Affinity maturation occurs because of mutations in the immunoglobulin gene variable regions, resulting in B cells with slightly altered antigen-binding sites. The memory cells also undergo affinity maturation, resulting in a pool of antibodies with higher average affinity. ![]() The second injection will activate memory cells that make class IgG antibodies against the antigen. Lab animals are usually injected at least twice with antigen when being used to produce antiserum. ![]() Antiserum drawn from an animal will thus contain antibodies from multiple clones of B cells, with each B cell responding to a specific epitope on the antigen ( Figure 20.3). This so-called polyclonal antibody response is also typical of the response to infection by the human immune system. Because most antigens are complex structures with multiple epitopes, they result in the production of multiple antibodies in the lab animal. These antibodies can be harvested in an antiserum, which is whole serum collected from an animal following exposure to an antigen. Within a few weeks, the animal’s immune system will produce high levels of antibodies specific for the antigen. What is cross-reactivity and why does it occur?Īntibodies used for research and diagnostic purposes are often obtained by injecting a lab animal such as a rabbit or a goat with a specific antigen.What property makes antibodies useful for research and clinical diagnosis?.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. 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 20.2). 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. 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.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. 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. What types of tests can be used to determine if a patient has HIV?. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |