete the monoclonal antibodies into a culture media, creating a stable and renewable antibody source that ensures each batch is identical.

The ability to have batch-to-batch homogeneity is a major advantage of monoclonal antibodies. They also reduce the probability of cross-reactivity and can provide improved results in assays that require protein level quantification. Monoclonal antibodies can be produced in large quantities, but they are expensive and time consuming to produce.

However, monoclonal antibodies have broad experimental and clinical uses. They are best used for:

• Detecting a specific antigen or single member of a protein family
• Getting consistent results between batches or experiments
• Quantifying protein expression
• Detecting changes in molecular conformation
• Immunotherapy
• Detecting a target for x-ray crystallography

Polyclonal Antibodies

Polyclonal antibodies bind to multiple different epitopes on a target antigen. They are a collection of antibodies derived from different B cells that recognize many epitopes on the same antigen. Each antibody recognizes a single, unique epitope located on the antigen. Because these antibodies are derived from different B cells, they are a heterogenous population of antibodies targeting the same antigen but not the same epitope. They are produced by injecting an immunogen into a host animal, which activates multiple B cells that target different epitopes on the immunogen. The polyclonal antibodies are harvested from blood serum and can be used straight from the serum or purified to create a solution without other serum proteins. Each batch has high variability because it is developed from a new animal being exposed to the immunogen.

Polyclonal antibodies are inexpensive to produce and can be produced quickly – a purified sample can be ready to use in less than four months. They are easy to store and highly stable, with increased antibody affinity against antigens because it recognizes multiple epitopes. Purification of the sample is usually required to minimize cross reactivity.

Polyclonal antibodies have a wide range of uses, but they are not ideal for quantification experiments or cases where cross-reactivity can cause issues. They are, however, excellent when used to:

• Detect known or unknown isoforms of antigens
• Capture as much antigen as possible
• Detect low levels of an antigen
• Detect a single target across varying salt concentrations and pH levels
• Detect targets with potential conformation changes, glycosylation, or polymorphisms
• Confirm the presence of denatured proteins

Monoclonal Versus Polyclonal Antibodies

Though both monoclonal and polyclonal antibodies originate from B cells in response to an antigen, they are very different. Monoclonal antibodies are ideal for diagnostic manufacturing and therapeutic drug development because they require large volumes of identical antibodies specific to a single, unique epitope. Polyclonal antibodies are best for general research applications because polyclonal antibody advantages typically outweigh the advantages of monoclonal antibodies.