Commercial antibodies are specialized protein molecules created and sold by biotechnology companies. These proteins are designed to identify and bind to other specific molecules with high precision, serving as reagents for activities from laboratory research to disease diagnosis and treatment. Their utility stems from their ability to target a single substance within a complex biological mixture, making them valuable in modern science.
Types of Commercial Antibodies
The main classes of commercial antibodies are defined by how they recognize their target molecule, known as an antigen. The two most established types are polyclonal and monoclonal antibodies. Polyclonal antibodies are a diverse mixture of molecules produced by different immune cells in an animal. As a result, they recognize multiple distinct sites, or epitopes, on a single target antigen.
This characteristic gives polyclonal antibodies a high overall affinity, making them robust for detecting low-quantity proteins. This makes them particularly useful in certain laboratory techniques where signal amplification is beneficial.
In contrast, monoclonal antibodies are a uniform population of identical antibody molecules. Each is derived from a single parent immune cell clone and is specific to one single epitope on the antigen. This homogeneity ensures every antibody binds to the exact same spot, which reduces the likelihood of binding to unintended molecules, a problem known as cross-reactivity.
A third class is recombinant antibodies, generated using genetic engineering techniques in a laboratory, avoiding the use of animals. This method allows for precise control over the antibody’s genetic sequence, leading to a highly consistent and reproducible product. Recombinant technology can also create various antibody formats, such as smaller fragments or humanized versions for therapeutic use.
Production of Commercial Antibodies
The methods for generating antibodies differ depending on the type. Polyclonal antibody production begins with the immunization of an animal, commonly a rabbit or goat, with the specific antigen. After several weeks, blood is collected, and the serum containing the desired antibodies is separated and purified.
The generation of monoclonal antibodies involves a process known as hybridoma technology. This procedure starts with immunizing an animal, typically a mouse, and harvesting its antibody-producing B-cells from the spleen. These cells are then fused with immortal myeloma (cancer) cells, creating hybrid cells called hybridomas. These hybridomas have the longevity of cancer cells and the antibody-producing capability of B-cells, allowing for continuous production of a single, specific antibody.
Recombinant antibodies are produced through in-vitro methods, such as phage display technology. This technique uses bacteriophages (viruses that infect bacteria) to display a library of antibody fragments on their surfaces. Scientists screen this library to find phages that bind to the target antigen with high affinity. The genetic material for that antibody fragment is then used to produce large quantities of the antibody in cell cultures.
Applications in Science and Medicine
The ability of antibodies to bind to specific molecular targets makes them useful in research, diagnostics, and therapeutics. In research laboratories, antibodies are used for detecting and visualizing proteins. Techniques like Western blotting identify a specific protein from a complex mixture, while immunohistochemistry (IHC) reveals the location of proteins within tissue slices.
In diagnostics, antibodies are the core component of many tests designed to detect biomarkers for diseases or other conditions. A widely recognized example is the home pregnancy test, which employs antibodies to detect the hormone human chorionic gonadotropin (hCG) in urine. Similarly, enzyme-linked immunosorbent assays (ELISA) use antibodies to diagnose infectious diseases like HIV and COVID-19.
Beyond detection, antibodies have become a major class of therapeutic drugs. Therapeutic antibodies are engineered to treat diseases like cancer and autoimmune disorders. Some of these antibodies work by binding to and blocking the function of proteins that drive disease. Others are designed to attach to cancer cells, flagging them for destruction by the patient’s immune system.
Challenges with Antibody Quality and Validation
Despite their widespread use, the reliability of commercial antibodies presents a challenge, contributing to the “reproducibility crisis” in science. Research funding is wasted annually due to antibodies that do not perform as advertised, leading to failed experiments and flawed conclusions.
One issue is specificity. Many antibodies exhibit cross-reactivity, where they bind to unintended proteins, generating false-positive signals. Another concern is affinity, the strength of the bond between the antibody and its target. An antibody with low affinity may not bind strongly enough to be effective.
Batch-to-batch variability is another problem, especially for polyclonal antibodies. Because these antibodies are produced in different animals or at different times, the antibody mixture can vary from one production lot to the next. This inconsistency means an experiment that works with one batch may fail with a new one.
To address these issues, validation is required. Validation is the process by which a researcher confirms that an antibody works as expected in their experimental setup. This involves testing for specificity and reproducibility. While manufacturers provide some validation data, the responsibility often falls to the end-user to perform in-house validation.