One of the primary defense systems for an animal or human is the immune system. The immune system produces antibodies or host proteins that are found in extracellular and plasma fluids. These molecules are a principal effector in the immune system and serve as a first response to eliminate or neutralize invading molecules and organisms.
Due to their ability to fight off infection, antibodies have multiple applications in the medical field. One of these applications is polyclonal antibodies. Polyclonal antibodies are produced by different B-cell clones in an organism and contain a complex mixture of multiple antibodies that recognize and bind to several different epitopes of a single antigen. These antibodies have a significant range of uses in the medical field, including research, diagnostics, and disease treatment.
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Different Species Options
Polyclonal antibodies are created by exposing a mammal to a specific antigen, then collecting the antibodies from that organism’s blood. There are multiple species that these antibodies can be collected from, with benefits and drawbacks to each.
This species is the most commonly used animal for polyclonal antibody production for a few reasons. Rabbits are housed easily due to their long life span and small size. They also have a strong immune system that is particularly well adapted to polyclonal antibody production, and their blood is not difficult to obtain. One of the benefits of using rabbits is also the main drawback—rabbits are small, and many animals must be immunized with the same antigen to obtain a sufficient quantity of antibodies.
An interesting alternative to rabbits, chickens can be a valuable source of antibodies. They produce antibodies in high concentrations within the egg yolk, so collection from the egg provides a way to avoid the invasive bleeding step while also acquiring a higher volume of antibodies. Unfortunately, chickens are not frequently used in research. This lack of knowledge, their specific housing requirements, and the difficulties of isolation/ purification make them less ideal for antibody production.
Mice and Rats
Mice and rats are frequently used in polyclonal antibody production because their small size and simplicity of obtaining make the entire process low-cost. However, these animals are very small and so have a limited blood volume in which to produce antibodies. Many animals need to be exposed to the antigen to create a sufficient volume.
Horses and Goats
Horses and goats are excellent sources of polyclonal antibodies when large quantities are required. Each also has little batch-to-batch variation and high phylogenetic difference from rabbits, allowing for double immunostainings. The drawbacks to using horses and goats are their inconvenient housing requirements and the high expense to maintain.
Sheep are able to produce larger volumes of polyclonal antibodies from a similar amount of antigen compared to other traditional laboratory animals. They are particularly suited to create antibodies adapted to small epitopes or small antigens. Unfortunately, the production method is complicated, and sheep are expensive to house and maintain.
Alpacas, llamas, and other camelids are important in polyclonal antibody production because of the antibodies they produce, VHH antibodies or nanobodies. These antibodies are smaller than average antibodies, allowing them to penetrate tissues that are difficult to access and also make contact with hardly accessible antigens. Similar to horses and goats, their main drawbacks are also their significant housing requirements and expense to maintain.
It is important not to rush into choosing the animal that will be used in the development of your polyclonal antibodies. In some cases, the unique properties of some of the more expensive hosts may be required; however, this will not always be the case, and less expensive methods can instead be used. A methodical and deliberate choice ensures time and money are not being applied in less-than-ideal circumstances.