Lab animals are usually injected at least twice with antigen when being used to produce antiserum. This diagram illustrates the process for harvesting polyclonal antibodies produced in response to an antigen. If an antibody has a high affinity/avidity for a specific antigen, it is less likely to cross-react with an antigen for which it has a lower affinity/avidity.įigure 2. Avidity is influenced by affinity as well as the structural arrangements of the epitope and the variable regions of the antibody. Affinity, which can be determined experimentally, is a measure of the binding strength between an antibody’s binding site and an epitope, whereas avidity is the total strength of all the interactions in an antibody-antigen complex (which may have more than one bonding site).

This single protein may stimulate the production of many different antibodies, some of which may bind to chemically identical epitopes on other proteins.Ĭross-reactivity is more likely to occur between antibodies and antigens that have low affinity or avidity.

Consider an antigen that consists of a single protein with multiple epitopes (Figure 1). Some antigens are so chemically similar that cross-reactivity occurs in other words, antibodies raised against one antigen bind to a chemically similar but different antigen. There are limitations to antibody specificity, however. A single antigen can have multiple epitopes for different, specific antibodies.Īn antibody’s specificity results from the antigen-binding site formed within the variable regions-regions of the antibody that have unique patterns of amino acids that can only bind to target antigens with a molecular sequence that provides complementary charges and noncovalent bonds. An antibody binds to a specific region on an antigen called an epitope. With in vitro assays, antibodies can be used to precipitate soluble antigens, agglutinate (clump) cells, opsonize and kill bacteria with the assistance of complement, and neutralize drugs, toxins, and viruses.įigure 1. The high specificity of antibodies makes them an excellent tool for detecting and quantifying a broad array of targets, from drugs to serum proteins to microorganisms. In addition to being crucial for our normal immune response, antibodies provide powerful tools for research and diagnostic purposes. We’ll return to this example in later pages. What types of tests can be used to determine if a patient has HIV?.Why does the hospital feel it is necessary to test every patient for HIV?.

The hospital decided to contact all of these patients and have them tested for HIV. Although the worker had only been employed for a short time, it was determined that he had come into contact with more than 1300 patients. While there was no proof that the infections originated from the tainted syringes, the hospital’s public health physician took immediate steps to determine whether any other patients had been put at risk. The hospital immediately fired the employee and had him arrested however, two patients that he had worked with later tested positive for HIV. In an unfortunate incident, a healthcare worker struggling with addiction was caught stealing syringes of painkillers and replacing them with syringes filled with unknown substances.

Antibody production definition